Potentiometric studies on the binary and ternary complexes of copper(II) containing dipicolinic acid and amino acids

The binary and ternary complexes of Cu(II) with dipicolinic acid as a primary ligand and some selected mono- and dicarboxylic amino acids as biologically important secondary ligands were studied potentiometrically. The acidity constants of the ligands were measured and used for determining the stability constants of the complexes formed in aqueous solutions at different temperatures at an ionic strength of 0.1 mol dm(-3) NaNO3. The formation of 1:1:1 ternary complexes is inferred from the potentiometric titration curves. The order of stability of the binary or ternary complexes in terms of the nature of the amino acid is investigated and discussed. The values of Delta log K for the binary and ternary complexes involving amino acids have been evaluated along with the thermodynamic parameters Delta H degrees, Delta S degrees, and Delta G degrees.