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  • 1995-1999  (10.378)
  • 1985-1989
  • 1975-1979
  • 1840-1849
  • 1997  (10.378)
  • Chemistry  (10.047)
  • Polymer and Materials Science  (3.277)
  • Computational Chemistry and Molecular Modeling
  • Electron microscopy
Datenquelle
Materialart
Erscheinungszeitraum
  • 1995-1999  (10.378)
  • 1985-1989
  • 1975-1979
  • 1840-1849
Jahr
Schlagwörter
  • 1
    Digitale Medien
    Digitale Medien
    Renewing olfactory receptor neurons in goldfish do not require contact with the olfactory bulb to develop normal chemical responsiveness (1997)
    Springer
    Journal of comparative physiology 181 (1997), S. 425-437 
    Details
    ISSN: 1432-1351
    Schlagwort(e): Key words Olfactory receptor cells ; Olfactory bulbectomy ; Olfactory axotomy ; Electrophysiology ; Electron microscopy
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract This study investigated whether contact with the olfactory bulb was necessary for developing and renewing olfactory receptor neurons (ORNs) to attain normal odorant responsiveness, and whether the anatomical and functional recoveries of the olfactory epithelium were similar in both bulbectomized (BE) and bilaterally axotomized (AX) preparations. In vivo electrophysiological recordings were obtained in response to amino acids, a bile acid [taurolithocholic acid sulfate(TLCS)] and a pheromonal odorant [17α, 20β,-dihydroxy-4-pregnen-3-one (17,20P)] from sexually immature goldfish. Both transmission and scanning electron microscopy indicated that the olfactory epithelium degenerated in BE and AX goldfish. Within 1–2 weeks subsequent to the respective surgeries, responses to high concentrations (〉0.1 mmol · l−1) of the more stimulatory amino acids remained, whereas responses were no longer obtainable to TLCS and 17,20P. At 4 weeks, responses to amino acid stimuli recovered to control levels, while responses to TLCS and 17,20P were minimal. By 7 weeks post bilateral axotomy, the olfactory epithelium recovered to a condition similar to control sensory epithelium; however, the rate of degeneration and proliferation of receptor neurons in BE preparations appeared to remain in balance, thus blocking further recovery of the olfactory epithelium. At 7 weeks post surgery, odorant responses of AX and BE goldfish to TLCS and 17,20P were still recovering.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s003590050126
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  • 2
    Digitale Medien
    Digitale Medien
    Cytodifferentiation of atypical adenomatous hyperplasia and bronchioloalveolar lung carcinoma: immunohistochemical and ultrastructural studies (1997)
    Springer
    Virchows Archiv 431 (1997), S. 415-424 
    Details
    ISSN: 1432-2307
    Schlagwort(e): Key words Bronchioloalveolar lung carcinoma ; Atypical adenomatous hyperplasia ; Surfactant apoprotein ; Urine protein 1 ; Electron microscopy
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract  We used immunohistochemistry and electron microscopy to evaluate the differentiation of cells comprising atypical adenomatous hyperplasia (AAH; n = 26), early bronchioloalveolar lung carcinoma (BAC; n = 11), and overt BAC (n = 16), which are assumed to constitute a continuous spectrum of developmental steps of BAC. Surfactant apoprotein (SAP), a marker for type 2 alveolar cells, was expressed in cells from all the lesions of AAH, early BAC, and overt BAC. However, the proportion of SAP-positive cells decreased and their distribution became more heterogeneous with advancing lesion grade. Urine protein 1, which is identical to the Clara cell-specific 10 kDa protein, was expressed in 70% of overt BAC, whereas only 20% of early BAC showed weak reactivity and none of AAH lesions showed any reactivity at all. Ultrastructurally, type 2 alveolar cell differentiation was predominant among cells from AAH and early BAC. Our results suggest that precursor cells of BAC differentiate predominantly towards type 2 alveolar cells. Cells comprising overt BAC retain this differentiation phenotype, but to a reduced extent. In contrast, concomitantly with progression, cells with Clara cell differentiation emerge and their proportion increases. Such phenotypic changes may reflect metaplasia occurring in tumour cells during the development of BAC.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004280050118
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  • 3
    Digitale Medien
    Digitale Medien
    Adenovirus-induced liver necrosis in a case of AIDS (1997)
    Springer
    Virchows Archiv 431 (1997), S. 469-472 
    Details
    ISSN: 1432-2307
    Schlagwort(e): Key words Adenovirus ; Liver pathology ; Electron microscopy ; AIDS
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract  Adenovirus-induced liver necrosis is rare. Before the era of AIDS (acquired immunodeficiency syndrome) this entity was seen predominantly in infants suffering from inborn immunodeficiency syndromes or from iatrogenic immunosuppression because of bone marrow or liver transplantation. Here, we report a case of a 30-year-old woman with AIDS who developed fever and rapidly progressing liver failure. A frozen section from a needle biopsy of the liver allowed a quick diagnosis of viral liver necrosis. The light-microscopic and electron microscopic aspects were typical of adenovirus infection and should be known to the surgical pathologist. The diagnosis was confirmed by immunohistochemistry and DNA hybridization analysis.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004280050125
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  • 4
    Digitale Medien
    Digitale Medien
    Argyrophilic tau-positive twisted and non-twisted tubules in astrocytic processes in brains of Alzheimer-type dementia: an electron microscopical study (1997)
    Springer
    Acta neuropathologica 95 (1997), S. 28-39 
    Details
    ISSN: 1432-0533
    Schlagwort(e): Key words Astrocytes ; Alzheimer-type dementia ; Electron microscopy ; Glial fibrillary tangles ; Tau protein
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract This report concerns pathological astrocytic tubular structures (astrocytic tubules, As-Tbs) that coexist with glial filaments in astrocytic processes in brains with presenile-onset Alzheimer-type dementia. The formation of As-Tbs appears to be related to the duration of disease and the intensity of Alzheimer histopathology. In three cases in which the disease was of extremely long duration, As-Tbs were found in the frontal and temporal neocortices, the temporal pole and the hippocampus using electron microscopy, whereas they were not found in two cases with a long, but not extremely long, illness duration. As-Tbs were almost exclusively found in the highly devastated neuropil, and we could not find them in regions of moderate neuronal degeneration despite intensive inspection. As reported previously, some As-Tbs was seen adjacent to extracellular neurofibrillary tangles (NFTs) and in perivascular astrocytes. Our novel finding is that they can exist independently from these, in the highly devastated neuropil. Two types of As-Tbs were observed, twisted tubules with periodic constrictions at 50- to 80-nm intervals and non-twisted tubules where no constrictions were seen but which had a 15-nm fuzzy outer contour. They were positively stained by anti-human tau antibody, an antibody that does not recognize extracellular NFTs. Thus, it is most likely that As-Tbs are not the sequestration of extracellular NFTs, and that they are of astrocytic origin. Moreover, As-Tbs showed argyrophilia. As-Tbs appear indistinguishable from dystrophic neurites under the light microscope. The present data suggest that they may be more widely distributed in the damaged cerebral neuropil than previously thought.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004010050762
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  • 5
    Digitale Medien
    Digitale Medien
    Scots pine needle injuries at subarctic industrial sites (1997)
    Springer
    Trees 11 (1997), S. 378-387 
    Details
    ISSN: 0931-1890
    Schlagwort(e): Key words Pinus sylvestris (L.) ; Electron microscopy ; Heavy metals ; Multi-stress-symptoms ; SO2
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract  Injuries to needles of Scots pines (Pinus sylvestris L.) growing in nutrient-poor soils on the Kola Peninsula collected in April 1991 were studied on a gradient of increasing distances (10 – 115 km) from the Monchegorsk nickel smelter, Russia, which emits SO2, Ni and Cu. The condition of the mesophyll cells was quantified from needles of the two latest age classes using a light and an electron microscope. The damage to the ultrastructure consisted of multistress symptoms caused by excess sulphur, heavy metals, frost, acidic precipitation and ozone. Injuries were most commonly manifested in the form of dark, irregularly shaped chloroplasts with protrusions and light thylakoids and plastoglobuli. These symptoms gradually disappeared with increasing distance and decreasing deposition rate. Concentrations of sulphur, copper and nickel decreased towards more distant sites where normal levels of the latter two elements were reached. Sulphur concentrations remained above background throughout the distance gradient. In the closest plots to the smelter area, cell collapse under the stomata and epidermis related to acute SO2 and heavy metal effects was found, whereas further away symptoms were more diverse, pointing towards the effects of ozone, acidic deposition and thereby decreased frost tolerance. The additive multistress symptoms were clearly seen in the area up to 40 km from the smelter where needle Cu concentration was above 110 ppm, Ni concentration above 39 ppm and S concentration above 1343 ppm.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004680050099
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  • 6
    Digitale Medien
    Digitale Medien
    Phenotypic variability of CADASIL and novel morphologic findings (1997)
    Springer
    Acta neuropathologica 94 (1997), S. 247-254 
    Details
    ISSN: 1432-0533
    Schlagwort(e): Key words CADASIL ; Electron microscopy ; Granular osmiophilic material ; αB crystallin ; Heat ; shock proteins
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is a non-arterio-atherosclerotic, non-amyloidotic arteriopathy affecting preferentially the small arteries and arterioles of the brain. The morphologic hallmark is the presence of a characteristic granular alteration of the arterial media that ultrastructurally corresponds to the accumulation of electron-dense material surrounding the smooth muscle cells. Although the presence of this granular osmiophilic material (GOM) was originally described as limited to brain vessels, identical electron microscopic findings have been demonstrated in the media of peripheral tissue arteries, allowing for a pathologic diagnosis of the disease by a simple skin, muscle or nerve biopsy. We report some atypical features identified in our CADASIL patients that broaden the phenotypic expression of this disease. Firstly, we identified a cortical infarct in an otherwise typical CADASIL patient. Secondly, we observed GOM in skin arteries of a 30-year-old man with hemiplegic migraine, the son of a woman who had died with CADASIL. This confirms that it may be possible to diagnose the disease at a preclinical stage by the ultrastructural evaluation of peripheral tissue biopsy material, particularly for individuals for whom there is a supporting family history. Thirdly, ultrastructural examination of the skin, and subcutaneous and striated muscle of an unrelated and apparently sporadic patient with neuropathologic and neuroradiologic evidence of CADASIL in meningeal and cerebral vessels failed to reveal diagnostic lesions in peripheral arteries. Thus, the possibility of a false-negative pathologic diagnosis in patients with a clinicoradiologic diagnosis of CADASIL, if one relies solely on a peripheral tissue biopsy, does exist. Additionally, we have identified heat shock proteins (Hsp70 and αB crystallin) and ubiquitin in the vascular myocytes of affected arteries. αB crystallin also seemed to be deposited extracellularly, which suggests that GOM also might be immunoreactive for αB crystallin.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004010050700
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  • 7
    Digitale Medien
    Digitale Medien
    Density and fine structure of peripheral nerves in various skin lesions of atopic dermatitis (1997)
    Springer
    Archives of dermatological research 289 (1997), S. 125-131 
    Details
    ISSN: 1432-069X
    Schlagwort(e): Key words Atopic dermatitis ; Peripheral nerve ;   ; Electron microscopy ; Protein gene product ; Substance P
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract The density and fine structure of the peripheral nerve system in various skin lesions of 64 patients with atopic dermatitis (AD) was quantitatively analyzed by immunohistochemical staining with antibodies directed against protein gene product (PGP) and substance P (SP). The density of PGP-positive peripheral nerves was 2.5 × 10 3 μm 2 /Δs (Δs = 0.24 mm 2 selected area) in early acute lesions, 3.8 × 10 3 μm 2 /Δs in subacute lesions, 4.9 × 10 3 μm 2 /Δs in lichenified lesions and 7.1 × 10 3 μm 2 /Δs in prurigo lesions of AD. The density of nerve fibers in subacute, lichenified and prurigo lesions was significantly higher than in uninvolved skin of AD patients (2.0 × 10 3 μm 2 /Δs). Electron microscopically, bulging of axons with many mitochondria and a loss of their surrounding sheath of Schwann cells suggests that the free nerve endings in skin lesions of AD are in an active state of excitation. Many pinocytotic vesicles in the periphery of basal keratinocytes facing nerve endings which contained many neurovesicles suggests reciprocal effects between keratinocytes and nerve endings. The number of SP-positive nerve fibers in AD lesions was far less than one-tenth of the number of PGP-positive nerve fibers.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004030050167
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  • 8
    Digitale Medien
    Digitale Medien
    Effects of brefeldin-A and monensin on organelle distribution and morphology in the preimplantation mouse embryo (1997)
    Springer
    Development genes and evolution 206 (1997), S. 503-514 
    Details
    ISSN: 1432-041X
    Schlagwort(e): Key words Preimplantation mouse embryo ; Brefeldin-A ; Monensin ; Golgi ; Electron microscopy
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract  The intracellular trafficking of integral membrane and secreted proteins is likely to be a key element involved in the morphogenesis and differentiation of the early mammalian embryo. In this study, we used transmission electron microscopy (TEM) to analyse the effects of brefeldin-A (BFA) and monensin, well known inhibitors of vesicular protein trafficking in somatic cells, on the structure of preimplantation mouse embryos. Both BFA and monensin distinctively altered the morphology of Golgi compartments in the blastomeres of treated morulae. BFA-treated morulae lacked recognizable Golgi complexes but possessed heterogeneous organelle clusters consisting of an abundance of smooth tubular and vesicular membrane compartments in addition to mitochondria, endosomes and lysosomes. Treatment of morulae with monensin was associated with swelling of Golgi compartments in addition to altering the morphology of mitochondria, lysosomes and the plasma membrane. BFA, and to a lesser extent monensin, inhibited cytokinesis as evidenced by the detection of binucleate blastomeres. In addition, BFA induced morulae to decompact. These latter effects have not been reported previously for these agents in mammalian somatic cell lines or other vertebrate or invertebrate embryos. These results provide the first demonstration of the structural effects of BFA and monensin on cells of the early mammalian embryo, some of which are consistent with the known actions of these agents on components of the vesicular protein trafficking system in mammalian somatic cells. This information serves as a foundation for the further use of these agents in studies of vesicular protein trafficking as an agent of preimplantation morphogenesis.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004270050081
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  • 9
    Digitale Medien
    Digitale Medien
    Komibinierte neuronale und endokrine Tumoren der Sellaregion (1997)
    Springer
    Der Pathologe 18 (1997), S. 419-424 
    Details
    ISSN: 1432-1963
    Schlagwort(e): Schlüsselwörter Gangliozytom ; Gangliogliom ; Hypophysenadenom ; Immunhistologie ; Ultrastruktur ; Key words Gangliocytoma ; Ganglioglioma ; Pituitary adenoma ; Immunohistochemistry ; Electron microscopy
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Beschreibung / Inhaltsverzeichnis: Summary Gangliocytomas or gangliogliomas of the sellar region are very rare tumors. In a great proportion of those cases an adenoma of the anterior pituitary develops from the cell type that is hyperstimulated by the releasing hormone produced from the gangliocytoma. Five GHRH secreting gangliocytomas are reported. Four of these were localized adjacent to a GH secreting adenoma. In one case, no adenoma tissue was found beside the ganglicytoma. As only the adenomas can secrete GH, the adenomas and not the gangliocytomas are directly responsible for acromegaly so that such an adenoma has to be present in cases of acromegaly. A CRH secreting gangliocytoma was combined with an ACTH cell adenoma that had induced Cushing’s disease. A ganglioglioma of the posterior pituitary had led to an inappropriate secretion of Vasopressin. The morphology of the different tumors is presented.
