Direct observation of bond formation in solution with femtosecond X-ray scattering

• Published in: Nature (London) Vol. 518; no. 7539; pp. 385 - 389
• Main Authors: Kim, Kyung Hwan, Kim, Jong Goo, Nozawa, Shunsuke, Sato, Tokushi, Oang, Key Young, Kim, Tae Wu, Ki, Hosung, Jo, Junbeom, Park, Sungjun, Song, Changyong, Sato, Takahiro, Ogawa, Kanade, Togashi, Tadashi, Tono, Kensuke, Yabashi, Makina, Ishikawa, Tetsuya, Kim, Joonghan, Ryoo, Ryong, Kim, Jeongho, Ihee, Hyotcherl, Adachi, Shin-ichi
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 19.02.2015; Nature Publishing Group
• Subjects: 639/638/263/910; 639/638/440; Aqueous solutions; Atoms & subatomic particles; Chemical bonds; Chemical engineering; Chemical engineering research; Chemical reactions; Gold; Humanities and Social Sciences; Lasers; letter; Methods; multidisciplinary; Science; Solvents; X-rays
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/nature14163

Time-resolved X-ray solution scattering is used to visualize and probe the dynamics of the individual steps in the formation of a gold trimer complex, including covalent bond formation, with a time resolution of ∼500 femtoseconds. Femtosecond visualization of bond formation The making and breaking of atomic bonds are essential processes in chemical reactions. Although the ultrafast dynamics of bond-breaking have been studied intensively using time-resolved techniques, it is very difficult to study the structural dynamics of bond-making, mainly because of its bimolecular nature. In this manuscript, the authors used femtosecond (fs) time-resolved X-ray solution scattering to visualize the formation of a gold trimer complex, [ Au(CN) 2 − ] 3 . Their experiments probe the dynamics of individual reaction steps, including covalent bond formation, bent-to-linear transition, bond contraction and tetramer formation with the time resolution of ∼500 fs. They also determined the three-dimensional structures of reaction intermediates with sub-ångström spatial resolution. This work represents the first example of following the entire process of bond formation both visually and quantitatively with femtosecond time resolution. The making and breaking of atomic bonds are essential processes in chemical reactions. Although the ultrafast dynamics of bond breaking have been studied intensively using time-resolved techniques 1 , 2 , 3 , it is very difficult to study the structural dynamics of bond making, mainly because of its bimolecular nature. It is especially difficult to initiate and follow diffusion-limited bond formation in solution with ultrahigh time resolution. Here we use femtosecond time-resolved X-ray solution scattering to visualize the formation of a gold trimer complex, [ Au(CN) 2 - ] 3 in real time without the limitation imposed by slow diffusion. This photoexcited gold trimer, which has weakly bound gold atoms in the ground state 4 , 5 , 6 , undergoes a sequence of structural changes, and our experiments probe the dynamics of individual reaction steps, including covalent bond formation, the bent-to-linear transition, bond contraction and tetramer formation with a time resolution of ∼500 femtoseconds. We also determined the three-dimensional structures of reaction intermediates with sub-ångström spatial resolution. This work demonstrates that it is possible to track in detail and in real time the structural changes that occur during a chemical reaction in solution using X-ray free-electron lasers 7 and advanced analysis of time-resolved solution scattering data.