Enhancement of water solubilization of quercetin by meglumine and application of the solubilization concept to a similar system

In the present work, meglumine, an aminocarbohydrate derived from glucose with a secondary amine group, was found to be able to increase the water-solubility of the well-known and beneficial flavonoid quercetin. pH proves to be a fundamental factor for this purpose. The solubility enhancement as a function of the pH as well as the mechanism behind this phenomenon were investigated. The state of charge of quercetin depending on pH has been estimated from the calculation of the pKa by COSMO-RS. A compromise between a satisfying solubility enhancement (6–7-fold) and reasonable stability against oxidation (70–75 % of quercetin still intact after 2 h) was found around pH 8. The solubilization mechanism is believed to be based on proton exchange between quercetin and the amine function of meglumine, and on the ability of meglumine to form numerous hydrogen bonds with water molecules through its five hydroxyl groups. Finally, it is shown that the underlying solubilization mechanism can be extended both to other polyphenols and to other hydrotropes.