    Notizen: Zusammenfassung Intraselläre Gangliozytome/Gangliogliome sind sehr seltene Tumoren, die in einem Großteil der Fälle ein Hypophysenadenom aus dem Zelltyp heraus entstehen lassen, der durch das gebildete Releasinghormon überstimuliert wird. Es wird über 5 GHRH-bildende Gangliozytome berichtet, von denen 4 einem STH-bildenden Hypophysenadenom benachbart waren. Ein Fall enthielt keine Adenomanteile. Diese müssen in Anbetracht der klinisch vorhandenen Akromegalie aber vorhanden sein, da nur das jeweilige Adenom, nicht aber die Gangliozytome für die Überfunktion unmittelbar verantwortlich sind. Ein CRH-bildendes Gangliozytom war mit einem zum Morbus Cushing führenden ACTH-Zelladenom kombiniert. Ein Gangliogliom des Hinterlappens hatte zu einer inadäquaten Vasopressinsekretion Anlaß gegeben. Die Morphologie der Tumoren wird dargelegt.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002920050236
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  • 10
    Digitale Medien
    Digitale Medien
    Ultrastructural subtypes of glutamate-immunoreactive terminals on rat trigeminal motoneurones and their relationships with GABA-immunoreactive terminals (1997)
    Springer
    Experimental brain research 114 (1997), S. 99-116 
    Details
    ISSN: 1432-1106
    Schlagwort(e): Key words Synapse ; Axo-axonic synaptic contacts ; Trigeminal motor nucleus ; Immunogold ; Electron microscopy ; Rat
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract  Electron-microscopic immunolabelling methods were used to study the relationships between glutamate-immunoreactive and γ-aminobutyric acid (GABA)-immunoreactive synapses on trigeminal motoneurones labelled by the retrograde transport of horseradish peroxidase. Serial sections were cut through the motor nucleus, alternate sections were incubated with antibodies to glutamate and GABA, and the immunopositive nerve terminal profiles were recognized using a quantitative, postembedding immunogold method. Boutons exhibiting high levels of glutamate immunoreactivity and GABA-immunoreactive boutons both formed axo-dendritic and axo-somatic synaptic contacts on labelled motoneurones. Boutons strongly immunopositive for glutamate were not immunopositive for GABA, and vice versa. Strongly glutamate immunoreactive boutons received axo-axonic synaptic contacts but did not form such contacts, while GABA-immunoreactive boutons formed axo-axonic synapses but did not receive them. The presynaptic elements at all axo-axonic synapses on to glutamate-immunoreactive boutons sampled were GABA-immunopositive. These data provide ultrastructural evidence in support of the roles of glutamate and GABA as transmitters at synapses on trigeminal motoneurones, and for presynaptic control of transmission at glutamatergic synapses by GABA acting at receptors at axo-axonic synapses. The vast majority (more than 90%) of strongly glutamate immunoreactive boutons contained spherical synaptic vesicles, in contrast to GABA-immunoreactive boutons, which contained pleomorphic vesicles. Most of the glutamate-immunoreactive boutons (67%) formed asymmetrical synaptic active zones, many of which (47% of total) were associated with subsynaptic dense ”Taxi” bodies (T-terminals), while a smaller population of boutons (21%) formed symmetrical synapses, and a few (11%) made synapses associated with subsynaptic cisternae (C-terminals). The heterogeneity of active zone ultrastructure of boutons identified as being glutamatergic on the basis of their high levels of immunolabelling is discussed in relation to possible differences in co-transmitters released, origins of the synaptic input or post-synaptic receptor subtypes activated.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/PL00005627
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  • 11
    Digitale Medien
    Digitale Medien
    Type III Ehlers-Danlos syndrome and pregnancy (1997)
    Springer
    Archives of gynecology and obstetrics 261 (1997), S. 39-43 
    Details
    ISSN: 1432-0711
    Schlagwort(e): Key words: Ehlers-Danlos type III ; Pregnancy ; Electron microscopy ; Prenatal diagnosis ; Premature rupture of membranes
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract. We report a case of type III Ehlers-Danlos syndrome with a favourable outcome. We review the literature and do not consider that pregnancy in patients with type III Ehlers-Danlos Syndrome represents a high risk situation.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004040050196
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  • 12
    Digitale Medien
    Digitale Medien
    Turbulent mixing of reactive gases in the convective boundary layer (1997)
    Springer
    Boundary layer meteorology 85 (1997), S. 197-222 
    Details
    ISSN: 1573-1472
    Schlagwort(e): Turbulence ; Chemistry ; Closure ; Convective boundary layer
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Geologie und Paläontologie , Physik
    Notizen: Abstract We study the interactions of chemistry and turbulent mixing of tracersin the convective boundary layer with a second-order closure model,including higher order chemistry terms. In order to limit the number of predictive equations we prescribe the profiles for ¯w¯Θ, ¯w¯θ ¯θ and the lengthscale l. However, for model validation we treat temperature and humidity asinert tracers, and compare the results with profiles observed during theAir Mass Transformation Experiment, and with similarity expressions for thesurface layer. We find good agreement of the mean profiles, but the (co-)variances are slightly underpredicted. Furthermore, the model usesdiagnostic equations expressing third moments of concentration in terms ofsecond moments and their vertical derivatives. They are compared withlarge-eddy model results, showing good agreement and, therefore, thesimplifications are justified. The model is applied to the transport of two gases subject to one bimolecular reaction. The importance of concentration correlations on themean transformation rate is studied. For two gases diffusing in oppositedirections we find for moderate and fast chemistry a 50% and90% decreased transformation rate due to the negatively correlatedconcentrations. These values are similar to large-eddy results of Schumannand Sykes et al. For two bottom-up tracers we find that the covariance ofboth reactive species is either positive or negative, increasing or reducingthe effective transformation rate depending on the Damköhler number (the ratio of the turbulent and the chemistry timescale). A significantdirect influence of chemistry on the flux divergence is found in bothcases. According to the model the effective transport to mid-levels of theboundary layer is increased when two reactive tracers diffuse in oppositedirections, and decreased in the case of two bottom-up tracers.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1000414710372
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  • 13
    Digitale Medien
    Digitale Medien
    Light and electron microscopic investigation of the process of healing of the naevus of Ota by Q-switched alexandrite laser irradiation (1997)
    Springer
    Virchows Archiv 431 (1997), S. 63-71 
    Details
    ISSN: 1432-2307
    Schlagwort(e): Key words Naevus of Ota ; Q-switched alexandrite laser ; Light microscopy ; Electron microscopy
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract  Melanocytes in the naevus of Ota were destroyed by irradiation using the Q-switched alexandrite laser. This laser is highly selective and highly absorbed by melanosomes. Other cells and tissue components of the dermis remained almost intact. Melanosomes were vaporized or fragmented to subelectron microscopical size, or degenerated. If the irradiated energy was sufficient, melanocytes vanished and large vacuoles several times the size of dermal melanocytes formed at the sites. If it was too weak, dermal melanocytes were also vaporized, but vacuoles formed within them. Nuclei were no longer discernible. Following irradiation macrophages infiltrated the irradiated areas and scavenged degenerated melanosomes and cellular debris. Thus, discoloration of the skin was markedly reduced. Although a few melanocytes and melanophages remained, pigmentation cleared to a satisfactory level. Melanocytes and keratinocytes were also injured in the epidermis; however, the epidermis recovered completely. No scarring was observed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004280050070
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  • 14
    Digitale Medien
    Digitale Medien
    Neuropeptide Y-immunoreactive intracardiac neurones, granule-containing cells and nerves associated with ganglia and blood vessels in rat and guinea-pig heart (1997)
    Springer
    Cell & tissue research 289 (1997), S. 445-454 
    Details
    ISSN: 1432-0878
    Schlagwort(e): Key words: Intracardiac neurones ; Innervation ; Heart ; Neuropeptide Y ; Immunocytochemistry ; Electron microscopy ; Rat (Sprague Dawley) ; Guinea-pig (Dunkin Hartley)
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract. Intrinsic neuropeptide Y-containing neurones in rat and guinea-pig hearts were studied at the ultrastructural level by the pre-embedding peroxidase-antiperoxidase immunocytochemical technique. Intracardiac neuronal cell bodies were often weakly or moderately immunostained, and the labelling was usually pronounced in the Golgi complex, multivesicular bodies, some cisterns of granular endoplasmic reticulum and large granular vesicles. Neuropeptide Y-immunoreactive nerve fibres were also observed in association with intracardiac neurones. A subpopulation of neuropeptide Y-immunoreactive granule-containing cells in the rat heart are described for the first time and were very heavily labelled; other granule-containing cells were non-immunoreactive, but were contacted by neuropeptide Y-containing nerves. Preterminal regions of nerve fibres that were located in nerve bundles were only weakly neuropeptide Y-immunoreactive, in contrast to the heavy labelling observed in varicosities that contained many synaptic vesicles. Many neuropeptide Y-immunoreactive nerve fibres were associated with the coronary vasculature and were particularly prominent in the walls of small arteries and arterioles where labelled nerve varicosities were present close to the smooth muscle cells. Immunoreactive nerves were also seen in the myocardium, usually near to capillaries. In axonal varicosities, the central core of large granular vesicles was immunolabelled, and electron-dense immunoreactive material outlined the membranes of small and large clear vesicles. The significance of neuropeptide Y-immunoreactive intracardiac neurones and granule-containing cells and the origin of associated labelled nerve fibres in the heart are discussed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004410050890
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  • 15
    Digitale Medien
    Digitale Medien
    Immuno-electron microscopy reveals that the excitotoxin quinolinate is associated with the plasma membrane in human peripheral blood monocytes/macrophages (1997)
    Springer
    Cell & tissue research 290 (1997), S. 633-639 
    Details
    ISSN: 1432-0878
    Schlagwort(e): Key words: Quinolinic acid ; Interferon-γ ; Kynurenine ; Electron microscopy ; Immunocytochemistry ; Excitotoxicity ; Human
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract.  Quinolinate (QUIN), a tryptophan-derived excitotoxin, was localized ultrastructurally in human peripheral blood monocytes/macrophages (MØ) by immuno-electron microscopy. A combined carbodiimide/glutaraldehyde/paraformaldehyde-based fixation procedure was developed for optimal retention of QUIN in the cell as well as minimal loss of ultrastructure; a silver-enhanced colloidal gold detection system was used for electron-microscopic analysis. Gold particles representing QUIN immunoreactivity were associated with the inner side of the plasma membrane in normal MØ. The number of gold particles increased significantly when QUIN levels were elevated by treatment with its precursor kynurenine, but location of the gold particles remained essentially the same under this condition. Treatment with interferon-γ increased the number of Golgi bodies, vacuoles and pseudopodia, reflecting the activated state of the cell. Significantly increased numbers of gold particles representing QUIN were detectable in approximately the same location as in the case of kynurenine treatment. Combined treatment with kynurenine and interferon-γ maximally increased the number of gold particles at the periphery of the cell. The pseudopodia were intensely stained with gold particles, while they were not detectable in the inner part of the cytoplasm or in any other organelle even under this activated condition. The significance of the specific location of QUIN revealed in the present study and its relation to the release and subsequent actions of QUIN are discussed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004410050969
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  • 16
    Digitale Medien
    Digitale Medien
    Synaptic exocytosis of dense-core vesicles in blue crab (Callinectes sapidus) stomach muscles (1997)
    Springer
    Cell & tissue research 289 (1997), S. 517-526 
    Details
    ISSN: 1432-0878
    Schlagwort(e): Key words: Neuromuscular junction ; Synaptic vesicles ; Vesicle fusion ; Electron microscopy ; Callinectes sapidus (Crustacea)
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract. Neuromuscular terminals of a single motoneuron to four muscles (CPV7a, GM5a, CV2, and CV3) in the stomach of the blue crab Callinectes sapidus showed structural evidence for the exocytotic release of dense-core vesicles exclusively at synapses. The primary evidence was the appearance of dense cores in the synaptic cleft, accompanied by indentations of the presynaptic or postsynaptic membrane. In their simplest form, these consisted of an omega-shaped figure of the presynaptic membrane enclosing one dense core, denoting release of a single dense-core vesicle. A larger indentation of the presynaptic membrane enclosing several dense cores denoted multiple release. A more complex form of multiple release was where the presynaptic membrane was normal, but the postsynaptic membrane elaborated into a sac projecting into the granular sarcoplasm and filled with dense cores. The postsynaptic sac in some instances was compressed into a thin, fingerlike extension, which lacked dense cores and, at its distal end, separated into small cisternae, suggesting a mechanism for membrane recycling. Profiles depicting single and multiple releases of dense-core vesicles were found more frequently at neuromuscular terminals that release relatively large amounts of transmitter with a single stimulus, such as CV2 and CV3, compared to those releasing smaller amounts, such as CPV7a and GM5a. The disparity in release sites among the four muscles of this single motor unit and the fact that many of the multiple-release figures were closely adjacent to the active zones for transmitter release suggest a possible modulatory role for dense-core vesicles in synaptic transmission. Such modulation may be long lasting, as implied by the postsynaptic sacs, which may permit prolonged release of the contents of their dense cores into the synaptic cleft. This is in keeping with the functional role of these stomach muscles, which is to be continuously active for long periods of time.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004410050897
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  • 17
    Digitale Medien
    Digitale Medien
    Immunoreactive excitatory amino acids in the parietal eye of lizards, a comparison with the pineal organ and retina (1997)
    Springer
    Cell & tissue research 287 (1997), S. 275-283 
    Details
    ISSN: 1432-0878
    Schlagwort(e): Key words: Parietal eye ; Pineal organ ; Retina ; Glutamate ; Aspartate ; Immunocytochemistry ; Electron microscopy ; Lacerta muralis ; Lacerta agilis ; Lacerta viridis (Lacertilia)
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract. The fine structure of the organ and the localization of the excitatory amino acids glutamate and aspartate were studied in the parietal eye of lizards by postembedding immunoelectron microscopy. The parietal eye contains cone photoreceptor cells, secondary neurons, and ependymal and lens cells. The photoreceptors form long inner and outer segments, some of them being paired as ”twin-photoreceptors” by zonulae adherentes. Perikarya of neurons bear sensory cilia (containing 9×2+0 pairs of tubules) extending into the intercellular space. No neurohormonal terminals are present in the parietal eye. A higher immunoreactivity to glutamate than to aspartate is found in the photoreceptors and in the secondary neurons of the parietal eye. Glutamate immunogold labeling is more intense in the axonal processes of photoreceptors and neurons and in most of the nerve fibers of the parietal nerve running to the brain stem. Weak aspartate and glutamate immunoreactivity can be detected in the ependymal and lens cells. A similar distribution of immunoreactive amino acids is found in the photoreceptors, secondary neurons, and ependymal glial elements of the pineal organ, and retina of the lateral eye of the same animals. Immunoreactive glutamate accumulates in the axons of photoreceptors and secondary neurons of the parietal eye suggesting that this excitatory amino acid acts as a synaptic mediator in the neural efferentation of the organ. Thus, the efferent light-conducting pathway of the parietal organ is similar to that of the pineal organ and lateral eye retina. As the Mullerian cells of the retina, the ependymal and lens cells of the parietal eye and the ependymal-glial cells of the pineal organ may play a role in the metabolism and/or elimination of excitatory amino acids released by photoreceptors.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004410050752
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  • 18
    Digitale Medien
    Digitale Medien
    Expression of basic fibroblast growth factor-like immunoreactivity in the nuclei of regenerating hepatocytes (1997)
    Springer
    Cell & tissue research 288 (1997), S. 517-527 
    Details
    ISSN: 1432-0878
    Schlagwort(e): Key words: Liver ; Subcellular fractions ; Immunohistochemistry ; Electron microscopy ; Rat (Wistar)
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract. This study, utilizing rats subjected to two-thirds partial hepatectomy or sham operation, was designed (1) to investigate the content of basic fibroblast growth factor (bFGF) in the subcellular fractions of regenerating and sham-operated rat livers by immunoblot experiments and enzyme-linked immunosorbent assay (ELISA), (2) to show that bFGF immunoreactivity and proliferating cell nuclear antigen (PCNA) immunoreactivity are markers for hepatocellular mitosis before and after partial hepatectomy, and (3) to observe the location and fine structure of the bFGF immunoreaction within the regenerating liver with special attention to bFGF immunoreactivity in the nuclei of regenerating hepatocytes. Immunoblot experiments and ELISA showed a transient increase in high-molecular-weight forms of bFGF in the nuclear subcellular fraction of regenerating liver 48 h after partial hepatectomy. By light microscopy, bFGF and PCNA immunoreactivities were detected in the nuclei of regenerating hepatocytes. Electron microscopy demonstrated bFGF-like immunoreactivity mainly in the nuclear euchromatin and rarely in the heterochromatin or nucleoli of regenerating hepatocytes. The transient increase in high-molecular-weight forms of bFGF in the nuclear euchromatin of regenerating hepatocytes, together with the concomitant expression of PCNA in the regenerating liver, suggests an important role of the high-molecular-weight forms of bFGF in hepatocyte proliferation and/or mitosis, although authentic bFGF with a molecular form of 18 kDa is not considered to be involved in hepatic regeneration.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004410050837
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  • 19
    Digitale Medien
    Digitale Medien
    Osmoregulatory mutants that affect the function of the contractile vacuole inChlamydomonas reinhardtii (1997)
    Springer
    Protoplasma 200 (1997), S. 99-111 
    Details
    ISSN: 1615-6102
    Schlagwort(e): Chlamydomonas reinhardtii ; Contractile vacuole ; Electron microscopy ; Videomicroscopy ; Osmoregulation ; Osmoregulatory mutants
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary Four independent osmoregulatory mutants,osml, osm3,osm4, and osm7, were isolated on the basis of their requirement for growth medium of high osmotic strength. In normal low-osmoticstrength medium, in contrast to wild-type cells, the mutants grow poorly or not at all; in distilled water mutant cells are immobilized and eventually swell and burst. The mutants were examined by ordinary brightfield and phase-contrast microscopy, videomicroscopy, and electron microscopy. The four mutants showed different defects in the contractile vacuole (CV) cycle. Timing of various stages of the CV cycle showed thatosm1 was affected primarily in the early stage of the cycle when the CV begins to grow,osm3 primarily in midcycle when vacuoles fuse to form the CV proper,osm7 at a late stage of the cycle at docking and fusion of the CV with the plasma membrane, andosm4 during contraction of the CV. At the electron microscopic level, in dilute medium, mutant cells by comparison with wild-type cells had large autophagosomes, swollen mitochondria, and dilated ER cisternae. Although electron microscopy showed general abnormalities of the contractile vacuoles consistent with the videomicroscopic observations of living cells, no obvious vacuole membrane abnormalities were seen which would explain the mutational defects. The mutations help define the separate processes that contribute to the coordinated CV cycle inChlamydomonas, and open the way to eventual isolation of some of the genes responsible for CV function.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01280738
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  • 20
    Digitale Medien
    Digitale Medien
    Structure and behavior of contractile vacuoles inChlamydomonas reinhardtii (1997)
    Springer
    Protoplasma 198 (1997), S. 73-84 
    Details
    ISSN: 1615-6102
    Schlagwort(e): Chlamydomonas reinhardtii ; Contractile vacuole ; Osmoregulation ; Videomicroscopy ; Electron microscopy
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary The contractile vacuole (CV) cycle ofChlamydomonas reinhardtii has been investigated by videomicroscopy and electron microscopy. Correlation of the two kinds of observation indicates that the total cycle (15 s under the hypo-osmotic conditions used for videomicroscopy) can be divided into early, middle, and late stages. In the early stage (early diastole, about 3 s long) numerous small vesicles about 70–120 nm in diameter are present. In the middle stage (mid-diastole, about 6 s long), the vesicles appear to fuse with one another to form the contractile vacuole proper. In the late stage (late diastole, also about 6 s long), the CV increases in diameter by the continued fusion of small vesicles with the vacuole, and makes contact with the plasma membrane. The CV then rapidly decreases in size (systole, about 0.2 s). In isosmotic media, CVs do not appear to be functioning; under these conditions, the CV regions contain numerous small vesicles typical of the earliest stage of diastole. Fine structure observations have provided no evidence for a two-component CV system such as has been observed in some other cell types. Electron microscopy of cryofixed and freeze-substituted cells suggests that the irregularity of the profiles of larger vesicles and vacuoles and some other morphological details seen in conventionally fixed cells may be shrinkage artefacts. This study thus defines some of the membrane events in the normal contractile vacuole cycle ofChlamydomonas, and provides a morphological and temporal basis for the study of membrane fusion and fluid transport across membranes in a cell favorable for genetic analysis.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01282133
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  • 21
    Digitale Medien
    Digitale Medien
    Selective UV-induced damage to short-wavelength receptor cells in the butterflyPapilio xuthus (1997)
    Springer
    Protoplasma 200 (1997), S. 112-115 
    Details
    ISSN: 1615-6102
    Schlagwort(e): Electron microscopy ; UV-induced cell damage ; Photoreceptor ; Eye ; Lepidoptera
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary A technique that allows the specific inactivation of short-wavelength-sensitive photoreceptive cells has been needed for a long time. Such a technique could be useful in studies on the role(s) of UV-receptors in circadian rhythmicity, recognition of floral patterns, homing behaviour, and mate selection in arthropods. We provide ultrastructural evidence that short-wavelength receptor cells can be selectively damaged without affecting other spectral-cell types. Since the method does not require the killing of the experimental animal, the latter can be used in behavioural or other follow-up tests.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01280739
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  • 22
    Digitale Medien
    Digitale Medien
    Electron microscopic and immunomorphological investigations on the mucosa of the human paranasal sinuses (1997)
    Springer
    European archives of oto-rhino-laryngology and head & neck 254 (1997), S. 230-235 
    Details
    ISSN: 1434-4726
    Schlagwort(e): Paranasal sinus mucosa ; Collagen type VII ; Subepithelial connective tissue ; Electron microscopy ; Immunofluorescence microscopy
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract The morphology of the mucosa from the human paranasal sinuses was investigated by electron microscopy. A total of 27 specimens was taken from 11 patients following midfacial fractures. All tissue samples were biopsied during surgery after informed consent had been given. In accordance with light microscopic investigations, the mucosa represented a highly prismatic epithelium consisting of kinocilia-carrying and mucus-producing (goblet) cells. Other cell types, such as those occurring in the respiratory epithelium of other areas, could not be demonstrated. Electron microscopic and immunomorphological investigations revealed collagen type VII beneath the lamina densa of the basal lamina. According to findings obtained to date, this collagen type accompanies only a multilayered epithelium. Another peculiarity was the small number of basophils and eosinophils. Pronounced acute reactions of the mucosa in this area cannot be expected, which is in contrast to that of the nasal mucosa.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00874094
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  • 23
    Digitale Medien
    Digitale Medien
    Ultrastructural findings of the macula utriculi in a case of a petrous apex cholesteatoma: a comparison with findings in a patient with an acoustic neuroma (1997)
    Springer
    European archives of oto-rhino-laryngology and head & neck 254 (1997), S. 255-258 
    Details
    ISSN: 1434-4726
    Schlagwort(e): Electron microscopy ; Inner ear ; Utricle ; Cholesteatoma ; Acoustic neuroma
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract The morphological characteristics of the vestibular sensory cells of the macula utriculi obtained during surgery in a patient with a petrous apex cholesteatoma were examined using scanning and transmission electron microscopy. Findings were compared to cells studied in a patient with acoustic neuroma. Scanning electron microscopy showed that compared to the apparently normal cells in the acoustic neuroma case, most sensory cells in the cholesteatoma case had large cuticular plates, irregular locations of cilia and no clear polarizations. Supporting cells showed profuse short microvilli on the whole surface. With transmission electron photomicrographs, type I hair cells were not seen and certain morphological changes were observed in type-1I-like cells and supporting cells. We presume that the degenerative changes in the vestibular epithelia were due to circulatory disturbances and/or direct pressure applied to the vestibular nerve at the internal auditory canal, with subsequent involvement of the macula utriculi.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00874100
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  • 24
    Digitale Medien
    Digitale Medien
    Electron microscopic localization of nitric oxide I synthase in the organ of Corti of the guinea pig (1997)
    Springer
    European archives of oto-rhino-laryngology and head & neck 254 (1997), S. 396-400 
    Details
    ISSN: 1434-4726
    Schlagwort(e): Guinea pig hair cells ; Electron microscopy ; Immunocytochemistry ; Nitric oxide synthase ; Sound transduction
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract Nitric oxide synthase (NOS) activity has been detected previously in the mammalian cochlea at a light microscopic level. Here we present results of electron microscopic analysis for post-embedding immunoreactivity of neural-type NOS I in the cochlea of the guinea pig. Strong enzyme immunoreactivity was identified in the cytoplasm of inner and outer hair cells. Gold-labeled NOS I antibodies were mainly located in electron-dense areas of the cytoplasm, whereas electron-lucent regions of the receptor cells were nearly free from any immunoreactivity. In both types of hair cells anti-NOS I antibodies were also visible in the cuticular plates, hair bundles and nuclei. Further ultrastructural analysis revealed that the submembranous cisternae of the outer hair cells were nearly free from any reaction product, demonstrating that the whole cytoplasm of this hair cell was not immunoreactive. Other NOS I immunoreactivity was identified in the cuticular plates of the inner and outer pillar cells and in the cytoskeletal elements located in the apical parts of Deiter cells, forming the lamina reticularis or in cytoskeletal-containing regions in basal Deiter cells. Anti-NOS antibodies were visible in the nuclei of various cell types. Our findings suggest that nitric oxide produced by NO I synthase in the organ of Corti may act as a modulator of hair cell physiology during the processes of signal transduction with frequence selectivity.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01642558
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  • 25
    Digitale Medien
    Digitale Medien
    Immunohistochemical and electron microscopical characterization of stromal cells in nasopharyngeal angiofibromas (1997)
    Springer
    European archives of oto-rhino-laryngology and head & neck 254 (1997), S. 196-199 
    Details
    ISSN: 1434-4726
    Schlagwort(e): Nasopharyngeal angiofibroma ; Ultrastructure ; Myofibroblast ; Immunohistochemistry ; Electron microscopy
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract Twenty-eight cases of nasopharyngeal angiofibroma were studied immunohistochemically for cytoskeletal phenotyping of stromal cells. Electron microscopy was also used to study the ultrastructure of five of the tumors. All typical stromal cells showed intensive immunostaining for vimentin, but were negative for smooth muscle actin and desmin. Ultrastructurally, most of these cells appeared to be exclusively fibroblasts. However, in some areas stromal cells were seen that morphologically resembled myofibroblasts by their shapes and arrangement, and were characterized by the coexpression of vimentin and smooth muscle actin. Electron microscopy confirmed their myofibroblastic nature. The present study showed that the typical stromal cells in nasopharyngeal angiofibromas were fibroblasts and not myofibroblasts. In these tumors myofibroblasts occurred only focally, in connection with fibrotic areas and exclusively as a vimentin+/actin+ cytoskeletal phenotype. This indicates that myofibroblasts are not primary stromal tumor cells in nasopharyngeal angiofibromas, but occur due to regressive changes.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00879273
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  • 26
    Digitale Medien
    Digitale Medien
    Polycarbonat-ein vielseitiger werkstoff mit zukunft (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 244 (1997), S. 43-66 
    Details
    ISSN: 0003-3146
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The market development of bisphenol-A-polycarbonate has shown higher growth than any other engineering thermoplastic. The reasons can be found in the permanent improvement of the cost/performance-relationship and in the technical use of the variability of the basic structure. Incorporation of specific monomer units leads to tailor-made properties for a wide range of applications, as for example medical devices, electronic parts and glazing.This process has not yet slowed down, rather it is accelerated by new results from research and development. The improvement of flaw behavior and pit replication for new grades of materials for the next generation of compact discs, new grades that can be sterilized by γ-radiation without degradation and the microstructuring by low-energy laser systems are examples for the ongoing expansion of polycarbonate applications. Surface modification by hardcoatings with nanosized particles will allow to enter the fast growing market of glazing.
