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  • 1990-1994  (28,778)
  • Polymer and Materials Science  (21,194)
  • Biochemistry and Biotechnology  (4,119)
  • Computational Chemistry and Molecular Modeling  (2,365)
  • Genetics  (1,100)
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  • 101
    Electronic Resource
    Electronic Resource
    Li+ counterion self-diffusion in ordered DNA (1994)
    New York : Wiley-Blackwell
    Biopolymers 34 (1994), S. 1605-1614 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The anisotropic self-diffusion coefficient of 7Li+ (I = 3/2) counterions has been studied in hydrated, macroscopically oriented Li-(B)DNA fibers at relatively high water contents, corresponding to approximate DNA-DNA helix axis distances of 22-35 Å, using the pulsed field gradient hmr spin-echo method. Self-diffusion coefficients parallel (D∥) and perpendicular (D⊥) to the DNA helix axis increase with increasing salt content and with increasing DNA-DNA helix axis distance. The observed anisotropy D∥/D⊥ decreases from 1.6 to 1.2 with the DNA-DNA separation increasing from 22 to 35 Å in the salt-free sample. This result can be understood by the obstruction effect caused by the DNA molecules themselves. The values of the Li+ self-diffusion coefficients in the most water-rich system with no added salt (corresponding to an approximate distance of 35 Å between the DNA helix axes) were D∥ ∼ 1.15 × 10-10 m2 s-1 and D⊥ ∼ 0.98 × 10-10 m2 s-1, compared to 9.14 × 10-10 m2 s-1 for the diffusion of Li+ in an aqueous solution of LiCl (∼ 2.1M). The possible occurrence of restriction effects in the DNA fibers have also been studied by determining the self-diffusion coefficient at different effective diffusion times. The self-diffusion coefficient of Li+ in the sample with the largest DNA-DNA helix axis distance seems to be independent of the effective diffusion time, which indicates that the lithium ions are not trapped within impermeable barriers. The possibility of diffusion through permeable barriers has also been investigated, and is discussed. © 1994 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360341205
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  • 102
    Electronic Resource
    Electronic Resource
    Nmr study of collagen-water interactionsIn memory of Jean Kopp, deceased 1989. (1994)
    New York : Wiley-Blackwell
    Biopolymers 34 (1994), S. 1615-1626 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A proton magnetic resonance study of different cross-linked collagens was performed as a function of water content and temperature. Collagens from three connective tissues (calf, steer, and cow) were chosen according to the different number of nonreducible multivalent cross-links, which increases during the life of animal. Samples were hydrated under five well-defined water activities (Aw) ranging from 0.44 to 0.85. The transverse and cross-relaxation times of water protons were studied as a function of temperature from -20 up to 100°C. From the temperature dependence of relaxation rates, the dynamics of water molecules can be described according to different processes: exchange of protons at the higher temperatures and dipole-dipole interactions that prevail at the lower temperatures. The exchange processes are analyzed as a function of the residence lifetime of water molecules at the protein interface and of the transfer of spin energy from water protons to macromolecule protons. The proton dipole-dipole interactions are related to the relaxation parameters of protein and water protons. All the relaxation parameters showed specific behavior for the 0.44 water activity for every tissue. The collagen tissue from calf also showed distinct behavior in comparison with other tissues. © 1994 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360341206
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  • 103
    Electronic Resource
    Electronic Resource
    Conformation of retro-bombolitin I in aqueous solution containing surfactant micellesA preliminary account of this work has been presented at the 22nd European Peptide Symposium [in Peptides 1992, Schneider, C. H. & Eberle, A. N., Eds., ESCOM, Leiden (1993) pp. 525-526]. (1994)
    New York : Wiley-Blackwell
    Biopolymers 34 (1994), S. 1535-1541 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Bombolitins are five naturally occurring heptadecapeptides acting at the membrane level and able to increase the activity of phospholipase A2. As for other peptides with similar function, the biological activity of bombolitins seems to be mainly due to their ability to form amphipathic helical structures. We synthesized and tested the retro sequence of bom-bolitin I (retro-bombolitin I). This peptide showed an activity similar to that of the natural sequence and was able to adopt a helical structure in the presence of an amphipathic environment consisting of SDS micelles. The secondary structure of this peptide was fully characterized by CD and nmr spectroscopy. © 1994 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360341111
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  • 104
    Electronic Resource
    Electronic Resource
    Thermal unfolding equilibria in homodimeric chicken gizzard tropomyosin coiled coils (1994)
    New York : Wiley-Blackwell
    Biopolymers 34 (1994), S. 1659-1667 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: CD studies are presented on thermal unfolding of coiled-coil homodimers of two genetic variant chains of chicken gizzard tropomyosin (CG-Tm). The experiments include the effects of cross-linking both isoforms and the dependence on protein concentration of unfolding in both reduced isoforms, variables not examined in extant work. The general shapes of the unfolding curves for singly cross-linked species depend on whether the crosslink is at C190 (its site on one isoform) or at C36 (its site on the other). These curves are compared with extant ones for various cross-linked species of rabbit tropomyosin. The comparison supports the view that the unfolding behavior of cross-linked species results from a complex interaction of strain at the cross-link, local variations in structural stability, and loop entropy. The observed concentration dependence of the transition temperature for the uncross-linked (reduced) species of CG-Tm is very small (2.9°C) for one variant homodimer and unobservably small (〈 2°C) for the other in the 100-fold concentration range (∼ 0.01-1.0 mg/mL) accessible here. These experimental values of ΔTm are much smaller than are predicted from extant values of the van't Hoff transition enthalpies, calling the latter into question. © 1994 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360341210
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  • 105
    Electronic Resource
    Electronic Resource
    On the synthesis of acrylamide oligomers (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 214 (1994), S. 115-122 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Die Synthese von Polyacrylamiden mit niedrigem Molekulargewicht (Mn = 500 - 1 000) durch metallaktivierte Polymerisation mit Wasserstoffperoxid in Wasser wird beschrieben. Von vier untersuchten Übergangsmetallsalzen erwiesen sich Cu2+ -Kationen als am effektivsten bei der Zersetzung von H2O2 und wurden deshalb als Aktivatoren verwendet. Die Versuche wurden bei drei Temperaturen (60, 80 und 95°C), drei verschiedenen H2O2-Konzentrationen (4, 5 und 6 Gew.-%, bezogen auf das Monomere) und vier unterschiedlichen Cu2+-Konzentrationen (900, 600, 300 und 0 ppm, Masse des Metalls bezogen auf das Monomere) durchgeführt. Dadurch konnten bei Monomerumsätzen über 95% Acrylamid-Oligomere mit Molekulargewichten im oben genannten Bereich erhalten werden. Innerhalb dieser Grenzen ist eine Molekulargewichtskontrolle nicht möglich, auch bei Verwendung verschiedener Cu2+-Konzentrationen. Die Grenzviskositäten sind ebenfalls sehr niedrig ([η] = 20 - 50 cm3/g), wobei zwischen diesen Werten und den Polymerisationsbedingungen keine Beziehung gefunden werden konnte. Die Ergebnisse ermöglichen die industrielle Herstellung von Acrylamid-Oligomeren.
    Notes: The synthesis of low-molecular-weight poly(acrylamide)s (M̄n = 500 - 1 000) is described. Metal-activated and non-activated polymerization in aqueous solution was investigated employing hydrogen peroxide as initiator. Among four transition metal salts considered, Cu2+ cations proved to be the most efficient in decomposing H2O2 molecules and were used as activator. The experiments were run at three reaction temperatures (60, 80 and 95°C), at three H2O2 levels (4, 5 and 6 wt.-% on monomer), and at four Cu2+ levels (900, 600, 300 and 0 ppm by weight of metal on monomer). Thus, ist was possible to prepare acrylamide oligomers with monomer conversions exceeding 95%, and with Mn values covering the narrow range indicated above. Within these low limits a molecular weight control is impossible, even with inclusion of the differentiated levels of Cu2+cations. Intrinsic viscosities are very low, too ([η]) = 20 - 50 cm3/g, without any relations of the individual values to variations of the given process parameters. The work provides an industrial route to very-low-molecular-weight acrylamide oligomers.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1994.052140111
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  • 106
    Electronic Resource
    Electronic Resource
    Aryl ether-ketone segmented polypyromellitimides (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 217 (1994), S. 71-78 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Aromatische Ether-Keton-Sequenzen wurden in eine Polyimidkette eingebaut, um diesen die thermoplastischen Eigenschaften der Polyetherketone zu verleihen. Zu diesem Zweck wurden drei aromatische Diamine mit Ether- und Ketongruppen zwischen den aromatischen Ringen hergestellt und mit Pyromellitsäuredianhydrid kondensiert. Das thermische Verhalten von daraus hergestellten Polymerfilmen wurde untersucht.
    Notes: Aromatic ether-ketone segments have been incorporated into polyimide backbone to impart the well-known thermoplastic properties of polyether ketones. For this purpose three aromatic diamines containing ether and ketone connecting groups between aromatic rings have been prepared and polymerized with pyromellitic dianhydride to yield polyimides. The thermal behavior of the polyimide cast films has been investigated.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1994.052170108
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  • 107
    Electronic Resource
    Electronic Resource
    Antistatic modification of polyester with carboxyterminated poly(oxyethylene) (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 217 (1994), S. 129-137 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Carboxy-terminierte Polyoxyethylene (PEO-acid) mit zahlenmittleren Molekulargewichten Mn = 8400, 3300 und 1000 wurden zur antielektrostatischen Modifizierung von Polyethylenterephthalat (PET) verwendet. Fasern aus PET-PEO-acid-Blends mit 2,0 oder 5,0 Gew.-% PEO-acid wurden bei 285°C mit einem normalen Extruder aus der Schmelze gesponnen und anschließend bei 80°C um das ca. 4,5fache verstreckt. Die Verarbeitbarkeit beim Verspinnen und Verstrecken war bei Verwendung von PEO-acid mit hohen Molekulargewichten ausgezeichnet. Die anti-elektrostatischen Eigenschaften wurden ebenfalls mit steigendem PEO-acid-Molekulargewicht besser. Da eine Umesterung beim Verspinnen nur in geringem Ausmaß stattfand, blieben die mechanischen Eigenschaften der Blend-Fasern gegenüber den PET-Fasern nahezu unverändert.
    Notes: Carboxy-terminated poly(oxyethylenes) (PEO-acid) with number-average molecular weights Mn = 8400, 3300, and 1000 were used for antielectrostatic modification of poly(ethylene terephthalate) (PET). The blend PET fibers containing 2.0 and 5.0 wt.-% of PEO-acids were melt-spun at 285°C with an ordinary extruder and then drawn about 4.5-fold at 80°C. The processabilities of spinning and drawing were excellent at higher molecular weights of PEO-acid. The anti-electrostatic properties of the blend fibers became also improved with increasing molecular weight of PEO-acid. Since little ester interchange reaction took place between PET and PEO-acid during meltspinning, the blend fibers could retain almost the same mechanical properties as the original PET fiber.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1994.052170113
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  • 108
    Electronic Resource
    Electronic Resource
    Preparation and characterization of spinning dopes for dry spinning of continuous alumina green fibers (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 217 (1994), S. 139-158 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Wäßrige Spinnmassen für das Trockenspinnen von Aluminiumoxid-Grünfasern wurden hergestellt. Dabei wurden basisches Aluminiumchlorid Al2(OH)5Cl · 2,5 H2O und SiO2-Sol als anorganische Komponenten und Polyvinylalkohol (PVA) als polymere organische Komponente eingesetzt.Bestimmte rheologische Eigenschaften der Mischungen sind essentiell, um eine gute Spinnbarkeit bei hohen Spinngeschwindigkeiten zu erhalten. Die Rheologie der Spinnmassen wird zum einen vom Molekulargewicht und dem Verseifungsgrad des PVA beeinflußt und zum anderen von der Zusammensetzung und der Konzentration der Mischung. Für Mischungen ohne SiO2 wurden die besten Ergebnisse bei einem PVA:Al2O3, Massenverhältnis von 18:82 und einem Oxidgehalt von ungefähr 27 Gew.-% erzielt. Der verwendete PVA hat ein mittleres Molekulargewicht von 70000 und einen Verseifungsgrad von 89%.Die Spinnmassen wurden mit Spinngeschwindigkeiten von bis zu 500 m/min zu kontinuierlichen Grünfasern versponnen. Die Struktur und das Alterungsverhalten von konzentrierten Lösungen von basischem Aluminiumchlorid wurden ausführlich untersucht.
    Notes: Aqueous spinning dopes for dry spinning of alumina green fibers were prepared by using basic aluminium chloride Al2(OH)5Cl · 2.5 H2O and SiO2 sol as inorganic components and poly(vinyl alcohol) (PVA) as polymeric organic component.Certain rheological properties of the mixtures are essential to achieve good spinnability at high spinning speeds. The rheology of the dope is influenced by the molecular weight and the degree of hydrolysis of the PVA, as well as by the composition and the concentration of the mixture. For mixtures without SiO2 best results were obtained at a PVA: Al2O3 mass ratio of 18:82 and an Oxide content of about 27 wt.-%. The PVA used has an average molecular weight of 70000 and a degree of hydrolysis of 89%.The dopes were spun to continuous green fibers at speeds up to 500 m/min. The structure and the ageing behaviour of concentrated solutions of basic aluminium chloride has been intensively studied.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1994.052170114
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  • 109
    Electronic Resource
    Electronic Resource
    Interpenetrating polymer networks of polyurethane and furfuryl alcohol, IIa. Processability and properties of pultruded fiber-reinforced composites (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 218 (1994), S. 41-52 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Die Herstellung von faserverstärkten interpenetrierenden Netzwerken (IPN) aus Polyurethan (PU) und Furfurylalkohol (FA) mittels Pultrusion wurde untersucht. Wie Viskositätsmessungen zeigen, nimmt die Topfzeit der PU/FA-IPN-Präpolymeren mit steigendem PU-Gehalt zu, und die Reaktivität ist hoch bei höheren Temperaturen. Aus morphologischen Untersuchungen geht hervor, daß mit steigendem PU-Gehalt die Benetzung der Fasern mit den PU/FA-Harzen verbessert wird. Die bei Zugversuchen erhaltenen Bruchflächen der glasfaserverstärkten PU/FA-IPNs mit PU-Gehalten unter 15 phr zeigen sogenannte “hackle patterns”. Die Zugfestigkeit der pultrudierten PU/FA-IPN-Composite ist bei einem PU-Gehalt von 5 phr am höchsten; Biegefestig-keit, Biegemodul und Wärmeformbeständigkeit nehmen jedoch mit zunehmendem PU-Gehalt ab. Die mechanischen Eigenschaften der mit Glas-, Carbon- oder Aramid- fasern (Kevlar 49) verstärkten pultrudierten Composite nahmen mit steigendem Volumenanteil der Fasern zu.
    Notes: A feasibility study of pultrusion of fiber-reinforced polyurethane/furfuryl alcohol (PU/FA) interpenetrating polymer/network IPN composites has been made. From the viscosity study, it was found that the pot life of the PU/FA IPN prepolymers increased with PU content and showed high reactivity at elevated temperature. It was confirmed from the morphological study that the wetting of fibers by the PU/FA IPN resins was improved with PU content. The appearance of the tensile failure surfaces of the pultruded glass fiber-reinforced PU/FA IPN composites showed “hackle patterns” for PU contents below 15 phr. The mechanical property study shows that the tensile strength of pultruded PU/FA IPN composites is the highest when the PU content is 5 phr. However, the flexural strength, flexural modulus and HDT decreased with PU content. The mechanical properties of various fiber-reinforced (glass, carbon, and Kevlar 49 aramid fiber) pultruded PU/FA IPN composites increased with fiber volume content.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1994.052180104
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  • 110
    Electronic Resource
    Electronic Resource
    Determination of 1-butene distribution in LLDPE by DSC analysis after thermal fractionated crystallizationThis paper is dedicated to the memory of Dr. Umberto Zucchini, deceased on January 19, 1993. He was appreciated as a scientist in the Ziegler-Natta catalysis as well as a man of great humanity. (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 219 (1994), S. 139-160 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Die Verteilung der Monomereinheiten (CCD) von LLDPE (1-Buten-Comonomer) wurde mittels thermischer Analyse untersucht. Nach der thermischen Behandlung der Polymeren durch thermisch fraktionierte Kristallisation (TFC) wurden die Schmelzendothermen in festgelegte Temperaturbereiche unterteilt. Die Verteilung der Endotherme gibt eine semiquantitative Aussage über die CCD.Beim Vergleich der thermischen Elutionsfraktionierung der gesamten Polymeren wie auch der einzelnen Fraktinen mit 13C-NMR-Messungen konnte eine gute Übereinstimmung festgestellt werden. Weiterhin wurde eine ungefähre Bestimmung der Ethylensequenzlänge durchgeführt.
