Potentiometric study on complexation of divalent transition metal ions with amino acids and adenosine 5′-Triphosphate

Abstract

Potentiometric equilibrium measurements have been performed at 25 degrees C and in an I = 0.10 M KCl ionic medium for the interaction of nickel(II), copper(II), and zinc(II) with adenosine 5'-triphosphate (ATP) and dicarboxylic amino acids (aa): aspartic acid (Asp) and glutamic acid (Glu). The formation of 1:1 and 1:2 binary and 1:1:1 ternary complexes was inferred from the potentiometric titration curves. It was deduced that adenosine 5'-triphosphate acts as a primary ligand in the ternary complexes involving the dicarboxylic amino acids. The complexation model for systems of adenosine 5'-triphosphate (ATP) and the dicarboxylic amino acids with nickel(II), copper(II), and zinc(II) have been established by the "BEST" software from the potentiometric data. Values of Delta log K (log beta(MAB) - (log beta(MA) + log beta(MB))) showed that the ternary complexes are less stable than the binary ones, suggesting that no interaction occurred between the ligands in the ternary complexes. The order of the values of the stability constants of all the ternary complexes was M(II)ATP(Asp) > M(II)ATP(Glu), and the same sequence was found in the binary complexes of metal ions with the amino acids. With respect to the metal ions, the stability constants of binary and ternary complexes decrease in the following order: copper(II) > nickel(II) > zinc(II).