Hydrotropic Concepts Applied to the Water-solubilization of Polyphenols : Example of Meglumine, Modeling, Physicochemical Study and Applications

The various issues raised in this work concern the understanding and use of solubilization phenomena in aqueous phase, in particular those related to hydrotropy concepts, with the dual aim of rationalizing the search for new hydrotropic agents and the solubilization behavior of polyphenolic compounds, with a view to applications in pharmaceuticals, agri-food and cosmetics. Indeed, many natural compounds are still limited in their use or their exploitation due to their low aqueous solubility. In the first chapter, the use of meglumine to solubilize quercetin in aqueous phase as a function of pH is studied by UV-Visible spectroscopy. The solubilization mechanism is investigated by 1H NMR and quercetin oxidation is quantified by HPLC. Finally, the order of quercetin deprotonation is determined using COSMO-RS modeling software. The second chapter reports on a concrete application of this solubilization: the encapsulation of quercetin in liposomes from an aqueous solution in a mildly alkaline medium. The study of the solubility of polyphenolic compounds is extended in chapter III, to better identify the various causes of their low aqueous solubility in relation to their chemical structure, and to rationalize the solubilizing effect of hydrotropic agents on specific polyphenols according to their structure. The preferential π-stacking between phloroglucinol and quercetin is studied specifically. Finally, the possibility of using meglumine and certain guanidine derivatives in association with linear fatty acids is investigated in chapter IV, with the aim of increasing the amphiphilic character of the former and the aqueous solubility of the latter. The resulting amphiphiles are characterized by classic surface-active methods, including Krafft temperature, micellar solubilization and emulsion stabilization

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

International audienceIn 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

Design and properties of a novel family of nonionic biobased furanic hydroxyester and amide surfactants

International audienceA series of original amphiphiles prepared by Morita-Baylis Hillman (MBH) coupling biobased furanic aldehydes with hydrophobic alkenes is explored. Structural variations result from the level of polarity on the furanic substrate, the type of activated alkenes (ester of amide), 2 the alkyl chain length and the presence of an unsaturation. The physicochemical properties such as the Krafft point, critical micellar concentration (CMC) and hydrophilic lipophilic behavior determined with the PIT-slope method have been explored. The glucosyloxymethyl furfural (GMF) derivatives exhibit higher water-solubility than the succinyl hydroxymethyl furfural (SMF) and the HMF-derived ones. Saturation of the acrylic linkage results in slightly lower CMC for GMF derived compounds by the enhanced solvation of the unsaturation. As expected, increasing the alkyl chain length diminishes the water-solubility, the CMC and the hydrophilicity. The decreasing hydrophilic behavior of surfactants is as follows: Gi > GiH > HSi. For the shorter HMF amphiphiles, the order is: HiN > Hi HiH. These surfactants cover a wide range of HLB values. The dodecyl GMF-G12-is as hydrophilic as C12E6 and the hexadecyl SMF-HS16-is much more hydrophobic than SPAN 40. Formation of stable emulsions with two cosmetic oils of different polarity is very encouraging for a possible application of this new family of biobased surfactants