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  • 1985-1989  (2,574)
  • 1975-1979  (1,819)
  • Computational Chemistry and Molecular Modeling  (2,383)
  • Physical Chemistry  (1,104)
  • Electron microscopy  (906)
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Year
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  • 1
    ISSN: 1432-2307
    Keywords: Clear cell sarcoma ; Melanosomes ; Cytochemistry ; Electron microscopy ; Nude mouse
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary In order to clarify the histogenesis of clear cell sarcoma of tendons and aponeuroses (CCS), two cases of human and one nude mouse-transplanted CCS line were studied using an ultrastructural and enzyme cytochemical approach. Most of the tumour cells obtained from the primary and transplanted CCS demonstrated melanosomes in various stages of development within the cytoplasm, whereas no melanosomes could be identified in the metastatic CCS. However, cholinesterase and tyrosinase activities could be demonstrated not only in the melanotic primary and transplanted CCS but also in the amelanotic metastatic CCS. The results therefore support the hypothesis that CCS is a soft tissue tumour derived from the neural crest.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-2307
    Keywords: Human heart ; Papillary muscle ; Hypertrophy ; Mitochondria ; Specific staining ; Electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Biopsy material of the hypertrophied human papillary muscle has been processed according to various electron microscopical techniques in order to study the mitochondrial ultrastructure and the association between mitochondria and sarcoplasmic reticulum (SR).En bloc staining with a Cu-Pb citrate solution resulted in specifically contrasted mitochondrial and sarcotubular membranes, characterized by numerous, discrete, electron-dense particles. The differences in staining patterns between the perinuclear mitochondria and their subsarcolemmal and interfibrillar counterparts suggest differences in chemical properties and/or metabolic activities. The selectively contrasted mitochondrial particles may represent a conglomorate of extrinisic and intrinisic respiratory enzymes and other membrane-associated proteins, while the majority of the electron-dense particles of the sarcotubular membrane may represent positively stained Ca2+-pumps. Ultrastructural findings in the present study strongly indicate that the slender mitochondrial projections represent an initial stage in a process leading to the formation of large and pleomorphic mitochondria. Intimate contact between adjacent mitochondria as well as between mitochondria and SR are documented. In the contact regions some of the specifically contrasted particles of the adjacent membranes had fused with each other. It is suggested that these particles represent membrane-bound transport proteins providing a system for interorganelle exchanges of metabolites and/or ions.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Virchows Archiv 415 (1989), S. 91-95 
    ISSN: 1432-2307
    Keywords: Carcinosarcoma ; Urinary bladder ; Immunohistochemistry ; Electron microscopy ; Rhabdomyoblast
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary A case of urinary bladder carcinosarcoma (UBCS) is reported with light, immunohistochemical and electron microscopical findings. The tumour consisted of a squamous cell carcinoma, variable spindle cell stromal elements compatible with fibrosarcoma, and rhabdomyoblasts. Intermediate filament co-expression of cytokeratin and vimentin was shown by immunohistochemistry. Electron microscopy (EM) confirmed the nature of the three components, and indicated some similarities between the three cell-types present. Comparisons with the previous UBCS in the literature are made.
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  • 4
    ISSN: 1432-2307
    Keywords: Human acute pancreatitis ; Zymogen granules ; Acinar cells ; Electron microscopy ; Immunocytochemistry ; Morphometry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary In the present study fine structural changes of acinar zymogen granules were investigated in human acute pancreatitis. Pancreatic tissue was obtained at surgery from 6 patients, prepared for ultrastructural analysis, and stained immunocytochemically for trypsinogen. Stereological parameters of zymogen granules were evaluated. The density of the immunocytochemical labelling for trypsinogen was estimated over zymogen granules, the rough endoplasmic reticulum, Golgi apparatus and the acinar lumina. In acute pancreatitis the number of zymogen granules was diminished and their size reduced. The density of the labelling for trypsinogen was unchanged over zymogen granules but showed a significant reduction over the rough endoplasmic reticulum, Golgi apparatus, and the acinar lumina. In general the integrity of zymogen granules was well preserved. Focally degenerative changes of zymogen granules and large autophagosomes were observed. From the immunogold labelling a disturbance of enzyme synthesis and secretion was suggested. Evidence is given that a disruption of the zymogen granule membranes and a fusion with lysosomal bodies might contribute to the pathogenesis of human acute pancreatitis.
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  • 5
    ISSN: 1432-2307
    Keywords: Hyperoxia ; Lung broncho-vascular reaction ; Electron microscopy ; Rat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary In order to clarify the early phenomena involved in the lung reaction to hyperoxia, twenty adult male rats were exposed to 100% oxygen at 1 ATA. Morphological pulmonary lesions were detectable after only 24 h hyperoxia, and included vasoconstriction and perivascular oedema, bronchiolar constriction, and pericyte reaction. The lesions were irregularly scattered within the lung parenchyma and occurred preferentially in areas centred on bronchiolo-vascular stems. Even at the latest stages, pulmonary heterogeneity was obvious, from the coexistence of areas damaged at different times. Neuro-epithelial-bodies were found under the bronchiolar epithelium; the morphological aspect of the neuro-endocrine cells observed was consistent with hyperoxia-induced modulation of their secretory activity. Taken together, our findings show the speed of development of hyperoxia-induced pulmonary changes and raise some pathogenic considerations.
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  • 6
    ISSN: 1432-2307
    Keywords: Thyroid neoplasms ; Electron microscopy ; Immunohistochemistry ; Calcitonin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary An ultrastructural study, both morphological and immunohistochemical, has been carried out on eight thyroglobulin-positive and nine thyroglobulin-negative medullary carcinomas of the thyroid. The morphometric analysis of granule size showed that all tumours contained cells with small granules and cells with medium size granules, whereas eight tumours had additional cells with large granules. The small granules had an electron dense core, while the medium and large sized granules were both pale-cored and dense-cored. The cells with small, medium or large secretory granules were all immunoreactive for calcitonin and CGRP. No ultrastructural differences were observed between thyroglobulin-positive and thyroglobulin-negative cases of medullary carcinoma of the thyroid.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Virchows Archiv 415 (1989), S. 1-6 
    ISSN: 1432-2307
    Keywords: Visceral leishmaniasis ; L. donovani ; Parasitism ; Liver pathology ; Electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Liver parenchymal cell parasitism with the amastigotes form ofL. donovani was detected by electron microscopy in human visceral leishmaniasis. Endocytosis was considered to be the mechanism by which the leishmania entered the cell. Evidence of well preserved parasites within hepatocytes suggest this parasitism as a possible reservoir for recrudescence.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Virchows Archiv 415 (1989), S. 297-300 
    ISSN: 1432-2307
    Keywords: Non-Hodgkin's lymphoma ; Electron microscopy ; Immunohistochemistry ; Intercellular junction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary A rare example of pleomorphic B cell non-Hodgkin's lymphoma is described in which tumour cells possessed simple intercellular junctions.
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  • 9
    ISSN: 1432-2307
    Keywords: Collagen secretion granule ; Myofibroblast ; Spindle cell tumour ; Electron microscopy ; Diagnosis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Collagen secretion granules, representing stages in the intracellular packaging, transport and secretion of collagen-fibril precursor, have been studied by transmission electron microscopy in non-neoplastic human myofibroblasts and in neoplastic cells from a preliminary study of tumours exclusively or partly of spindle cell type. Vesicles, newly separated from Golgi saccules and containing finely fibrillar material, were identified as early presecretory granules, the most immature type of granule. Later stages exhibited longitudinally arranged, densely fibrillar bundles. Subsequently, secretory granules developed more homogeneously dense content. Fibril-containing cisternae near the plasma membrane were interpreted as either endocytotic or lysosomal structures, or as participants in the final stages of secretion. The features by which collagen secretion granules can be distinguished from other Golgi products, in particular melanosomes, Weibel-Palade bodies and lysosomes, are pointed out. The significance of these organelles for cell identification and tumour diagnosis is discussed.
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 1432-2307
    Keywords: Salivary gland ; Myoepithelioma ; Neoplasm ; Electron microscopy ; Immunohistochemistry ; Cytoplasmic filaments
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The histological and ultrastructural features of five major salivary gland tumours, which have little or no evidence of duct- or gland-type differentiation in routine sections, are described. Four of the cases have the tumour cells organized as narrow, anastomosing cords of cells separated by a myxoid and vascularized stroma; we have designated such lesions as reticular-type myoepitheliomas. The fifth case has a solid growth pattern and is largely composed of hyaline cells, that is, a plasmacytoid myoepithelioma. Ultrastructurally, one reticular myoepithelioma reveals myoepithelial cell differentiation with microfilament aggregates, while the other three examples are composed of modified myoepithelial cells displaying widened intercellular spaces, prominent synthesis of extracellular glycosaminoglycans, distinct basal lamina development, and obvious accumulations of cytoplasmic intermediate filaments. In electron micrographs, the modified myoepithelial cells of the plasmacytoid variant closely resemble the tumour cells in the reticular form. Three cases had expression of both glial fibrillary acid protein (GFAP) and vimentin, but only one of the myoepitheliomas contained muscle-specific actin. At least focally, each of the cases exhibited a considerable spectrum of cytokeratin filaments. Using double-labeled immunofluorescent microscopy of one reticular variant and the plasmacytoid myoepithelioma, there was individual tumour cell co-expression of GFAP and vimentin focally in the plasmacytoid myoepithelioma, but co-expression of cytokeratins 13, 16 and GFAP were not noted in either case. As expected, co-expression of high- and low-molecular weight cytokeratin filaments was wide-spread in both myoepitheliomas. Most described myoepitheliomas have a solid growth pattern and are composed of spindle and plasmacytoid cells, but based on cytological features and growth patterns in this series, it is apparent that polygonalshaped cells with novel architecture can occur in myoepitheliomas. The results also indicate the close relationship between pleomorphic adenoma and such variants of myoepithelioma.
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  • 11
    ISSN: 1432-198X
    Keywords: IgA nephropathy ; Electron microscopy ; Glomerular basement membrane lesions ; Prognosis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Seventy-three patients with IgA nephropathy (IgAGN), under the age of 15 years at the time of the discovery of the disease, were investigated with respect to glomerular basement membrane (GBM) lesions. Irregular attenuation or widening of GBM, especially on the epithelial side, was observed in 28 cases (38%). These two changes are referred to aslysis of GBM and were considered to be the primary and specific changes among the GBM lesions in IgAGN. GBM thickening with layering of lamina densa was found in 37 of 73 cases (51%), but this change has been observed in other types of glomerular diseases. GBM lesions similar to those seen in IgAGN were also observed in Henoch-Schönlein purpura nephritis (HSPN) and poststreptococcal acute glomerulonephritis (PSAGN). Lysis of GBM was observed only in IgAGN, HSPN and PSAGN. Subepithelial and intramembranous deposits appeared to have an important role in the development of these GBM lesions. The presence of GBM lesions was correlated with a high incidence of cellular crescents but not with other clinical or light microscopic findings. The presence of these GBM lesions in IgAGN does not have a significant effect on the prognosis, at least in childhood. The affected GBM seemed to recover without leaving any significant residual damage in most cases. In the long-term prognosis of the disease non-immunological factors, such as ageing or hypertension, seem to be important.
