Features of the Solvation of Glycyl-l-alanine in Various Aqueous–Organic Mixtures at T = 298.15 K

Abstract

In the present work, an assessment of the processes of glycyl-L-alanine solvation is given when the nature of an aqueous− organic mixture changes. For this purpose, the enthalpies of the glycyl-L-alanine dissolution in aqueous solutions of ethanol, 1-propanol, 2propanol, acetonitrile, 1,4-dioxane, acetone, and dimethyl sulfoxide were measured by isothermal calorimetry at T = 298.15 K. Corresponding enthalpies of solvation (Δ solv H°) were determined by combining the obtained values (Δ sol H°) with the standard enthalpies (Δ sub H°) of glycyl-L-alanine sublimation. In addition, we derived the enthalpic coefficients of the pairwise interactions (h xy ) between glycyl-L-alanine and organic solvent molecules, as well as the transfer enthalpies (Δ tr H°) from water in admixture with them. A comparative analysis of changes in the transfer enthalpies of glycyl-L-alanine, glycylglycine and glycyl-L-tyrosine from water to similar water−organic mixtures is presented. The modified Kamlet−Taft equation was used to quantify the contribution of some physicochemical properties of organic solvents (polarity/polarizability, cohesion energy density, basicity, and acidity) to the energy of intermolecular interactions of glycyl-L-alanine−cosolvent.