제 목 : Transmission Electron Microscope Toward Atomic Structure and Dynamics of Molecules
연 사 : 유병국 박사(California Institute of Technology)
일 시 : 2019년 8월 29일(목) 오후 4시 30분
장 소 : 화학관 2층 서병인강의실 (330226호실)
Transmission Electron Microscope Toward Atomic Structure and Dynamics of Molecules
Presenter: Dr. Byung-Kuk Yoo1 (California Institute of Technology)
Structure of molecules is the determiner of their properties. Transmission Electron Microscope (TEM) has versatile advantages for scientists thanks to its atomic spatial resolution. As a CryoEM method, micro electron-diffraction (MicroED) has determined a variety of macromolecules with sub-Angstrom resolution until very recently. Moreover, this technique has been further advanced to address the broad needs in structure determination of small molecules. In the first part of the presentation, how MicroED is used to determine the atomic structure of an inorganic molecule will be demonstrated. A heterometallic Mn/Ca cluster (Mn4CaOn) is a synthetic model compound for oxygen-evolving complex of the natural enzyme: photosystem II, which has been vigorously studied as an important biological water oxidation catalyst. Having powder samples of this molecule directly from the synthesis, we were able to collect suitable crystallographic data from nano- and micro-crystals as a movie while the crystals are continuously rotated and solved the structure in atomic resolution in minutes. Our results prove that MicroED is ideal to determine structures for (in)organic chemists in the fields of drug discovery with minimal crystallization trials.
In the second part of the talk, I explore TEM as an in-situ tool in pursuit of understanding dynamics. Unlike the conventional TEM, femtosecond time-resolved TEM has a time resolution that is 10 orders of magnitude better than that of TEM. Instead of using thermionic electrons in TEM, laser-driven single pulses of electrons allow various modes of detection such as imaging, diffraction, and spectroscopy, all with unprecedented spatiotemporal resolution; sub-nanometer and femtosecond. I will discuss the development of 4D Ultrafast EM and summarize the up-to-date accomplishments that represent its broad capability in chemical, materials, and biological sciences. As one of those examples, I will introduce how this technique provides a structural dynamic probe for catalytic active site in photocatalytic materials and visualizes the femtosecond atomic movement at the titanium active center in a single-site photocatalyst. Our findings contribute fundamental insights for developing advanced photocatalysts and suggest broad ranges of applications in materials science.
1 Staff Scientist @
Howard Hughes Medical Institute Research Laboratory, Broad Center for the Biological Sciences
Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA