In the case of electron diffraction, recent results in collaboration with the Jan Pieter Abrahams’ Lab at Leiden university show that complete sampling of Bragg spacings can be achieved with ASI’s Cheetah 120 or ASI’s first electron camera detector in combination with continuous crystal rotation. This detector holds a 512×512 pixels Timepix chip (pixel size 55 μm) and is of unprecedented sensitivity with a high dynamic range (13.5 bit) and very high signal-to-noise ratio. Rotational electron diffraction data at room temperature of pharmaceutical compounds and protein nano-crystals was collected at 200 keV (λ=0.025 Å) with a frame rate of 9.1 fps at extreme low dose conditions (±0.01 e-.Å-2.s-1). Furthermore, it was demonstrated that in the case of pharmaceuticals, 50° of continuous rotation data could be collected at room temperature from 200 nm thin compound nano-crystals showing high resolution Bragg spots up to 0.8 Å. The atomic structure could be solved using direct methods.
Pictures and data are courtesy of van Genderen et al. Acta A (2016).
The biggest bottleneck in protein crystallography is that many proteins do not form crystals large enough for 3D structure determination by X‐ray crystallography. For sub-micron sized 3D protein crystals there are several alternatives: intense XFEL sources, electron diffraction and electron imaging. Recently, known crystal structures of 3D sub-micron protein crystals could be refined using XFEL and electron diffraction data. ASI’s detector has been used to collect rotation electron diffraction of 100 nm protein crystals with better than 2 Ångstrom resolution. This will pave the way for Electron Crystallography as a new tool to determine the structures of proteins that do not grow X-ray diffraction grade crystals.