Design,preparation Of Oxidase-MOFs Composites And Study Of Their Synergistic Catalysis

Enzymes,as natural biocatalysts with prominent activity,high selectivity and low physiological toxicity,hold great promise for applications in pharmaceutical,food,fine chemicals production and environmental detection.However,industrial enzyme applications are severely limited by its fragile properties,such as poor operability,low tolerance to organic solvents and heat,and poor long-term stability.To overcome these problems,the enzyme is usually immobilized on/in the porous solid materials with good biocompatibility.Metal-organic frameworks(MOFs)are a kind of porous materials formed by coordination bonds between inorganic metal ions and organic ligands.Compared with traditional porous materials,MOFs serves as the ideal matrixes for enzyme immobilization due to their high specific surface area,high porosity,structural diversity,easy modification and good biocompatibility.In this thesis,a series of novel enzyme-MOFs composites have been prepared by using several important oxidases,and the synergistic catalysis between enzymes and chemical catalysts was constructed.The interaction between enyzme and MOFs is studied,and the relationship between the structure and catalytic performance of the composites has been investigated in detail.The main contents amd resuilts of this thesis are as follows:1.In order to improve the activity and stability of the immobilized enzyme,we designed a rational synergic catalytic system(Cyt c-Pd)based on Cytochrome c(Cyt c)and peroxidase mimic(Pd nanoparticles),then integrated it into ZIF-8 by biomimetic mineralization in aqueous at room temperature.Modern characterization techniques demonstrated that Cyt c-Pd had been successfully embedded in ZIF-8.The as-synthesized Cyt c-Pd@ZIF-8 composites exhibted an increased turnover number(approximately 2.4-fold for k_cat)and an enhanced catalytic efficiency(approximately 2.3-fold for k_cat/K_M)compared to free Cyt c.Due to the shielding effect of ZIF-8,the immobilized Cyt c showed the significantly improved resistance against harsh conditions(e.g.high temperatures and organic solvents)and operability.The catalytic activity enhancement of Cyt c-Pd@ZIF-8 was mainly attributed to the positive conformational change of enzyme regulated by Pd-enzyme interface owing to the allosteric effects of Cyt c-Pd,which exerted a high affinity toward the substrates by exposing heme group of Cyt c.2.Alcohol dehydrogenase(ADH)is a kind of NAD⁺(?-nicotinamide adenine dinucleotide)dependent oxidoreductases,which catalyze the oxidation of primary and secondary alcohols with a simultaneous cofactor reduction of NAD⁺to the reduced form(NADH).The extended application of these oxidoreductases has been restricted because cofactors are consumed during the enzymatic transformation.In order to improve the catalytic efficiency of ADH,ADH was encapsulated into metal-organic framework HKUST-1 through an in situ approach to construct a synergistic chemo-and bio-catalysis system,where ADH was for the conversion of benzyl alcohol to benzaldehyde,and HKUST-1 was in charge for the regeneration of NAD⁺in the presence of H₂O₂.It was found that HKUST-1 was a versatile catalyst for efficient oxidation of NADH in different p H,temperature and buffer solution.Owing to the NAD⁺regeneration by HKUST-1,ADH@HKUST-1 achieved a4.3-fold higher benzaldehyde yield than that of free ADH.Besides,compared with free ADH,ADH@HKUST-1 showed the excellent long-term storage,recycling performance and stability against urea and organic solvents.3.In order to improve the efficiency of enzyme-driven cascades,a close and coordinated relationship between catalysts involved in the cascades is usually estabilished.The biomimetic quasi MOF(qNM)with highly efficient peroxidase-like activity was synthesized via a modulator-induced defect-formation strategy followed by pyrolysis.The q NM served as nanoreactor for enzyme catalysis process and also contributed its biomimetic activity to co-operation with GOx or?-Gal/GOx for the efficient enzyme-driven cascades.It was found that q NM was an excellent catalyst for oxidations of various peroxidase substrates(e.g.ABTS,THB,OPD and TMB).The excellent activity of q NM was attibuted to the presence of Fe²⁺species,which facilitated the transition between Fe²⁺and Fe³⁺species to produce more·OH by H₂O₂ decomposition.The q NM also served as the potential matrix for GOx immobilization.The immobilized GOx not only showed a comparable catalytic efficiency to free GOx,but also exhibited excellent stability against high temperatures and organic solvents.Compared with the mixture of each component in the solution,the combination of GOx or?-Gal/GOx in q NM achieved 2.67 and 1.83-fold enhancements in the activity of catalytic cascades,respectively.This dissertation may provide a new idea for the design of efficient,stable and functional enzyme-MOF composite catalysts,which holds promise for applications in biosensors,catalysis and pharmaceuticals.