Solute–Solvent Interactions of Amino Acids in Aqueous 1-Propyl-3-Methylimidazolium Bromide Ionic Liquid Solutions at 298.15 K

Abstract

Densities, viscosities, and refractive indices of three amino acids (glycine, L-alanine, and L-valine) in aqueous solutions of an ionic liquid, 1-propyl-3-methylimidazolium bromide, have been measured at 298.15 K. These data have been used to calculate apparent molar volumes (V _φ ), viscosity B-coefficients, and molar refractions of these mixtures. The standard partial molar volumes ($V_{\phi}^{0}$) and standard partial molar volumes of transfer ($\Delta_{\mathrm{tr}}V_{\phi}^{0}$) have been determined for these amino acid solutions from these density data. The resulting values of $V_{\phi}^{0}$ and $\Delta_{\mathrm{tr}}V_{\phi}^{0}$ for transfer of amino acids from water to aqueous ionic liquid solutions have been interpreted in terms of solute + solvent interactions. These data also indicate that hydrophobic interactions predominate in L-alanine and L-valine solutions. Linear correlations were found for both $V_{\phi}^{0}$ and the viscosity B-coefficient with the number of carbon atoms in the alkyl chain of the amino acids, and have been used to estimate the contribution of the charged end groups ($\mathrm{NH}_{3}^{+}$, COO⁻), the CH₂ group, and other alkyl chains of the amino acids. The viscosity and molar refractivity results have been used to confirm the conclusions obtained from volumetric properties.