    Type of Medium: Electronic Resource
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  • 12
    Electronic Resource
    Electronic Resource
    Springer
    Anatomy and embryology 180 (1989), S. 237-242 
    ISSN: 1432-0568
    Keywords: Perineurium ; Lanthanum ; Diffusion barriers ; In vivo ; Electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary While the perineurium as a diffusion barrier has been extensively investigated by light and electron microscopy, copy, such studies have been largely restricted to the use of protein tracers. In the present study the permeability of the perineurium to a physiologically more relevant ionic tracer has been assessed. In vivo the rat sural or tibial nerve was either microinjected with lanthanum nitrate solution for endoneurial application or bathed in the lanthanum solution for epineurial application. The findings generally demonstrated an effective barrier to the tracer which failed to penetrate the inner layers of the perineurium. Only at the highest lanthanum concentration and longest time intervals employed did trace quantities occasionally penetrate the barrier and then only in the presence of some cytopathological changes to the outermost perineurial cells. The usefulness of the microinjection method was limited by the slight but unavoidable trauma to the perineurium. The findings are related to those of other studies which have used electron dense tracers, also to studies using physiological including electrophysiological techniques and morphological including freeze-fracture methods.
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  • 13
    Electronic Resource
    Electronic Resource
    Springer
    Archives of dermatological research 281 (1989), S. 165-172 
    ISSN: 1432-069X
    Keywords: Netherton's syndrome ; Retinoid therapy ; Etretin ; Electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary A young female patient, expressing the symptom triad of Netherton's syndrome, i.e., ichthyosis linearis circumflexa Comèl, trichorrhexis invaginata and other hair shaft defects, and atopic diathesis, has been treated successfully with the new retinoid preparation Etretin. Our electron microscopical study especially focused on the ultrastructural effect on the characteristic, active part of the skin lesions, which is only found within a narrow borderline just preceding the lesion's margin. In untreated skin, this part is characterized by dermal inflammation, immigrating inflammatory cells, and specific keratinization disturbances: synthesis of keratinization proteins is suppressed, serum exudates invade the epidermis, either filling the intercellular spaces of the upper spinous and the granular layer as finely granular, amorphous material, or they are partly phagocytosed and lie within intracellular, round-oval inclusions. The portions of the lesions lying towards the center are unspecific and represent recovery stages, ultrastructurally resembling stages of normal wound repair. Oral therapy with Etretin did not heal the basic defect, but drastically reduced exoserosis and the deposition of intra- and extracellular material. Keratinization seemed to normalize. The condition of the hair was also improved.
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  • 14
    ISSN: 1432-0533
    Keywords: Senile plaque-like structure ; Periodicacid methenamine silver (PAM) method ; Electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Numerous diffuse senile plaque-like structures (SPLSs) were found in the cerebral cortex from cases with dementia of the Alzheimer type by means of the methenamine-Bodian method. SPLSs varied in shape and size. They were never recognized in the original Bodian, PAS and Congo red preparations, but were positive with anti-β-protein immunostaining and periodic-acid methenamine silver (PAM) methods, which are thought to specifically stain amyloid substance. With PAM electron microscopy, we found sparse aggregations of amorphous, often ramified, structures with fine granular silver deposits in SPLS. Routine electron microscopic examination on the same portion where SPLS were confirmed by PAM electron microscopy revealed amorphous, partially fibrous structures. These structures might be amyloid or amyloid-precursor substance. In SPLSs only a few degenerated neurites and astrocytic processes with glycogen granules were seen. We consider SPLSs to be a kind of senile plaque.
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  • 15
    ISSN: 1432-0533
    Keywords: Schwann cell ; Oligodendrocyte ; Electron microscopy ; Myelin ; Optic nerve
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Neonatal rats were exposed to Tellurium (Te), via the mother's milk, from the day of birth until sacrifice at 7, 14, 21, and 28 days of age. Light and electron microscopy revealed Schwann cell and myelin degeneration in the sciatic nerves at each age studied. These changes were similar to those described in weanling rats as a result of Te intoxication. In the CNS, hypomyelination of the optic nerves was convincingly demonstrated at 14, 21, and 28 days of age, accompanied by some evidence of myelin degeneration. These changes were also seen in the ventral columns of the cervical spinal cords, although less markedly, and were confirmed by quantitative methods. There was little evidence of oligodendrocyte pathology in the CNS, and it appears that degeneration of these cells is not the primary cause of the CNS hypomyelination, in contrast to the PNS where Schwann cell degeneration has been shown to precede the myelin pathology.
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  • 16
    Electronic Resource
    Electronic Resource
    Springer
    Acta neuropathologica 78 (1989), S. 472-483 
    ISSN: 1432-0533
    Keywords: Astroblastoma ; Electron microscopy ; Immunohistochemistry ; Organ culture ; Tanycytes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Two examples of cerebral astroblastoma have been studied by electron microscopy and immunohistochemistry, one of them having been maintained in vitro in an organ-culture matrix system for 8 months and the explants studied by light and electron microscopy at different time intervals. The fine structural characteristics were those of a glial cell type with features intermediary between those of astrocytes and ependymocytes. They recapitulated the structure of the tanycyte, a glial precursor cell which is normally found scattered along the ependymal lining of the embryonal and neonatal mammalian brain, but is distinct from epithelial ependymocytes. The possible origin of some astroblastomas from such a cell would account for a number of characteristics in this enigmatic type of glioma.
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  • 17
    Electronic Resource
    Electronic Resource
    Springer
    Anatomy and embryology 180 (1989), S. 273-280 
    ISSN: 1432-0568
    Keywords: Wallerian degeneration ; Myelin breakdown ; Light microscopy ; Electron microscopy ; Marchi staining
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Morphological aspects of myelin breakdown in the posterior funiculus during Wallerian degeneration were studied in kittens subjected to lumbosacral dorsal rhizotomies 6–8 days after birth. The first sign of myelin breakdown was characterized by swollen or shrunken nerve fibers. Shortly thereafter there was an increased occurrence of collapsed myelin sheaths and later of rounded myelin bodies. Myelin was clearly seen in microglial cells. Correlative observations on Marchi-stained material indicated the simultaneous and frequent appearance of Marchi-positive bodies (MPB:s) and myelin bodies. Due to the rapidity of the degeneration process in the kitten, the increase in the occurrence of Marchi-positive granules (MPG:s) seemed to start concomitantly with increased occurrence of MPB:s. However, the frequent occurrence of MPG:s outlasted that for MPB:s. The findings indicate that the MPB:s may be the counterpart to myelin bodies and the MPG:s to lipid droplets. Microglial cells may be responsible for the primary uptake of degenerating myelin and the subsequent transformation of myelin bodies to lipid droplets. The much faster breakdown of myelin and elimination of lipid material in the degenerating posteror funiculus of the kitten, as compared to the adult, seemed to be due not only to the lower myelin content in the kitten, but also to a higher density of microglia and a greater efficiency in the myelin breakdown process in the degenerating posterior funiculus of the kitten.
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  • 18
    Electronic Resource
    Electronic Resource
    Springer
    Acta neuropathologica 79 (1989), S. 10-17 
    ISSN: 1432-0533
    Keywords: Locus ceruleus ; Pick bodies ; Lewy bodies ; Immunocytochemistry ; Electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary In classical Pick's disease with typical Pick bodies, inclusions resembling those present in the cerebral cortex are frequently found in the locus ceruleus. In three such cases Pick bodies were studied by light and electron microscopy and compared with Lewy bodies, inclusions more commonly found in this location. In contrast to the situation in the cerebral cortex, nerve cells with multiple Pick bodies were often found in the locus ceruleus, but in other respects definite light and electron microscopic differences between Pick bodies and Lewy bodies were present. Pick bodies were slightly basophilic and never had a central core or a peripheral halo. They were intensely argyrophilic. Differences in immunocytochemical reactions were especially marked with antibodies to tau and to paired helical filaments. Pick bodies displayed an intense reaction with these two antibodies, contrasting with that of Lewy bodies, which either lacked reactivity or reacted in a peripheral band. By electron microscopy the Pick bodies were composed of random filaments with smooth contour, whereas typical Lewy bodies had fuzzy deposits on filaments that radiated from a central core. Pick bodies in the locus ceruleus therefore maintained their immunocytochemical and electron microscopic characteristics and did not take on the character of Lewy bodies. Such differences point to a different pathogenesis and perhaps etiology of these two types of inclusions and attest to the marked difference clinically and pathologically between Pick's and Parkinson's diseases.
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  • 19
    Electronic Resource
    Electronic Resource
    Springer
    Acta neuropathologica 77 (1989), S. 664-666 
    ISSN: 1432-0533
    Keywords: Hemimegalencephaly ; Golgi study ; Electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Pathological findings in a case of hemimegalencephaly are presented. Hemispherectomy, performed because of intractable seizures, allowed an electron microscopic and Golgi study. Glial abnormalities consisted of hyperplasia of glia cells with giant astrocytes often containing several nuclei and proliferation of numerous Rosenthal fibers. Golgi stain showed many giant neurons with a perikaryon covered by perisomatic processes, and a complex dendritic tree. Glial abnormalities could be correlated with the firmness of the hemisphere and intense hypersignal on magnetic resonance imaging. Giant neurons were associated with an increase in size of the perikaryon and dendritic tree; this pattern suggests a polyploidy.
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  • 20
    ISSN: 1432-0533
    Keywords: Cerebral ischemia ; Ischemic neuronal injury ; Long-term recovery ; Mongolian gerbil ; Electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Unilateral transient cerebral ischemia was produced in Mongolian gerbils by clipping the left common carotid artery for 1h. About 60% of the gerbils with neurological symptoms had post-ischemic seizures. The majority of those that had seizures died within a few days, and sections of their cerebral cortices contained many dark and shrunken neurons. However, the gerbils that did not have seizures survived without any severe complications. In the cerebral cortex of the latter, the neurons with diffuse or peripheral pallor of the perikarya were seen along with a small number of dark and shrunken neurons. Diffuse pallor occurred within a few hours following ischemia in layers III, V and VI, and disappeared 1 or 2 days after recirculation. Electron microscopically, these neurons showed dispersion of ribosomes, simple and elongated profiles of rough endoplasmic reticulum (r-ER), clustered vacuoles, and mild to moderate mitochondrial swelling. Occasional net-like tubulomembranous structures, probably derived from r-ER, were observed. On the other hand, peripheral pallor became apparent after 5 days following ischemia, usually involving layer II first and gradually extending to the deeper layers. Concomitantly, the amount of neuropil decreased and the dendrites exhibited tortuosity and irregularity in layer II. Electron microscopically, these neurons showed marked swelling of peripheral perikarya and polyribosomes and organelles were located peripherally to the nuclei. In addition, numerous degenerated axon terminals and distended dendrites were observed around the neurons. These observations indicate that diffuse pallor represents damage directly induced by ischemia and subsequent recirculation, while peripheral pallor is the delayed and remote effect of ischemia, probably due to degeneration of neuronal processes.
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  • 21
    Electronic Resource
    Electronic Resource
    Springer
    Acta neuropathologica 78 (1989), S. 555-560 
    ISSN: 1432-0533
    Keywords: Sporadic motor neuron disease ; Lewy body-like hyaline inclusions ; Immunocytochemistry ; Electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Lewy body-like hyaline inclusions were immunocytochemically and electron microscopically investigated in a patient with sporadic motor neuron disease. The hyaline inclusions were chiefly observed within the perikarya of both normal-looking and chromatolytic anterior horn cells in the lumbar spinal cord, but some were detected in the axons and dendrites. Usually, a single inclusion was found in the perikaryon, but in rare cases two or more were observed. Immunocytochemically, these inclusions were intensely immunostained with anti-ubiquitin anti-body. Ultrastructurally, the hyaline inclusions were chiefly composed of randomly arranged linear structures associated with ribosome-like granules, varying from compactly arranged linear densities to more loosely packed ones. They contained scattered vesicles of various sizes and occasionally a focal accumulation of randomly arranged 10-nm neurofilaments or 13–25-nm filamentous structures.
