Binary and ternary nickel (II) complexes with 2-methylquinoline-8-carboxylic acid and some amino acids

In this work, the ligand 2-methylquinoline-8-carboxylic acid (HL) was prepared using a modification of a previous protocol, and its protonation constants were studied. The stability constants of the binary nickel (II) – ligand L and the ternary nickel (II) – ligand L – amino acids (B) systems were investigated. The amino acids selected for this study were glycine (Gly), α-alanine (αAla), β-alanine (βAla), proline (Pro), serine (Ser), methionine (Met), threonine (Thr), phenylalanine (Phe), aspartic acid (Asp), glutamic acid (Glu), histidine (His) and cysteine (Cys). The stability constants were pH-metrically measured in 1.0 mol dm−3 NaCl at 25°C. The least squares program LETAGROP was used for the analysis of the potentiometric data. Species distribution diagrams as a function of pH are briefly discussed.