Solvent Effects on Tautomeric and Microscopic Protonation Constants of Glycine in Different Aqueous Solutions of 1,4-Dioxane

The acid-base equilibria of glycine have been studied in different aqueous solutions of 1,4-dioxane(0-50 % by v/v) using potentiometric method. In this study, the macro and micro protonationconstants of the amino acid and its tautomeric constant have been determined at 25 °C and constantionic strength 0.1 mol dm-3 (NaCl). The protonation and the tautomeric constants of glycine indifferent binary mixtures were analyzed in terms of Kamlet, Abboud and Taft (KAT) parameters.Single-parameter correlations of the constants versus α (hydrogen-bond donor acidity), β (hydrogenbondacceptor basicity) and π* (dipolarity/polarizability) are poor in all solutions. Multi-parametercorrelations show better results, but dual-parameter correlations represent significant improvementswith regard to the single- and multi-parameter models. Linear correlation is observed when theexperimental protonation constant values are plotted versus the calculated ones, while the KATparameters are considered. Finally, the results are discussed in terms of the effect of the solvent onprotonation and tautomeric constants.