    Zusätzliches Material: 27 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/apmc.1997.052440103
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  • 27
    Digitale Medien
    Digitale Medien
    Polyamide, polyester und polyoxymethylen. Die klassischen technischen kunststoffe und ihre perspektiven (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 244 (1997), S. 67-92 
    Details
    ISSN: 0003-3146
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Beschreibung / Inhaltsverzeichnis: Polyamide, Polyester und Polyoxymethylen sind mit einem weltweiten Verbrauch von derzeit 2,4 Mio t pro Jahr wichtige technische Kunststoffe. Sie werden aufgrund ihrer besonderen Eigenschaftsprofile überwiegend im Fahrzeugbau und in der Elektroindustrie für hochbelastete Funktionsbauteile eingesetzt. Der vorliegende Beitrag behandelt Polymerisationswege, Eigenschaften und ausgewählte neue Entwicklungen dieser Polymerklassen.Teilaromatische Polyamide stoßen durch ihre Dimensionsstabilität und thermische Belastbarkeit in Anwendungen vor, die bisher Duromeren oder Metallen vorbehalten waren. Glasfaserverstärkte Polyamide mit besonders hoher Dauerwärmebeständigkeit übemehmen wichtige Funktionen im Motorbereich von Fahrzeugen. Polyamid-Blends sind als Karosseriewerkstoffe ein Schlüssel zu leichten Autos mit niedrigem Treibstoffverbrauch. Halogenfrei flammgeschützte Polyamide erhöhen Sicherheit und Umweltverträglichkeit in brandgefährdeten Anwendungsbereichen.Polybutylenterephthalat als technisch wichtigster Polyester eröffnet in Mischung mit amorphen Polymeren neue Perspektiven durch geringerenVerzug und bessere Oberfläche bei glasfaserverstärkten Teilen. Polybutylennaphthalat erweitert den Anwendungsbereich zu höheren Temperaturen. Von Polybutylenterephthalat abgeleitete Copolyester sind biologisch abbaubar und daher vielversprechend für kompostierbare Folien.Polyoxymethylen-Copolymere haben ihre Stärke in der günstigen Kombination aus Steifigkeit, Dimensionsstabilität, Gleit/Reibe-Verhalten und Beständigkeit gegen heißes Wasser und Kraftstoff.Aufgrund ihres hohen und noch weiter steigerungsfähigen Leistungsvermögens werden Polyamide, Polyester und Polyoxymethylen das in den letzten Jahren gezeigte Wachstum in Zukunft weiter ausbauen können.
    Notizen: Polyamide, polyester and polyoxymethylene having presently a worldwide sales volume of 2,4 million tons a year are important engineering thermoplastics. Based on their special property profiles they are mainly used in the automotive and electronic industry for high performance functional parts. This contribution presents polymerisation processes, properties, and selected new developments for these polymer classes.Semiaromatic polyamides due to their dimensional stability and thermal resistance lend themselves to applications which were so far reserved for thermosets or metals. Glass fiber reinforce polyamides designed to have the highest possible heat ageing resistance can take important functions under the hood. A polyamide blend used as a material for exterior body parts is key to light weight cars with strongly reduced fuel consumption. Halogene free flame retardant polyamide increases fire safety and environmental safety in flame sensitive applications.Polybutyleneterephthalate as the technically most important polyester offers new perspectives in blends with amorphous polymers leading to lower distortion and better surface quality in glass fiber reinforced parts. Polybutylenenaphthalate is widening the range of application of polyesters towards higher temperatures. Copolyesters derived from polybutyleneterephthalate are biologically degradable and are therefore promising materials for fermentable foils.Polyoxymethylene copolymers show an outstanding combination of stiffness, dimensional stability, friction and wear as well as resistance against hot water and fuel.As a result of their excellent properties and the existing potential for further improvements polyamide, polyester and polyoxymethylene will continue to grow above average in the future.
    Zusätzliches Material: 18 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/apmc.1997.052440104
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  • 28
    Digitale Medien
    Digitale Medien
    Sind polyurethanwerkstoffe ein reifes gebiet? (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 244 (1997), S. 121-133 
    Details
    ISSN: 0003-3146
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The world-wide production of polyurethanes has exceeded 6 mio. metric tons in 1994. Compared with the produced amounts of large-scale thermoplastics such as PE, PVC, PP and PS, polyurethanes keep the 5th place.Polyurethanes (PUR) are segmented polymers, which can be synthesized from preformed building blocks in a modular unit construction system. The chemical modules and the various possibilities of combination will be discussed here.Tailor-made polyurethane materials can be divided into two main-fields of application: foams and compact PUR.The main constituents of polyurethane materials are diisocyanates and polyols. These key- chemicals are well characterised with respect to their technological, economical and ecological properties. Taking into account the availability, the masses of production and the experiences that have been collected with the PUR main constituents, these PUR precursors seem to be very mature already.In contrast to this, the PUR-materials made from these building blocks still offer numerous novel problem-solutions, resulting from the variability of the diisocyanate-poly-addition reaction: PUR materials are most commonly segmented into several phases. The formation of hard- and softsegments can be easily demonstrated by looking at thermoplastic polyurethanes (TPU). A deeper understanding of this phase separation and the molecular organisation within these materials promises to realize prospectic polymeric architectures with new and improved properties. PUR materials will still be able to offer new answers to future requirements in balancing economical and ecological needs. By looking at the life-cycles of soft and hard-foams, polyurethane-coatings and thermoplastic PUR-elastomers, this contribution will adress the question: “Is PUR-chemsitry still a challenging field?”
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/apmc.1997.052440106
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  • 29
    Digitale Medien
    Digitale Medien
    Fire-retardant action of potassium nitrate in polyamide 6 (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 245 (1997), S. 23-35 
    Details
    ISSN: 0003-3146
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Beschreibung / Inhaltsverzeichnis: Die Zugabe von 10-20 Gew.-% Kaliumnitrat (KN03) zu Polyamid 6 (PA 6) vermindert die Brennbarkeit des Polymeren. Das thermische Verhalten der KN03/PA 6-Mischung wurde mittels Thermogravimetrie, Differentialkalorimetrie und Analyse der fluchtigen Anteile untersucht. Feste Zersetzungsprodukte der Mischung wurden mittels Infrarotspektroskopie, Rontgendiffraktometrie und Elektronenresonanzspek-'troskopie analysiert. Es wurde gefunden, daß KNO3 dem Flielßen und Tropfen der Schmelze vorbeugt und die Karbonisierung auf der Oberflache des Polymeren fordert. Das verringert die Brandgefahr und verbessert die Feuerbestandigkeit. Andererseits geht KNO3 mit PA 6 in der kondensierten Phase eine exotherme Reaktion ein und setzt Sauerstoff frei, der wiederum die Brennbarkeit von PA 6 begiinstigt. Der Mechanismus der chemischen Wechselwirkung van KNO3 mit PA 6 wird diskutiert.
    Notizen: The addition of 10-20 wt.-% of potassium nitrate (KNO3) to polyamide 6 (PA 6) improves the fire retardance of the polymer. The thermal decomposition behaviour of the PA 6/KN03-mixture was studied using thermogravimetry, differential scanning calorimetry and thermal volatilisation analysis. Solid products of the thermal decomposition of the mixture were analysed by infrared spectroscopy, X-ray diffraction and electron paramagnetic resonance. It was found that KNO, prevents flowing and dripping of the melt and promotes charring on the surface of the polymer which decreases its fire hazard and improves its fire retardance. On the other hand, KNO3 exothermally reacts with PA 6 in the condensed phase and supplies oxygen to the gas phase which increases the combustibility of PA 6. The mechanism of the chemical interaction of KN03 with PA 6 is discussed.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/apmc.1997.052450103
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  • 30
    Digitale Medien
    Digitale Medien
    Effect of tricalcium phosphate, hydroxyethyl methacrylate, and ethylene glycol dimethacrylate on the mechanical properties of acrylic bone cement (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 245 (1997), S. 49-62 
    Details
    ISSN: 0003-3146
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Beschreibung / Inhaltsverzeichnis: Der Einfluß einer Beimischung von Tricalciumphosphat (TCP), Hydroxyethylmethacrylat (HEMA) und Ethylenglycoldimethacrylat (EGDMA) auf die Eigenschaften eines chirurgischen Knochenzements wurde untersucht. Die in Zugversuchen entstandenen Bruchflächen wurden mittels Rasterelektronenmikroskopie charakterisiert. Der Einfluß der Additive auf den Temperaturanstieg während der Polymerisation wurde geprüft. Zug-, Biege- und Druckfestigkeit des ausgehärteten Zements nahmen mit zunehmendem TCP-Gehalt ab, der Elastizitätsmodul stieg dagegen an. Die Zugfestigkeit nahm mit steigendem HEMA-Gehalt geringfügig zu und blieb oberhalb 15 Gew.-% HEMA konstant. Zug-, Biege- und Druckfestigkeit zeigten bei einem EGDMA-Gehalt von 2 Gew.-% (in HEMA) ein Maximum. HEMA und EGDMA beschleunigten die Polymerisation, wogegen TCP retardierend wirkte.
    Notizen: The effects of the addition of tricalcium phosphate (TCP), hydroxyethyl methacrylate (HEMA), and ethylene glycol dimethacrylate (EGDMA) on the properties of standard surgical Simplex-P radiopaque bone cement have been investigated. The fracture surface after tensile test was studied by scanning electron microscopy. The influence of these components on the temperature rise during polymerization was investigated. It was found that the tensile strength, the bending strength, and the compressive strength decreased with increasing TCP content, whereas the inverse was observed for the Young's modulus. The tensile strength slightly increased with increasing HEMA content and then it levelled off when the HEMA content was higher than 15 wt.-%. It seemed that there were maximum tensile, bending and compressive strengths when 2 wt.-% EGDMA (in HEMA) was added. Polymerization occurred more rapidly when HEMA and EGDMA were added, whereas the inverse result was found with TCP.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/apmc.1997.052450105
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  • 31
    Digitale Medien
    Digitale Medien
    The relative physical and thermal properties of polyurethane elastomers. Effect of chain extenders derived from dihydroxynaphthalene (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 245 (1997), S. 89-104 
    Details
    ISSN: 0003-3146
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Beschreibung / Inhaltsverzeichnis: Polyurethanelastomere wurden in Gegenwart von zwei Dihydroxynaphthalin(DHN)-Verbindungen und deren bromierter Derivate als Kettenverlängerer hergestellt. Als Polyole wurden Polycaprolactondiol und Polytetramethylenglykol und als Diisocyanat-Komponenten Diphenylmethandiisocyanat (MDI) und Dicyclohexylmethan-4,4′-diisocyanat (HMDI) eingesetzt. Der Einfluß der Struktur der Kettenverlängerer auf die physikalischen und thermischen Eigenschaften der Polyurethane wurde untersucht. Wegen der besseren Phasenmischungswirkung der 1,5-DHN-Segmente haben die damit hergestellten Polyurethane höhere Glasübergangstemperaturen und bessere dynamische Eigenschaften als die Polyurethane auf 2,7-DHN-Basis. Der Einbau von bromierten DHN-Einheiten erschwert die Entflammbarkeit. Durch das große freie Volumen der Bromatome wird jedoch die Rotation der DHN-Einheiten eingeschränkt, was zu Polyurethanen mit verringerten Phasenmischungs- und Kristallisationsgraden führt. Die bromhaltigen Polyurethane zeigen zudem eine Verschlechterung der mechanischen und physikalischen Eigenschaften und eine erhöhte Löslichkeit.
    Notizen: Polyurethane elastomers were synthesized based on polyols such as poly(caprolactonediol) and poly(tetramethylene glycol), diisocyanates such as diphenylmethane-4,4′-diisocyanate (MDI) and dicyclohexylmethane-4,4′-diisocyanate (HMDI), and two dihydroxynaphthalenes (DHNs) and their brominated derivatives used as chain extenders. The effects of the chemical structures of the chain extenders on the physical and thermal properties of the polyurethanes were investigated. Because of the higher degree of phase mixing of the 1,5-DHN unit, the 1,5-DHN-based polyurethanes have higher Tg values and higher dynamic properties than 2,7-DHN-based polyurethanes. Introduction of bromine atoms increased the flame retardance. However, the large free volume of bromine atoms restricted the rotation of DHNs, thus, directly decreasing the degree of phase-mixing and crystallinity of the polyurethanes. Introducing bromine atoms also decreased the mechanical and dynamic properties and increased the solubility of the polyurethanes.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/apmc.1997.052450108
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  • 32
    Digitale Medien
    Digitale Medien
    Synthesis and characterization of polypyrrolepolyurethane cationomer composites (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 245 (1997), S. 139-147 
    Details
    ISSN: 0003-3146
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Beschreibung / Inhaltsverzeichnis: Aus Poly(oxytetramethylen), 4,4′-Bibenzyldiisocyanat, N-Methyldiethanolamin als Kettenverlängerer und Acrylsäure/Polyacrylsäure als Quaternisierungsagens wurden Poly(etherurethan)-Kationomere hergestellt. In aus diesen Kationomeren hergestellten Filmen wurde Pyrrol (15 Gew.-%) in Gegenwart von CuCl2 polymerisiert. Die Filme wurden mittels dynamisch-mechanischer Analyse, Thermogravimetrie und Differentialthermoanalyse charakterisiert. Die elektrische Leitfähigkeit beträgt für den Film ohne Polypyrrol 7.5 · 10-12 Ω-1 cm-1 und mit Polypyrrol 4.5 · 10-6 Ω-1 cm-1.
    Notizen: Poly(ether urethane) cationomers based on poly(oxytetramethylene), 4,4′-bibenzyldiisocyanate, N-methyldiethanolamine as chain extender, and acrylic acid/poly(acrylic acid) as quaternization agent were synthesized. Pyrrole (15 wt.%%) was polymerized in films of the ionomer containing CuCl2. The films were characterized by dynamic mechanical analysis, thermogravimetry and differential scanning calorimetry. The electric conductivity of the film without polypyrrole is 7.5 · 10-12 Ω-1 cm-1, while incorporation of polypyrrole increases the conductivity to 4.5 · 10-6 Ω-1 cm-1.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/apmc.1997.052450112
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  • 33
    Digitale Medien
    Digitale Medien
    Synthesis, characterization and polymerization of waxy monomers (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 245 (1997), S. 155-164 
    Details
    ISSN: 0003-3146
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Beschreibung / Inhaltsverzeichnis: Wachsartige Monomere und Vernetzer wurden aus kommerziellen Wachsen durch Veresterung mit 2-Hydroxyethylmethacrylat, Glycerindimethacrylat oder Glycidylmethacrylat oder durch Funktionalisierung mit 2-Isocyanatoethylmethacrylat synthetisiert. Die erhaltenen opaken Methacrylate mit Schmelzpunkten zwischen 45 und 80°C wurden in Substanz bzw. Toluollösung in Gegenwart von Radikalinitiatoren polymerisiert. Die Polymeren zeichnen sich durch eine breite Molmassenverteilung aus. Im Gegensatz zur Substanzpolymerisation ist der Doppelbindungsumsatz nach der Lösungspolymerisation nahezu vollständig. Aufgrund der hohen Molmasse der Monomeren ist der beobachtete Polymerisationsschrumpf sehr gering. Polymerisate mit Vernetzermonomeren zeigen eine verbesserte mechanische Stabilität.
    Notizen: Waxy monomers and crosslinkers, respectively, were synthesized from commercially available waxes by esterification with 2-hydroxyethyl methacrylate, glycerol dimethacrylate, or glycidyl methacrylate or by functionalization with 2-isocyanatoethyl methacrylate. The resulting opaque methacrylates with melting points between 45 and 80°C were polymerized in bulk and in toluene solution in presence of free radical initiators. The obtained polymers were characterized by a broad molecular weight distribution. Opposite to the bulk polymerization, the double bond conversion in solution polymerization is nearly quantitative. The observed volume shrinkage during polymerization is very low due to the high molecular weight of the monomers. Polymerizates containing crosslinking comonomers exhibit improved mechanical stability.
    Zusätzliches Material: 5 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/apmc.1997.052450114
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  • 34
    Digitale Medien
    Digitale Medien
    Zur Kinetik der stabilisierten Fällungs-polymerisation eines Kationischen Monomeren in wäßrigen Natriumchlorid-Lösungen (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 245 (1997), S. 165-181 
    Details
    ISSN: 0003-3146
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Beschreibung / Inhaltsverzeichnis: The stabilized free-radical precipitation polymerization of the cationic monomer N-(2-methacryloyloxyethyl)-N,N-dimethylbenzylammonium chloride (MADAMBQ) in aqueous solutions of sodium chloride was studied by reaction calorimetry. Poly(ethylene oxide) was used as stabilizer. The rate of polymerization reaches its maximum immediately after initiation and remains nearly constant up to 50 % conversion followed by a decrease that could be described by a first order kinetics. The particles formed are approximately 1 to 30 μm in diameter and are stable over a period of several months.A model based on the theory of homogeneous particle nucleation is suggested to describe the kinetic course of polymerization, taking into account the rate of polymerization in both phases. With the assumption that the concentration of monomer in the phases is determined by a Nernst distribution law, the kinetics of the early stage of polymerization can be modelled reasonably well.The solution polymerization and the unstabilized precipitation polymerization of MADAMBQ was also studied.
    Notizen: Die Kinetik der stabilisierten Fällungspolymerisation des kationischen Monomeren N-(2-Methacryloyloxyethyl)-N,N-dimethylbenzylammoniumchlorid (MADAMBQ) in wäßrigen Natriumchlorid-Lösungen wurde mittels Reaktionskalorimetrie untersucht. Polyethylenoxid höherer Molmasse wurde als Stabilisator eingesetzt. Die Reaktionsgeschwindigkeit ist über einen größeren Umsatzbereich nahezu konstant und fällt anschließend mit dem Umsatz annähernd linear ab. Die Teilchengrößenverteilung der gebildeten Dispersion ist bimodal mit Teilchen von etwa 1 bis 30 μm Durchmesser.Zur Beschreibung des Geschwindigkeitsverlaufs der Fällungspolymerisation wird ein Modell vorgeschlagen, das die Polymerisation in der Wasser- sowie in der Polymerphase berücksichtigt. Die Teilchenbildung soll durch homogene Nukleierung erfolgen. Es wird angenommen, daß die Konzentration des Monomeren in den Phasen durch ein Nernstsches Verteilungsgleichgewicht bestimmt wird. Zu Vergleichszwecken wurde auch die Polymerisation von MADAMBQ in Lösung und als nicht stabilisierte Fällungspolymerisation durchgeführt.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/apmc.1997.052450115
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  • 35
    Digitale Medien
    Digitale Medien
    An investigation of the grafting of cellulose powder with acrylamide under a magnetic field (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 246 (1997), S. 1-9 
    Details
    ISSN: 0003-3146
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Beschreibung / Inhaltsverzeichnis: Cellulosepulver, hergestellt durch Nitrierung von Eichen-Furfural-Lignocellulose, wurde mit Acrylamid radikalisch gepfropft. Die Pfropfreaktion wurde sowohl in Gegenwart eines äußeren Magnetfeldes (0,15-0,35 T) als auch ohne Magnetfeld durchgeführt. Der Einfluß von Monomerkonzentration, Initiatorkonzentration, Polymerisationszeit und temperatur sowie der magnetischen Feldstärke auf den Polymerisationsverlauf wurde untersucht. Es wurde festgestellt, daß der Pfropfumsatz mit zunehmender Feldstärke signifikant ansteigt.
    Notizen: Cellulose powder obtained from oak furfural lignocellulose by nitration reaction was grafted with acrylamide using a radical initiation. The grafting reactions were carried out and compared both in presence and in absence of a continuous external magnetic field with the intensity extended between 0.15-0.35 T. The effect of monomer and initiator concentration, time and temperature of reaction and magnetic field intensity onto the grafting process were examined. It was observed that the presence of a magnetic field leads to a significant increase of the graft conversion.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/apmc.1997.052460101
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  • 36
    Digitale Medien
    Digitale Medien
    Radical polymerization of poly(butyl acrylate) in the presence of poly(L-lactic acid), 1. Synthesis, characterization and properties of blends (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 246 (1997), S. 49-63 
    Details
    ISSN: 0003-3146
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Beschreibung / Inhaltsverzeichnis: Poly(L-milchsäure) ist ein biokompatibler, semikristalliner, thermoplastischer Polyester mit ungünstigen mechanischen Eigenschaften. Daher wurde in einem “reactive blending”-Prozeß ein Acrylkautschuk, n-Butylacrylat, mittels einer Suspensionspolymerisation in Wasser auf in einem organischen Lösungsmittel gelöste Poly(L-milchsäure) gepfropft. Die gebildeten Copolymeren konnten isoliert und durch NMR-Spektroskopie und DSC-Messungen charakterisiert werden. Die Untersuchung der mechanischen Eigenschaften ergab keine befriedigenden Ergebnisse, weil die Kautschukphase wahrscheinlich aus viskosen linearen Makromolekülen besteht und daher keine elastischen Eigenschaften besitzt. In weiteren Arbeiten soll der Syntheseweg so modifiziert werden, daß durch den Einbau von Diacrylaten eine zumindest partielle Vernetzung der Kautschukphase erreicht wird.
