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  • 1999  (5)
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  • 1995-1999  (5)
  • 1985-1989
  • 1980-1984
  • 1975-1979
  • 1960-1964  (2)
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  • 1
    Electronic Resource
    Electronic Resource
    Bisphenol-A content of resin monomers and related degradation products (1999)
    Springer
    Clinical oral investigations 3 (1999), S. 114-119 
    Details
    ISSN: 1436-3771
    Keywords: Key words Fissure sealants ; Bisphenol A ; Bisphenol A ; dimethacrylate ; Hydrolysis ; Saliva
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  Recently, it was reported that Bisphenol-A (BPA) was released from one fissure sealant (Delton) into saliva causing estrogenic activity in vitro. The aim of this study was to chemically analyze the BPA content of different fissure sealant resin monomers and their release of BPA under hydrolytic conditions. BPA content was first measured in commercially available monomers of bisphenol-A glycidyldimethacrylate (Bis-GMA), bisphenol-A dimethacrylate (Bis-DMA) and bisphenol-A diglycidylether (BADGE). Then, Bis-GMA-monomer and Bis-DMA-monomer in methanol were subjected to pH values of 0 to 11 for 30 minutes at 50°C, to porcine liver esterase, and to pooled saliva for up to 24 hours. The BPA-content was determined by high-performance liquid chromatography (HPLC). Bis-GMA-monomer and BADGE-monomer from one manufacturer did not contain any detectable amounts of BPA (≤2 ppm); Bis-DMA and BADGE-monomer from a second manufacturer contained BPA quantities of 4–155 ppm. For Bis-GMA-monomer, no BPA could be detected under any hydrolytic conditions chosen (detection limit: ≤1%). For Bis-DMA-monomer an increase of BPA was observed at pH 11, resulting in a conversion of approx. 100% Bis-DMA to BPA. When Bis-DMA was subjected to esterase, a conversion of 82.5 % resulted after 24 h; saliva led to an 81.4 % conversion of Bis-DMA after 24 h. Hence, we conclude that the results reported in the literature may be attributed to the Bis-DMA-content of the fissure sealant tested (Delton). No BPA-release is expected under physiologic conditions from fissure sealants based on Bis-GMA if pure base monomers are used.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s007840050088
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Ab initio MD simulations of a prototype of methyl chloride hydrolysis with explicit consideration of three water molecules: a comparison of MD trajectories with the IRC path (1999)
    Springer
    Theoretical chemistry accounts 102 (1999), S. 262-271 
    Details
    ISSN: 1432-2234
    Keywords: Key words: Ab initio molecular dynamics ; Hydrolysis ; Intrinsic reaction coordinate ; Proton transfer ; Solvent effect ; Methyl chloride
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract. Ab initio molecular dynamics simulations at the Hartree-Fock/6-31G level of theory are performed on methyl chloride hydrolysis with explicit consideration of one solute and two solvent water molecules at a temperature of 298 K. The reaction involves the formation of a reactant complex and the energy surface to the transition state is found to be simple. Two types of trajectories toward the product are observed. In the first type, the system reaches an intermediate complex (complex-P1) region after two nearly concerted proton transfers involving the attacking water molecule and the solvent water molecules. These trajectories resemble the intrinsic reaction coordinate trajectory. The thermal motion of the atoms leads the system to another intermediate complex (complex-P2) region. A second type of trajectory is found in which the system reaches the complex-P2 region directly after the proton transfers. In both of these forward trajectories, back proton transfers lead the system to a final complex-F region which resembles protonated methanol.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002140050497
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    “In situ”13C NMR study of ethyl alcohol interaction with sulfuric acid (1999)
    Springer
    Reaction kinetics and catalysis letters 68 (1999), S. 35-43 
    Details
    ISSN: 1588-2837
    Keywords: Hydrolysis ; oxonium ions ; ethyl sulfates ; rapid exchange of protons
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract “In situ” NMR study of ethyl alcohol interaction with sulfuric acid of various concentrations confirmed that in accordance with chemical experience the main reaction product in an excess of concentrated acid is the mono-ethyl sulfate. Only traces of diethyl sulfate are formed in a large excess of 95% acid. In addition, ethyloxonium ions and protonated esters, which rapidly exchange protons with solvating water molecules, are detected as the reaction intermediates. The13C chemical shifts of methylene fragments in protonated esters and ethyl oxonium ions are more than 10 ppm higher than in neutral molecules. The study of reaction products at different sulfuric acid concentrations indicated that similarly to dissociation of concentrated sulfuric acid, hydrolysis of mono-ethyl sulfate requires at least two water molecules.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02475485
