Metal Complexes of some Model Peptide Derivatives. Part-IX. Complexation Equilibria of Cobalt-, Nickel-, Copper- and Zinc(II) with Salicyloylglycylglycine

Department of Chemistry, University College of Science, 92 Acharya Prafnlla Chandra Road, Calcutta-700 009

Manuscript received 33 July 1990, revised 39 October 1991, accepted 6 December 1991

Combined pH-metric and spectrophotometric study on the complexation equilibria of Co^II, Ni^II, Cu^ll and Zn^II with the model peptide ligand. salicyloylglycylglycine, (o)HO -C₆H₄CONHCH₂CONHCH₂COOH provided evidence of formation of only 1 : 1 metal : ligand complexes, M(H_-2 L)^2-. in which the metal ions are coordinated by the two deprotonated amide nitrogen atoms along with phenolic and carboxylic oxygen atoms of the ligand. Proton-ligand and metal-ligand constants were determined in 50% (v/v) ethanol-water medium at a fixed ionic strength (l=0.2 M NaNO₃) at 30 + 0.1º. The complexation equilibria were worked out and correlated with the mode of bonding of the ligand.