Equilibrium Studies of Binary and Ternary Complexes Involving Tricine and Some Selected a-Amino Acids

Abstract

The formation equilibria for the binary complexes of CoII, NiII, CuII, ZnII, CdII, MnII, PbII, ThIV, UO2 II, and CeIII with tricine and for the ternary complexes involving some α-amino acids (glycine, α-alanine, proline, serine, asparagine, and aspartic acid) were investigated using pH-metric technique. The formation of binary and ternary complexes was inferred from the pH-metric titration curves. It was deduced that tricine acts as a primary ligand in the ternary complexes involving the monocarboxylic amino acids (glycine, α-alanine, proline, serine, and asparagine), whereas it behaves as a secondary ligand in the ternary systems containing the dicarboxylic aspartic acid. The ternary complex formation was found to take place in a stepwise manner. The stability constants of the complexes formed in aqueous solutions were determined potentiometrically under the experimental conditions (t=25°C, I=0.1 mol dm−3 NaNO3). The order of stability of the ternary complexes in terms of the nature of the amino acids is investigated and discussed. The values of Δlog K for the ternary complexes have been evaluated and discussed. Evaluation of the effects of ionic strength and temperature of the medium on the stability of the ternary system M II-tricine-α-alanine (M II=CoII, NiII, and CuII) has been studied. The thermodynamic parameters were calculated and discussed.