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  • American Association for the Advancement of Science  (25,970)
  • Institute of Electrical and Electronics Engineers (IEEE)
  • International Union of Crystallography (IUCr)
  • 2000-2004  (30,286)
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  • 1
    Electronic Resource
    Electronic Resource
    New methods for diffraction stress measurement: a critical evaluation of new and existing methods (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 33 (2000), S. 1059-1066 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: New methods of diffraction stress analysis of polycrystalline materials, consisting of cubic elastically anisotropic crystallites, are proposed and compared with existing methods. Whereas for the existing methods knowledge of the diffraction elastic constants is presupposed, three new methods are presented that require only knowledge of the (macroscopic) mechanical elastic constants. The stress values obtained with these new methods on the basis of the mechanical elastic constants are more reliable than those obtained with the methods on the basis of the diffraction elastic constants. New and existing methods are illustrated by means of measurements of X-ray diffraction from a magnetron-sputtered TiN layer.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889800004258
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  • 2
    Electronic Resource
    Electronic Resource
    Global least-squares determination of Eulerian angles from single electron diffraction patterns of tilted crystals (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 33 (2000), S. 1088-1101 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Three-dimensional structure determination using electron diffraction of crystalline samples necessitates the determination of the Eulerian angles of tilted samples. For experimental tilt series, even with approximately known tilt, the resolution of the final three-dimensional reconstructions is reduced as a result of the large errors of the refined tilt angles and crystal axes positions. The presented new least-squares procedure determines the orientation of the crystal with very high accuracy from a single electron diffraction pattern. Instead of evaluating the averaged pattern geometry, each diffraction spot position is individually included in an analytical non-linear fit. This procedure is very stable against potential experimental errors, as demonstrated by Monte Carlo simulations. As a test sample, a three-dimensional microcrystal of an organic crystal compound was used. Contrary to the conventional method, which produced erroneous Miller indices for some reflections, the indexing obtained with the new algorithm was more consistent for each individual pattern. Preliminary data from frozen hydrated protein crystals, the samples of which are beam sensitive and for which only a few patterns can be recorded from a single crystal, indicate that the new angle determination promises to be particularly beneficial under such conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889800005951
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  • 3
    Electronic Resource
    Electronic Resource
    Data smoothing and distortion of X-ray diffraction peaks. II. Application (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 33 (2000), S. 1136-1142 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Based on the analysis of geometric relations, it is found that the amplitude of the distortion of the full width at half-maximum (FWHM) of a peak after smoothing is the largest among the distortions of the seven parameters of a peak: maximum intensity, FWHM, shape, asymmetry, integral intensity, peak position and integral width. Hence the FWHM distortion is used as a criterion of smoothing. The 1% and 5% error limits of smoothing are calculated. Quadratic and quartic polynomial Savitzky–Golay filters are compared. Aberrations of an X-ray diffraction (XRD) peak caused by using double, matched, 1.5 and 0.7 FWHM filters are described in more detail by means of the analyses of internal and external factors. It is found that the smoothing-induced distortions of an actual XRD peak trend towards those of ideal curves. The distortions are classified according to three types of peak. A possible method to obtain the actual peak parameters, called `system smoothing refinement', is presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889800006944
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  • 4
    Electronic Resource
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    Computing in macromolecular crystallography using a parallel architecture (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 33 (2000), S. 1154-1161 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Despite advances in computer technology, computing in macromolecular crystallography keeps pace in its demand for CPU power. Improvements in CPU speed, together with advances in computing methods that depend on it, often translate into the possibility to solve structures that would otherwise require additional experiments. Programs for data reduction, molecular-replacement programs employing multidimensional searches on a grid in real, Patterson or reciprocal space, and phasing and refinement programs, currently have, among others, the highest requirements for CPU power. For these and other programs, speed-up of calculations as a result of parallel execution on multiprocessor computers is possible. This paper outlines the use of the OpenMP programming interface and reports its successful application for parallelization of ESSENS [Kleywegt & Jones (1997). Acta Cryst. D53, 179–185] and SHELXL [Schneider & Sheldrick (1997). Methods Enzymol. 277, 319–343]. Parallel computing, which is possible as a result of the inherent parallelism of crystallographic algorithms, extends the range of problems in macromolecular crystallography that programs can be applied to and can significantly reduce the time required for progressing from a data set to a refined model.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S002188980000697X
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  • 5
    Electronic Resource
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    Development of a graphical interface for the Rietveld refinement program DBWS (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 33 (2000), S. 1189-1189 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889800005410
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  • 6
    Electronic Resource
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    BEAM-ish: a graphical user interface for the physical characterization of macromolecular crystals (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 33 (2000), S. 1187-1188 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889800005732
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  • 7
    Electronic Resource
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    Comment on CRUNCH: a phase refinement program for high-resolution macromolecular structures by Langs, Blessing & Smith (2000) (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 33 (2000), S. 1194-1194 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889800008323
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  • 8
    Electronic Resource
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    High-pressure studies of the cubic to rhombohedral transformation in NbO2F (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 33 (2000), S. 1175-1176 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The Pm\bar{3}m to R\bar{3}c high-pressure transition of NbO2F has been studied in detail using diamond anvil cells and synchrotron X-ray radiation. The transition starts at 0.28 GPa and is complete at 0.65 GPa. The bulk modulus for the cubic phase became 24.8 (11) GPa, which is roughly two times higher than for the rhombohedral phase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889800007275
