Speciation of ternary complexes of L-histidine and L-glutamic acid with some toxic metal ions in polar medium

Formation of ternary complexes of Pb-II, Cd-II and Hg-II ions with L-histidine and L-glutamic acid was studied pH metrically in the concentration range of 0-60% v/v DMSO-water mixtures maintaining an ionic strength of 0.16 mol L-1 at 303.0 K. Alkalimetric titrations were carried out in different concentrations of metal (M = Pb-II, Cd-II and Hg-II) to histidine (L) to glutamic acid (X). Stability constants of ternary complexes were calculated and various models were refined with MINIQUAD75. The best fit chemical models were selected based on statistical parameters and residual analysis. The species detected are M(LH2)(XH), M(LH)(2)(XH) and M(L)(LH)(XH), for Pb-II and Cd-II, and M(LH2)(XH) for Hg-II. The chemical speciation, metal bioavailability and transportation are explained based on the stability constants.