Enantioselective liquid-liquid extraction of tryptophan enantiomers by a recyclable aqueous biphasic system based on stimuli-responsive polymers

The hydrophobic organic solvents/water biphasic system had been always used in the traditional enantioselective liquid-liquid extraction (ELLE). In recent years, aqueous biphasic systems (ABSs) are considered as a promising method used in the ELLE. In the present work, a recyclable ABS composed of a temperature-responsive polymer poly(MAH- β -CD- co -NIPAAm) (P N-CD ) and a pH-responsive polymer poly(AA-DMAEMA-BMA) (P ADB ) was employed in the enantioseparation of tryptophan enantiomers . The polymer P N-CD acted as not only the phase-forming component but also the chiral selector, which can be recycled by changing the temperature. The polymer P ADB can be used as the phase-forming component, which can also be recycled by adjusting the pH. The phase behaviors of this P N-CD /P ADB ABS had been studied. The influencing parameters were studied for this chiral separation process, including the polymer concentration, initial tryptophan concentration, extraction temperature, and system pH. The maximum separation factor ( α ) of 1.42 was obtained by one-step extraction under the optimal conditions. Meanwhile, the distribution coefficients of L -tryptophan ( L -Trp) and D -tryptophan ( D -Trp) were 2.79 and 1.96, respectively. This study develops a green and sustainable strategy for enantioseparation by using the ELLE.