Synthesis of molecularly imprinted polymer modified magnetic particles for chiral separation of tryptophan enantiomers in aqueous medium.

Molecularly imprinted polymers coated magnetic particles (Fe3O4@MIPs) were prepared and used as adsorbents in solid phase extraction for efficient enantioseparation of racemic tryptophan (Trp) in aqueous medium. The amino-modified magnetic particles (Fe3O4-NH2) were first synthesized by one-pot hydrothermal method. Then the template molecules (L-Trp) were assembled on the surface of Fe3O4-NH2. Finally, Fe3O4@MIPs were prepared via a sol-gel method using L-Trp@Fe3O4-NH2 complex as matrix, 3-aminopropyltriethoxylsilane and n-octyltriethoxysilane as functional monomers. The as-prepared Fe3O4@MIPs were spherical with an average diameter about 149 ± 6.0 nm. The thickness of MIPs layer was approximately 3.5 ± 2.3 nm. The adsorption isotherms data of Fe3O4@MIPs toward L-Trp and D-Trp were well described by the Langmuir model. The maximum adsorption capacities of Fe3O4@MIPs for L-Trp and D-Trp were calculated to be 17.2 ± 0.34 mg/g and 7.2 ± 0.19 mg/g, respectively. The material exhibited good selectivity toward L-Trp with imprinting factor of 5.6. Excitingly, the enantiomeric excess (ee) of Trp in supernatant after adsorption of racemic Trp by Fe3O4@MIPs was as high as 100%. The result suggests that the imprinted caves in Fe3O4@MIPs are highly matched with L-Trp molecule in space structure and spatial arrangement of active functional groups. The work also demonstrates that sol-gel technology has great potential in preparation of MIPs for chiral separation.