L-Tryptophan with Ca (II), Mg (II) and Zn (II) in Acetonitrile-Water Mixtures

Abstract

Speciation of binary complexes of Ca(II), Mg(II) and Zn(II)with L-Serine and L-Tryptophan  in (0-50% v/v) (Acetonitrile)-Water mixture has been studied pH-metrically at a temperature of 303 K and at an ionic strength of 0.16 mol. The models for binary species contain  ML₂H₂, ML₂H and ML₂ for Ca(II), Mg(II) and Zn(II). The trend in the variation of stability constants with the mole fraction of Acetonitrile was explained on the basis of electrostatic and non-electrostatic forces. The stability constants have been calculated with the computer program MINIQUAD 75 and are selected based on statistical parameters. The best fit chemical models of the protonation equilibria were based on crystallographic R-factor, χ2, skewness and kurtosis. All the stability constants of L- Serine and L- Tryptophan increase with increasing Acetonitrile content. This is attributed to the dielectric constant of the medium Distribution of the species with pH at different compositions of Acetonitrile-Water media was also presented.