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  • 9
    Electronic Resource
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    LAPODS: a computer program for refinement of lattice parameters using optimal regression (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 33 (2000), S. 1177-1179 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: LAPODS is an upgraded version of the program LAPOD for the refinement of lattice parameters using the method of Cohen [Langford (1971). J. Appl. Cryst. 4, 259–260]. The improved version has a number of advanced features. It can detect the most significant systematic errors automatically by means of a statistical F test; it can also operate in a manual mode with corrections set by the user or input manually. The single-value decomposition (SVD) method is used so that the refinement is now more stable. The general formula to calculate the specimen-transparency error has been incorporated and a transparency correction can now be made when the absorption is intermediate between the limiting cases of `thick' or `thin' samples.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889800006622
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  • 10
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    Solving the generalized indirect Fourier transformation (GIFT) by Boltzmann simplex simulated annealing (BSSA) (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 33 (2000), S. 1212-1216 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The structure of colloidal particles can be studied with small-angle X-ray and neutron scattering (SAXS and SANS). In the case of randomly oriented systems, the indirect Fourier transformation (IFT) is a well established technique for the calculation of model-free real-space information. Interaction leads to an overlap of inter- and intraparticle scattering effects, preventing most detailed interpretations. The recently developed generalized indirect Fourier transformation (GIFT) technique allows these effects to be separated by assuming various models for the interaction, i.e. the so-called structure factors. The different analytical behaviour of these structure factors from that of the form factors, describing the intraparticle scattering, allows this separation. The mean-deviation surface is defined by the quality of the fit for different parameter sets of the structure factor. Its global minimum represents the solution. The former non-linear least-squares approach has proved to be inefficient and not very reliable. In this paper, the incorporation of the completely different Boltzmann simplex simulated annealing (BSSA) algorithm for finding the global minimum of the hypersurface is presented. This new method increases not only the calculation speed but also the reliability of the evaluation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889800008372
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  • 11
    Electronic Resource
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    Synchrotron radiation X-ray powder diffractometer with a cylindrical imaging plate (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 33 (2000), S. 1241-1245 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A synchrotron radiation X-ray powder diffractometer for samples of very small amount has been developed to collect high-quality diffraction patterns under extreme conditions, i.e. at low temperature and/or high pressure. A new cylindrical imaging plate (CIP) is used as a detector, in addition to a conventional flat-type imaging plate (FIP). By using the CIP system, the diffraction data in a diffraction angle range −44 ≤ 2θ ≤ 122° are collected with a dynamic range of about 106. The alignment of the diffractometer, measurement and analysis are automatically operated by a workstation. A performance test shows that the CIP system has spatial resolution of about 0.07° with a dynamic range of 106. The diffraction pattern of a standard sample of Si measured by the CIP system has high quality; the refinement of the structure reaches Rw = 3.68% even in the case of a small amount of sample (about 2 µg) and a short exposure time (60 s). Examples of experiments at low temperatures under ambient and high pressures are also presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889800009286
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  • 12
    Electronic Resource
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    Powder diffraction beyond the Bragg law: study of palladium nanocrystals (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 33 (2000), S. 1262-1270 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: An experimental method of measurement of the subtle changes of structure of metal nanocrystals occurring on chemisorption of oxygen, interaction with inert gas and hydrogen, etc., is proposed. The measured patterns and their evolution are interpreted via atomistic simulations. Described are quantitative observations of the changes in peak position, intensity and half width of the 111 diffraction peak of a palladium catalyst caused by modifying the gaseous environment. The results of the measurements are in line with an atomistic model proposed earlier and prove that the measured average lattice constant of palladium clusters evolves according to their surface relaxation. The evolution of the measured peak intensity suggests surface ordering effects and was used to propose a detailed structural model of nanocrystalline metal particles. The transition of palladium into β-Pd-H in hydrogen under normal conditions was used as a structure probe and provided evidence for the presence of icosahedral clusters in a highly dispersed catalyst. The icosahedral phase is not significantly modified under hydrogen atmosphere and does not transform into the β hydride.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889800009869
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  • 13
    Electronic Resource
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    Microcrystallography with an X-ray waveguide (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 33 (2000), S. 1231-1240 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A waveguide microdiffraction setup is described for an undulator beamline at the European Synchrotron Radiation Facility. The composite optics consists of a waveguide, which confines the beam vertically, and a horizontally focusing multilayer mirror. A beam size of about 0.1 × 3 µm (vertical × horizontal) at λ = 0.095 nm has been obtained. The sample stage comprises a three-axis gantry with micrometre precision and a three-axis piezo-scanner with about 0.1 µm repeatability. Diffraction experiments are demonstrated for selected inorganic and polymeric samples. Possibilities for scanning diffractometry and small-angle scattering experiments are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889800009249
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  • 14
    Electronic Resource
