Studies On Enzyme Immobilization In Metal-Organic Frameworks And Their Catalytic Performance

Metal-organic frameworks (MOFs) are a kind of nanoporous materials emerging in the past twenty years. Their structures are similar to zeolites, with higher specific surface area and porosity. MOFs have been well studied in the fields of gas storage, adsorption and separation, membrane separation, heterogeneous catalysis, drug control release, photoelectric magnetic and so on. In addition, MOFs were also used for enzyme immobilization, which can solve the problem that the enzyme is difficult to recover and cannot be reused.Enzyme immobilization is an enzyme loading method, using such as adsorption, embedding method to limit the enzyme to the surface or pores of the carriers, while after the loading the immobilized enzymes still have similar catalytic activity just like free enzymes, to achieve the recovery of enzymes. Enzyme immobilization has many advantages, for example, the immobilized enzyme has better stability, easy to storage and transportation, and can be used repeatedly to achieve reuse.In this work, we used solvent thermal synthesis method with the template precursors through the experiments. We compared the products with the literature to make sure the materials'structures are good. The BET of the hierarchical UiO-66 (H-UiO-66) is 917 m2·g-1,in good agreement with literature value. In this work we used it to immobilize pepsin. At a proper loading condition of 35?, pH=3.6, the maximum adsorption capacities of H-UiO-66, PCN-222, SBA-15 immobilized pepsin are 0.96 g/g,0.755 g/g,0.366 g/g, respectively.In this work, we used hemoglobin as a substrate to measure the catalytic activity of pepsin and immobilized pepsin, and also investigated the reuse of the immobilized enzyme. The free pepsin activity of concentration of 1 mg/mL,0.8 mg/mL is 17×103 U/g and 18.5×103 U/g. We used H-UiO-66 to immobilize pepsin of 2 mg/mL. The measured enzyme activity is:1.1×103U/g. While immobilized by PCN-222 and SBA-15, the collected enzyme activity is much lower. At 35? and pH=3.6, and the acetic acid buffer environment, enzyme catalytic reaction was carried out.1 hour later, the solid was filtered out, washed with the acetate buffer, and freeze dried. The enzyme activity was 0.65×103U/g, the recovery rate was 56.5%. Under the same conditions, the reaction of 2 hours, after washing and freeze drying, the enzyme activity is 0.57×103 U/g, the recovery rate of enzyme activity is 49.3%.