    Notes: The chemical composition distribution (CCD) of LLDPE (1-butene comonomer) has been studied by thermal analysis. After an opportune thermal treatment of the polymers, thermal fractionated crystallization (TFC), the melting endotherms have been subdivided in areas with fixed temperature ranges. The distribution of the endotherms in different areas gave a semiquantitative idea of the CCD.The comparison with thermal rising elution fractionation and 13C NMR data of the whole polymers and fractions showed fairly good correlations. An approximate evaluation of the average ethylene sequence length was also obtained.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1994.052190112
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  • 111
    Electronic Resource
    Electronic Resource
    Synthesis and biological activity of chlorine-containing polyketones (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 220 (1994), S. 1-10 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Chlorhaltige Polyketone mit niedrigem Molekulargewicht wurden nach Friedel-Crafts aus Anisol, Chloracetylchlorid and Dichloralkanen (Dichlormethan, 1,2-Dichlorethan) in Kohlenstoffdisulfid hergestellt. Die Harze wurden mittels IR-Spektroskopie und Dampfdruckosmometrie charakterisiert. Das thermische Verhalten wurde thermogravimetrisch und differentialkalorimetrisch untersucht. Die Zersetzungscharakteristik wurde nach Broido und Doyle ermittelt. Die Prüfung der mikrobiellen Aktivität der Harze gegenüber Bakterien, Pilzen und Hefen ergab, daß sich die meisten Harze als Biozide verwenden lassen.
    Notes: Chlorine-containing polyketones of low molecular weight were synthesized from anisole, chloroacetyl chloride and dichloroalkanes, i. e. dichloromethane and 1,2-dichloroethane, by the Friedel-Crafts reaction using carbon disulfide as solvent. The resins were characterized by IR spectra and vapour pressure osmometry. The thermal properties were studied by thermogravimetry and differential scanning calorimetry. The characteristics of the decomposition reactions were evaluated by the Broido and Doyle methods. All the resins were tested for their microbial activity against bacteria, fungi and yeast. The results show that most of the resin can be used as biocides.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1994.052200101
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  • 112
    Electronic Resource
    Electronic Resource
    Hydrolytic stability and mechanical properties of poly(ester urethanes) (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 220 (1994), S. 49-60 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Der Einfluß der Hydrolysedauer bei 70°C auf die Molmasse und die mechanischen Eigenschaften handelsüblicher Polyesterurethane (Estane 54600, 54610 und 54650) wurde untersucht. Die Kinetik der Hydrolyse läßt sich als Reaktion erster Ordnung mit einer mittleren Induktionsperiode von etwa 7 Tagen beschreiben. Die resultierende Molmassenabnahme verursacht eine signifikante Verschlechterung der Eigenschaften, insbesondere der Bruchdehnung und der Zugarbeit bis zum Bruch, während die elastischen Eigenschaften weit weniger beeinträchtigt wurden. Eine quantitative Beziehung zwischen der relativen Änderung der Zugfestigkeit und der Molmasse wird vorgeschlagen. Die in der Reihenfolge 54650 〉 54600 〉 54610 abnehmende Hydrolysebeständigkeit der Estane läßt sich mit Unterschieden in deren chemischer Zusammensetzung erklären.
    Notes: The effect of hydrolysis time at 70°C on molar mass and mechanical properties of commercial poly(ester urethanes), i.e., Estanes 54600, 54610, and 54650, was analyzed. Kinetics of hydrolysis is plausibly described in terms of a first-order reaction with an average induction period of about 7 days. The resulting reduction of molar mass brought about a significant decrease in ultimate properties, particularly in stress at break and tensile energy to break, while elastic properties were affected much less. A quantitative correlation between relative changes in tensile strength and molar mass was attempted. Hydrolysis resistance of Estanes decreasing in the succession 54650 〉 54600 〉 54610 was related to their chemical composition.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1994.052200105
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  • 113
    Electronic Resource
    Electronic Resource
    Effect of a curing accelerator on the glass transition temperature of non-stoichiometric epoxy amine networks (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 220 (1994), S. 99-109 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Netzwerke aus Bisphenol-A-diglycidylether und 4,4′-Diaminodiphenylmethan wurden sowohl in Gegenwart unterschiedlicher Imidazolkonzentrationen als auch in Abwesenheit von Beschleunigern hergestellt. Dabei wurde das Verhältnis von Epoxidgruppen zu Aminwasserstoff variiert. Es wurde sowohl ein Überschuß an Aminwasserstoff als auch an Epoxidgruppen sowie ein stöchiometrisches Verhältnis von Epoxidgruppen zu Aminwasserstoff eingesetzt.Die Netzwerke wurden mittels thermomechanischer Analyse, Torsionspendelanalyse und uniaxialer Kompressionsmodulmessungen im Kautschukplateau untersucht. Weiterhin wurde eine Sol-Gel-Analyse der vernetzten Proben durchgeführt.Es wird gezeigt, daß Imidazol bei Einsatz eines Überschusses an Aminwasserstoff keinen signifikanten Einfluß auf die Glasübergangstemperatur und den löslichen Anteil der Proben hat. Im Falle eines stöchiometrischen Verhältnisses von Epoxidgruppen zu Aminwasserstoff oder eines Epoxidharzüberschusses hat Imidazol einen beachtlichen Einfluß auf die Glasübergangstemperatur der synthetisierten Netzwerke. Eine Abhängigkeit des löslichen Anteils der Proben von der Imidazolkonzentration konnte hauptsächlich bei Netzwerken festgestellt werden, die mit Epoxidüberschuß synthetisiert wurden.
    Notes: Networks were prepared from Bisphenol A diglycidylether and 4,4′-diaminodiphenylmethane both in the presence of different amounts of imidazole and in the absence of any accelerator. The ratio of epoxy groups to amino hydrogen was varied: the networks were made with amino hydrogen excess, a stoichiometric ratio of epoxy groups to amino hydrogen, and an epoxy excess.The resulting networks were investigated by thermomechanical analysis, by torsion pendulum analysis and by uniaxial compression modulus measurements in the rubbery-plateau zone. Further characterization was done by sol gel analysis of the cured samples.It was shown that imidazole does not significantly influence the glass transition temperature and the soluble content of the samples of an excess of amino hydrogen was used. In the case of a stoichiometric ratio of epoxy groups to amino hydrogen and in the case of an epoxy excess, imidazole considerably influences the glass transition temperature of the networks. A dependence of the soluble content of the samples on imidazole concentration used for network synthesis was found mainly in epoxy excess systems.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1994.052200109
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    An example of free radical graft polymerization where the mechanism from-to applies (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 221 (1994), S. 33-43 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Das Pfropfen natürlicher oder synthetischer Polymerer durch radikalische Polymerisation ist ein zur chemischen Modifizierung dieser Polymeren gebräuchliches Verfahren. Einige dieser chemischen Systeme zeigen bei genügend hohen Monomerkonzentrationen ein unerwartetes Ansteigen der Polymerisationsgeschwindigkeit, die in manchen Fällen auch wieder sinkt. Der Einfluß einer änderung der Monomerkonzentration auf die Pfropfausbeute bei der mit Cerionen initiierten Pfropfpolymerisation von Methylacrylat, Vinylacetat und einer Mischung beider Monomerer auf Cellulose wird diskutiert, wobei auf einen Drei-Komponenten-Pfropfmechanismus (“von”, “von-auf” und “auf”) Bezug genommen wird. Vermutlich wird das oben beschriebene Verhalten durch den Polymerisationsmechanismus “von-auf” verursacht. Daraus können Rückschlüsse auf die Copolymerstruktur gezogen werden.
    Notes: Free-radical grafting on natural and synthetic polymers is a method widely used to modify these polymers chemically. A number of these chemical systems show an unexpected behaviour of the polymerization rate when the monomer concentration is sufficiently high: it decreases and sometimes it increases afterwards. Here, the effect of varying the monomer concentration on the graft yield when grafting methyl acrylate, vinyl acetate and a mixture of both monomers onto cellulose initiated by ceric ions is discussed, considering a three-component mechanism of grafting (mechanisms from, onto and from-to). It is suggested that the unexpected behaviour indicated above is accounted for by the presence of the grafting mechanism from-to. Some knowledge about the copolymer structure can be reached by using this mechanistic approach.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1994.052210103
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  • 115
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    Sulfobetaine polyurethane ionomers, 5. Tensile properties of polyether polyurethane ionomer and related compounds with Co2+ and Pb2+ (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 221 (1994), S. 61-65 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Die Zug-Dehnungseigenschaften eines Polyetherpolyurethan-Ionomeren mit Sulfobetaingruppen wurden untersucht und mit denen des entsprechenden nichtionischen Polyurethans sowie davon abgeleiteten Compounds mit Pb2+ und Co2+ verglichen. Die Sulfonierung und die Behandlung mit Schwefelwasserstoff verbessern die Dehnungseigenschaften aufgrund der zunehmenden Phasensegregation bzw. der Bildung von Mikrophasen mit Halbleitereigenschaften durch Einschluß von Metallsulfiden. Die Komplexierung mit Pb2+ Co2+ verringert die Dehnungseigenschaften, bedingt durch teilweise Neutralisierung der ionischen Zentren.
    Notes: Stress-strain properties of sulfobetaine polyurethane ionomer based on polyether were studied comparatively to the non-ionic polyurethane and derived compounds with Pb2+ and Co2+. Sulfonation and treatment with H2S improve the tensile properties due to the increased phase segregation and to the semiconducting microphases formed by clustering of metal sulfides, respectively. Complexation with Pb2+ and Co2+ diminishes the tensile properties owing to the partial neutralization of ionic centers.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1994.052210106
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  • 116
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    Electroinitiated polymerization of some new monomers with schiff's base structure and pyrrole moieties (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 221 (1994), S. 103-115 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Monomere mit Pyrrol-Einheiten und dem Strukturelement der Schiffschen Basen wurden durch elektrochemische Oxidation bei gleichzeitiger Fällungspolymerisation in 1,2-Dichlorethan oder Acetonitril hergestellt. Als Monomere wurden Pyrrol-2-aldehydazin, N,N'-bis(2-pyrrolylmethylen)-1,4-diaminobenzol bzw. N,N'-bis(2-pyrrolylmethylen)-4,4′-diaminobiphenyl und als Elektrolyte Tetrabutylammoniumperchlorat, Tetrabutylammoniumtetrafluoroborat sowie Natrium-p-toluolsulfonat eingesetzt. Die dotierten Polymeren wurden mittels Elementaranalyse, IR-Spektroskopie und Thermoanalyse charakterisiert.
    Notes: Pyrrole-2-aldehyd azine, N,N'-bis(2-pyrrolylmethylene)-1,4-diaminobenzene and N,N'-bis(2-pyrrolylmethylene)-4,4′-diaminobiphenyl were polymerized by electro-chemical precipitating oxidation reaction in 1,2-dichloroethane and acetonitrile, respectively, in the presence of electrolytes like tetrabutylammonium perchlorate, tetrabutylammonium tetrafluoroborate and sodium p-toluene sulfonate. The doped resulted polymers were characterized by elemental analysis, IR spectroscopy and thermal analysis.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1994.052210109
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  • 117
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    Characterization of thermoplastic poly(ethylene terephthalate)-glass fibre composites, 2Part 1 cf.7.. Mechanical behaviour (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 221 (1994), S. 137-153 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Der Einfluß der Verarbeitungsbedingungen auf die Morphologie und die mechanischen Eigenschaften von unidirektionalen Composites aus Poly(ethylenterephthalat) und Glasfasern wurde untersucht. Im ersten Teil dieser Arbeit wurde über den Einfluß von Glasfasern auf die Kristallisationskinetik und die Matrixmorphologie von Poly(ethylenterephthalat)(PET) berichtet. Dabei wurden die Schmelz-und Kristallisa-tionsbedingungen, die thermische Stabilität und die Zugabe von Kristallisationskeimen (Talkum und Natriumbenzoat) berücksichtigt. Auf der Grundlage dieser Ergebnisse wurden mit Glasfasern gefüllte PET-Streifen unter verschiedenen Bedingungen zu Preßformplatten verarbeitet. Dynamische und statische Kurzzeit-Scherversuche sowie Langzeit-Biegefestigkeitsversuche wurden durchgeführt und unter Berücksichtigung der Verarbeitungsbedingungen und der Mikrophasenstruktur analysiert.
    Notes: The aim of this study was to understand how changes in processing conditions affect the morphology and ultimately mechanical performances of unidirectional poly(ethylene terephthalate) / glass fibre composites. In a previous paper, we have presented the influence of fibres on the crystallization kinetics and on the matrix morphology of poly(ethylene terephthalate) (PET), considering fusion-crystallization conditions, thermal stability and the addition of nucleating agents in the matrix (talc or sodium benzoate). Based on the results of that crystallization study, various processing conditions were implemented on compression-moulded plated made from PET-glass pultruded ribbons. Short-term (dynamic and static) shear tests and long-term flexural fatigue tests were performed to characterize the effects of moulding conditions. The mechanical results were analysed considering both processing conditions and microstructural parameters.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1994.052210112
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  • 118
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    Triazine-based polymers, 2. Synthesis and characterization of polyethers (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 221 (1994), S. 187-205 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Polyether auf Triazinbasis können mittels phasentransferkatalysierter Polykondensation bei Raumtemperatur und Reaktionszeiten von 1 bis 3 h hergestellt werden. Von mehr als 20 Polyethern wurden Löslichkeiten, Glasübergangstemperaturen, thermogravimetrische Daten, Reißdehnungen, Reißfestigkeiten, Elastizitätsmoduli und Schlagzähigkeiten bestimmt. Von den Polymeren aus 2,4-Dichlor-6-diethylamino-s-triazin und Bisphenol A wurde zusätzlich der Kristallisationsgrad mittels Röntgenweitwinkelstreuung ermittelt. Das Inkrement des 1,3,5-Triazintriylrings wurde bestimmt, so daß die Glastemperaturen einiger Polyether nach van Krevelen berechnet werden konnten.
    Notes: Triazine-based polyethers can be synthesized by phase transfer catalysed interfacial polycondensation at room temperature and reaction times of about 1 to 3 h. In this way, more than 20 polyethers were synthesized and solubilities, glass transition temperatures, thermogravimetric data, elongations at break, tensil strengths, elasticity moduli and impact strengths were determined. In addition, the degree of crystallinity was investigated for the polymer obtained from of 2,4-dichloro-6-diethylamino-s-triazine and bisphenol A by wide angle X-ray diffraction. The increment of the 1,3,5-triazinetriyl ring was determined, which made it possible to calculate the glass transition temperatures of some polyethers according to van Krevelen.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1994.052210116
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  • 119
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    Synthesis of block copolymers by using polysilanes (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 221 (1994), S. 207-216 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Methylmethacrylat wurde mit Poly(methylphenylsilan) als Photoinitiator polymerisiert. Durch Photolyse der in dem so hergestellten Polymethylmethacrylat (PMMA) noch enthaltenen Polysilanketten in Gegenwart von Vinylmonomeren wie Styrol wurden Blockcopolymere erhalten. Diese wurden eingesetzt, um Blockcopolymere mit Cyclohexenoxid herzustellen. Dies geschieht durch die Bildung von an PMMA gebundenen Silylradikalen, die in Gegenwart von N-Ethoxy-2-methylpyridinium-hexafluor-phosphat zu den entsprechenden Kationen oxidiert werden.
    Notes: Poly(methyl phenyl silane) was used to photoinitiate the polymerization of methyl methacrylate. Poly(methyl methacrylate) (PMMA), obtained this way, contains remaining polysilane chains. Photolysis of this PMMA in the presence of vinyl monomers such as styrene makes it possible to prepare block copolymers. Such PMMA prepolymers were also used to induce the polymerization of cyclohexene oxide through formation of PMMA-attached silyl radicals and subsequent oxidation to the corresponding ions in the presence of N-ethoxy-2-methylpyridinium hexafluorophosphate resulting in the formation of a block copolymer.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1994.052210117
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    Grafting of acrylonitrile onto bagasse dissolving pulp with KMnO4/oxalic acid systemPaper accepted for presentation at the 9th Arab Chemical Conference (Egyptian Chemical Society) from 10-13 April 1993 at the National Research Centre, Cairo, Egypt. (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 222 (1994), S. 25-30 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Chemiezellstoff wurde unter Verwendung eines KMnO4-Oxalsäure-Redoxinitiatorsystems mit Acrylnitril gepfropft. Der Einfluß von Monomer- und Initiatorkonzentration, Oxalsäurekonzentration, Reaktionszeit und -temperatur wurde untersucht.
    Notes: Bagasse dissolving pulp was grafted with acrylonitrile by using a KMnO4 oxalic acid redox initiator system. The effects of monomer concentration, reaction time, initiator concentration, acid concentration and reaction temperature were investigated.
    Additional Material: 5 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1994.052220103
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  • 121
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    Effect of mixer rotor speed on interfacial crosslinking of epoxidized natural rubber and poly(acrylic acid) (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 222 (1994), S. 31-48 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Der Einfluß der Mischerdrehzahl auf die Vernetzung von Polyacrylsäure (PAA) und epoxidiertem Naturkautschuk (ENR) wurde durch rheologische Untersuchungen (nach Monsanto), dynamisch-mechanische Analyse (DMA), Rasterelektronemikroskopie (SEM) und die Messung physikalischer Eigenschaften belegt. Hohe Mischerdrehzahlen verschlechtern demzufolge die Vernetzung von PAA und ENR. IR-Messungen deuten darauf hin, daß während des Mischens mit hohen Mischerdrehzahlen ENR-Elastomerketten mechanochemisch abgebaut werden.
