Formation and confirmation of binary complexes of calcium(II), magnesium(II ) and zinc(II) with L-histidine in dioxan-water media

Abstract

A computer assisted pH-metric investigation has been carried out on the speciation of binary complexes of Ca(II), Mg(II) and Zn(II) with L-histidine. The titrations are carried out with sodium hydroxide in varying concentrations (0-60% v/v) of dioxan-water mixtures at an ionic strength of 0.16 mol L -1 and at a temperature of 303 K. Ca(II), Mg(II) and Zn(II) form the binary complexes of ML 2 H 4 , ML 2 H 3 , ML 2 H 2 , ML 2 H and ML 2 in dioxan-water mixtures. The effect of systematic errors in the concentrations of the substances on the stability constants is in the order acid > alkali > ligand > metal> Log F. The effect of solvent, dielectric constant of the medium and the electrostatic interactions between the complex species on the stability of the complexes are discussed.