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Catalysis by zinc ion in the reactions of carcinogenic chromium(VI) with thiols

✍ Scribed by Joaquin F. Perez-Benito; Natividad Saiz; Elisenda Amat

Publisher
Elsevier Science
Year
1998
Tongue
English
Weight
146 KB
Volume
135
Category
Article
ISSN
1381-1169

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✦ Synopsis

The reactions of Cr VI with nine biological and nonbiological thiols RSH in aqueous acetate buffer pH 5.60 have Ε½ y . been followed by an spectrophotometric method, and a relatively stable intermediate the thioester RSCrO has been 3 Ε½ . Ε½ . Ε½ . observed. The rate constants corresponding to the formation k , decomposition k , and redox transformation k of 1 y1 2 that intermediate have been obtained in both the absence and presence of zinc ion. This ion acts as a true catalyst for both the formation and decomposition of the observed intermediate. The equilibrium constants for the formation of RSCrO y from 3 Ε½ . y Cr VI and RSH for the different thiols have been determined. A mechanism is proposed for the formation of RSCrO in 3

the presence of catalyst according to which the rate-determining step would be the bimolecular reaction between a zinc-thiolate complex and an acetyl-chromate ester, involving an interchange of ligands.

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