Cd2+ and Zn2+ interactions with amino acids N-substituted by a sulfonic group.Effect of the additional ligand 2,2'-bipyridine on the metal-induced amine deprotonation

The interaction of N-(phenylsulfonyl)glycine and N-(tolylsulfonyl)glycine (L) with Cd2+ and Zn2+ was investigated through dc polarography, pH-metric titrations, and H-1 NMR spectroscopy. 2,2'-Bipyridine as additional ligand lowers the pK(a) of Cd2+-promoted deprotonation of the sulfonamide nitrogen (from 8 in the binary system to 7.6 in the presence of the heteroaromatic base), as previously observed for the Cu2+ ion, and, most of all, enables the Zn2+ ion to substitute for the sulfonamide nitrogen bound hydrogen of these ligands. It is known that Zn2+ is ineffective in such a substitution in binary Zn2+-L systems.