Thermochemical investigation of L-glutamine dissolution processes in aqueous co-solvent mixtures of acetonitrile, dioxane, acetone and dimethyl sulfoxide at T = 298.15 K

Abstract

This article reports on the results of calorimetric studies of the processes of L-glutamine dissolution in some aqueous-organic mixtures, namely (H2O + acetonitrile), (H2O + 1,4-dioxane), (H2O + acetone) and (H2O + dimethyl sulfoxide) at T = 298.15 K and mole fractions of an organic solvent up to x2 ~ 0.25. The standard values of solution (ΔsolH°) and transfer (ΔtrH°) enthalpies of L-glutamine from water to a mixed solvent as well as the enthalpic coefficients of pair-wise interactions (hxy) were calculated. The interrelation between enthalpic characteristics of L-glutamine dissolution (transfer) and the composition of water-organic mixtures was determined. It is found that the values of hxy are correlated with some physicochemical properties of different organic solvents. Contributions of the organic solvent properties (molar volume, cohesion energy density, polarity/polarizability, acidity, and basicity) to the energy of pair-wise interactions of L-glutamine - organic solvent were estimated quantitatively using of a modified Kamlet-Taft equation. The parameters of pair-wise interactions were additionally used to assess the contributions of the side chains of several L-amino acids to the energy of the intermolecular interactions amino acid-organic co-solvent in aqueous solutions.