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  • 1
    Digitale Medien
    Digitale Medien
    The Important Role of Active Site Water in the Catalytic Mechanism of Human Carbonic Anhydrase II – A Semiempirical MO Approach to the Hydration of CO2 † (1998)
    Springer
    Journal of molecular modeling 4 (1998), S. 355-365 
    Details
    ISSN: 0948-5023
    Schlagwort(e): Keywords Human Carbonic Anhydrase II ; Semiempirical MO Theory ; AM1 ; Enzyme Catalysis
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract The approach of CO2 to a series of active site model complexes of human carbonic anhydrase   II (HCAII) and its catalytic hydration to bicarbonate anion have been investigated using semiempirical MO theory (AM1). The results show that direct nucleophilic attack of zinc-bound hydroxide to the substrate carbon occurs in each model system. Further rearrangement of the bicarbonate complex thus formed via a rotation-like movement of the bicarbonate ligand can only be found in active site model systems that include at least one additional water molecule. Further refinement of the model complex by adding a methanol molecule to mimic Thr-199 makes this process almost activationless. The formation of the final bicarbonate complex by an internal (intramolecular) proton transfer is only possible in the simplest of all model systems, namely {[Im3Zn(OH)]+·CO2}. The energy of activation for this process, however, is 36.8 kcal·mol−1 and thus too high for enzymatic catalysis. Therefore, we conclude that within the limitations of the model systems presented and the level of theory employed, the overall mechanism for the formation of the bicarbonate complex comprises an initial direct nucleophilic attack of zinc-bound hydroxide to carbon dioxide followed by a rotation-like rearrangement of the bicarbonate ligand via a penta-coordinate Zn2+ transition state structure, including the participation of an extra active site water molecule.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s008940050094
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  • 2
    Digitale Medien
    Digitale Medien
    Kinetic and thermodynamic study of the mechanism of reversible intermolecular electron-transfer reactions between horse heart cytochrome c and a series of cobalt imine complexes (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 39-46 
    Details
    ISSN: 0947-6539
    Schlagwort(e): cobalt ; cytochrome c ; electron transfer ; kinetics ; volume profile ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The Kinetics and Thermodynamics of the Reversible Outer-Sphere Electron-Transfer Reactions between Horse Heart Cytochrome cII/III and [Co(phen)3]3+/2+ and [Co(bpy)3]3+/2+ were studied in detail, in particular as a function of temperature and pressure. It was possible to construct a volume profile for both reactions from the pressure data. The transition state was found to be halfway between the reactant and product states on a volume basis in all studied systems. This is in agreement with the λ≠ parameter estimated from the Marcus theory. For all the systems investigated, the differences in the activation volumes are in good agreement with the reaction volumes determined from spectrophotometric and electrochemical measurements at elevated pressure, and from the difference in the partial molar volumes of the metal complexes. The activation and reaction volumes of the bipyridine system are significantly smaller than those of the corresponding phenanthroline and terpyridine systems. A detailed mechanistic analysis is presented. The results show that the different kinetic and thermodynamic techniques employed complement one another.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19970030108
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 3
    Digitale Medien
    Digitale Medien
    REACTIVITY OF NUCLEOPHILES TOWARDS X-3-(p-TOLYLSULFONYL)-1,2,3-BENZOXATHIAZOLE 2,2-DIOXIDES: KINETICS, ACTIVATION VOLUMES AND MECHANISM (1997)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 10 (1997), S. 175-181 
    Details
    ISSN: 0894-3230
    Schlagwort(e): cyclic sulfamates ; nucleophiles ; reactivity ; kinetics ; mechanism ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: ---The kinetics of the reaction of four X-3-(p-tolylsulfonyl)-1,2,3-benzoxathiazole 2,2-dioxides (X=5-Cl, 5-Br, 5-NO2 and 6-NO2) with hydroxide ion and imidazole in aqueous acetonitrile and aqueous ethanol solutions were investigated at various pressures. The volumes of activation were all found to be negative and consistent with a bimolecular reaction involving considerable solvent electrostriction. No significant dependence on the solvent composition was found. © 1997 by John Wiley & Sons, Ltd.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 4
    Digitale Medien
    Digitale Medien
    Electronically Tuned trans Labilization Controls the Substitution Behavior of RhodoximesThe authors acknowledge financial support from the Deutsche Forschungsgemeinschaft, Fonds der Chemischen Industrie, MURST, and the Max Buchner Forschungsstiftung. (1995)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 34 (1995), S. 2245-2247 
    Details
    ISSN: 0570-0833
    Schlagwort(e): kinetics ; reaction mechanisms ; rhodium compounds ; substitutions ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/anie.199522451
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