Biocatlysis Enhancement By The Engineering Of Metal-organic Frameworks

Metal-Organic Frameworks(MOFs)are the novel porous materials that formed by the coordination between metal ions/clusters and organic ligands,and are well explored in various areas for its controllable physicochemical properties.Recently,more researchers paid attention on the applications of MOFs in bio-catalysis area,for example,MOFs were extensively explored that functioned as the matrix for enzyme immobilization.However,most MOFs are microporous and the pores are too narrow to be accessible for enzymes(larger than 3 nm in most cases).For the whole cell catalysis,MOFs were reported to be protective of cells against the harsh environmental conditions,but the chemical property of MOFs were not explored yet so far.Thus,it is a meaningful project to build the coupling system of MOFs and whole cell catalysis to enhance the biocatalysis efficiency.In this work,we designed the novel hierarchically porous and photo sensitive MOFs to immobilize multi-enzymes and couple with the whole cell catalysis respectively,the biocatalysis performance showed distinct enhancement in this strategy.The main contents are as follows:(1)To match the pores diameter of MOFs with the enzyme size,we developed the hierarchical porous MOFs by using the hydrogel as a novel template.The hydrogel was constructed by the hydrogen bond between melamine and salicylic acid,and was removable by hot water washing.In this way,the mesopores can be created.The hierarchically structured ZIF8(HZIF-8)was obtained with the adjustable pore diameter(16.2～27.5 nm)and mesopores volume(45.97～59.17%).The process of this strategy is facile,mild,and is universal to get other hierarchically structured MOFs(HZIF-67).The immobilized enzymes system GOx-HRP@HZIF-8,showed the 7.7 or 2.7-folds higher enzymatic efficiency(kcat/Km)to that of free enzymes or the immobilized enzymes system using microporous ZIF-8 as matrix.Furthermore,the enzymatic stability of GOxHRP@HZIF-8 against harsh temperature and pH conditions was enhanced for the confinement effect attributed to mesopores of HZIF-8.GOxHRP@HZIF-8 remained 51.7%residual enzymatic activity after using for 25 cycles.At last,we studied the substrate diffusion enchantment contributed.by mesopores of HZIF-8 via Knoevenagel reaction.(2).We designed a novel photo sensitive MOFs(BUCT-T)as the first step to couple with whole cell catalysis.The crystallographic nature of BUCT-T was analyzed,and the CO2 photoreduction performance was measured as well.Formate acid was obtained with the rate of 2.8 mmol g1 h-1,which rate was higher than the previous reports.At last,the mechanism of BUCT-T photoreduction was fully studied by Transient Fluorescence Spectroscopy,Photocurrent Response Curve,Spin Electron Resonance,in situ Infrared Spectroscopy,et al.(3)The photo sensitive BUCT-T was used to increase the metabolic production.Saccharomyces Cerevisiae was chosen as the model bacteria and the reduced confactor based Free Fatty Acid(FFA)was as the model product in this hybrid system.BUCT-T was mixed in culture medium of Saccharomyces Cerevisiae,and the formate acid obtained by CO2 photoreduction was supplied to bacteria in situ to enhance the cofactor regeneration.In this hybrid system,FFA production was 278.68±9.23 mg/L,which was 33.6%higher than that in commonly cultured Saccharomyces Cerevisiae.We also found that,the intracellular reduced cofactor content increased rapidly when formate acid was introduced into the culture medium,this result indicated that FFA production was improved by the formate acid enhanced reduced cofactor regeneration process.