Solubility, Dissolution Thermodynamics and Preferential Solvation of Meloxicam in (Methanol + Water) Mixtures

Solubility of meloxicam in {methanol + water} mixtures from 293.15 to 313.15 K has been determined and correlated by means of the Jouyban–Acree model. By using the van’t Hoff and Gibbs equations the respective apparent thermodynamic quantities for the dissolution and mixing processes, namely Gibbs energy, enthalpy, and entropy, were calculated. A non-linear enthalpy–entropy relationship was observed in the plot of enthalpy vs. Gibbs energy exhibiting negative but variable slopes in the composition region 0.00 < x1 < 0.60 and variable negative and positive slopes in the other mixtures. Based on the inverse Kirkwood–Buff integrals it follows that meloxicam is preferentially solvated by water molecules in water-rich mixtures but preferentially solvated by methanol molecules in mixtures 0.31 < x1 < 1.00.