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  • 22
    Electronic Resource
    Electronic Resource
    Springer
    Acta neuropathologica 78 (1989), S. 594-604 
    ISSN: 1432-0533
    Keywords: Neurocysticercosis ; Pathogenesis ; Histochemistry ; Immunohistochemistry ; Electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary This study was based on two cases of disseminated human neurocysticercosis from India. The material availabel was examined grossly, and by light microscopy, histochemistry, immunomorphology and electron microscopy. The results showed that the parasites commonly embolized to the anatomically discernable gray-white matter junction of the brain and were located in cavities, the walls of which were dilated vascular channels. The parasite-nutrition process was through endocytosis and microtrichal activity. To camouflage themselves from the host-defense mechanisms, the parasites apparently covered themselves with host-tissue-like material. Host reactivity to the parasite was heralded morphologically by the physical anchoring of the parasite by activated endothelial cells, loss of the host-tissue-like cover and an acute polymorphonuclear leucocytic response.
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  • 23
    Electronic Resource
    Electronic Resource
    Springer
    Acta neuropathologica 79 (1989), S. 340-346 
    ISSN: 1432-0533
    Keywords: Paraganglioma ; Melanin ; Orbit ; Immunocytochemistry ; Electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary A paraganglioma of the orbit in a 21-year-old woman is presented, containing oculo-cutaneous melanin in many tumor cells, occasionally adjacent to neurosecretory granules, and in macrophages. This tumor expands the list of neuroectodermal tumors with potential melaninization.
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  • 24
    Electronic Resource
    Electronic Resource
    Springer
    Anatomy and embryology 180 (1989), S. 243-257 
    ISSN: 1432-0568
    Keywords: Dorsal lateral geniculate nucleus ; Synapse formation ; Synaptic glomerulus ; Rat ; Electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Synapse formation and maturation were examined in the rat dorsal lateral geniculate nucleus (dLGN) from birth to adulthood. Examination of animals, whose ages were closely spaced in time, showed that the maturation of the synaptic organization of the nucleus takes place chiefly during the first 3 weeks of postnatal life. This period of maturation may be divided into 3 broad stages. During the first stage, which spans the first 4 days of life, there are only a few immature synapses scattered throughout the nucleus; occasionally aggregates of 3 or 4 synapses are encountered. Dendrodendritic synapses first appear at the end of this stage. The second stage, which lasts from the end of the first stage through day 8, is characterized by intensive synaptogenesis as well as extensive growth and degeneration. For the first time, large boutons resembling retinal terminals form multiple synaptic contacts with dendrites and dendritic protrusions; these synaptic arrangements are partially covered by glial processes. A feature characteristic of the developing dLGN during the first 2 postnatal weeks, and particularly during the second stage, is the presence of membrane specializations that resemble vacant postsynaptic densities. These specializations, which may be unapposed or opposite another neuronal process, decrease in frequency as the number of synapses increases. It is not known whether these densities are converted to synapses or whether they result from loss of presynaptic elements. The third stage in the process of synaptogenesis, which spans a period between days 10 and 20, is characterized by myelination and by the diminution of growth cones, degenerating profiles and vacant postsynaptic densities. There is also a very significant increase in the number and maturation of synapses including synaptic glomeruli. However, it is not until the end of this stage that synapses appear qualitatively indistinguishable from synaptic arrangements identified in adult animals.
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  • 25
    Electronic Resource
    Electronic Resource
    Springer
    Archives of dermatological research 281 (1989), S. 254-259 
    ISSN: 1432-069X
    Keywords: Innermost cell layer ; Tonofilaments ; Huxley's cells ; Henle's cells ; Anagen hair follicles ; Electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary To elucidate the biologic roles and further cytologic characteristics of the innermost cell (IMC) layer of the outer root sheath (ORS), human anagen hair follicles were ultrastructurally examined. In the lower follicle, the transeversely running tonofilaments in the inner side of the cytoplasm of the IMCs showed a massive accumulation, facing the keratinized part of a Huxley's cell protruding through a Henle's pore. In a rare instance, a spindle-shaped cell was seen between the IMC layer and the keratinized Henle's layer. At the lower isthmus portion, some of the IMCs containing a large number of tonofilaments showed a partial degeneration of the inner side of the cytoplasm. More distally, intercellular spaces between the keratinized IMCs and keratinized Henle's cells were partly dilated and contained amorphous substances. It is suggested that the IMCs in the lower follicle may play a role to support and cover the inner hair structures, tightly as hoops of a barrel. In the isthmus portion, the IMCs may loosely support and guide the keratinized Henle's cells undergoing degeneration.
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  • 26
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    Experimental brain research 75 (1989), S. 563-568 
    ISSN: 1432-1106
    Keywords: Retina ; Diencephalon ; Co-culture ; Synapses ; Electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Explants of chick embryo diencephalon co-cultured with explants of retina display areas of complex neuropil containing large retinal-like endings which establish synaptic contact with conventional and presynaptic dendrites. Transection of fibre bundles linking retinal to diencephalic explants results in the degeneration of endings of this type, suggesting that axons of extrinsic (retinal) origin innervate the diencephalic explants in an in-vivo-like manner.
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  • 27
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    Experimental brain research 78 (1989), S. 425-434 
    ISSN: 1432-1106
    Keywords: Avian forebrain ; Synapses ; Stereology ; Disector ; Electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The lobus parolfactorius (LPO) of the chick has been shown to undergo an increase in the mean synaptic numerical density (Nv syn) in response to one-trial passive avoidance learning (Stewart et al. 1987). The present study was undertaken in order to describe the pattern of normal development of synapses in the LPO, to further investigate the significance of this plastic response. The LPO's from each hemisphere of pre-hatch (16 days), and post-hatch (1 day, 9 day and 22 day old) chicks were processed for electron microscopy. Synapses were classified into asymmetric spine, asymmetric shaft, symmetric spine, and symmetric shaft synapses, on the basis of the density of the post-synaptic thickening and the nature of the post-synaptic target. A 3-dimensional stereological probe was used (the ‘disector’) to calculate Nv syp, and mean projected height (H syp) of the post-synaptic density (PSD). Mean values for each age and hemisphere were compared with a 2-way analysis of variance test using paired samples. A six-fold increase in Nv syp was seen between 16 days in ovo, and 9 days post-hatch. There was a hemispheric asymmetry at 9 days post-hatch, with the left hemisphere LPO containing 1.6 times as many synapses per μm-3. There was a subsequent period of reduction in synaptic density in the left hemisphere LPO between 9 and 22 days post-hatch. The Nv of all classes of synapse increased with age, but the proportions of the symmetrical synapses with respect to the total number of synapses, decreased with age. This decrease was of a similar magnitude for each hemisphere. A hemispheric difference was seen in post-hatch asymmetric synapses, with a greater proportion of asymmetric spine synapses in the left hemisphere. The magnitude of the hemispheric asymmetry was constant throughout the 3 week period of post-hatch development, but was not present in pre-hatch chicks. The PSD increased in length in each hemisphere by approximately 40% between post-hatch day 1 and post-hatch day 9. These data show that the LPO contains a synaptic population which undergoes substantial modification during the first week post-hatch. An asymmetry exists at post-hatch day 9 which is not present at the earlier ages investigated, nor indeed after 22 days post-hatch. This may have significance with regard to studies of passive avoidance learning in the one-day old chick, where an increase in both the size and number of synapses in the LPO has been demonstrated (Stewart et al. 1987). It is possible that ‘training’, in this situation, may simply enhance the timing of synaptic events that result as a consequence of normal development.
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  • 28
    ISSN: 1432-1106
    Keywords: Nerve growth factor ; C6 glioma cells ; Chromaffin cells histofluorescence ; Electron microscopy ; Immunocytochemistry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary In order to maintain a chronic supply of growth factor for medulla cells in vitro, chromaffin cells from rat, African green monkeys and man were co-cultured with C6 glioma cells, which secrete growth factors that sustain sympathetic neurons in vitro. The response of chromaffin cells to coculture was compared to treatment of medullary cells with nerve growth factor (NGF) alone. Dispersed chromaffin cell preparations were obtained by a trypsin-collagenase procedure, and subjected to differential plating on collagen-coated surfaces. With both human and monkey tissue, non-chromaffin cells did attach to the culture plates and an enriched chromaffin cell population could be replated. Rat adrenal medulla cells survived very poorly in vitro and were not enriched in this procedure. Cultured human and monkey chromaffin cells survived as epithelial cells (50%) and showed neuritic outgrowth on 55 to 66% of the cells after eight days when treated with nerve growth factor (NGF). These cells showed strong catecholamine histofluorescence, tyrosine hydroxylase (TH) and dopamine beta hydroxylase (DBH) immunoreactivity. In contrast, only ten percent of adult rat chromaffin cells survived in culture, although NGF treatment rescued an additional 20% of the cells and induced neuritic outgrowth after one week in vitro. C6 glioma cells were treated with mitomycin C bromodeoxyuridine to inhibit mitosis and were plated with the various medulla cells in a one to one ratio. Both human and monkey chromaffin cells expressed extensive and enhanced neuritic arborization within eight days of co-culture, (64–82% respectively) and exhibited intimate contact with the glioma cells as seen at the ultrastructural level. Importantly, survival of adult rat adrenal medulla cells was enhanced to 50% or more with 40% of the cells extending neurites when co-cultured with glioma cells for seven days. Chromaffin cells from all three species reacted for TH, DBH and PNMT in co-culture and were histofluorescent. The majority of these cells were also immunoreactive for serotonin and enkephalin, while only 37% of chromaffin cells indicated the presence of NPY. These data indicate that adrenal medulla can be maintained in vitro as the neuronal phenotype when co-cultured with growth factor producing cells and that this strategy may be useful for in vivo transplantation studies.
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  • 29
    ISSN: 1432-072X
    Keywords: Aggregation substance ; Enterococcus faecalis ; Electron microscopy ; Field emission scanning electron microscopy ; Immunogold labelling technique ; Sex pheromone system
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The distribution of sex pheromone induced aggregation substance was studied on the cell surface of various Enterococcus faecalis strains. In the accompanying paper we have shown that the aggregation substance appears as a layer of hairlike structures. Using direct and indirect immunogold technique, transmission electron microscopy and high resolution scanning electron microscopy we investigated the appearance and distribution of the aggregation substance. The “hairs” increase in number with increasing exposure to sex pheromones (maximum density: 1300/μm2). We show that these structures are unequally distributed over the cell surface, even if the cells were induced by sex pheromones for a long period of time. Statistical analysis of the unequal distribution indicates that aggregation substance is incorporated into pre-existing “old” cell-walls and that this incorporation shows a saturation ca. 40 min after addition of sex pheromones.
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  • 30
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    Archives of gynecology and obstetrics 246 (1989), S. 169-179 
    ISSN: 1432-0711
    Keywords: Human fetal endometrium ; Electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Human fetal endometrium was examined by light and electron microscopy. Our study shows the following new morphological aspects: (1) Glands are already present. (2) Endometrium undergoes a maturation process during gestation and at late gestational age resembles late proliferative endometrium. (3) The nuclear bodies are present in cell nuclei throughout gestation. (4) Nucleolar channel systems (NCS) sometimes appear at a late gestational age. (5) Cells with the same morphology as that of endocrine cells are found in the basal layers of endometrium at a late gestational age. The significance of these morphological aspects is discussed.
