pH-responsive functionalized surface active ionic liquid as an enhanced medium for efficient extraction and in-situ separation of flavonoids in Vitex negundo L. Leaves

Abstract

In this study, a functionalized surface active ionic liquid (SAIL) was designed and prepared, which exhibits pH-responsive behavior and high yield for 6 target flavonoids from the leaves of Vitex negundo L. Firstly, a series of functionalized SAIL [N-Cn, N'–CO2H-Im]Br (n = 10, 12, 14, 16) were prepared and used for extraction of the target components, [N-C14, N'–CO2H-Im]Br showed the highest yield. Secondly, optimized extraction conditions obtained by Plackett-Burman design (PBD) and response surface methodology (RSM) were concentration of 45.5 mM, liquid–solid ratio of 11.6 (mL/g), extraction time of 38.5 min, extraction temperature of 40 °C, and ultrasonic power of 400 W. The yield obtained by [N-C14, N'–CO2H-Im]Br of vitexin, isovitexin, hyperoside, luteolin, quercetin, apigenin is 2.04, 1.81, 1.24, 1.51, 2.47 and 1.21 mg/g, respectively, which is 1.11–1.56 folds higher than non-functionalized SAIL ([C14min]Br) and 1.50–5.36 folds higher than traditional solvents. More importantly, the solvent system can realize the in-situ separation of the target compound by adjusting pH. When pH is changed from 6.1 to 4.9, the system is divided into two phases, and the target compounds were separated to the upper phase with a high recovery rate. Finally, molecular simulation was used to reveal the extraction mechanism of functionalized SAIL on target compounds. The results showed that the target flavonoids were compatibilized to the palisade region of micelles, and the weak interaction between the target flavonoids and functionalized SAIL was mainly van der Waals force.