Immobilization Of Lipase On Polypropylene Microporous Membranes

Polypropylene microporous membrane exhibits high potentials for comprehensive applications due to its chemical inertness, well-controlled porosity and conveniences for preparation. However, as enzyme-immobilized support, the poor biocompatibility of this membrane probably leads to some nonbiospecific interactions between enzyme and membrane surface, therefore, resulting in the partial denaturation of enzyme protein and the loss of enzyme activity. In an attempt to minimize the influence of these unfavorable interactions, the immobilization of Candida rugosa lipase on polypropylene microporous membranes was investigated systematically. On the one hand, lipases were covalently bound on the surface-activated membranes using hexamethylendiamine (HMDA) as spacer, which can extend the distance from enzyme to support and reduce the interactions between them. On the other hand, the membrane surface was modified respectively by glycopolymer, polypeptides and phospholipid analogous polymers to create a biocompatible interface for lipase adsorption. It is expected that this interface can minimize the unfavorable interactions between enzyme and support, and create a biofriendly microenvironment for immobilized lipases. Based on the above work, the preliminary research on the hydrolysis of olive oil in biphasic enzyme-membrane reactor was performed. The relative experiments and results are summarized as follow.The surface of polypropylene microporous membranes was activated by the graft polymerization of methyl methacrylate initiated with ultraviolet-photo. HMDA was used as spacer, and glutaraldehyde as crosslinking agent to couple lipase to the HMDA. The chemical changes of the membrane surface were confirmed by attenuated total reflectance Fourier transform infrared spectroscopy (ATR/FT-IR) and X-ray photoelectron spectroscopy (XPS). Effect of immobilization conditions on lipase' s activity was investigated. It was observed that, at the optimal condition, the immobilized-lipases retain 42% of the free lipase's activity. In addition, the experimental results of thermal stability show that the residual activity of the immobilized lipases is 82% at 50 ℃ for 2 h.The glycopolymer-modified polypropylene membranes were prepared by the plasma-induced polymerization of a-allyl glucoside (AG) on the membrane surface, which was synthesized by one-step reaction of allyl alcohol with glucose. The chemical and morphological changes of the membrane surface were characterized by ATR/FT-IR, XPS and scanning electron microscopy (SEM). Results on the basis of the enzyme adsorption capacity, activity and thermal stability were compared with those ofthe nascent membranes. It was found that, after modification, the activity retention of lipases decreases to some extend. It may be due to the markedly increased hydrophilicity on the membrane surface weakening the interfacial activation of lipases. In addition, the experimental results of thermal stability show that, as for PAG-modified membranes, the residual activity of the immobilized lipases at 50 ℃ for 2 h is 48%, higher than that of the nascent ones.Poly(y-ethyl-L-glutamate) (PELG) and poly(y-stearyl-L-glutamate) (PSLG), two polypeptides with short and long hydrophobic side chains respectively, were tethered on the polypropylene membrane surface through the ring opening polymerization of N-carboxyanhydride of y-ethyl-L-glutamate (y-stearyl-L- glutamate) initiated by amino groups. The chemical and morphological changes of the membrane surface were characterized by ATR/FT-IR, XPS and SEM. Lipases from Candida rugosa were immobilized on these membranes by adsorption. Results on the basis of the enzyme adsorption capacity, activity and thermal stability were compared with those of the nascent membranes. It was found that, as for the modified membranes, the activity retention of the immobilized enzymes increases from 57% to 72% and to 62% respectively for the PSLG-modified and PELG-modified membranes. In addition, the experimental results of thermal stability show that the residual activity of the i...