Synthesis of chiral hollow polymer microspheres and their applications in the spectroscopic chiral discrimination of tryptophan isomers

Hollow polymer microspheres (HPMs) were synthesized, which were then hydrolyzed in aqueous ammonia to produce carboxyl (–COOH) groups on their surface. L-phenylalanine (L-Phe) was grafted to the hydrolyzed HPMs (H-HPMs) through amidation reactions, endowing the H-HPMs with chirality. The resultant chiral HPMs (C-HPMs) were used for the chiral discrimination of tryptophan (Trp) isomers. Due to the same rotatory   direction of L-Phe and L-Trp, the C-HPMs showed greatly higher selectivity toward L-Trp than its isomer. After being adsorbed by the C-HPMs, the absorbance of the residual L-Trp is significantly lower than that of the residual D-Trp, and thus spectroscopic chiral discrimination of the Trp isomers was successfully achieved. The Trp isomers were also discriminated by the chiral solid polymer microspheres (C-SPMs), while the difference in the absorbance of the residual L-Trp and D-Trp is remarkably smaller than that obtained by the C-HPMs. The outstanding discrimination capability of the C-HPMs might be ascribed to their high surface permeability resulted from their unique hollow structure.