PH-Sensitive Chiral Poly (N-acryloyl-L-alanine)Hydrogel:Design, Preparation And Performance Studies

In recent years, polymeric hydrogel has received considerable attention for its three-dimensional network structures. Because of the special structure of hydrolel, it could swell or shrink in suitable solvent and has been applied in many fields. Stimulus responsive hydrogels is a hydrogel with special properties. If the hydrogel is synthesized from stimuli responsive polymers, it may exhibit reversible changes of physical properties in response to external stimuli including pH, temperature, electric current and ionic strength. The application and study of stimulus responsive hydrogels become more popular recently. In this paper, noval pH-sensitive chiral hydrogels had been designed and prepared, its properties were characterized and the enantio-differentiating release ability of it were studied.In the second chapter, we combined the two concepts, i.e. chirality and pH-sensitivity, in one single hydrogel. Such hydrogels were prepared via free radical co-polymerization by 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’-methylenebisacrylamide as cross-linking agent and K2S2O8as initiator. The hydrogels were obtained and exhibited remarkable swelling in water and pH-responsivity. In the hydrogel, PNAA chain provided chiralty and pH-sensitivity and HP-β-CD plays essential roles to form pores and channels. The hydrogels were characterized by FT-IR and SEM. The morphology of the obtained hydrogels was observed by SEM. In a comparison among the micrographs, increasing the content of HP-β-CD in the hydrogels led to a significant increase in pore size from0.5μm to2μm. The pH-sensitivity of hydrogels had been studied, the maximum equilibrium swelling ratio of the hydrogels reached150times in deionized water, but the swelling ratio of the hydrogels is just2times in acid solution (pH=2). Circular dichroism and UV-vis absorption spectroscopies of hydrogels demonstrated the optical activity of the hydrogels. The hydrogels performed chiral recognition and enantio-differentiating release abilities toward proline enantiomers, in which L-proline was preferentially adsorbed, whereas D-proline was preferentially released. In the enantio-differentiating release of hydrogels,71%of D-proline and55%of L-proline was diffused outside the hydrogels, the difference of release D-and L-proline is12%.By the study, we found that excessive swelling rario of hydrogel is disadvantage for chiral application. So we designed a noval hydrogel that contained hydrophobic polymer chain to decrease swelling ratio. In the third chapter, we designed and prepared another novel type of hydrogel. Such hydrogels were prepared by free radical co-polymerization by using N-acryloyl-L-alanine as monomer and octadecyl acrylate as comonomer, while K2S2O8served as initiator and N,N’-methylenebisacrylamide as cross-linking agent. The resulting hydrogels exhibited remarkable pH-responsivity and swelled to different degrees depending on alkaline and acidic states. The maximum equilibrium swelling ratio of the hydrogels is just14times. The optical activity of the hydrogels was demonstrated by circular dichroism and UV-vis absorption spectroscopies. More interestingly, the hydrogels showed enantio-differentiating release abilities toward proline enantiomers, in which65%D-proline and46%L-proline was released, the difference of release D-and L-proline is increase.