| 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 < w1 < 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 waterrich
mixtures but preferentially solvated by Transcutol molecules in mixtures
0.12 < x1 < 1.00. |