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

Equilibrium constants have been measured potentiometrically for the mixed-ligand complexes, copper (U)-amines (A)-dipeptides (L). The aromatic amines (A) used are 5-nitro-l,lO-phenanthroline (Nphen), 2,2'-pyridyl benzimidazoline (pybz), 1,lO-phenanthroline (phen) and 2,2'-pyridyl imidazoline (pyz). The dipeptides used are glycylglycine (gg), glycyl-l-alanine (ga) and glyeyl-l-Ieucine (gl), The formation of two types of ternary complexes at different pH values are reported. The values of the formation constants are compared with Cu-ethylenediamine (en)-dipeptide system. The effect of the increasing rt-acid character of the amines (A) on the deprotonation of the dipeptides (L) in the ternary complex (CuALH) 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 aqueo.us medium. The formation of two different ternary species at different pH values with different reduction potentials is observed.