The Study On Facet-dependent Activities Of Nanozymes And Their Biological Applications

Almost all of the reactions in the biological environment are carried out under the catalysis of enzymes.The applications of natural enzymes have been limited by their limited stability and loss of activation in harsh environments(e.g.,non-physiological p H,high temperature,or in the presence of inhibitors)althouth they have high catalytic activity.Therefore,the research of artificial enzymes is vitally important.Among them,nanomaterials(nanozymes)are developing rapidly because of their high stability,low cost and recycled utilization.However,there are still some drawbacks in the application of nanomaterials,such as lower efficiency and potential nano-toxicity compared with traditional natural enzymes.Therefore,the development of high performance nanozymes with higher activity,higher stability and strict safety is the key issue for future research.The fundmental understanding of the relationship between the activity of nanozymes and physicochemical properties of nanomaterials is of guiding significance in the development and design of nanozymes.Based on investigating the study of nanozymes,the main physicochemical properties of nanomaterials that affect the activity of naozymes,such as size,composition and morphology have been discussed.However,there were lack of the related researches about understanding the structure-activity relationship between surface facet,the alignment of surface atoms,which play an important role in catalytic reactions and the catalytic activity of nanozyme.Therefore,the research subject was proposed-the study on facet-dependent activities of nanozymes and their biological applications.The aim of this research was to investigate the effect of facet on the activity of nanozymes on antioxidant stress and the promotion of oxidation,and further explored the effect of antioxidant stress and antibacterial activity of nanozymes in the cell and bacteria models,respectively.The research was carried out with the following three main works.The main research methods,results and conclusions are listed as follows:1.The palladium(Pd)nanocrystals with high catalytic activity and wide application were chosed as the model system.The synthesis of Pd nanocrystals with the {111} and {100} surfaces were carried out by a hydrothermal method with a capping agent and tunning the reaction kinetics,respectively.The morphology and crystal surface facets were characterized by transmission electron microscope and X ray diffraction.The surface coating of Pd nanocrystals were further confirmed by Fourier transform infrared spectroscopy,X-ray diffraction and thermogravimetric analyses.The above results indicate that the PVP on the surface of Pd nanocrystals is negligible and thus the difference between Pd nanocrystals mainly is attributed to the surface facet.2.Electron spin-resonance spectroscopy was used to compare the activity of detoxifying reactive oxygen species of two types of Pd nanocrystals and found that lower surface energy {111}-faceted Pd octahedrons had greater antioxidant enzyme-like activity than higher surface energy {100}-faceted Pd nanocubes.Our in vitro experiments also found that Pd octahedrons are more effective than Pd nanocubes at reducing the damage of oxidative stress.Those reductions in ROS preserve the homogeneity of mitochondrial membrane potential and attenuate damage to important biomolecules,thereby allowing a substantially higher number of cells to survive oxidative challenges.Our computations of molecular mechanisms for the antioxidant activities of {111}-and {100}-faceted Pd nanocrystals,as well as their activity order,agree well with experimental observations.These findings can guide the design of antioxidant-mimicking nanomaterials,which could have therapeutic or preventative potential against oxidative stress related diseases.3.With a combined experimental and theoretical approach,we unveil that Pd nanocrystals exhibit facet-dependent oxidase and peroxidase-like activities that endow them with excellent antibacterial properties via generation of reactive oxygen species.The antibacterial efficiency of Pd nanocrystals against Gram-positive bacteria is consistent with the extent of their enzyme-like activity,that is {100}-faceted Pd cubes with higher activities kill bacteria more effectively than {111}-faceted Pd octahedrons.Surprisingly,a reverse trend of antibacterial activity is observed against Gram-negative bacteria,with Pd octahedrons displaying stronger penetration into bacterial membranes than Pd nanocubes,thereby exerting higher antibacterial activity than the latter.Our findings provide a deeper understanding of facet-dependent enzyme-like activities and might advance the development of noble metal-based nanomaterials with both enhanced and targeted antibacterial activities.In conclusion,we firstly proposed that the catalytic activity of nanozymes could be improved by tunning surface facets of nanomaterials and this structure-activtity relationship can be reflected in biological applications.This will provide new insights into the optimization of the activity of nanozymes and more posssibilities for the biological application of nanozymes.