Keywords: ternary complex systems, divalent metal ions, l-cysteine and diphenylamine ligands, aqueous media
Summary:Abstract Ternary Complex formation of the divalent metal ions, Zn2+ and Ca2+ with the bio- relevant amino acid, L-Cysteine and the nitrogen-containing diphenylamine ligand were investigated by means of the potentiometric technique at 25 oC and I= 0.20 mol•dm-3 NaNO3. The acid-base properties of the L-Cysteine bio-ligand were investigated at different ionic strength. The dissociation constants of L-Cysteine and diphenylamine were determined and used for determining the stability constants of the binary and ternary complexes formed in the aqueous media under the above- mentioned experimental conditions. 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 systems were calculated. The values of ∆ log10 K, percentage of relative stabilization, %R.S. and log10 X for the ternary systems were evaluated and discussed. The concentration distribution of the L-Cysteine species formed in solution was evaluated. The mechanism of ternary complexes formed was discussed.