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

Raju Sala,Nageswara Rao Gollapalli,Ananda Kumar Bokka,Bharath Kumar Naik Kethavath

doi:10.4314/bcse.v26i2.6

Raju Sala, Nageswara Rao Gollapalli + Show 2 more

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https://doi.org/10.4314/bcse.v26i2.6

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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, ML 2 , ML 2 H, ML 2 H 2 and ML 2 H 4 for Co(II); ML 2 , ML 2 H, ML 2 H 2 and ML 2 H 4 for Ni(II); and MLH, ML 2 , ML 2 H and ML 2 H 2 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

Highlights

Classical curve-fitting methods that use the least-squares methods [1, 2] are applied to estimate the number of species simultaneously present at equilibrium, their stoichiometries, and their stability constants
The metal complexes can be more active than the free ligands and some side effects may decrease upon complexation
As the number of species increased, the models gave better statistics denoting the better fit. This indicates that the final model appropriately fits the experimental data. Such exhaustive modelling is performed on Co(II)histidine system in 10% dimethyl sulfoxide (DMSO)

Summary

Introduction

Classical curve-fitting methods that use the least-squares methods [1, 2] are applied to estimate the number of species simultaneously present at equilibrium, their stoichiometries, and their stability constants. Bioavailability of a particular metal depends on its complex chemical reactions of dissolution, binding and complexation with the constituents of the environmental aquatic phase [3]. The metal complexes can be more active than the free ligands and some side effects may decrease upon complexation. The complexes can exhibit bioactivities which are not shown by the free ligand. The mechanism of action can involve binding to a metal ion in vivo or the metal complex may be a vehicle for activation of the ligand as the cytotoxic agent. Coordination may lead to significant reduction of drug-resistance [4, 5]

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