Preparation And The Catalytic Performance Of Lipase Immobilized On Magnetic Silica-based Nanoflowers

Monodisperse core-shell magnetic nanoflowers materials,which possess high specific surface area,pore volume and easily separation and enrichment,have potential applications in enzyme immobilization.In this paper,Monodisperse core-shell magnetic nanoflowers were used as carrier,and covalent binding methods were employed to fabricate immobilized enzymes.The details were summarized as follows:First,traditional core-shell magnetic nanomartials is usually hampered by their small mesoporous and complicated preparation process.To overcome these drawbacks effectively,the core-shell magnetic SiO₂-nanoflowers（SiO₂-nanoflowers）were prepared based on this ameliorated Winsor III reaction system.The obtained SiO₂-nanoflowers with magnetic core and flower-like organosilica shell possess radial-wrinkle,high specific surface area（629.7m²/g）and pore volume（1.636 cm³/g）and high magnetization（17 emu/g）.The SiO₂-nanoflowers were employed as support for Candida antarctica lipase B（CALB）covalent immobilization（CALB@SiO₂-nanoflowers）.The CALB@SiO₂-nanoflowers showed better pH stability and thermal stability than free CALB,and remain 90%of initial activity after stored in room temperature for 42 days.In addition,the CALB@SiO₂-nanoflowers could catalyzethe synthesis of alkyl levulinates through the esterification of levulinic acid alcohols with different chain length（n-butyl alcohol,n-caprylic alcohol,n-lauryl alcohol）in a solvent-free system effectively.After recycling 10times,the CALB@SiO₂-nanoflowers retained more than 60.12%of its initial activity in catalyzing the synthesis of butyl-levulinates and more than 88.07%and 96.29%of the initial activities in catalyzing the synthesis of long chain alkyl levulinates,which was much higher than commercial N435.Second,the core-shell magnetic hybrid-nanoflowers（H-SiO₂-nanoflowers）were prepared based on last chapter by adding 1,2-Bis（triethoxysilyl）ethane（BTSE）as organosilicone source.The obtained H-SiO2-nanoflowers-19 and H-SiO2-nanoflowers-37with thinner organosilica shell and higher magnetization was than SiO₂-nanoflowers.The H-SiO2-nanoflowers-19 and H-SiO2-nanoflowers-37 were employed as supports for Candida antarctica lipase B（CALB）covalent immobilization.The H-SiO₂-nanoflowers-19and H-SiO₂-nanoflowers-37 showed better thermal,pH and storage stabilities than free CALB and CALB@SiO₂-nanoflowers.In addition,the CALB@H-SiO₂-nanoflowers-37could catalyzethe synthesis of alkyl levulinates through the esterification of levulinic acid alcohols with different chain length（n-butyl alcohol,n-caprylic alcohol,n-lauryl alcohol）in a solvent-free system effectively.After recycling 10 times,the CALB@SiO2-nanoflowers showed better than commercial CALB@SiO2-nanoflowers and N435.Third,this work attempted to optimize the enzymatic production of Glycerine carbonate（GC）from glycerol and Dimethyl carbonate（DMC）by transesterification using CALB@H-SiO₂-nanoflowers-37.GC was successfully synthesized under the optimized conditions at a GC conversion as high as 88.53%.After recycling 7 times,the CALB@H-SiO2-nanoflowers-37 retained more than 78.82%of its initial activity in catalyzing the synthesis of GC,and the yield of GC was more than 73.09%.which was much higher than commercial N435（58.34%,29.35%）and CALB@CMI@nanoflowers（17.06%,10.29%）.