    Notes: It is evident from Monsanto rheometric studies, dynamic mechanical analysis (DMA), physical property measurements and scanning electron microscopy (SEM) that the mixer rotor speed has an effect on the crosslinking of poly(acrylic acid) (PAA)/epoxidized natural rubber (ENR) blends. These studies reveal that mixing at high rotor speed deteriorates the crosslinking process between PAA and ENR. Infrared (IR) spectroscopic studies suggest that during mixing at high rotor speed ENR elastomer chains suffer breakdown through mechanochemical reactions.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1994.052220104
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  • 122
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    Synthesis of highly porous styrene-divinylbenzene copolymers prepared in the presence of 2,2,4-trimethylpentane (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 222 (1994), S. 89-102 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Styrol-Divinylbenzol-(St-DVB-)Copolymere wurden in Gegenwart von 2,2,4-Trimethylpentan als Treibmittel hergestellt. Die Mengen an Verdünnungsmittel bzw. Vernetzer (DVB) wurden in den Grenzen 20-60 Vol.-% bzw.2-40 Vol.-% zur Bildung von verschiedenen Netzwerken variiert. Die charakterisitischen Eigenschaften der Netzwerke, wie Roh- und Reindichte, Porenvolumen, Porendurchmesser, Porendurchmesserverteilung und spezifische Oberfläche wurden durch Quecksilberporosimetrie bestimmt. Die Kompression, die am Anfang jeder Messung zu beobachten war, wurde bestimmt. Die Variation der Porenverteilung wurde anhand der Syntheseparameter diskutiert. Diese Resultate, in Verbindung mit den berechneten Porendurchmessern und mit Rasterelektronenmikroskop-Aufnahmen, zeigen, daß eine Mikrogel-Struktur vorliegt. Eine Überlappung des Netzwerkes tritt bei über 50 Vol.-% Verdünnungsmittel ein. Ein Makroporositätsbereich konnte bei Copolymeren mit spezifischer Oberflöche größer als 130 m2/g definiert werden.
    Notes: A large number of styrene-divinylbenzene copolymers (St-DVB) were synthesized using 2,2,4-trimethylpentane as pore-forming agent. Diluent and crosslinking agent (DVB) contents were varied in the ranges 20-60 vol.-% and 2-40 vol.-%, respectively, to generate various St-DVB networks. Network features as apparent and skeletal densities, pore volume, mean pore diameter, specific surface area and pore size distributions were measured by mercury porosimetry. A compressing process occurring at the beginning of each measurement has been revealed and measured. Depending on the two synthesis parameters, the changes in pore diameter distributions are discussed. Those results, combined with the calculated average pore diameter and microscopy observations, allow to conclude that the synthesized matrices have a microspheres-based structure with a network-overlapping process occurring over 50 vol-% of dilution. A macroporosity domain has been defined for networks having specific surface areas greater than 130 m2/g.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1994.052220107
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  • 123
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    Synthesis and characterization of N-alkylated polyamide-imides (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 222 (1994), S. 103-109 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Neue aromatische Polyamidimide (PAI) wurden durch Reaktion von Torlon® 4203L (ein handelsübliches PAI) mit verschiedenen Halogenalkanen (Methyliodid, Ethyliodid, n-Butylbromid) hergestellt. Die Glastemperaturen dieser amorphen PAI liegen zwischen 238 und 276°C, die Grenzviskositäten betragen 51 bis 53 mL/g. Die PAI sind leicht löslich in polaren, aprotischen Lösungsmitteln wie z.B. N-Methylpyrrolidon, Dimethylformamid, Dimethylacetamid u.a. Der Einbau der Alkylsubstituenten in die Amidgruppen der PAI verbesserte die Verarbeitbarkeit aus der Schmelze, verringerte allerdings die thermischen Eigenschaften im Vergleich zu einem konventionellen PAI. Die bei 330°C und einer Frequenz von 0,1 rad/s gemessenen Schmelzviskositäten der hergestellten PAI betragen 103-105 Pa.s. Andererseits sind die Schmelzviskositäten der modifizierten PAI geringer als die von Torlon® 4203L, das mit dem konventionellen Polyetherimid Ultem-1000 vergleichbar ist.
    Notes: New aromatic polyamide-imides (PAI) containing various alkyl substituents were prepared by the substitution reaction of Torlon® 4203L (commercialized PAI resin) with the corresponding alkyl halides such as methyl iodide, ethyl iodide, and n-butyl bromide. The resulting amorphous PAIs with glass transition temperatures ranging from 238 to 276°C had inherent viscosities in the range of 51 to 53 mL/g. These polymers were readily soluble in aprotic polar solvents such as N-methylpyrrolidone, dimethylformamide, dimethyl acetamide, etc. Furthermore, the incorporation of various alkyl substituents into amide groups of the PAI resin increased the melt processability, but slightly decreased the thermal properties compared with conventional PAI resin. The melt viscosities of resulting PAIs determined at 330°C under the frequency of 10-1 rad/sec were in the range of 103-105 Pa.s. On the other hand, the modified PAIs showed significantly lower melt viscosities than Torlon® 4203L, which was almost comparable to the conventional polyetherimide, Ultem-1000.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1994.052220108
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  • 124
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    A biomaterial-based carbon fiber (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 222 (1994), S. 147-163 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Es wurde versucht, Sisalfasern zu kostengünstigen Kohlefasern zu carbonisieren. Vorbehandlung, Pyrolyse- und Carbonisierungsvorgang sowie Struktur und Eigenschaften der gebildeten Produkte wurden untersucht. Anwendungsmöglichkeiten für die aus Sisal hergestellten Kohlefasern mit mäßigen mechanischen Eigenschaften werden vorgeschlagen.
    Notes: An attempt to convert natural sisal fiber into low cost carbon fibrous materials was made. The pretreatment, pyrolysis and carbonization processes of raw sisal fiber as well as structure and properties of the resultant product were investigated. It was found that the sisal-based carbon fiber with moderate mechanical performance can be manufactured under the conditions applied. In addition, the application of the obtained sisal-based carbon fiber serving as functional material is presented.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1994.052220111
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    Deposition of hydrophobic layers onto acrylic fibers by plasma polymerization (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 222 (1994), S. 189-200 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Die Abscheidungscharakteristik hydrophober Beschichtungen auf Acrylfaseroberflächen wurde untersucht. Der Einfluß von fluorhaltigen oder Siloxanmonomeren und der Variation der Plasmaeigenschaften wurde durch die Messung der Abscheidungsgeschwindigkeiten und der Wasser-Kontaktwinkel sowie der Untersuchung der chemischen Oberflächeneigenschaften ermittelt.
    Notes: Experiments aimed at the deposition of hydrophobic coatings on acrylic fiber surfaces are described. The effects of utilizing fluorine-containing and siloxane monomers and of varying plasma parameters have been assessed by measuring deposition rates, observing surface chemistry and determining water contact angels.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1994.052220114
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    Dendritische und “hyperbranched” PolymereVortrag anläßlich der Tagung der Fachgruppe “Makromolekulare Chemie” der Gesellschaft Deutscher Chemiker über “Fortschritte in der Polymersynthese” in Bad Nauheim, 21.-22. März 1994. Beispiele für die Beeinflussung von Polymereigenschaften durch gezielte Synthese von dreidimensionalen Strukturen (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 223 (1994), S. 13-27 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Dendritic polymers are highly branched structures with globular shape and high number of functionalities. In a divergent or convergent stepwise synthesis perfect macromolecules with controlled size and architecture are obtained. From the broad variety of dendrimer structures some examples are given and the properties of these unusual polymers are illustrated. For comparison the hyperbranched polymers, dendritic structures with defects made in a one-pot polycondensation reaction, are discussed. Differences and conformities of properties like molecular weight distributions, functionalities, solubility, viscosity behavior and glass transition temperatures for both globular polymer structures are explained.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1994.052230102
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    Progress in synthesis and application of segmented polymersDedicated to Prof. Dr. H. Sinn on the occasion of his 65th birthday (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 223 (1994), S. 47-60 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Maßgeschneiderte segmentierte Polymere spielen eine Schlüsselrolle bei der Entwicklung von neuen polymeren Materialien. In Abhängigkeit von den molekularen Architekturen der segmentierten Polymeren kann die Ausbildung von Polymermorphologien und von Eigenschaftssynergien gesteuertwerden. An ausgewählten Beispielen werden grundlegende Konzepte und neuere Entwicklungen vorgestellt. Segmentierte Silikon-Flüssigkautschuke, wo unverträgliche Silikonsegmente von zwei mischbaren Oligo(caprolacton)-Segmenten flankiert werden, sind wirkungsvolle Zähmodifikatoren für Epoxidharze. In nanophasenseparierten IPNs auf Basis dieser Silikon-modifizierter Epoxidharze kann die Schlagzähigkeit ohne Verlust der Dimensionsstabilität erhöht werden. Kompatibilisierte Blends aus segmentierten phenolischen Polyurethan- und epoxidfunktionellen Nitril-Flüssigkautschuken bilden diskrete Blend-Mikrophasen, die in Epoxidprepregs dispergiert sind und strukturelles Verkleben von Aluminium in Faser-Metall Laminaten ermöglichen. Reaktive Blendtechnologien werden entwickelt, um während der Polymerverarbeitung, z.B. von Polypropylen/Polyamid 6 Blends, in-situ Phasenvermittler herzustellen. Durch Einbau von definierten Oligo(tetrafluoroethene) Segmenten in Kodensationspolymere werden neben thermischen und mechanischen Eigenschaften auch Oberflächenspannungen und Gasdurchlässigkeiten variiert.
    Notes: Tailor-made segmented polymers play a key role in the development of novel polymeric materials exhibiting unsual bulk and surface properties. As a function of molecular architectures of segmented polymers, it is possible to control polymer morphologies and to achieve property synergisms. Selected examples are presented to illustrate basic concepts and recent developments. Segmented reactive liquid rubbers, containing an immiscible silicone segment flanked by two miscible oligo(caprolactone) segments, are efficient epoxy toughening agents. In such nano-phase-separated silicone-modified IPNs impact strength is improved without sacrificing dimensional stability. Compatibilized blends of segmented phenolic polyurethane and nitrile liquid rubbers produce rubber blend microphases dispersed in epoxy prepregs which are used to bond aluminum sheets in structural laminates. Reactive blending technologies are developed to produce segmented polymers as blend compatibilizers during melt processing, e.g., of polypropylene/polyamide 6 blends. Incorporation of oligo(tetrafluoroethene) segments into various condensation polymers modifies thermal and mechanical properties as well as surface tension and gas permeabilities.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1994.052230104
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    Olefinpolymerisation mittels metallocenkatalysatorenHerrn Prof. Dr.rer.nat., Dr.-Ing. E. h. Hansjörg Sinn mit den besten Wünschen zum 65. Geburtstag gewidmet (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 223 (1994), S. 101-120 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Metallocenes have gained widespread interest as catalysts for olefin polymerization due to their high activity and versatility. A large range of new polymers with narrow molecular weight distribution and different microstructures can be produced with these “single-site” catalysts. These highly active catalysts which are able to produce 40 tonnes of polyethylene per gram zirconium per hour are even capable of incorporating remarkable amounts of sterically demanding olefins and dienes in copolymerization with ethylene. Isotactic, syndiotactic, stereoblock and isoblock polyolefins are accessible by variation of the metallocene ligands. Similarly, the isotacticity and molecular weight of the generated polyolefins are influenced by the ligand structure. By heterogenization of the metallocene on metal powder or silica polymers with substantially higher molecular weight, higher melting points and other new properties may be attained. Cyclic olefins like cyclopentene, norbornene or dimethanooctahydronaphthalene polymerize without ring-opening to yield highly melting and poorly soluble polymers. By separation of the racemic catalyst into enantiomers, optically active alkanes and alkenes are accessi-ble. Trimers are obtained with ee of 95%. These results provide new insights into the mechanism of Ziegler-Natta catalysis.
    Additional Material: 8 Ill.
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    URL: http://dx.doi.org/10.1002/apmc.1994.052230108
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    Propylene polymerization with metallocene catalysts in industrial processesDedicated to Prof. Dr. Dr. Ing. E. h. Hansjörg Sinn on the occasion of his 65th birthday (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 223 (1994), S. 155-164 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Product demands for polypropylene polymers cover a wide range of properties. Metallocene catalysts open up the way to influence the molecular properties of polypropylene by altering the ligand system of the metallocene complexes. This leads to new products with application properties which are not available with conventional catalysts. Concepts are presented to adapt metallocenes to modern, industrial polymerization processes. Some examples illustrate the particular advantages of this new generation of catalysts.
    Additional Material: 6 Ill.
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    Hochmolekulare lösliche polymere mit coronandenstruktur-synthese und eigenschaften (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 223 (1994), S. 193-201 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: New polymers with an alternating sequence of aliphatic chains and coronands were synthesized via Diels-Alder addition polymerization of bis(2-pyrones) with bismaleimides. The chemical structures of these polymers 6 are supported by NMR spectra, model reactions and crystal X-ray structure analysis. The tetrafunctional maleimide 5 was synthesized and the cyclization of 5 to the bicycle 9 with 2 mol monopyrone 8 was carried out.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/apmc.1994.052230114
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    The biodegradation of polymers: Recent resultsPaper presented at the “15th Annual International Conference on Advances in the Stabilization and Degradation of Polymers” in Luzern (Switzerland), June 2-4, 1993. (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 216 (1994), S. 21-35 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: After a general introduction including definition of biodegradability, the recent literature is briefly summarized. The results obtained in our laboratory for various polymers in three different composting units are then presented. They demonstrate that there is an urgent need for a quantitative method to characterize polymer biodegradation. For that purpose, a manometric method which allows the measurement of the oxygen consumed by the growing microorganisms has been developed. It has been tested with various inocula of increasing complexity: one Streptomyces sp., a mixture of three Streptomyces (badius, setonii and viridosporus), a compost extract or sewer sludge, growing in the presence of low molecular weight molecules as sole carbon source. Its performances and limitations are discussed. It is then applied to various polymer systems: polyesters and their constituent units, autoxidized polyethylene (APE) and its model compounds, polyvinyl alcohol (PVAl), starch and cellulose. The biodegradability of these polymers is characterized and their potential use as biodegradable materials for packaging, sanitary and agricultural uses is discussed.
    Additional Material: 9 Ill.
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    URL: http://dx.doi.org/10.1002/apmc.1994.052160102
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  • 132
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    Cetylpyridinium chloride-modified poly(ethyleneimine) for the removal and separation of inorganic ions in aqueous solution (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 215 (1994), S. 175-188 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Die Entfernung und Trennung einer Reihe von Metallionen mit Hilfe des wasserläoslichen Cetylpyridiniumchlorid-modifizierten Poly(ethylenimin)s (PEI-CPC) wurden in Kombination mit der Membranfiltration untersucht. Die Liquid-Phase Polymer-Based Retention(LPR)-Methode wurde zur Abtrennung von niedermolekularen Spezies beiverschiedenen pH-Werten und bei mehreren Elementkonzentrationen herangezogen. Die Studie umfaßt wäassrige Läosungen der Anionen Chromat und Phosphat sowie der Kationen Cu(II), Zn(II), Co(II), Ni(II), Cr(III), Fe(III), Cd(II), Pb(II) und Sr(II). Die Ergebnisse zeigen, daß eine hohe Retention für beide Anionen und auch für die meisten untersuchten Metallionen erzielt wurde. PEI-CPC zeigte gute Abtrenneigenschaften für Chromat-und Phosphationen selbst bei relativ hohen Anionenkonzentrationen 85 bzw. 150 mg · L-1und ebenso fäu die meisten untersuchten Metallionen. Im Falle der Cu(II)-, Ni(II)-und Sr(II)-Lonen wurde eine selektive Interaktion beobachtet. Das Polymerreagenz und seine Interaktionsprodukte wurden durch IR- und UV/Vis-Spektrometrie sowie Viskosimetrie charakterisiert. Zusäatzlich wurde das Interaktionsverhalten durch die Retentionsfäahigkeit untersucht. Eine gute Korrelation wurde zwischen den Retentionsdaten und den IR-und UV/VIS-Spektren der Interaktionsprodukte des Polymerreagenzes mit den Metallionen gefunden.
    Notes: The removal and separation of a series of ions by the water-soluble cetylpyridinium chloride-modified poly(ethyleneimine) (PEI-CPC) in conjunction with membrane filtration were investigated. The Liquid-Phase Polymer-Based Retention (LPR) method was applied to study the removal of the low-molecular species at different pH values and at several element concentrations. The study comprises aqueous solutions of the anions chromate and phosphate, and of the cations Cu(II), Zn(II), Co(II), Ni(II), Cr(III), Fe(III), Cd(II), Pb(II) and Sr(II). The results show that a high retention was attained in neutral solutions for both anions and also for most metal ions investigated. PEI-CPC exhibited good removing abilities for chromate and phosphate ions even at relatively high concentrations of anions (85 and 150 mg · L -1, respectively) and also for most of the metal ions studied. In the case of Cu(II), Ni(II), Cd(II), and Sr(II) ions, selective interactions were observed. The polymer reagent and its interaction products were characterized by IR, UV/VIS spectrometry, and viscometry. In addition, the interaction behaviour was investigated by the retention ability. A good correlation was found between the retention data and the IR and UV/VIS spectra of the interaction products of the polymer reagent with the metal ions.
    Additional Material: 7 Ill.
