Interactions of 1-butyl-2,3-dimethylimidazolium bromide ionic liquid with glycine, l-alanine and l-valine: A volumetric and NMR spectroscopic study

The densities of glycine, l-alanine and l-valine in aqueous and aqueous solutions of 1-butyl-2,3-dimethylimidazolium bromide [BMMIm]Br have been determined at (283.15, 288.15, 293.15, 298.15 and 303.15) K and atmospheric pressure. The apparent molar volumes, standard partial molar volumes, standard partial molar volume of transfer and hydration numbers have been calculated. The values of standard partial molar volume of transfer for three amino acids are negative at all temperatures studied. The values of standard partial molar volume of transfer become more negative with the increase of hydrophobicity of the amino acid side-chains. These volumetric parameters are interpreted in terms of various mixing effects between amino acids and [BMMIm]Br in aqueous solutions. Furthermore, the 1H NMR measurements of binary mixtures of amino acids and [BMMIm]Br dissolved in D2O have been carried out. The influence in electron density around the protons of [BMMIm]Br followed the order: l-valine > l-alanine > glycine. The results were interpreted on possible molecular interactions between the intrinsic hydrophilicity/hydrophobicity of amino acid side-chains and [BMMIm]Br.