Design of deep eutectic solvents modified palygorskite for selective recognition, mechanism study and stable preservation of quercetin

Considering the effect of secondary metabolites on quercetin (QC) separation and purification in plants, herein, four types of hydrophilic deep eutectic solvents (DESs) composed by organic acids and glycosyl-, quaternary ammonium- or alcohol-based hydrogen bond acceptors were designed and modified on the palygoskite (Pal) surface to improve the selectivity of QC via dispersive solid-phase extraction (D-SPE). The selectivity study followed the following order: Pal- [Choline chloride (ChCl)] [Levulinic acid (Lev)] > Pal- [Glycerol (Gly)] [L-Proline (Pro)] > Pal- [Glucose (Glu)] [D-lactic acid (Lac)] > Pal- [Benzyl triethyl ammonium chloride (BTBAC)] [D-lactic acid (Lac)]. Based on the single-factor method, Response surface methodology (RSM) by using a Box-Behnken design (BBD) was applied to assess the mutual interactions and effects between the three factors and the optimized preparation conditions. The optimal nanoparticles (Pal- [ChCl] [Lev]) showed the best adsorption capacity for QC (29.81 mg/g) in the mixture of methanol and phosphate buffered solution (PBS) and high selectivity which was 1.95 times and 2.12 times that of luteolin and rutin hydrate, respectively. Mechanism exploration indicated that Pal-DESs selectively adsorbed QC via electrostatic interaction, π-π stacking and hydrogen bonds. Furthermore, the screened DES of ([ChCl] [Lev]) could act on QC aqueous solution to improve its solubility and stability during preservation. The proposed QC separation strategy centered on the guiding role of DESs in selective adsorption. Additional alternatives for the synthesis of high-efficiency and hydrophilic functional adsorbents for flavonoids were made available by this green DESs regulation concept.