    Notizen: Poly(L-lactic acid) is a biocompatible polyester, semicrystalline, thermoplastic, with low versatility in mechanical properties. To overcome this problem, a reactive blending procedure was performed by grafting an acrylic rubber, n-butyl acrylate, via water suspension polymerization onto poly(L-lactic acid) dissolved in an organic solvent. It was possible to isolate the copolymeric phase formed from the two polymers and characterize it by using NMR and DSC techniques. Mechanical tests on blends gave no satisfactory response, probably because the rubbery phase is composed essentially of viscous linear macromolecules, not able to perform elastic properties. Work is in progress to modify the synthetic pathway to incorporate diacrylates in order to realize a rubbery phase at least partially cross-linked.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/apmc.1997.052460104
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  • 37
    Digitale Medien
    Digitale Medien
    Tin-coupled styrene-butadiene rubbers (SBRs). Relationship between coupling type and propertiesBased on a paper presented at the 148th Meeting of the Rubber Division, American Chemical Society, Cleveland, Ohio, 17-20 October 1995. (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 246 (1997), S. 85-96 
    Details
    ISSN: 0003-3146
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Beschreibung / Inhaltsverzeichnis: Zur Entwicklung von neuen Styrol-Butadien-Kautschuken (SBRs) für Reifenanwendungen sind mehrere Arten von Zinn-Polymer-Bindungen (Styryl-, Butadienyl-, Isoprenyl- and α-Methylstyryl-Zinn) sowohl in linearen als auch in verzweigten Ketten untersucht worden. Die dynamisch-mechanischen Eigenschaften von Vulkanisaten mit Ruß wurden analysiert, um eine Beziehung zwischen den Strukturparametern der Polymeren und den Materialeigenschaften herzustellen. Der Polymer-Füll-stoff-Wechselwirkungsparameter, der durch das Verhältnis von mechanischen und dynamischen Termen definiert ist, wurde zur Charakterisierung der Verbindungen herangezogen. Der Einbau von verschiedenen Zinn-Polymer-Bindungen in lineare und in verzweigte SBR-Ketten bewirkte eine Verbesserung der Hystereseeigenschaf-ten der Vulkanisate und eine Veranderung des Wechselwirkungsparameters.
    Notizen: Following the development of new SBRs for tyre applications, several kinds of tin-polymer bonds (styryl-, butadienyl-, isoprenyl- and α-methylstyryltin) have been studied, in both branched and linear chains.Dynamic-mechanical properties of the carbon black vulcanizates have been analyzed to establish a relationship between structural parameters of polymers and compound properties. The filler-polymer interaction parameter, defined by a ratio of mechanical and dynamic terms, has been used for the evaluation of the compounds. The introduction of different types of tin-polymer bonds, in branched and linear chains of the SBRs, implies an improvement in the hysteresis properties of the vulcanizates as well as a modification of the interaction parameter.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/apmc.1997.052460107
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  • 38
    Digitale Medien
    Digitale Medien
    A novel spin-finishing method for antistatic modification of polyester fiber. Surface reaction onto amine-containing copoly(amide-ethers) blended with polyester fiber (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 246 (1997), S. 109-123 
    Details
    ISSN: 0003-3146
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Beschreibung / Inhaltsverzeichnis: Copoly (amid-ether) rnit zwei unteschiedlichen Aminfunktionalitäten wurden als antistatische Modifikatoren für Polyethylenterephthalatfasern (PET) eingesetzt. Die tertiären Aminogruppen schmelzegesponnener Copolymerfilamente wurden rnit drei Alkylierungsmitteln umgesetzt, wobei ein Sulfobetain, ein Carbobetain bzw. Ammoniumionen gebildet wurden. Dadurch wurde der scheinbare spezifische Widerstand der Filamente auf größfienordnungsmäßfiig 106 bis 108 Ω/cm verringert. Da sich die quaternisierten Copolymeren beim Blend-Spinnen rnit PET zersetzen, wurden Blendfasern von PET mit einem Copolymeren nach dem Schmelzespinnen einer Quaternisierung oder Vernetzung rnit Alkylierungsmitteln bzw. Epoxyvernetzern unterzogen, was die antistatischen Eigenschaften der Fasern im Vergleich rnit der unbehandelten Faser verbesserte. Insbesondere die mit Epoxiden vernetzten Fasern wiesen antistatische Eigenschaften auf, wie sie mit dieser Modifizierungsmethode bislang nicht erreicht wurden. Die antistatischen Eigenschaften blieben nach dem Fkben erhalten, da sowohl die hydrophilen als auch die ionischen Gruppen auf der Faseroberflache immobilisiert waren. Da Quaternisierung bzw. Vernetzung in einem Arbeitsgang rnit dem Verspinnen und Verstrecken der Fasern innerhalb einer kurzen Reaktionszeit erfolgen, sollte diese “spin-finishing„ genannte Methode konventio- nellen Verfahren bezuglich Kosten und Produktivitat uberlegen sein.
    Notizen: Copoly(amide-ethers) containing two types of tertiary amine units were made as antistatic modifiers for poly(ethylene terephthalate) (PET) fibers. The filaments of the copolymers were melt-spun and reacted with three alkylating agents in order to quaternize the tertiary amine into a sulfo-betaine, a carbobetaine, and an ammonium ion. The apparent electric resistivity of the filaments was greatly reduced by this reaction, being in the range of 106 to 108 Ω/cm. However, because these quaternized copolymers incurred decomposition during blend spinning with PET, a blend PET fiber containing one type of copoly(amide-ether) was melt-spun and subjected to quaternization of the amino groups as well as to surface crosslinking with various alkylating and epoxy agents. The quaternized blend fibers obtained showed improved antistatic properties compared with the original blend fiber. Particularly, the fibers crosslinked with epoxy compounds were found to have the best antistatic properties that had ever been attained with this type of modification. The antistatic properties were retained even after dyeing, because both hydrophilic and ionic groups had been effectively immobilized on the surface. Since this quaternization and crosslinking could be conducted on-line with spinning and drawing within a short reaction time, this modification technique is called “spin-finishing method”, which should be superior to the conventional methods in terms of cost performance and productivity.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/apmc.1997.052460109
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  • 39
    Digitale Medien
    Digitale Medien
    Etching of a low-density polyethylene film by fuming nitric acid (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 249 (1997), S. 33-46 
    Details
    ISSN: 0003-3146
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Beschreibung / Inhaltsverzeichnis: Filme aus Polyethylen niedriger Dichte (LDPE) wurden mit rauchender Salpetersäure behandelt. Die Oberflächeneigenschaften sowie die Bildung polarer Gruppen wie auf der geätzten Filmoberfläche wurden mit SEM-, IR- und XPS-Methoden analysiert. Die mechanische Festigkeit eines aus dem geätzten LDPE-Film und einem Epoxidharz hergestellten Laminats sowie die Bedruckbarkeit der geätzten Oberflächen wurden untersucht und mit einer unbehandelten Probe verglichen. Die Oberflächenrauhigkeit und die Gegenwart polarer Gruppen erhöhen die mechanische Festigkeit des Laminats aus dem geätzten Film durch mechanische Verankerung und chemischer Wechselwirkungen. Die Oberfläche des behandelten LDPE-Films ist besser bedruckbar als die des unbehandelten Films.
    Notizen: Low-density polyethylene (LDPE) films were treated with fuming nitric acid (FNA). The surface characteristics and also the insertion of polar groups like on the etched LDPE film surface were measured by SEM, IR and XPS analyses, respectively. The mechanical performance of a laminate of the etched film with epoxy resin and also the printability of the etched film surface were tested and compared with the unetched sample. The surface roughening and the presence of polar groups enhance the mechanical strength of the laminate of FNA-treated film due to mechanical interlocking and chemical interaction. The printability of the treated film surface is also superior to that of the untreated LDPE film surface.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/apmc.1997.052490103
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  • 40
    Digitale Medien
    Digitale Medien
    Celluloseether als Trennschichten hydrophiler Polymermembranen (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 249 (1997), S. 11-32 
    Details
    ISSN: 0003-3146
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Beschreibung / Inhaltsverzeichnis: This paper reports on polymer membranes characterized by a surface layer of hydroxyalkyl derivatives of cellulose. Water compatible polymers like hydroxyalkyl derivatives of cellulose are preferably those exhibiting good chemical stability and desired membrane characteristics. Normally, water-compatible polymers used in the coating solutions must be rendered water-insoluble after coating. By adapting crosslinking conditions on separation problems, the membranes are useful for many processes in the fields of biotechnology, food and chemical industry.The membranes presented here possess the advantage of being highly resistant to chemical and biological degradation and, hence, have long lifetimes under many process conditions.
    Notizen: Es wird die Entwicklung hydrophiler Polymermembranen diskutiert, die nach Beschichtung mit Celluloseethern und anschließender Vernetzung auf den asymmetrischen Trägermembranen interessante Permeations- und Trenneigenschaften bei hervorragenden chemischen Stabilitäten, vor allem beim Membrantrennverfahren der Nanofiltration, aufzeigen. Weiterhin werden Aussagen zu den Gastrenneigenschaften der Celluloseetherkompositmembranen getroffen.Erläutert werden die Permeations- und Trenndaten der Kompositmembranen in Korrelation zur Vernetzung der Celluloseether anhand verschiedener Einflußgrößen, was qualitative und gegebenenfalls quantitative Aussagen zum Vernetzungsmechanismus der Celluloseetherderivate erlaubt. Dabei stehen die Vernetzungstemperatur, der Einfluß der katalysierenden Wasserstoffionen und bedingt die Vernetzungszeit im Vordergrund. Abgerundet werden die Arbeiten durch Ermittlungen rheologischer Daten, die in Zusammenhang zu den Vernetzungsreaktionen und damit zu membranspezifischen Größen stehen.Infolge der hervorragenden chemischen Stabilität der Celluloseether werden Einsatzmöglichkeiten der Kompositmembranen zur Nanofiltration niedermolekularer Verbindungen aus organisch hochbelasteten Systemen beschrieben.
    Zusätzliches Material: 30 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/apmc.1997.052490102
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  • 41
    Digitale Medien
    Digitale Medien
    Products of polycondensation of 4,4′-biphenyldithiol with some hydrocarbon dihalides (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 251 (1997), S. 13-21 
    Details
    ISSN: 0003-3146
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Beschreibung / Inhaltsverzeichnis: Polysulfide wurden mit hoher Ausbeute durch Hochtemperatur-Lösungspolykondensation von 4,4′-Dimercaptobiphenyl mit ausgewählten aliphatischen und aromatisch-aliphatischen Dihalogenkohlenwasserstoffen hergestellt. Um die optimalen Polykondensationsbedingungen zu bestimmen, wurde der Einfluß folgender Faktoren auf die reduzierte Viskosität und die Ausbeute der Polysulfide ermittelt: Art des organischen Lösungsmittels, Art des Halogenwasserstoff-Akzeptors, Konzentration der organischen Reagenzien, Reaktionstemperatur und -zeit. Die Polykondensation des Dithiols mit Bis(4-chlormethylphenyl)methan wurde als Modellsystem eingehender untersucht. Die Polysulfidstrukturen wurden mittels Elementaranalyse, IR-Spektroskopie und Röntgenstrukturanalyse bestätigt. Aus der thermogravimetrischen Analyse wurden die Zersetzungstemperatur, der Gewichtsverlust bei dieser Temperatur und das Maximum der Zersetzungsgeschwindigkeit erhalten. Weiterhin wurden einige physikalisch-chemische, mechanische und dielektrische Eigenschaften ermittelt. Die beste thermische und chemische Bestandigkeit zeigt das aus dem Dithiol und 4,4′-Bis(chlormethyl)biphenyl hergestellte Polysulfid, was auf dessen vorwiegend aromatische Struktur zuriickgefuhrt werden kann.
    Notizen: Polysulfides were synthesized with high yield by high-temperature solution polycondensation of 4,4′-biphenyldithiol with selected aliphatic and aromatic-aliphatic hydrocarbon dihalides. To determine the optimum polycondensation conditions, the influence of the following factors on reduced viscosity and yield was studied: type of organic solvent, type of hydrogen halide acceptor, concentration of reagents, reaction temperature, and reaction time. A thorough examination was carried out only for the polycondensation of dithiol with bis(4-chloromethylphenyl)methane chosen as model system. The structures of the polysulfides were confirmed by elemental analysis, X-ray analysis, and infrared spectroscopy. The temperature of initial decomposition, the percentage of mass loss, and the temperature of the fastest decomposition, process were determined from curves of differential thermal and thermogravimetric analysis. Some physicochemical, mechanical and electrical properties were determined. The highest thermal and chemical resistance has been found for the polysulfide obtained from 4,4′-biphenyldithiol and 4,4′-bis(chloromethyl)biphenyl, probably because of the predominantly aromatic structure.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/apmc.1997.052510102
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  • 42
    Digitale Medien
    Digitale Medien
    Organic-inorganic hybrid sol-gel materials, 2. Application for dental composites (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 251 (1997), S. 61-72 
    Details
    ISSN: 0003-3146
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Beschreibung / Inhaltsverzeichnis: Drie organisch-anorganische Hybridmaterialien wurden nach dem Sol-Gel-Verfahren durch kovalenten Einbau von Poly(styrol-co-methylmethacrylat)(Poly(St-co-MMA))-, Polymethylmethacrylat(PMMA)- und Polystyrol(PS)-Struktureinheiten in ein SiO2-Netzwerk hergestellt und als Füllstoffe (bis zu 60 Gew.-%) in Dentalharzen verwendet. Der Einfluß der Füllstoffe auf einige mechanische Eigenschaften der Harze wurde untersucht. Die Härte der gefüllten Dentalharze nahm mit steigendem Füllstoffgehalt zu, wogegen die Biegefestigkeit abnahm. Die Druckfestigkeit der gefüllten Harze war besser als die des ungefüllten Harzes, nahm jedoch mit steigendem Füllstoffgehalt ab.
    Notizen: By incorporating poly(methyl methacrylate) (PMMA), polystyrene (PS), and poly(styrene-co-methyl methacrylate) (poly(St-co-MMA)) structure units covalently into the SiO2 glass network via a sol-gel approach, three organic-inorganic hybrid materials (PMMA-SiO2, PS - SiO2, and poly(St-co-MMA) - SiO2) have been prepared. The three hybrid sol-gel materials were used as filler (up to 60 wt.-%) for dental composite resins. The effect of the three filler materials on several mechanical properties of the dental composite resins was investigated. The hardness of the filled dental composites increased with increasing filler content, whereas the bending strength decreased. The compressive strength of the composites was improved, compared with the unfilled resin, but decreased with inreasing filler content.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/apmc.1997.052510106
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  • 43
    Digitale Medien
    Digitale Medien
    Adsorption of BTX compounds from aqueous solutions by water-insoluble starch (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 251 (1997), S. 107-116 
    Details
    ISSN: 0003-3146
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Beschreibung / Inhaltsverzeichnis: Die Adsorption von Benzol, Toluol und p-Xylol (BTX) aus wäßrigen Lösungen mittels hochvernetzter kationischer Stärke mit tertiären Amingruppen wurde untersucht. Der endotherme Adsorptionsvorgang ist vom Anfangs-pH-Wert und der Anfangskonzentration abhängig und kann mit einer Langmuir-Isotherme beschrieben werden.Die Adsorptionswärme (Δ) bei pH 4 beträgt für Benzol, Toluol und Xylol 29,45 kJ mol-1, 34,41 kJ mol-1 bzw. 35,58 kJ mol-1, bei pH 10 30,17 kJ mol-1, 35.56 kJ mol-1 bzw. 39,39 kJ mol-1. Die adsorbierte Menge nimmt in der Reihenfolge Benzol 〉 Toluol 〉 Xylol ab.
    Notizen: The removal of benzene, toluene and p-xylene (BTX) compounds from aqueous solutions with highly crosslinked cationic starch containing tertiary amine groups was investigated. The adsorption process has found to be initial pH- and initial concentration-dependent, endothermic, and follows the Langmuir isothermal adsorption.The heats of adsorption (ΔH) at initial pH = 4 of benzene, toluene and p-xylene compounds are 29.45 kJ mol-1, 34.41 kJ mol-1, and 35.58 kJ mol-1, respectively, those at initial pH = 10 are 30.17 kJ mol-1, 35.56 kJ mol-1, and 39.39 kJ mol-1, respectively. The order of the amount of adsorbed BTX compounds on the adsorbent is benzene 〉 toluene 〉 p-xylene.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/apmc.1997.052510110
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  • 44
    Digitale Medien
    Digitale Medien
    Thermogravimetric and ESR studies of polymer/metal precursors for high-temperature superconductors (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 251 (1997), S. 157-170 
    Details
    ISSN: 0003-3146
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Beschreibung / Inhaltsverzeichnis: Bi-Sr-Ca-Cu-Komplexverbindungen von Polymethacrylsäure (PMAA) und Kresolnovolaken, die als Precursoren für Hochtemperatursupraleiter (HTSL) eingesetzt werden, sowie deren Cu-Komplexsalze wurden ESR-spektroskopisch und thermogravimetrisch untersucht. In den PMAA-Proben wurden drei verschiedene Cu2+-Spezies nachgewiesen: i) Cu2+-Paare, ii) isolierte Cu2+-Ionen und iii) Cu2+-Cluster. Bei niedrigem Cu-Gehalt der Proben bilden die Cu2+-Paar-Bindungen den Hauptanteil, bei hohem Cu-Gehalt überwiegen die Clusterbindungen. In den Novolakproben wurden nur isolierte Cu2+-Ionen und Cu2+-Cluster nachgewiesen. Die Einführung der Cu-Ionen erniedrigt die thermische Stabilität der Polymeren, der thermische Abbau erfolgt stufenweise. In den PMAA-Proben wird die erste Abbaustufe bei ≈ 220°C durch die Cu2+-Paar-Komplexe verursacht.
    Notizen: Bi-Sr-Ca-Cu complexes of poly(methacrylic acid) (PMAA) and cresol novolac, which are precursors for high-temperature superconductors (HTSC) and Cu complexes of those polymers were investigated by ESR spectroscopy and thermogravimetry. In the PMAA samples three different kinds of Cu2+ species were detected: i) Cu2+ pairs, ii) isolated Cu2+ ions and iii) Cu2+ clusters. While Cu2+ pairs are the main species at low Cu concentrations, clusters become dominant at high Cu contents. In the novolac samples Cu2+ was only detected in isolated sites and clusters. The introduction of Cu ions lowered the thermal stability of the polymers and led to a stepwise decomposition. In the PMAA samples the first decomposition step at ≈ 220°C is caused by the Cu2+ pair complexes.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/apmc.1997.052510114
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  • 45
    Digitale Medien
    Digitale Medien
    Polymerization of 1,3-butadiene with neodymium chloride/2-ethylhexanolate/triethylaluminium catalyst systemIPCL communication No. 325. (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 251 (1997), S. 193-205 
    Details
    ISSN: 0003-3146
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Beschreibung / Inhaltsverzeichnis: Neodymchlorid-2-ethylhexanolate mit der allgemeinen Formel NdCl3 · nL wurden durch eine Liganden-Austauschreaktion zwischen Neodymchloridisopropanolat (I) und 2-Ethylhexanol (EH) hergestellt. Die Hexanolate NdCl3 · 1,5 EH (II) und NdCl3 · 2,5 EH (III) wurden durch Elementaranalyse und Gravimetrie charakterisiert. Die katalytische Aktivität der Hexanolate bei der Homopolymerisation von 1,3-Butadien in Gegenwart von Triethylaluminium wurde untersucht. Die Verbindung III zeigte eine höhere Aktivität als die Verbindung II. Höhere Katalysator- und Cokatalysatorkonzentrationen sowie eine höhere Temperatur steigerten den Umsatz, wogegen die Viskosität der Produkte abnahm. Mit zunehmender Reaktionszeit erhöhten sich sowohl der Umsatz als auch die Viskosität. Die cis-1,4-Konformation wurde durch die Variation von Temperatur und Cokatalysatorkonzentration beeinflußt. Der gesamte Anteil der cis-1,4-Stuktur lag jedoch in allen Fällen über 99%, während die Produkte nur einen sehr geringen Vinyl-Anteil von 〈1% enthielten. Die Zugabe einer elektronenspendenden Verbindung verringerte den cis- 1,4-Gehalt aber auf 87%.
    Notizen: Neodymium chloride 2-ethylhexanolates of the general formula NdCl3 · nL were prepared by ligand exchange reaction between neodymium chloride ispropanolate (I) and 2-ethylhexanol (EH). These hexanolates, NdCl3 · 1.5 EH (II) and NdCl3 · 2.5 EH (III), were characterized by elemental analysis and gravimetry. The catalytic activity of these hexanolates in combination with triethyl aluminium in the homopolymerization of 1,3-butadiene was studied, and the activity was found to be higher with III than II. The conversions increased with increasing the catalyst and co-catalyst concentrations and the temperature, whereas the intrinsic viscosity decreased. The conversions and the intrinsic viscosity decreased. The conversions and the intrinsic viscosity increased with reaction time. The cis-1,4 structure was influenced by variation in temperature and co-catalyst concentration, however, the total cis-1,4 structure was always more than 99% with very low vinyl content (〉1%). Addition of an external electron donor decreased the cis-1,4 content to 87%.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/apmc.1997.052510117
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  • 46
    Digitale Medien
    Digitale Medien
    The effects of desolvation methods of the recrystallized MgCl2-alcohol adduct on catalyst characteristics and the bulk density of polyethylene (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 253 (1997), S. 17-25 
    Details
    ISSN: 0003-3146
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Beschreibung / Inhaltsverzeichnis: MgCl2-Träger für einen Ethylenpolymerisationskatalysator wurden mit Hilfe der Rekristallationsmethode hergestellt, wobei Methanol als Lösungsmittel diente. Der Einfluß verschiedener Lösungsmethoden des rekristallisierten MgCl2-Alkohol-Adduktes auf die morphologischen Charakteristika der Katalysatoren wurde untersucht. Die Lösungsmethode beeinflußt die Eigenschaften der Katalysatoren beträchtlich. Die dargestellten Katalysatoren wiesen unterschiedliche Ti/Mg-Verhältnisse auf, sowohl was die Oberfläche als auch die gesamten Katalysator-Partikel betrifft. Betrachtet man die Ti-Verteilung und Aktivitätsprofile, dann erweisen sich nicht nur die Polymerisationsbedingungen, sondern auch die Ti-Verteilung auf dem Katalysator als wichtige Faktoren, welche die Dichte der Polymeren beeinflussen.
