Formation constants for the ternary complexes of vanadium(III), 8-hidroxyquinoline, and the amino acids histidine, cysteine, aspartic and glutamic acids

Solution equilibria of V(III)-8-hydroxyquinoline (H8HQ) and aspartic acid (H2Asp), glutamic acid (H2Glu), cysteine (H2Cys) and histidine (HHis) ternary systems, have been studied through potentiometric measurements. The formation constants of the resulting mixed ligand complexes at 25 °C were calculated using 3.0 mol·dm− 3 KCl ionic strength. The species distribution diagrams for the complexes in solution were generated considering the formation of the [V(8HQ)(H2Asp)]2 + and V(8HQ)(Asp) complexes in the vanadium(III)-H8HQ-H2Asp system. Several species were observed: [V(8HQ)(HGlu)]+, V(8HQ)(Glu) and [V(8HQ)(Glu)(OH)]− in the vanadium(III)-H8HQ-H2Glu system; species; [V(8HQ)(H2Cys)]2 +, [V(8HQ)(HCys)]+, V(8HQ)(Cys) and [V(8HQ)(Cys)(OH)]− for the vanadium(III)-H8HQ-H2Cys system, and the complexes [V(H8HQ)(HHis)]4 + and [V(8HQ)(His)]+ in the vanadium(III)-H8HQ-HHis system.