Polarity-controlled deep eutectic solvents-based biphasic system for the selective separation of geniposidic acid and aucubin from Eucommia ulmoides male flowers

Owing to their unique characteristics, deep eutectic solvents (DESs) have the potential to replace organic solvents in the extraction and separation of chemicals from natural sources. In this study, a novel biphasic system composed of hydrophilic and hydrophobic DESs was designed for the selective separation of geniposidic acid (GPA) and aucubin (AU) from Eucommia ulmoides male flowers. Fifteen DESs with different hydrophilicity/hydrophobicity were used to design the biphasic system. The biphasic system designed using tetrabutyl ammonium chloride-hexanoic acid and choline chloride- D, L -malic acid was found to be an optimal extraction system. The influence of the phase volume ratio, system concentration, water content in the DESs, equilibrium temperature, and pH of the phosphate buffer solution was investigated through single-factor experiments. Under optimal conditions, maximum extraction efficiencies were observed for GPA in the top phase ( E GPA  = 94.59%) and AU in the bottom phase ( E AU  = 80.41%). Further, density functional theory calculations indicated that H-bond interaction was the main factor influencing the selective separation of GPA and AU. This DES-based biphasic system is efficient and environmentally friendly and could be used in the separation of other homologues present in natural products.