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  • 1
    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
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  • 2
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 122 (1989), S. 315-320 
    ISSN: 0009-2940
    Keywords: Acetylacetone, hexafluoro- ; Diol formation / Enolization ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Eine spektroskopische und mechanistische Untersuchung der Enolisierung und Diol-Bildung von Hexafluoracetylaceton in Gegenwart von Wasser und AlkoholDie Reaktionen von Hexafluoracetylaceton (Hfac) (6) mit Wasser, Methanol, Ethanol und Isopropylalkohol wurde im einzelnen anhand von 1H-, 13C-, 17O-, 19F-NMR- und UV-VIS-Spektroskopie untersucht. Dabei konnten die Zwischen- und Reaktionsprodukte bei der Enolisierung und Diol-Bildung spektroskopisch identifiziert werden. Die vorgeschlagenen Reaktionswege werden unter Bezug auf früher in der Literatur berichtete Daten diskutiert. Ein wichtiges Ergebnis dieser Untersuchung ist der direkte Nachweis für die Bildung der Addukt-Spezies Hfac(OH)4 (10), Hfac(OMe)2 (13a) und Hfac(OEt)2 (13b).
    Notes: The reactions of hexafluoroacetylacetone (hfac) (6) with water, methanol, ethanol, and isopropyl alcohol were studied in detail using 1H-, 13C-, 17O-, 19F-NMR, und UV-VIS spectroscopy. The reported spectra enable the identification of intermediate and product species, and allow a mechanistic analysis of the enolization and diol formation. The suggested mechanisms are discussed with reference to earlier data reported in the literature. An important feature of this study is the direct evidence presented for the formation of the adduct species hfac(OH)4 (10), hfac(OMe)2 (13a), and hfac(OEt)2 (13b).
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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