Speciation of binary complexes of Co(II), Ni(II), and Cu(II) with L-phenylalanine (Phe) in the presence of water-anionic surfactant mixtures in the concentration range of 0.0-2.5% w/v SLS has been studied pH-metrically at a temperature of 303 K and at an ionic strength of 0.16 mol L −1. The selection of best fit chemical models is based on statistical parameters and residual analysis. The predominant species detected were ML, ML 2 , and ML 2 H 2 for Co(II), Ni(II), and Cu(II). The trend in the variation of stability constants with the mole fraction of SLS was explained on the basis of electrostatic and non-electrostatic forces. Distribution of the species with pH at different compositions of SLS-water media was also presented.

Chemical speciation of binary complexes of Pb(II) and Cd(II) ions with maleic acid have been studied pH metrically in the concentration range of 0-50% v/v ethylene glycol (EG)-water mixtures maintaining an ionic strength of 0.16 molL −1 at 303 K. Alkalimetric titrations were carried out in different relative concentrations of metal and maleic acid. 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 ML 2 , ML 3 , and ML 2 H for Pb(II) and Cd(II). The chemical speciation, metal bioavailability, and transportation are explained based on the distribution diagrams.

Knowledge of the protonation constants of dipeptides is important and necessary for complete understanding of their physiochemical behavior. The effect of dielectric constant of medium on protonation equilibria has been studied by determining protonation constants of glycylglycine pH-metrically in various concentrations (0-60%v/v) of acetonitrile-water and ethylene glycol-water mixtures, at an ionic strength of 0.16 mol L −1 and at 303.0 ± 0.1 K. The protonation constants were calculated with the computer program MINIQUAD75 and selection of the best fit chemical models is based on the statistical parameters. Linear and non-linear variations of stepwise protonation constants with reciprocal of dielectric constant of the solvent mixtures have been attributed to the dominance of electrostatic and non-electrostatic forces, respectively. Distribution of species, protonation equilibria, and effect of influential parameters on the protonation constants have also been presented.

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