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  • 1
    Electronic Resource
    Electronic Resource
    Post-refinement of oscillation diffraction data collected at a synchrotron radiation source (1986)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 19 (1986), S. 134-139 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: `Post-refinement' is a technique used to compare the intensity of partially recorded reflections on oscillation photographs with their full intensity observed elsewhere on the same or a different film. A reflection's partiality depends on crystal orientation, crystal cell dimension and crystal mosaicity, and post-refinement is a very sensitive tool for the refinement of these parameters. A previous paper [Rossmann, Leslie, Abdel-Meguid & Tsukihara (1979). J. Appl. Cryst. 12, 570–581] describes how post-refinement can be applied to data derived from a set of oscillation films. In this paper the technique has been extended to the refinement of anisotropic beam divergence and wavelength dispersion as is normally found on synchrotron sources. In an example it is shown that post-refinement is sufficiently sensitive to detect small wavelength variations due to changes in temperature of the monochromating crystal.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889886089793
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  • 2
    Electronic Resource
    Electronic Resource
    Laue diffraction from protein crystals using a sealed-tube X-ray source (1991)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 24 (1991), S. 146-148 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: It is shown that Laue diffraction patterns may be obtained from a protein crystal using the continuous radiation emitted by a tungsten sealed-tube X-ray source and that precise structure amplitudes may be extracted from these patterns.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889890010846
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  • 3
    Electronic Resource
    Electronic Resource
    Quantitive analysis of Laue diffraction patterns recorded with a 120 ps exposure from an X-ray undulator (1992)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 25 (1992), S. 414-423 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: X-ray Laue diffraction patterns with an exposure time of 120 ps have been obtained from single crystals of an indole alkaloid and of the enzyme lysozyme using the X-rays emitted as a single bunch of electrons traverses a hard X-ray undulator inserted in CESR, the Cornell Electron–Positron Storage Ring. The patterns were recorded on a sensitive storage-phosphor detector. Despite complexities posed by the sharp variation of the incident X-ray spectrum with wavelength and the weakness of the diffraction patterns, accurate crystallographic structure amplitudes were extracted from the Laue intensities by the generalized scale-factor approach to the determination of the wavelength- and position-dependent correction factors. The results show that crystallography is feasible on the 100 ps time scale and open up the prospect of time-resolved measurements of ultra-rapid changes in molecular structure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889891014826
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  • 4
    Electronic Resource
    Electronic Resource
    Two open-flow cryostats for macromolecular crystallography (1994)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 27 (1994), S. 133-139 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Two open-flow cryostats for macromolecular crystallographic studies, which make it possible to freeze macromolecular crystals very rapidly and maintain them for long periods of time at reduced temperatures, have been constructed. Both systems avoid the use of opaque shrouds and hence permit monitoring of the optical properties of protein crystals at all temperatures. The first uses a cold-gas stream derived from boil-off of liquid nitrogen, with a surrounding warm-gas stream, and covers a temperature range of 80 K to room temperatures. The second uses a cold-gas stream derived from boil-off of either liquid helium or liquid nitrogen to cover a temperature range of 10 to 70 K or above 80 K, respectively. Special care has been taken to make it possible to switch back and forth between the two cryogenic liquids in routine operation. The temperature stability of the cold-gas stream is ±0.5 K, which is achieved by controlling both the flow rate of the gas stream and the power of a heater within the cold-gas stream prior to its exit from the nozzle. The liquid helium consumption is less than 21 h−1 at a working temperature of 40 K.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889893008519
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  • 5
    Electronic Resource
    Electronic Resource
    Cooling Rates During Flash Cooling (1998)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 31 (1998), S. 252-257 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Flash cooling of macromolecular crystals was investigated by measurement of the cooling rates achieved by different cryoprotectant solutions (glycerol, sucrose and polyethylene glycol) with different sample volumes (0.2–0.8 mm3) and by different cooling agents (cold nitrogen or helium gas, liquid nitrogen and liquid propane). Samples were not cooled instantaneously; it usually took 0.5 to 1 s to reach the glass transition temperature and 1 to 2 s to reach the final temperature. The cooling rate varied from 5̃0 to 700 K s−1 depending on the volume of the sample, the cooling agent used and the temperature at the time of measurement. The cooling rate may affect the distribution of unit-cell dimensions, structural states and the average structure throughout the volume of the crystal, and hence its mosaic spread.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889897009229
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  • 6
    Electronic Resource
    Electronic Resource
    Macromolecular crystallography with synchrotron radiation by J. R. Helliwell (1993)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 49 (1993), S. 602-603 
    Details
    ISSN: 1399-0047
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0907444993008777
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  • 7
    Electronic Resource
    Electronic Resource
