Deep-eutectic solvents simultaneously used as the phase-forming components and chiral selectors for enantioselective liquid-liquid extraction of tryptophan enantiomers

Two-phase system was widely used for the enantioselective liquid-liquid extraction (ELLE) of various enantiomers. The organic solvents are generally used as the extractants, moreover, the additional chiral selectors should be added to the extraction system. In this study, a biphasic recognition chiral extraction (BRCE) system based on hydrophilic and hydrophobic DESs was developed for the ELLE of tryptophan enantiomers. DESs can be simultaneously used as the phase-forming components and chiral selectors. The hydrophobic/hydrophilic methyl trioctyl ammonium chloride- L(+)-Diethyl L-tartrate/HP-beta-CD-L-(-)-Malic Acid (MTAC-DE/HC-MA) system was screened as the optimal extraction system. The molar ratios of hydrogen-bond acceptor (HBA) and hydrogen-bond donor (HBD) in DESs were optimized for the enantioseparation. The other factors of phase volume ratio, initial tryptophan concentration, pH value, and extraction temperature were studied. The maximum enantiomeric excess (e.e.) value of 38.46% was obtained under the optimal conditions by one-step extraction. This BRCE system used for the chiral separation of tryptophan enantiomers has the advantages of environmental friendliness, simple operation, and high efficiency, which has the practical application potentiality in the continuous enantioseparation process. (C) 2020 Elsevier B.V. All rights reserved.