Preparation Of Poly(carboxybetaine Methacrylate)-Grafted Carriers For Enzyme Immobilizations

Enzyme is a kind of biocatalyst.Compared with chemical catalyst,it has the characteristics of high catalytic efficiency,mild reaction conditions and high specificity in the catalytic process.However,since most enzymes are proteins,they are easily deactivated under harsh conditions and difficult to recycle from the reaction system leading to the increase of use cost.The development of enzyme immobilization technology has solved the problems of inactivation and difficult recovery.Carrier of enzyme immobilization is an important factor that affects the performances of immobilized enzyme.Among a variety of carriers,polymer-coated nanoparticles are favorable carriers for enzyme immobilization for their advantages of high specific surface area,small mass transfer resistance and a large number of active groups for covalent bonding of enzymes.Of the various polymers,zwitterionic polymers have been found to work as protein stabilizers.Inspired by the literature outcomes,we have developed a novel nanoparticle-based carrier modified by grafting a highly hydrophilic zwitterionic polymer,poly(carboxybetaine methacrylate)(pCBMA),on silica nanoparticles(SNPs),which was denoted as SNPs-pCBMA.For comparison,an uncharged polymer,poly(glycidyl methacrylate)(pGMA),was also grafted onto SNPs to prepare SNPs-pGMA.The two types of polymer-grafted SNPs were characterized and used for the covalent bonding of two enzymes,catalase and lipase(pGMA-CAT,pCBMA-CAT,pGMA-CRL and pCBMA-CRL).The characterization results show that the two polymer-grafted supports were successfully prepared,and the aggregation state of SNPs-pGMA was more severe than that of SNPs-pCBMA.For enzyme immobilization,the results revealed that both the immobilized enzymes on SNPs-pCBMA exhibited higher thermal and storage stability than those on SNPs-pGMA,due to protective effects of the zwitterionic polymer.For example,by incubation at 50°C for 20 min,the residual activities of pCBMA-CAT and pCBMA-CRL kept 60.5% and 60.3% of their initial activities,respectively,higher than those of pGMA-CAT and pGMA-CRL(55.6% and 48.3%,respectively).The immobilized enzymes on SNPs-pCBMA also exhibited higher stability under neutral and alkaline conditions and good reusability.Taken together,the zwitterionic polymer pCBMA was beneficial to improve the stability of the immobilized enzyme,and the pCBMA-grafted materials were promising supports for enzyme immobilizations.