    Multiplicity distribution of reflections in Laue diffraction (1987)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 43 (1987), S. 656-674 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: If a crystal is illuminated by a polychromatic beam of X-rays, then many orders of each Bragg reflection may be stimulated simultaneously, and overlap exactly in scattering angle. The overlap of these multiple orders along a ray (a central line in reciprocal space) poses a problem for Laue methods. A theory of the distribution of multiple orders as a function of the relevant experimental parameters is presented, with the following conclusions: (1) If the angular acceptance of the detector is unrestricted, then a remarkably large proportion (72.8%) of all Bragg reflections occur on single rays for the case of an infinite range of incident wavelengths. (2) This proportion increases to greater than 83% when more realistic experimental values of λmax and λmin are used. (3) This proportion depends only on the ratio of λmax to λmin and not on the space group, unit-cell dimensions, crystal orientation or the limiting resolution of the crystal d*max (provided d*max 〈 2/λmax). (4) The total number of single rays, like the total number of all stimulated Bragg reflections, is approximately proportional to the wavelength range. (5) The proportion of reflections at a given resolution d* that lie on single or double rays depends markedly on d*, and on the ratio of λmax to λmin; it is generally lower at low resolution than at high. (6) Restricted angular acceptance of the detector can reduce significantly both the proportion and the total number of single rays. (7) Agreement between the theoretical distributions and those derived from analysis of X-ray Laue photographs of macromolecular crystals, and from extensive computer simulations, is good. It is evident that, under a wide variety of experimental conditions, the effect of multiple orders is not a serious limitation on the use of the Laue method for structure determination. The analysis presented has some relevance to polychromatic neutron diffraction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108767387098763
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  • 8
    Electronic Resource
    Electronic Resource
    Angular distribution of reflections in Laue diffraction (1991)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 47 (1991), S. 352-373 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: An analysis is presented of the angular distribution of reflections in Laue diffraction, with particular application to the spatial overlap problem in synchrotron macromolecular crystallography. Spatial overlaps of spots on the detector occur when the angular separations of adjacent diffracted beams are very small. The maximum density of spots occurs at θc = sin−1 (λminD*/2) and the majority of spots in this region of θ have short wavelengths. At higher θ the mean wavelength increases steadily. On a flat detector the spots of a Laue pattern lie on intersecting conics. Each conic corresponds to a zone plane of reciprocal-lattice points (RLPs), whose zone axis is represented by a point uvw in the direct lattice. If P[uvw] is the distance of uvw from the origin and ψ is the angle between the zone axis and the incident beam, then the average spacing between spots on a conic is proportional to P sin ψ and the width of the clear gap bordering a conic is proportional to 1/P. This explains why the densest conic arcs are flanked by the larger clear spaces and shows that local spatial overlap problems are inherently one dimensional in character. The vast majority of small angular separations are associated with pairs of adjacent single-order reflections. Multiples have larger separations from their nearest neighbours, which are always singles. The detailed analysis shows the factors that govern the spatial overlap of spots and indicates tactics for experimental design. The analysis is also relevant to polychromatic neutron diffraction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108767391000703
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  • 9
    Electronic Resource
    Electronic Resource
    Time-Resolved Crystallography (1998)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 54 (1998), S. 833-841 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Time-resolved crystallography has been successfully applied on the time scale from seconds via milliseconds and nanoseconds to picoseconds on a variety of systems. This brief review largely deals with macromolecular systems, on which there has been substantial recent progress. The strategies for design of a successful experiment that eliminates or minimizes potential artefacts have been identified, and the specifically crystallographic components of these strategies have been implemented. The remaining computational challenge is to identify and extract time-independent structures, each corresponding to a distinct reaction intermediate, whose populations vary with time and give rise to the time-dependent X-ray diffraction data. The fourth dimension, time, has been added to the three spatial dimensions of crystallography; it can no longer be regarded as purely a static technique.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108767398010605
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  • 10
    Electronic Resource
    Electronic Resource
    Deconvolution of Energy Overlaps in Laue Diffraction (1995)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 28 (1995), S. 482-494 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The energy-overlap problem in Laue diffraction often makes a Laue diffraction data set incomplete in a systematic way: low-resolution reflections more commonly overlap with other reflections than do reflections at higher resolution. We describe the development and testing of a harmonic deconvolution procedure that resolves energy overlaps accurately and is based on the wavelength-normalization curve obtained from single reflections. The conditions for satisfactory harmonic deconvolution are identified by examination of a series of data sets that differ in their redundancy. This procedure has been incorporated in the software system LaueView [Ren & Moffat (1995). J. Appl. Cryst. 28, 461–481]. Results on Laue data sets from crystals of lysozyme and α-haemolysin demonstrate that Laue data sets can be more than 90% complete even at 10 Å resolution and that structure amplitudes derived from these deconvoluted multiples can be as accurate as those derived from the best monochromatic data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889895003219
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