Enhanced solubilization of hydrophobic compounds in aqueous solutions by the hydrotropic action of ionic liquids

The ability of aqueous solutions of ionic liquids (ILs) to solubilize hydrophobic compounds is demonstrated in this work and a mechanism to explain this enhanced solubility is proposed. Vanillin and gallic acid, two natural antioxidants, and ibuprofen and naproxen, two drugs are here studied. Their solubility in aqueous solutions of ILs was measured in the whole composition range, from pure water to pure ILs, and an increase in the solubility of up to 100-fold was observed. The effects of the IL chemical structures, their concentration and temperature on the solubility of the hydrophobic model compounds were evaluated and compared with the performance of conventional hydrotropes. Using Dynamic Light Scattering, NMR and molecular dynamics (MD) simulations, it was possible to infer that the enhanced solubility of biomolecules in IL aqueous solutions is related to the formation of IL-biomolecule aggregates. Finally, it was demonstrated that the hydrotropy induced by ILs can be used to recover solutes, by precipitation, from aqueous media, simply by using water as anti-solvent. The results gathered in this work have a significant impact on the understanding of ILs aqueous solutions as novel solvents with enhanced performance.