Preparation Of Magnetic Polyamine Microsphere And Its Application In Enzyme Immobilization

As one hot topic in many fileds, magnetic polymer microsperes demonstrate theadvantages of momodispersion, biocompatibility, and can be functionalized easily. Thecapacity of magnetic resonponse of magnetic polymer microsperes facilitates the recycling ofthe microsphere under the external magnetic field.Polyethyleneimine (PEI) is one of the most widely used water-soluble cationicpolymer. It has been widely used in biological engineering, immobilization of enzymes,environmental treatment, gene therapy etc.The main content of this research are as follows:1. Different methods have employed to increase the hydrophobicity of Fe3O4nanoparticles. It was found that magnetic W/O Pickering emulsions of water and liquidparaffin can be stabilized by Fe3O4nanoparticles modified with KH-570, sodium stearate anddi-C12DMAC. However, the emulsion phase was inversed as PEI was added to the water.2. Magnetic polyamine microspheres were prepared by using the Pickeringemulsion of PEI, liquid paraffin and Fe3O4nanoparticles, using the stearic acid modifiedCaCO3nanoparticles as stabilizer. Glutaradehyde was added dropwise into the emulsion tocrosslink PEI. The influences of the amount of CaCO3nanoparticles, Fe3O4nanoparticles andthe volume ratio of oil-water of inner phase on the size distribution of emulsion particles, andthe influence of the amount of crosslinker on the size, hydrophobicity and the swellingproperty of microspheres were investigated. SEM images showed that the outer surface ofmicrospheres was rough covered with fine holes. The isoelectric point of the microsphere is9.6. The thermogravimetric analysis indicated that the thermal stability of PEI significantlyincreased after crosslinking.3. The adsorption of lipase on the magnetic polyamine microsphereswas explored.The influences of hydrophobicity, the content of Fe3O4nanoparticles, adsorption time, initialconcentration of lipase, pH, temperature, ionic strength and metal ions on the adsorption oflipase were studied. The adsorption of microspheres for lipase reached equilibrium at60minutes. The maximum adsorption capacity was206.8mg/g, at pH6.0-7.0and45℃. Theadsorption isotherm can be fitted with Langmuir adsorption. The adsorption of lipase on themicrospheres was the result of hydrophobic interaction and electrostatic attraction.4. The investigation of catalytic performance of immobilized lipase showed theactivity of enzyme can be enhanced by increasing the hydrophobicity or reducing the contentof Fe3O4nanoparticles of the microspheres. After immobilization, the optimum pH for theactivity of enzyme decreased, and the optimum temperature for the lipase to exert its maxiumactivity increased. The immobilized lipase showed the better tolerance to the negative effectsof metal ions and temperature. The kinetic analysis showed the Michaelis constant of lipaseand the maximum velocity of reaction catalyzed by the enzyme were reduced byimmobilization. The activation energies of free and immobilized lipase were nearly the same.