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

Abstract Binary and ternary complexes of nickel(II) with dipicolinic acid (H 2 dipic) 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] + , NiL 2 and [NiL 3 ] − 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.