Construction Of Mn/Cu Bimetallic Organic Framework Derivatives Nanozymes And Application Of Superoxide Dismutase-Like Activity

Superoxide dismutase（SOD）is an important part of the antioxidant system in vivo,which can catalyze the disproportionation of superoxide anions to maintain the stability of reactive oxygen species（ROS）content in vivo.SOD is also a natural antioxidant,which has been widely used in cosmetics,medicine,agriculture and food.However,natural SOD has some inherent defects such as easy inactivation,difficult preparation and purification,and high cost,which limit its further application to some extent.With the development of nanoscience and technology,many nanomaterials have been found to have enzyme-like activities,which are defined as nanozymes,which can overcome the problems of poor stability and high cost of natural enzymes to a certain extent.In this thesis,from the most widely distributed two kinds of natural SOD（Cu or Mn active center SOD）,the simulation of its catalytic active center and simulation of the microenvironment,through heat treatment and simulation of the microenvironment,successfully constructed two kinds of SOD-like activity of nanozymes,and explore their application in the field of detection and food preservation.The details are as follows:1.A metal-organic framework（MOF）material（Cu-BTC）prepared by solvothermal method with Cu as the center and Trimesic acid（H₃BTC）as the ligand was used as the raw material.The Cu center in Cu-BTC was partially exchanged with Mn by post-synthetic exchange method.A series of bimetallic MOFs（Mn/Cu-BTC）with different Mn doping amounts were prepared.It was found that when the concentration of Mn²⁺was 0.4 M,the SOD-like activity of Mn/Cu-BTC was the best,and the SOD-like activity of Mn/Cu-BTC-0.4 was increased by 1.33 times compared with that of Cu-BTC.This is attributed to the fact that Mn²⁺tends to transfer electrons to Cu²⁺during the reaction,which accelerates the electron transfer rate of the reaction.Comparing the enzyme-like activities of Mn/Cu-BTC-0.4 calcined products under different atmospheres,the properties of calcined products under air or mixed atmospheres decreased,while the calcined products under N₂atmosphere（marked as Mn/Cu-C-N₂）increased by 20%compared with those without.This is due to the disappearance of Mn²⁺and the appearance of Mn⁴⁺in the calcined products under air or mixed atmosphere,which reduces the activity.While in N₂ atmosphere,the contents of Mn²⁺and Cu⁺increased by 10.77%and 5.92%respectively,which improved the activity.2.Inspired by the catalytic process of SOD in the active center of Mn,that is,the hydroxyl group near the center of Mn participates in the construction of hydrogen bond network to transfer protons required in the reaction process,which can improve the catalytic efficiency.Using Cu-BTC prepared at room temperature as core,2,5-dihydroxyterylene acid as ligand,Mn²⁺as metal center,manganese MOF（denoted as Mn-MOF-74）was prepared in situ on the surface of Cu-BTC by surfactant induction method,and bimetallic MOF derivatives（denoted as Mn/Cu-MOF）with core-shell structure were formed.When the amount of Cu-BTC was 0.3 g（Mn/Cu-MOF-0.3）,the catalytic activity of the prepared material was the best,and the enzyme-like activity was 2.84 times and 1.53 times of that of Cu-BTC and Mn-MOF-74 in the mono-metal center,respectively.On the one hand,Mn²⁺in Mn/Cu-MOF-0.3 tends to transfer electrons to Cu²⁺,which accelerates the electron transfer.On the other hand,the introduction of hydroxyl improves the catalytic microenvironment,which can transfer the protons required in the reaction process and also improves the enzyme-like activity.3.Mn/Cu-C-N₂ and Mn/Cu-MOF-0.3 prepared in the previous two chapters with good SOD activity were selected as catalysts respectively,and combined with the magnetic separation strategy,the magnetic separation colorimetric sensor platform for Aflatoxin B₁（AFB₁）was successfully constructed.The sensor platform based on Mn/Cu-C-N₂ can detect AFB₁ in the range of 1～1000ng/m L,and the detection limit is 0.12 ng/m L.However,the sensor platform based on Mn/Cu-MOF-0.3 can realize the specific detection of AFB₁ in the range of 0.1～3000 ng/m L,and the detection limit is 0.07 ng/m L.The difference in detection performance because the catalytic activity of Mn/Cu-MOF-0.3 is 50%higher than that of Mn/Cu-C-N₂,which makes it possess higher detection sensitivity.Moreover,both sensor platforms have good selectivity,which can realize AFB₁ detection of peanut samples.4.The cytotoxicity of Mn/Cu-C-N₂ and Mn/Cu-MOF-0.3 was further investigated.The results showed that the cell survival rate of the former was 90.2%,while that of the latter was only 46.0%.Then,Mn/Cu-C-N₂ was mixed with chitosan/starch to make the plastic wrap.Blueberry was selected as the sample to explore the preservation and antioxidant properties of the plastic wrap.The comparative study showed that the addition of Mn/Cu-C-N₂ did not affect the preservation performance of the film,but greatly improved its antioxidant performance.The content of anthocyanin wrapped in the film decreased by 17.1%after 7 days,while that of ordinary plastic wrap decreased by 56.2%,which was attributed to the fact that Mn/Cu-C-N₂ could inhibit the accumulation of reactive oxygen species.