Catalysis And Biosynthesis Of Extracellular Nanometer Polyenzymes

Compared with inorganic catalyst,enzyme can reduce the activation energy of chemical reaction,so it has high efficiency;enzyme can only catalyze one or a kind of chemical reaction,so it has specificity;as a biocatalyst,the condition of enzyme catalysis is mild.However,under the conditions of high temperature,strong acid or strong alkali,the free enzyme structure will change and lose its activity,and it is not easy to be rcycled.The immobilized enzyme is stable and easy to be separated from the reaction system,adapted to harsh reaction conditions and can be reused.The metal organic framework materials(MOFs)have many properties,such as regular pore structure,large specific surface area and metal-site-rich.It's an excellent carrier for enzyme immobilization.In this paper,MOFs was used to immobilize enzymes,to improve the stability of the enzyme,to achieve recycle and to improve the catalytic efficiency of the enzyme.A new type of photocatalyst was synthesized and combined with enzymes,which has realized the reduction from CO2 to methanol,and regeneration of NADH.The main work of this paper is as follows:(1)The immobilized enzyme carrier of magnetic metal-organic framework material was successfully constructed.The Fe304 nanoparticles was used as "nucleus",using layer by layer self-assembly technology,consructed a HKUST-1 shell on the surface of Fe304.Successfully realized the immobilization of glucose oxidase(GOx)and horseradish peroxidase(HRP).By controlling the spatial position of the enzymes,three bienzyme nanosystems have been obtained.(2)The reaction conditions and kinetics of bienzyme nanosystems were systematically studied.Studys showed that the enzyme activity was highest at pH 6 and 20?.The nanosystem in which the GOx was located at the outside layerof HKUST-1 and the HRP was located at the inside layer of HKUST-1 was find the best way of immobilization,and it showed superior kinetic properties.The Michaelis constant was 0.8 mmol·L-1 and the maximum reaction rate was 11.3 ?mol·L-1·min-1.The nanosystem in which the HRP was located at the outside layerof HKUST-1 and the GOx was located at the inside layer of HKUST-1 showed best operational stability with a glucose conversion of 80.6%even after repeated used ten cycles.(3)The nano catalytic system combining photocatalytic reduction with enzyme catalysis was synthesized,and successfully realized the reduction of CO2 and the regeneration of NADH cofactor.We designed and synthesized the metalloporphyrin complex.Under visible light illumination,NADH was regenerated and realized the reduction from CO2 to formic acid,the yield of formic acid reached 174 mmol·L-1·h-1.Alcohol dehydrogenase(ADH)and for naldehyde dihydrogenase(FaldDH)were introduced to this photocatalytic system.A composite system of photocatalyst and biocatalyst was established,which has realized NADH regeneration and the reduction from CO2 to methanol.