Modulating The Bioactivity And Catalystic Performance Of Enzymes/Porous Organic Frameworks

Enzymes,which are composed of many amino acid molecules with special sequences by weak interaction,can be easily affected by harsh conditions,and immobilizing enzymes into supports could enhance their stability and maintain their natural activity.However,they can also be affected by the microenvironment that created by surrounding supports due to their fragile structures.Porous organic frameworks(such as MOFs,COFs and HOFs)recently have became the ideal supports for enzyme immobilization to protect enzymes and keep the high efficiency of biocatalytsis in various biological and chemical reactions.Different from other common supports,porous organic frameworks are highly crystalline with specific,adjustable structures,which provid an excellent platform for immobilizing enzymes.Herein,porous organic frameworks(MOFs and COFs)had been selected as the enzyme supports,and the activities of enzymes were enhanced by the precise design of porous organic frameworks and the optimization of synthesis methods,providing several biocomposites that behaved higher activity than free enzymes.(1)36 kinds of microporous and macroporous binary/ternary MTV-MOFs(Multivariate Metal-Organic Frameworks)were designed and synthesized for immobilizing enzyme(BCL)via a multivariate strategy.The framework-enzyme interactions were fine-tuned by continuously changing the pore microenvironment of MTV-MOFs,and the activities of immobilized enzyme were gradually optimized from 9 % to 78 %,the activity of the enzyme that immobilized in macroporous MOFs was even better than that of free enzyme(up to 120 %).To systematically study this interaction,we developed the component-adjustment-ternary plot method to approach the optimal activity of encapsulated BCL and revealed a nonlinear correlation,first incremental and then decremental,between the BCL activity and the hydrophilic linker’ ratios in MTV-MOFs.These findings confirmed the influences of the spatial arrangement of functional groups(N atoms)in MTV-MOFs on enzymatic activity.In other words,the functional groups arranged along the three-dimensional space across the MTV-MOFs crystal have unique sequences,which could change the enzyme structure between closed-lid and open-lid conformations.The conformation changes of immobilized enzyme were then explored by ATR-FTIR spectra and fluorescence studies,confirming the changes of enzyme structure between closed-lid and open-lid conformations and the existence of the optimal hydrophilic point of MOFs.BCL that immobilized within MTV-MOFs not only exhibited the improved stability in harsh conditions,but also gave the better conversions than free enzyme in the kinetic resolution reactions with high ee value(99 %),demonstrating its potential in practical applications.(2)De novo encapsulation was first successfully employed for embedding enzyme into COFs material via a solid phase grinding method,and BCL@COF-Tp Pa biocomposite was obtained.The activity of BCL@COF-Tp Pa was much better than that of the traditional hydrothermal synthesized enzyme@COFs,because the solid phase grinding method could avoid the harsh conditions in COFs synthesis.Compared to metal-connected MOFs,metal free COFs showed unrivalled superiority for immobilizing enzymes,not only benefiting from its high stability,but also profiting by their metal free nature in which BCL@COFs showed much higher activity than BCL@MOFs(3.4-14.4 times higher)and even free BCL(1.4 times higher).Moreover,we demonstrated the advantages of de novo strategy for synthesizing BCL@COFs compared to traditional post-synthetic BCL-on-COF-Tp Pa,such as fewer enzyme leaching,higher activity and stronger protections.Finally,BCL@COF-Tp Pa was applied in the kinetic resolution reaction,showing superior conversions than that of free BCL and all BCL@MOFs with 99 % ee.