    Notizen: The MgCl2 supports for an ethylene polymerization catalyst were prepared by the recrystallization method using methanol as a solvent. The effects of different desolvation methods of the recrystallized MgCl2-alcohol adduct on the morphological characteristics of the catalysts were examined. The desolvation method greatly affects the characteristics of the catalyst. The prepared catalysts had different Ti/Mg ratios with respect to both surface content and entire catalyst particles. Considering Ti distribution and activity profiles, not only the polymerization conditions but also the Ti distribution on the catalyst appear to be an important factor which affects the bulk density of the polymers.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/apmc.1997.052530102
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  • 47
    Digitale Medien
    Digitale Medien
    Synthesis of aromatic poly(ether ketone)s with ferrocene units in the main chain (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 253 (1997), S. 89-97 
    Details
    ISSN: 0003-3146
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Beschreibung / Inhaltsverzeichnis: Aromatische Poly(etherketon)e mit Ferrocen-Einheiten in der Hauptkette wurden durch direkte Polykondensation von 1,1′-Ferrocendicarbonsäure mit Diphenylether oder 1,4-Diphenoxybenzol hergestellt. Als Katalysatoren wurden Trifluormethansulfonsäure, Methansulfonsäure/P2O5 (Eatons Reagens) oder Trifluormethansulfonsäure/P2O5 verwendet. Polykondensationen bei Raumtemperatur für 24 h ergaben Poly(arylenetherketon)e mit Grenzviskositäten bis zu 40 mL g-1. Die Monoacylierung von Diphenylether mit Ferrocencarbonsäure wurde im Hinblick auf die Effektivität von Eatons Reagens als Katalysator und Lösungsmittel eingehender untersucht.
    Notizen: Aromatic poly(ether ketone)s with ferrocene units in the main chain were prepared by direct polycondensation of 1,1′-ferrocenedicarboxylic acid with diphenyl ether or 1,4-diphenoxybenzene using various catalysts such as trifluoromethanesulfonic acid (triflic acid), a combination of methanesulfonic acid/P2O5 (Eaton's reagent) or a combination of triflic acid/P2O5. Polycondensations at room temperature for 24 h gave poly(arylene ether ketone)s with inherent viscosities up to 40 mL g-1. Monoacylation of diphenyl ether with ferrocenecarboxylic acid was studied in detail in order to show the efficiency of polymer formation employing Eaton's reagent as catalyst and solvent.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/apmc.1997.052530107
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  • 48
    Digitale Medien
    Digitale Medien
    Mechanical and structural characteristics of phenolphthalein poly(ether sulfone)/ultra-high molecular weight polyethylene blends (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 251 (1997), S. 73-80 
    Details
    ISSN: 0003-3146
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Beschreibung / Inhaltsverzeichnis: Die mechanischen und strukturellen Eigenschaften von Blends aus Phenolphthalein-Polyethersulfon und ultrahochmolekularem Polyethylen (UHMWPE) wurden anhand von Zug- und Biegeversuchen, Raster- und Transmissionselektronenmikroskopie untersucht. Die Zugabe einer geringen Menge UHMWPE (2 Gew.-%) führt zu einer Verstärkung der PES-C-Matrix. Höhere UHMWPE-Konzentrationen verschlechtern die mechanischen Eigenschaften. Die Strukturuntersuchungen zeigen, daß die Blends im gesamten Zusammensetzungsbereich mehrphasig sind. Bei geringen UHMWPE-Konzentrationen ist die UHMWPE-Phase gleichmäßig verteilt und entlang der Fließrichtung orientiert, was mit der starken Grenzflächenadhäsion zur Verbesserung des mechanischen Verhaltens beiträgt. Mit steigender UHMWPE-Konzentration nimmt die Domänengröß der UHMWPE-Phase zu.
    Notizen: Mechanical and structural properties of blends of phenolphthalein poly(ether sulfone) (PES-C) with ultra-high molecular weight polyethylene (UHMWPE) were investigated using tensile and bending testing, scanning electron microscopy and transition electron microscopy. The incorporation of minor amounts of UHMWPE (2 wt.-%) into PES-C has a reinforcement effect. With higher concentrations of UHMWPE, the mechanical properties decrease gradually. Structural studies demonstrated that the blends are multiphasic in the whole composition range. The minor UHMWPE, dispersed uniformly and oriented along the flow direction, as well as the strong interfacial adhesion contribute to the increase of the mechanical performance of the blends. The domain size of the UHMWPE phase was found to increase with the increase of its concentration.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/apmc.1997.052510107
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  • 49
    Digitale Medien
    Digitale Medien
    Redox copolymer with N-bromosulfonamide groups for the decomposition of cyanide ions in dilute aqueous solutions (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 251 (1997), S. 117-130 
    Details
    ISSN: 0003-3146
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Beschreibung / Inhaltsverzeichnis: Ein Redoxcopolymeres, ein makroporöses Poly(Styrol-co-Divinylbenzol) (S/DVB)-Harz mit N-Bromsulfonamidgruppen, wurde angewandt, um Cyanide aus wäßrigen Lösungen zu entfernen. Dieses Harz enthält aktives Brom in den funktionellen Gruppen (1.86 mmol g-1, 3.72 meq g-1) und weist Oxidationseigenschaften auf. Es wurde sowohl in statischen als auch in dynamischen Systemen für die Oxidation von Cyanidionen zu nichttoxischen Verbindungen angewandt. Die Reaktionen wurden in wäßrigen Lösungen mit 26-2600 mg L-1 CN- bei unterschiedlichen pH-Werten durchgeführt. Die Ergebnisse zeigten, daß dieses Harz die Cyanide leicht zu Cyanaten oxidiert, die ca. 1000 mal weniger toxisch sind. Bei Kontakt mit dem Harz fiel die Cyanidkonzentration in den Lösungen unter 0.05 mg L-1 CN-. Die —SO2NBrNa-Gruppen gingen dabei in —SO2NH2-Gruppen über. Diese konnten wiederum mit Natriumhypochlorit- und Natriumbromid-Lösungen reaktiviert werden. Es wurde auch eine Alternative zu der Cyanidionenoxidation mit N-Bromsulfonamid-Harz untersucht, indem ein analoges N-Chlorsulfonamid-Harz in Gengenwart von katalytischen Mengen von Bromiden angewandt wurde.
    Notizen: A redox copolymer, macroporous poly(styrene-co-divinylbenzene) (S/DVB) resin having N-bromosulfonamide groups, was used for removal of cyanide ions from aqueous solutions. This resin contains active bromine in functional groups (1.86 mmol g-1, i. e. 3.72 meq g-1) and shows oxidative properties. It was employed in static and flow system for oxidation of cyanide ions to non-toxic compounds. The reactions were carried out in aqueous media containing 26-2600 mg L-1 CN- at different pH values. The data showed that the resin having active bromine easily oxidized cyanides, forming cyanates being 1000-times less toxic than cyanides. In contact with the resin the concentration of cyanides in tested solutions dropped below 0.05 mg L-1 CN-. During the oxidation processes the —SO2NBrNa groups transform to —SO2NH2 groups. They can be reactivated by use of sodium hypochlorite and bromide solutions. As an alternative to oxidation of cyanides by N-bromosulfonamide resin, the oxidation of these ions by N-chlorosulfonamide resin with addition of a small amount of bromides was examined.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/apmc.1997.052510111
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  • 50
    Digitale Medien
    Digitale Medien
    Mitteilungen/Announcements (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 251 (1997), S. 207-208 
    Details
    ISSN: 0003-3146
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: No Abstract
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/apmc.1997.052510118
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  • 51
    Digitale Medien
    Digitale Medien
    Hydrolytic and thermal stability of novel polyurethane elastomers (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 252 (1997), S. 33-43 
    Details
    ISSN: 0003-3146
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Novel Polyester glycols with alkyl side groups were used for the improvement of thermal stability and hydrolytic stability of polyester urethane elastomers. The novel polyester glycols used are poly( β -methyl- δ -valerolactone)glycol (PMVL), poly(3-methyl pentamethylene adipate) glycol (PMPA), poly(nonamethylene-co-2-methyl octamcthylene carbonate) gycol (PNCO). A mixture of PNCO and poly(dimethyl siloxane)gycol (PNCO/PDMS) was also used. Polyurethane network elastomers were prepared from 4,4′-diphenylmethane diisocyanate (or 2,4-tolylene diisocyanate), and a mixture of 1,4-butane diol and trimethylol propane by a prepolymer method. Mechanical properties, Tg, thermal stability, and hydrolytic stability were measured. Morphology were also measured by means of polarizing microscopy, dynamic viscoelastometer, and ESR. The properties of novel polyurethane elastomers have good mechanical properties comparable to those of the general purpose polyester urethanes, and better thermal and hydrolytic stability than PTMG-based polyurethane. These polyurethane elastomers were exposed in out door during 2 year in Nagasaki, JAPAN. The novel polyurethane clastomers held alomost constant values for gel fraction, swelling ratio, relative modulus during 12 months, while poly(oxytetramethylene oxide)-based polyurethane as a control decreased the these values. Relationship of degradation behaviors with chemical structure and morphology were discussed.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/apmc.1997.052520103
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  • 52
    Digitale Medien
    Digitale Medien
    Oxidizability of lactams and lactam-based polyamidesDedicated to Dr Jan Šebenda on the occasion of his 70th birthday (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 252 (1997), S. 139-151 
    Details
    ISSN: 0003-3146
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: In the chain oxidation of N-alkylamides with molecular oxygen, propagation is the ratedetermining step under conditions when the oxidation rate is independent of oxygen pressure. The oxidizability of lactams and lactam-based polyamides correlates with the energy of the formation of N-alkylamide radical by abstraction of hydrogen from the methylene group adjacent to nitrogen. While for lactams this energy depends on the number of carbons in the lactam ring, for N-alkylamides and polylactams such dependence is not observed.
    Zusätzliches Material: 1 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/apmc.1997.052520110
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  • 53
    Digitale Medien
    Digitale Medien
    Use of EPR to image nitroxyl radicals in hals stabilized polymers (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 252 (1997), S. 179-193 
    Details
    ISSN: 0003-3146
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: An X-band EPR-Imaging apparatus which allowed us to determine the distribution of nitroxyl radicals within solid samples of polymeric materials containing hindered amine stabilizers, is described. It is shown that EPR Imaging represents a powerful tool for investigating the growth and decay of nitroxyls formed in polymers irradiated under air for long periods. Since the variations of the radical concentration can be monitored both in time and in the space, this technique provides valuable information not easily attainable by means of other methods.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/apmc.1997.052520113
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  • 54
    Digitale Medien
    Digitale Medien
    Photo-oxidation mechanisms of poly(2,6-dimethyl-1,4-phenylene oxide). (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 252 (1997), S. 237-256 
    Details
    ISSN: 0003-3146
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: A re-examination of the photo-oxidation mechanism of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) at both long and short irradiation wavelengths under accelerated conditions is reported. The formation rate of poly-2,6-dimethylphenoxy (PDMP) radicals, have been observed by esr spectroscopy, while benzylic-type radicals have been detected by spin trapping experiments using nitrosodurene under UV irradiation conditions. The changes of FTIR spectra obtained under accelerated photo-oxidative conditions show the formation of primary oxidation products such as aromatic aldehydes and quinones. The direct formation of radical cations and superoxide anions by a photo-induced electron-transfer reaction is suggested under our conditions. In addition, some results on the of photo-oxidation PPO/PS blends as a function of polystyrene tacticity are also reported. In the case of syndiotactic polystyrene the blend photostability shows some differences in comparison with the blend containing atactic polystyrene. This effect has been ascribed to the absence of excimers in syndiotactic polystyrene which are not revealed by fluorescence measurements. Finally, the chemical modification of PPO with bromine gave a bromomethylated PPO with different amounts of CH2 Br groups, which has been used for further substitution reactions with alkoxy sodium salts of 4-hydroxy-2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) and 4-hydroxy-1,2,2,6,6-pentamethylpiperidine (PMPP). The accelerated photo-oxidation of a modified copolymer PPO-PMPP containing a 60% PMPP moieties as side groups and its blends with pure PPO has been followed by FTIR and esr spectroscopies. Some comparisons with a commercially available hindered amine light stabilizers (HALS) and a modified copolymer PPO-PMPP are also reported under the same photo-oxidative conditions.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/apmc.1997.052520116
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  • 55
    Digitale Medien
    Digitale Medien
    Zähigkeit und Relaxationsverhalten von Polymethylmethacrylat, Polystyrol und Polycarbonat (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 253 (1997), S. 27-49 
    Details
    ISSN: 0003-3146
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Beschreibung / Inhaltsverzeichnis: For innovative applications of plastics, which take advantage of special properties of polymeric materials, comprehensive understanding on strengthening and toughening mechanisms is required. The temperature-dependent mechanical behaviour of PMMA, PS and PC under dynamic loading conditions were investigated by means of an instrumented Charpy impact tester. The elastic-plastic fracture mechanics parameters, the energy-determined J-integral, and the deformation-determined crack opening displacement, δ, enable to do structure-related quantification of micromechanical processes. The J-integral values showed a maximum, resulting from an energy-dissipative process. The maximum values for PMMA occurred at 50°C and for PC at 40°C , which is related to the secondary(β) relaxation as evaluated from the frequency dependence of the mechanical loss factor. The 0-relaxation initiated shear deformation mechanisms, which led to a local increase of toughness. In polycarbonate, toughness is strongly increased due to a stress-induced shear flow process at temperatures higher than -25°C. Correlations between morphology and toughness can be derived with the help of optical investigations of stable crack propagation on fracture surfaces.
    Notizen: Innovative Kunststoffanwendungen, die die speziellen Eigenschaften polymerer Werkstoffe gezielt ausnutzen, erfordern vertiefte Kenntnisse über festigkeits- und zähigkeitsbestimmende Mechanismen. Das sich in Abhängigkeit von der Temperatur ändernde Werkstoffverhalten von PMMA, PS und PC wurde bei dynamischer Beanspruchung mittels instrumentierter Kerbschlagbiegeprüfung bestimmt. Mit der verformungsbestimmten Rißöffnungsverschiebung δ und dem energiebestimmten J-Integral stehen Kenngrößen der Fließbruchmechanik zur Verfügung, die eine strukturbezogene Quantifizierung der temperaturabhängigen mikromechanischen Prozesse erlauben. Die J-Integralwerte zeigen für PMMA bei 50°C und für PC bei -60°C ein durch einen energiedissipativen Prozeß verursachtes Maximum. Dieses Maximum steht, wie sich aus der Interpretation der Frequenzabhängigkeit des mechanischen Verlustfaktors ergibt, mit der Neben(β)-Relaxation in Beziehung. Dabei initiiert die β-Relaxation Scherdeformationsmechanismen, die ihrerseits die lokale Zähigkeitserhöhung bewirken. Ab -25°C führt für PC ein spannungsinduzierter Scherfließprozeß zu einer erheblichen Zähigkeitssteigerung. Durch die Einbeziehung lichtmikroskopischer Untersuchungen des stabilen Rißfortschritts auf der Bruchfläche können Morphologie-Zähigkeits-Korrelationen abgeleitet werden.
    Zusätzliches Material: 16 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/apmc.1997.052530103
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  • 56
    Digitale Medien
    Digitale Medien
    Thermostable block copolymers, 2Part 1 cf. 16.. Preparation and characterization of soluble blockcopolyimides (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 253 (1997), S. 71-88 
    Details
    ISSN: 0003-3146
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Beschreibung / Inhaltsverzeichnis: Eine Reihe von Polyamidimid-Polyimid-Blockcopolymeren (PAI-PI-BCPs) wurde durch Polykondensation von PAI-Blöcken mit Amino-Endgruppen und PI-Blöcken mit Anhydrid-Endgruppen hergestellt. Zur Synthese der Blöcke mit Molekulargewichten im Bereich von ca. 2000 bis 15000 wurden nur technisch leicht zugängliche Monomere, wie Trimellitsäureanhydridchlorid, Benzophenontetracarbonsäuredianhydrid, 4,4′-Diaminodiphenylmethan, 2,4-Toluylendiamin und 4,4′-Diaminodiphenylsulfon eingesetzt. Dabei zeigte sich, daß durch den blockartigen Aufbau die Löslichkeit-und damit die Verarbeitbarkeit-im Vergleich zu den reinen, unlöslichen Polyimiden wesentlich verbessert werden konnte, bei nahezu gleichbleibender Thermostabilität. So wurden BCPs mit guten mechanischen Eigenschaften, Thermostabilitäten bis ca. 480°C (Thermogravimetrie, 5% Gewichtsverlust) und guten Löslichkeiten in Dimethylacetamid und anderen polaren aprotischen Lösungsmitteln erhalten.
    Notizen: New poly(amide-imide)-poly(imide) block copolymers (PAI-PI-BCPs) were prepared by polycondensation of amino-terminated PAI-blocks with anhydride-terminated PI-blocks. For the syntheses of the blocks with molecular weights from 2000 to 15000 only commercially available monomers were used, e.g. trimellitic acid anhydride chloride, benzophenone tetracarboxylic acid dianhydride, 4,4′-diaminodiphenylmethane, 2,4-toluenediamine and 4,4′-diaminodiphenylsulfone. The BCPs were shown to have better solubility compared to the pure, insoluble PIs with only minor decrease of the thermostability. Thus, BCPs with good mechanical properties, thermostabilities up to 480°C (thermogravimetric analysis, 5% weight loss) and good solubility in dimethylacetamide and other polar aprotic solvents were obtained.
    Zusätzliches Material: 4 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/apmc.1997.052530106
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  • 57
    Digitale Medien
    Digitale Medien
    Block and graft copolymers with polysiloxane and poly(N-acyliminoethylene) sequences (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 253 (1997), S. 139-149 
    Details
    ISSN: 0003-3146
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Beschreibung / Inhaltsverzeichnis: Eine Reihe von Polysiloxan/Poly(N-acetyliminoethylen)-(PSiO/PNAI)-Block- und -Pfropfcopolymeren wurde durch Polymerisation von 2-Methyl-2-oxazolin (MeOZO) mit funktionellen Polysiloxan-Prepolymeren als Initiatoren synthetisiert. Die Copolymeren wurden mit IR- und 1H NMR-Spektroskopie sowie Elementaranalyse, Differentialkalorimetrie und Thermogravimetrie charakterisiert. Der Einbau sowohl von hydrophoben als auch von hydrophilen Sequenzen verleiht den Polymeren amphiphile Eigenschaften. Ihre Eigenschaften in Lösung und als Feststoffe lassen die Produkte für Anwendungen als nichtionische Emulgatoren, Oberflächenmodifikatoren, Gele, usw. geeignet erscheinen.
    Notizen: A series of polysiloxane/poly(N-acetyliminoethylene) (PSiO/PNAI) block and graft copolymers were synthesized by the initiation of 2-methyl-2-oxazoline (Me-OZO) polymerization with functional polysiloxane prepolymers. The copolymerization products were characterized by IR- and 1H NMR spectroscopy, elemental analysis, DSC and thermogravimetry. The insertion of both hydrophobic and hydrophilic sequences in the macromolecular structure induces a behavior characteristic of amphiphilic compounds. Their solution and solid state behavior evidenced peculiarities which make them able to act as nonionic emulsifiers, surface modifiers, gels, etc.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/apmc.1997.052530111
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  • 58
    Digitale Medien
    Digitale Medien
    The state of water in styrene-grafted and sulfonated poly(vinylidene fluoride) membranes (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 253 (1997), S. 151-167 
    Details
    ISSN: 0003-3146
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Beschreibung / Inhaltsverzeichnis: Der Zustand von Wasser in Protonenaustausch-Membranen, hergestellt durch Pfropfen von Styrol auf Polyvinylidenfluorid-Filme (PVDF-g-PS) mittels Elektronenstrahlen und anschließendes Sulfonieren (PVDF-g-PSSA), wurde mittels Differentialkalorimetrie (DSC), Raman-Spektroskopie und Rontgen-Diffraktion (SAXS) ermittelt. Die Raman-Untersuchungen zeigten, daß einzelne Wassermolekule durch hydrophobe Wechselwirkungen an die Polymerketten gebunden sind. Die DSC-Untersuchungen zeigten, daß Wasser in den Membranen in drei verschiedenen Umgebungen vorliegt: nicht gefrierendes ionisch gebundenes Wasser, gefrierendes freies Wasser und gefrierendes gebundenes Wasser. Die Menge an nicht gefrierendem Wasser betragt unabhangig vom Pfropfungsgrad etwa 10 H2O/SO3H (mol/mol). Die Menge an gefrierendem Wasser ist stark vom Pfropfungsgrad abhangig. Oberhalb eines Pfropfungsgrades von 50% werden Werte von 40 H20/S03H (mol/mol) erreicht. Die Leitfahigkeit von nur nicht gefrierendes Wasser enthaltenden Membranen ist gering, d. h., das ionisch gebundene Wasser kann nicht allein die fur den Transport von Protonen und Wasser notwendigen Kanale bilden. Die SAXS Untersuchungen zeigten, daß Wasser/Sulfonsaure-Cluster in Membranen aus hydratisiertem PVDF-g-PSSA mit einem Bragg-Abstand von 25 Å gebildet werden. Diese Cluster formen die Kanale fur den Ionentransport und die Leitfähigkeit.
