Influence of Dielectric Constant on Protonation Equilibria of Phenylalanine and Maleic Acid in Ethylene Glycol-Water Mixtures

The influence of dielectric constant of medium on protonation equilibria has been studied by determining protonation constants of Phenylalanine and Maleic acid pH metrically in various concentrations (0-60 %v/v) of ethylene glycol-water mixtures, at an ionic strength of 0.16 mol L-1 and at 303.0 K. MINIQUAD75 computer program has been used for the calculation of protonation constants. Linear and non-linear variations of step-wise protonation constants with reciprocal of dielectric constant of the solvent mixtures have been attributed to the dominance of the electrostatic and non-electrostatic forces, respectively. The trend is explained on the basis of solute-solute and solute-solvent interactions, solvation, proton transfer processes and dielectric constants of the media.