New molecular imaging technique to examine complex coordination molecules

Coordinating compounds have molecular structures consisting of one or more metallic atoms in the center, surrounded by non-metallic atoms. Their fascinating physical and chemical properties, which have important applications in materials science, largely depend on their molecular structure. Thus, a definitive analysis of their molecular structure is necessary not only to understand their properties, but also to design specific coordination compounds with targeted functions.

Although several analytical methods are available for the structural determination of coordinating compounds, they each have their own limitations. For example, X-ray crystallography can only determine the structure of crystalline compounds, while nuclear magnetic resonance cannot provide accurate results when paramagnetic atoms are involved. A newer microscopy technique, High Angle Ring Dark Field Transmission Electron Microscopy (HAADF-STEM), which has revolutionized the field of molecular imaging with real-time visualization of single coordinating molecules, is also limited. to the observation of simple and planar. molecules. Therefore, the structural determination of various conformations (all possible spatial orientations of atoms) of crystalline and amorphous polynuclear coordination molecules remains unexplored.

To fill this gap, a team of researchers from the Tokyo Institute of Technology, led by Professor Kimihisa Yamamoto and Associate Professor Takane Imaoka, have developed a new imaging method using a metal atom tracer in HAADF-STEM. to determine the conformational structures of highly branched polynuclear coordination complexes and compounds. Their discoveries are published in Scientists progress. Explaining the new method, Imaoka says, “Using iridium as a metal tracer, because its high atomic number (Z = 77) will provide better visualization with HAADF-STEM, we have synthesized dendritic phenylazomethine (DPA) compounds attached to iridium. Next, we determined the optimal operating conditions for HAADF-STEM, under which the different conformations of these highly branched DPA compounds could be determined with the greatest precision. “

To determine the optimal operating conditions for HAADF-STEM, the researchers observed samples of the iridium-DPA compound, dispersed on the surface of graphene nanopowder, under various operating conditions. They found that reducing the beam current to 7 pA and the exposure time per pixel to eight microseconds and the use of low magnification helped reduce damage to the iridium-DPA compound and made it possible to observe with success its structure. Iridium atoms appear as bright spots on HAADF-STEM images, indicating their position in the structure of the molecule.

Once the HAADF-STEM image of the iridium-DPA molecule was obtained under optimal conditions, the researchers compared it to simulated images of all possible conformations of the molecule to find the closest match. The structures captured in the HAADF-STEM experimental images correspond extremely well to the simulated conformational structures. Thus, the most precise conformational orientation of a molecule can be easily determined by comparing HAADF-STEM and simulated images.

The potential applications of this heavy metal guided HAADF-STEM technology are not limited only to structural analysis coordination compounds. Highlighting future work, Imaoka remarks, “Our study is a pioneering effort in imaging conformational structures of complex macromolecules. As this technology is effective for both crystalline and amorphous compounds, we believe that this technology can also be applied for the determination of the structures of multinuclear peptides by complexation with tracer metal atoms, and work in this area is already in progress. Classes.

– This press release was provided by Tokyo Institute of Technology

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