Adjusting The Biocatalytic Performance Of Metal-organic Framework-based Nanoenzymes Based On Pore Engineering

Biocatalysis has been widely used in industrial catalysis,because of its mild reaction conditions and high selectivity.However,natural enzymes often have some problems,such as poor stability and difficulty in recycling,which heavily limit their application.There are two strategies to solve these problems : One way is to improve the stability and recyclability of the enzyme by loading enzyme on the carrier;another is to develop nanomaterials with biocatalytic activity.Metal-organic frameworks have attracted extensive attention due to their high specific surface a rea,highly adjustable pore size/composition,and chemical modification properties.These characteristics allow the metal organic framework suitable to solve the problems of natural enzymes.In this paper,based on the structural characteristics of the met al-organic framework,we developed two methods to prepare the metal-organic frameworks based nanoenzymes.(1)In view of the large substrate diffusion resistance caused by small pore size in the current metal-organic framework supported biological enzyme system,a novel method based on biomimetic mineralization was developed to prepare mesoporo us metal-organic framework(MIL-100(Fe))to encapsulate enzymes as biocatalysis.Based on the theory of biomimetic mineralization,enzymes can aggregate metal ions and organic ligands at room temperature,which can rapidly induce the formation of metal organic framework encapsulated nanoenzyme catalysts.The results of XRD and SEM test showed that the original crystal structure of MIL-100(Fe)remained after immobilization.Furthermore,UV,BET,XPS and CLSM were used to confirm that the enzyme was coated in MIL-100(Fe).This strategy can be applied to different types of biological enzymes,including Cal B,GOx and ?-Gal.Due to the protective effect of the framework,the enzyme @MIL-100(Fe)exhibited highly catalytic efficiency,high selectivity and stability.Compared with unencapsulated enzymes,nanoenzymes still maintain high catalytic performance after 5 cycles.(2)In view of the unstable chemical properties of natural enzymes and the difficulty of direct chemical modification,a chemical post-modification method was developed to adjust pores chemical environment of metal organic framework-based nanoenzymes,which can help us to control the performance of biocatalysis.Based on the theory that the iron center site in porphyrin can be easily decorated,we can adjust the pore's chemical environment of porphyrin-based metal-organic framework nanoenzymes(PCN-222(Fe))by loading different hydrophilic and hydrophobic molecules: pyridine,alkyl 4-hexylpyridine with long-chain alkyl and 4-butanol pyridine with hydroxyl.By post-synthesis modification,nanoenzymes can maintain the original crystal structure,which was confirmed by XRD,SEM,XPS tests.The catalytic activity of the modified materials was comfirmed by the model of catalytic oxidation reaction of TMB.The results exihibited that the affinity of TMB was improved by the modification of 4-hexylpyridine.This work provides a new idea for controlling the biocatalysis by inducing different molecules of metal-organic framework-based nanoenzymes.