Natural DNA Supported Metal Nano-Catalysts: Preparation, Characterization And Study On Their Catalytic Activity

With the development and combination of nanotechnology and green organic synthesis, supported metal nano-catalysts have attracted many attentions. Comparing with traditional metal catalysts, they have many advantages, such as environment-benign, high catalytic activity and recycling, which meet the requirement of sustainable development and low carbon economy.Meanwhile, as an important biopolymer, DNA is reported to be a suitable supporter to support metal nanoparticles. But the high cost and small amount of production limit the development and application this kind of DNA supported metal nanoparticles. Based on these two parts, in this thesis we mainly study on the new kind of metal nano-catalysts supported by cheap natural DNA. There are three parts included in this thesis. The first part is about the recent progress of supported metal nano-catalyst and DNA supported metal nanoparticles. The second part involves the reparation and characterization of the natural DNA supported metal nanoparticles. In the third part we use these them as catalysts in several organic reactions, such as reduction, oxidation and tandem reactions. Moreover, the relationship between the high catalytic activity of these catalysts and their unique structure is also researched.Firstly, by chemical reduction, we synthesized the water-soluble DNA supported metal nanoparticles (M-DNA nanohybrids) for the first time using cheap natural DNA. It is found these nanohybrids maintain the properties of both metal nanoparticles and DNA, such as good water solubility, air stability and reversible solubility in different solvents. After detailed characterization, we found there are strong interactions between metal nanoparicles and DNA, which are located in the position of the base pair in DNA. This preparation method could be expanded to several metals with good reproducibility and suitable for mass production. The as-synthesized M-DNA nanohybrids have many unique properties and potential applications.After then, we apply these DNA supported metal nanoparticles as nano-catalysts in several different organic reactions with good results.Pd-DNA nanohybrids show high catalytic activity in the reduction hydrogenation of nitro compounds to the corresponding amines. High temperature and pressure are not involved in this reactions and the catalyst could be reused for 5 times. It is also found different M-DNA showed different chemoselectivity in the hydrogenation reactions. The selectivity of Pd-DNA mainly is C=C > NO2 >> C=O; in contrast, Pt-DNA prefer to reduce NO2 prior to C=C. By comparison of M-DNA with other supported metal nano-catalysts, we found these good chemoselectivities origin from the combining effects of the different components in these water-soluble M-DNA catalytic system.In the aerobic oxidation of secondary alcohols to the corresponding ketones, Au-DNA nanohybrids exhibit good catalytic activity. The reaction yields could reach quantitively and the catalysts could also recycle for 7 times.Afterwards, Au-DNA nanohybrids are used in the one-pot tandem oxidative amidation directly from alcohols and amines to synthesize amide. Compared with previous reports, the reaction conditions are very convenient and mild while a broader substrate scope is achieved. Also the Au-DNA could be reused for 5 times. We further investigate the high catalytic reactivity of Au-DNA and the mechanism of this tandem reaction. The formation of product amide is found to depend on this novel catalytic system of Au-DNA water solutions. Moreover, the suitable interactions and binding affinity between Au nanoparticles and DNA bring both good stability and higher catalytic reactivity which at last cause the good catalytic performance of Au-DNA.In summary, we have developed a new kind of natural DNA supported metal nano-catalysts which have novel properties. They have showed high catalytic reactivity in several organic reactions and are of great value in the practical applications. This work provides a new sight and direction for the development of both metal nano-catalyst and green organic synthesis.