    Notizen: The state of water in proton exchange membranes prepared by pre-irradiation (electron beam, 100 kGy) grafting of styrene onto poly(vinylidene fluoride) films (PVDF-g-PS), followed by sulfonation (PVDF-g-PSSA), has been studied with thermal analysis, Raman spectroscopy and small angle X-ray diffraction (SAXS). Raman spectra show that, in addition to free liquid water in the membranes, single water molecules are weakly bound to the polymer backbone. Thermal analysis shows that there are three types of water molecules in the membrane; non-freezable water associated with the ionic sites, freezable free water, and freezable bound water. The amount of non-freezable water is around 10 H2O/SO3H (mol/mol), and is independent of the degree of grafting (d.o.g.). The amount of freezable water is strongly dependent on the d.o.g. as long as the grafting has not penetrated the whole of the film, and reaches a value of around 40 H2O/SO3H (mol/mol) above a d.o.g. of 50%. The conductivity of membranes containing only the non-freezable water is low, i. e. the ionically bound water alone does not form the domains necessary for proton and water transport. SAXS measurements show that water/sulfonic acid clusters in hydrated PVDF-g-PSSA membranes with a Bragg distance of 25 Å are formed; these form the ion conducting channels in the membrane.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/apmc.1997.052530112
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  • 59
    Digitale Medien
    Digitale Medien
    MITTEILUNGEN/ANNOUNCEMENTS (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 253 (1997), S. 211-211 
    Details
    ISSN: 0003-3146
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/apmc.1997.052530117
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  • 60
    Digitale Medien
    Digitale Medien
    Tensile and flexural behavior of polypropene sheets with different crystallinities of surface layer (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 253 (1997), S. 201-210 
    Details
    ISSN: 0003-3146
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Beschreibung / Inhaltsverzeichnis: Die Zug- und Biegemoduli von preßgeformten Polypropen-Probekörpern mit unterschiedlichen Oberflächenkristallinitäten wurden basierend auf der Annahme eines Schicht-Verbund-Modells untersucht. Es zeigte sich, daß die Spannungs-Dehnungs-Kurven der Zugversuche und die Werte der Biegeablenkung im wesentlichen von der Oberfächenkristallinität abhängen, jedoch erwiesen sich die Bruchspannungen als von der Oberflächenkristallinität unabhängig. Es wird angenommen, daß das beobachtete Zug- und Biegeverhalten der Proben auf der Grundlage eines Schicht-Verbund-Modells, bei dem eine massive, starre Platte zwischen zwei weichen Schichten eingebettet ist, charakterisiert werden kann.
    Notizen: The tensile and flexural moduli of the compression-molded sheets of polypropene with different surface layer crystallinity were investigated based on a layered composite model. It was found that the tensile stress-strain curve and flexural deflection depended largely on the surface layer crystallinity, but the ultimate strain-at-break values were independent of the surface layer crystallinity. It is suggested that the tensile and flexural behavior can be characterized using a layered composite model in which a bulk plate was sandwiched between two surface layers.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/apmc.1997.052530116
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  • 61
    Digitale Medien
    Digitale Medien
    The role of charge transfer complexes in the photodegradation of polyolefins (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 252 (1997), S. 45-54 
    Details
    ISSN: 0003-3146
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Addition of HALS-stabilisers, the cut-off wavelength of the light source, the temperature and the oxygen pressure have an influence on the UV-degradation mechanism of polyolefins. All these parameters influences the conversion of oxygen into polymeric carbonyls. The results are explained assuming that the initiation of the UV-degradation of pololefins is due to substrate-oxygen charge transfer complexes (CTCs).
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/apmc.1997.052520104
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  • 62
    Digitale Medien
    Digitale Medien
    Fracture behavior of exposed HDPE specimens with an embrittled layer due to UV-exposure (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 252 (1997), S. 69-88 
    Details
    ISSN: 0003-3146
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The applicability of fracture mechanics was studied on UV-exposed HDPE Charpy specimens. The failure distribution of the stress at failure measured in three-points bending tests showed a bifurcation in failure processes. At high stresses yielding occurs, resulting in large strain at failures. At lower stresses crack propagation causes low strain at failures. Due to the bifurcation in failure processes the ductile-brittle transition temperature of exposed specimens is hard to determine.Specimens notched after exposure showed a decrease in the critical stress intensity values. The effective notch depth of exposed specimens was found to be larger than the thickness of the oxidized layer measured by FT-IR and density measurements.
    Zusätzliches Material: 21 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/apmc.1997.052520106
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  • 63
    Digitale Medien
    Digitale Medien
    Deactivation processes of 2-hydroxyphenyl-1,3,5-triazines  -  polymeric and monomeric UV absorbers of the benzotriazole and triazine class (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 252 (1997), S. 119-138 
    Details
    ISSN: 0003-3146
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: In the 2-hydroxyphenyl-1,3,5-triazines, the intramolecular hydrogen bond is stronger than in the corresponding 2-hydroxyphenylbenzotriazoles. Compounds with only one aryl group in the 2-hydroxyphenyl-1,3,5-triazine series show proton-transferred fluorescence with large Stokes shift and high quantum yield. No such fluorescence is observed, in contrast, for compunds with three aryi groups bearing no electrondonating groups on the aryl moieties. When the hydrogen atom of the intramolecular hydrogen bond is replaced by CH3, the respective derivative shows fluorescence with a normal Stokes shift.Various copolymers of MA-TIN 1 (2-[2-hydroxy-3-tert.-butyl-5-(O-[2-hydroxy-3-(2-methylpropenoyloxy)propyl]-2-carbonyloxyethyl)phenyl]benzotriazole), and MA-TZ 1 (2,4-Bis(2,4-dimethyl-phenyl)-6-[2-hydroxy-4-(2-hydroxy-3-[2-methylpropenoyloxy])propoxyphenyl]-1,3,5-triazine) with styrene, methyl methacrylate, and methacrylic acid have been synthesized by radical polymerization. The absorption spectra in the longwavelength UV region appear unchanged compared to those of the monomeric UV absorbers indicating that the stabilizer chromophores are conserved intact in the polymer. Both the monomeric and the polymeric stabilizers exhibit a strongly Stokesshifted, temperature-dependent, low-quantum-yield, proton-transferred fluorescence. This may be taken as evidence that the intramolecular hydrogen bond, which is essential for the photostability of this type of UV absorber, remains intact also in the copolymers. Activation energies of the radiationless deactivation process can be evaluated from the temperature dependence of this fluorescence. These energies lie between 4 and 5 kJ/mol for most of the benzotriazole and triazine stabilizers investigated.Fluorescence-decay measurements with crystalline MA-TIN 1 at different temperatures reveal a close correspondence of the temperature dependence between decay times and relative quantum yields. The radiationless process is thence concluded to originate from the proton-transferred level S1'. The decay time at room temperature is estimated at 70 ps, close to the value for crystalline TIN P (2-(2-hydroxy-5-methylphenyl)benzotriazole). The proton-transferred fluorescence of MA-TIN 1 exhibits a biexponential decay profile whereas solid TIN P, in contrast, displays only one single lifetime.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/apmc.1997.052520109
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  • 64
    Digitale Medien
    Digitale Medien
    Buckling transitions in superhelical DNA: Dependence on the elastic constants and DNA size (1997)
    New York : Wiley-Blackwell
    Biopolymers 41 (1997), S. 5-25 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Buckling transitions in superhelical DNA are sudden changes in shape that accompany a smooth variation in a key parameter, such as superhelical density. Here we explore the dependence of these transitions on the elastic constants for bending and twisting, A and C, important characteristics to DNA's bending and twisting persistence lengths. The large range we explore extends to other elastic materials with self-contact interactions, modeled here by a Debye-Hückel electrostatic potential.Our collective description of DNA shapes and energies over a wide range of ρ = A/C reveals a dramatic dependence of DNA shape and associated configurational transitions on ρ: transitions are sharp for large ρ but masked for small ρ. In particular, at small ρ, a nonplanar circular family emerges, in agreement with Jülicher's recent analytical predictions; a continuum of forms (and associated writhing numbers) is also observed.The relevance of these buckling transitions to DNA in solution is examined through studies of size dependence and thermal effects. Buckling transitions smooth considerably as size increases, and this can be explained in part by the lower curvature in larger plasmids. This trend suggests that buckling transitions should not be detectable for isolated (i.e., unbound) DNA plasmids of biological interest, except possibly for very large ρ. Buckling phenomena would nonetheless be relevant for small DNA loops, particularly for higher values of ρ, and might have a role in regulatory mechanisms: a small change in superhelical stress could lead to a large configurational change.Writhe distributions as a function of ρ, generated by Langevin dynamics simulations, reveal the importance of thermal fluctuations. Each distribution range (and multipeaked shape) can be interpreted by our buckling profiles. Significantly, the distributions for moderate to high superhelical densities are most sensitive to ρ, isolating different distribution patterns. If this effect could be captured experimentally for small plasmids by currently available imaging techniques, such results suggest a slightly different experimental procedure for estimating the torsional stiffness of supercoiled DNA than considered to date. © 1997 John Wiley & Sons, Inc.
    Zusätzliches Material: 13 Ill.
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  • 65
    Digitale Medien
    Digitale Medien
    Conformational analysis and molecular dynamics simulation of α-(1 → 2) and α-(1 → 3) linked rhamnose oligosaccharides: Reconciliation with optical rotation and NMR experiments (1997)
    New York : Wiley-Blackwell
    Biopolymers 41 (1997), S. 83-96 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Molecular mechanics and dynamics calculations were carried out on the disaccharides α-L-Rhap-(1 → 2)-α-L-Rhap-(1 → OMe) (1) and α-L-Rhap-(1 → 3)-α-L-Rhap-(1 OMe) (2), and the trisaccharide α-L-Rhap-(1 → 2)-α-L-Rhap-(1 → 3)-α-L-Rhap-(1 → OMe) (3). The semiflexible conformational behavior of these molecules was characterized by the occupation of a combination of different glycosidic linkage and side-chain conformational positions whose relative occupations were sensitive to dielectric screening. Molecular dynamics simulations of the trisaccharide 3 showed little difference between the linkage conformations in the trisaccharide and the component disaccharides 1 and 2.Experimental optical rotation data of 1 and 2 were obtained as a function of temperature in varying solvents. The molecular models were combined with the semiempirical theory of Stevens and Sathyanarayana to yield calculated optical rotations. Interpretation of the data of both 1 and 2 implied that a combination of conformations, both in glycosidic and side-chain positions, could explain the experimental data. Solvents effects were important in influencing the conformational mix and averaged optical rotation.Three-bond heteronuclear coupling constants 3JC, H were obtained for the glycosidic linkages of 1 and 2 in D2O and DMSO. Analysis of the coupling constants with a Karplus curve showed that small reductions in the glycosidic torsion angles of the conformations of the models used here of ca. 10°-15° in φ and 5°-10° in ψ were required to give better agreement with experiment; a combination of conformations for both 1 and 2 was consistent with the data. There was a negligible influence on the coupling constants of 1 on changing the solvent from D2O to DMSO. © 1997 John Wiley & Sons, Inc.
    Zusätzliches Material: 9 Ill.
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  • 66
    Digitale Medien
    Digitale Medien
    Protein folding: Optimized sequences obtained by simulated breeding in a minimalist model (1997)
    New York : Wiley-Blackwell
    Biopolymers 41 (1997), S. 165-180 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: For a minimalist model of protein folding, which we introduced recently, we investigate various methods to obtain folding sequences. A detailed study of random sequences shows that, for this model, such sequences usually do not fold to their ground states during simulations. Straightforward techniques for the construction of folding sequences, based solely on the target structure, fail. We describe in detail an optimization algorithm, based on genetic algorithms, for the “simulated breeding” of folding sequences in this model. We find that, for any target structure studied, there is not only a single folding sequence but a patch of sequences in sequence space that fold to this structure. In addition, we show that, much as in real proteins, nonhomologous sequences may fold to the same target structure. © 1997 John Wiley & Sons, Inc.
    Zusätzliches Material: 13 Ill.
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  • 67
    Digitale Medien
    Digitale Medien
    Fourier transform IR studies of the self-association of N-tert-butoxycarbonyl-α-amino acids (1997)
    New York : Wiley-Blackwell
    Biopolymers 41 (1997), S. 205-212 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The self-association of several N-urethanyl-L-amino acids (N-t-Boc-glycine, N-t-Boc-L-alanine, N-t-Boc-L-methionine, and N-t-Boc-O-Bz-L-tyrosine has been investigated in carbon tetrachloride by Fourier transform (FTIR) spectrometry. The fractions of nonbonded OH and NH groups have been determined from the intensities of the free OH and NH-stretching vibrations. The FTIR spectra have been examined in the carbonyl stretching regions by using Fourier self-deconvolution techniques. The results show that intermolecular hydrogen bonds are formed between the carboxylic acid group of one molecule and the urethane group of another molecule, suggesting that the leading factor for the self-association of N-t-Boc amino acids is the acidity of the OH groups. In N-t-Boc glycine, more heterodimers are formed than in the other amino acids. In N-t-Boc-O-Bz-L-tyrosine where the steric hindrance of the substituent implanted on the Cα atom is higher, the concentration of homodimers and heterodimers is lower than in N-t-Boc-L-alanine or N-t-Boc-L methionine. © 1997 John Wiley & Sons, Inc.
    Zusätzliches Material: 6 Ill.
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  • 68
    Digitale Medien
    Digitale Medien
    A heteropolymer model study for the mechanism of protein folding (1997)
    New York : Wiley-Blackwell
    Biopolymers 41 (1997), S. 239-250 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A heteropolymer model of randomly self-interacting chains in two dimensions is studied with numerical simulations in order to elucidate the folding mechanism of protein. We find that the model occasionally shows folding propensity depending on the sequence of random numbers given to the chain. We study the thermodynamic and kinematic roles in the folding mechanism by grouping the local energy minima found in the simulations into clusters according to the similarity of their conformations. It is suggested that the local minima to which some heteropolymers show a folding tendency are always the lowest energy states of the energy spectrum within a cluster, though which cluster is selected depends on the sequence. For the eight random sequences we study, we find that the energy gap between the ground state and excited states is little correlated with folding or nonfolding. We rather find that folding propensities are correlated with the global structure of the average energy surface, implying a dominant kinetic role in the folding mechanism, although thermal factors cannot be ignored as the mechanism of choosing the ground state within a cluster of states connected by small deformations. We suggest that a hierarchical cluster structure plays an important role in selecting a unique folded state out of the huge number of local minima of heteropolymers. © 1997 John Wiley & Sons, Inc.
    Zusätzliches Material: 11 Ill.
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  • 69
    Digitale Medien
    Digitale Medien
    Ordered aggregation of ribonucleic acids by the human immunodeficiency virus type 1 nucleocapsid protein (1997)
    New York : Wiley-Blackwell
    Biopolymers 41 (1997), S. 301-312 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The nucleocapsid protein NCp7, which is the major genomic RNA binding protein of human immunodeficiency virus type 1, plays an important role in several key steps of the viral life cycle. Many of the NCp7 activities, notably the nucleic acid annealing and the genomic RNA wrapping ones, are thought to be linked to a nonspecific binding of NCp7 to its nucleic acid targets. The mechanism of these activities is still debated but several clues are in favor of an intermediate aggregation of nucleic acids by NCp7. To check and characterize the nucleic acid aggregating properties of NCp7, we investigated the interaction of NCp7 with the model RNA homopolymer, polyA, by quasielastic light scattering and optical density measurements. The ordered growth of monodisperse large particles independently of the nucleic acid size and the almost complete covering of polyA by NCp7 strongly suggested an ordered aggregation mechanism. The aggregate kinetics of growth in the optimum protein concentration range (≥2 μM) were governed by a so-called Ostwald ripening mechanism limited by transfer of NCp7-covered polyA complexes from small to large aggregates. The aggregation process was strongly dependent on both Na+ and Mg2+ concentrations, the optimum concentrations being in the physiological range. Similar conclusions held true when polyA was replaced by 16S + 23S ribosomal RNA, suggesting that the NCp7 aggregating properties were only poorly dependent on the nucleic acid sequence and structure. Finally, as in the NCp7 annealing activities, the basic regions of NCp7, but not the zinc fingers, were found critical in nucleic acid aggregation. Taken together, our data indicate that NCp7 is a highly efficient nucleic acid aggregating agent and strengthen the hypothesis that aggregation may constitute a transient step in various NCp7 functions. © 1997 John Wiley & Sons, Inc.
    Zusätzliches Material: 5 Ill.
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  • 70
    Digitale Medien
    Digitale Medien
    NMR three-dimensional solution structure of the serine protease inhibitor cyclotheonamide A (1997)
    New York : Wiley-Blackwell
    Biopolymers 41 (1997), S. 349-358 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The nmr solution conformation of cyclotheonamide A (CtA) was determined in aqueous media. The data produced 15 distance and 10 torsional constraints which were used to generate conformations using restrained simulated annealing (SA) and distance geometry/simulated annealing (DG/SA) calculations. Two different calculation protocols were performed to ensure proper sampling of conformational space and even though the torsional restraints were input differently, both calculation methods yielded the same conformation of CtA. In the structure calculations, all solutions of the Karplus equation were sampled simultaneously using the restrained SA protocol and large ranges were used for the dihedral restraints in the DG/SA protocol because all solutions to the Karplus equation could not be sampled simultaneously. The solution conformation was also compared to the solid state x-ray conformations of CtA bound to thrombin and trypsin. The conformation of the residues important for active site binding (d-Phe, h-Arg, and Pro) are nearly identical in aqueous solution and solid state with largest differences at the a-Ala and v-Tyr residues. CtA appears to be preordered in structure and does not undergo a significant conformational change upon binding to the enzyme active site. © 1997 John Wiley & Sons, Inc.
    Zusätzliches Material: 2 Ill.
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  • 71
    Digitale Medien
    Digitale Medien
    The reconstruction of a protein backbone from Cα coordinates (1997)
    New York : Wiley-Blackwell
    Biopolymers 41 (1997), S. 381-389 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A Monte Carlo Protein Building method to construct the backbone and Cβ atomic coordinates from known Cα coordinates is reported. The method selects values of dihedral angles from ranges established from a statistical analysis of the relationship between dihedral angles of the backbone and Cα coordinates for a protein data base. The averaged coordinates from ten backbone models of a protein were used to define a mean structure that was refined by energy minimization using the AMBER force field (GB/SA). By the latter method the average atomic deviation and rmsd of the backbone and Cβ atoms for 24 proteins is between 0.14 and 0.32 Å (average 0.22 Å) and 0.22 and 0.61 Å (average 0.43 Å), respectively. A comparison with other methods is made. © 1997 John Wiley & Sons, Inc.
    Zusätzliches Material: 2 Ill.
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  • 72
    Digitale Medien
    Digitale Medien
    The reconstruction of side-chain conformations from protein Cα coordinates (1997)
    New York : Wiley-Blackwell
    Biopolymers 41 (1997), S. 391-405 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A model of nine proteins including side-chain atoms have been built from the known Cα coordinates and amino acid sequences using a Monte Carlo Protein Building Annealing method. The Cartesian coordinates for the side-chain atoms were established with bond lengths and angles selected randomly from within previously determined ranges. A simulated annealing technique is used to generate some 300 structures with differing side-chain conformations. The atomic coordinates of the backbone atoms are fixed during the simulated annealing process. The coordinates of the side-chain atoms of 300 low energy conformations are averaged to obtain a mean structure that is minimized with the Cα atoms constrained to their position in the x-ray structure using the OPLS/AMBER force field with the GB/SA water model. The rms deviation of the main-chain atoms (without Cβ) compared with the corresponding crystal structures is in the range 0.20-0.64 Å. The rms deviation of the side-chain atoms is between 1.72 and 2.71 Å and for all atoms is between 1.19 and 1.99 Å. The method is insensitive to random errors in the Cα positions and the computational requirement is modest. © 1997 John Wiley & Sons, Inc.
    Zusätzliches Material: 5 Ill.
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  • 73
    Digitale Medien
    Digitale Medien
    Simulation of electrostatic and hydrodynamic properties of Serratia endonuclease (1997)
    New York : Wiley-Blackwell
    Biopolymers 41 (1997), S. 443-450 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: We analyze the electrostatic and hydrodynamic properties of a nuclease from the pathogenic gram-negative bacterium Serratia marcescens using finite-difference Poisson-Boltzmann methods for electrostatic calculations and a bead-model approach for diffusion coefficient calculations.Electrostatic properties are analyzed for the enzyme in monomeric and dimeric forms and also in the context of DNA binding by the nuclease. Our preliminary results show that binding of a double-stranded DNA dodecamer by nuclease causes an overall shift in the charge of the protein by approximately three units of elementary charge per monomer, resulting in a positively charged protein at physiologic pH. In these calculations, the free enzyme was found to have a negative (-1 e) charge per monomer at pH 7. The most dramatic shift in pKa involves His 89 whose pKa increases by three pH units upon DNA binding. This shift leads to a protonated residue at pH 7, in contrast to the unprotonated form in the free enzyme. DNA binding also leads to a decrease in the energetic distances between the most stable protonation states of the enzyme. Dimerization has no significant effect on the electrostatic properties of each of the monomers for both free enzyme and that bound to DNA.Results of hydrodynamic calculations are consistent with the dimeric form of the enzyme in solution. The computed translational diffusion coefficient for the dimer model of the enzyme is in very good agreement with measurements from light scattering experiments. Preliminary electrooptical calculations indicate that the dimer should possess a large dipole moment (approximately 600 Debye units) as well as substantial optical anisotropy (limiting reduced linear electric dichroism of about 0.3). Therefore, this system may serve as a good model for investigation of electric and hydrodynamic properties by relaxation electrooptical experiments. © 1997 John Wiley & Sons, Inc.
