Thermodynamic quantities relative to solution processes of Naproxen in aqueous media at pH 1.2 and 7.4

Abstract

Based on van’t Hoff and Gibbs equations, the thermodynamic functions Gibbs free energy, enthalpy, and entropy of solution, mixing and solvation of naproxen (NAP) in water at pH 1.2 and 7.4, were evaluated from solubility values determined at several temperatures. The solubility at pH 7.4 and 25.0°C was almost 150 times higher with respect to pH 1.2. The enthalpies of solution were positive and greater for pH 1.2, while the entropies of solution were both negative, thereby implying a greater molecular organization at pH 7.4. The results were discussed in terms of solute–solvent interactions.