Effect of dielectric constant of medium on chemical speciation of L-histidine complexes of Co(II), Ni(II) and Cu(II)

Abstract

Chemical speciation of binary complexes of Co(II), Ni(II) and Cu(II) ions with L-histidine have been studied pH metrically in the concentration range of 0–60% v/v DMSO-water mixtures maintaining an ionic strength of 0.16 M at 303 K. Alkalimetric titrations were carried out in different relative concentrations of metal and histidine. Stability constants of various models of binary complexes were refined with MINIQUAD75. The best-fit chemical models were selected based on statistical parameters and residual analysis. The species detected are MLH, ML­₂, ML₂H, ML₂H₂ and ML₂H₄ for Co(II); ML­₂, ML₂H, ML₂H₂ and ML₂H₄ for Ni(II); and MLH, ML₂, ML₂H and ML₂H₂ for Cu(II). The chemical speciation, metal bioavailability and transportation are explained based on the distribution diagrams.

KEY WORDS: L-Histidine, Chemical speciation, Essential metals, Binary complexes, Bioavailability, DMSO

Bull. Chem. Soc. Ethiop. 2012, 26(2), 227-238.

DOI: http://dx.doi.org/10.4314/bcse.v26i2.6