Revealing the Crystal Structure of the Purine Base Xanthine with 3D Electron Diffraction

3D electron diffraction (3D-ED) techniques can be used for structure determination, circumventing challenges posed to conventional and bulk X-ray diffraction techniques such as sub-micron sized crystals, the strong effects of texture, the presence of defects, and polyphasic samples. Such challenges previously prevented the structure solution of xanthine, a purine base chemically similar to guanine which may also be found in organisms. In this work, we use 3D-ED to elucidate the crystal structure of xanthine. The electron diffraction data obtained from a single microcrystal is also of sufficient quality to determine hydrogen positions, confirming the presence of the 7H-tautomer as expected. This study highlights the potential for the use of 3D-ED on biogenic nanocrystals, for example opening opportunities to understand the links between crystal anisotropy, birefringence, and organism characteristics.