Interactions of glycine with polyethylene glycol studied by measurements of density and ultrasound speed in aqueous solutions at various temperatures

Density and ultrasound speed were measured accurately for binary glycine–water and ternary glycine–water–polyethylene glycol 400 (PEG400) solutions at (293.15, 298.15, 303.15 and 308.15) K. The data were used in evaluating thermodynamic properties as apparent molar volumes (V∅) and apparent molar isentropic compressions (KSΦ) of glycine in water and in PEG400 solutions. Infinite dilution values of these parameters, V∅o, and KSΦo, were obtained from their plots as a function of molality and have been utilized in obtaining transfer volumes and transfer compressions of glycine from water to PEG400 solutions of various molalities. Apparent molar isobaric expansions were determined from the temperature dependence of V∅ and V∅o values. All the results were interpreted in terms of glycine–water and glycine–water–PEG400 interactions. The partial hydrophobic character of PEG400 structure was found to play an important role in determining the transfer properties.