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  • Chemistry  (350)
  • 1995-1999  (350)
  • 1998  (350)
  • 1
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 70 (1998), S. 1195-1208 
    ISSN: 0020-7608
    Keywords: GABAB analogs ; pharmacophoric pattern ; molecular similarity ; quantum chemical calculations ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In order to determine the structural requirements that are important for GABAB binding affinity, a quantum-chemical-based conformational study has been performed, followed by a similarity analysis which includes 12 GABAB analogs. Due to the flexibility of the structures, a semigrid GABAB analog [2RS-(5,5-dimethyl) morpholinyl-acetic acid] has been used as a template for the amonium moiety in order to help to identify the active conformation. Both in vacuo, and solvent-simulated calculations, for the physiological media modeled as water molecules, have been compared, for this analog, at ab initio (G94, 6-31+G(d,p)) and semiempirical (PM3) levels, respectively. On the basis of this comparison, the results of in vacuo PM3 calculations have been chosen for the similarity analysis. We have included, in the calculations, a group of molecules heterogeneous enough to become representative of the different families that can bind to the GABAB receptor site. Following their comparison we report the leading characteristics that can be related to their binding capability and define a pharmacophoric pattern for GABAB analogs. The latter is compared with the one previously found for the binding affinity at the GABAA receptor site.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 70: 1195-1208, 1998
    Additional Material: 9 Ill.
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  • 2
    ISSN: 0021-9304
    Keywords: biodegradable barrier films ; canine periodontal defects ; rabbit subcutaneous implants ; mass loss ; polymer degradation rate ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Biodegradable barrier films were made by coagulating a solution of poly(DL-lactide) in N-methyl-2-pyrrolidone on porous polyethylene pads wetted with saline solution. The semisolid films were cut into 10 × 10 mm barriers and implanted subcutaneously in rabbits. At monthly intervals, the polymer implant sites were compared histologically to those implanted with USP negative control plastic. The polymer films were retrieved from the surrounding tissue, dried, weighed, and the changes in molecular weight determined using gel permeation chromatography. The molecular weight of the polymer decreased at a relatively constant rate over 5 months; however, no significant mass loss occurred until 5 months postimplantation. Also, no distinct histological differences were noted between the polymer barrier and the control plastic sites until 6 months when histiocytes and multinucleated giant cells showed a modest increase around fragmented polymer films. Similar barrier films also were fitted over naturally occurring buccal dehiscence defects in beagle dogs and the tissue sites compared histologically at 6 months to sham-operated control sites. New bone and dense connective tissues closely approximated segments of the remaining polymer and demonstrated the biocompatibility of the biodegradable films. Histomorphometric analyses of treated sites compared to sham controls showed that the polymer barrier is effective in promoting bone and cementum regeneration in periodontal defects in dogs. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 42, 303-311, 1998.
    Additional Material: 7 Ill.
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  • 3
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 39 (1998), S. 176-183 
    ISSN: 0021-9304
    Keywords: hydroxyapatite ; crystallinity ; materials characterization ; alkaline phosphatase activity ; osteocalcin concentration ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: The clinical success of dental implants is governed by implant surfaces and bone cell responses that promote rapid osseointegration and long-term stability. The specific objective of this study was to investigate osteoblast precursor cell responses to hydroxyapatite (HA) surfaces of different treatments. Since the nature of bone cell responses in vitro is influenced by the properties of HA ceramics, this study was divided into two components: a chemical and crystallographic characterization of the HA ceramics and an in vitro cell culture study. The sintered HA samples were observed to have the highest crystallite size as compared to the as-received HA and calcined HA samples. No differences in the surface roughness and chemical composition were observed among the sintered, calcined, and as-received HA surfaces. In concurrence with the X-ray diffraction, high resolution XPS resolution of Ca 2p also indicated a higher crystallinity on sintered HA samples as compared to the calcined and as-received HA samples. As indicated by increased alkaline phosphatase-specific activity, increased cell-surface and matrix-associated protein, and 1,25 (OH2) vitamin D3-stimulated osteocalcin production, a more differentiated osteoblast-like phenotype was observed on the sintered HA surfaces compared to the as-received HA and calcined HA surfaces. An increased osteoblast-like cell activity on the sintered HA surfaces suggested that the crystallite size of HA surfaces may play an important role in governing cellular response. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 39, 176-183, 1998.
