Studies on transition-metal–peptide complexes. Part 2. Equilibrium study of the mixed complexes of copper(II) with aliphatic dipeptides and amino-acids

Abstract

In a total of 39 equilibrium systems, the stability constants of mixed dipeptide–amino-acid complexes of copper(II) have been determined at 25 °C and ionic strength I= 0.2 mol dm^–3 KCl. The dipeptides used are glycylglycine, glycyl-DL-α-alanine, and DL-α-alanyl-DL-α-alanine, and the amino-acids are glycine, α-alanine, α-aminobutyric acid, norvaline, β-alanine, serine, threonine, ornithine, lysine, asparagine, glutamine, aspartic acid, and glutamic acid. From the exceptionally high relative stabilities of the mixed-ligand complexes containing β-alanine and aspartic acid, it is concluded that in these complexes the amino-acids occupy one equatorial and one axial site in the co-ordination sphere of the copper(II)