Abstract
Ultrabright pulses produced in X-ray free-electron lasers (XFELs) offer new possibilities for industry and research, particularly for biochemistry and pharmaceuticals. The unprecedented brilliance of these next-generation sources enables structure determination from sub-micron crystals as well as radiation-sensitive proteins. The European X-Ray Free-Electron Laser (EuXFEL), with its first light in 2017, ushered in a new era for ultrabright X-ray sources by providing an unparalleled megahertz-pulse repetition rate, with orders of magnitude more pulses per second than previous XFEL sources. This rapid pulse frequency has significant implications for structure determination; not only will data collection be faster (resulting in more structures per unit time), but experiments requiring large quantities of data, such as time-resolved structures, become feasible in a reasonable amount of experimental time. Early experiments at the SPB/SFX instrument of the EuXFEL demonstrate how such closely-spaced pulses can be successfully implemented in otherwise challenging experiments, such as time-resolved studies.
Highlights
European X-Ray Free-Electron Laser Facility GmbH, Holzkoppel 4, 22869 Schenefeld, Germany; Department of Chemistry and Physics, La Trobe Institute for Molecular Science, La Trobe University, Melbourne, VIC 3086, Australia
Traditional synchrotron-based crystallography experiments often use individual crystals mounted on goniometers to sample the rocking curve in order to measure a complete set of diffraction spot intensities [20]
Due to the high brilliance and X-ray pulse delivery patterns, macromolecular crystallography experiments at Free Electron Lasers (FELs) sources typically employ a serial approach where each recorded diffraction image is produced from a new crystal, a method known as serial femtosecond crystallography (SFX) [21,22]
Summary
X-ray based methods have a rich history of contributing to biological structure determination. Synchrotrons offered a fundamental improvement in the X-ray photon flux and enabled routine atomic structure determination of biological macromolecules as well as new, tunable wavelength-based experimental phasing methods, such as single- and multi-wavelength anomalous dispersion (SAD and MAD) [6,7,8]. XFELs produce ultrashort pulses, often only ~50 fs long, or in some cases even shorter These pulses are produced by the self-amplified spontaneous emission (SASE) process [17]. ~50 fs pulse length can be considered a practically static image in many cases Producing these very short pulses is technically possible at synchrotrons—but only by sacrificing the comparatively lower peak intensity by a further three orders of magnitude [13,19]
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