Thermodynamics Research Center / ThermoML | Journal of Chemical Thermodynamics

ABSTRACT

Apparent molar volume, apparent molar isentropic compression of glycine, L-alanine and L-valine in binary aqueous solutions of (0.05, 0.15, 0.25 and 0.35) mol kg 1 sodium ibuprofen (Na-IBP) have been determined at temperatures (288.15, 293.15, 298.15, 303.15 and 308.15) K from density and ultrasonic speed measurements. Apparent molar volume at infinite dilution, apparent molar isentropic compression at infinite dilution and the experimental slopes were obtained from Masson's equation. These values are used for calculating the number of water molecules hydrated to the amino acids. The structure-making/breaking ability of solutes was discussed using Hepler s Criterion. Transfer parameters at infinite dilution from aqueous to aqueous Na-IBP solutions have been calculated and were interpreted in terms of hydrophilic hydrophilic, hydrophilic hydrophobic and hydrophobic hydrophobic interactions on the basis of co-sphere overlap model. The linear correction of V0 for a homologous series of amino acids has been utilized to calculate to contribution of the charged end groups (NH3+ ;COO-), (CH2) groups, and the other alkyl chain of the amino acids to V0. The pair and triplet interaction coefficients have also been calculated from both the properties. The volume and compression data suggest that hydrophilic hydrophilic interactions are predominant in these systems. It is inferred that the effect of Na-IBP on protein stability need not be necessarily due to preferential hydration, it can also interact with the hydrophilic groups of the constituents of proteins affecting its stability.