ISSN:
0018-019X
Keywords:
Chemistry
;
Organic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
The stabilities of Zn complexes of cysteine and histidine have been determined together with those with those of three derivatives of each n which one of their three donor functions (carboxyl, amino, and mercapto and imidazole, respectively) has been blocked. Using potentionmetric titrations of aqueous solutions, the 1:1 and 1:2 complexes of all for cysteine- and all four histidine-derived ligands are observed among te various species present (ligands, 1:1 and 1:2 complexes, and protonatd derivatives thereof). All cysteine-derived complexes are more stable than the corresponding histidine-derived complexes by 1-2 orders of magnitude for the 1:1 composition and by 1-6 order of magnitude for the 1:2 composition. For the cysteine series, the sequence of stabilities is cysteine 〉 cysteine ethyl ester ≫ N(α)-acetylcysteine ≫ SMethylcysteine. For the histidine series, the corresponding sequence is histidine 〉 histidine methyl ester 〉 N,N (imidazole)-dimethylhistidine 〉 N(α)-acetylhistidine. The order of stabilities can be explained by the relative strengths of the Zn-S vs. Zn-N coordination, y charge effects, and by chelate ring sizes.
Additional Material:
4 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/hlca.19930760133
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