Comparative studies on the complex-formation equilibria of mercury(II) with acetylcysteine and captopril

The complex-formation equilibria of mercury(II) with acetylcysteine and cap topril have been studied by pH-metric and liquid-liquid extraction methods applying dithizone as a competitive ligand during the latter measurements. The stability constants of three differently protonated Hg(II)/ligand 1:2 c omplexes of extreme stability have been determined by the combination of ex traction and pH-metric data. The formation of the less stabil Hg(II)-ligand 1:3 complexes with the coord ination of three sulfhydrilate groups has been followed and the values of b eta(130)/beta(120) determined from potentiometric measurements. The differences in the Hg(II) complex formation and protonation equilibria between the two ligands and the possible binding sites in the complexes hav e been discussed.