Ternary complexes in solution. Comparison of the coordination tendency of some polybasic oxygen acids toward the binary complexes of Cu(II) andAMP,ADP orATP

Abstract

Potentiometric equilibrium measurements have been made at 25±0.1°C (μ=0.1 mol dm−3 KNO3) for the interaction of adenosine-5′-mono-, -di- and -triphosphate (AMP,ADP andATP) and Cu(II) with biologically important secondary ligand acids (malic, maleic, succinic, tartaric, citric and oxalic acids) in a 1:1:1 ratio and the formation of various 1:1:1 mixed ligand complex species inferred from the potentiometricpH titration curves. Initial estimates of the formation constants of the resulting species and the acid dissociation constants ofAMP,ADP,ATP, and secondary ligand acid, have been refined with the SUPERQUAD computer program. In some systems ΔlogK values are positive, i.e. the ternary complexes are found to be more stable than the corresponding binary complexes. In some Cu(II) ternary systems the interligand interactions between the coordinate ligands, possibly H bond formation, have been found to be most effective in deciding the stability of the ternary complexes formed in solution. Stabilities of mixed ligand complexes increase in the orderAMP maleic > tartaric > malic > citric > oxalic acid.