Preparation and characterization of dendritic composite magnetic particles as a novel enzyme immobilization carrier

Three kinds of composite carriers (S-type, M-type, MS-type) were prepared and assessed their application in immobilizing lipase. The S-type carrier was prepared by copolymerization of tetraethyl orthosilicate and a dendritic monomer derived from 3-aminopropyltriethoxysilane and methyl acrylate, and the MS-type carrier by copolymerization of tetraethyl orthosilicate and 3-aminopropyltriethoxysilane or a dendritic monomer on the surface of magnetic microparticle (Fe3O4). The carriers were characterized by means of IR spectrum, titration and particle size analyzer. Subsequent immobilization experiments clearly indicated that the MS-type was the best in lipase immobilization among the three types of carriers. Moreover, the immobilized PPL by simple adsorption could be reused without detectable decline for its activity until up to four cycles, while the immobilized PPL by cross-linking could be reused up to five cycles without any loss in activity. Interestingly, hydrolysis of 2-phenyl-1-propyl acetate catalyzed by PPL immobilized on the S-type and MS-type carriers showed a higher enantioselectivity (18–32% up) than that by free PPL. The optimal immobilization conditions of PPL on MS-type carriers were as follows: 50 mg PPL/g; the stirring time: 60 min; pH 7.0; room temperature.