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    An imaging-plate detector for small-angle neutron scattering (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 33 (2000), S. 1253-1261 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Small-angle neutron scattering (SANS) measurements have been performed on long-flight-path pinhole-collimation SANS instruments using, as a two-dimensional position-sensitive detector, both a neutron imaging plate, incorporating gadolinium, and a two-step transfer method, with dysprosium foil as the image transfer medium. The measurements are compared with corresponding data taken using conventional position-sensitive gas proportional counters on the SANS instruments in order to assess the viability of the imaging techniques. The imaging plates have pixel sizes of about two orders of magnitude smaller than those of the gas proportional counter. The reduced pixel size provides definite advantages over the gas counter in certain specific situations, namely when limited space necessitates a short sample-to-detector distance, when only small samples (comparable in size to the detector pixels) are available, or when used in conjunction with focusing beam optics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889800009067
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  • 15
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    Peter Goodman (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 33 (2000), S. 1302-1302 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889800011420
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  • 16
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    Evolution structurale de la nacrite en fonction de la nature des molécules organiques intercalees (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 33 (2000), S. 1351-1359 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Nacrite has been intercalated with two polar organic molecules: dimethyl sulfoxide (DMSO) and N-methylacetamide (NMA). The homogeneous nacrite complexes have been studied by X-ray diffraction (XRD) and infrared (IR) spectroscopy. The XRD study is based on a comparison between experimental and calculated patterns. The structures of the intercalated compounds have been determined, including the mutual positions of the layers after intercalation and the positions of the intercalated molecules in the interlayer space. It has been shown that the intercalation process causes not only a swelling of the interlayer space but also a shift in the mutual in-plane positions of the layers. This shift depends on the nature of the intercalated molecules and is related to their shape and the hydrogen bonds which are established with the surrounding surfaces. For a given molecule, the intercalation process is the same for the different polytypes of the kaolinite family. These XRD results are consistent with those of IR spectroscopy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889800011730
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  • 17
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    Estimating nanoparticle size from diffraction measurements (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 33 (2000), S. 1335-1341 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Nanometre-sized particles are of considerable current interest because of their special size-dependent physical properties. Debye–Scherrer diffraction patterns are often used to characterize samples, as well as to probe the structure of nanoparticles. Unfortunately, the well known `Scherrer formula' is unreliable at estimating particle size, because the assumption of an underlying crystal structure (translational symmetry) is often invalid. A simple approach is presented here which takes the Fourier transform of a Debye–Scherrer diffraction pattern. The method works well on noisy data and when only a narrow range of scattering angles is available.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889800010888
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  • 18
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    X-ray diffractometer for structural studies of surfaces and interfaces (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 33 (2000), S. 1342-1350 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A novel high-precision X-ray diffractometer for structural studies of crystal surfaces and interfaces is presented. In the construction of this instrument, separate detector and sample circles were adopted. This arrangement allows either horizontal or vertical sample geometries to be combined with a variety of sample chambers. The base of the diffractometer is a hexapod with six hydraulic telescopic struts, which confer six degrees of freedom on the platform. This design replaces the conventional stack of translation and rotation stages for aligning the sample with the X-ray beam. An innovative fast control and data acquisition system eliminates the dead time associated with reorienting a conventional diffractometer. With this new system, the time it takes to perform angular scans is limited only by the available counting rate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889800011468
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  • 19
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    A new version of the method for analysing peak broadening caused by local tilt distribution in double-crystal X-ray diffraction measurements (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 33 (2000), S. 1376-1385 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A new method of analysing X-ray peak broadening caused by local tilt distribution in mosaic structures is proposed for double-crystal X-ray diffraction measurements. In the new method, the dependence of whole peak profiles on various reflection indices hkl is analysed, whereas that of only the peak full width at half-maximum (FWHM) is analysed in a conventional broadening analysis. The theoretical formula tells us that not only the FWHM values but also the whole profiles become independent of hkl after rescaling the horizontal axis Δθ of measured patterns to Δθ/cosθc, where θc is the angle between the (001) and (hkl) planes. A new criterion is proposed to judge whether X-ray peak broadening is caused by the local tilt distribution or not; the advantage provided by the new criterion, using whole peak profiles, is high accuracy in making this judgment. It is experimentally verified that the hkl independence holds in terms of whole peak profiles. The advantage of the method is demonstrated experimentally by applying it to InAsP/InGaAsP strained layer superlattice samples.
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    URL: http://dx.doi.org/10.1107/S0021889800012772
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  • 20
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    A small-angle neutron scattering model for polydisperse spherical particles with diffusion zones and application to soft magnetic metallic glass (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 33 (2000), S. 1386-1392 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: An analytical expression for the small-angle neutron scattering intensity of diluted systems of polydisperse spherical particles, with diffusion zones, embedded in a matrix is presented. It is used within a nonlinear regression procedure to analyse small-angle neutron scattering experiments with polarized neutrons on an Fe73.5Si15.5B7CuNb3 alloy. The results for the nuclear and magnetic scattering length densities allow verification of the inhibitor concept introduced for the explanation of the limited sizes of precipitates developing during nanocrystallization. In the case of amorphous Fe73.5Si15.5B7CuNb3 alloy, the observed nanocrystals of the Fe3Si type are surrounded by an Nb-enriched shell, which stops the growth of the precipitates. With the results of polarized neutron scattering experiments, it is shown that magnetic and nuclear small-angle neutron scattering signals have the same origin. Additionally, the precision of the fits is improved by complementary use of polarized neutrons.