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  • 31
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    Rheumatology international 9 (1989), S. 49-51 
    ISSN: 1437-160X
    Keywords: Synovium ; Monoclonal antibodies ; Immunohistochemistry ; Electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The cells making up the lining of the synovium have long been known as type A and B synoviocytes, with an intermediate form sometimes also described. Accumulating evidence shows that the type A cells are macrophages and the type B cells are fibroblasts. Recently, a definite orientation of these cells within the synovial lining has been observed. The number of synovial lining cells increases in joint disease, and this now seems more likely to be due to cellular recruitment rather than local proliferation.
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  • 32
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    Journal of neurology 236 (1989), S. 361-363 
    ISSN: 1432-1459
    Keywords: Mitochondrial encephalomyopathy ; MELAS ; Mitochondrial inclusion ; Pilovacuolar inclusion ; Electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The case of a 33-year-old man with clinical features of mitochondrial encephalomyopathy is presented. He suffered from recurrent cerebral infarctions, cerebellar ataxia, deafness, retinopathy, weakness, and cardiac and renal disorders. Biochemical and light microscope investigations of skeletal muscle did not show any mitochondrial abnormality. Electron microscopy revealed the presence of a hitherto unreported peculiar “pilovacuolar” inclusion in numerous mitochondria, composed of an electron dense pile or rod within a vacuole, while globular or crystalline inclusions were absent.
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  • 33
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    European archives of oto-rhino-laryngology and head & neck 246 (1989), S. 428-432 
    ISSN: 1434-4726
    Keywords: Otitis media with effusion ; Mucociliary system ; Eustachian tube ; Electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary We have examined the function and fine structure of the mucociliary system of the eustachian tube in an experimental study of otitis media with effusion induced by X-ray irradiation. Functional examination demonstrated that the ciliary activity was diminished in such a condition, while morphological observations showed pathological findings including compound cilia, vacuolation of ciliated cells and expansion of intercellular space. These findings show that irradiation-induced otitis media with effusion results in impairment of the mucociliary system. As evidenced by these studies, the mucociliary system in the eustachian tube has an important role in the clearance of fluid produced in the tympanic cavity as well as affording improvement in this disease.
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  • 34
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    Journal of Physical Organic Chemistry 2 (1989), S. 26-34 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A set of 4-monosubstituted cyclopentenes, , were synthesized and their relative rates (kX/kH) for bromination and chlorination were determined in methanol, ethanol and acetic acid at 25 °C by competitive method. log(kX/kH) for most of the substituents can be correlated by means of Taft's equation, log(kX/kH) = ρI σI + C. In methanol ρI, Br2 = -2·91, ρI, Cl2 = -0·49, in ethanol ρI, Br2 = -3·07, ρI, Cl2 = -0·70 and in acetic acid ρI, Br2 = -1·64, ρI, Cl2 = -0·65. The presence of C(〈0) is due to a constant steric effect. The deviation of X = H is ascribed to the absence of the steric effect and that of X = CO2Me and CO2Et is accounted for in terms of anchimeric assistance. For chlorination no anchimeric assistance was observed.
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  • 35
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    Journal of Physical Organic Chemistry 2 (1989), S. 57-88 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The cation radical vinylcyclobutane (VCB) rearrangement is found to be a reaction of substantial scope, synthetic utility, and exceptional kinetic facility. In conjuction with cation radical cyclobutanation, it constitutes an effective method for net (indirect) Diels-Alder addition to electron rich dienophiles. Reactions can be carried out with either aminium salt or photosensitized electron transfer (PET) initiation and are powerfully facilitated by ionizable substituents such as p-anisyl, phenylthio, and phenoxy at the 2-position of the vinylcyclobutane. The intramolecularity of the reaction is clearly established and in four discrete systems preferred sr (suprafacial/retention) stereochemistry is observed. A theoretical basis for sr stereochemistry in the cation radical VCB rearrangement is advanced. The transition state for the reaction is considered to be similar to that for the direct cation radical Diels-Alder cycloaddition, another cation radical pericyclic reaction which converges on the same product. This model of the VCB rearrangement transition state is used to rationalize the strong rate-retarding effect of a Z-methyl substituent attached to the vinyl group and of a methyl substituent at the 4-position of the vinylcyclobutane ring cis to the vinyl substituent.
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  • 36
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    Journal of Physical Organic Chemistry 2 (1989), S. 1-14 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The mechanism of aromatic nucleophilic substitutions by amines in protic solvents is well established; on the contrary the mechanism/s of the reactions in aprotic solvents is/are still subject of controversy. The present paper describes several systems for which fourth-order kinetics (third-order in amine) were observed. A mechanism is proposed to account for this as well as other observation such as: overall negative energies of activation, quadratic dependence of kA with non-nucleophilic tertiary bases, spectacular effects of hydrogen-bond donor (HBD) and hydrogen-bond acceptor (HBA) catalysts, etc. Other alternative mechanisms are also discussed.
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  • 37
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The kinetics and mechanisms of the reactions between 1-phenylethyl benzenesulfonates (1-PEB) with N,N-dimethylanilines are investigated in methanol at 35·0°C. Reactivity and selectivity trends were found to be similar to those for the reactions of 1-PEB with anilines, but the magnitudes of cross interaction constants, ρXZ, between substituents X in the nucleophile and Z in the leaving group were substantially smaller indicating no hydrogen-bond bypass bridge formation in the transition state. However, the magnitude of ρXZ suggested a direct electrostatic interaction between the reaction centers in the nucleophile and leaving group in the frontside nucleophilic attack with a loose transition state structure.
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  • 38
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    Journal of Physical Organic Chemistry 2 (1989), S. 183-186 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The harmonic vibrational frequencies were calculated analytically at the 6-31** level for azetidine using the GAUSSIAN 82 program. The results strongly indicate the presence of several errors in a recent assignment of the fundamentals of azetidine based on a normal coordinate analysis and a revised assignment is suggested. It is concluded that reliable vibrational data for azetidine in the gas phase are needed in order to resolve the remaining ambiguities in the interpretation of the spectra.
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  • 39
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    Journal of Physical Organic Chemistry 2 (1989) 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
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  • 40
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    Journal of Physical Organic Chemistry 2 (1989), S. 110-116 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The transamination reaction of α-amino acids with glyoxylic acid as catalyzed by copper(II) ions was investigated kinetically in an aqueous medium at pH 5·0 and 30·0°C. L-Phenylalanine transferred its amino group to glyoxylic acid most readily among seven different amino acids used here in the single-walled bilayer vesicle formed with N,N-dihexadecyl-Nα-[6-(trimethylammonio)hexanoyl]-L-histidinamide bromide (N+C5His2C16). Such rate enhancement was found to originate from the cooperative trifunctional catalysis: a coordination effect exercised by copper(II) ions, a general acid-base catalysis by the imidazolyl group of the lipid, and a hydrophobic field effect provided by the bilayer vesicle. Lack of any of the three functions failed to give out significant rate enhancement. As regards correlation between the reactivity and the nature of α-amino acids, the copper(II)-catalyzed transamination was progressively enhanced as hydrophobicity of the α-amino acid was increased in the N+C5His2C16 vesicle.
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  • 41
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    Journal of Physical Organic Chemistry 2 (1989), S. 43-50 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The cyclic vinyl ether dihydro-1,4-dioxin is converted to its cyclic hemiacetal hydration product, 2-hydroxy-1,4-dioxane, in aqueous solution by an acid-catalyzed reaction for which kH+ = 1·80 × 10-5 M-1 S-1 at 25°C. This reactivity and the solvent isotope effect kH+/kD+ = 2·2 show that the reaction occurs by rate-determining proton transfer from catalyst to substrate and not by a pre-equilibrium mechanism as recently proposed.2
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  • 42
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    Journal of Physical Organic Chemistry 2 (1989), S. 161-176 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Cyclobutanediyl (2) has been studied in both its singlet and triplet states by ab initio electronic structure theory. The triplet, which is the ground state of the molecule, exists in both C2h and C2v forms which interconvert via a Cs transition state. For the singlet, only a C2h form is found. It passes, via a Cs transition state, onto the C2v surface on which bicyclobutane (3) is the only minimum. The ring-flipping (inversion) process in 3 includes the singlet biradical as an intermediate, and involves a novel, non-least motion path similar to one previously proposed by Gassman. Semiclassical periodic orbit theory indicates that the various minima on both the singlet and triplet surfaces can interconvert via quantum mechanical tunneling.
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  • 43
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    Journal of Physical Organic Chemistry 2 (1989), S. 89-92 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Spectral characteristics of several simple substituted B,B-bis(mesityl)pyrroloboranes are reported which support a theoretical treatment by Bonacic-Koutecky and Michl (J. Am. Chem. Soc. 107, 1765 (1985)) describing the excited states of simple aminoboranes as an example of twisted internal charge transfer. In the aminoboranes the pyrrolo moiety functions as the electron donor group and the empty p-orbital of the boron atom as the acceptor.
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  • 44
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    Journal of Physical Organic Chemistry 2 (1989), S. 103-109 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A preliminary theoretical study of the mechanisms for the reactions of the perchlorofluoroethanes CF2ClCCl3 (1), CF2ClCCl2F (2) and CF3CCl3 (3), with nucleophiles has been carried out by the MNDO method, following the experimentally suggested process shown in Scheme 1. The unlikely chlorophilic attack in the first step of Scheme 1 has been shown to be feasible for 1, 2 and 3 by analysis of the MO interactions. The second step has been found to be affected by the anionic hyperconjugation which stabilizes the anions CF2ClCCl2- (4), CF2ClCClF- (5) and CF3CCl2- (6) and would make reactions (2) (the second step) unfeasible in gas phase, but in solution reaction (2) may still easily occur for 4 and 5.
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  • 45
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    Journal of Physical Organic Chemistry 2 (1989), S. 146-160 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The alkaline hydrolysis of several alkylphosphonates and alkylphosphonyl chlorides has been investigated by molecular mechanics calculations (MM2, 1985 version). The difference of the steric energies (ΔE) between tetracoordinate substrate and pentacoordinate transition state of phosphorus compounds represents the activation energy (ΔE≠) in hydrolysis. The change of ΔE for various alkyl groups relative to methyl group (ΔΔER) is suggested as a measure of the steric effect of substituents. Thus the correlation analysis involving log k and ΔΔER of the branched alkyl group gives good results and it is reasonable to anticipate that analogous treatment using ΔΔER for the straight chain alkyl group is not satisfactory owing to the minor contribution of steric effect of the latter. However, the multiple regression analysis of log k with ΔΔER and Taft's σ* provides very good results. As shown by us, for the hydrolytic reactions studied, the proposed ΔΔER is much better than Taft's Es and Charton's ν, the commonly used well-known steric parameters in the chemistry of carbon compounds.
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  • 46
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    Journal of Physical Organic Chemistry 2 (1989), S. 205-213 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Mechanism of the Grignard reactions of aromatic ketones in THF was studied by spectroscopic and kinetic methods. The stable radical intermediates generated in the initial electron transfer from Grignard reagent to ketones are in a state of aggregated dimer of corresponding ion-radical pairs; in which two ketone anion radicals are bridged by a dimer di-cation of Grignard reagent. Subsequent alkyl radical transfer from dimeric Grignard reagent cation moiety to ketone anion radical aggregated each other are promoted by a participation of another neutral Grignard reagent. Proposed mechanism by present authors is able to explain well addition products/reduction products ratios in the Grignard reactions.