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    URL: http://dx.doi.org/10.1002/apmc.1994.052150115
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    Reaction of hals in polypropylene during light exposure: Part 1-iso-octane as reaction model compound -Paper presented at the “15th Annual International Conference on Advances in the Stabilization and Degradation of Polymers” in Luzern (Switzerland), June 2-4, 1993. (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 216 (1994), S. 101-112 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The photo and thermal reactivity of nitroxyl radicals derived from di-, (oligo)meric hindered amine light stabilizers (HALS) on iso-octane, a model compound for polyprophylene, was studied and compared to that of monomeric 2,2,6,6-tetramethyl- piperi-dine-N-oxyl (TEMPO).The exchange-interaction among 〉N—O. groups seems to affect only the thermal process.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/apmc.1994.052160107
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    Application of chemiluminescence to polymer degradation studies. Thermal oxidation of polyamide 6.Paper presented at the “15th Annual International Conference on Advances in the Stabilization and Degradation of Polymers” in Luzern (Switzerland), June 2-4, 1993. (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 216 (1994), S. 169-186 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Chemiluminescence (CL) technique was used to study the thermal oxidation of polyamide 6 samples with different ratio of terminal basic and acid groups, which perform a distinct effect on kinetics of the isothermal CL - time runs at 120-140°C. The isothermal experiments are complemented by nonisothermal ramp experiments where the CL intensity is monitored against temperature at a programmed rate of temperature increase.The relation of parameters such as initial CL intensity, integrated value of CL intensity for both isothermal and nonisothermal experiments and rate constants corresponding to CL - time curves was discussed within the results of other oxidation stability tests as absroption of oxygen, thermogravimetry, etc.
    Additional Material: 11 Ill.
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    URL: http://dx.doi.org/10.1002/apmc.1994.052160112
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    Modified styrene-isoprene-styrene block copolymer membranes complexed with cobalt-containing schiff's bases for oxygen permeation (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 217 (1994), S. 31-41 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Die strahleninduzierte Pfropfpolymerisation von 4-Vinylpyridin (VP) und 1 -Vinylimidazol (VIm) auf ein Styrol-Isopren-StyroI-Blockcopolymeres (SIS) sowie die Gasdurchlässigkeit von daraus hergestellten Membranen wurde untersucht. Eine Komplexierung der modifizierten SIS-Copolymeren (SIS-g-VP bzw. SIS-g-VIm) mit Cobalt enthaltenden Schiffschen Basen (CoS) als fixierte Sauerstoffträger verbesserte deren Sauerstoffdurchlässigkeit. Der Mechanismus des Sauerstofftransports wird diskutiert.
    Notes: The grafting of 4-vinylpyridine (VP) and 1-vinylimidazole (VIm) onto styrene-isoprene-styrene (SIS) triblock copolymer by radiation-induced graft copolymerization was studied. The effect of grafting degree on gas permeability of membranes made of grafted copolymers was investigated. The complex formation of the modified SIS (SIS-g-VP or SIS-g-VIm) with cobalt-containing Schiff's bases (CoS) in chloroform solution was studied. Facilitated transport of molecular oxygen in modified SIS membranes containing CoS as fixed carrier of oxygen, and oxygen permeability in modified SIS membranes due to the oxygen binding ability to CoS was observed. Mechanism of oxygen transport across the SIS-g-VP-CoS and SIS-g-VIm-CoS membrane is discussed.
    Additional Material: 5 Ill.
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    URL: http://dx.doi.org/10.1002/apmc.1994.052170104
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    Electron beam initiated grafting of methyl methacrylate onto polyethylene: Structure and properties (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 217 (1994), S. 61-69 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Polyethylen (PE, 100 Gew.-Teile) wurde mit Methylmethacrylat (MMA, bis zu 5 Gew.-Teilen) gemischt und anschließend mit Elektronen (bis zu 20 Mrad) bestrahlt, um PE/MMA-Pfropfcopolymere herzustellen, deren Bildung mittels IR-Spektroskopie nachgewiesen wurde. Gelbildung wies auf eine Vernetzung während der Bestrahlung hin. Zunehmende MMA-Konzentration und höhere Bestrahlungsdosen verringerten die Kristallit-Schmelztemperatur und den Kristallisationsgrad des PE. Zugfestigkeit, Bruchdehnung und Dielektrizitätskonstante wurden gemessen und diskutiert.
    Notes: Polyethylene (PE, 100 parts by weight) was mixed with methyl methacrylate (MMA, up to 5 parts by weight) at 120°C and subsequently exposed to electron radiation of different doses (up to 20 Mrad) to prepare PE/MMA graft copolymers. Successful grafting was verified by IR spectroscopy. Gel formation indicated crosslinking. Grafting increased with increasing MMA concentration and increasing irradiation dose. Crystalline melting temperature and percent crystallinity were lower than those of untreated PE. Tensile strength, elongation at break and dielectric constant of grafted samples were measured and discussed.
    Additional Material: 7 Ill.
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    URL: http://dx.doi.org/10.1002/apmc.1994.052170107
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    Reactive blending of thermosets: Molecular, morphological and mechanical analysis (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 217 (1994), S. 159-190 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Mit einer Reihe unterschiedlicher Methoden wurde versucht, die Zähigkeit tri- und tetrafunktioneller Epoxid- sowie ungesättigter Polyesterharze zu erhöhen. Die Epoxidharze wurden durch harte, thermisch stabile Konstruktionskunststoffe, ein Bisphenol-A Polycarbonat bzw. ein thermoplastisches Polyetherimid (Ultem 1000), modifiziert. Bei den ungesättigten Polyesterharzen wurde ein anderes Verfahren angewendet: Zwei handelsübliche flüssige Kautschuke wurden chemisch modifiziert, um ihre Reaktivität gegenüber den funktionellen Gruppen der Matrix zu steigern: Ein hydroxyterminiertes Polybutadien und ein aminoterminiertes Butadien-Acrylnitril-Copolymeres wurden zu Polymeren mit Isocyanat- bzw. Maleimidendgruppen umgesetzt. Ein weiteres hier beschriebenes System zielt darauf ab, die rasch abnehmende Steifheit der Polyestermatrix bei Temperaturen oberhalb Raumtemperatur zu verringern. Dazu wurde ein hitzehärtbares Bismaleimidharz als zweite co-reaktive Komponente in den Polyester eingebracht.
    Notes: A number of different approaches were used to enhance the toughness of tri- and tetrafunctional epoxies and of unsaturated polyester resins. In the case of epoxies, tough, thermally stable, engineering thermoplastics, namely a bisphenol-A polycarbonate and a thermoplastic poly(ether imide) (Ultem 1000) were employed as modifiers. For unsaturated polyesters a different approach was adopted: two commercial liquid rubbers were chemically modified to enhance their reactivity towards the matrix functionalities. In particular, a hydroxy-terminated polybutadiene and an aminoterminated butadiene-acrylonitrile copolymer were transformed into isocyanate-terminated and maleimide-terminated rubbers, respectively. A further system which is described in the present contribution is aimed at mitigating another deficiency of the polyester matrix, namely its rapidly decreasing rigidity at temperatures above room temperature. In this case, a thermosetting bismaleimide was incorporated into the resin as a co-reactive second component.
    Additional Material: 28 Ill.
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    Recycling of egyptian bagasse pith wastes in the synthesis of cationic resins (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 218 (1994), S. 1-10 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Eine Reihe sulfonierter kationischer m-Kresol-Paraformaldehyd-Harze wurden aus dem Mark ägyptischer Bagasse hergestellt. Reaktionsbedingungen werden angegeben, und die Eigenschaften der hergestellten Bagassemark/m-Kresol/Formaldehyd-Harze werden mit denen von Harzen ohne Bagassemark verglichen. Die synthetisierten Polymere sind stabil in Wasser, verdünnten Mineralsäuren (1 M) und organischen Lösungsmitteln sowie gegenüber thermischer Behandlung. Die Harze besitzen Kationenaustauscherkapazitäten von bis zu 2,91 meq/g (bezogen auf trockenes Harz) und werden als Austauschermaterialien für eine mögliche Trennung zweiwertiger Kationen getestet.
    Notes: A series of sulfonated cationic resins have been prepared and characterized from Egyptian bagasse pith wastes (as a source of cheaper and renewable material) with m-cresol and paraformaldehyde as a crosslinking agent. Reaction conditions for the preparation are presented and properties of the synthesized sulfonated bagasse pith-m-cresol-formaldehyde resins are described and compared with resin not containing bagasse pith. The synthesized resins are stable in water, dilute mineral acids (1 M), organic solvents, and to thermal treatment. The resins having a cation exchange capacity up to 2.91 meq g-1 of dry resin, are being introduced as new exchangers. The synthesized resins are used in the study of the possible separation of some bivalent cations.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/apmc.1994.052180101
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    Condensation of DNA by basic protiens does not depend on protien composition (1994)
    New York : Wiley-Blackwell
    Biopolymers 34 (1994), S. 285-292 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We have studied by electron microscopy the size and morphology of the complexes obtained with different DNAs (between 500 and 5243 base pairs long) and four different proteins: sea urchin histone H1; sea cucumber histone φ0, chicken erythrocyte histone H5, and clupeine. Surprisingly, the type of protein used has only a marginal influence on the complexes formed. The molecular weight and topology of DNA do not show any influence. The size of the complexes depends strongly on the ratio of positive to negative charges and also on the ionic conditions. Our studies have been mainly carried out at a ratio of 0.4. Under these conditions the average thickness of rods and toroids observed varies between 165 Å at 1.5 mM salt to 290 Å at 100 mM salt, with minor variations around these values depending on the type of DNA and protein used. We conclude that the formation of DNA condensates is mainly determined by a balance of electrostatic and intermolecular forces, the influence of specific interactions is only marginal. This conclusion seems to apply not only to the complexes described here, but also to chromatin fibers and to DNA condensed by low molecular weight counterions and other compounds (polyamines, inorganic ions, ethanol, etc.). © 1994 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360340214
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    Vacuum-UV CD spectrum of the X-form of double-stranded poly(dA-dT) (1994)
    New York : Wiley-Blackwell
    Biopolymers 34 (1994), S. 299-301 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360340216
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    Thermodynamics of cyclophilin catalyzed peptidyl-prolyl isomerization by nmr spectroscopy (1994)
    New York : Wiley-Blackwell
    Biopolymers 34 (1994), S. 171-175 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: One-dimensional nmr exchange spectroscopy was carried out to determine thermodynamic parameters of cyclophilin-induced cis-trans isomerization of succinyl-Ala-Phe-Pro-Phe-p-nitroanilide. Rate measurements were possible at physiological temperatures. The kc/Km of rat cyclophilin was found to he 12.8 (±0.5) s-1 μM-1 at 37°C, intermediate to previously reported values that used a coupled enzyme assay extrapolated to this temperature. Activation energies (ΔG≠) for the uncatalyzed and catalyzed reaction at 37°C were found to be 19.7 and 17.1 kcal/mol, respectively, and were primarily due to an enthalpic barrier. © 1994 John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360340203
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    Discontinuous volume transitions induced by calcium-sodium ion exchange in anionic gels and their neurobiological implications (1994)
    New York : Wiley-Blackwell
    Biopolymers 34 (1994), S. 209-215 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Discontinuous volume transitions in poly(acrylic acid) gels were studied by determining equilibrium swelling curves of small gel beads immersed in salt solutions containing varying concentrations of Ca2+ and Na+. Reversible contractions of gel membranes associated with Ca2+-Na+ exchange were examined using both isometric and isotonic recording devices. A discontinuous change in electric conductance was demonstrated in association with Ca2+-Na+ exchange in gel membranes. These experimental findings provide a sound physicochemical basis for elucidating the mechanism of nerve excitation. © 1994 John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360340207
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    Specificity of trypsin digestion and conformational flexibility at different sites of unfolded lysozyme (1994)
    New York : Wiley-Blackwell
    Biopolymers 34 (1994), S. 217-226 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Fourteen tryptic peptides and nine intermediates were identified as products of trypsin digestion of reduced and S-3-(trimethylated amino) propylated lysozyme. Kinetics of the appearance and disappearance of these products were observed by monitoring the peak areas on the chromatogram. In spite of the complicated reaction pathways, kinetics of the digestion of proteins and several intermediate products show simple decay curves with a single rate constant. In this paper, the trypsin susceptibility of the individual cleavage site is defined as a hydrolytic rate constant of the susceptible peptide bond in the presence of 10 nM trypsin. The cleavage sites of unfolded lysozyme are classified into two groups in terms of the trypsin susceptibility: one has a high susceptibility (10-20 h-1) and the other a low susceptibility (1.0-2.0 h-1). In the unfolded state of lysozyme, in conclusion, the region from residues 15 to 61 has a strong resistance to trypsin digestion; on the other hand, the C-terminal half of the polypeptide chain is flexible enough to fit into the active site of trypsin.In addition, six kinds of pentapeptides were synthesized as analogues of lysozyme fragments including Arg 14, Arg 21, Lys 33, Arg 45, Arg 61, and Arg 73. Kinetics of typtic digestion of them were observed. Both kcat and KM were determined for these synthetic pentapeptides. The susceptibility of each cleavage site in pentapeptides is determined and compared with that corresponding in proteins. The susceptibility is usually higher when the susceptible peptide chain is flexible. However, susceptibilities of a few sites in proteins are lower than those in pentapeptides. This means that the peptapeptides, this means that the peptide chains tend to fold locally to prevent trypsin from binding to the sites. It was found that the sites of Arg 21 and Arg 45 are indeed resistant to trypsin, but the site of Lys 33 is not so much, although the hydrolytic rate at Lys 33 itself is extremely slow. © 1994 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360340208
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    Electrophoretic mobility of DNA in gels. I. New biased reptation theory including fluctuations (1994)
    New York : Wiley-Blackwell
    Biopolymers 34 (1994), S. 239-247 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In weak electric fields, the motion of DNA molecules undergoing gel electrophoresis may be described by biased reptation. We argue that the degree of molecular orientation induced by the field is determined by a competition between longitudinal fluctuations and drift of the molecule along the tube. A self-consistent calculation shows that the end-to-end vector of long molecules varies with the square root of the field strength, and not linearly as previously supposed. This leads to a number of new predictions about the field dependence of the molecular mobility and the size limit of resolution. We present the results of computer simulations that support the predictions of the theory of biased reptation including fluctuations. Finally, we discuss the correspondence with experimental data and the implications of our findings for the optimization of DNA electrophoresis. © 1994 John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360340210
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    Electrophoretic mobility of DNA in gels. II. Systematic experimental study in agarose gels (1994)
    New York : Wiley-Blackwell
    Biopolymers 34 (1994), S. 249-259 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A systematic study has been undertaken to prove or disprove the predictions of a revised reptation model, biased reptation with fluctuations (BRF). Our data, which scan about two orders of magnitude of DNA sizes and of electric fields, and a fourfold range of gel concentrations, are in qualitative and quantitative agreement with the model and support the applicability of this theory to DNA gel electrophoresis. In particular, we show that the mobility in the compression zone scales as the first power of the electric field, and that the limit of separation scales as the inverse first power of the electric field, for low enough fields. © 1994 John Wiley & Sons, Inc.
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    Monte Carlo and Poisson-Boltzmann calculations of the fraction of counterions bound to DNA (1994)
    New York : Wiley-Blackwell
    Biopolymers 34 (1994), S. 227-237 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The counterion density and the condensation region around DNA have been examined as functions of both ion size and added-salt concentration using Metropolis Monte Carlo (MC) and Poisson-Boltzmann (PB) methods. Two different definitions of the “bound” and “free” components of the electrolyte ion atmosphere were used to compare these approaches. First, calculation of the ion density in different spatial regions around the polyelectrolyte molecule indicates, in agreement with previous work, that the PB equation does not predict an invariance of the surface concentration of counterions as electrolyte is added to the system. Further, the PB equation underestimates the counterion concentration at the DNA surface, compared to the MC results, the difference being greatest in the grooves, where ionic concentrations are highest. If counterions within a fixed radius of the helical axis are considered to be bound, then the fraction of polyelectrolyte charge neutralized by counterions would be predicted to increase as the bulk electrolyte concentration increases.A second categorization - one in which monovalent cations in regions where the average electrostatic potential is ledd than -kT are considered to be bound - provides an informative basis for comparison of MC and PB with each other and with counterion-condensation theory. By this criterion, PB calculations on the B from of DNA indicate that the amount of bound counterion charge per phosphate group is about .67 and is independent of salt concentration. A particularly provocative observatiob is that when this binding criterion is used, MC calculations quantitatively reproduce the bound fraction predicated by counterion-condensation theory for all-atom models of B-DNA and A-DNA as well as for charged cylindera of varying lineat charge densities. For example, for B-DNA and A-DNA, the fractions of phosphate groups neutralized by 2 Å hard sphere counterions are 0.768 and .817, respectively. For theoretical studies, the rediys enclosing the region in which the electrostatic potential is calculated studies, the radius enclosing the region in which the electrostatic potential is calculated to be less than -kT is advocated s a more suitable binding or condensation radius that enclosing the fraction of counterions given by (1 - ξ-1). A comparsion of radii calculated using both of these definitions is presented. © 1994 John Wiley & Sons, Inc.
