Solubility and Preferential Solvation of the Flavonoid Naringenin in Some Aqueous/Organic Solvent Mixtures

The solubility of the antioxidant flavonoid naringenin as well as its preferential solvation was studied in different aqueous solutions containing 0–100 % (v/v) of acetonitrile (ACN) and 1,4-dioxane (DOX) at temperature 25.0 ± 0.1 °C. From the solubility data, both the Gibbs energy changes involved with the solublization process, ΔGso\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ \Delta G_{\text{s}}^{\text{o}} $$\end{document}, and the preferential solvation parameters of the solute naringenin by these co-solvents, δxcosolv,S, were determined. The results show that the equilibrium solubility increases with increasing co-solvent concentration. Moreover, it became clear that the preferential solvation of naringenin is sensitive to changes in solvent composition, so the preferential solvation parameters δxACN,S and δxDOX,S are negative in water-rich mixtures but positive in compositions from 50 % (v/v) ACN (xACN = 0.25) and DOX (xDOX = 0.17) up to the pure co-solvents. Possibly, in water-rich mixtures the structuring of water molecules around the non-polar groups by hydrophobic hydration contributes to lowering of the net δxcosolv,S to negative values. The preferential solvation by the co-solvent in the range 50–100 % (v/v) could be related to the greater basicity of the co-solvents and its interactions with hydroxyl groups of the flavonoid.