Thermodynamics of metal complexes with ligand-ligand interaction. Mixed complexes of copper(II) and zinc(II) with adenosine 5′-triphosphate and l-phenylalanine or l-tyrosine

Thermodynamic parameters for the formation of copper(II) and zinc(II) mixed complexes with ATP and l-phenylalanine or l-tyrosine were determined by means of potentiometric and calorimetric measurements at t = 25°C and I = 0.1 mol dm-3 (KNO3) in aqueous solution. ΔG0, ΔH0 and ΔS0 values for the binary systems of the two amino acids were also determined under the same experimental conditions. On the basis of the obtained results, the occurrence of solvophobic and of other non-covalent interactions between the non-coordinating side-chain moleties of the bonded ligands has been ascertained in the investigated zinc(II) mixed complexes. For copper(II) mixed complexes, ΔG0, ΔH0 and ΔS0 values do not allow a straightforward assessment of the occurrence of stacking interaction. The origin of this difference in behaviour of the two metal ions is also discussed.