Study of thermodynamic properties of aqueous binary mixtures of L-threonine, L-valine and L-arginine at low temperatures (T/K=275.15, 279.15 and 283.15)

The experimental values of density (rho) and speed of sound (u) in aqueous solutions of L-threonine, L-valine and L-arginine are reported at T = (275.15, 279.15 and 283.15) K. The derived parameters, apparent molar volume of solute (V-phi), isentropic compressibility (k(S)) of solution, apparent molar compressibility of solute (k(phi)) in dilute aqueous solutions of L-threonine, L-valine and L-arginine have been computed using values of density (rho) and speed of sound (u). The limiting values of apparent molar volume of solute (V-phi(0)), apparent molar isentropic compressibility of solute (k(phi)(0)) and apparent molar expansivity (phi(0)(E)) are also obtained. The results are discussed in the light of solute-solvent interactions, and structure making and structure breaking abilities of the solute in aqueous medium. From the results obtained for d phi(0)(E)/dT, it has been observed that L-threonine behaves as a structure maker, whereas L-valine and L-arginine act as structure breakers when dissolved in water at temperatures studied in present work. (C) 2012 Elsevier Ltd. All rights reserved.