Science journal published the important progress in the study of single molecule reaction kinetics by Guo Xuefeng of Peking University, Zhang Deqing of Chinese Academy of Sciences and Kendall n. Houk of UCLA

Chemical reaction kinetics plays an important role in basic research and practical application Through the study of chemical reaction kinetics, not only the internal mechanism of chemical reaction can be revealed, but also the chemical reaction can be effectively regulated, which has practical significance for synthesis and chemical production However, for a long time, because of the high speed and complex mechanism of chemical reaction, many chemical reaction processes are still unclear and need to be studied Recently, Guo Xuefeng research group of School of chemistry and molecular engineering of Peking University, Zhang Deqing research group of Institute of chemistry of Chinese Academy of Sciences and Kendall n Houk research group of University of California Los Angeles have developed a new method and technology of single molecule electrical detection based on single molecule device platform, which has realized the research of chemical reaction dynamics at single molecule level Schematic diagram of device structure: reversible fast conversion of nucleophilic addition process between carbonyl and hydroxylamine source: Science Advanced In the past year, Guo Xuefeng's research group and collaborators of School of chemistry and molecular engineering of Peking University have observed the fine stereoelectronic effect of biphenyl groups by using carbon based single molecular devices, and revealed the effect of different conformations due to the rotation of single bonds between benzene rings on molecular conductivity (Science 2016, 352, 1443; nano lett 2017, 17, 856; J Phys Chem Lett 2017, 8, 2849); the kinetic process of molecular motor hydrolysis was studied by using silicon-based single molecular devices, and it was found that the rotation speed of molecular motor observed by unmarked electrical detection method was one order of magnitude faster than that observed by fluorescent labeling method (ACS Nano 2018, 11, 12789) At the invitation of cell sub journal Chem, he wrote a review article in the field of single molecule devices, which showed the broad application prospect of the platform based on single molecule devices in the basic research of single molecule reaction dynamics and single molecule biophysics (CHEM 2017, 3, 373) Recently, Guo Xuefeng's research group and collaborators designed and synthesized conjugated molecules with benzene ring as the framework and fluorene as the core, and modified the amino group at the end Functional molecules with carbonyl functional groups were connected between graphene electrodes through stable amide bonds Chemical reactions were monitored in real time by using a self built high-speed electrical test platform Large conjugated structure and strong coupling of amide covalent bond ensure the good conductivity of the molecule; in the process of chemical reaction, the change of molecular structure will lead to the change of molecular orbital, which will affect the conductive channel and the conductivity of the device Therefore, through real-time and fast detection of the conductivity change of the device, the process and rate of the structural change of the molecule in the chemical reaction can be obtained, so as to realize the direct observation of the chemical reaction at the single molecule level By statistical distribution of conductance state and introducing hidden Markov model to fit the change process on time scale, we can obtain the kinds and numbers of intermediates involved in the reaction process, reaction rate and other kinetic parameters Taking the reaction of carbonyl and hydroxylamine as an example, they studied the formation process of ketoxime During the monitoring process, two different conductivity States appeared and transformed rapidly, and showed different trends with different solvent proportion, as shown in the figure below This is because in the process of reaction, the conversion between reactants and intermediates has a low potential barrier, and they can convert rapidly to each other; the process from intermediates to products needs to cross a very high potential barrier, so the process of forming products is relatively difficult With the change of water / ethanol ratio, the dielectric constant of the solvent changes, which affects the stability of reactants and intermediates in the solvent, so their life span will change accordingly In this way, they have successfully detected the intermediates formed in the reaction process and their life span, obtained the rate constant of the conversion process between reactants and intermediates through the hidden Markov model, and revealed the influence of solvent effect on the chemical reaction Solvent dependence test: I-T curve in 0% (a), 20% (b), 40% (c), 60% D, 80% (E), 100% (f) ethanol and corresponding bistable statistical distribution source: Science Advanced This highly sensitive and easy-to-use method provides a new idea for the study of chemical reactions, the capture of intermediates / transition states and related kinetics By tracking chemical reactions at the single molecule level, not only the ensemble average effect can be avoided, but also a large number of detailed changes in chemical reactions can be captured, which is a single molecule level A powerful method for the study of chemical reaction kinetics has taken an important step for the visualization of single molecule chemical reactions This work was published online in science advanced on February 9 under the title of "direct single molecular dynamic detection of chemical reactions" (SCI Advanced 4, eaar2177 (2018), DOI: 10.1126/sciadv.aar2177) On February 19, chemical & Engineering News magazine of the United States made a highlight report on this work with the title of "graphene device reeveals step by step dynamics of single mobile reaction" The report spoke highly of this work, and pointed out: "this student presentations adaptive and electronic combination of molecular electronics, quantum chemistry and single molecular chemical physics"; "chemical reaction kinetics are directly reviewed at the single event level, Providing a textbook like clarity "The first co authors of this paper are key Xin of Guo Xuefeng's research group, Jia Chuancheng, Liu Zitong of Zhang Deqing's research group and Li Yanwei of Kendall n Houk's research group Professor Guo Xuefeng, researcher Zhang Deqing and Professor Kendall n Houk are co authors The research was jointly supported by NSFC, the Ministry of science and technology and the National Research Center of Molecular Science in Beijing Paper link: http://advances.sciencemag.org/content/4/2/eaar2177 brief introduction of Professor Guo Xuefeng: http://www.chem.pku.edu.cn/szll/zzjs/wlhxyjs1/55902.htm brief introduction of Professor Guo Xuefeng and researcher Zhang Deqing: http://www.ic.cas.cn/jggk/xrld/200907/t20090720_.html brief introduction of Professor Kendall n Houk, researcher Zhang Deqing: Https://www.chemistry.ucla.edu/directory/houk-kendall-n Kendall n Houk Professor