Rational post-synthesis of lipase-magnetic MOF conjugates with boosted enzymatic performance

Metal-organic frameworks (MOFs) have shown great potential as supports for enzyme immobilization, but their application is limited by separation difficulties due to their nanoscale size. Herein, magnetic MOFs (Fe3O4@MIL-53-NH2(Al)) were prepared under mild conditions, and an ionic liquid (IL) was used as linker to covalently immobilize lipase in Fe3O4@MIL-53-NH2-IL/PPL. The IL was composed of imidazolium cations and bis(trifluoromethylsulfonyl)imide anions, which enhanced the hydrophobicity of the support. The synthesized biocatalyst Fe3O4@MIL-53-NH2-IL/PPL showed excellent activity, 2.4 times higher than free lipase, and its denaturation, thermal, and storage stability were all satisfactory. The activity of the biocatalyst remained at up to 88.4% after ten recycles. The excellent magnetic responsiveness facilitated the collection of the biocatalyst, which may be beneficial to its reusability, and the multiple interactions between lipase and support may enhance the structural stability of lipase, which was investigated by circular dichroism spectroscopy. Compared to free lipase, both the substrate affinity and catalytic efficiency of Fe3O4@MIL-53-NH2-IL/PPL were improved. The magnetic MOF composite materials prepared through the post-synthesis method exhibited good potential in the field of lipase immobilization. The preparation method of immobilized lipase in this work provides a meaningful reference for the application of other MOF composites in the field of enzyme immobilization.