Comprehensive application of XFEL micro crystallography for novel organic compounds

There is a growing demand for structure determination from small crystals, and the three-dimensional electron diffraction (3D ED) technique can be employed for this purpose. However, 3D ED has certain limitations related to crystal thickness and data quality. We here present the application of serial X-ray crystallography (SX) with X-ray free electron lasers (XFELs) to tiny crystals of novel compounds dispersed on a substrate. For XFEL exposures, two-dimensional (2D) scanning of the substrate, coupled with rotation, enables highly efficient data collection. This approach is especially effective for challenging targets, including pharmaceuticals and organic materials that form preferred-oriented flat crystals in low-symmetry space groups. Some of these crystals have been difficult to solve or have yielded incomplete solutions using 3D ED. Our extensive analyses confirmed the superior quality of the SX data, regardless of crystal orientations. Additionally, 2D scanning with XFEL pulses gives an overall distribution of the samples on the substrate, which can be useful for evaluating the properties of crystal grains and the quality of layered crystals. Therefore, this study demonstrates that XFEL crystallography has become a powerful tool for conducting structure studies on small crystals of organic compounds.