Solution Equilibria of Ternary Systems Involving Nickel(II) Ion, Picolinic Acid, and the Amino Acids Histidine, Cysteine, Aspartic and Glutamic Acids

Abstract

Solution equilibria of the ternary systems Ni(II)–picolinic acid (Hpic) and the amino acids aspartic acid (H2asp), glutamic acid (H2glu), cysteine (H2cys) and histidine (Hhis), where the amino acids are denoted as HiL, have been studied pH-metrically. The formation constants of the resulting mixed ligand complexes have been determined at 25 °C using a ionic strength 1.0 mol·dm−3 NaCl. In the Ni(II)–Hpic–H2asp and Ni(II)–Hpic–H2glu systems, the complexes [Ni(pic)H2L]+, Ni(pic)HL, [Ni(pic)L]− and [Ni(pic)L(OH)]2− were detected. In the Ni(II)–Hpic–H2cys system the complexes [Ni(pic)H2L]+ and [Ni(pic)L]− are present. Additionally, in the Ni(II)–Hpic–Hhis system the species [Ni(Hpic)HL]2+, Ni(pic)L and [Ni(pic)L(OH)]− were identified. The species distribution diagrams as functions of pH are briefly discussed.