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  • 1
    Electronic Resource
    Electronic Resource
    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
    Keywords: Keywords Human Carbonic Anhydrase II ; Semiempirical MO Theory ; AM1 ; Enzyme Catalysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s008940050094
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    Paper (German National Licenses)
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  • 2
    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)
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