Hydration properties of glycylglycine in aqueous ionic liquid solutions at different temperatures: Volumetric and acoustic approach

The apparent molar volume and isentropic compression of glycylglycine in aqueous 1-methylimidazolium chloride, [mim][Cl], 1-ethyl-3-methylimidazolium chloride [C2mim][Cl], and 1-methyl-3-octylimidazolium chloride [C8mim][Cl] solutions have been calculated from the measured experimental data on density and speed of sound at temperature, T = 288.15, 298.15 and 308.15 K. The apparent molar volumes at infinite dilution, Vϕ0 and the apparent isentropic molar compression at infinite dilution Kϕ , S0, were also calculated. Furthermore, apparent specific volumes, apparent molar expansivity, Eϕ0, Hepler's constant values, ∂ E ϕ 0 ∂ T P and hydration numbers, nH, have been evaluated to support the conclusions obtained from the volumetric and acoustic studies. The Hepler's constant values were found negative which indicating the peptide under study is predominantly a structure breaker due to hydrophobic hydration of small peptide in aqueous ionic liquid.