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  • 4
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 1317-1328 
    ISSN: 0887-624X
    Keywords: vapor phase deposition ; polybenzoxazoles ; poly(phenylenebenzoxazole) ; thermal depolymerization ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Vapor phase deposition was carried out on multifunctional aliphatic and aromatic benzoxazoles to yield powdered samples of poly(dimethylenebenzoxazoles). Representative aliphatic and aromatic poly(dimethylenebenzoxazoles) were also synthesized through solution methods using 4-amino-3-hydroxyhydrocinnamic acid and 2-(4-(bromomethyl)phenyl)-6-(bromomethyl)benzoxazole, respectively, as monomers. Both aromatic and aliphatic polybenzoxazoles containing —CH2CH2— units in the polymer backbone displayed catastrophic weight loss over a very narrow temperature range. This is in contrast with other polybenzoxazoles which show a gradual weight loss over 500-1000°C. Vapor phase deposition carried out under vacuum on the polymers gave similar polymers in the collection zone suggesting the catastrophic weight loss is attributed to thermal depolymerization of the polymer through a diradical intermediate similar to the thermolysis and polymerization of [2.2]paracyclophane. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1317-1328, 1998
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  • 5
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 3107-3114 
    ISSN: 0887-624X
    Keywords: PTFE ; auto-adhesion ; surface grafting ; amphoteric monomer ; Ar plasma ; XPS ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The surfaces of Ar plasma-pretreated polytetrafluoroethylene (PTFE) films are further functionalized via UV-induced graft copolymerization with amphoteric N,N′-dimethyl(methacryloylethyl)ammonium propansulfonate (DMAPS) either in Ar atmosphere, or under atmospheric conditions and in the absence of a polymerization initiator. The so-modified PTFE films from either process are capable of exhibiting adhesive-free adhesion or auto-adhesion with one another when brought into intimate contact in the presence of a small quantity of water. The lap shear adhesion strength increases with increasing graft concentration and can readily exceed the yield strength of the PTFE substrate. Two plasma-pretreated PTFE films also readily undergo thermal graft copolymerization with concurrent lamination when lapped together in the presence of a small quantity of the DMAPS monomer solution at elevated temperature in the atmosphere. The surface compositions of the graft-copolymerized PTFE films and the delaminated surfaces were characterized by X-ray photoelectron spectroscopy (XPS). In most cases, adhesional failure occurred near the graft-substrate interphase. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 3107-3114, 1998
    Additional Material: 9 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 21 (1998), S. 671-673 
    ISSN: 0935-6304
    Keywords: gas chromatography ; monosaccharides ; pentafluorobenzylhydroxylamine ; electron capture detector ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 2 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 69 (1998), S. 117-128 
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The requirements for H2-antagonist activity so far identified for most of the known antagonists of histamine are the presence of a heterocyclic ring containing a basic center linked via a methylene chain to a substituted guanidine or thiourea polar side chain. Metiamide is a potent H2 antagonist (pA2=6.06). We have used the ab initio Hartree-Fock (HF) method in order to study the conformational properties of the N3(SINGLE BOND)H tautomers of metiamide molecule and histamine monocation. Three basis set (the 3-21G*, 6-31G**, and 6-31+G**) were used, the results compared, and the geometric parameters fully optimized. Our results indicate the preference of metiamide for a folded conformation with an intramolecular hydrogen bonding between the imidazole ring and one of the NH groups. The optimized geometrical parameters and charge distributions of both molecules, using the Mulliken, and natural bond order (NBO) analysis, are given and discussed.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 69: 117-128, 1998
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  • 8
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 70 (1998), S. 341-350 
    ISSN: 0020-7608
    Keywords: alumina ; periodic SCF ; surface potential ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The electronic structure of the (001) and (110) α-alumina surfaces was determined by periodic Hartree-Fock method in statically relaxed geometries. Both (001) and (110) surfaces generate specific surface states into the energy gap. Significant influence of charge-transfer effect on the surface-adsorbate potential is possible in both cases studied. The inclusion of the exponential part to the standard potential forms was suggested for the description of the interaction potential in such cases.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 70: 341-350, 1998
    Additional Material: 9 Ill.
