Studies on transition-metal–peptide complexes. Part 12. Copper(II) complexes of dipeptides containing phenylalanine and tyrosine

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Abstract
The thermodynamic quantities relating to the copper(II) complexes of glycyl-L-phenylalanine, glycyl-L-tyrosine, L-phenylalanylglycine, and L-tyrosylglycine have been determined pH-metrically and calorimetrically at 25 °C and at an ionic strength of 0.2 mol dm–3(KCl). From these data and the u.v., visible, and e.s.r. spectra of the complexes, it has been established that, besides metal–ligand co-ordination characteristic of simple aliphatic dipeptides, there are interactions between the d-electron orbitals of the copper(II) and the 6π-electron system of the aromatic amino acid, between the hydrophobic parts of the molecule, and between the copper(II) and the phenolate group of the ligand.