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Substrate hydrolysis by combinations of Trichoderma xylanases (1999)
    Springer
    World journal of microbiology and biotechnology 15 (1999), S. 23-26 
    Details
    ISSN: 1573-0972
    Keywords: Hydrolysis ; Trichoderma ; xylanases ; xylans
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract The hydrolysis of five xylan substrates was examined using combinations of two pairs of xylanases from two species of Trichoderma. Antisynergy was observed in acetylated xylan isolated from aspen when the maximum hydrolysis achieved by certain xylanase combinations was significantly lower than that achieved by the most effective enzyme in the combination. Cooperative interactions among xylanases were observed in pine holocellulose where xylanase combinations were more effective than single xylanases.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008865100607
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    Paper (German National Licenses)
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  • 5
    Electronic Resource
    Electronic Resource
    Kinetics and Mechanism of Base Hydrolysis in Cobalt(III) Complexes - The Case of a Complex CoLCl2+ where L has the Novel Topology of a Square-Pyramidal NN4 Coordination Cap (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 643-650 
    Details
    ISSN: 1434-1948
    Keywords: Cobalt(III) complexes ; Tetrapodal pentadentate ligand ; Hydrolysis ; Kinetics ; Mechanism ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Multi-wavelength stopped-flow spectrophotometry was used to study the kinetics of base hydrolysis of the octahedral cobalt(III) complex CoLCl2+ (2), in which the tetrapodal pentadentate ligand L has an NN4 donor set and forms a square-pyramidal coordination cap [L = 2,6-bis(1′,3′-diamino-2′-methylprop-2′-yl)pyridine, 1]. The kinetic investigation, carried out at different temperatures, pressures and ionic strengths I, led to second-order kinetics, rate = kOH [2][OH-], with kOH = 0.139 ± 0.001 M-1s-1 (I = 0.1 M) and kOH = 0.0570 ± 0.0004 M-1s-1 (I = 1.0 M) at 298 K. The temperature and pressure dependence of kOH resulted in ΔH
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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    Paper (German National Licenses)
  • 6
    Electronic Resource
    Electronic Resource
    The Reaction of Oxides with Water at High Pressures and TemperaturesDedicated to Prof. Dr. H. Brockmann on the occasion of his 60th birthday (1964)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 3 (1964), S. 47-54 
    Details
    ISSN: 0570-0833
    Keywords: Oxides ; Water ; High-pressure chemistry ; Hydrolysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reactions of the oxides SiO2, MoO3, and WO3 with steam at temperatures between 400 and 700 °C and pressures of 5 to 500 atm were studied by means of the transfer method. The results were evaluated by a new method. In the system Sio2/H2O the formation of gaseous Si(OH)4, Si2O(OH)6, and [SiO2(OH)2]x was found to occur in three different water-density ranges. In the systems MoO3/H2O and WO3/H2O the gaseous compounds MoO2(OH)2 and WO2(OH)2, which were already known, exist up to densities of approximately 0.05g/cm3. At higher densities, at which the supercritical phase begins to show the properties of a liquid to an ever increasing extent, isopolymolybdic or isopolytungstic acids appear.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.196400471
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    Paper (German National Licenses)
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  • 7
    Electronic Resource
    Electronic Resource
    Proton Transfer, Acid-Base Catalysis, and Enzymatic Hydrolysis. Part I: ELEMENTARY PROCESSESPart II (Catalytic Mechanisms) will appear shortly in this journal.Dedicated to Dr. W. Foerst on the occasion of his 65th birthday (1964)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 3 (1964), S. 1-19 
    Details
    ISSN: 0570-0833
    Keywords: Proton transfer ; Catalysis ; Enzyme catalysis ; Hydrolysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The proton occupies a special position as a promoter and mediator in chemical reactions occurring in solution. Many reactions in organic chemistry are catalysed by acids or bases; likewise, most enzymes contain active groups which promote acid-base catalysis. To understand the reaction mechanisms involved, it is necessary to identify the elementary steps as well as their course in time. Systematic investigation of these elementary steps as well as their course in time. Systematic investigation of these elementary steps has become possible only with the development of new methods for studying very fast reactions. The present paper reviews the information obtained in this type of investigation. The result is a relatively complete picture of the elementary proton transfer mechanisms and a comprehensive description of the modes and laws of acid-base and enzymatic catalysis.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.196400011
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    Paper (German National Licenses)
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