Speciation of L-aspartic acid complexes of Co(II), Ni(II), Cu(II) and Zn(II) in acetonitrile- and ethylene glycol-water mixtures

Abstract

Chemical speciation of binary complexes of Co(II), Ni(II), Cu(II) and Zn(II) with L-aspartic acid was investigated pH-metrically in acetonitrile- and ethylene glycol-water mixtures. The stability constants were calculated using the computer program MINIQUAD75. The best-fit chemical models were selected based on statistical parameters and residual analysis. The models for the binary species contained ML₂H₂, ML₂H and ML₂ for Co(II) and Zn(II), ML, ML₂H₂ and ML₂ for Ni(II) and Cu(II) in acetonitrile- and ethylene glycol-water mixtures. The trend in variation of stability constants with change in the dielectric constant of the medium was explained on the basis of electrostatic and non-electrostatic forces. Distribution of the species with pH at different variations (0.0-60.0% v/v) in acetonitrile- and ethylene glycol-water mixtures was also presented.

KEY WORDS: Complex equilibria, L-Aspartic acid, Acetonitrile, Ethylene glycol, MINIQUAD75

Bull. Chem. Soc. Ethiop. 2012, 26(2), 239-247.

DOI: http://dx.doi.org/10.4314/bcse.v26i2.7