Stereoselective complex formation between simple dipeptides and hydrogen and copper(II) ions

Abstract

Formation constants for the various complexes formed between H⁺ and Cu²⁺ and some dipeptides containing amino-acid residues of differing optical hands (Gly-Val, Gly-Phe, and Leu-Leu) have been measured at 25 °C and I= 0.10M(K[NO₃]). There is no stereoselectivity when only one of the amino-acids is optically active. When both residues contain asymmetric centres there is no significant stereoselectivity in the complexes formed prior to ionization of the amide hydrogen ion, but it is significant once ionization has taken place. Dipeptide complexes containing amino-acid residues of the same chirality {e.g.[Cu(L-Leu-L-Leu)]} are more stable than those formed by racemic dipeptides {e.g.[Cu(L-Leu-D-Leu)]}.