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    URL: http://dx.doi.org/10.1107/S0021889800013248
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  • 21
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    Bayesian estimation of hyperparameters for indirect Fourier transformation in small-angle scattering (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 33 (2000), S. 1415-1421 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Bayesian analysis is applied to the problem of estimation of hyperparameters, which are necessary for indirect Fourier transformation of small-angle scattering data. The hyperparameters most frequently needed are the overall noise level of the experiment and the maximum dimension of the scatterer. Bayesian methods allow the posterior probability distribution for the hyperparameters to be determined, making it possible to calculate the distance distribution function of interest as the weighted mean of all possible solutions to the indirect transformation problem. Consequently no choice of hyperparameters has to be made. The applicability of the method is demonstrated using simulated as well as real experimental data.
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    URL: http://dx.doi.org/10.1107/S0021889800012930
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  • 22
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    Grain-size dependence of intergranular magnetic correlations in nanostructured metals (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 33 (2000), S. 451-455 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Magnetic small-angle neutron scattering experiments were performed on nanostructured Fe, Co and Ni samples of varying grain size, produced by inert-gas condensation. The experiments show that the spontaneous spatial magnetic correlations forming in zero-field extend over many individual grains. These correlations depend strongly on grain size. In Fe, they have a minimum at a grain size of around 35 nm and increase sharply for smaller grain sizes. The crossover occurs at grain sizes comparable with Lcrit = πδ, where δ is the bulk domain-wall width. For grain sizes below Lcrit, the results are explained on the basis of the random-anisotropy model, which takes into account that the magnetic alignment between the grains competes with the anisotropies of the individual grains. Above Lcrit, where domain walls can form within one grain, the magnetization direction corresponds to the anisotropy direction varying from grain to grain, and the magnetic correlation length increases approximately linearly with grain size. Furthermore, the measurements on Fe, Co and Ni show that the spatial magnetic correlations measured by SANS are always larger than Lcrit. This is in agreement with results of theoretical studies showing that nonuniform magnetization configurations can only exist in grains with sizes D 〉 Lcrit.
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    URL: http://dx.doi.org/10.1107/S0021889800099970
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  • 23
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    Small-angle neutron scattering investigation of deuteride (hydride) precipitation and decomposition in single-crystal Pd (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 33 (2000), S. 442-446 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Small-angle neutron scattering (SANS) measurements of deuteride formation and decomposition in single crystal Pd have been performed. The purpose of this work was to determine and compare the particle morphology during deuteride precipitation and reversion, with the overall goal of developing a model for the pressure hysteresis known to exist in the Pd-H system. Anisotropic Porod scattering at low Q was observed as the samples were driven well into the two-phase region from either solid solution (the α →α' transformation) or from 100% α' (the 'α →α reversion). This scattering is attributed to the formation of large, presumably semi-coherent or completely incoherent, tens-of-microns thick plates on well-defined habit planes. The orientation and dispersion of these larger plates was different for deuteride formation and decomposition: a very coarse dispersion on the {110}α habit plane developed during deuteride formation, while a much finer dispersion on the {100}α' habit plane occurred during deuteride reversion from the 100% deuteride phase. The latter orientation is consistent with the system selecting the habit plane orthogonal to the softest host direction to minimize the elastic accommodation energy of the precipitates. We suspect the {110}α' habit plane observed during deuteride formation is related to large over-pressure loading conditions. An isotropic SANS response from plates with thicknesses of 20 to 30 Å was also observed during deuteride formation and reversion. These plates are thought to act as (coherent) precursors to the large plate formation.
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    URL: http://dx.doi.org/10.1107/S0021889899013667
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  • 24
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    Structural study of monoclinic KGd(WO4)2 and effects of lanthanide substitution (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 34 (2001), S. 1-6 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The crystal structure of monoclinic KGd(WO4)2 (KGW) has been refined at room temperature by using single-crystal X-ray diffraction data. The unit-cell parameters are a = 10.652 (4), b = 10.374 (6), c = 7.582 (2) Å, β = 130.80 (2)°, with Z = 4, in space group C2/c. The linear thermal expansion tensor has been determined and the principal axes are [302], [010] and [106]. The principal axis with maximum thermal expansion (\boldalpha'_{33} = 23.44 × 10−6 K−1), {\bf X}'_{3}, was located 12° from the c axis. Undoped crystals of KGW and crystals that were partially doped by Pr, Nd, Ho, Er, Tm and Yb were grown by the top-seeding-solution growth slow-cooling method. The effect of doping on the KGW structure was observed in the cell parameters and in morphological changes. The changes in parameters follow the changes in lanthanide ionic radii. The doped crystals show {021} and {\bar{2}21} faces in addition to the {110}, {\bar{1}11}, {010}, {130} and {310} faces which basically follow the habit of the undoped KGW crystals. The development of the faces is related to the number of the most important periodic bond chains parallel to them.
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    Small-angle X-ray scattering by PVP–water mixtures (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 34 (2001), S. 62-64 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Small-angle X-ray scattering experiments reveal the formation of large-scale structures when a 60 wt% poly(vinylpyrrolidone) (PVP)–water mixture is cooled to 260 K. The formation of these structures leads to an enhancement of continuous small-angle scattering with decreasing temperature. This is accompanied by the appearance of sharp Bragg peaks that have a very short lifetime. The scattering angles of these peaks are in accordance with a hexagonal columnar structure. It appears that such structures occasionally live long enough to undergo rotational Brownian motion.