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  • 9
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 70 (1998), S. 1127-1136 
    ISSN: 0020-7608
    Keywords: pharmacophoric pattern ; antiepileptic activity ; conformational analysis ; N-valproyl glycine ; N-valproyl glycinamide ; valpromide ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Two closely related N-substituted valpromide derivatives: N-valproyl glycinamide and N-valproyl glycine are comparatively analyzed, the first of which is antiepileptic active whereas the second is not. The study is based on a conformational analysis using an AM1 Hamiltonian that not only search for the lower energy structures of each derivative but also for the energy involved in their mutual interconversion. Open structures have been compared with cyclic ones, the latter including those stabilized by either inter or intra molecular hydrogen bonds (dimers and monomers, respectively). H-bond formation has been also evaluated by means of ab initio G94(6-31+G(d,p)) calculations for a smaller system (N-formylglycine/glycinamide) modeling both vacuum and solvent conditions. The conformational and electronic characteristics of the open and cyclic monomers, as well as of the dimer N-valproyl glycinamide and N-valproyl glycine structures are discussed. On the basis of the results of their comparative analysis, we have redefined the pharmacophore previously proposed for N-substituted valpromides [Tasso, Bruno-Blanch, Estiu, Int. J. Quant. Chem. 65(6), 1107 (1997)], relaxing some of the associated requirements. The corrected model requires one carbon atom or any bioisosteric substituent in an anticlinal conformation relative to the aminic nitrogen of the amide moiety, in addition to one hydrogen atom that should be antiperiplanar to the carbonyl oxygen. This model offers an explanation to the different response of N-valproyl glycinamide and N-valproyl glycine against convulsion, which is based on conformational restrictions.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 70: 1127-1136, 1998
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  • 10
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 58 (1998), S. 204-214 
    ISSN: 0006-3592
    Keywords: ethanol ; lignocellulose ; fermentation ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Technologies are available which will allow the conversion of lignocellulose into fuel ethanol using genetically engineered bacteria. Assembling these into a cost-effective process remains a challenge. Our work has focused primarily on the genetic engineering of enteric bacteria using a portable ethanol production pathway. Genes encoding Zymomonas mobilis pyruvate decarboxylase and alcohol dehydrogenase have been integrated into the chromosome of Escherichia coli B to produce strain KO11 for the fermentation of hemicellulose-derived syrups. This organism can efficiently ferment all hexose and pentose sugars present in the polymers of hemicellulose. Klebsiella oxytoca M5A1 has been genetically engineered in a similar manner to produce strain P2 for ethanol production from cellulose. This organism has the native ability to ferment cellobiose and cellotriose, eliminating the need for one class of cellulase enzymes. The optimal pH for cellulose fermentation with this organism (pH 5.0-5.5) is near that of fungal cellulases. The general approach for the genetic engineering of new biocatalysts has been most successful with enteric bacteria thus far. However, this approach may also prove useful with Gram-positive bacteria which have other important traits for lignocellulose conversion. Many opportunities remain for further improvements in the biomass to ethanol processes. These include the development of enzyme-based systems which eliminate the need for dilute acid hydrolysis or other pretreatments, improvements in existing pretreatments for enzymatic hydrolysis, process improvements to increase the effective use of cellulase and hemicellulase enzymes, improvements in rates of ethanol production, decreased nutrient costs, increases in ethanol concentrations achieved in biomass beers, increased resistance of the biocatalysts to lignocellulosic-derived toxins, etc. To be useful, each of these improvements must result in a decrease in the cost for ethanol production. © 1998 John Wiley & Sons, Inc. Biotechnol Bioeng 58:204-214, 1998.
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