not rotated during the exposure), since it is possible to record full reflections using a polychromatic X-ray beam. frames) are usually collected for a sample being kept still ( i.e. Importantly, the algorithm relies only on diffraction spot positions and does not require an orientation matrix, wavelength spectrum etc.Ī typical Laue X-ray diffraction experiment performed for a single-crystal sample is depicted schematically in Fig. Hence, to fill this gap, in the current short contribution a simple yet efficient ab initio method to refine instrument-model parameters is reported. In cases where such reference data are not available, the data processing is much more problematic. photoactive yellow protein, PYP Borgstahl et al., 1995 ▸) prior to actual experiments. Such cases require the collection of a reference data set on a known protein crystal standard ( e.g. This option is provided, for example, in the PRECOGNITION suite (Šrajer et al., 2000 ▸), which, however, is not open source and is not fully optimized for small-molecule crystals where sparse diffraction patterns are observed. Therefore, in more difficult cases, where sufficiently accurate instrument-model parameters are not available (an inaccurate IM is quite common on a busy user-operated synchrotron beamline, where equipment is regularly moved or exchanged depending on different user requirements etc.), the entire data processing is significantly hampered (if it is possible at all), since the LaueUtil suite does not have capabilities either to determine or to refine the IM. detector distance, detector size and position, goniostat zeros etc.) (Paciorek et al., 1999 ▸). Nevertheless, the success of this approach depends heavily on an appropriate description of the goniometer geometry used, described with a mathematical instrument model (IM) including parameters of the experimental setup ( e.g. (2011 ▸) and implemented in the LaueUtil software. For small-molecule crystals the latter step is most efficiently achieved with the algorithm proposed by Kalinowski et al. Consequently, the data processing pipeline concentrates here on the integration of diffraction spots (Kalinowski et al., 2012 ▸ Szarejko et al., 2020 ▸) and crystal orientation-matrix determination. These in turn are further analysed so as to obtain electron-density photodifference maps and later structural models of transient species (Trzop et al., 2014 ▸ Jarzembska et al., 2014 ▸, 2019 ▸ Makal et al., 2012 ▸ Benedict et al., 2011 ▸ Coppens et al., 2017 ▸ Vorontsov et al., 2010 ▸). Such problems can be significantly reduced by employing the RATIO method (Coppens et al., 2009 ▸), in which the Laue experiment provides only light-ON to light-OFF reflection intensity ratios ( ). Among other factors, this is caused by a number of wavelength-dependent corrections which have to be applied. However, data processing in the case of a polychromatic X-ray beam is considerably more difficult than the monochromatic approach (Coppens & Fournier, 2015 ▸). In this regard, the time-resolved (TR) X-ray diffraction Laue method, applied originally for macromolecular samples (Ren et al., 1999 ▸ Hajdu et al., 1987 ▸), constitutes the most efficient approach, as it allows effectively single-pulse diffraction experiments thanks to a high X-ray flux. Studies of short-lived light-induced excited states in crystals of small molecules are currently feasible almost exclusively at high-intensity X-ray sources, such as synchrotrons (Hatcher & Raithby, 2014 ▸ Coppens, 2011 ▸ Coppens et al., 2010 ▸). detector distance or primary X-ray beam centre) reliably, even when their initial estimates are rather inaccurate. Finally, examination of data sets collected at both BioCARS 14-ID-B (Advanced Photon Source) and ID09 (European Synchrotron Radiation Facility) beamlines indicated that the approach is capable of retrieving goniometer parameters ( e.g. Tests performed on simulated data sets for small-molecule and protein crystals confirmed the validity of the proposed instrument-model refinement approach. The method has been shown to work well on both simulated and experimental data. The approach was primarily designed to work with synchrotron X-ray Laue diffraction data collected for small-molecule single-crystal samples. unit length) reciprocal vectors computed for adjacent frames. The method is based on least-squares minimization of differences between respective normalized ( i.e. A simple yet efficient instrument-model refinement method for X-ray diffraction data is presented and discussed.
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