Study of the interaction between ethanol and natural amino acids containing ionic side groups in water at T = 298.15 K

Abstract

The enthalpies of solution of L-a-aspartic acid, L-a-glutamic acid, L-a-arginine, L-a-lysine, and L-a-histidine have been measured in aqueous ethanol solutions at 298.15 K. From the obtained experimental results, the standard enthalpies of solution of amino acids in waterethanol solutions have been determined. These data were used to calculate the heterogeneous enthalpic pair interaction coefficients based on McMillan-Mayer's formalism. These values were interpreted in the terms of the ionic or no polar effect of the side chains of L-a-amino acids on their interactions with a molecule of ethanol in water. Keywords L-a-Amino acids Á Ethanol Á Aqueous solution Á Enthalpies of solution Á Enthalpic pair interaction coefficients List of symbols h A,EtOH The heterogeneous enthalpic pair interaction coefficient between zwit terions of amino acids and ethanol molecule h A,EtOH,EtOH The enthalpic triplet interaction coef ficient D sol H 1 m ðWÞ Standard enthalpies of solution of L-a-amino acids in water (W) D sol H 1 m ðW þ EtOHÞ Standard solution enthalpies of the La-amino acids (A) in ethanol (EtOH) and water (W) mixtures m EtOH Molal concentration of ethanol in water (mol kg-1

Temperature Dependences and Enthalpic Discrimination of Homochiral Pairwise Interactions of Six α-Amino Acid Enantiomers in Pure Water

“…The enthalpic pairwise interaction coefficient is the interaction energy between a pair of solute molecules when they approach each other from infinite distance in dilute solutions, accompanying the contribution from rearrangement of solvent molecules in solvation shells. 44,45 The sign and magnitude of h xx are determined by the competitive balance of all contributions from different interaction factors, mainly including (i) the direct solute−solute interactions caused by the short-range intermolecular forces, (ii) the restructuring of partial solvent molecules arising from the overlapping of solvation shells of solutes, and (iii) the change of solute−solvent interactions, etc. 46−48 Therefore, the h xx coefficient is sensitive to the structural alteration of solutes and the perturbations of environmental factors such as medium, temperature, pressure, etc.…”

“…The enthalpic pairwise interaction coefficient is the interaction energy between a pair of solute molecules when they approach each other from infinite distance in dilute solutions, accompanying the contribution from rearrangement of solvent molecules in solvation shells. , The sign and magnitude of h xx are determined by the competitive balance of all contributions from different interaction factors, mainly including (i) the direct solute–solute interactions caused by the short-range intermolecular forces, (ii) the restructuring of partial solvent molecules arising from the overlapping of solvation shells of solutes, and (iii) the change of solute–solvent interactions, etc. − Therefore, the h xx coefficient is sensitive to the structural alteration of solutes and the perturbations of environmental factors such as medium, temperature, pressure, etc. − Quantitatively, solute–solute interactions characterized by homotactic or heterotactic enthalpic pairwise coefficients ( h xx or h xy ) can be analyzed by considering the additivity of functional groups (or moieties) in solute molecules, which was first formulated by Savage and Wood and known as the SWAG additivity principle . According to the SWAG approach, the features of the second virial coefficients of thermodynamic functions between groups (or moieties) in a pair of interacting solute molecules can be generally classified as follows. , …”