Novel smart chiral magnetic microspheres for enantioselective adsorption of tryptophan enantiomers

Multifunctional microspheres simultaneously possessing chirality, magnetism and thermosensitivity show great potentials in direct enantiomeric separation. Herein we report a novel type of smart chiral magnetic microspheres with core/shell/shell structures (Fe 3 O 4 @SiO 2 @PNCD) and its application in enantioselective adsorption of tryptophan (Trp) enantiomers. The prepared Fe 3 O 4 @SiO 2 @PNCD are composed of a Fe 3 O 4 nanoparticle core, an acidic-resistant SiO 2 middle shell and a thermosensitive microgel functional shell (PNCD). The PNCD plays an important role in the enantioselective adsorption of Trp enantiomers. The β -cyclodextrin ( β -CD) molecules on the PNCD act as smart receptors or chiral selectors, and can selectively recognize and bind L -Trp enantiomers into their cavities by forming host-guest inclusion complexes. The poly( N -isopropylacrylamide) (PNIPAM) chains on the PNCD serve as microenvironmental adjustors for the association constants of β -CD/ L -Trp complexes. The fabricated Fe 3 O 4 @SiO 2 @PNCD demonstrate fascinating temperature-responsive chiral recognition and adsorption selectivity toward Trp enantiomers. Most importantly, the desorption of Trp enantiomers and the regeneration of the Fe 3 O 4 @SiO 2 @PNCD can be easily achieved via simply changing the operation temperature. Moreover, the regenerated Fe 3 O 4 @SiO 2 @PNCD can be readily recovered from the amino acids enantiomeric solution under an external magnetic field for reuse. The present study provides a novel strategy for the direct enantioselective adsorption and separation of various enantiomeric compounds.