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    URL: http://dx.doi.org/10.1002/bip.360340209
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    Change in mobility of side chains due to neutralization of charged poly(L-lysine) with dansyl group (1994)
    New York : Wiley-Blackwell
    Biopolymers 34 (1994), S. 101-108 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Poly(L-lysine) having dansyl (5-dimethylamino-1-naphthalene-sulfonyl) groups to its side chains was prepared. The fluorescence spectra and fluorescence anisotropy ratios of the dansyl (DNS) group were measured in various conditions. In aqueous solution the increase in emission intensity was observed reflecting the alkali-induced coil-to-helix transition. In aqueous-methanolic solutions with methanol content above 60 wt %, the poly(L-lysine) with DNS group (DNS-PLL) was probed to show α-helical conformation from CD spectra. With addition of alkali, the increase in fluorescence intensity of α-helical DNS-PLL and the drastic change in fluorescence anisotropy ratio were observed. In this case the rotational mobility of DNS probe decreases, gives a minimum at a certain concentration of added alkali, and then increases again up to approximately the initial level. At the concentration where the rotational mobility gives the minimum, intensity of scattered light gives a maximum. This shows that suppression of the mobility of DNS side chains is caused by the intermolecular aggregation of α-helical DNS-PLL. This concentration of added alkali corresponds to the midpoint of neutralization to charged side chains of the DNS-PLL. The interaction that causes aggregate of α-helical DNS-PLL is suggested to be the intermolecular hydrogen bonding between neutralized and unneutralized side chains. © 1994 John Wiley & Sons, Inc.
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    URL: http://dx.doi.org/10.1002/bip.360340111
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    Spatial translational motions of base pairs in DNA molecules: Application of the extended matrix generator method (1994)
    New York : Wiley-Blackwell
    Biopolymers 34 (1994), S. 121-142 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We have used the elementary generator matrices outlined in the preceding paper to examine the conformational plasticity of the nucleic acid double helix. Here we investigate kinked DNA structures made up of alternating B- and A-type helices and intrinsically curved duplexes perturbed by the intercalation of ligands. We model the B-to-A transition by the lateral translation of adjacent base pairs, and the intercalation of ligands by the vertical displacement of neighboring residues. We report a complete set of average configuration-dependent parameters, ranging from scalars (i.e., persistence lengths) to first- and second-order tensor parameters (i.e., average second moments of inertia), as well as approximations of the associated spatial distributions of the DNA and their angular correlations. The average structures of short chains (of lengths less than 100 base pairs) with local kinks or intrinsically curved sequences are essentially rigid rods. At the smallest chain lengths (10 base pairs), the kinked and curved chains exhibit similar average properties, although they are structurally perturbed compared to the standard B-DNA duplex. In contrast, at lengths of 200 base pairs, the curved and kinked chains are more compact on average and are located in a different space from the standard B- or A-DNA helix. While A-DNA is shorter and thicker than B-DNA in x-ray models, the long flexible A-DNA helix is thinner and more extended on average than its B-DNA counterpart because of more limited fluctuations in local structure. Curved polymers of 50 base pairs or longer also show significantly greater asymmetry than other DNAs (in terms of the distribution of base pairs with respect to the center of gravity of the chain). The intercalation of drugs in the curved DNA straightens and extends the smoothly deformed template. The dimensions of the average ellipsoidal boundaries defining the configurations of the intercalated polymers are roughly double those of the intrinsically curved chain. The altered proportions and orientations of these density functions reflect the changing shape and flexibility of the double helix. The calculations shed new light on the possible structural role of short A-DNA fragments in long B-type duplexes and also offer a model for understanding how GC-specific intercalative ligands can straighten naturally curved DNA. The mechanism is not immediately obvious from current models of DNA curvature, which attribute the bending of the chain to a perturbed structure in repeating tracts of A · T base pairs. © 1994 John Wiley & Sons, Inc.
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    Conformational analysis of chitobiose and chitosan (1994)
    New York : Wiley-Blackwell
    Biopolymers 34 (1994), S. 203-208 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The relaxed potential energy surfaces of chitobiose were calculated based on the MM3-force field by optimizing dimer structures on a 10° grid spacing of the torsional angles about the glycosidic bonds (Φ,Ψ). The 36 conformations; the four combinations of the hydroxymethyl group orientations coupled with the nine of the secondary group ones -  were assumed for each Φ,Ψ conformation. The four conformations, each differing in the hydroxymethyl group orientations, were considered for the whole Φ,Ψ space, and all the 36 conformations, for the restricted space of low energy. While the resulting energy map and the structures of the energy minima were similar to those proposed for cellobiose in many respects, more restricted energy profile was suggested for the relaxed map of chitobiose where differences in the energy level between the global minimum and the local minima were within 5.4 kcal/mol, compared with the equivalent value of 3.6 kcal/mol for cellobiose. Further depression of the global minimum occurred when the acidic residue was used. The Monte Carlo samples of the chitosan chain were generated based on the relaxed map to predict the unperturbed coil dimension in solution. The chitosan chains showed Gaussian behavior at x = 500 (x, degree of polymerization) and gave the characteristic ratio Cx, of about 70, which was much larger than the experimental values observed for the chitosan and cellulosic chains. © 1994 John Wiley & Sons, Inc.
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    URL: http://dx.doi.org/10.1002/bip.360340206
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    Three-dimensional Hartree-Fock crystal-orbital calculation on crystalline diprotonated deoxycytidine-5′-monophosphate monohydrate: Toward rationalizing nucleic acid semiconductivity (1994)
    New York : Wiley-Blackwell
    Biopolymers 34 (1994), S. 921-932 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A three-dimensional Hartree-Fock crystal-orbital calculation on the crystal of diprotonated deoxycytidine-5′-monophosphate monohydrate has been carried out using the CRYSTAL92 routine package. According to the calculation, this crystallohydrate can be considered a quasi one-dimensional hole semiconductor with the indirect fundamental gap of 1.66 eV and with a possibility for the uv-excited quasi one-dimensional electron photoconductivity. The physical source for such properties is the charge transfer from the phosphate to the water molecule and cytosine residue, favored by the strong electrostatic interaction between nucleotide zwitterions and by the formation of the infinite spirals of hydrogen-bonded zwitterions along one of the crystallographic axes. © 1994 John Wiley & Sons, Inc.
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    A CD study of the α-helix nucleation hypothesis (1994)
    New York : Wiley-Blackwell
    Biopolymers 34 (1994), S. 969-973 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: One of the dilemmas in predicting the secondary structure of proteins from their amino acid propensity for a given conformation is the presence of all amino acids in all types of secondary structure, regardless of their propensity for that specific structure. One explanation is the nucleation hypothesis that only a few residues with a strong propensity for the secondary structure, such as the α-helix structure, initiates its formation and propagates the structure through indifferent sequences until strong breakers terminate the growth on both ends. Eight 15-mer peptides were studied to examine the α-helix nucleation hypothesis. The nucleation sequence of VAEAK, with high helix propensity, was mixed with an indifferent sequence of TSDSR in all possible permutations. From the percent α-helix structure derived from the CD at 222 nm, it appears that helicity does not propagate through the indifferent sequence. © 1994 John Wiley & Sons, Inc.
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    URL: http://dx.doi.org/10.1002/bip.360340715
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    Thermodynamic basis of site-specific cooperativity (1994)
    New York : Wiley-Blackwell
    Biopolymers 34 (1994), S. 1001-1005 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Cooperative phenomena in biological macromolecules arise from the interaction of many distinct subsystems, such as structural domains or binding sites. Cooperative properties of the system as a whole, like protein folding or allosteric transitions, are subject to the restrictions imposed by thermodynamic stability. These restrictions, however, do not apply in the case of individual subsystems open to interactions with the rest of the macromolecule. The site-specific properties of such subsystems can be understood in general thermodynamic terms from those of a multicomponent system under particular conditions. The analogy provides a thermodynamic basis for site-specific Cooperativity. © 1994 John Wiley & Sons, Inc.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360340803
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    Conformation and sweet tastes of L-aspartyl dipeptide methyl esters (1994)
    New York : Wiley-Blackwell
    Biopolymers 34 (1994), S. 1037-1048 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In order to investigate the conformational preferences to elicit tastes, conformational free energy calculations using an empirical potential (ECEPP/2) and the hydration shell model were carried out on the L-aspartyl dipeptide methyl esters, L-+HAsp--L-Xaa-OMe, in the hydrated state, where Xaa includes sweet (Phe, Tyr, Met, and Gly), bitter (Ala, Trp, Val, Leu, and Ile), and tasteless (Ser, Thr, and Abu) residues. The refined preferred conformation of the Phe dipeptide (aspartame) with side chain χ21 conformation g- is g-Fg- in the hydrated state, which is consistent with the structure deduced from 1H-nmr experiments. Irrespective of the Xaa and taste, all the dipeptides have the same conformation for the Asp residue, which is attributable to the hydrogen bond between protonated amino hydrogen and carboxylate oxygen and the favored hydration of the carboxylate group. This implies that the L-aspartyl residue is a necessary factor for the dipeptides to be sweet not a sufficient factor. The computed conformational preferences for sweet, bitter, and tasteless dipeptides in the hydrated state indicate to us that the conformation about the N—Cα bond of the Xaa residue, i.e., the orientation of the hydrophobic moiety with respect to the AH/B functionalities in the aspartyl moiety, seems to be crucial to elicit the tastes. In addition, the hydrophobicity and the size of the Xaa residue are found to play a major role in determining the tastes. These well accord with the related works reported previously. © 1994 John Wiley & Sons, Inc.
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    URL: http://dx.doi.org/10.1002/bip.360340807
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    Comparative interactions of magnesium and calcium counterions with polygalacturonic acid (1994)
    New York : Wiley-Blackwell
    Biopolymers 34 (1994), S. 1059-1064 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The comparative interaction of Mg2+ and Ca2+ counterions on carboxyl groups of polygalacturonic acid is developed. Ultracentrifugation, conductimetry, potentiometry, and CD were used in this work. Evidence is provided for a simple electrostatic interaction of Mg2+ counterions; on the opposite side, cooperative interaction of Ca2+ counterions is again demonstrated, causing chain-chain association. © 1994 John Wiley & Sons, Inc.
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    URL: http://dx.doi.org/10.1002/bip.360340809
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    The amplitude of local angular motion of purines in DNA in solution (1994)
    New York : Wiley-Blackwell
    Biopolymers 34 (1994), S. 463-480 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Nuclear magnetic resonance and optical experiments are combined to determine the rms amplitude of local angular motion of purines in DNA in solution. A 12 base-pair duplex DNA with the sequence d (CGCGAATTCGCG)2 is deuterated at the H8 positions of adenine and guanine by exchange with solvent dklstwxzat 55°C. The deuterium nmr spectrum of this DNA is measured at 30 mg/mL at 30°C in an 11.76 Tesla magnet (76.75 MHz). The time-resolved fluorescence polarization anisotropies (FPA) of this same sample and also a greatly diluted sample (0.215 mg/mL) were measured after addition of ethidium. FPA measurements of the dilute sample yield the hydrodynamic radius, RH = 9.94 ± 0.2 Å, while those at the nmr concentration are employed to characterize the collective motions in terms of either an enhanced viscosity or dimer formation. The rms amplitude of local angular motion was determined by analyzing the 2H-nmr spectrum, in particular the line width, using recently developed theory for the transverse relaxation rate (R2Q) together with essential information about the collective motions from these and other optical studies. When the principal-axis frame of the electric field gradient tensor is assumed to undergo overdamped libration around each of its three body-fixed axes in an isotropic deflection potential, then the rms amplitude of local angular motion around any single axis is found to lie in the range 10°-11°, provided the high DNA concentration acts to enhance the viscosity, and is about 9°-11°, if it acts to produce end-to-end dimers. The proton nmr relaxation data of Eimer et al. are reanalyzed and shown to yield an rms amplitude of angular motion of the cytosme H5-H6 internuclear vector of 9°-10°, depending upon its orientation with respect to the helix axis. In all of these analyses, full account is taken of the collective twisting and bending deformations, which have a small but significant effect on the results. It is shown that the rms amplitudes of local angular motion do not depend strongly on the model (potential), provided that isotropic rotation around the same number of axes is allowed and that one compares rms angles of the same dimensionality. The rms amplitudes of local angular motion in solution are comparable to those observed for the same sequence at low levels of hydration in the solid state. © 1994 John Wiley & Sons, Inc.
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    Solution structure and dynamics of a glycoinositol phospholipid (GIPL-6) from Leishmania major (1994)
    New York : Wiley-Blackwell
    Biopolymers 34 (1994), S. 1155-1163 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: By use of a combination of 1H nuclear Overhauser effect measurements, restrained molecular dynamics simulations, and 13C spin-lattice relaxation time measurements, the solution behavior of the glycan moiety of a complex glycoinositol phospholipid termed G1PL-6, from the protozoan parasite Leishmania major has been determined. The glycan moiety of GIPL-6 has the following structure, which is characterized by the presence of an internal β-galactofuranose residue: The glycan does not adopt a single conformation in solution, due to significant torsional variations about the two phosphodiester linkages and certain glycosidic linking in the molecule. The present of the internal galactofuranose residue results in an average solution conformation of the oligosaccharide, which resembles a “hairpin,” with the galactofuranose residue at the apex. © 1994 John Wiley & Sons, Inc.
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    URL: http://dx.doi.org/10.1002/bip.360340905
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    Theoretical conformational analysis of the opioid δ antagonist H-Tyr-Tic-Phe-OH and the μ agonist H-Tyr-D-Tic-Phe-NH2 (1994)
    New York : Wiley-Blackwell
    Biopolymers 34 (1994), S. 1213-1219 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A molecular mechanics study (grid search and energy minimization) of the highly δ receptor-selective δ opioid antagonist H-Tyr-Tic-Phe-OH (TIP; Tic: tetrahydroisoquinoline-3-car-boxylic acid) resulted in four low energy conformers with energies within 2 kcal/mol of that of the lowest energy structure. These four conformers contain trans peptide bonds only and represent compact structures showing various patterns of aromatic ring stacking. The centrally located Tic residue imposes several conformational constraints on the N-terminal dipeptide segment; however, the results of molecular dynamics simulations indicated that this tripeptide still shows some structural flexibility, particularly at the Phe3 residue. Analogous studies performed with the structurally related μ receptor-selective μ agonist H-Tyr-D-Tic-Phe-NH2 resulted in low energy structures that were also compact but showed patterns of ring stacking different from those obtained with TIP. Superim-position of low energy conformers of TIP and H-Tyr-D-Tic-Phe-NH2 revealed that the Phe3 residues of the L-Tic- and the D-Tic peptide were always located on opposite sides of the plane defined by the Tic residue, thus providing an explanation for the distinct activity profiles of the two compounds in structural terms. Attempts to demonstrate spatial overlap between the pharmacophoric moieties of low energy conformers of TIP and the nonpeptide δ antagonist naltrindole were made by superimposing either the Tyr1 and Tic2 aromatic rings and the N-terminal amino group or the Tyr1 and Phe3 aromatic rings and the N-terminal amino group of the peptide with the corresponding aromatic rings and nitrogen atom in the alkaloid structure. In each case a low energy structure of TIP was found that showed good spatial overlap of all three specified pharmacophoric groups. These two conformers may represent candidate structures for the δ receptor-bound conformation of TIP. © 1994 John Wiley & Sons, Inc.
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    URL: http://dx.doi.org/10.1002/bip.360340909
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    Relaxed-residue conformational mapping of the three linkage bonds of isomaltose and gentiobiose with MM3(92) (1994)
    New York : Wiley-Blackwell
    Biopolymers 34 (1994), S. 625-638 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Isoenergy surfaces were calculated for the α- and β-anomers of isomaltose and gentiobiose, based on 46,656 conformers for each disaccharide. Low-energy regions exist for each of the three staggered positions about the C-5′ — C-6′ bonds, and known crystal structures lie in two of these regions. As expected, the molecular partition function showed greater flexibility for these three-bond-linked disaccharides than for comparable two-bond-linked structures. A model miniature crystal of gentiobiose accounts for most of the remaining structural differences between the modeled isolated molecule and the crystal structure. Based on models of isolated molecules of isomaltose and gentiobiose, the predicted Boltzmann-weighted nmr coupling constants were satisfactory, as were predicted optical rotations for gentiobiose. © 1994 John Wiley & Sons, Inc.
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    On higher buckling transitions in supercoiled DNA (1994)
    New York : Wiley-Blackwell
    Biopolymers 34 (1994), S. 565-597 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A combination of detailed energy minimization and molecular dynamics studies of closed circular DNA offers here new information that may be relevant to the dynamics of short DNA chains and/or low superhelical densities. We find a complex dependence of supercoiled DNA energies and geometries on the linking number difference ΔLk as physiological superhelieal densities (|σ| ∼ 0.06) are approached. The energy minimization results confirm and extend predictions of classical elasticity theory for the equilibria of elastic rods. The molecular dynamics results suggest how these findings may affect the dynamics of super-coiled DNA.The minimization reveals sudden higher order configurational transitions in addition to the well-known catastrophic buckling from the circle to the figure-8. The competition among the bending, twisting, and self-contact forces leads to different families of supercoiled forms. Some of those families begin with configurations of near-zero twist. This offers the intriguing possibility that nicked DNA may relax to low-twist forms other than the circle, as generally assumed. Furthermore, for certain values of ΔLk, more than one interwound DNA minimum exists. The writhing number as a function of ΔLk is discontinuous in some ranges; it exhibits pronounced jumps as ΔLk is increased from zero, and it appears to level a characteristic slope only at higher values of ΔLk. These findings suggest that supercoiled DNA may undergo systematic rapid interconversions between different minima e both close in energy and geometry.Our molecular dynamics simulations reveal such transitional behavior. We observe the macroscopic bending and twisting fluctuations of interwound forms about the global helix axis as well as the end-over-end tumbling of the DNA as a rigid body. The overall mobility related to |σ| and to the bending, twisting, and van der Waals energy fluctuations. The general character of molecular motions is thus determined by the types of energy minima found at a given ΔLk. Different time scales may be attributed to each type of motion: The overall chain folding occurs on a time scale almost an order of magnitude faster than the end-over-end tumbling. The local bending and twisting of individual chain residues occur at an even faster rate, which in turn correspond to several cycles of local variations for each large-scale bending and straightening motion of the DNA. © 1994 John Wiley & Sons, Inc.
