Solvation behavior of glycine and glycyl dipeptide in aqueous 1-butyl-3-methylimidazolium bromide ionic liquid solutions at different temperatures

Abstract

Densities and speeds of sound of glycine and glycyl dipeptide (glycylglycine) in aqueous 1-butyl-3 methylimidazolium bromide, [C4mim][Br] solutions have been measured at T=(288.15, 298.15 and 308.15) K. From the experimental data of density and speed of sound, the apparent molar volumes (Vϕ), apparent molar volumes at infinite dilution (Vϕ0), apparent molar isentropic compression (Kϕ,s) and apparent molar isentropic compression at infinite dilution (Kϕ,S0) have also been determined. Further, the partial molar volumes of transfer (ΔtrVϕ0) and partial molar isentropic compression of transfer (ΔtrKϕ,S0) of glycine and glycyl dipeptide from water to aqueous [C4mim][Br] solutions were calculated to enlighten the interactions such as solute–solute, solute–solvent and solvent–solvent present in these solutions. The apparent molar expansivity (Eϕ0), Hepler's constant values ∂Eϕ0∂TP,thermal expansion coefficient (α) and hydration number (nH) have been evaluated to assist the interpretations earned from the volumetric and acoustic analysis. The Hepler's constant values were found negative for glycine and glycyl dipeptide at all concentrations of ionic liquid except at lower concentration with glycyl dipeptide. The negative sign indicates the co-solutes act a structure breaker.