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    Aminoguanidinium hexafluorozirconate: a new ferroelectric (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 34 (2001), S. 47-54 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Analysis of the atomic arrangement in anhydrous aminoguanidinium hexafluorozirconate, CN4H8ZrF6, reported by Bukvetskii, Gerasimenko & Davidovich [Koord. Khim. (1990), 16, 1479–1484], led to the prediction that it is a new ferroelectric [Abrahams, Mirsky & Nielson (1996). Acta Cryst. B52, 806–809]. Initial attempts to verify the prediction were inconclusive because of the variety of closely related materials produced under the original preparation conditions. Clarification of these conditions led to the formation of pure CN4H8ZrF6 and the growth of single crystals with dimensions as large as 7 × 7 × 2 mm. Highly reproducible calorimetric and dielectric permittivity anomalies reveal the Curie temperature Tc = 383 (1) K. At this temperature, the heat capacity Cp exhibits an entropy change of 0.7 (1) J mol−1 K−1, while the relative permittivity εr exhibits an inflection and the dielectric loss a distinct peak; the dielectric anomaly at Tc is observed only at the lowest (0.1–1 kHz) frequencies used. Dielectric hysteresis is demonstrable at 295 K under the application of ∼1 MV m−1 alternating fields and remains observable at all T 〈 Tc but not at T ≥ Tc; the prediction of ferroelectricity is hence confirmed. The value of the spontaneous polarization Ps is 0.45 (9) × 10−2 C m−2 at 298 K, with piezoelectric coefficient d33 = 1.9 (5) pC N−1 and pyroelectric coefficient p3 = 4 (1) µC m−2 K−1. Tilts of less than ∼11° by the two symmetry-independent CN4H{}_{8}^{2+} ions, combined with rotations of ∼20° or less by the N—NH3 and C—(NH2)2 groups about the central C—N bond in each cation, as all H atoms rotate into or become symmetrically distributed about the planes at z = 0 or ½, allow them to conform to mirror symmetry via polar atomic displacements of ∼0.4 Å or less by N or C, and of 0.7 Å or less by H. Corresponding displacements of less than 0.08 Å within the two symmetry-independent ZrF{}_{6}^{2-} anions also result in mirror symmetry, satisfying the structural criteria required for the development of ferroelectricity.
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    André Guinier (1911–2000) (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 34 (2001), S. 88-88 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
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    URL: http://dx.doi.org/10.1107/S0021889800011432
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    Harry Brumberger (1926–2000) (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 34 (2001), S. 88-88 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
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    URL: http://dx.doi.org/10.1107/S0021889801000966
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    A very simple and cheap greasing device for crystallization plates (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 34 (2001), S. 224-224 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A device to grease a 24-well crystallization plate can be easily made with a disposable plastic syringe and a sample-retention vial from a centrifugal filter device. It takes only 2 min to grease one plate with the device.
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    Global indicators of X-ray data quality (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 34 (2001), S. 130-135 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Global indicators of the quality of diffraction data are presented and discussed, and are evaluated in terms of their performance with respect to various tasks. Based on the results obtained, it is suggested that some of the conventional indicators still in use in the crystallographic community should be abandoned, such as the nominal resolution dmin or the merging R factor Rmerge, and replaced by more objective and more meaningful numbers, such as the effective optical resolution deff,opt and the redundancy-independent merging R factor Rr.i.m.. Furthermore, it is recommended that the precision-indicating merging R factor Rp.i.m. should be reported with every diffraction data set published, because it describes the precision of the averaged measurements, which are the quantities normally used in crystallography as observables.
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    An X-ray interferometer with a large and variable path length difference (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 34 (2001), S. 166-171 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The first chromatic hard X-ray interferometer with a large and variable path length difference has been built and successfully tested. Interference fringe visibility was measured as a function of the path length difference. Based on the measurements, fringe visibility analysis was performed to give the transmitted beam coherence lengths. The results agree very well with expected coherence values based on the angular and spectral acceptances of the interferometer.
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    The reliability index R2 as a versatile tool in structure analysis of inorganic and small molecular compounds (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 34 (2001), S. 178-186 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Applications of R_2 in small-molecule crystallography are described. Ways of using R_2 to evaluate initial models of a structure are discussed. These models, obtained from Patterson methods, are usually small. They may include one or more heavy atoms and pseudosymmetry is sometimes present in the model. The R_2 criterion is used also to identify misplaced atoms prior to the start of the expansion process. Finally, R_2 is used during structure expansion by the application of phase refinement or Fourier methods. Details of the procedures of extension, as well as the role of R_2 therein, are presented and evaluated. Results obtained with various test structures are discussed.
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    EXPGUI, a graphical user interface for GSAS (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 34 (2001), S. 210-213 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A description and justification of the EXPGUI program is presented. This program implements a graphical user interface and shell for the GSAS single-crystal and Rietveld package. Use of the Tcl/Tk scripting language allows EXPGUI to be platform independent. Also included is a synopsis of how the program is implemented.