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    URL: http://dx.doi.org/10.1002/bip.360340502
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    Masthead (1994)
    New York : Wiley-Blackwell
    Biopolymers 34 (1994) 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360340601
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    Effects of DNA charge and length on the electrophoretic mobility of intercalated DNA (1994)
    New York : Wiley-Blackwell
    Biopolymers 34 (1994), S. 1349-1358 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: DNA molecules ranging in size from 1 to 630 kilobase pair and intercalated with either ethidium bromide (EtBr) or propidium iodide (PI) were electrophoresed in 1% agarose at four different electric field strengths. The extent of intercalation of EtBr under the conditions of our electrophoresis experiments was determined by a spectroscopic technique, whereas the extent of intercalation of PI was inferred from previous studies. The effects of the increase in DNA contour length and the concomitant decrease of linear charge density were separated based on our analysis of the mobility data. We conclude that the main factor responsible for the reduced electrophoretic mobility of intercalated DNA is the diminished linear charge density and not the increased contour length. © 1994 John Wiley & Sons, Inc.
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    URL: http://dx.doi.org/10.1002/bip.360341007
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    The potential energy surface of methyl 3-O-(α-D-mannopyranosyl)-α-D-mannopyranoside in aqueous solution: Conclusions derived from optical rotation (1994)
    New York : Wiley-Blackwell
    Biopolymers 34 (1994), S. 1395-1401 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The optical rotation of methyl 3-O -(α-D-mannopyranosyl)-α-D-mannopyranoside is calculated semiempirically as a function of the linkage dihedral angles φ (H1-C1-O1-C3′) and ψ (C1-O1-C3′-H3′). Comparison with the observed optical rotation in aqueous solution indicates the existence of at least two conformers in solution, which implies a degree of linkage flexibility. The result is in agreement with some, but not all, calculated potential energy surfaces, and with recently published nmr data. © 1994 John Wiley & Sons, Inc.
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    URL: http://dx.doi.org/10.1002/bip.360341010
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    Defect peptide chemistry: Perturbations in the structure of a homopentapeptide induced by a guest residue interrupting side-chain regularityDedicated to Prof. Murray Goodman on the occasion of his 65th birthday. (1994)
    New York : Wiley-Blackwell
    Biopolymers 34 (1994), S. 1409-1418 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The fully blocked pentapeptide Tfa-(Deg)2-L-Abu-(Deg)2-OtBu (Tfa:triflouroacetyl; Deg: Cα,α-diethylglycine; OtBu: tert-butoxy) adopts in the crystal state a regular, right-handed 310-helical structure stabilized by three N — H … O = C intramolecular 1 ← 4 (or C10) H bonds, as determined by an x-ray diffraction analysis. However, a Fourier transform ir absorption and 1H-nmr study strongly supports the view that in deuterochloroform solution the four Deg residues at both termini of the peptide main chain are involved in successive, fully extended C5 forms. A comparison with the stable, fully developed, multiple C5 conformation of Tfa-(Deg)5-OtBu indicates that incorporation of an Abu guest residue, interrupting the side-chain uniformity of the host (Deg)5 homopeptide, while altering only marginally the conformation in a solvent of low polarity, is responsible for a dramatic perturbation of the crystal-state structure. © 1994 John Wiley & Sons, Inc.
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    URL: http://dx.doi.org/10.1002/bip.360341012
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    A crystal structure with features of an antiparallel α-pleated sheet (1994)
    New York : Wiley-Blackwell
    Biopolymers 34 (1994), S. 1463-1468 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A single-crystal x-ray diffraction analysis of Boc-L-Ala-D-aIle-L-Ile-OMe has been carried out. The analysis has shown (a) that the tripeptide molecules have in part an α-extended conformation, the torsion angles of the L-Ala and D-aIle residues being ϕ1 = -75.1° and ψ1 = -25.8° and ϕ2 = 67.3° and ψ2 = 44.1°, respectively, and (b) that the molecules are organized in rippled planes where they occur in relative antiparallel orientation linked together side by side by H bonds. This molecular organization of the tripeptide corresponds closely to that of an antiparallel α-pleated sheet, and likely constitutes the first example of a structure of this kind for which a characterization at the atomic level has been achieved. A molecular dynamics study has shown that the molecular conformation of the tripeptide in the crystalline state is determined primarily by intermolecular interactions. © 1994 John Wiley & Sons, Inc.
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    URL: http://dx.doi.org/10.1002/bip.360341103
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    Dynamics and thermomechanical stability of DNA in solution (1994)
    New York : Wiley-Blackwell
    Biopolymers 34 (1994), S. 1483-1493 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We present an analysis of the response of native DNA solutions to well-defined elongational flow fields. At low strain rates the DNA duplex behaves as an expanded coil. It shows a noncritical coil-stretch transition, suggesting relatively little hysteresis of the relaxation time. On the other hand, the relaxation time is consistent with a nonfree draining coil. At higher strain rates we observe midpoint scission. This has been modeled very successfully as a thermomechanically activated process. Scission occurs at hydrolyzable weak linkages along the constituent strands. Complete scission of the DNA helix is, however, considerably less prevalent than would be expected given the low stability of the constituent strands. We speculate upon the molecular origin and biological consequences of this enhanced stability. © 1994 John Wiley & Sons, Inc.
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    URL: http://dx.doi.org/10.1002/bip.360341106
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    β-Alanine containing cyclic peptides with predetermined turned structure. VPrevious parts of this series are in Refs. 15-18. (1994)
    New York : Wiley-Blackwell
    Biopolymers 34 (1994), S. 1505-1515 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In the present paper we describe the synthesis, purification, single crystal x-ray analysis, and solution structural characterization by nmr spectroscopy, combined with restrained molecular dynamic simulations, of the cyclic hexapeptide cyclo-(Pro-Phe-β-Ala-Phe-Phe-β-Ala). The peptide was synthesized by classical solution methods and the cyclization of the free hexapeptide was accomplished in good yields in diluted methylenechloride solution using N, N-dicyclohexyl-carbodiimide. The compound crystallizes in the monoclinic space group P21 from methanol/ethyl acetate. The molecule adopts in the solid state a conformation characterized by cis β-Ala6-Pro1 peptide bond. The α-amino acid residues are at the corner positions of turned structures. The Pro1-Phe2 segment is incorporated in a pseudo type I β-turn, while Phe4-Phe5 is in a typical type I β-turn. Assignment of all 1H and 13C resonances was achieved by homo- and heteronuclear two-dimensional techniques in dimethylsulfoxide (DMSO) solutions. The conformational analysis was based on inter-proton distances derived from rotating frame nuclear Overhauser effect spectroscopy spectra and homonuclear coupling constants. Restrained molecular dynamic simulation in vacuo was also performed to built refined molecular models. The molecule is present in DMSO solution as two slowly interconverting conformers, characterized by a cis-tran isomerism around the β-Ala6-Pro1 peptide bond. This work confirms our expectations on the low propensity of β-alanyl residues to be positioned at the corners of turned structure. © 1994 John Wiley & Sons, Inc.
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    URL: http://dx.doi.org/10.1002/bip.360341108
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    Kinked structures of isolated nicotinic receptor M2 helices: A molecular dynamics study (1994)
    New York : Wiley-Blackwell
    Biopolymers 34 (1994), S. 1647-1657 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The pore-lining M2 helix of the nicotinic acetylcholine receptor exhibits a pronounced kink when the corresponding ion channel is in a closed conformation [N. Unwin (1993) Journal of Molecular Biology, Vol. 229, pp. 1101-1124]. We have performed molecular dynamics simulations of isolated 22-residue M2 helices in order to identify a possible molecular origin of this kink. In order to sample a wide range of conformational space, a simulated annealing protocol was used to generate five initial M2 helix structures, each of which was subsequently used as the basis of 300 ps MD simulations. Two helix sequences (M2α and M2δ) were studied in this manner, resulting in a total often 300 ps trajectories. Kinked helices present in the trajectories were identified and energy minimized to yield a total of five different stable kinked structures. For comparison, a similar molecular dynamics simulation of a Leu23 helix yielded no stable kinked structures. In four of the five kinked helices, the kink was stabilized by H bonds between the helix backbone and polar side-chain atoms. Comparison with data from the literature on site-directed mutagenesis of M2 residues suggests that such polar side-chain to main-chain H bonds may also contribute to kinking of M2 helices in the intact channel protein. © 1994 John Wiley & Sons, Inc.
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    URL: http://dx.doi.org/10.1002/bip.360341209
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    Computer simulation of the free energy of peptides with the local states method: Analogues of gonadotropin releasing hormone in the random coil and stable states (1994)
    New York : Wiley-Blackwell
    Biopolymers 34 (1994), S. 815-839 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The Helmholtz free energy F (rather than the energy) is the correct criterion for stability; therefore, calculation of F is important for peptides and proteins that can populate a large number of metastable states. The local states (LS) method proposed by H. Meirovitch [(1977) Chemical Physics Letters, Vol. 45, p. 389] enables one to obtain upper and lower bounds of the conformational free energy, FB (b, l) and FA (b, l), respectively, from molecular dynamics (MD) or Monte Carlo samples. The correlation parameter b is the number of consecutive dihedral or valence angles along the chain that are taken into account explicitly. The continuum angles are approximated by a discretization parameter l; the larger are b and l, the better the approximations; while FA can be estimated efficiently, it is more difficult to estimate FB. The method is further developed here by applying it to MD trajectories of a relatively large molecule (188 atoms), the potent “Asp4-Dpr10” antagonist [cyclo(4/10)-(Ac-Δ3Pro1-D-pFPhe2-D-Trp3-Asp4-Tyr-5-D-Nal6-Leu7-Arg8-Pro9-Dpr10-NH2)] of gonadotropin releasing hormone (GnRH). The molecule was simulated in vacuo at T = 300 K in two conformational states, previously investigated [J. Rizo et al. Journal of the American Chemical Society, (1992) Vol. 114, p. 2860], which differ by the orientation of the N-terminal tail, above (tail up, TU) and below (tail down. TD) the cyclic heptapeptide ring. As in previous applications of the LS method, we have found the following: (1) While FA is a crude approximation for the correct F, results for the difference, ΔFA = FA(TD) - FA(TU) converge rapidly to 5.6(1) kcal/mole as the approximation is improved (i.e., as b and l are increased), which suggests that this is the correct value for ΔF; therefore TD is more stable than TU. (The corresponding difference in entrophy. TΔSA = 1.3(2) kcal/mole, is equal to the value obtained by the harmonic approximation.) (2) The lowest approximation, which has the minimal number of local states, i.e., based on b = 0 (no correlations) and l = 1 (the angle values are distributed homogeneously), also leads to the correct value of ΔF, within the error bars. This is important since the lowest approximation can be applied even to large proteins. (3) The method enables one to define the entropy of a part of the molecule and thus to measure the flexibility of this part. We have verified that the results for T[SA(TU) - SA(TD)] of the tail alone converged to 2.4(1) kcal/mole, which demonstrates the relatively high flexibility of the tail in the TU state. In order to study the random coil state, the Asp4-Dpr10 analogue and its linear version were simulated by MU at 1000 K. We have been able to calculate a lower bound, ∼ 25 kcal/mole for T[S(linear) - S(cyclic)], which is the reduction in the conformational entropy caused by the ring closure. © 1994 John Wiley & Sons, Inc.
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    URL: http://dx.doi.org/10.1002/bip.360340703
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    Solution structure of a core peptide derived from scyllatoxin (1994)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 18 (1994), S. 205-215 
    Details
    ISSN: 0887-3585
    Keywords: peptide folding ; disulfide framework ; insect toxins ; NMR ; distance geometry ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: An analysis of the sequences of scyllatoxin and charybdotoxin suggested that it would be possible to design a core peptide sequence which would still fold to give the β-hairpin and helix seen in the toxins, but which would eliminate one disulfide and connecting residues. The core sequence was modeled, then synthesized and purified. The cysteines oxidize in air to give the same disulfide pairings as seen in the parent toxins as the major product. The three-dimensional structure of the core sequence peptide, termed Max, was determined using proton NMR spectroscopy and found to be identical in secondary structure to the toxins. However differences were found in the relative orientation of the β-hairpin and helix. The use of this structural motif, found in many insect toxins, as a disulfide framework for exploring sequence/structure/activity relationships is discussed. © 1994 John Wiley & Sons, Inc.
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    URL: http://dx.doi.org/10.1002/prot.340180302
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    Thermodynamics of ubiquitin unfolding (1994)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 18 (1994), S. 246-253 
    Details
    ISSN: 0887-3585
    Keywords: microcalorimetry ; heat capacity ; enthalpy ; hydrogen bonding ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The energetics of ubiquitin unfolding have been studied using differential scanning microcalorimetry. For the first time it has been shown directly that the enthalpy of protein unfolding is a nonlinear function of temperature. Thermodynamic parameters of ubiquitin unfolding were correlated with the structure of the protein. The enthalpy of hydrogen bonding in ubiquitin was calculated and compared to that obtained for other proteins. It appears that the energy of hydrogen bonding correlates with the average length of the hydrogen bond in a given protein structure. © 1994 John Wiley & Sons, Inc.
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    URL: http://dx.doi.org/10.1002/prot.340180305
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    Hydrogen bond strength and β-sheet propensities: The role of a side chain blocking effect (1994)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 18 (1994), S. 262-266 
    Details
    ISSN: 0887-3585
    Keywords: protein structure prediction ; protein stability ; hydrogen bond ; β-sheet ; amino acid propensity ; steric effect ; hydrogen exchange ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Amino acid side chains can enhance peptide group hydrogen bond strength in protein structures by obstructing the competing hydrogen bond to solvent in the unfolded state. Available data indicate that the steric blocking effect contributes an average of 0.5 kJ per residue to protein hydrogen bond strength and accounts for the intrinsic α-sheet propensities of the amino acids. In available data for helical models, the contribution to α-helix propensities is obscured especially by large context-dependent effects. These issues are all related by a common side chain-dependent steric clash which disfavors peptide to water H-bond formation, peptide to catalyst complexation in hydrogen exchange reactions (Bai et al., Proteins 17:75-86, 1993), and peptide to peptide H-bonding in the helical main chain conformation (Creamer and Rose, Proc. Natl. Acad. Sci. U.S.A. 89:5937-5941, 1992) but not in α-strands. © 1994 John Wiley & Sons, Inc.
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    URL: http://dx.doi.org/10.1002/prot.340180307
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    A method for α-helical integral membrane protein fold prediction (1994)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 18 (1994), S. 281-294 
    Details
    ISSN: 0887-3585
    Keywords: membrane ; protein ; structure ; prediction ; G-protein coupled receptor ; rhodopsin ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Integral membrane proteins (of the α-helical class) are of central importance in a wide variety of vital cellular functions. Despite considerable effort on methods to predict the location of the helices, little attention has been directed toward developing an automatic method to pack the helices together. In principle, the prediction of membrane proteins should be easier than the prediction of globular proteins: there is only one type of secondary structure and all helices pack with a common alignment across the membrane. This allows all possible structures to be represented on a simple lattice and exhaustively enumerated. Prediction success lies not in generating many possible folds but in recognizing which corresponds to the native. Our evaluation of each fold is based on how well the exposed surface predicted from a multiple sequence alignment fits its allocated position. Just as exposure to solvent in globular proteins can be predicted from sequence variation, so exposure to lipid can be recognized by variable-hydrophobic (variphobic) positions. Application to both bacteriorhodopsin and the eukaryotic rhodopsin/opsin families revealed that the angular size of the lipid-exposed faces must be predicted accurately to allow selection of the correct fold. With the inherent uncertainties in helix prediction and parameter choice, this accuracy could not be guaranteed but the correct fold was typically found in the top six candidates. Our method provides the first completely automatic method that can proceed from a scan of the protein sequence databanks to a predicted three-dimensional structure with no intervention required from the investigator. Within the limited domain of the seven helix bundle proteins, a good chance can be given of selecting the correct structure. However, the limited number of sequences available with a corresponding known structure makes further characterization of the method difficult. © 1994 John Wiley & Sons, Inc.
