Formation of binary complexes of Co(II), Ni(II) and Cu(II) with L-DOPA in dioxan-water mixtures

Abstract

Complexation of essential metal ions with (S)-2-amino-3-(3,4-dihydroxyphenyl) propanoic acid (dopa) in (0-60% v/v) dioxan-water mixtures has been studied pH-metrically at a temperature of 303 K and an ionic strength of 0.16 M. The existence of different binary species was established from modeling studies using the computer program MINIQUAD75. The best-fit chemical models were selected based on statistical parameters like crystallographic R factor and sum of the squares of residuals in mass-balance equations. The models for binary complex systems contain the chemical species ML, ML₂, MLH, ML₂H and ML₂H₂ for Co(II), Ni(II) and Cu(II) in dioxan-water mixtures. The trend in the variation of stability constants with change in the mole fraction of the medium was explained based on electrostatic and non-electrostatic forces. Distribution of the species with pH at different compositions of dioxan-water mixtures was also presented.

KEY WORDS: Binary species, Stability constants, Metal, Dopa, Dioxan, pH-metry

Bull. Chem. Soc. Ethiop. 2011, 25(1), 43-52.