Ternary complexes of copper (II) involving dipeptides and aromatic amines: Effect of π-acidity of aromatic amines on the deprotonation of the peptide group in the ternary complex

Abstract

Equilibrium constants have been measured potentiometrically for the mixed-ligand complexes, copper (II)-amines (A)-dipeptides (L). The aromatic amines (A) used are 5-nitro-1,10-phenanthroline (Nphen), 2,2'-pyridyl benzimidazoline (pybz), 1,10-phenanthroline (phen) and 2,2'-pyridyl imidazoline (pyz). The dipeptides used are glycylglycine (gg), glycyl-1-alanine (ga) and glycyl-1-Ieucine (gl). The formation of two types of ternary complexes at different <i>p</i>H values are reported. The values of the formation constants are compared with Cu-ethylenediamine (en)-dipeptide system. The effect of the increasing π-acid character of the amines (A) on the deprotonation of the dipeptides (L) in the ternary complex (CuAL_-_H) has been discussed. Electrochemical studies of the binary complex Cu-en and one of the ternary complex, Cu-en-gg has also been carried out in aqueous medium. The formation of two different ternary species at different <i>p</i>H values with different reduction potentials is observed.