Researchers from RIKEN have made a groundbreaking discovery in the field of crystallography, demonstrating that extremely intense X-ray pulses can accurately determine the positions of hydrogen atoms in small organic crystals. This achievement holds significant implications for various areas such as drug discovery and materials research.
X-ray diffraction has been the preferred method for determining crystalline material structures since William Lawrence Bragg and William Henry Bragg first demonstrated the scattering of X-rays from crystals 110 years ago. However, many materials form crystals that are too small to be analyzed using this technique.
To overcome this limitation, scientists have explored alternative approaches, including electron-based methods that require thin samples. Another promising avenue involves utilizing ultra-intense, ultrashort X-ray pulses generated by X-ray free electron lasers (XFELs), which are large facilities spanning kilometers.
The RIKEN team, led by Kiyofumi Takaba, Saori Maki-Yonekura, and Koji Yonekura, utilized an XFEL to determine the structure of a small organic molecule called rhodamine-6G. They compared the results with those obtained using 3D electron diffraction for the same molecule.
Remarkably, both techniques allowed the researchers to determine the positions of hydrogen atoms, which are the smallest atoms comprising a single proton and electron. The accuracy of hydrogen atom positions depended on the type of bonds between hydrogen atoms. This achievement was published in the journal Nature Chemistry.
Takaba emphasized the significance of visualizing hydrogen atoms in small organic crystals using XFEL diffraction, noting that the position of a hydrogen atom provides insights into the polarity of chemical bonds and significantly impacts the properties and functions of organic molecules.
While the molecular structures obtained by XFEL and electron diffraction were similar, they offered complementary information due to the different interactions of electrons and X-rays with the samples. XFEL allowed for more precise determination of atomic coordinates, while electron diffraction was more sensitive to the distribution of electric charges in the molecule.
Notably, neither method required special sample preparation, making them practical for use. The team plans to further investigate how specimens interact with different probes, anticipating that this will expand the applications and enhance the theoretical understanding of these techniques.