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Tokyo Institute of Technology
The high-angle circular dark-field scanning transmission electron microscope can be used to determine the complex conformational structure of crystalline and amorphous polynuclear non-planar coordination molecules, as shown by scientists at Tokyo Institute of Technology (Tokyo Institute of Technology). Using iridium as a tracer metal, they successfully determined the different conformations of the highly branched coordination compound molecules. This opens up possibilities for the imaging and design of complex inorganic and organic molecules.
The molecular structure of coordination compounds consists of one or more metal atoms in the center, surrounded by non-metal atoms. Their fascinating physical and chemical properties with important applications in materials science depend to a large extent on their molecular structure. Therefore, a clear analysis of their molecular structure is necessary, not only to understand their properties, but also to design specific coordination compounds with target functions.
Although there are a variety of analytical methods that can be used to determine the structure of coordination compounds, they each have their limitations. For example, X-ray crystallography can only determine the structure of crystalline compounds, and when paramagnetic atoms are involved, nuclear magnetic resonance cannot provide accurate results. A newer microscopy technique, the high-angle circular dark-field scanning transmission electron microscope (HAADF-STEM), has completely changed the field of molecular imaging through the real-time visualization of individual coordination molecules, but it is also limited to the observation of simple and planar molecules. Therefore, the structure determination of various conformations (all possible spatial orientations of atoms) of crystalline and amorphous multinuclear coordination molecules has not yet been explored.
To bridge this gap, researchers at Tokyo Institute of Technology, led by Professor Yamamoto Kokisa and Associate Professor Imaoka Takane, developed a new imaging method that uses the metal atom tracer in HAADF-STEM to determine complex and highly branched The multinuclear coordination compound. Their findings are published in "Science Progress". When explaining the new method, Professor Imaoka said, “Using iridium as a metal tracer because of its high atomic number (Z=77) will provide better visualization through HAADF-STEM. We synthesized an iridium-fixed dendritic benzine Azamethine (DPA) compounds. Then, we determined the best operating conditions for HAADF-STEM, under which the different conformations of these highly branched DPA compounds can be determined most accurately."
In order to determine the best operating conditions for HAADF-STEM, the researchers observed samples of iridium-DPA compounds dispersed on the surface of graphene nanopowders under various operating conditions. They found that reducing the electron beam current to 7 pA, reducing the exposure time of each pixel to 8 microseconds and using a low magnification helped reduce the damage to the iridium-DPA compound and can successfully observe its structure. Iridium atoms appear as bright spots in the HAADF-STEM image, indicating their position in the molecular structure.
After obtaining the HAADF-STEM image of the iridium-DPA molecule using the optimal conditions, the researchers compared it with simulated images of all possible conformations of the molecule to find the closest match. The structure captured in the experimental HAADF-STEM image is in good agreement with the simulated conformational structure. Therefore, by comparing HAADF-STEM and simulated images, the most accurate conformational orientation of the molecule can be easily determined.
The potential applications of this heavy metal-guided HAADF-STEM technology are not limited to structural analysis of coordination compounds. Professor Imaoka emphasized his future work, “Our research is a pioneering effort in imaging the conformational structure of complex macromolecules. Since this technology is effective for both crystalline and amorphous compounds, we believe that this technology can also be used to determine the structure of multinuclei. Through and Tracer metal atoms are complexed to synthesize peptides. Work in this field is already in progress." Further exploration of data science techniques will help more accurately measure atomic positions. More information: Conformation analysis of single multinuclear coordination molecules guided by metal atoms , Science Progress (2021). DOI: 10.1126/sciadv.abd9887 Journal Information: Progress in Science
Citation provided by Tokyo Institute of Technology: New molecular imaging technology projects complex coordination molecules from a new perspective (August 6, 2021), retrieved on December 6, 2021 from https://phys.org/news/2021-08 -molecular-imaging-technique -complex-molecules.html This document is copyrighted. Except for any fair transaction for private learning or research purposes, no part may be copied without written permission. The content is for reference only.
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