Speciation of ternary complexes of lead(II), cadmium(II) and mercury(II) with L-dopa and phenanthroline in propanediol-water mixtures

The formation constants of ternary complexes of title systems have been determined pH-metrically in biologically relevant conditions at an ionic strength of 0.16 mol dm(-3) and 303 K. The overall stability constants have been evaluated using MINIQUAD75 computer program. The complexation equilibria have been derived on the basis of species distribution diagram. In the present study L-Dopa and 1, 10-phenanthroline are found to be compatible ligands, proving greater stability of ternary complexes as compared to binary ones. The trend in variation of stability constants with change in dielectric constant of medium is explained on the basis of electrostatic and non-electrostatic forces. Distributions of the species with pH at different compositions of propanediol water mixtures are also presented. The factors responsible for the compatibility of both the ligands have also been discussed.