Der Pharma Chemica
Journal for Medicinal Chemistry, Pharmaceutical Chemistry and Computational Chemistry


Influence of Dielectric Constant on Complex Equilibria of L- dopa Complexes of Toxic Metal ions

Author(s): N. Padmaja and G. NageswaraRao

Binary complexes of L-dopa with toxic metal ions such as Pb(II), Cd(II) and Hg(II) have been studied in 0.0-60.0% v/v 1,4 dioxan-water media at 303 K and an ionic strength of 0.16 mol dm- 3. The active forms of the ligand are LH3 +, LH2 and LH-. The best fit chemical models are arrived at based on firm statistical grounds employing crystallographic R-factor, χ 2, Skewness and Kurtosis. The predominant species formed are MLH+, ML2H2 and ML2H-. The stability constants of the binary systems decrease in the order Hg(II) > Cd(II) > Pb(II). The trend in variation of complex stability constants with change in the dielectric constant of the medium is explained on the basis of electrostatic and non-electrostatic forces. The species distribution with pH at different compositions of dioxan-water mixtures and plausible equilibria for their formation are also presented. The chemical speciation and bioavailability of the toxic metal ions is also described.

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