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Shinichi ADACHI (KEK, Japan)

Visualizing chemical reactions in solution with femtosecond X-ray` scattering

Title: Visualizing chemical reactions in solution with femtosecond X-ray` scattering
Author: Shinichi ADACHI
Affiliation: Photon Factory, Institute of Materials Structure Science, KEK, Japan
Email: shinichi.adachi[at]kek.jp
URL: http://pfwww.kek.jp/adachis/sa/index.html
http://pfwww.kek.jp/adachis/NW14/NW14.htm
Abstract: Bond formation is an essential process in chemistry, but it is challenging to keep track of detailed atomic movements associated with bond formation because of its bimolecular nature. Bond formation in solution phase has been especially elusive because it is difficult to initiate and follow such diffusion-limited bimo-lecular processes with ultrafast time resolution. In this regard, Au oligomer complex, [Au(CN)2–]n, offers a good model system in which to study the dynamics of bond formation in solution [1,2]. Using femtosecond time-resolved X-ray scattering, we successfully visualized in real time the birth of a gold trimer complex, [Au(CN)2–]3, that occurs via photo-induced formation of Au-Au covalent bonds [3].
The ground state of the trimer has Au atoms that are weakly bound to each other by aurophilic interac-tion and aligned in a bent geometry. Upon photoexcitation, the ground state rapidly converts into the first excited state where Au-Au covalent bonds are formed among Au atoms aligned in a linear geometry. Sub-sequently, the state transforms to a triplet state in 1.6 ps while accompanying further contraction of Au-Au bonds by 0.1 Å. Later, the triplet state of the trimer converts to a tetramer on nanosecond time scale. This work showcases the possibility of tracking detailed structural changes in solution with sub-ps temporal and sub-angstrom spatial resolutions, thanks to the advent of X-ray free electron lasers and the advance of data analysis of time-resolved solution scattering data.
References: [1] Rawashdeh-Omary, M. A., Omary, M. A., Patterson, H. H. & Fackler, J. P., J. Am. Chem. Soc. 123, 11237–11247 (2001).
[2] Iwamura, M., Nozaki, K., Takeuchi, S. & Tahara, T., J. Am. Chem. Soc. 135, 538–541 (2013).
[3] Kim, K. H., Kim, J. G., Nozawa, S., Sato, T., Oang, K. Y., Kim, T. W., Ki, H., Jo, J., Park, S., Song, C., Sato, T., Ogawa, K., Togashi, T., Tono, K., Yabashi, M., Ishikawa, T., Kim, J., Ryoo, R., Kim, J., Ihee, H. & Adachi, S., Nature, 518, 385-389 (2015).
Biographical Sketch: 1992.3: Ph.D. at Kyoto University, Graduate School of Engineering, Division of Molecular Engineering, under the supervision of Prof. I. Morishima
1992.4-1992.9: JSPS Research Fellow, Japanese Society of Promotion of Science, at Photon Factory, National Laboratory for High Energy Physics (KEK), with Prof. N. Sakabe
1992.10-2003.7: Researcher, RIKEN Wako & Harima Campus, Biophysical Chemistry Laboratory, with Dr. T. Iizuka and Dr. Y. Shiro
2003.8– 2010.10: Associate Professor, Photon Factory, Institute of Materials Structure Science, High Energy Accelerator Research Organization (KEK)
2010.10-present: Professor, Photon Factory, Institute of Materials Structure Science, High Energy Accelerator Research Organization (KEK)

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