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The binary and ternary systems of Cu(II) complexes with adenosine 5′ triphosphate (ATP), phosphocreatine (PCr) and the amino acids (aa) serine (Ser), tyrosine (Tyr), threonine (Thr) and glycine (Gly) were investigated. The study was performed in aqueous solution using potentiometry, ultraviolet visible and EPR spectroscopies. The stability constants of the complexes were determined by potentiometry (T = 25 °C, I = 0.1 mol/L, KNO3). The spectroscopic studies have confirmed that all systems form stable complexes. Δlog K(log βCuaaL − (log βCuaa + log βCuL)) showed that when L = ATP, the ternary complexes are less stable than the binary ones, suggesting that no interaction occurs between the ligands in the ternary complexes. When L = PCr and aa was Ser or Tyr the ternary complexes were more stable than the binary ones. As PCr acts as a bidentate ligand, there is one non-coordinated position and both Ser and Tyr have an OH group free. Since there is no possibility of interaction when the amino acid is Gly, which does not have an OH group, it seems that the interaction in the ternary complexes with Ser and Tyr is made through the OH group of the amino acids. In the case of Thr, this amino acid has an OH group in the β carbon, similarly to Ser, but it has a terminal methyl group which can difficult the interaction with PCr. |
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