Solvent effect on protonation equilibria of l-cysteine and l-threonine in aqueous solutions of ctab-water mixtures

The protonation constants of L-Cysteine and L-Threonine have been studied pH metrically in various concentrations (0.0-2.50% v/v) of CTAB- water mixtures maintaining an ionic strength of 0.16 mol L-1 at 303.0 K. The protonation constants have been calculated with the computer program MINIQUAD75 and the best fit chemical models are selected based on statistical parameters. Linear variation of step-wise protonation constants (log K) with reciprocal of dielectric constant of the solvent mixture has been attributed to the dominance of the electrostatic forces.