Controlled Synthesis Of Core-Shell Nanospheres And Their Study For Lipase Immobilization

Immobilization technologies overcome the poor stability and reusability of free enzymes,making them possible for the industrial applications.However,due to the influence of the supports,the immobilization methods and the structure of the enzymes themselves,the activity of enzymes after immobilization is much lower than that of free ones.In recent years,how to improve the activity of immobilized enzymes has become one of the urgest demands in this field.For example,various hydrophobic supports have been used for lipase immobilization since the active sites of lipases can be opened in a hydrophobic environment based on their "interfacial activation",realizing high catalytic activity.Nevertheless,because of the dynamic equilibrium of the conformational change,the simple activation cannot achieve a long-term performance of activity after immobilization,the increase of lipase activity as well as its commercial application are still limited.This study demonstrated a "hyperactivation-protection" strategy of lipases after immobilization on poly(n-butyl acrylate)-polyaldehyde dextran(PBA-PAD)core-shell nanospheres.Polyaldehyde dextran was used as the macroinitiator and emulsifier to participate in the emulsion polymerization of n-butyl acrylate,and PBA-PAD core-shell nanospheres with various aldehyde density were synthesized,which got controllable particle size and uniform morphology.These nanospheres could be used directly without tedious postprocessing.We applied the PBA-PAD NSs for lipase(from porcine pancrea)immobilization.The inner hydrophobic PBA domain helps to rearrange lipases conformation to a more active form after immobilization into the PAD shell.More importantly,the outer PAD shell with dense polysaccharide chains prevents the immobilized lipases from contacting with outside aqueous medium and reverting their conformation back to an inactive form.As a result,compared with the free PPL,PBA-PAD-PPL NSs got high temperature and alkaline tolerance.Under optimal conditions,the activity of lipases immobilized in PBA-PAD NSs was enhanced 40 times over the free ones,much higher than in any previous report.Furthermore,the immobilized lipases retained more than 80%of their activity after 10 reaction cycles.The PBA-PAD NSs with controlled size and desirable biocompatibility can be facilely prepared through emulsion polymerization.Moreover,the activity and stability of lipases can be greatly increased after chemically immobilizing them in the PAD shell of the nanospheres,which provides a deep insight into the lipase immobilization.Therefore,we envision a potential for the large scale application of this new immobilization procedure.