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  • 47
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    Journal of Physical Organic Chemistry 2 (1989), S. 232-242 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Characteristic vector analysis of a set of six physical and empirical parameters of 103 commonly used organic solvents (bp, ∊r, μ, nD, ETN, and δ) gives four vectors describing 95% of the total data variability. Non-hierarchical cluster analysis, applied to our results, leads to ten separate classes of organic solvents.
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  • 48
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    Journal of Physical Organic Chemistry 2 (1989) 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
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  • 49
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    Journal of Physical Organic Chemistry 2 (1989), S. 15-25 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Solvolysis of 2-X-2-phenylpropane (1-X) in 25 vol% acetonitrile in water at 25°C produces 2-hydroxy-2-phenylpropane (1-OH) and 2-phenylpropene (3). The carbocationic intermediate discriminates between different nucleophiles; azide anion, acetate anion, and methanol are more efficient nucleophiles than water, kN3/kH2O = 42 kOAc/kH2O = 3, and kMeOH/kH2O = 2·9 (ratio of second-order rate constants). The fraction of the elimination product 3 increases with increasing basicity of the leaving group X as well as by addition of general bases. The Brønsted parameter for this catalysis is small, β = 0·13, with substituted acetate anions. The kinetic deuterium isotope effect for the dehydronation of the intermediate has been measured (assuming the reaction from intermediate to alcohol is insensitive to isotopic substitution) employing the hexadeuterated substrate d6-1-X as k3H/k3d6 = 3·5 ± 0·2 for the chloride 1-Cl with acetate anion, and, without added base, 3·1 ± 0·2 for the acetate 1-OAc, and 3·1 ± 0·2 for the p-nitrobnzoate 1-PNB, respectively, and ∼5 for the protonated methyl ether 1-OMeH+. The variation in isotope effect with change in leaving group is discussed in terms of elimination from contact ion pairs and ‘free’ carbocation. The overall kinetic isotope effect for the solvolysis was found to be kobsH/kobsd6 = 1·31 (1-OMeH+), 1·38 (1-OAc), 1·40 (1-PNB), and 5·7 (1-OH2+). These isotope effects consist of the isotope effect k12H/k12d6 for the formation of the substitution product 1-OH and k13H/k13d6 for production of the olefin 3. It is concluded that the latter isotope effect is enlarged owing to a branched mechanism in which the deprotonation of the carbocationic intermediate competes with formation of the substitution product. As large an isotope effect as k13H/k13d6 ∼6·5 has been measured for 1-OMeH+.
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  • 50
    ISSN: 1432-0878
    Keywords: Anterior pituitary gland ; Electron microscopy ; Growth hormone ; Spontaneous dwarf rats (dr/dr)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The spontaneous dwarf rat is a novel experimental model animal on the study of pituitary dwarfism. The fine structure of the anterior pituitary cells was studied in the immature and mature dwarf rats. Pituitary glands were removed from 5-, 10-, 20-day-old immature dwarfs, adult (45 days-16 weeks) dwarfs and normal 3-month-old rats and processed for electron-microscopic observation. In the control animals, growth hormone cells were readily identified by their ultrastructural characteristics, such as the presence of numerous electron-dense secretory granules, 300–350 nm in diameter, well developed rough endoplasmic reticulum and a prominent Golgi complex. In contrast, growth hormone cells were not found in the anterior pituitary gland of the spontaneous dwarf rat at any age examined. Other pituitary cell types, i.e., luteinizing hormone/ follicle stimulating hormone, thyroid stimulating hormone, adrenocorticotropic hormone and prolactin cells, appeared similar in their fine structure to those found in the control rats. In the pituitary gland of dwarf rats, a number of polygonal cells were observed either with no or relatively few secretory granules. The rough endoplasmic reticulum was arranged in parallel cisternae and the Golgi complex was generally prominent in these cells. In addition, many were found to have abundant lysosomes. A few minute secretory granules were occasionally observed; however, the immunogold technique failed to localize growth hormone or prolactin in the granules. The nature of these cells remained obscure in this study. Since their incidence and fine structural features, other than the secretory granules, were quite similar to those of the growth hormone cells in normal rats, we postulate that these cells are dysfunctional growth hormone cells. These results suggest that the cause of the growth impairment in the spontaneous dwarf rat is due to a defect in the functional growth hormone cells in the pituitary gland, and since other pituitary cell types appeared normal, the disorder seems to be analogous to the isolated growth hormone deficiency in the human.
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  • 51
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The principal components factors F1 and F2 in the equation \documentclass{article}\pagestyle{empty}\begin{document}$$ \log K = {\rm BDP}_0 + S_1 F_1 + S_2 F_2 $$\end{document} have been used to obtain S1 and S2 values for sets of hydrogen-bond bases against 32 reference acid/solvent systems. The constants S1 and S2 define an angle θ = tan-1 S2/S1 that is a measure of the electrostatic:covalent bonding ratio in the hydrogen-bond complex. It is shown that θ can vary from 53 (4-fluorophenol in CH2Cl2)to 86 degrees (Ph2NH in CCl4) depending on the reference acid and solvent. This variation in θ can lead to family dependent behaviour in plots of log K for bases against a given reference acid system vs log K for bases against another reference acid system, and precludes the construction of any general scale of hydrogen-bond basicity using log K values. Amongst a quite wide range of reference acid/solvent systems θ varies only from 64 to 73 degrees, and for bases against these reference systems a ‘reasonably general’ scale could be set up. Such a scale could be extended to bases against reference acid/solvent systems outside the 64-73 degree range provided that certain classes of base (e.g. pyridines, alkylamines) were excluded from the additional reference acid/solvent systems.
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  • 52
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    Journal of Physical Organic Chemistry 2 (1989), S. 300-322 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Various modifications of the Marcus equation have been applied to the problem of photochemical proton transfer, using available data on general acid-catalyzed photohydration reactions. These include incorporation of asymmetry and tightness parameters, as well as distance variation as a function of exoor endothermicity. The intersecting state model of Formosinho has also been successfully applied to these reactions. The overall conclusion from all of these approaches is that the reactions are characterized by somewhat asymmetric and ‘loose’ transition states, with a small but significant degree of charge development on the in-flight proton at the transition state. Estimates of the intrinsic barriers and work terms place these in the 5-7 kcal and 2-3 kcal ranges respectively. A simple valence bond configuration mixing model leads to similar qualitative conclusions about the nature of the transition states in these reactions.
    Additional Material: 10 Ill.
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  • 53
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The difference in reactivity of small [n]cyclophanes towards CF3CO2H is discussed in terms of charge densities, strain energies and proton affinities. These data are calculated with MNDO and MINDO/3 for para-, meta- and ortho-cyclophanes and for their ipso-protonation products; an attempt is made to transform gas phase ΔHf0 values into liquid phase ΔH0f values. Experimental evidence is presented that the acid catalyzed rearrangement of [5]paracyclophane to its ortho-isomer proceeds via two consecutive 1,2-carbon shifts without deprotonation; intermediate adducts were identified by NMR-spectroscopy. Thus, a gradual shift in reaction pattern in the series [4]-, [5]- and [6]paracyclophane is observed experimentally, in line with the calculational results.
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  • 54
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    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 2 (1989) 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
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  • 55
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    Journal of Physical Organic Chemistry 2 (1989), S. 367-376 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The relative rates of hydrogen atom abstraction from a series of twelve saturated cyclic ethers and sulfides were determined at 70°C. The abstracting radical could be generated from bromotrichloromethane both photolytically or by the thermal decomposition of AIBN. The reaction rates did not show a dependence upon method of radical generation. Reaction occurred only at the position adjacent to the heteroatom. The reactivity of the cyclic ethers was in the order C4H8O 〉 C6H12O 〉 C3H6O 〉 C5H10O. This trend would indicate appreciable influence by ring strain, however, the slightly greater reactivity of tetrahydrofuran relative to oxepane suggests a contribution by stereoelectronic factors as well. The reactivity of the cyclic sulfides, which reacted faster than the corresponding ethers, was in the order C4H8S 〉 C5H10S 〉 C6H12S. This would imply little influence of ring strain. The major structural effect would be that of variable electron donating ability of the sulfur atom. The rate of reaction of thietane was also determined. It was found to preferentially undergo SH2 attack at the sulfur atom followed by ring opening rather than hydrogen abstraction. The reactivities of both series of compounds were decreased by the inductive effect of a second heteroatom beta to the reaciton site.
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  • 56
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    Journal of Physical Organic Chemistry 2 (1989), S. 410-416 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Barriers for group transfers between nucleophiles have been postulated to be lowered when the transferring group can carry a considerable negative charge. Furthermore, anions readily subject to one electron oxidation appear to lead to lower barriers than do those of high oxidation potential. These suggestions are pursued here on the identity reaction ArSe- + ArSeSeAr → ArSeSeAr + ArSe-. Indeed the reaction is very fast, as shown by the appearance of only a single peak in the 77Se-NMR in an acetonitrile solution containing both ArSeNa and ArSeSeAr. The rate constant can be only very roughly estimated at low temperatures and dilute solutions, and is likely diffusion controlled for Ar = phenyl and p-methoxyphenyl. A stable intermediate (ArSe)3-, analogous to Br3-, is indicated, but quantitative stability could not be determined, from either the NMR or the UV spectra. Some properties of 77Se-NMR are discussed.
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  • 57
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    Journal of Physical Organic Chemistry 2 (1989), S. 425-427 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Distribution between pentane and trifluoromethanesulfonic acid (TFMSA) and carbon-13 NMR measurements showed that benzene and toluene are not protonated to any significant extent in TFMSA. This finding contradicts previous reports, and validates the ranking of superacids based on the extent of benzene protonation.
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  • 58
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A two-hydron transfer mechanism involving hydron transfers from carbon to nitrogen and from nitrogen to carbon was studied. The rearrangement of 1,3,3-triphenylpropene (1) into 1,1,3-triphenylpropene (2) catalyzed by 2,10-diazabicyclo[4.4.0]dec-1-ene (3) in benzene at 25·00°C was studied by 2H-labeling experiments and kinetic 2H-isotope effects. The synthesis and purification of [6,10-2H2]-2,10-diazabicyclo[4.4.0]dec-1-ene ([6,10-2H2]-3), [3-2H]-1,3,3-triphenylpropene ([3-2H]-1), [3-2H]-1,1,3-triphenylpropene ([3-2H]-2) and [3,3-2H2]-1,1,3-triphenylpropene ([3,3-2H2]-2) together with their precursors are reported. Partial reaction of [3-2H]-1 with [6,10-1H2]-3 gave 42% conversion into product 2, which was shown by 1H NMR to be composed of 88% [3-1H]-2 and 12% [3-2H]-2. Partial reaction of [3-1H]-1 with [6,10-2H2]-3 gave 43% of 2, composed of 73% [3-1H]-2 and 27% [3-2H]-2.These results clearly show that a substantial fraction of the reaction takes place in a bifunctional manner but isotope exchange and/or monofunctionally catalyzed reactions interfere. The following kinetic deuterium isotope effects on the rearrangement 1 → 2 were measured: kHH/kDH = 6·56; kHH/kHD = 1·19; kHH/kDD = 7·08; kHD/kDD = 5·94; and kDH/kDD = 1·08.On the basis of these results, a concerted two-hydron transfer mechanism is excluded. Instead, a stepwise mechanism is favored, in which at first the 3-hydron of 1 is abstracted by 3 yielding an ion pair(s), the carbanion of which in a separate step is then hydronated to yield the product 2.The abstraction of the 3-hydron from 1 might be hydrogen bond assisted. The two hydron transfer transition states are together rate limiting, although they limit the rate to different extents. A detailed mechanistic analysis is presented together with the results of an investigation of the nature of the catalyst. The dimerization constant for 3 was determined by 1H NMR to be 1·67 l mol-1 at 25·0°C. Isotopomer composition was measured by 1H NMR and GLC was used for the separation of the substrate and products. Computer-assisted capillary GLC was used for the kinetics.
