Effect of temperature and polarity on the solubility and preferential solvation of sinapic acid in aqueous mixtures of DMSO and Carbitol

Reported equilibrium mole fraction solubilities of sinapic acid (3) in {DMSO (1) + water (2)} and {Carbitol (1) + water (2)} mixtures at several temperatures were analyzed in terms of the Hildebrand solubility parameter of these aqueous mixtures. Moreover, the preferential solvation parameters of sinapic acid in these aqueous saturated mixtures at (298.15 and 313.15) K were determined based on the inverse Kirkwood-Buff integrals (IKBI) as widely described in the literature. Sinapic acid is preferentially solvated by water in water-rich mixtures, i.e. (0.00 < x₁ < 0.21 in {DMSO (1) + water (2)}) and (0.00 < x₁ < 0.12 in {Carbitol (1) + water (2)}) but preferentially solvated by the cosolvents in the other mixtures composition. In the former cases these results could be interpreted as a consequence of hydrophobic hydration around the non-polar moieties of sinapic acid. Moreover, in the last cases, the observed trends could be due to the Lewis acidic behavior of sinapic acid in front of DMSO or Carbitol molecules because both cosolvents exhibit higher Lewis basic character than water, as indicated by the respective solvatochromic parameters. A single cosolvency model for representing the equilibrium solubility of sinapic acid in binary solvents at various temperatures was also provided based on a combination of Hansen solubility parameters and Jouyban-Acree model.