Thermodynamics of mixing of sodium naproxen and procaine hydrochloride in ethanol + water cosolvent mixtures

thermodynamic functions gibbs energy, enthalpy, and entropy of mixing of sodium naproxen and procaine hydrochloride were evaluated. mixing quantities were calculated based on fusion calorimetric values obtained from differential scanning calorimetry measurements and equilibrium solubility values reported in the literature for both drugs in ethanol + water mixtures. by means of enthalpy-entropy compensation analysis, non-linear δh°mix vs. δg°mix plots were obtained which indicates different mechanisms involved in the dissolution of these drugs according to mixtures composition. nevertheless, the molecular and ionic events involved in the dissolution of this drug in this cosolvent system are unclear.