Speciation of binary complexes of Ca(II), Mg(II) and Zn(II) with L-dopa in dioxane–water mixtures

Abstract

Speciation of binary complexes of Ca(II), Mg(II) and Zn(II) with L-3,4-dihydroxyphenylalanine (dopa) in (0–60% v/v) dioxane (DOX)–water mixtures have been studied pH-metrically at a temperature of 303 K and at an ionic strength of 0.16mol L−1. The models for binary species contain MLH, ML2H2, ML2H and ML2 for Ca(II) and Mg(II) and MLH, ML, ML2H2, ML2H and ML2 for Zn(II). The trend in the variation of stability constants with the mole fraction of dioxane was explained on the basis of electrostatic and non-electrostatic forces. Distribution of the species with pH at different compositions of DOX-water media was also presented.