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  • 59
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The Kinetics of reactions of phenacyl benzenesulphonates with benzylamines were investigated in methanol at 45·0 °C and the cross-interaction constants λXY, λYZ and βXZ were determined in order to elucidate the transition-state structure. The unusually small magnitude of λXY can only be accounted for by the resonance ‘shunt’ effect of the α-CO group of the phenacyl system. Large |λYZ| values indicate a small degree of bond breaking whereas relatively large |βXZ| values compared with those for the dissociative SN2 reaction indicate a relatively tight transition state for the reactions. Further, the similar magnitudes of βXZ values compared with those of the corresponding aniline nucleophile series suggest a similar transition-state structure for the two armatic amine nucleophile series.
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  • 60
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    Journal of Physical Organic Chemistry 2 (1989), S. 507-518 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The hydrolysis reactions of N-(2,4,6-trinitrophenyl)piperidine (2) and N-(2,4,6-trinitrophenyl)-morpholine (3) were studied. Two kinetic processes well separated in time are observed in both reactions. The fastest process, which is reversible, leads to the formation of a species of λmax 260 and 410 nm and is attributed to the formation of a σ complex of stoichiometry 1 : 2 due to the addition of a second HO- to the σ complex of 1 : 1 stoichiometry. The slowest process leads quantitatively to picrate ion. The equilibrium constants for the formation of the σ complexes of 1:1 and 1:2 stoichiometries and the rate of formation and decomposition of the latter complex were determined. The kinetic data for the slow process lead to the conclusion that the picrate ion is formed from the attack of HO- on the two σ complexes, confirming previous findings. There are some differences in the calculated rates for 2 and 3 which may be an indication that the elimination of the amine is partially rate determining.
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  • 61
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The rate of decarboxylation of 6-nitrobenzisoxazole-3-carboxylate ion increases sharply with increasing head group size in a series of cetyltrialkylammonium bromides (C16H33NR3Br: R = Me, CTABr; R = Et, CTEABr; R = n - Pr, CTPABr; R = n - Bu, CTBABr) with rate enhancements of 102 (CTABr) and 2·8 × 103 (CTBABr). Micellized tetradecylquinuclidinium bromide and hexadecyl-N-methylmorpholinium bromide are slightly better catalysts than CTABr, as is 1,3-bis(N-cetyl-N,N-dimethylamino)propane dibromide, but p-octyloxybenzyltrialkylammonium bromides (alkyl = Me, n - Bu) are less effective than the corresponding CTA+ surfactants. These differences in catalytic efficiency depend on the head group structure and the extent to which the cationic head groups become less accessible to water rather than the overall micellar structure.
    Additional Material: 3 Tab.
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  • 62
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: 1H, 13C, 15N and 17O NMR chemical shifts, 1JNH and 1JCH coupling constants and line widths (Δν1/2) of the 14N and 17O resonance lines were determined for 2-pyrrolidinone neat and for several 2-pyrrolidinone-solvent systems. The 17O NMR chemical shift of 2-pyrrolidinone was clearly most sensitive to the solvent effects, but changes with the solvent were also observable in the 13C (C=O) and 15N NMR chemical shifts, the 1JNH coupling constants and especially the line widths of the 14N and 17O resonance lines. In general, the results reflected a hydrogen bonding effect between the oxygen atom of 2-pyrrolidinone and the proton-donating solvents and a weak molecular interaction of the NH proton of 2-pyrrolidinone with the proton-accepting solvents. The results are compared with the NMR data for the corresponding binary mixtures of 1-ethyl-2-pyrrolidinone.
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  • 63
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    Journal of Physical Organic Chemistry 2 (1989), S. 580-584 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Rate constants were determined for the combination reactions of a series of cation radicals derived from substituted anthracenes with acetate, p-nitrobenzoate, trifluoroacetate, nitrate and perchlorate ions. Rate constants, depending on the identities of the cation radicals and the nucleophiles, ranging from about 200 to 2 × 1010 1 mol-1 s-1 were observed in acetonitrile at 293 K. The key steps in the reaction are (1) reversible complex formation between the anion and the cation radical followed by (2) irreversible bond formation \documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{*{20}c} {\rm{Ar}^{ + \cdot } + \rm{X}^ - \rightleftharpoons {{\rm{Ar}^{ + \cdot } } \mathord{\left/ {\vphantom {{\rm{Ar}^{ + \cdot } } {\rm{X}^ - }}} \right. \kern-\nulldelimiterspace} {\rm{X}^ - }}} &&&&& {(1)} \\ {{{\rm{Ar}^{ + \cdot } } \mathord{\left/ {\vphantom {{\rm{Ar}^{ + \cdot } } {\rm{X}^ - }}} \right. \kern-\nulldelimiterspace} {\rm{X}^ - }} \to \rm{Ar}^ \cdot - \rm{X}} &&&&& {(2)} \\ \end{array} $$\end{document}.The preliminary results show that cation radical-anionic nucleophile reactions can be very facile. The cation radicals of 9-nitro- and 9-cyanoanthracene are particularly reactive, giving rise to rate constants close to the diffusion-controlled limit with all anionic nucleophile studied and even react moderately rapidly with perchlorate ion. The reaction with perchlorate ion can be compared to the behavior of stable carbenium ions that coexist with the anion in solution and in crystalline salts.
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  • 64
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    Journal of Physical Organic Chemistry 2 (1989), S. 611-622 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The solvent effect on two SN2 reactions was evaluated by discrete, continuum and discrete-continuum models. The potential energy profiles were found to change dramatically on introduction of the solvent effect. The double-well shape which characterizes the F- + CH3F → FCH3 + F- reaction in the gas phase becomes unimodal when the solvent is introduced, in good agreement with experimental data. The solvation parameters are found to intervene in the reaction coordinate. Recent Monte Carlo and molecular dynamics calculations are discussed.
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  • 65
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    Journal of Physical Organic Chemistry 2 (1989), S. 631-645 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The kinetics of the aromatic nucleophilic substitution (SNAr) reactions of 1,2-dinitrobenzene (1,2-DNB) with butylamine (BA) and piperidine (PIP) were investigated as a function of the amine concentration and temperature, in chloroform, ethyl acetate, tetrahydrofuran (THF), acetonitrile (ACN), dimethylformamide (DMF), dimethyl sulphoxide (DMSO). benzene, toluene, chlorobenzene and diisopropyl ether.In the set of solvents consisting of ethyl acetate, THF, ACN, DMF and DMSO, neither reaction is catalysed (kA = k1). The sequence and range of reactivity for BA and PIP are similar in these solvents. These results indicate that reactions in which nitro in the leaving group behave differently from SNAr reactions with other leaving groups, such as halogens or alkoxy groups, since an intramolecular hydrogen bond may be expected between the leaving nitro group and the ammonium H of the nucleophiles. The correlations of the rate coefficients obtained with Taft and Kamlet's solvatochromic method support these conclusions.On the other hand, these reactions show mild acceleration with relatively non-polar solvents such as the aromatics and diisopropyl ether. The donor properties of these solvents and experiments with solvent mixtures suggest the formation of electron donor-acceptor complexes between them and 1,2-DNB. Hence the preferential solvation of 1,2-DNB by the donor solvent accounts for the mechanism observed.
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  • 66
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    Journal of Physical Organic Chemistry 2 (1989), S. 93-102 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Organocerium(III) reagents reacted with α,β-unsaturated carbonyl compounds to give 1, 2-addition products (allylic alcohols) in good to high yields. The reaction was studied from a mechanistic point of view by the use of (E)- and (Z)-1-(4′-methoxyphenyl)-3-phenyl-2-propen-1-ones and 4,4-ethylenedioxy-2,6-dimethyl-2,5-cyclohexadienone as the probe compounds. A polar pathway was suggested for the reaction with the former enones. On the other hand, the operability of single electron transfer processes was demonstrated in the reaction with the latter probe compound.
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  • 67
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Bis(1,2-diaryl-1,2-ethylenedithiolato)metal(0) complexes (1; metal = Ni, Pd, and Pt) react with quadricyclane (Q) to give selectively 1:1 adducts which are identical with the adducts between 1 and norbornadiene (NBD). In the adducts, two sulfur atoms of the different dithiolato ligands are added to one of the double bonds of NBD. The reactions of 1 with Q are 103-104 times faster than those with NBD. The more electropositive dithiolatometal complexes react faster with Q and NBD. The adducts are dissociated to the free dithiolatometal complexes and NBD by UV-irradiation (254-436 nm). Upon irradiation with 254 nm light, the photodissociation occurs before the decomposition of the dithiolatometal complexes.
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  • 68
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    Journal of Physical Organic Chemistry 2 (1989), S. 117-130 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Gas phase ion/molecule reactions have been used to probe the structure of ions obtained by electron impact upon 1-(diphenylmethylene)cyclopropane and 2,2-diphenyl-1-methylenecyclopropane. The resulting ions of molecular composition C16H14 (m/z 206+) were reacted with charge transfer reagents (6·9 〈 IP 〈 8·8eV), giving evidence for the presence of isomeric ions with different reactivities. The less reactive ion is identified as a trimethylenemethane species (TMM+) in which one cyclopropane bond is broken; the more reactive ions are assigned as vertical ions in which the cyclopropane ring is unaffected. The vertical ions have recombination energies of 8·44 ± 0·05eV, whereas TMM+ has one of 7·41±0·05eV. The TMM+ fraction is not constant; it increases with increasing IP of the reagent. This is attributed to a reagent-catalyzed isomerization of the vertical ion to TMM+. In addition, the reagent ions are observed to undergo a unique reaction with the neutral methylenecyclopropane derivatives: electron transfer and ring opening to yield TMM+. These findings limit the application of the customary equilibrium measurements as a method to determine the substrate IP.
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  • 69
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    Journal of Physical Organic Chemistry 2 (1989), S. 177-182 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: 4-O2NC6H4OCH2CH2NHPh undergoes clean base-catalyzed Smiles photorearrangement to 4-O2NC6H4N(Ph)CH2CH2OH in dimethyl sulfoxide-water (25:75). A linear plot of φ-1 vs [OH-]-1 indicated that the limiting quantum yield at high [OH-] is 0·12 and that uncatalyzed photorearrangement does not occur. Rate constants for the deprotonation step were determined for a variety of bases having conjugate acid pKa values in the range 5-10. When plotted according to the Brønsted Catalysis Law, these data gave a non-linear plot approaching slopes of zero and unity above and below a pKa of 6-7. This indicates that the proton-donating intermediate in this photo-Smiles rearrangement is the zwitterion diradical (pKa ≈ 7) rather than the Meisenheimer complex (pKa ≈ 2).
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  • 70
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    Journal of Physical Organic Chemistry 2 (1989), S. 225-231 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The gas-phase pyrazole elimination of N-alkyl pyrazoles has been studied using MNDO semi-empirical molecular orbital (MO) theory with complete geometry optimization of all stationary points. We found that the activation energies (Ea) of the concerted processes are around 80 kcal/mol, 25 Kcal/mol higher than experimental values. But the differences in Ea between compounds with different substituents are in good agreement with the experimental ones.
