Biomimetic Mineralization Inducing Lipase-Metal-Organic Framework Nanocomposite for Pickering Interfacial Biocatalytic System

In this study, a brand new biocatalytic system was successfully accomplished by combination of metal-organic frameworks (MOFs) biomimetic mineralization and Pickering interfacial system for enhanced lipase catalysis and recycling in organic media. Specifically, a highly porous lipase-loaded MOF composite was synthesized via biomimetic mineralization of ZIF-8 around lipase from Candida rugosa (CRL). With increasing enzyme loading amount, the role of CRL in modulating size, crystallinity, and interior or exterior structure of the composite was meticulously clarified. In this process, we disclosed a gradation from the crystal into an amorphous form for CRL-loaded ZIF-8 and more importantly discovered an enrichment of enzymes on the surface of the crystals. Combining this phenomenon with results of dynamic light scattering, zeta potential, and water contact angle, as well as styrene-induced interface solidification, we confirmed the surface-embedded CRL of the crystal played a role in adjusting the surface chemical characteristics of the composite that directly affected the stability of the emulsion and the distribution rule of stabilizers on the oil-water interface. Furthermore, through the comparison of hydrolyses involving a small substrate (p-nitrophenyl butyrate) and a larger one (p-nitrophenyl palmitate), a stable oil-in-water Pickering emulsion with an optimized quantity and integrity of oil droplets was proved to achieve the highest catalytic efficiency. Notably, because size selectivity of the ZIF-8 shell induced different locations of the substrates in contact with the enzymes, an obvious discrepancy in catalysis efficiency was observed for substrates with different sizes. Impressively, we could employ this system for transesterification by changing only the encapsulated enzyme (lipase B from Candida antarctica expressed in Aspergillus) and optimizing the oil/water ratio. The excellent catalytic performance highlighted the versatility of this interfacial biocatalytic system.