The Construction Of MOFs With Micro-mesoporous Structure And Its Application In Biocatalysis

Enzyme catalysis is widely used in biocatalysis,biomedicine,medical diagnosis and other fields due to its mild reaction conditions,green chemistry and high efficiency.However,the high temperature,organic solvents and other harsh conditions in the application environment would damage the three-dimensional conformation of the enzyme structure,which lead to enzyme inactivation.To solve this problem,this paper explored a new method using MOFs as the carrier for enzyme immobilization.The influence of micro pore mesoporous structure of the classical MOFs ZIF-8 on the apparent catalytic activity and stability of immobilized enzyme was explored,which provided the research basis for the rational design of immobilized enzyme.Based on the competitive coordination strategy,a series of MOFs materials with microporous mesoporous composite structure composed of different ligands were constructed by competitive coordination of Zn²⁺with nucleoside monophosphate and 2-methylimidazole.The successful preparation of microporous MOFs was confirmed by FTIR,Raman spectra,XRD,SEM and nitrogen adsorption curves.Elemental analysis showed that when the molar ratio of adenosine monophosphate to 2-methylimidazole was 3/40,micropores and mesopores existed on one material,and the specific surface area of MOFs with micropores and mesopores structure was 943.9 m²/g.Besides,the introduction of nucleoside monophosphate could significantly enhance the stability of MOFs under acid conditions,and the structure of MOFs remains basically unchanged after being treated for 2 hours under acid conditions.A variety of nucleosides of monophosphate confirmed the universality of this method.In this paper,the micro-mesoporous MOFs-enzyme composites were prepared by in-situ embedding in water phase.A series of MOFs-enzyme composites with high catalytic activity and stability were prepared by in-situ growth method.Compared with ZIF-8-enzyme composites,the apparent catalytic activity of the micro-mesoporous MOFs-enzyme composites was 30 times higher.The interaction between ligands and amino acids in MOFs further stabilized the protein conformation and significantly improved the tolerance of enzyme molecules against organic solvents and high temperature conditions.After 2 hours of treatment in a variety of adverse environments,the micro-mesoporous MOFs-enzyme composites retained about 80%of relative activity,while the natural enzyme retained less than 20%.At the same time,the catalytic activity of MOFs-enzyme composites did not decrease significantly after 7 times of reuse.The in-situ growth competitive coordination immobilization system was further extended to the co immobilization of double enzymes,and the micro-mesoporous MOFs-glucose oxidase/horseradish peroxidase double enzymes composites catalyst was prepared.The catalytic activity of micro-mesoporous MOFs double enzymes system was twice as high as that of immobilized single enzyme.The proximity effect of micro porous MOFs on the double enzymes significantly increased the concentration of hydrogen peroxide,the utilization rate of the intermediate product of the cascade reaction,and thus increased the catalytic efficiency of the double enzymes system.The apparent activity of micro-mesoporous MOFs double enzymes composites was about 1/3 of free double enzymes.Tcomposite had high stability under high temperature,organic solvent,denaturant and other harsh conditions,and could retain more than 60%activity after 2 hours of treatment in these environment.Besides,the composites had good reusability,which could retain more than 70%activity after 7 times of recycling.This study provided the basis for the in-situ preparation of microporous mesoporous MOFs enzyme composite catalytic system with high catalytic performance in water phase,and would further promote the construction and application of high-efficiency MOFs biocatalysis system.