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

Solution equilibria of the ternary systems Ni(II)-picolinic acid (Hpic) and the amino acids aspartic acid (H(2)asp), glutamic acid (H(2)glu), cysteine (H(2)cys) and histidine (Hhis), where the amino acids are denoted as H (i) L, have been studied pH-metrically. The formation constants of the resulting mixed ligand complexes have been determined at 25 A degrees C using a ionic strength 1.0 mol center dot dm(-3) NaCl. In the Ni(II)-Hpic-H(2)asp and Ni(II)-Hpic-H(2)glu 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-H(2)cys 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.