Thermodynamic study of the solubility of sodium sulfadiazine in some ethanol + water cosolvent mixtures

Abstract

Sodium sulfadiazine (SD-Na) is a drug extensively used for the treatment of certain infections caused by several kinds of microorganisms. Although SD-Na is widely used nowadays in therapeutics, the physicochemical information about their aqueous solutions is not complete at present. In this context, by using the van't Hoff and Gibbs equations the thermodynamic functions Gibbs energy, enthalpy, and entropy of solution for SD-Na in ethanol + water cosolvent mixtures, are evaluated from solubility data determined at temperatures from 278.15 to 308.15 K. The drug solubility is greatest in neat water and lowest in neat ethanol at all the temperatures studied. This behavior shows the negative cosolvent effect for this electrolyte drug in this solvent system. By means of enthalpy-entropy compensation analysis, non-linear ΔHsoln0-app vs. ΔGsoln0-app plot with positive slope from neat ethanol up to 0.60 in mass fraction of water and negative from this composition to neat water is obtained; accordingly to this result, it follows that the dissolution process of this drug in ethanol-rich is entropy-driven, whereas, in water-rich mixtures the process is enthalpy-driven. Nevertheless, the molecular and ionic events involved in the dissolution of this drug in this cosolvent system are unclear.