Monodisperse core-shell magnetic organosilica nanoflowers with radial wrinkle for lipase immobilization

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The monodisperse core-shell magnetic organosilica nanoflowers were successfully synthesized by a method based on the bicontinuous microemulsion phase of the Winsor III system. The obtained nanoflowers with magnetic core and flower-like organosilica shell possess radial-wrinkle, tunable perpendicular channels, and high magnetization (62emu/g). The nanoflowers were employed as support for Candida antarctica lipase B (CALB) covalent immobilization. The maximum amount of CALB immobilized on the nanoflowers was 93mg/gsupport, while the specific hydrolytic activity was 22,700U/gsupport. Meanwhile, the CALB@nanoflowers showed better pH stability than free CALB and CALB@MMPS, which can remain 65% of initial activity after incubated in cyclohexane at 60°C for 96h, and remain 90% of initial activity after stored in room temperature for 42days. In addition, the CALB@nanoflowers could catalyze the 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@nanoflowers retained more than 85% of its initial activity in catalyzing the synthesis of butyl-levulinates and more than 96% of the initial activity in catalyzing the synthesis of long chain alkyl levulinates, which was much higher than commercial N435. With these desired characteristics, the design of hydrophobic nanoflowers with tunable wrinkle channels for lipases immobilization opens up a new way to improve the catalytic activity and stability of the lipases, and may have potential applications in various lipase-based industrial processes.