Effect of temperature on volumetric and isentropic compressibility of glycine in aqueous KCl/NaCl solutions

Density (ρ) and ultrasonic velocity (u) values of glycine in 1.0 M aqueous KCl and 1.0 M aqueous NaCl solutions have been measured as a function of amino acids concentration at T = (298.15, 303.15, 308.15, 313.15, 318.15 and 323.15) K. Using the ρ and u data, the thermodynamic parameters such as partial molal volume (φ{symbol}⁰_v), isentropic compressibility (κ_s), change in isentropic compressibility (Δκ_s), relative change (Δκ_s/κ₀) in isentropic compressibility and partial molal isentropic compressibility (φ{symbol}⁰_k), values have been computed. The increase in partial molal volume with temperature is attributed to the volume expansion of hydrated zwitterions. The φ{symbol}⁰_v and φ{symbol}⁰_k values of glycine in 1.0 M aqueous KCl and NaCl solutions are larger than the corresponding values in water. The larger partial molal volumes of glycine in 1.0 M aqueous KCl and NaCl is ascribed to the formation of 'zwitterion-K⁺/Na⁺/Cl^-' and 'K⁺/Na⁺/Cl^--water dipole' aggregates in solutions. The variation of κ_s, Δκ_s and Δκ_s/κ₀ with amino acid/zwitterions concentration and temperature is discussed in terms of zwitterions-ions, zwitterions-water dipoles, ion-ion, ion-water dipoles due to intermolecular/interionic interactions occurring in the systems.