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  • 71
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    Journal of Physical Organic Chemistry 2 (1989), S. 255-262 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The photostimulated reaction of neopentyl halides with different nucleophiles by the SRN1 mechanism of nucleophilic substitution has been studied. Neopentyl halides do not react with carbon nucleophiles, diethylphosphite, diphenylphosphonite and azide ions, but they react with arsenide and selenide ions. The photostimulated reaction of neopentyl bromide with diphenylarsenide ions gave only the straightforward substitution product neopentyldiphenylarsine. On the other hand, the photostimulated reaction of bromobenzene with dineopentyl arsenide ions gave three arsines: dineopentylphenylarsine, neopentyldiphenylarsine and triphenylarsine. Neopentyl chloride reacts under irradiation with diphenylphosphide ions giving good yields of the substitution product.
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  • 72
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    Journal of Physical Organic Chemistry 2 (1989) 
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    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
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  • 73
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    Journal of Physical Organic Chemistry 2 (1989), S. 281-299 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Mechanisms of the hydrolysis of urea have been investigated using the MNDO and AMI methods. All geometries were fully optimized and the transition states were characterized by calculating force constants. The results showed that: (i) The unimolecular decomposition process via the direct intramolecular proton transfer is preferred to both the A1 and the bimolecular nucleophilic attack by water, in agreement with the experimental results of Shaw et al. in the low acidity medium. (ii) The diprotonated form of urea exists as an equilibrium species, which undergoes the A2 type hydrolysis more favorably than the monoprotonated form, as Moodie et al. found in the intermediate acidity medium. (iii) The A2 hydrolysis of the monoprotonated form is very similar to those of acetamide and methyl carbamate. (iv) As the number of the solvate water molecules increases, the activation barrier for the A2 process of the monoprotonated form increases while that for the unimolecular decomposition of the free base form decreases, indicating a possibility of the barrier height reversal in the bulk solvent in favor of the latter process, thus accommodating all the experimentally found trends in the urea hydrolysis. The A1 mechanisms involving six-membered ring type intermediates can be ruled out as untenable since no such equilibrium species was obtained by both the MNDO and AM1 calculations.
    Additional Material: 17 Ill.
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  • 74
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The spectroscopic evidence for the predominance of the equatorial conformers in the title compounds was confirmed by the study of derivatives containing counterpoise substituents, and by chemical equilibration of anancomeric models. ΔG27o°C [P(O)Ph2] ≳ 3·2 kcal/mol was determined in the dioxane, and ΔG55o°C [P(O)Ph2] = 1·42 ± 0·12 kcal/mol in the oxathiane. It follows then that the strong anomeric interaction observed previously in S—C—P segments does not show up in the six-membered heterocycles 2 and 7, which contain O—C—P moieties. This may be due to an inherent inability of oxygen to act as an electron donor to the axial P(O)Ph2 substituent, or to a dominant repulsive steric interaction in the axial conformers.
    Additional Material: 2 Tab.
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  • 75
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: An excellent linear correlation of oxygen-17 substituent chemical shifts (SCS) for twelve α, α, α-trifluoroacetophenones with single σ+ constants, δ = 24·6σ+ + 556·3 (correlation coefficient 0·998) has been observed. However, from this plot, an SCS of 34·3 ppm for 1,1,1-trifluoroacetone will give a corresponding σ+ (γ+) value of 1·44 for a methyl group, which is not in agreement with 0·63-0·79 obtained from solvolytic rate data.
    Additional Material: 1 Ill.
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  • 76
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    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 2 (1989), S. 383-388 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Norbornadiene, isolated in argon, xenon and nitrogen matrices at 20 K, was irradiated with UV light. Characterized by UV-VIS-IR absorption spectroscopy the photoproduct, representing a single species, was assigned to quadricyclane. This result is compared with the literature data on photochemistry of norbornadiene in the gas and liquid phase. The role of the rigid matrix environment on selectivity of the photochemical reaction is discussed.
    Additional Material: 3 Ill.
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  • 77
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    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 2 (1989) 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
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  • 78
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    Journal of Physical Organic Chemistry 2 (1989), S. 448-454 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The interaction between pyridoxal-5′-phosphate (PLP) and pyridoxamine-5′-phosphate (PMP) was studied by d.c. and differential pulse polarography. Two reduction waves (or two peaks) were observed. The first wave corresponds to the reduction of the adduct and the second to the reduction of free PLP. The behaviour was similar in analogous Schiff bases. The effects of pH, PMP concentration and the capillary characteristics were studied. The apparent formation constant as a function of the pH was calculated. Thermodynamic parameters were estimated at pH 7 and 0 · 1 M ionic strength. The polarographic and kinetic results show that the overall electrode process appears to be irreversible in a basic medium.
    Additional Material: 4 Ill.
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  • 79
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    Journal of Physical Organic Chemistry 2 (1989), S. 476-483 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Dipole moments of para-substituted benzoyl chlorides and bromides, partly measured in benzene and partly recalculated from elderly literature, were analysed in terms of bond moments and additional contributions expressing the conjugation. Although the gross moments are similar, their decomposition yields different pictures for acyl chlorides and bromides. Only in the latter can significant electron transfer from the halogen be observed. On the other hand, conjugation with the benzene nucleus is strong in both aromatic acyl chlorides and bromides, but stronger in chlorides. There is agreement with the evidence from some other physical quantities but not from all.
    Additional Material: 2 Ill.
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  • 80
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Benzyl cations, free of counter ions, have been generated from the nuclear decay of tritium atoms contained exclusively in the side-chain of multi-labelled toluene and allowed to react in competition experiments with benzene and toluene. The aromatic substitution was studied in both the gaseous and liquid phase, employing pure aromatics or aromatics dissolved in n-hexane, carbon tetrachloride and nitromethane as the reaction medium. In the gaseous systems, at 20 Torr total pressure, High meta substitution of toluene indicates extensive isomerization of the excited intermediates, while the increase of the kT/kB value in the Presence of NH3 suggests that selective transalkylation competes with proton transfer to ammonia from the benzyl cation adducts with benzene, but not with toluene. High positional and low substrate selectivities were measured in solution, the decrease in kT/kB (from 2·8 to 1·7) in the different solvents being accompanied by an increase in the o/2p ratio. Competition experiments between benzene and methanol indicate that the reaction is not diffusion controlled. The influence of the reaction medium on the substrate selectivity is explained by postulating the formation of a cation-solvent adduct, where the solvent molecule undergoes displacement by the substrate. Positional selectivity would be controlled in a subsequent step.
    Additional Material: 1 Tab.
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  • 81
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The basic hydrolysis of 2,4-dinitrochlorobenzene (DNCB) and 2,4-dinitrofluorobenzene (DNFB) was studied in the presence of β-cyclodextrin (CDOH) and in the presence of hydroxy-functionalized micelles containing either a primary hydroxy group [hexadecyl-2-hydroxyethyldimethylammonium bromide (CHEDAB)] or a secondary hydroxy group [headecyl-2-hydroxypropyldimethylammonium bromide (CHPDAB) and 2-hydroxyhexadecyltrimethylammonium bromide (2-OHCTAB)].In all systems a biphasic reaction was observed. The first phase consisted of a competition between the additive (either micelle or cyclodextrin) and hydroxide ion for the aromatic substrate, and the second phase consisted of the hydrolysis of the trapped aryl micellar or cyclodextryl ether.The percentage of trapping of the aromatic substrate by the cyclodextrin was similar to that found for reactions in the hydroxy-functionalized micelles (CHPDAB and 2-OHCTAB) which contained secondary hydroxy groups. The relative rates of reaction for DNFB and for DNCB, i.e. F/Cl rate ratios, in the presence of CDOH were similar to those obtained in the presence of 2-OHCTAB but less than that obtained in the presence of CHEDAB. These results support the assumption that in CDOH the secondary hydroxy groups of C-2 or C-3 are involved in covalent bond formation with the aromatic substrate rather than the primary hydroxy group of C-6. All the reactions studied proceed much more slowly in the presence of CDOH than in the presence of the hydroxy-functionalized micelles. This may reflect a catalytic effect of the positively charged surface present in the micelles but not in the cyclodextrin.
    Additional Material: 3 Ill.
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  • 82
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Using the solvatochromic indicator method, a scale of solvent hydrogen-bond basicity, β1 (General), has been set up using a series of double regression equations, \documentclass{article}\pagestyle{empty}\begin{document}$$ \nu = \nu _0 + s\pi _1^* + b\beta _1 $$\end{document} for 11 aniline-type indicators. A similar solvent scale, β1 (Special), has been constructed by the homomorphic comparison method using only results by Laurence et al. on the indicators 4-nitroaniline and 4-nitro-N,N-dimethylaniline. Results are available from our previous work on a general solute scale, β2H, and we have also obtained a special solute scale, β2 (pKHB) from available log K values for hydrogen-bond complexation of bases with 4-fluorophenol in CCl4. However, the two solute β2 scales are virtually identical.It is shown that there is a general connection between β1(General) and β2H, with r = 0·9775 and s.d. = 0·05 for 32 compounds, and between β1(Special) and β2H, with r = 0·9776 and s.d. = 0·06 for the same 32 compounds. The latter correlation over 60 compounds yields r = 0·9684 and s.d. = 0·07. However, there are so many compounds in these regressions for which the differences in the solvent and solute β values are larger than the total expected error of 0·07 units that the use of β1 to predict β2 or vice versa is a very hazardous procedure. About 70 new β1 values obtained by the double regression method are also reported.
    Additional Material: 6 Tab.
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  • 83
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    Journal of Physical Organic Chemistry 2 (1989), S. 573-579 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The MM2 force field has been extended so that calculations may be carried out on siloxanes. The parameters chosen give a good fit to available experimental data.
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  • 84
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    Journal of Physical Organic Chemistry 2 (1989), S. 602-610 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: In order to assist in the interpretation of the D5h molecular structure of [45] (1,2,3,4,5)ferrocenophane (1) obtained from x-ray crystallographic analysis, a hypothetical hydrocarbon C30H40 (2) was derived from 1 by removing the iron atom and subjected to geometry optimization by molecular mechanics. A stable D5 conformer was found for 2, which has a g+ g- g+ helical bridge conformation and a ring-ring distance almost identical with that in 1 and ferrocene itself. Optimization of a perhydrogenated hydrocarbon model gave a highly strained C1 structure.
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  • 85
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    Journal of Physical Organic Chemistry 2 (1989), S. 623-630 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Photolysis of dichlorodiphenylmethane in glassy 2-methyltetrahydrofuran at 77 K results in the formation of diphenylcarbene and the diphenylchloromethyl radical, which were detected by their fluorescence emission and excitation spectra. The relative yields of the carbene and biradical are shown to vary dramatically as a function of photolysis time. The photolability of the diphenylchloromethyl radical is also demonstrated. These results were interpreted in terms of a two-step mechanism, in which the diphenylchloromethyl radical is an intermediate in the formation of diphenylcarbene.
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  • 86
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The formation of a σ-like complex by reaction between 1,3,5-trinitrobenzene and 1,8-diazabicyclo [5.4.0]-undec-7-ene was investigated in toluene at various temperatures. The kinetic data showed autocatalytic behaviour. Inspection of the reaction mixtures at zero reaction time indicated the presence of an equilibrium preceding the attack of the nucleophile, affording a molecular complex (substrate-nucleophile) which is responsible for the observed kinetic features. The present and the previous data led to the conclusion that the catalytic behaviours usually observed in SNAr reactions (in apolar solvents with amines as nucleophiles) are better explained by the presence of substrate-catalyst interactions than by catalysis on departure of the proton and leaving group from the zwitterionic intermediate.