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    URL: http://dx.doi.org/10.1002/prot.340180309
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    Crystallization and preliminary crystallographic studies of the precursor and mature forms of a neutral lipase from the fungus Rhizopus delemar (1994)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 18 (1994), S. 301-306 
    Details
    ISSN: 0887-3585
    Keywords: triglyceride lipase ; proenzyme ; molecular replacement ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: A neutral lipase from the filamentous fungus Rhizopus delemar has been crystallized in both its proenzyme and mature forms. Although the latter crystallizes readily and produces a variety of crystal forms, only one was found to be suitable for X-ray studies. It is monoclinic (C2, a = 92.8 Å, b = 128.9 Å, c = 78.3 Å, β = 135.8) with two molecules in the asymmetric unit related by a noncrystallographic diad. The prolipase crystals are orthorhombic (P212121, with a = 79.8 Å, b = 115.2 Å, c = 73.0 Å) and also contain a pair of molecules in the asymmetric unit. Initial results of molecular replacement calculations using the refined coordinates of the related lipase from Rhizomucor miehei identified the correct orientations and positions of the protein molecules in the unit cells of crystals of both proenzyme and the mature form. © 1994 John Wiley & Sons, Inc.
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    URL: http://dx.doi.org/10.1002/prot.340180311
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    Correlated mutations and residue contacts in proteins (1994)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 18 (1994), S. 309-317 
    Details
    ISSN: 0887-3585
    Keywords: protein structure prediction ; predicted contact maps ; correlated mutations ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The maintenance of protein function and structure constrains the evolution of amino acid sequences. This fact can be exploited to interpret correlated mutations observed in a sequence family as an indication of probable physical contact in three dimensions. Here we present a simple and general method to analyze correlations in mutational behavior between different positions in a multiple sequence alignment. We then use these correlations to predict contact maps for each of 11 protein families and compare the result with the contacts determined by crystallography. For the most strongly correlated residue pairs predicted to be in contact, the prediction accuracy ranges from 37 to 68% and the improvement ratio relative to a random prediction from 1.4 to 5.1. Predicted contact maps can be used as input for the calculation of protein tertiary structure, either from sequence information alone or in combination with experimental information. © 1994 John Wiley & Sons, Inc.
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    URL: http://dx.doi.org/10.1002/prot.340180402
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    Analysis of Cα geometry in protein structures (1994)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 18 (1994), S. 324-337 
    Details
    ISSN: 0887-3585
    Keywords: protein structure ; secondary structure ; peptide geometry ; Ramachandran plot ; β-turns ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The polypeptide of a protein molecule can be considered as a chain of Cα atoms linked by pseudobonds between the Cα atoms of successive amino acid residues. This paper presents an analysis of the angle and dihedral angles made by these pseudobonds in protein structures determined at high resolution by X-ray crystallography. This analysis reveals a strong correlation between Cα geometry and the protein fold. The regular features of protein secondary structure such as α-helix and α-sheet are very clearly defined. In addition, it is possible to identify with some confidence the discrete populations of particular conformations of α-turn. Comparison with the traditional Ramachandran type of plot demonstrates that an analysis of protein structure on the basis of Cα geometry provides a richer description of protein conformation. In addition, the characteristics of this geometry could be a useful guide in model building of protein structure. © 1994 John Wiley & Sons, Inc.
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    URL: http://dx.doi.org/10.1002/prot.340180404
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    Crystallization of a fragment of human fibronectin: Introduction of methionine by site-directed mutagenesis to allow phasing via selenomethionine (1994)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 19 (1994), S. 48-54 
    Details
    ISSN: 0887-3585
    Keywords: X-ray crystallography ; extracellular matrix ; multiwavelength anomalous diffraction (MAD) ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Crystals of a fragment of human fibronectin encompassing the 7th through the RGD-containing 10th type III repeats (FN7-10) have been produced with protein expressed in E. coli. The crystals are monoclinic with one molecule in the asymmetric unit and diffract to beyond 2.0 Å Bragg spacings. A mutant FN7-10 was produced in which three methionines, in addition to the single native methionine already present, have been introduced by site-directed mutagenesis. Diffraction-quality crystals of this mutant protein have been grown in which methionine was replaced with selenomethionine. The introduction of methionine by site-directed mutagenesis to allow phasing from selenomethionyl-substituted crystals is shown to be feasible by this example and is proposed as a general approach to solving the crystallographic phase problem. Strategies for selecting propitious sites for methionine mutations are discussed. © 1994 Wiley-Liss, Inc.
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    URL: http://dx.doi.org/10.1002/prot.340190107
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    Combining evolutionary information and neural networks to predict protein secondary structure (1994)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 19 (1994), S. 55-72 
    Details
    ISSN: 0887-3585
    Keywords: secondary structure prediction ; prediction of secondary structure class ; prediction of secondary structure content ; evolutionary information ; multiple alignment profiles ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Using evolutionary information contained in multiple sequence alignments as input to neural networks, secondary structure can be predicted at significantly increased accuracy. Here, we extend our previous three-level system of neural networks by using additional input information derived from multiple alignments. Using a position-specific conservation weight as part of the input increases performance. Using the number of insertions and deletions reduces the tendency for overprediction and increases overall accuracy. Addition of the global amino acid content yields a further improvement, mainly in predicting structural class. The final network system has a sustained overall accuracy of 71.6% in a multiple cross-validation test on 126 unique protein chains. A test on a new set of 124 recently solved protein structures that have no significant sequence similarity to the learning set confirms the high level of accuracy. The average cross-validated accuracy for all 250 sequence-unique chains is above 72%. Using various data sets, the method is compared to alternative prediction methods, some of which also use multiple alignments: the performance advantage of the network system is at least 6 percentage points in three-state accuracy. In addition, the network estimates secondary structure content from multiple sequence alignments about as well as circular dichroism spectroscopy on a single protein and classifies 75% of the 250 proteins correctly into one of four protein structural classes. Of particular practical importance is the definition of a position-specific reliability index. For 40% of all residues the method has a sustained three-state accuracy of 88%, as high as the overall average for homology modelling. A further strength of the method is greatly increased accuracy in predicting the placement of secondary structure segments. © 1994 Wiley-Liss, Inc.
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    URL: http://dx.doi.org/10.1002/prot.340190108
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    Expression, purification, and crystallization of restriction endonuclease PvuII with DNA containing its recognition site (1994)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 19 (1994), S. 77-79 
    Details
    ISSN: 0887-3585
    Keywords: endonuclease overexpression ; crystallization ; X-ray diffraction ; protein-DNA complex ; Type II restriction enzyme ; vapor diffusion ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: We have overexpressed the type II restriction endonuclease PvuII (R.PvuII) in E. coli, prepared large amounts of the homogeneous enzyme, and crystallized it with an oligonucleotide carrying a PvuII recognition site. The cocrystals are orthorhombic space group P212121 with cell constants a = 95.8 Å, b = 86.3 Å, c = 48.5 Å, and diffract X-rays to at least 2.7 Å. There is a complex of two protein subunits and one oligonucleotide duplex in the asymmetric unit. © 1994 Wiley-Liss, Inc.
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    URL: http://dx.doi.org/10.1002/prot.340190110
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    Masthead (1994)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 19 (1994) 
    Details
    ISSN: 0887-3585
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prot.340190201
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    Crystallization and preliminary X-ray crystallographic analysis of phospholipid transfer protein from maize seedlings (1994)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 19 (1994), S. 80-83 
    Details
    ISSN: 0887-3585
    Keywords: maize protein ; crystals ; X-ray diffraction ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Phospholipid transfer protein from maize seedlings has been crystallized using trisodium citrate as precipitant. The crystal belongs to the orthorhombic space group P212121 with unit cell dimensions of a = 24.46 Å, b = 49.97 Å, and c = 69.99 Å. The presence of one molecule in the asymmetric unit gives a crystal volume per protein mass (Vm) of 2.36 Å 3/Da and a solvent content of 48% by volume. The X-ray diffraction pattern extends at least to 1.6 Å Bragg spacing when exposed to both CuKα and synchrotron X-rays. A set of X-ray data to approximately 1.9 Å Bragg spacing has been collected from a native crystal. © 1994 Wiley-Liss, Inc.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/prot.340190111
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    α-Helix-forming propensities in peptides and proteins (1994)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 19 (1994), S. 85-97 
    Details
    ISSN: 0887-3585
    Keywords: protein conformation ; secondary structure ; protein folding ; helix stability ; helix formation ; conformational entropy ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Much effort has been invested in seeking to understand the thermodynamic basis of helix stability in both peptides and proteins. Recently, several groups have measured the helix-forming propensities of individual residues (Lyu, P. C., Liff, M. I., Marky, L. A., Kallenbach, N. R. Science 250:669-673, 1990; O'Neil, K. T., DeGrado, W. F. Science 250:646-651, 1990; Padmanabhan, S., Marqusee, S., Ridgeway, T., Laue, T. M., Baldwin, R. L. Nature (London) 344:268-270, 1990). Using Monte Carlo computer simulations, we tested the hypothesis that these differences in measured helix-forming propensity are due primarily to loss of side chain conformational entropy upon helix formation (Creamer, T. P., Rose, G. D. Proc. Natl. Acad. Sci. U.S.A. 89:5937-5941, 1992). Our previous study employed a rigid helix backbone, which is here generalized to a completely flexible helix model in order to ensure that earlier results were not a methodological artifact. Using this flexible model, side chain rotamer distributions and entropy losses are calculated and shown to agree with those obtained earlier. We note that the side chain conformational entropy calculated for Trp in our previous study was in error; a corrected value is presented. Extending earlier work, calculated entropy losses are found to correlate strongly with recent helix propensity scales derived from substitutions made within protein helices (Horovitz, A., Matthews, J. M., Fersht, A. R. J. Mol. Biol. 227:560-568, 1992; Blaber, M., Zhang, X.-J., Matthews, B. M. Science 260:1637-1640, 1993). In contrast, little correlation is found between these helix propensity scales and the accessible surface area buried upon formation of a model polyalanyl α-helix. Taken in sum, our results indicate that loss of side chain entropy is a major determinant of the helix-forming tendency of residues in both peptide and protein helices. © 1994 Wiley-Liss, Inc.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/prot.340190202
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    1.56 Å structure of mature truncated human fibroblast collagenase (1994)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 19 (1994), S. 98-109 
    Details
    ISSN: 0887-3585
    Keywords: crystallography ; hydroxamate ; high resolution ; metalloproteinase ; zinc ; X-ray ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The X-ray crystal structure of a 19 kDa active fragment of human fibroblast collagenase has been determined by the multiple isomorphous replacement method and refined at 1.56 Å resolution to an R-factor of 17.4%. The current structure includes a bound hydroxamate inhibitor, 88 waters and three metal atoms (two zincs and a calcium). The overall topology of the enzyme, comprised of a five stranded β-sheet and three α-helices, is similar to the thermolysin-like metalloproteinases. There are some important differences between the collagenase and thermolysin families of enzymes. The active site zinc ligands are all histidines (His-218, His-222, and His-228). The presence of a second zinc ion in a structural role is a unique feature of the matrix metalloproteinases. The binding properties of the active site cleft are more dependent on the main chain conformation of the enzyme (and substrate) compared with thermolysin. A mechanism of action for peptide cleavage similar to that of thermolysin is proposed for fibroblast collagenase. © 1994 Wiley-Liss, Inc.
    Additional Material: 11 Ill.
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    URL: http://dx.doi.org/10.1002/prot.340190203
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  • 183
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    Kinetic study on myoglobin refolding monitored by five optical probe stopped-flow methods (1994)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 19 (1994), S. 110-119 
    Details
    ISSN: 0887-3585
    Keywords: folding intermediate ; urea denaturation ; stopped-flow circular dichroism ; molten globule ; hemindicyanide ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The refolding kinetics of horse cyanometmyoglobin induced by concentration jump of urea was investigated by five optical probe stopped-flow methods: absorption at 422 nm, tryptophyl fluorescence at around 340 nm, circular dichroism (CD) at 222 nm, CD at 260 nm, and CD at 422 nm. In the refolding process, we detected three phases with rate constants of 〉 1 × 102 s-1, (4.5-9.3) S-1, and (2-5) × 10-3 s-1. In the fastest phase, a substantial amount of secondary structure (40%) is formed within the dead time of the CD stopped-flow apparatus (10.7 ms). The kinetic intermediate populated in the fastest phase is shown to capture a hemindicyanide, suggesting that a “heme pocket precursor” recognized by hemindicyanide must be constructed within the dead time. In the middle phase, most of secondary and tertiary structures, especially around the captured hemindicyanide, have been constructed. In the slowest phase, we detected a minor structural rearrangement accompanying the ligand-exchange reaction in the fifth coordination of ferric iron. We present a possible model for the refolding process of myoglobin in the presence of the heme group. © 1994 Wiley-Liss, Inc.
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    URL: http://dx.doi.org/10.1002/prot.340190204
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  • 184
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    Decoupling of melting domains in immobilized ribonuclease A (1994)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 19 (1994), S. 120-131 
    Details
    ISSN: 0887-3585
    Keywords: enzymes ; protein immobilization ; microcalorimetry ; protein melting domains ; protein DSC ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Ribonuclease A has been immobilized on silica beads through glutaraldeyde-mediated chemical coupling in order to improve the stability of the protein against thermal denaturation. The thermodynamic and binding properties of the immobilized enzyme have been studied and compared with those of the free enzyme. The parameters describing the binding of the inhibitor 3′ -CMP (Ka and ΔH) as monitored by spectrophotometry and calorimetry were not significantly affected after immobilization. Conversely both the stability and unfolding mechanism drastically changed. Thermodynamic analysis of the DSC data suggests that uncoupling of protein domains has occurred as a consequence of the immobilization. The two state approximation of the protein unfolding process is not longer valid for the immobilized RNase. Protein stability strongly depends on the hydrophobicity properties of the support surface as well as on the presence of the inhibitor and pH. For example, after immobilization on a highly hydrophobic surface, the enzyme is partially in the unfolded state. The binding of a ligand is able to reorganize the protein structure into a native-like conformation. The refolding rates are different for the two protein domains and vary as a function of pH and presence of the inhibitor 3′-CMP. © 1994 Wiley-Liss, Inc.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/prot.340190205
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  • 185
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    Temperature-induced complementarity as a mechanism for biomolecular assembly (1994)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 19 (1994), S. 73-76 
    Details
    ISSN: 0887-3585
    Keywords: molecular recognition ; protein assembly ; protein folding ; protein interactions ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Recent advances in the measurement and theory of “hydration” interactions between biomolecules provide a basis on which to formulate mechanisms of biomolecular recognition. In this paper we have developed a mathematical formalism for analyzing specificity encoded in dynamic distributions of surface polar groups, a formalism that incorporates newly recognized properties of directly measured “hydration” forces. As expected, attraction between surfaces requires complementary patterns of surface polar groups. In contrast to usual expectations, thermal motion can create these complementary surface configurations. We have demonstrated that assembly can occur with an increase in conformational entropy of polar residues. Elevated temperature then facilitates recognition rather than hinders it. This mechanism might underlie some temperature-favored assembly reactions common in biological systems that are usually associated with the “hydrophobic effect” only. © 1994 Wiley-Liss, Inc.
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    URL: http://dx.doi.org/10.1002/prot.340190109
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  • 186
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    Coiled-coil stutter and link segments in keratin and other intermediate filament molecules: A computer modeling study (1994)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 20 (1994), S. 174-184 
    Details
    ISSN: 0887-3585
    Keywords: coiled-coils ; keratin ; intermediate filament proteins ; link segments ; heptad phasing ; computer modeling ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Structural discontinuities have previously been identified in four regions of the coiled-coil rod domain structure present in intermediate filament (IF) protein molecules. These include a point at which a phase shift occurs in the heptad periodicity characteristic of the sequence of polar and apolar residues in α-helical coiled-coils, and three links that lack a heptad substructure. We have studied these regions by computer-based molecular modeling and comparative sequence analysis and conclude that the phasing discontinuity can be accommodated without significant distortion of the overall double-helical chain conformation; the L2 link has a similar conformation in all different types of IF molecules, a favorable conformation being one in which the two strands wrap tightly around each other; the L12 links vary in length between different IF types but contain important sequence similarities suggestive of a partial β structure; the L1 links show larger variations in length, a lower degree of similarity, and probably diverse structures. Variations in the overall charges of the different links suggest that ionic interactions may playa significant role in filament assembly. The results also have general significance for other α-fibrous proteins in which either the characteristic heptad phasing undergoes a discontinuity or where a short non-coiled-coil sequence occurs within a coiled-coil rod domain structure. © 1994 Wiley-Liss, Inc.
