Uncovering the curcumin solubilization ability of selected natural deep eutectic solvents based on quaternary ammonium compounds

• Published in: Journal of molecular liquids Vol. 361; p. 119661
• Main Authors: Huber, Verena, Hioe, Johnny, Touraud, Didier, Kunz, Werner
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01-09-2022
• Subjects: COSMO-RS; Curcumin; Natural Deep Eutectic Solvents; NMR; Quaternary Ammonium Compounds; Solubilization; NMR; Curcumin; Natural Deep Eutectic Solvents; COSMO-RS; Solubilization; Quaternary Ammonium Compounds
• ISSN: 0167-7322; 1873-3166
• DOI: 10.1016/j.molliq.2022.119661

•Screening of curcumin solubility in nine natural deep eutectic solvents based on choline chloride, betaine, and carnitine.•COSMO-RS prediction of the chemical potential of curcumin in ethanolic solutions of the NADES compounds.•Influence of the acids’ molecular conformation on their solubilization power.•1H and NOESY NMR assessment of the intermolecular interactions between curcumin and the NADES compounds.•Interplay of targeted hydrogen bonding and non-directed intermolecular interactions as driving force of solubility synergy.
The solubility of curcumin in ethanolic solutions can be increased twentyfold through the addition of natural deep eutectic solvents (NADES). Instead of only screening nine different NADES based on choline chloride, betaine, and carnitine mixed with lactic, levulinic, and pyruvic acid in terms of their solving ability, they were investigated regarding the mechanism of solvation as well. The curcumin solubility enhancement was assessed via UV/Vis measurements, while the investigation of the intermolecular effects was performed theoretically by COSMO-RS predictions of the chemical potential and experimentally via 1H and NOESY NMR measurements. The addition of the quaternary ammonium compounds to ethanol resulted in a solubility increase regardless of additional functionalities, which was not the case for the acids, where functionalities showed a significant influence. A solubility synergy in the levulinic acid NADES was reached, which could be explained through the combination of COSMO-RS and NMR experiments, yielding indications that an interplay of non-specific and directed intermolecular interactions was the responsible driving force for an efficient solubility enhancement of curcumin. Thus, the NADES based on levulinic acid achieved the best results.