Journal of Chemical Thermodynamics, Vol.98, 214-230, 2016
Solvation behavior of some amino acids in aqueous solutions of non-steroidal anti-inflammatory drug sodium ibuprofen at different temperatures analysed by volumetric and acoustic methods
Apparent molar volume (V-empty set), apparent molar isentropic compression (K-empty set,K-s) 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 (V-empty set(0)), apparent molar isentropic compression at infinite dilution (K-empty set,s(0)) and the experimental slopes (S-V) and (S-K) were obtained from Masson's equation. These values are used for calculating the number of water molecules hydrated (n(H)) to the amino acids. The structure-making/breaking ability of solutes was discussed using Hepler's Criterion. Transfer parameters (Delta V-empty set(0)) and (Delta K-empty set,s(0)) 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 (V-empty set(0)) 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 (V-empty set(0)). 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. (C) 2016 Elsevier Ltd. All rights reserved.
Keywords:Amino acids;Sodium ibuprofen (Na-IBP);Apparent molar volume;Hydration number;Co-sphere overlap model;Interaction coefficient