Potentiometric Studies on Binary and Ternary Complexes of Di- and Trivalent Metal Ions Involving Some Hydroxamic Acids, Amino Acids, and Nucleic Acid Components

Summary. Formation of binary and ternary complexes of Cu^II, Co^II, Ni^II, Zn^II, Fe^III, Al^III, and Cr^III metal ions with some selected aliphatic and aromatic hydroxamic acids and some biologically important amino acids or nucleic acid components was investigated using the potentiometric technique at 25°C and I=0.10moldm^–3 NaNO₃. The acid-base properties of the ligands were investigated and discussed. The acidity constants of the ligands were determined and used for determining the stability constants of the complexes formed in aqueous medium under the experimental conditions. The ternary complex formation was found to occur in a stepwise manner. The stability constants of these binary and ternary systems were calculated. The order of stability of the ternary complexes in terms of the nature of hydroxamic acid, amino acid, nucleic acid component and metal ions was investigated and discussed as well as the values of log K and log X for the ternary systems. The concentration distribution of the various complex species in solution was evaluated. In addition, evaluation of the effect of temperature of the medium on the stability of the ternary system M^III – benzohydroxamic acid – L-histidine or adenine (M^III=Fe^III, Al^III, and Cr^III) has been studied. The thermodynamic parameters were calculated and discussed.