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    Harry Brumberger (1926–2000) (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 34 (2001), S. 225-225 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    URL: http://dx.doi.org/10.1107/S0021889801004642
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    Neutron transmission through pyrolytic graphite monochromators (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 34 (2001), S. 258-262 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: Thermal neutron transmission measurements have been made as a function of wavelength on a pyrolytic graphite monochromator crystal that has been set to diffract a horizontal beam at different take-off angles. The major dips in the transmission caused by the various reflections have been identified. These results can be used for the design of a beamline on which more than one instrument is placed. The transmission data show that it is best for the monochromator with the greatest (horizontal) take-off angle to be placed upstream, with monochromators with decreasing take-off angles progressively further downstream. The order of instruments for which the wavelength is greater than 0.43 nm is unimportant.
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    Orientation distribution analysis in deformed grains (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 34 (2001), S. 280-288 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: Some improvements are proposed for the statistical analysis of orientation data within individual grains, in particular by allowing for crystallographic symmetries. A method based on quaternions is then presented to characterize orientation spreads including anisotropic effects. Based on this approach, some analyses of disorientation distributions (orientation distribution functions, disorientation noise and the description of sub-boundary disorientation) are reconsidered. The analysis is illustrated by a practical application to the microtextures of a hot deformed aluminium alloy crystal.
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    Microstructural transformation of vanadium pentoxide powder obtained by high-energy vibrational ball-milling (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 34 (2001), S. 381-385 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: An X-ray powder profile analysis of vanadium pentoxide powder milled in a high-energy vibrational ball-mill is presented. The strain- and size-induced broadening of the Bragg reflection for two different crystallographic directions ([001] and [100]) were determined by Warren–Averbach (WA) analysis, using a pattern-decomposition method assuming a pseudo-Voigt function. The deformation process causes a decrease in the domain size, and a near isotropic saturation value of ∼10 nm is reached after severe milling. The initial stages of milling produce a propensity for size broadening, whereas, with increasing milling time, microstrain broadening is predominant. WA analysis indicated significant plastic strain along with spatial confinement of the internal strain fields, probably in the crystallite interfaces. Transmission electron microscopy revealed a drastic change in particle shape after 64 h of milling, indicating the existence of size anisotropy which, however, decreased with further increase of the milling time.
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    New approach to stress analysis based on grazing-incidence X-ray diffraction (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 34 (2001), S. 427-435 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A new development in the determination of residual stresses in thin surface layers and coatings is presented. The procedure, based on the grazing-incidence X-ray diffraction geometry (referred to here as the `g-sin2 ψ' geometry), enables non-destructive measurement at a chosen depth below the sample surface. The penetration depth of the X-ray radiation is well defined and does not change during the experiment. The method is particularly useful for the analysis of non-uniform stresses in near-surface layers. The g-sin2 ψ geometry was applied for measurements of the residual stresses in TiN coatings. Anisotropic diffraction elastic constants of textured material were used to determine the stress value from the measured lattice strains. A new method of data treatment enables reference-free measurements of residual stresses.
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    Neutron Laue diffraction experiments on a large unit cell: concanavalin A complexed with methyl-α-D-glucopyranoside (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 34 (2001), S. 454-457 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: A neutron Laue diffraction experiment on a complex of concanavalin A with methyl-α-D-glucopyranoside extensively soaked in D2O (space group I213, a = 167.8 Å), which resulted in 3.5 Å diffraction data, is described. In a programme of structural studies of crystalline saccharide complexes of concanavalin A, the unit cell of the cubic I213 complex of concanavalin A with methyl-α-D-glucopyranoside is one of the largest. With its cell edge of 167.8 Å and its asymmetric unit of molecular weight 50 kDa, it represents a challenge for current neutron diffraction technology. The size of the crystal used in this experiment, although large (4 × 3 × 2 mm), was not the largest ever produced for this complex. The degree of spatial overlapping observed in the Laue experiment, however, suggests that use of larger crystals would be a disadvantage. On the basis of these observations, several technical improvements for macromolecular neutron crystallography are suggested.
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    Structural studies of the 30S subunit of ribosomes Thermus thermophilus by small-angle neutron and X-ray scattering (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 33 (2000), S. 515-518 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: Three different small-angle neutron scattering facilities, the "YUMO" camera at JINR (Dubna, Russia), the V4 camera at HMI (Berlin, Germany) and D11 camera at ILL (Grenoble, France), were used in the investigation of 30S ribosomal subunit from Thermus thermophilus. Parallel X-ray measurements on X33 camera at DESY (Hamburg, Germany) were used to control the identity of deuterated particles. The neutron and x-ray contrast variation data were interpreted by direct method using spherical harmonics. Structural models of the 30S ribosomal subunit from Thermus thermophilus and its RNA -rich core with the resolution 3.5 nm were constructed. A comparison between the 30S Thermus thermophilus and 30S E.coli models shows that primary difference between them consists in the special distributions of the protein component whereas the special distributions of the RNA component coincide well in both models.
