Thermodynamic study of the solubility of ibuprofen and naproxen in some ethanol + propylene glycol mixtures

By using the Gibbs and van’t Hoff equations the thermodynamic functions Gibbs free energy, enthalpy, and entropy of solution, mixing and solvation of ibuprofen (IBP) and naproxen (NAP), in some ethanol (EtOH) + propylene glycol (PG) cosolvent mixtures, were evaluated from both drugs solubility values determined at several temperatures. The drugs solubility was greater in pure EtOH and lower in PG in almost all the cases studied. The solvation of these drugs was almost constant in all the cosolvent mixtures tested. By means of enthalpy–entropy compensation analysis, non-linear ΔHsoln°ΔHsoln° vs. ΔGsoln°ΔGsoln° compensation plots with positive and negative slopes were obtained for IBP and NAP, respectively. These behaviors are probably due to the increase in solvation of IBP by EtOH molecules; whereas in the NAP case, it is probably due to the solvent-structure loosing.