Revealing the Crystal Structure of the Purine Base Xanthine with Three-Dimensional (3D) Electron Diffraction

Three-dimensional
(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
submicrometer-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 that 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.