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    In situ structure determination of the ribosomal protein L14 in the large 50S subunit of Escherichia coli (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 33 (2000), S. 524-525 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
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    SAXS, SANS and X-ray crystallography as complementary methods in the study of biological form and function (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 33 (2000), S. 519-523 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: X-ray crystallography is the single most powerful method for the determination of accurate and precise macromolecular structures. The study of macromolecular motions, however, is, despite some successes with time-resolved crystallography not within the realms of the method. Further, the study of large macromolecular complexes sometimes poses tremendous problems of various kinds for x-ray crystallography and many laboratories approach large structures by solving individual domains. We herein present two examples employing small-angle x-ray and/or neutron scattering (SAXS, SANS) to study (i) conformational changes, and (ii) protein-lipid complexes complementing information from x-ray crystallography. The structural changes of creatine kinase upon substrate binding were investigated as an example of conformational changes not comprehensible from crystallography in the absence of crystal structures of the substrate-ligated enzyme. We also present studies of apolipoprotein E, reconstituted with lipid, in which a combined approach using SAXS/SANS, x-ray crystallography and other techniques yields a model of the complex not accessible by either of the methods alone.
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    European Crystallography Prize (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 34 (2001), S. 537-537 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Structural and morphological investigation of amorphous hydrogenated silicon carbide (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 34 (2001), S. 465-472 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: Amorphous hydrogenated silicon carbide thin films were deposited by plasma enhanced chemical vapor deposition (PECVD) at temperatures ranging from 573 to 623 K, with different concentrations of silane and methane, exploring two deposition parameters: the radio frequency (r.f.) power and the hydrogen dilution. The aim of the work was to induce, predominantly, the formation of Si—C heteronuclear bonds in a homogeneous network. The composition was determined by Rutherford backscattering and the chemical bonding by Fourier transform infrared spectrometry. The local structural order was analyzed by means of extended X-ray absorption fine structure at the Si K edge. The morphology was investigated by small-angle X-ray scattering in order to determine the possible presence of voids in the amorphous matrix. The morphological investigation was completed by transmission electron microscopy. Better-structured films were obtained for a composition close to stoichiometry, grown with an r.f. power of 100 W and with 300 s.c.c.m. (standard cubic centimeter per minute) of hydrogen dilution.
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    Correction for thermal diffuse scattering in single-crystal time-of-flight neutron diffraction: first applications (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 34 (2001), S. 493-495 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: The thermal diffuse scattering (TDS) correction developed by Popa & Willis [Acta Cryst. (1997), A53, 537–545] for single-crystal pulsed neutron diffraction is examined via a series of experimental data sets collected at the spallation neutron source IPNS. The effect on the derived temperature parameter values is assessed and compared with reference structures obtained from gamma-ray diffraction. The importance of carrying out TDS corrections is emphasized. Suggestions are made regarding the method of evaluation of the TDS in situations where the elastic constants are unknown.
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    SIR2000-N, a program for large and small crystal structures (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 34 (2001), S. 523-526 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: The program SIR2000 [Burla et al. (2000). Acta Cryst. A56, 451–457] was designed for the ab initio solution of macromolecular crystal structures, provided that the data resolution is no lower than 1.2 Å. As the phasing procedure of SIR2000 is rather time consuming, modifications have been introduced to improve its efficiency and to make it additionally suitable for small molecules (new version SIR2000-N). The role of the tangent refinement in modern phasing procedures is enlightened.
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    Modelling of small-angle X-ray scattering data using Hermite polynomials (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 34 (2001), S. 510-518 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: A new algorithm, called the term-selection algorithm (TSA), is derived to treat small-angle X-ray scattering (SAXS) data by fitting models to the scattering intensity using weighted Hermite polynomials. This algorithm exploits the orthogonal property of the Hermite polynomials and introduces an error-reduction ratio test to select the correct model terms or to determine which polynomials are to be included in the model and to estimate the associated unknown coefficients. With no a priori information about particle sizes, it is possible to evaluate the real-space distribution function as well as three- and one-dimensional correlation functions directly from the models fitted to raw experimental data. The success of this algorithm depends on the choice of a scale factor and the accuracy of orthogonality of the Hermite polynomials over a finite range of SAXS data. An algorithm to select a weighted orthogonal term is therefore derived to overcome the disadvantages of the TSA. This algorithm combines the properties and advantages of both weighted and orthogonal least-squares algorithms and is numerically more robust for the estimation of the parameters of the Hermite polynomial models. The weighting feature of the algorithm provides an additional degree of freedom to control the effects of noise and the orthogonal feature enables the reorthogonalization of the Hermite polynomials with respect to the weighting matrix. This considerably reduces the error in orthogonality of the Hermite polynomials. The performance of the algorithm has been demonstrated considering both simulated data and experimental data from SAXS measurements of dewaxed cotton fibre at different temperatures.
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    M. A. Viswamitra (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 34 (2001), S. 537-537 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Contribution to X-ray analysis of carbo-nitrided steel layers (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 34 (2001), S. 549-557 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The non-destructive X-ray diffraction method is used to analyse carbo-nitrided steel layers after wear testing. These measurements are carried out on the two major phases of the material, i.e. the martensite and the retained austenite. Such measurements are particularly difficult for three reasons. First, strong gradients exist across the wear track. Second, the diffraction peaks obtained for the martensite are broadened, as a result of the overlap of different reflections of the tetragonal structure. Third, the studied material is multiphase. Its major phases are martensite and austenite, but it also contains carbide and nitride clusters, which lead to incoherent scattering of X-rays. A new quantitative phase analysis method is thus proposed to define the volume fractions of these different constituents of the material. This method accounts for the evolution of the background level during wear. A micro-mechanical model is then developed to process the diffraction peak positions obtained for the martensite and the retained austenite. This model defines the `true' stress and carbon content of both phases. It also allows separation of the reflections of the martensite. The true widths of the diffraction peaks, which characterize the plastic deformation, can thus be quantified. Results for wear-test specimens show a strong plastic deformation of the retained austenite during contact fatigue. This leads to a partial transformation of this phase into martensite. In the martensite, on the contrary, the plastic deformation remains low but the carbon content decreases. This is caused by a stress-induced precipitation of carbides.
