Stability of nickel(II) binary and ternary complexes with dipicolinic acid and the amino acids serine, threonine, methionine and phenylalanine

Binary and ternary complexes of nickel(II) with dipicolinic acid (H2dipic) and the amino acids serine (Hser), threonine (Hthr), methionine (Hmet) and phenylalanine (Hphe), have been investigated in aqueous solutions at a 1.0 mol·dm− 3 NaCl ionic strength and 25 °C. The types of complexes formed and their overall stability constants were established on the basis of computer analysis of potentiometric results using the least-squared program LETAGROP. In the Ni(II)-amino acid (HL) systems the complexes [NiL]+, NiL2 and [NiL3]− were detected. In the ternary systems only the heteroligand complexes Ni(dipic)(HL), [Ni(dipic)(L)]− and [Ni(dipic)(L)(OH)]2 − were observed. The species distribution diagrams as functions of pH are briefly discussed.