    Zusätzliches Material: 1 Ill.
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  • 74
    Digitale Medien
    Digitale Medien
    Structural characterization (shape and dimensions) and stability of polysaccharide/lipid nanoparticles (1997)
    New York : Wiley-Blackwell
    Biopolymers 41 (1997), S. 511-520 
    Details
    ISSN: 0006-3525
    Schlagwort(e): biovector ; light scattering ; lipid ; microgel ; polysaccharide ; soft sphere ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The structure of a new supramolecular drug carrier (named Biovectors - BV) was studied using light scattering and scanning electronic microscopy techniques. This system consists of a polysaccharide core of chemically cross-linked maltodextrins to which phospholipids (and, in some cases, cholesterol) are added. Both polysaccharide cores and BV cross-linked with phosphate (negatively charged) and epichlorhydrin (no net charge) are spherical particles. The increase in the ionic strength of the medium increases the density of the charged polysaccharide cores. The lipid strongly interacts with neutral and negatively charged cores, decreasing both intra- and interparticle interactions. The results (mainly, ρ = Rg/Rh 〈 0.775 in some cases) suggest that BV are gel-like particles of variable density, referred to as microgels or soft spheres. Neutral polysaccharides have a strong tendency to self-aggregate. This self-aggregation of polysaccharide neutral cores is prevented by the addition of lipid or dimethylsulfoxide. © 1997 John Wiley & Sons, Inc. Biopoly 41: 511-520, 1997
    Zusätzliches Material: 5 Ill.
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  • 75
    Digitale Medien
    Digitale Medien
    Protein hinge bending as seen in molecular dynamics simulations of native and M61 mutant T4 lysozymes (1997)
    New York : Wiley-Blackwell
    Biopolymers 41 (1997), S. 533-544 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A dynamical model of interdomain “hinge bending” of T4 lysozyme in aqueous solution has been developed on the basis of molecular dynamics (MD) simulation. The MD model study provides a description of the conformational reorganization expected to occur for the protein in aqueous solution as compared to the crystalline environment. Three different 500 ps molecular dynamics simulations were calculated, each using a distinctly different crystal conformation of T4 lysozyme as the starting points of the MD simulations. Crystal structures of wild-type lysozyme and “open” and “closed” forms of M6I variant structures were analyzed in this study. Large-scale, molecular-conformational rearrangements were observed in all three simulations, and the largest structural change was found for the open form of the M6I allomorph. All three simulated proteins had closed relative to the wild-type crystal structure, and the closure of the “jaws” of the active site cleft occurred gradually over the time course of the trajectories. The time average MD structures, calculated over the final 50 ps of each trajectory, had all adapted to conformations more similar to each other than to their incipient crystal forms. Using a similar MD protocol on cytochrome P450BM-3 [M. D. Paulsen and R. L. Ornstein (1995) Proteins: Structure Function and Genetics, Vol. 27, pp. 237-243] we have found that the opposite type of motion relative to the starting crystal structure, that is, the open form of the crystal structure, had opened to a greater degree relative to the incipient crystal structure form. Therefore we do not believe that either result is merely a simulation artifact, but rather the protein dynamics are due to protein relaxation in the absence of crystal packing forces in the simulated solution environments. © 1997 John Wiley & Sons, Inc. Biopoly 41: 533-544, 1997
    Zusätzliches Material: 6 Ill.
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  • 76
    Digitale Medien
    Digitale Medien
    Structural comparison between retro-inverso and parent peptides: Molecular basis for the biological activity of a retro-inverso analogue of the immunodominant fragment of VP1 coat protein from foot-and-mouth disease virus (1997)
    New York : Wiley-Blackwell
    Biopolymers 41 (1997), S. 569-590 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Antibodies induced against intact foot-and-mouth disease Virus (FMDV) particles bind to the retro-inverso analogue of fragment 141-159 of the viral coat protein VP1 of FMDV, variant A, equally well as to the parent peptide. A conformational investigation of this retro-inverso peptide was carried out by nmr spectroscopy and restrained molecular modeling in order to identify the structural basis for the antigenic mimicry between these retro-inverso and parent peptides. In 100% trifluoroethanol a well-defined left-handed α-helical region exists from residue 150 to residue 159, which is consistently present in all conformational families obtained from restrained modelling. A less-defined left-handed helical region is present in the tract 144-148, which is also consistent for all structures. Conformational flexibility exists about Gly149, which leads to two types of structures, either bent or linear. In the bent structures, a three-residue inverse tight turn is found, which can be classified as an inverse γ-turn centered at Gly149. The overall structural features of the retro-inverso peptide are shown to be similar to those of the parent L-peptide. The two molecules, however, are roughly mirror images because they share inherently chiral secondary structure elements. By comparing these conformational conclusions with the x-ray structure of the Fab complex of a corresponding VP1 antigenic fragment, a rationale is proposed to account for the topological requirements of specific recognition that are implied by the equivalent antigenic activity of the natural and retro-inverso compounds. © 1997 John Wiley & Sons, Inc. Biopoly 41: 569-590, 1997.
    Zusätzliches Material: 12 Ill.
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  • 77
    Digitale Medien
    Digitale Medien
    Conformational preferences of Leu-enkephalin in reverse micelles as membrane-mimicking environment (1997)
    New York : Wiley-Blackwell
    Biopolymers 41 (1997), S. 591-606 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Leu-enkephalin ; [13C, 15N]-backbone-labeled ; reverse micelles ; conformation ; CD ; FTIR ; nmr ; distance geometry ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Enkephalin represents one of the bioactive peptide molecules most extensively investigated both in solution and in the crystal state. Depending upon the environment chosen for such studies, three main conformational states were identified for this flexible, linear pentapeptide - i.e., an extended conformation, a single-bend, and a double-bend structure. Since CD and Fourier transform ir (FTIR) spectra of Leu-enkephalin solubilized in negatively charged reverse micelles of bis (2-ethylhexyl)sulfosuccinate sodium salt/isooctane/water were supportive of a restricted conformational space of the aromatic side chains and of a bended type fold, we have analyzed by nmr the conformational preferences of Leu-enkephalin in reverse micelles using a synthetic [13C, 15N]-backbone-labeled sample. The overall conformation derived from nuclear Overhauser effect spectroscopy (NOESY) and 15N-filtered rotating frame NOESY (ROESY) spectra and by distance geometry calculations is a double-bend fold of the backbone that is comparable to one of the known x-ray structures. Thereby the tyrosine side chain is inserted into the hydrophobic core of the reverse micelles in a restrained conformational space as well evidenced by NOEs between the aromatic ring protons and the surfactant. The proximity of the aromatic rings of tyrosine and phenylalanine indicate a preferred structure consistent with the postulated conformation of the opioid peptide in the δ-receptor-bound state. These results confirm the interesting and promising properties of reverse micelles as membrane mimetica. © 1997 John Wiley & Sons, Inc. Biopoly 41: 591-606, 1997
    Zusätzliches Material: 11 Ill.
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  • 78
    Digitale Medien
    Digitale Medien
    Prediction of β-turns in proteins by 1-4 and 2-3 correlation model (1997)
    New York : Wiley-Blackwell
    Biopolymers 41 (1997), S. 673-702 
    Details
    ISSN: 0006-3525
    Schlagwort(e): protein folding ; coupling effect ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A 1-4 and 2-3 residue-correlation model is proposed to predict the β-turns in proteins. The average rate of correct prediction for the 455 β-turn tetrapeptides and 4018 non-β-turn tetrapeptides in the training data base is 80.1%, and that for the 223 β-turn tetrapeptides and 12562 non-β-turn tetrapeptides in the testing data base is 80.9%. Compared with the rates of correct prediction based on the residue-independent model reported previously, the quality of prediction is significantly improved by the new model, implying that the correlation effect between the 1st and the 4th residues and that between the 2nd and 3rd residues along a tetrapeptide are important for forming a β-turn in a protein during the process of its folding. © 1997 John Wiley & Sons, Inc. Biopoly 41: 673-702, 1997
    Zusätzliches Material: 4 Tab.
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  • 79
    Digitale Medien
    Digitale Medien
    Effect of the side group on the helix-forming tendency of α-alkyl-β-L-aspartamyl residues (1997)
    New York : Wiley-Blackwell
    Biopolymers 41 (1997), S. 721-729 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Poly(β-L-aspartate)s ; helical conformations ; quantum mechanical calculations ; cooperative energy effects ; helix stability ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The conformational preferences of the monomeric units of a series of poly(α-alkyl-β-L-aspartate)s were examined by quantum mechanical calculations. α-Alkyl-β-aspartamyl m-oligopeptides with a number of residues m ranging from 1 to 7 and arranged in the conformations experimentally observed for their corresponding polymers were computed. Both their total relative energies and their cooperative energy differences were compared as a function of the length of the oligopeptide and the nature of the alkyl side group. Results revealed that the 13/4 helical arrangement is the most stable structure for the isolated polymer chain for any side group, although a 17/4 helix becomes favored in the case of methyl and ethyl groups due to the packing effects. On the other hand, the stability of the 4/1 helix appears to be the preferred conformation for side groups with a branched constitution. © 1997 John Wiley & Sons, Inc. Biopoly 41: 721-729, 1997
    Zusätzliches Material: 5 Ill.
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  • 80
    Digitale Medien
    Digitale Medien
    Experimental evidence at atomic resolution for intramolecular N(SINGLEBOND)H · · · π (phenyl) interactions in a family of amino acid derivatives (1997)
    New York : Wiley-Blackwell
    Biopolymers 42 (1997), S. 1-6 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: No abstract.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
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  • 81
    Digitale Medien
    Digitale Medien
    Mapping of ligand binding sites of the cholecystokinin-B/gastrin receptor with lipo-gastrin peptides and molecular modeling (1997)
    New York : Wiley-Blackwell
    Biopolymers 41 (1997), S. 799-817 
    Details
    ISSN: 0006-3525
    Schlagwort(e): gastrin ; lipo-gastrin derivatives ; cholecystokinin-B/gastrin receptor ; molecular modeling ; ligand binding sites ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Double-tailed lipo-tetragastrin derivatives of increasing fatty acid chain length were used to identify the minimum size of the fatty acid moieties (≥C10) that restricts the access to the CCK-B/gastrin (CCK: cholecystokinin) receptor via a membrane-bound pathway. Then dimyristoyl-mercaptoglycerol/maleoyl-gastrin adducts of increasing peptide chain length were synthesized to define the minimal peptide size required for receptor binding affinities comparable to those of underivatized gastrin peptides despite anchorage of the lipid tails in the membrane bilayer. The experimental results indicated that most of the little-gastrin sequence, i.e., 2-17, is needed for optimal interaction of the molecule with the binding cleft of the receptor. From these data experimentally based restraints could be derived for docking of lipo-gastrin onto a CCK-B/gastrin receptor model applying molecular dynamics simulations and energy minimizations. In the receptor-bound state some of the secondary structure elements of gastrin as determined by nmr analysis of gastrin-peptides in low dielectric constant media are retained. The N-terminal gastrin portion interacts in a more or less extended conformation with the receptor surface, and upon a sharp kink at the Ala-Tyr dipeptide portion the C-terminal pentapeptide amide part inserts deeply into the helix bundle. Besides Arg-57 on top of helix 1 of the receptor, for which no potential interaction with the ligand could be detected, the other amino acid residues identified by mutagenesis studies as involved in gastrin recognition were found to interact with the C-terminal portion of gastrin. Even taking into account the strong limitations of such a model system, it represents an interesting tool for rationalizing the experimental results of the extensive structure-function studies performed previously on gastrin and to delineate more precisely the putative ligand binding site on the extracellular face of the receptor. © 1997 John Wiley & Sons, Inc. Biopoly 41: 799-817, 1997
    Zusätzliches Material: 10 Ill.
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  • 82
    Digitale Medien
    Digitale Medien
    FKBP-like catalysis of peptidyl-prolyl bond isomerization by micelles and membranes (1997)
    New York : Wiley-Blackwell
    Biopolymers 42 (1997), S. 49-60 
    Details
    ISSN: 0006-3525
    Schlagwort(e): micellar catalysis ; cis/trans isomerization ; peptidyl-prolyl cis/trans isomerase ; proline ; FKBP12 ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Under physiological conditions, peptidyl-prolyl cis/trans isomerases catalyze powerfully the cis/trans isomerization of the -Xaa-Pro- bond (Xaa: natural amino acids) in oligopeptides and proteins (PPIases; EC 5.2.1.8). However, incorporation of proline containing tetrapeptide-4-nitroanilides in micelles and phospholipid vesicles also leads to increased rates of this unimolecular conformational interconversion. The isomerization rate was dependent on the detergent and vesicle concentration, respectively. The observed rate constants fit the pseudophase model of micellar catalysis allowing the calculation of micellar turnover numbers (kcismic) and dissociation constants (KCmic). Comparing kcismic values to the rate constants of the uncatalyzed cis to trans isomerization, an acceleration factor of about 20-fold was obtained for Suc-Ala-Phe-Pro-Phe-4-nitroanilide (Suc: succinyl) bound to zwitterionic SB12 (N-dodecyl-N,N-dimethylammonium-3-propanesulfonate) micelles. In addition, a marked increase in the population of the trans conformer relative to cis was noted for all investigated combinations of peptides and detergents. In a series of tetrapeptides, Suc-Ala-Xaa-Pro-Phe-4-nitroanilide kcismic/KCmic as well as kcismic values are linearly correlated with the high performance liquid chromatography capacity factor R′ describing the hydrophobicity of the amino acid Xaa. The same correlation can describe quantitatively the dependency of kcar/Km on substrate hydrophobicity for the FKBP12-catalyzed isomerization. Despite the great differences in catalytic power, these results confirm the suspicion that micelles and FKBP12 may share a common component in the catalytic mechanism of peptidyl-prolyl bond isomerization. © 1997 John Wiley & Sons, Inc. Biopoly 42: 49-60, 1997
    Zusätzliches Material: 4 Ill.
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  • 83
    Digitale Medien
    Digitale Medien
    Tapping mode atomic force microscopy of scleroglucan networks (1997)
    New York : Wiley-Blackwell
    Biopolymers 42 (1997), S. 89-100 
    Details
    ISSN: 0006-3525
    Schlagwort(e): tapping mode atomic force microscopy ; scleroglucan networks ; denaturation-renaturation ; fractal dimension ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Tapping mode Atomic Force Microscopy (TmAFM) has been used to study the fungal polysaccharide scleroglucan deposited from aqueous solution and dimethyl sulfoxide (DMSO) onto a mica surface. The solutions from which the microscope samples were produced were prepared by first dissolving the solid scleroglucan in 0.1M NaOH, then neutralizing the solution with HCl, followed by dilution to the required concentration in either water or DMSO. It was found that from the aqueous solution described above, scleroglucan forms networks. Based on a comparison of the denatured-renatured and aqueous solution samples, network formation is due to the imperfect registration between the chains forming the triple helices. The relatively large stiffness of the scleroglucan triple helix is also assumed to contribute to the formation of the extended networks. The triple helix diameter was measured to be 0.92 ± 0.27 nm, which is in the same range as that obtained by other researchers using similar techniques. Denatured scleroglucan, deposited from DMSO onto mica, forms a web-like layer on top of which there are sphere-like structures. These morphologies are believed to be due to triple helix denaturation yielding highly flexible single chains in DMSO, which results in coiling and web-like dense packing of scleroglucan upon deposition onto mica. Most interestingly after addition of water to the samples deposited from DMSO, some of the chains can be renatured into short, stiff rod-like structures which are similar to the structures observed by other researchers. The imaging data for aqueous solution deposition can be analyzed by plotting maximum end-to-end distance versus the perimeter of the networks deposited onto mica. This yields a Flory-like exponent of 0.67, which is almost similar in value to that obtained by other researchers for linear structures of scleroglucan but less than that expected for a polymer chain following a self-avoiding walk (v = 0.75) model on a two-dimensional surface. The fractal dimension that can be used to characterize the networks was determined graphically to be 1.22 ± 0.06. © 1997 John Wiley & Sons, Inc. Biopoly 42: 89-100, 1997
    Zusätzliches Material: 11 Ill.
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  • 84
    Digitale Medien
    Digitale Medien
    Binding geometries of triple helix selective benzopyrido [4,3-b]indole ligands complexed with double- and triple-helical polynucleotides (1997)
    New York : Wiley-Blackwell
    Biopolymers 42 (1997), S. 101-111 
    Details
    ISSN: 0006-3525
    Schlagwort(e): triple helix stabilization ; intercalation ; DNA ligands ; benzo[4,3-b]indole ; polynucleotides ; linear dichroism ; CD ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The binding modes of three benzopyrido [4,3-b]indole derivatives (and one benzo[-f]pyrido [4-3b] quinoxaline derivative) with respect to double helical poly(dA) · poly(dT) and poly[d(A-T)]2 and triple-helical poly(dA) · 2poly(dT) have been investigated using linear dichroism (LD) and CD: (I) 3-methoxy-11-amino-BePI where BePI = (7H-8-methyl-benzo[e]pyrido [4,3-b]indole), (II) 3-methoxy-11-[(3′-amino) propylamino]-BePI, (III) 3-methoxy-7-[(3′-diethylamino)propylamino] BgPI where BgPI = (benzo[g]pyrido[4,3-b]indole), and (IV) 3-methoxy-11-[(3′-amino)propylamino] B f P Q where B f P Q = {benzo[-f]pyrido[4-3b]quinoxaline}. The magnitudes of the reduced LD of the electronic transitions of the polynucleotide bases and of the bound ligands are generally very similar, suggesting an orientation of the plane of the ligands' fused-ring systems preferentially perpendicular to the helix axis. The LD results suggest that all of the ligands are intercalated for all three polynucleotides. The induced CD spectrum of the BePI chromophore in the (II-BePI)-poly[d(A-T)]2 complex is almost a mirror image of that for the (I-BePI)-poly(dA) · poly(dT) and (I-BePI)-poly(dA) · 2poly(dT) complexes, suggesting an antisymmetric orientation of the BePI moiety upon intercalation in poly[d(A-T)]2 compared to the other polynucleotides. The induced CD of I-BePI bound to poly(dA) · 2poly(dT) suggests a geometry that is intermediate between that of its other two complexes. The concluded intercalative binding as well as the conformational variations between the different BePI complexes are of interest in relation to the fact that BePI derivatives are triplex stabilizers. © 1997 John Wiley & Sons, Inc. Biopoly 42: 101-111, 1997
    Zusätzliches Material: 5 Ill.
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  • 85
    Digitale Medien
    Digitale Medien
    Molecular modeling of c-erbB2 receptor dimerization: Coiled-coil structure of wild and oncogenic transmembrane domains - Stabilization by interhelical hydrogen bonds in the oncogenic form (1997)
    New York : Wiley-Blackwell
    Biopolymers 42 (1997), S. 157-168 
    Details
    ISSN: 0006-3525
    Schlagwort(e): molecular modeling ; c-erbB2 receptor ; dimerization ; coiled-coil structure ; wild transmembrane helices ; oncogenic transmembrane helices ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Dimerization models of c-erbB2 transmembrane domains (Leu651-Ile675) are studied by molecular mechanics and molecular dynamics simulations. Both wild and Glu mutated transmembrane helices exhibit the same relative orientation for favorable associations and dimerize preferentially in left-handed coiled-coil structures. The mutation point 659 belongs to the interfacing residues, and in the transforming domain, symmetric hydrogen bonds between Glu carboxylic groups stabilize the dimeric structure. The same helix packing found for the wild dimers, except side-chain - side-chain hydrogen bonds, suggests that the transmembrane domains dimerize according to similar process. Structural and energetical characterization of the models are presented. © 1997 John Wiley & Sons, Inc. Biopoly 42: 157-168, 1997
    Zusätzliches Material: 6 Ill.
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  • 86
    Digitale Medien
    Digitale Medien
    Electrophoresis of proteins in semidilute polyethylene glycol solutions: Mechanism of retardation (1997)
    New York : Wiley-Blackwell
    Biopolymers 42 (1997), S. 183-189 
    Details
    ISSN: 0006-3525
    Schlagwort(e): electrophoresis ; retardation ; native proteins ; semidilute polymer solution ; scaling theory ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The retardation of proteins in the Mt range of 15-500 kDa in capillary electrophoresis conducted in semidilute solutions of the polymer polyethylene glycol (Mt range 0.2-8.0 × 106), was measured. The purpose was to test the predictions of the scaling theory with regard to the relation of retardation to (a) the Mt of the polymer, (b) the concentration of the polymer, and (c) the radius of the protein particles. These predictions derive from a mechanism that relates retardation to the screening length of the polymer solution, viewed as the average distance between the entanglement points of polymer chains.For the molecular weight range from 60 to 500 kDa of (near) spherical proteins, the retardation was found to be related to polymer concentration c asμ/μo = exp(-Ac0.69)where μ/μ0 is the retardation expressed as the ratio between the mobility in polymer solution and that in free solution. The value of the exponent of 0.69 is in close agreement with the value of 0.75 predicted by the scaling theory. Parameter A was found (a) to scale as the 0.04th power of Mt (polymer), approximating the predicted value of 0; and (b) to be proportional to particle radius as predicted. All measured values of retardation were independent of electric field strength in the range of 37-370 V/cm. Thus, experimental findings are consistent with the mechanism relating electrophoretic retardation to the screening length of the polymer network in the specified molecular weight range of proteins.Under the same conditions, log(μ/μ0) of proteins with Mt's less than 60 kDa (a) scales as the -0.06th power of Mt (polymer), and (b) is proportional to polymer concentration, suggesting a retardation mechanism that is not related to the screening length. © 1997 John Wiley & Sons, Inc. Biopoly 42: 183-189, 1997
    Zusätzliches Material: 5 Ill.
