ISSN:
1434-193X
Keywords:
Hydrolysis
;
Nucleophilicity
;
α-Effect
;
Metal ion complexes
;
Oximes
;
Biomimetic models
;
Chemistry
;
General Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
---A kinetic study of the reactivity in the cleavage of p-nitrophenyl acetate of a series of 2-pyridineoximes, 1-4, and their complexes with NiII, ZnII and CuII is reported. Complexation of the oximic ligands leads to a remarkable increase in the acidity of the oximic group, following the order CuII 〉 NiII 〉 ZnII. The oximates of free ligands and their metal complexes, being α-nucleophiles, are quite effective in promoting the cleavage of PNPA. However, the reactivity, as defined by the second-order rate constants, is not predictably related to the acidity of the oximic function. The corresponding Brønsted plot shows a linear behaviour up to a pKa value of ca. 8, above which the reactivity of the uncomplexed oximic functions levels off to a limiting value. In the case of the metal ion complexes, a large effect of the ligand structure on the reactivity was observed. As a consequence, complexes of appropriate ligands and metal ions show a reactivity that exceeds the apparent limiting one of the oximates. The origin of such effects and their possible implications in the development of new reactivators of phosphorylated acetylcholinesterase are discussed.
Additional Material:
1 Ill.
Type of Medium:
Electronic Resource
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