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  • 87
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    Journal of Physical Organic Chemistry 2 (1989) 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
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  • 88
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The ups and downs, and reasons therein, of the π-complex theory of the mechanism of the benzidine rearrangements, and the possible role of π-complexes in a newer understanding of the rearrangements, are described.
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  • 89
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    Journal of Physical Organic Chemistry 2 (1989), S. 531-539 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Acid-catalysed condensation of resorcinol with aromatic aldehydes results in 2,8,14,20-tetrasubstitued calix[4] areneoctols. Sixteen compounds of this type containing different aromatic substituents were synthesized. The ring closure step, under the conditions of the reaction, is a reversible process. Four configurations are possible for every constitution, viz. cccc, cctt, ccct and ctct, but only cccc and cctt were formed in detectable amounts. In seven cases the thermodynamically more stable cccc isomers (1a-5a, 7a, 8a) and also the kinetically controlled cctt isomers (1b-5b, 7b, 8b) could be isolated. The configurations of the compounds were assigned by temperature-dependent 1H NMR analysis. The conformational motions of the macrocyclic ring permit only the cccc isomers to show coalescence for the signals of the aromatic Hb protons. The coalescence temperature was determined for isomers 1a (ΔG384≠ = 83·5 kJmol-1) and 3a (ΔG369≠ = 83·7 kJ mol-1). For steric reasons the ‘chair-chair’ conformers B and the ‘quasi-boat-chair’ conformers F are favoured. 1H and 13C NMR shifts show that compounds 1a-5a and 1b-5b have a quasi-axial arrangement of the aromatic substituents, whereas 6-9 have a quasi-equatorial arrangement of the substituents.
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  • 90
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    New York, NY [u.a.] : Wiley-Blackwell
    Molecular Reproduction and Development 1 (1989), S. 264-277 
    ISSN: 1040-452X
    Keywords: Nucleoproteins ; Element concentrations ; Electron microscopy ; Image analysis ; X-ray spectrophotometry ; Flow cytofluorometry ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: After cryosubstitution and Epon embedding, or after Nanoplast embedding and very thin sectioning, the chromatin of ejaculated or diluted boar spermatozoa appears to be formed of DNA fibers embedded in a quite homogeneous matrix. After sodium dodecyl sulfate (SDS) treatment, and to a lesser extent after freeze-thawing, the DNA fibers are present mostly between cords, probably proteinaceous in nature. The quantity of free sulfhydryl (SH) groups, as calculated from staining by DACM and flow fluorometry, is increased in thawed or SDS-treated cells. The quantity of NH2 groups, calculated from electron microscopy image analysis of alcoholic phosphotungstic acid-stained cells, is decreased in thawed nuclei. The DNA is more accessible to the fluorochrome ethidium bromide after freeze-thawing, and its sensitivity to HCI hydrolysis is modified, during the Feulgen-like staining procedure using acriflavine. The X-ray energy dispersive analysis of cryosections of nuclei indicates that the slight separation of DNA and nucleoproteins in freeze-thawed spermatozoa could result from a dramatic modification of the nuclear ionic environment during thawing.
    Additional Material: 17 Ill.
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  • 91
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: IR spectroscopy is presented as a convenient means to monitor the formation of acyl (and alkyl) cations from corresponding acid chlorides, with Lewis acids at low temperature in the solid state. Phenylacetyl chloride is co-deposited (under vacuum at -173°C with antimony pentafluoride on a KBr window), as in the ‘molecular beam’ method of cation generation. The initial IR spectrum of the deposition shows (in addition to starting materials) that a small amount of phenylacetyl cation (2274 cm-1) has been formed. Warming the solid matrix to -123°C Promotes the smooth conversion of acid chloride to acyl cation. Ultraviolet irradiation (through quartz windows) at -123°C to -73°C facilitates this conversion but does not result in the loss of carbon monoxide from the acyl cation to form benzyl cation. When benzyl chloride is used in place of phenylacetyl chloride, there is no noticeable difference between IR spectra taken before and after warming and/or photolysis of the solid deposition.
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  • 92
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    Journal of Physical Organic Chemistry 2 (1989), S. 214-224 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The solvolysis of 21 different 3- or 17-androstanyl tosylates or chlorides with halogen, hydroxy or oxo substituents in 17- or 3-position shows rate constant variations in hexafluoro isopropanol of up to 6·3 with regular differences for epimeric substituents. Similar variations ae seen over a distance of ∼10 Å in 13C-NMR shifts at C-17-ones of androstan-17-ones with varied halogen substituents in C-3, whereas the shielding observed at other distant carbon atoms excludes significant through bond effects. It is shown how, on the basis of suitable Coulomb-type equations and of force field minimized geometries, both the stability variation of carbocationic transition states and the carbonyl group polarization are predictable by linear electric field effects, using the same parametrization.
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  • 93
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    Journal of Physical Organic Chemistry 2 (1989), S. 263-270 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Reactivity of dialkyl 2-(dimethylamino)ethyl phosphates, (RO)2P(O)OCH2CH2NMe2 (R = Me, PhCH2) was studied in aqueous solutions. Depending on the initial substrate's concentration, reaction can involve the unimolecular fragmentation to N,N-dimethylaziridinium dialkylphosphate, or the bimolecular isomerization to the zwitterionic derivative. The latter reaction proceeds via two consecutive SN2 steps and involves the formation of two ionic intermediates which were synthesized independently and allowed to react to give the zwitterionic product. Rate constants for the isomerization of the dimethyl ester (R = Me), as well as rate constant for the reaction between the corresponding intermediates have been determined, and the reactivity of the dimethyl ester has been compared with that of the dibenzyl derivative.
    Additional Material: 1 Ill.
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  • 94
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The crystal and molecular structures of dimesitylketene (1) and bis(3,5-dibromo-2,4,6-trimethylphenyl)ketene (2), the first free ketenes to be studied by X-ray diffraction, have been determined. The molecules of 1 and 2 have crystallographic C1 and C2 symmetry, respectively, and exist in a propeller conformation. Molecular mechanics calculations of 1 and 2 using a modification of Allinger's new allene parameters reproduce satisfactorily the structural parameters of the ketenes. The torsional angles of the aryl rings in 1 and 2 are similar (ca. 50°) and are regarded as ‘intrinsic’ values for a 1,1-dimesitylvinyl propeller. From the similarity in aryl torsional angles in 1 and 2 it is concluded that the buttressing effects in 2 (if any) are not markedly manifested in the structural parameters of 2.
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  • 95
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    Journal of Physical Organic Chemistry 2 (1989), S. 323-330 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Photoreactions of Cr(CO)5(Im) (Im = 1,3-dimethyl-4-imidazolin-2-ylidene) have been investigated by laser flash and continuous photolysis. Quantum yields for the disappearance of Cr(CO)5(Im) in benzene under Ar or CO were very low, although transients observed by laser flash photolysis reacted rapidly with CO. This suggests that photodissociation of the carbene ligand is very minor. The laser flash photolysis at 337 nm in benzene (B) gave a transient (λmax = 630 nm), which converted to the second transient (λmax = 455 nm) within ∼100 ns. The kinetic studies of these transients revealed that the first one is a ‘free’ coordinatively unsaturated species (Cr(CO)4(Im)) and the second one carries a solvent molecule as a ligand (Cr(CO)4(Im)(B)). From the comparison of Cr(CO)4(Im) and Cr(CO)5, apparently lower reactivity of Cr(CO)5 was found to be due to the strong coordination of a solvent molecule. The Im ligand neutralizes the deficit of electron density on Cr. A simple synthesis of Cr(CO)5(Im) was also described.
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  • 96
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    Journal of Physical Organic Chemistry 2 (1989), S. 359-362 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The reaction pathway of urea formation by selenium-catalysed carbonylation of secondary amines with carbon monoxide in the presence of oxygen was studied using piperidine as a secondary amine. It was established that selenium reacts with carbon monoxide and piperidine to give carbamoselenoate as an intermediate, which affords biscarbamoyl diselenide by the oxidation with molecular oxygen. Aminolysis of biscarbamoyl diselenide gives the urea derivative, accompanying the regeneration of selenium catalyst.
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  • 97
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    Journal of Physical Organic Chemistry 2 (1989), S. 377-382 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The rates of N-methylation of pyridine and its ring-substituted derivatives by trimethyl phosphate were measured in D2O and in CDCl3. Relative rates, together with the solvent activity coefficients of substrates for the transfer form chloroform to water, were used for determining the solvent activity coefficients of the activated complexes for this SN2 reaction. The results indicate early activated complexes for all pyridines, with the most nucleophilic substrate showing the most reactant-like activated complex.
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  • 98
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    Journal of Physical Organic Chemistry 2 (1989), S. 389-409 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A gas-phase experimental investigation of the competition between carbon and oxygen alkylation of a series of cyclic and acyclic enolate ions is described. Perfluoropropylene is shown to react in a characteristic way with oxyanions and carbanions to produce distinctive ionic products. The relative yields of these products formed in reactions with ambident enolate ions provides a measure of their intrinsic carbon vs. oxygen regioselectivity. The results for a series of enolates derived from aldehydes, ketones, esters, amides and related compounds show a wide range of reactivity which is a function of the nature of the central substituent. Most aldehyde and ketone enolates react mainly through oxygen, while enolates with σ-acceptor of π-donor type central substituents react mainly thorugh carbon. Ring-size in cyclic ketone enolates also influences C vs. O regioselectivity, i.e. small-ring enolates react mainly through carbon, while larger ring enolates (C7-C9) react preferentially through oxygen. The enolate reactivity patterns can be generally accounted for by the keto-enol energy differences for the parent carbonyl compounds, although some exceptions are evident. The origins of the highly variable, kinetically determined regioselectivities are discussed.
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  • 99
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    Journal of Physical Organic Chemistry 2 (1989), S. 417-424 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Two organometallic reagents, butyllithium in heptane solution and dibutylmercury in the gas phase, have been studied by means of core electron spectroscopy. The property of particular interest was the charge polarization as reflected by the ESCA shifts. In the butyllithium compound the C1s binding energy is shifted to a lower value by 1·8 eV for C-1 (situated closest to the Li+ ion) relative to the heptane solvent carbon. This is due to the anionic character of the C-1. The interpretation of the experiments was supported by comparing the results with ab initio calculations made on geometry-optimized butyllithium, butyl anion and butane.
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  • 100
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    Journal of Physical Organic Chemistry 2 (1989), S. 455-466 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Mixtures of bicyclo[3.2.0]hept-2-ene and bicyclo[2.2.1]hept-2-ene, with one isomer labeled with two deuterium atoms, were isomerized in the gas phase at 276 °C. By following the concentration ratios of d0 and d2 versions of bicyclo[2.2.1]hept-2-ene as functions of time one finds that the partitioning of bicyclo[3.2.0]hept-2-ene between the primary products bicyclo[2.2.1]hept-2-ene and cyclopentadiene plus ethene is 2:1. This and earlier stereochemical results permit the calculation of the partitioning of the [3.2.0] olefin between the orbital symmetry allowed [1,3] carbon shift-with-inversion product and several forbidden or non-concerted reaction channels (approximately 1:1) and the stereochemistry of the ethene d2 formed from exo,exo-[6,7-2H2]bicyclo[3.2.0]hept-2-ene directly (1:1 E: Z).
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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