Abstract
Complexes of the divalent metal ions, Ca2+ and Zn2+ with the bio-relevant alpha-amino acids, L-cysteine and glycine were investigated by means of the potentiometric technique. The dissociation constants of the bio-ligands were determined and used for determining the stability constants of their binary and ternary complexes formed in aqueous solutions at 25 +/- 0.1 degrees C and constant ionic strength of 0.20 mol center dot dm(-3) NaNO3. The acid-base properties of glycine were investigated at different ionic strengths, ranging from 0.01 to 0.30 mol center dot dm(-3) NaNO3 at 25.0 +/- 0.1 degrees C. The concentration distribution of the different glycine species formed in solution due to variation of pH was evaluated and discussed. The formation of the different 1:1 and 1:2 binary complexes and 1:1:1 ternary complexes were inferred from the potentiometric pH-metric titration curves. The ternary complex formation occurred in a stepwise manner with l-cysteine acting as the primary ligand. The stability constants of these binary and ternary complex systems were evaluated. The increment Delta log(10)K values, percentage of relative stabilization (%R.S.) and log(10)X for the ternary complexes were evaluated and are discussed.