Nano temperature-switchable supramolecular solvent: Preparation, characterization and application in efficient extraction and enrichment of phytochemicals

Abstract

In this study, a nano temperature-switchable supramolecular solvent (NTS-SUPRAS) system was designed, prepared and characterized for efficient extraction and enrichment of phytochemicals, the extraction mechanism was also investigated. The NTS-SUPRAS was synthesized by natural deep eutectic (NADES), 1,2-Propanediol and water, then the ternary phase diagrams were plotted according to their mass fractions. Dynamic light scattering (DLS), conductivity and FT-IR were used to characterize the solvent, and an exciting discovery was the nanoscale of NTS-SUPRAS. The particle size of its reverse micelles self- aggregated was positively correlated to the water content, which was increased from 3.8 nm to 77.9 nm as the water content increased from 5 % to 20 %. Temperature-switchable of NTS-SUPRAS was proved by the appearance of phase separation when regulate temperature from 25 °C to 10 °C. Then, six phytochemicals in Cajanus cajan(Linn.) leaves were efficiently extracted and enriched by vortex-assisted extraction. The extraction factors such as solid–liquid ratio, vortex time, NADES content and water content were optimized using the one-factor optimization method and response surface analysis to obtain the optimal extraction conditions. The results showed that the extraction efficiency of NTS-SUPRAS was 1.18–2.32 folds higher than that of traditional solvents for different polar substances, and the total extraction yield could be reached 21.13 mg/g. The phytochemicals were highly recovered by temperature-switching and macroporous adsorption resin with a recovery rate up to 98.6 %, and the reusability of NTS-SUPRAS could still keep at 90.43 % of the initial one after three cycles. Finally, the extraction mechanism of NTS-SUPRAS was investigated using density functional theory (DFT), founding that the hydrogen bonding between NTS-SUPRAS and the phytochemicals was attributed to the high extraction rate. This nano temperature-switchable supramolecular solvent has the advantages of green, low cost, simple preparation, high extraction rate, easy recycling and good reusability, which is suitable for industrialized application and production. In addition, the nanoscale and the temperature-switchable characteristics also provide new prospects for high-value utilization of phytochemicals.