Preparation of chitosan-based molecularly imprinted material for enantioseparation of racemic mandelic acid in...

An S-mandelic acid imprinted chitosan resin was synthesized by cross-linking chitosan with glutaraldehyde in 2% acetic acid solution. S-Mandelic acid imprinted chitosan resin was used to enantioselectively separate racemic mandelic acid in aqueous medium. When keeping the pH of sample solution (100 mM Tris-H₃ PO₄ ) at 3.5 and adsorption time at 40 min, the enantiomer excess of mandelic acid in supernatant was 78.8%. The adsorption capacities of S-mandelic acid imprinted chitosan resin for S- and R-mandelic acid were determined to be 29.5 and 2.03 mg/g, respectively. While the adsorption capacities of non-imprinted cross-linked chitosan for S- and R-mandelic acid were 2.10 and 2.08 mg/g, respectively. The result suggests that the imprinted caves in S-mandelic acid imprinted chitosan resin are highly matched with S-mandelic acid molecule in space structure and spatial arrangement of action sites. Interestingly, the enantiomer excess value of mandelic acid in supernatant after adsorption of racemic mandelic acid by R-mandelic acid imprinted cross-linked chitosan was 25.4%. The higher enantiomer excess value by S-mandelic acid imprinted chitosan resin suggests that the chiral carbons in chitosan and the imprinted caves in S-mandelic acid imprinted chitosan resin combine to play roles for the enantioselectivity of S-mandelic acid imprinted chitosan resin toward S-mandelic acid. Furthermore, the excellent enantioselectivity of S-mandelic acid imprinted chitosan resin toward S-mandelic acid demonstrates that using chiral chitosan as functional monomer to prepare molecularly imprinted polymers has great potential in enantioseparation of chiral pharmaceuticals.