Theoretical Study On The Mechanisms Of Oxidoreductase Mimetic Activities Of Noble Metal-based Nanomaterials

Nanozyme is a new generation of artificial enzyme,which has the advantages of good stability,high catalytic efficiency,easy preparation and economy,etc.,and has been widely used in fields including biological detection and environmental sciences.However,it also remains a great challenge during its rapid development process.In this dissertation,density functional theory calculation methods and experimental verifications are used to investigate the catalytic mechanisms and structure-activity relationships of four oxidoreductases,including oxidase,peroxidase,catalase and superoxide dismutase(SOD)activities of noble metal nanomaterials,and the following results were obtained:The adsorption energy,dissociation energy barrier and reaction energy of O2 on these four metal surfaces are calculated to study the oxidase mimetic activities on(111)surfaces of Au,Ag,Pd and Pt.It is found that there exists a linear relationship between the adsorption energies of O2 on the metal surfaces and corresponding decomposition energy barriers,so that the oxidase mimetic activity of the metals can be rapidly predicted based on the adsorption energies of O2.In addition,the enzyme mimetic activities of metals can be reasonably tunable by adjusting the alloy composition.The predicted activity orders of these four different metals and their alloys by calculations are consistent with the experimental results.And a general mechanism of 3O2 activation on metal surfaces is proposed based on the results.In addition,it is revealed the origin of metal nanomaterials exhibiting SOD mimetic activity is the adsorption and recombination of ·OOH on metal surfaces.The results provide a more profound perspective for the oxidoreductase activities of noble metal-based nanomaterials,and also provide a basis for rational design and optimizing the enzyme mimetic activities of metal nanomaterials.To study the influence of changes in electron-structure of nanomaterials on oxidase mimetic activity,groups with different properties,such as-SCH3 and-NO2 are used to modified the Pt(111)surface.It is found that the electron-donating group-SCH3 can effectively reduce the work function of the metal,reduce the decomposition energy barrier of O2 on the metal surface,and further enhance the oxidase mimetic activity of the metal.The results provide a theoretical basis for improving the enzyme activity of metal nanomaterials.Four oxidoreductases mimetic activities of Pd(111)and Pd(100)are studied.It is found that the catalase and superoxide dismutase-like activities of(111)-faceted Pd octahedrons are higher than that of(100)-faceted Pd cubes.And experiments in vitro have established that the former can exhibit SOD mimetic activity quenching O2·-more effectively than the latter,so the abilities of protecting biological molecules and cell organisms of Pd(111)are better.On the contrary,Pd(100)has higher oxidase and peroxidase mimetic activities than Pd(111),and exhibits higher antibacterial property.The results provide a theoretical basis for the treatment of diseases caused by oxidative stress under clinical conditions and the designing of noble metal nanomaterials with highly efficient targeting bacterial activity.Moreover,it is found that the catalase activity of the graphdiyne(GDY)can be effectively improved by dispersing Pd onto the material.And the catalytic activity is related to the valence states of Pd clusters,that is,low valence state Pd' exhibits higher catalytic activity than high valence state Pd2+.These results provide important information for the design of nanozyme with high catalytic activities.