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    URL: http://dx.doi.org/10.1002/prot.340200207
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  • 187
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    Crystallization and characterization of the recombinant human Clara cell 10-kDa protein (1994)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 20 (1994), S. 191-196 
    Details
    ISSN: 0887-3585
    Keywords: human Clara cell 10-kDa protein ; X-ray diffraction ; phospholipase A2 inhibitor ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Crystals of recombinant human Clara cell 10-kDa protein were grown both from ammonium sulfate and polyethylene glycol (PEG) solutions. Crystals grown from ammonium sulfate solution have been characterized by X-ray diffraction studies as monoclinic with the space group C2 and lattice constants a = 69.2 Å, b = 83.0 Å, c = 58.3 Å, and β = 99.7°. The monoclinic crystals diffract to beyond 2.5 Å. Some of the crystals grown from PEG were of a similar habit to those grown from ammonium sulfate, but others were triclinic with the space group P1 and cell constants a = 40.3 Å, b = 46.3 Å, c = 51.3 Å, α = 117.7°, β = 102.3°, and γ = 71.4°. These crystals diffract to beyond 3.2 Å. © 1994 Wiley-Liss, Inc.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/prot.340200209
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    Conformational analysis of hemopexin by fourier-transform infrared and circular dichroism spectroscopy (1994)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 20 (1994), S. 185-190 
    Details
    ISSN: 0887-3585
    Keywords: heme ; secondary structure ; conformation ; hemopexin ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Hemopexin is a serum glyco-protein that binds heme with the highest known affinity of any characterized heme-binding protein and plays an important role in receptormediated cellular heme uptake. Complete understanding of the function of hemopexin will require the elucidation of its molecular structure. Previous analysis of the secondary structure of hemopexin by far-UV circular dichroism (CD) failed due to the unusual positive ellipticity of this protein at 233 nm. In this paper, we present an examination of the structure of hemopexin by both Fourier-transform infrared (FTIR) and circular dichroism spectroscopy. Our studies show that hemopexin contains about 55% β-structure, 15% α-helix, and 20% turns. The two isolated structural domains of hemopexin each have secondary structures similar to hemopexin. Although there are significant tertiary conformational changes indicated by the CD spectra, the overall secondary structure of hemopexin is not affected by binding heme. However, moderate changes in secondary structure do occur when the heme-binding domain of hemopexin associates with heme. In spite of the exceptionally tight binding at neutral pH, heme is released from the bis-histidyl heme-hemopexin complex at pH 5.0. Under this acidic condition, hemopexin maintains the same overall secondary structure as the native protein and is able to resume the heme-binding function and the native structure of the hemeprotein (as indicated by the CD spectra) when returned to neutral pH. We propose that the state of hemopexin identified in vitro at pH 5.0 resembles that of this protein in the acidic environment of the endosomes in vivo when hemopexin releases heme during receptor-mediated endocytosis. © 1994 Wiley-Liss, Inc.
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    URL: http://dx.doi.org/10.1002/prot.340200208
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    Masthead (1994)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 20 (1994) 
    Details
    ISSN: 0887-3585
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prot.340200301
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  • 190
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    Preliminary crystallographic analysis of an enzyme involved in erythromycin biosynthesis: Cytochrome P450eryF (1994)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 20 (1994), S. 197-201 
    Details
    ISSN: 0887-3585
    Keywords: cytochrome P450 ; erythromycin ; P450eryF ; crystallization ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Cytochrome P450eryF was overexpressed in Escherichia coli and purified in high yield. Crystals of the protein in the presence of the substrate, 6-deoxyerythronolide B, have been obtained by the hanging drop vapor diffusion method, using polyethylene glycol 4000 as a precipitant. The crystals belong to the orthorhombic space group P212121 with unit cell dimensions of a = 54.16 Å, b = 79.67 Å, and c = 99.48 Å and one molecule per asymmetric unit. A complete native data set has been collected to a resolution of 2.1 Å, and anomalous dispersion difference Patterson maps have revealed the location of the single heme iron atom. © 1994 Wiley-Liss, Inc.
    Additional Material: 5 Ill.
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    URL: http://dx.doi.org/10.1002/prot.340200210
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  • 191
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    Homology modeling of the Abl-SH3 domain (1994)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 20 (1994), S. 203-215 
    Details
    ISSN: 0887-3585
    Keywords: SH3 ; Abl ; molecular modeling ; homology modeling ; molecular dynamics ; protein structure prediction ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: A tertiary structure model of the Abl-SH3 domain is predicted by using homology modeling techniques coupled to molecular dynamics simulations. Two template proteins were used, Fyn-SH3 and Spc-SH3. The refined model was extensively checked for errors using criteria based on stereochemistry, packing, solvation free-energy, accessible surface areas, and contact analyses. The different checking methods do not totally agree, as each one evaluates a different characteristic of protein structures. Several zones of the protein are more susceptible to incorporating errors. These include residues 13, 15, 35, 39, 45, 46, 50, and 60. An interesting finding is that the measurement of the Cα chirality correlated well with the rest of the criteria, suggesting that this parameter might be a good indicator of correct local conformation. Deviations of more than 4 degrees may be indicative of poor local structure. © 1994 Wiley-Liss, Inc.
    Additional Material: 7 Ill.
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    URL: http://dx.doi.org/10.1002/prot.340200302
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  • 192
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    Homologous modeling of the lysosomal protective protein/carboxypeptidase L: Structural and functional implications of mutations identified in galactosialidosis patients (1994)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 18 (1994), S. 81-93 
    Details
    ISSN: 0887-3585
    Keywords: serine carboxypeptidase ; protein modeling ; mutation analysis ; comparative modeling ; cathepsin A ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The deficiency of the lysosomal protective protein/carboxypeptidase L (CARB L) causes the lysosomal storage disorder, galactosialidosis, characterized by neuraminidase and β-galactosidase deficiencies in patients' cells. The three enzymes form a complex inside the lysosome, and the neuraminidase and β-galactosidase deficiencies are secondary to CARB L deficiency. Sequence similarity and common enzymological properties suggest that the protomeric tertiary structure of CARB L is conserved within a family of serine carboxypeptidases which includes the yeast carboxypeptidase Y, killer expression I gene product and several plant carboxypeptidases. We used this homology to build a model of the CARB L structure based on the recently published X-ray atomic coordinates of the wheat carboxypeptidase II (CPDW-II) which shares 32% primary structure identity with CARB L. Small insertions and deletions were accommodated into the model structure by energy minimization using the DREIDING II force field. The Cα atomic-coordinates of the final CARB L model have a RMS shift of 1.01 Å compared to the corresponding conserved residues in the CPDW-II template structure. The correct orientation of the homologous catalytic triad residues Ser150, His429 and Asp392, the potential energy calculations and the distribution of hydrophobic and hydrophillic residues in the structure all support the validity of the CARB L model. Most missense mutations identified in galactosialidosis patients were located in secondary structural elements except for the Tyr211→Asn mutation which is in a loop. The other mutant residues have their side chains deeply buried in the central β-sheet of the model structure except for the Phe412→Val mutation which is located in the dimer interface. The predicted effects of specific mutations on CARB L structural stability correlates well with recently published transient expression studies of mutant CARB L (Shimmoto, M. et al., J. Clin. Invest., 91:2393-2399, 1993). © 1994 John Wiley & Sons, Inc.
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    URL: http://dx.doi.org/10.1002/prot.340180110
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  • 193
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    Protein simulations using techniques suitable for very large systems: The cell multipole method for nonbond interactions and the Newton-Euler inverse mass operator method for internal coordinate dynamics (1994)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 20 (1994), S. 227-247 
    Details
    ISSN: 0887-3585
    Keywords: cell multipole method ; Newton-Euler inverse mass operator ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Two new methods developed for molecular dynamics simulations of very large proteins are applied to a series of proteins ranging up to the protein capsid of tomato bushy stunt virus (TBSV).For molecular dynamics of very large proteins and polymers, it is useful to carry out the dynamics using internal coordinates (say, torsions only) rather than Cartesian coordinates. This allows larger time steps, eliminates problems with the classical description of high energy modes, and focuses on the important degrees of freedom. The resulting equation of motion has the form where for T is the vector of generalized forces, M(θ) is the moments of inertia tensor, is the vector of torsions, and C is a vector containing Coriolis forces and nonbond forces. The problem is that to calculate the acceleration vector from M, C, and Trequires inverting. M(θ), an order N3calculation. Since the number of degrees of freedom might be 300,000 for a million atom system, solving these equations every time step is impractical, restricting internal coordinate methods to small systems. The new method, Newton-Euler Inverse Mass Operator (NEIMO) dynamics, constructs the torsional accelerations vector directly by an order N process, allowing internal-coordinate dynamics to be solved for super larger (million atom) systems, The first use of the NEIMO method for molecular dynamics of proteins is presented here.A second serious difficulty for large proteins is calculation of the nonbond forces. We report here the first application to proteins of the new Cell Multipole Method (CMM) to evaluate the Coulomb and van der Waals interactions. The cost of CMM scales linearly with the number of particles while retaining an accuracy significantly better than standard non bond methods (involving cutoffs).Results for NEIMO and CMM are given for simulations of a wide range of peptide and protein systems, including the protein capsid of TBSV with 488,000 atoms. The computational times for NEIMO and CMM are demonstrated to scale linearly with size. With NEIMO the dynamics time steps can be as large as 20 fs (for small peptides), much larger than possible with standard Cartesian coordinate dynamics.For TBSV we considered both the normal form and the high pH form, in which the Ca2+ ions are removed. These calculations lead to a contraction of the protein for both forms (probably because of ignoring the RNA core not observed in the X-ray). © 1994 Wiley-Liss, Inc.
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    Estimation of changes in side chain configurational entropy in binding and folding: General methods and application to helix formation (1994)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 20 (1994), S. 68-84 
    Details
    ISSN: 0887-3585
    Keywords: side chain conformation ; protein folding ; protein binding ; helix formation ; helix stability ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Theoretical estimations of changes in side chain configurational entropy are essential for understanding the different contributions to the overall thermodynamic behavior of important biological processes like folding and binding. The configurational entropy of any given side chain in any particular protein can be evaluated from the complete energy profile of the side chain. Calculations of the energy profiles can be performed using the side chain single bond dihedrals as the only independent variables as long as the structures at each value of the dihedrals are allowed to relax through small changes in the valence bond angles. The probabilities of different side chain conformers obtained from these energy profiles are very similar to the conformer populations obtained by analysis of side chain preferences in the proteins of the Protein Data Bank. Also, side chain conformational entropies obtained from the energy profiles agree extremely well with those obtained from the Protein Data Bank conformer populations. Changes in side chain configurational entropy in binding and folding can be computed as differences in conformational entropy because, in most cases, the frequency of the rotational oscillation around the energy minimum of any given conformer does not appear to change significantly in the reaction. Changes of side chain conformational entropy calculated in this way were compared with experimental values. The only available experimental data-the effect of side chain substitution on the stability of α-helices-were used for this comparison. The experimental values were corrected to subtract the solvent contributions. This comparison yields an excellent agreement between calculated and experimental values, validating not only the theoretical estimates but also the separability of the entropic contributions into configurational terms and solvation related terms. © 1994 Wiley-Liss, Inc.
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  • 195
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    Microtube batch protein crystallization: Applications to human immunodeficiency virus type 2 (HIV-2) protease and human renin (1994)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 20 (1994), S. 98-102 
    Details
    ISSN: 0887-3585
    Keywords: X-ray diffraction ; aspartic protease ; AIDS ; recombinant protein ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: For therapeutically relevant targets, the evaluation of enzymes in complex with their inhibitors by cocrystallization and high resolution structural analysis has become a vital component of structure-driven drug design and development. Two approaches, hanging drop vapor diffusion and a novel microtube batch method, were utilized in parallel to grow crystals of recombinant HIV -2 protease and recombinant human renin in complex with inhibitors. In the case of HIV -2 protease in complex with a reduced amide inhibitor, crystallization was achieved only by the microbatch method. In the case of human renin, the addition of precipitant was required for crystal growth. The microbatch method described here is a useful supplementary or alternative approach for screening parameters and generating crystals suitable for high resolution structural analysis. © 1994 Wiley-Liss, Inc.
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  • 196
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    Solvent-induced organization: A physical model of folding myoglobin (1994)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 20 (1994), S. 124-138 
    Details
    ISSN: 0887-3585
    Keywords: leghemoglobin ; hydrophobic ; interactions ; hydrophobicity ; protein folding ; structure prediction ; protein dynamics ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The essential features of the in vitro refolding of myoglobin are expressed in a solvable physical model. Alpha helices are taken as the fundamental collective coordinates of the system, while the refolding is assumed to be mainly driven by solvent-induced hydrophobic forces. A quantitative model of these forces is developed and compared with experimental and theoretical results. The model is then tested by being employed in a simulation scheme designed to mimic solvent effects. Realistic dynamic trajectories of myoglobin are shown as it folds from an extended conformation to a close approximation of the native state. Various suggestive features of the process are discussed. The tenets of the model are further tested by folding the single-chain plant protein leghemoglobin. © 1994 Wiley-Liss, Inc.
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    An evaluation of implicit and explicit solvent model systems for the molecular dynamics simulation of bacteriophage T4 lysozyme (1994)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 18 (1994), S. 19-33 
    Details
    ISSN: 0887-3585
    Keywords: Discover program ; protein dynamics ; computer simulation ; protein motions ; counterions ; dielectric ; protein electrostatics ; aqueous simulation ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: In this report we examine several solvent models for use in molecular dynamics simulations of protein molecules with the Discover program from Biosym Technologies. Our goal was to find a solvent system which strikes a reasonable balance among theoretical rigor, computational efficiency, and experimental reality. We chose phage T4 lysozyme as our model protein and analyzed 14 simulations using different solvent models. We tested both implicit and explicit solvent models using either a linear distance-dependent dielectric or a constant dielectric. Use of a linear distance-dependent dielectric with implicit solvent significantly diminished atomic fluctuations in the protein and kept the protein close to the starting crystal structure. In systems using a constant dielectric and explicit solvent, atomic fluctuations were much greater and the protein was able to sample a larger portion of conformational space. A series of nonbonded cutoff distances (9.0, 11.5, 15.0, 20.0 Å) using both abrupt and smooth truncation of the nonbonded cutoff distances were tested. The method of dual cutoffs was also tested. We found that a minimum nonbonded cutoff distance of 15.0 Å was needed in order to properly couple solvent and solute. Distances shorter than 15.0 Å resulted in a significant temperature gradient between the solvent and solute. In all trajectories using the proprietary Discover switching function, we found significant denaturation in the protein backbone; we were able to run successful trajectories only in those simulations that used no switching function. We were able to significantly reduce the computational burden by using dual cutoffs and still calculate a quality trajectory. In this method, we found that an outer cutoff distance of 15.0 Å and an inner cutoff distance of 11.5 worked well. While a 10 Å shell of explicit water yielded the best results, a 6 A shell of water yielded satisfactory results with nearly a 40% reduction in computational cost. © 1994 John Wiley & Sons, Inc.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prot.340180105
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  • 198
    Electronic Resource
    Electronic Resource
    Molecular surface representations by sparse critical points (1994)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 18 (1994), S. 94-101 
    Details
    ISSN: 0887-3585
    Keywords: surface representation ; molecular recognition ; protein docking ; surface triangulation ; molecular graphics ; molecular visualization ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: We have defined a molecular surface representation that describes precisely and concisely the complete molecular surface. The representation consists of a limited number of critical points disposed at key locations over the surface. These points adequately represent the shape and the important characteristics of the surface, despite the fact that they are modest in number. We expect the representation to be useful in areas such as molecular recognition and visualization. In particular, using this representation, we are able to achieve accurate and efficient protein-protein and protein-small molecule docking. © 1994 John Wiley & Sons, Inc.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prot.340180111
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  • 199
    Electronic Resource
    Electronic Resource
    Poly (2,6-dimethyl-1,4-phenylene oxide)/poly (butadiene) diol interpenetrating polymer networks: Phase morphological characteristics and glass transition temperature behavior (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 257-263 
    Details
    ISSN: 0887-624X
    Keywords: IPNs ; PPO ; poly (butadiene) diol ; SEM ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The fracture surface topography of simultaneous interpenetrating polymer networks (SIN'S) of poly (2,6-dimethyl-1,4 phenylene oxide) (PPO)/poly (butadiene) diol was examined by scanning electron microscopy (SEM). The phase morphology of the IPNs is highly dependent on PPO/poly (butadiene) diol mass ratio. A single-phase morphology of the IPNs was achieved when the content of poly (butadiene) diol is below 40 wt % in the initial composition. The SEM observations are also wholly consistent with the glass transition temperature behavior obtained in the differential scanning calorimetric (DSC) measurements. © 1994 John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1994.080320206
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  • 200
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    Electronic Resource
    Synthesis and properties of aromatic poly (ether sulfone)s and poly (ether ketone)s based on methyl-substituted biphenyl-4,4′-diols (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 317-322 
    Details
    ISSN: 0887-624X
    Keywords: aromatic nucleophilic substitution polymerization ; methyl-substituted bisphenols ; aromatic poly (ether sulfone)s ; aromatic poly (ether ketone)s ; thermal behavior ; photo-crosslinking ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Novel methyl-substituted aromatic poly (ether sulfone)s and poly (ether ketone)s were synthesized from combinations of 3,3′,5,5′-tetramethylbipheny-4,4′-diol and 2,2′,3,3′,5,5′-hexamethylbiphenyl-4,4′-diol, and 4,4′-dichlorodiphenyl sulfone and 4,4′-difluorobenzo-phenone by nucleophilic aromatic substitution polycondensation. The polycondensations proceeded quantitatively in a N-methyl-2-pyrrolidone-toluene solvent system in the presence of anhydrous potassium carbonate to afford the polymers with inherent viscosities between 0.86 and 1.55 dL/g. The methyl-substituted poly (ether sulfone)s and poly (ether ketone)s showed good solubility in common organic solvents such as chloroform, tetrahydrofuran, pyridine, m-cresol, and N,N-dimethylacetamide. The tetramethyl- and hexamethyl-substituted aromatic polyethers had higher glass transition temperatures than the corresponding unsubstituted polymers, and did not decompose below 350°C in both air and nitrogen atmospheres. The films of the methyl-substituted poly (ether ketone)s became insoluble in chloroform by the irradiation of ultraviolet light, indicating the occurrence of photochemical crosslinking reactions. © 1994 John Wiley & Sons, Inc.
    Additional Material: 5 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1994.080320213
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