Studies on the Sulfur-containing Chelating Agents. XXVI. Formation of Mixed Ligand Chelates Containing Penicillamine and Sulfhydryl Compounds

Abstract

Formation of new mixed ligand chelates consisting of penicillamine, bivalent metals, such as mercury, lead and cadmium, and some of the secondary ligands, such as mercaptoacetic acid, N-acetylpenicillamine, glutathione, 2-mercaptoethylamine, α-mercaptopropionyl glycine and penicillamine methyl ester, in the ratio of 1 : 1 : 1 were recognized potentiometrically, but there was no indication for the existence of the similar mixed ligand chelate in the cases of ethylmercaptan, glycine and histidine. The mixed ligand chelate is formed in two steps ; the simple penicillamine metal chelate is formed in the first step, and the secondary ligand becomes to coordinate to 1 : 1 penicillamine chelate to yield the 1 : 1 : 1 mixed ligand chelate in the second step. The order of the relative formation constants of mixed ligand chelates was Cd2+>Hg2+>Pb2+. The formation constants of mixed ligand chelates are linearly correlated to the dissociation constants of sulfhydryl group in secondary ligands. Moreover, among these mixed ligand chelates, the decrease of binding affinity of the carboxyl group in penicillamine tends to increase the formation of the mixed ligand chelate.