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  • 87
    Digitale Medien
    Digitale Medien
    Comparison of van der Waals and semiempirical calculations of the molecular volumes of small molecules and proteins (1997)
    New York : Wiley-Blackwell
    Biopolymers 42 (1997), S. 191-202 
    Details
    ISSN: 0006-3525
    Schlagwort(e): molecular volume ; van der Waals radius ; molecular orbital calculation ; accessible surface area ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Molecular volumes for hydrocarbons, amino acids, peptides, and 14 globular proteins were calculated by techniques using van der Waals radii and by semiempirical molecular orbital methods. The resulting values were compared to experimentally determined volumes. The values obtained by methods employing van der Waals radii were found to be up to three times smaller than the experimentally determined values in the case of proteins, 25% smaller than the experimental values for peptides, and up to 50% greater than experimental values for simple hydrocarbons. For the semiempirical calculations, neither the type nor precision of the calculation altered the percentage of the electron density required to reproduce the experimentally observed volumes for any of the different types of molecules tested. For molecules en vacuo, the amount of electron density included was approximately 98.5% of the total calculated value. For solvated molecules, the percentage was closer to 99.5%. From the results of our studies, we conclude that semiempirical techniques are more reliable, less arbitrary, and hence are more accurate for the determination of molecular volumes. The methods by which we employ semiempirical techniques for determination of molecular volume will be described in detail. © 1997 John Wiley & Sons, Inc. Biopoly 42: 191-202, 1997
    Zusätzliches Material: 7 Ill.
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  • 88
    Digitale Medien
    Digitale Medien
    Qualitative and quantitative analysis of the secondary structure of cytochrome C Langmuir-Blodgett films (1997)
    New York : Wiley-Blackwell
    Biopolymers 42 (1997), S. 227-237 
    Details
    ISSN: 0006-3525
    Schlagwort(e): fourier transform ir spectroscopy ; protein conformations ; cytochrome C ; Langmuir-Blodgett film ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A qualitative and quantitative analysis of the conformation of Langmuir-Blodgett (LB) dried films of cytochrome C on silicon wafers was performed by Fourier transform ir (FTIR) spectroscopy. A deconvolution procedure was applied to the amide I band analysis, in order to determine the percentage of the different secondary structures. Qualitative analysis was performed by examining difference spectra.Films obtained by spreading protein solutions at pH 7.4 and 1, dried at 25 and 100°C, on silicon wafers were also examined in order to detect spectral components associated with denatured protein domains, and to compare them with cytochrome C LB films.FTIR spectroscopy showed that the following important changes characterise LB film spectra: (a) the α-helix component is higher (its percentage is 57 and 54%) than the one estimated in dried film obtained by spreading the solutions at pH 7.4 on a silicon substrate (43%), (b) there is an increase in the intensity of bands attributed to protonated carboxy group bands, involved and not involved in the formation of hydrogen bonds, and a decrease in those attributed to deprotonated carboxy groups, (c) the intensity of several bands attributed to aromatic amino acids and aliphatic chains increases, and (d) bands due to O(SINGLEBOND)H stretching vibrations of crystallization water are present.These conformational changes could be induced by protein-protein interaction caused by the close packing of molecules that occurs during LB film formation; it cannot be excluded that they may be accompanied by partial changes in the tertiary structure of the protein. A preferential orientation of protein molecules in LB films is also a possibility. © 1997 John Wiley & Sons, Inc. Biopoly 42: 227-237, 1997
    Zusätzliches Material: 4 Ill.
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  • 89
    Digitale Medien
    Digitale Medien
    DNA recognition by Zn [Cysteinyl-His-OMe]2: A minimal zinc finger docking unit (1997)
    New York : Wiley-Blackwell
    Biopolymers 41 (1997), S. 407-418 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Zinc fingers, 30-residue peptides anchored on Zn(II) coordinated to pairs of cysteines and histidines, recognize DNA triplets and, as tandem modules, effect sequence read out. The focus of zinc finger-DNA interaction studies thus far has been to probe the nature of the binding of the 12-residue recognition element of the finger with DNA code bases. To understand the possible role of the Zn(II) ligand and to assess its own DNA interaction profile, [(CH)2Zn] (C: cysteine; H: histidine; Figure 1) was constructed from bis-t Boc-cystinyl-di-His-OMe via thiol-disulfide exchange, Zn(II) complexation, and deprotection. [(CH)2Zn] binds with polyd- (G·C)·polyd(G·C) with association constants - 1.8 × 107 M-1 (specific DNA-phosphate) and 3.3 × 103 M-1 (nonspecific DNA-phosphate); perturbs its B-DNA profile; and enhances the Tm from 62.5 to 70.15°C in a concentration-independent manner, with an ideal reversal profile on cooling, not observed in the DNA alone; releases polyd(G·C)·polyd(G·C)-bound ethidium bromide; enhances the fluorescence of polyd(G·C)·polyd(G·C)-bound ethidium bromide at low concentrations; and quenches it at higher ranges. [(CH)2Zn] also binds to d(ACGCTGGGCGT), the sequence associated with Zif-268, 3-finger binding site. Such interactions were not seen in parallel studies with (a) polyd(A·T)·polyd(A·T) and [(CH)2Zn] and (b) {[C′H2] (C′: cystine; H: histidine; the direct metal-free precursor of [(CH)2Zn]}, ionic zinc nitrate, and covalent zinc acetyl acetonate Zn(AcAc)2, with poly[d(G·C)·polyd(G·C)].The results are rationalized on the basis of two types of association between [(CH)2Zn] and polyd(G·C)·polyd(G·C), a nonspecific recognition of the sugar phosphate backbone, by an imidazole of [(CH)2Zn] and a specific one involving the amino group of [(CH)2Zn] and the guanine base of DNA. Control experiments show that the latter greatly promotes DNA recognition. The possibility for such specific interactions with relatively small structures of the type [(CH)2Zn] would be of use in the design of DNA recognition elements and also provide an explanation for the experimentally found variation in the placement of the zinc finger docking unit around the major groove of DNA. © 1997 John Wiley & Sons, Inc.
    Zusätzliches Material: 7 Ill.
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  • 90
    Digitale Medien
    Digitale Medien
    CD conformational studies on synthetic peptides encompassing the processing domain of the ocytocin/neurophysin precursor (1997)
    New York : Wiley-Blackwell
    Biopolymers 41 (1997), S. 461-476 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Synthetic peptides of different size, reproducing the proteolytic processing site of proocytocin, were studied by CD under several experimental conditions in order to ascertain the ability of different solvents to stabilize secondary structural motifs, such as α-helix tracts and β-turns. A combination of deconvolution methods and empirical calculations subtracting the contributions due to unordered structures from the spectra suggests that in solution (a) mainly two distinct families of ordered conformers containing structurally different β-turns are present, (b) the relative stability of the different conformers depends from the nature of the solvent, and (c) in the case of the larger peptides, a population containing an α-helical conformation is also present. From the biological point of view the presence of at least two families of ordered conformers could be in line with current theories assuming that the catalytic effect of the receptor microenvironment may be determinant in shifting the equilibrium toward the active conformation. © 1997 John Wiley & Sons, Inc. Biopoly 41: 461-479, 1997
    Zusätzliches Material: 9 Ill.
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  • 91
    Digitale Medien
    Digitale Medien
    pH responsive microdomain formation in a De Novo polypeptide (1997)
    New York : Wiley-Blackwell
    Biopolymers 41 (1997), S. 521-532 
    Details
    ISSN: 0006-3525
    Schlagwort(e): recombinant DNA ; pH responsive hydrophobic microdomains ; dn31 gene ; gel filtration chromatography ; CD ; fluorescence probe analysis ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Recombinant DNA technology has been employed to produce a polypeptide capable of forming pH responsive hydrophobic microdomains. The design of this peptide is based upon an idealized conceptual model in which electrostatic, hydrophobic, and hydration forces are responsible for the association of amphipathic α-helical elements. Reduction in solution pH is responsible for reducing electrostatic repulsions between similarly charged residues, promoting the hydrophobic collapse of helical elements. A polymerizable synthetic element (dn31) has been synthesized and inserted into an appropriate expression vector. A clone containing a single copy of the dn31 gene (designated dn31x1) was isolated and the corresponding gene product DN3Lx1 isolated. The physical properties of DN3Lx1 were examined in solution by gel filtration chromatography, CD, and fluorescence probe analysis. It was determined that DN3Lx1 self-associates in solution with the degree of aggregation dependent on pH and ionic strength. An initial objective of this work was to examine domain organization in higher molecular weight species containing ten or more repetitive sequences. However, attempts to express multiple repeats of DN3Lxn from concatemers were unsuccessful. © 1997 John Wiley & Sons, Inc. Biopoly 41: 521-532, 1997.
    Zusätzliches Material: 8 Ill.
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  • 92
    Digitale Medien
    Digitale Medien
    Conformational study of asialo-GM1 (GA1) ganglioside (1997)
    New York : Wiley-Blackwell
    Biopolymers 42 (1997), S. 19-35 
    Details
    ISSN: 0006-3525
    Schlagwort(e): conformation ; ganglioside GA1 ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: In order to investigate the significance of preferred conformations of the saccharide for the steric orientation and recognition of glycosphingolipids at the membrane surface, the conformational free energy calculations were carried out on the asialo-GM1 [GA1; β-D-Gal(1 → 3) β-D-GalNAc(1 → 4) β-D-Gal(1 → 4) β-D-Glc-O-ceramide] using a new program CONCARB (CONformational study program for CARBohydrate) in the unhydrated and hydrated states. The overall backbone conformation of GA1 appears nearly to be extended with a little bent at the glycosidic II-III linkage, in which two pyranose rings of Gal(IV)-GalNAc-(III) moiety orient approximately perpendicular to those of Gal(II)-Glc(I) moiety. This is consistent with the structures deduced from high-sensitivity differential scanning calorimetry experiments and the nmr study on GA1. The calculated glycosidic torsion angles of the lowest free energy conformation of GA1 in the hydrated state are in accord with the structures of relevant oligosaccharides deduced from nmr experiments and hard sphere exoanomeric calculations. A comparison of the values of glycosidic torsion angles φ and π of GA1 and its constituent oligosaccharides indicates that the overall backbone conformation of each oligosaccharide is retained when the oligosaccharide chain becomes longer. This implies that the short-range interactions between the nearest-neighbored saccharides are of significant importance in stabilizing the overall backbone conformation of GA1 in both the unhydrated and hydrated states. The different orientation and hydrogen bonds of hydroxymethyl and hydroxyl groups from one oligosaccharide to another suggest that the medium- and long-range interactions are also of consequence. Hydration seems to affect significantly the conformation of these groups, but not to perturb remarkably the overall backbone conformation of GA1. © 1997 John Wiley & Sons, Inc. Biopoly 42: 19-35, 1997
    Zusätzliches Material: 6 Ill.
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  • 93
    Digitale Medien
    Digitale Medien
    Energetics of drug-DNA interactions (1997)
    New York : Wiley-Blackwell
    Biopolymers 44 (1997), S. 201-215 
    Details
    ISSN: 0006-3525
    Schlagwort(e): DNA ; thermodynamics ; calorimetry ; drugs ; intercalators ; groove binders ; free energy ; solvent-accessible surface area ; polyelectrolyte effect ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Understanding the thermodynamics of drug binding to DNA is of both practical and fundamental interest. The practical interest lies in the contribution that thermodynamics can make to the rational design process for the development of new DNA targeted drugs. Thermodynamics offer key insights into the molecular forces that drive complex formation that cannot be obtained by structural or computational studies alone. The fundamental interest in these interactions lies in what they can reveal about the general problems of parsing and predicting ligand binding free energies. For these problems, drug-DNA interactions offer several distinct advantages, among them being that the structures of many drug-DNA complexes are known at high resolution and that such structures reveal that in many cases the drug acts as a rigid body, with little conformational change upon binding. Complete thermodynamic profiles (ΔG, ΔH, ΔS, ΔCp) for numerous drug-DNA interactions have been obtained, with the help of high-sensitivity microcalorimetry. The purpose of this article is to offer a perspective on the interpretation of these thermodynamics parameters, and in particular how they might be correlated with known structural features. Obligatory conformational changes in the DNA to accommodate intercalators and the loss of translational and rotational freedom upon complex formation both present unfavorable free energy barriers for binding. Such barriers must be overcome by favorable free energy contributions from the hydrophobic transfer of ligand from solution into the binding site, polyelectrolyte contributions from coupled ion release, and molecular interactions (hydrogen and ionic bonds, van der Waals interactions) that form within the binding site. Theoretical and semiempirical tools that allow estimates of these contributions to be made will be discussed, and their use in dissecting experimental data illustrated. This process, even at the current level of approximation, can shed considerable light on the drug-DNA binding process. © 1998 John Wiley & Sons, Inc. Biopoly 44: 201-215, 1997
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  • 94
    Digitale Medien
    Digitale Medien
    Editorial (1997)
    New York : Wiley-Blackwell
    Biopolymers 44 (1997), S. 321-321 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: No abstract.
    Materialart: Digitale Medien
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  • 95
    Digitale Medien
    Digitale Medien
    Conformation and interactions of bioactive peptides from insect venoms: The bombolitins (1997)
    New York : Wiley-Blackwell
    Biopolymers 43 (1997), S. 419-431 
    Details
    ISSN: 0006-3525
    Schlagwort(e): bombolitins ; conformation ; amphipathic helices ; lytic peptides ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Bombolitins are five structurally related heptadecapeptides originally isolated from the venom of a bumblebee, acting at membrane level and able to enhance the activity of Phospholipase A2. The biological activity of this class of natural peptides seems to be related to the their ability to form amphiphilic helical structures in the presence of phospholipid aggregates or related membrane model systems. We have carried out systematic investigations on a series of bombolitins and their synthetic analogs in order to establish the conditions in which amphipathic helices are formed and to elucidate the details of the interaction with phospholipids and related model systems. We have shown that bombolitins and their analogs interact with phospholipid aggregates and detergent micelles forming amphiphilic helices. By means of the Langmuir film balance technique, coupled with fluorescence microscopy, we have shown that bombolitins perturbe the structure of phospholipid monolayers, forming phase separated peptide domains. In aqueous solution, in the absence of detergent or phospholipids, bombolitins form oligomeric aggregates with consequent conformational transition from a random coil to an α-helical structure. In the aggregate structure, evidence was obtained that helices are oriented in an antiparallel fashion. In this article we summarize the most recent results of conformational studies by CD, NMR and computer simulations on a series of bombolitins and retro-, all-D- and all-D-retro-analogs. © 1998 John Wiley & Sons, Inc. Biopoly 43: 419-431, 1997
    Zusätzliches Material: 14 Ill.
    Materialart: Digitale Medien
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  • 96
    Digitale Medien
    Digitale Medien
    Crystallographic insights into DNA minor groove recognition by drugs (1997)
    New York : Wiley-Blackwell
    Biopolymers 44 (1997), S. 105-121 
    Details
    ISSN: 0006-3525
    Schlagwort(e): crystal structures ; minor groove drugs ; oligonucleotides ; sequence recognition ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: This review surveys the crystal structures between minor groove drugs and oligonucleotides, of which over thirty have now been determined. The various factors that are involved in the observed A/T sequence selectivity of these drugs are examined in structural terms. The roles of, in particular, hydrogen-bond recognition and sequence-dependent groove width, are assessed, and as a consequence the minor groove drugs have been classified into two categories, dependent on the relative roles played by these two factors in sequence recognition. Implications for the recognition of non-A/T sequences are discussed. © 1997 John Wiley & Sons, Inc. Biopoly 44: 105-121, 1997
    Zusätzliches Material: 16 Ill.
    Materialart: Digitale Medien
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  • 97
    Digitale Medien
    Digitale Medien
    DNA recognition and nucleosome organization (1997)
    New York : Wiley-Blackwell
    Biopolymers 44 (1997), S. 423-433 
    Details
    ISSN: 0006-3525
    Schlagwort(e): DNA recognition ; nucleosome recognition ; deformation ; DNA-binding protein ; conformational fluctuations ; protein-DNA complexes ; histone octamer ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The affinity of a DNA sequence for the histone octamer in a core nucleosome depends on the intrinsic flexibility of the DNA. This parameter can be affected both by the sequence-dependent conformational preferences of individual base steps and by the nature and location of the exocyclic groups of the DNA bases. By adopting highly preferred conformations particular types of base step can influence the rotational positioning of the DNA on the surface of the histone octamer. The asymmetry of the next higher order of chromatin structure is determined in part by the asymmetric binding of the globular domain of histone H5 to the core nucleosome. © 1998 John Wiley & Sons, Inc. Biopoly 44: 423-433 1997
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
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  • 98
    Digitale Medien
    Digitale Medien
    Helix bending as a factor in protein/DNA recognition (1997)
    New York : Wiley-Blackwell
    Biopolymers 44 (1997), S. 361-403 
    Details
    ISSN: 0006-3525
    Schlagwort(e): helix bending ; protein/DNA recognition ; B-DNA ; FREEHELIX ; roll ; tilt ; kink ; curvature ; writhe ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Normal vectors perpendicular to individual base pairs are a powerful tool for studying the bending behavior of B-DNA, both in the form of normal vector plots and in matrices that list angles between vectors for all possible base pair combinations. A new analysis program, FREEHELIX, has been written for this purpose, and applied to 86 examples of sequence-specific protein/DNA complexes whose coordinates are on deposit in the Nucleic Acid Data Base. Bends in this sample of 86 structures almost invariably follow from roll angles between adjacent base pairs; tilt makes no net contribution. Roll in a direction compressing the broad major groove is much more common than that which compresses the minor groove. Three distinct types of B-DNA bending are observed, each with a different molecular origin: (1) Localized kinking is produced by large roll at single steps or at two steps separated by one turn of helix. (2) Smooth, planar curvature is produced by positive and negative roll angles spaced a half-turn apart, with random side-to-side zigzag roll at intermediate points, rather than a tilt contribution that might have been expected theoretically. (3) Three-dimensional writhe results from significant roll angles at a continuous series of steps. Writhe need not change the overall direction of helix axis, if it is continued indefinitely or for an integral number of helical turns. A-DNA itself can be formally considered as possessing uniform, continuous writhe that yields no net helix bending. Smooth curvature is the most intricate deformation of the three, and is least common. Writhe is the simplest deformation and is most common; indeed, a low level of continuous writhe is the normal condition of an otherwise unbent B-DNA helix of general sequence. With one exception, every example of major kinking in this sample of 86 structures involves a pyrimidine-purine step: C-A/T-G, T-A, or C-G. Purine-purine steps, especially A-A, show the least tendency toward roll deformations. © 1998 John Wiley & Sons, Inc. Biopoly 44: 361-403, 1997
    Zusätzliches Material: 14 Ill.
    Materialart: Digitale Medien
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  • 99
    Digitale Medien
    Digitale Medien
    Association of cyclic peptides in aqueous solution measured by fluorescence quenching (1997)
    New York : Wiley-Blackwell
    Biopolymers 41 (1997), S. 1-4 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: No abstract.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
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  • 100
    Digitale Medien
    Digitale Medien
    Characterization of lipid membrane dynamics by simulation: I. Torsion angle motions of the linear chains (1997)
    New York : Wiley-Blackwell
    Biopolymers 41 (1997), S. 37-50 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The torsion angle motions, generated from molecular dynamics (MD) simulations, of the two aliphatic chains of 1,2-dimyristoyl-sn-glycero-3-phosphatidylcholine (DMPC) in its lipid monolayer were evaluated by comparing these motions to those of an equivalent isolated (free) n-alkane chain, and the same n-alkane chain in its crystal lattice. The time-dependent autocorrelation and (1,2)-, (1,3)-, (1,4)-, and (1,5)-cross-correlation functions were constructed to analyze the torsion angle motions. It was found that the torsion angle motions of the DMPC lipid monolayer aliphatic chains are intermediate to those of the free n-alkane chain and the same n-alkane chain in its crystal lattice, particularly for short correlation times. The torsion angle motions of the aliphatic chains of DMPC are also found to be essentially independent of the charge state on the head group. The linear aliphatic chains of a DMPC lipid monolayer behave most like the isolated n-alkane chains with respect to torsion angle flexibility, even though the pairs of aliphatic chains of each DMPC are part of an ordered monolayer assembly. The aliphatic chains of the DMPC molecules in their monolayer exhibit at least two types of wave motions. One of the wave motions is the same in form, though somewhat more diffuse, as a traveling wave found in n-alkane crystals. The other wave motion involves major torsion angle transitions, and has some characteristics of the soliton properties observed in n-alkane crystals near their respective melt transition temperatures. © 1997 John Wiley & Sons, Inc.
    Zusätzliches Material: 16 Ill.
    Materialart: Digitale Medien
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