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, 2-propanol, acetonitrile, 1,4-dioxane, acetone, and dimethyl sulfoxide were measured by isothermal calorimetry at T = 298.15 K. Corresponding enthalpies of solvation (Δ_solvH°) were determined by combining the obtained values (Δ_solH°) with the standard enthalpies (Δ_subH°) 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_trH°) from water in admixture with them. A comparative analysis of changes in the transfer enthalpies of glycyl-l-alanine, glycyl-glycine 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.