Dissociation functions of glycine and β-alanine in propan-2-olwater mixtures at various temperatures and their thermodynamical analysis

Abstract

The dissociation constants of glycine and β-alanine by carboxylic, p K 1, and amino, p K 2, groups have been determined in propan-2-ol-water mixtures with the alcohol content 0, 20, 40, 60, 80% wt by galvanic cells without liquid junction in the temperature range 278.15–318.15 K (with interval of 5 K) for glycine and 278.15–328.15 K (with interval of 10 K) for β-alanine. The ionic product p K s m in the propan-2-ol-water system in the temperature range 278.15–328.15 K has been evaluated using literary data. The standard thermodynamic functions of dissociation of amino acids by carboxylic and amino groups have been calculated. The transfer Gibbs energy of the α-amino acid ionic forms: protonated (H 2Z +) and deprotonated (Z −), in methanol-water, ethanol-water and propan-2-ol-water systems at 298.15 K have been obtained. The character of ΔG t 0(H 2Z −), ΔG t 0(HZ ±), ΔG t 0(Z −) dependencies from physicochemical parameters of the solvent: 1 ϵ , E T N, B KT, density of the cohesion energy E coh, has been analyzed. The splitting of the ΔG d,1 0, ΔG d,2 0 values into the contributions of short- and long-range interactions have been carried out in the consideration of borders of the ionic association area. The short-range contribution in Gibbs energy of dissociation predominates.