Speciation of complexes of Co (II), Ni (II) and Cu (II) with L-histidine in dioxan-water mixtures

Abstract

L-Histidine complexes of Co (II), Ni (II) and Cu (II) metal ions were studied pH-metrically in 0-60% v/v dioxan-water mixtures at a temperature of 303 K and at an ionic strength of 0.16mol L -1. Exhaustive modeling was performed to identify the species present in the present systems. The models contain MLH, ML 2H 4, ML 2H 2, ML 2H and ML 2 for Co (II), ML 2H 4, ML 2H 2, ML 2H and ML 2 for Ni (II), and MLH, ML 2H 2, ML 2H and ML 2 for Cu (II). The appropriate experimental conditions were verified by introducing errors intentionally in the concentrations of ingredients. The trend in the variation of stability constants with the dielectric constants of dioxan is explained on the basis of electrostatic and non-electrostatic forces. The bioavailability of metals and their transportation are explained based on the distribution diagrams.