pH-Sensitive Chiral Hydrogels Consisting of Poly(N-acryloyl-l-alanine) and β-Cyclodextrin: Preparation and Enantiodifferentiating Adsorption and Release Ability

Both chiral hydrogels and pH-sensitive hydrogels have received considerable attention in recent years. In the present study, we combined the two intriguing concepts, i.e., chirality and pH sensitivity, in one single hydrogel. Such hydrogels were prepared via free radical copolymerization using chiral N-acryloyl-l-alanine (NAA) as monomer, the inclusion complex of glycidyl methacrylate (GMA) and hydroxypropyl-β-cyclodextrin (HP-β-CD) as comonomer, N,N′-methylenebis(acrylamide) as cross-linking agent, and K2S2O8 as initiator. The hydrogels were successfully obtained and exhibited remarkable swelling in water and pH responsivity. The hydrogels were characterized by circular dichroism and UV–vis absorption spectroscopies, demonstrating the optical activity of the hydrogels. The hydrogels performed chiral recognition and enantiodifferentiating release abilities toward proline enantiomers, in which l-proline was preferentially adsorbed whereas d-proline was preferentially released. The present study established a platform for preparing versatile, in particular, optically active hydrogels. Noticeably, the hydrogels are expected to find practical applications as novel materials for chiral drugs delivery.