Title : Thermodynamic properties of aqueous L-threonine-[BMIm][Cl] solutions
Abstract:
Amino acids as fundamental structural units of peptides and proteins have an important role in biological systems by affecting solubility, denaturation and activity of biomolecules [1-3]. Study of these effects on thermophysical properties of model compounds in the presence of electrolytes solutions provide information about solute-solvent and solute-solute interactions on biomolecules [4-5]. Ionic liquids (ILs) as organic electrolytes and green solvents are composed of an organic cation and an inorganic anion which are liquid at ambient conditions. In the past decade, extensive investigations showed that the use of ILs as reaction media for processes involving biologically relevant compounds is promising in view of their successful application in kinetic resolution, biocatalysis, biosynthesis, separation and purification processes [6]. The scope of this information is valuable to explore the interactions of amino acids in ILs. To reach this purpose, densities, ρ of L-threonine in water and in aqueous 1-butyl-3-methylimidazolium chloride, [BMIm][Cl] solutions of different molalities over the temperature range T = (288.15-318.15) K have been determined using vibrating-tube digital density meter (DMA 4500M, Anton Paar, Austria). The density data have been used to calculate the apparent molar volume, V_∅, partial molar volume, V_2^o and partial molar volumes of transfer, ?_tr V_2^o. The V_2^o values of L-threonine in aqueous [BMIm][Cl] solutions are higher than those in water and thus exhibit positive ?_tr V_2^o, which are indicative of strong interactions between L-threonine and [BMIm][Cl]. The volumetric interaction parameters, V_AB and V_ABB and hydration numbers, n_H have also been calculated to discuss the solute-solvent interactions occurring in these systems.
Keywords: L-threonine, 1-butyl-3-methylimidazolium chloride, Partial molar volume, Partial molar expansibilities, Hydration numbers.
