Dissolution thermodynamics and preferential solvation of gliclazide in (Transcutol® + water) mixtures

Abstract

ABSTRACT The equilibrium solubility of gliclazide (3) in {Transcutol (1) + water (2)} mixtures at several temperatures was reported in the literature. However, no deep attempt was made to correlate gliclazide solubility with the composition of the aqueous-cosolvent mixtures. Moreover, no apparent thermodynamic calculations for the dissolution processes were performed. Thus, the reported solubility data were modelled by means of some well-known correlation models. By using the van’t Hoff and Gibbs equations, the respective apparent thermodynamic quantities of dissolution and mixing processes, namely Gibbs energy, enthalpy, and entropy, were calculated. Non-linear enthalpy–entropy relationship was observed for gliclazide in the plot of enthalpy vs Gibbs energy exhibiting negative slope in the composition region 0.00 < w 1 < 0.10 and variant but mainly positive slopes in the other mixtures. Hence, the driving mechanism for gliclazide transfer process from more polar to less polar solvent systems is the entropy in water-rich mixtures and the enthalpy in the other solvent compositions. Furthermore, the preferential solvation of gliclazide by both solvents was analysed by using the inverse Kirkwood-Buff integrals observing that gliclazide is preferentially solvated by water molecules in water-rich mixtures but preferentially solvated by Transcutol molecules in mixtures 0.12 < x 1 < 1.00.