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    On the diffractive determination of single-crystal elastic constants using polycrystalline samples (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 34 (2001), S. 585-601 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The diffractive determination of single-crystal elastic constants using polycrystalline samples represents the inverse problem to the (`direct') experiment of conventional diffractive residual-stress analysis. Both problems are rather sensitive to the quality of the experimental data and to the applied micro-mechanical models. This especially holds for the case of samples for which texture cannot be neglected. The current methods in the field are briefly described and specific difficulties are discussed. The key relations for the BPGeo micro-mechanical model (in which a texture-weighted geometric mean is applied in the stress analysis) are given for the general case. The necessity for careful analysis of the reliability of the results of planned experiments using theoretically modelled `experimental' data obtained with the applied micro-mechanical models is demonstrated for a set of line-shift data from a uniaxial tensile experiment on steel. The possibility of resolving the so-called d0 problem using the original line-position data for a structure refinement is demonstrated.
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    Simulation of electron density maps for two-dimensional crystal structures using Mathematica (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 34 (2001), S. 658-660 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The simulations presented here are based on the program Mathematica as a tool to present electron density maps of two-dimensional crystal structures. The models give further insights into the relationship between the thermal displacement parameters and the quality of the electron density maps. Furthermore, users can readily test the effects of several crystallographic parameters on the electron density maps, such as, the number of reflections, the thermal displacement parameters and the unit-cell dimensions.
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    Ultrafine nanostructure of partially crystallized bulk amorphous Zr54.5Ti7.5Al10Cu20Ni8 (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 34 (2001), S. 666-668 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Bulk amorphous Zr54.5Ti7.5Al10Cu20Ni8 was investigated by means of small-angle neutron scattering and high-resolution electron microscopy. Partially crystallized states were generated by annealing. The scattering data were analyzed in terms of a model taking into account both properties of the particles and interparticle interference. The mean radius of the particles is 1.3 nm. They are surrounded by a depletion zone with mean thickness of 2.6 nm. The volume fraction of the particles is estimated from the interparticle interference effect; its upper limit after annealing at 653 K for 4 h is 12%. Electron microscopy confirms the size determined from the scattering data and shows that the particles are crystalline.
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    Measurement of subtle strain modifications in heterostructures by using X-ray mapping in reciprocal space (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 34 (2001), S. 715-721 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The application of X-ray mapping in reciprocal space to the measurement of subtle strain modifications in heterostructures is analysed, focussing on strain analysis in non-cubic crystals. Special attention is paid to the enhancement of the precision of the mapping technique in comparison with conventional diffraction profile measurements. The capabilities of the mapping-based strain analysis are illustrated by selected examples of epitaxially grown structures (obeying Vegard's rule), as well as implanted structures with unknown mismatches between the lattice parameters of the damaged layer and of the crystal bulk.
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    A furnace for in situ X-ray diffraction studies of insertion processes in electrode materials at elevated temperatures (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 34 (2001), S. 654-657 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A furnace is described for in situ X-ray diffraction studies, in transmission mode, of structural changes in electrode materials for Li-ion (polymer) batteries in the ambient to 300°C temperature range. The method exploits the thin flat-cell geometry of the lithium-polymer battery concept. The flat sample is able to oscillate about a horizontal axis in its own plane in the X-ray beam, to provide better averaging during the diffraction experiment. The use of the device is demonstrated in a study of lithium intercalation in graphite (a commonly used anode material in lithium-ion batteries) during electrochemical cycling and storage at 70°C.
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    MWP-fit: a program for multiple whole-profile fitting of diffraction peak profiles by abinitio theoretical functions (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 34 (2001), S. 669-676 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A computer program has been developed for the determination of microstructural parameters from diffraction profiles of materials with cubic or hexagonal crystal lattices. The measured profiles or their Fourier transforms are fitted by ab initio theoretical functions for size and strain broadening. In the calculation of the theoretical functions, it is assumed that the crystallites have log-normal size distribution and that the strain is caused by dislocations. Strain and size anisotropy are taken into account by the dislocation contrast factors and the ellipticity of the crystallites. The fitting procedure provides the median and the variance of the size distribution and the ellipticity of the crystallites, and the density and arrangement of the dislocations. The efficiency of the program is illustrated by examples of severely deformed copper and ball-milled lead sulfide specimens.
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    Planar faults in layered Bi-containing perovskites studied by X-ray diffraction line profile analysis (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 34 (2001), S. 699-703 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Profile fitting procedures associated with integral breadth studies and Fourier analysis are applied to the study of the complex Bi-containing layered perovskite SrBi2Nb2O9. Strong line broadening anisotropy is evidenced. Both `size' and `strain' effects contribute to the observed width. However, `size' broadening along the [00l] direction is essentially caused by stacking faults. The coherently diffracting domain sizes are deduced from Fourier analysis of the diffraction patterns and a rough estimate of the mean distance between faults is given. Thermal annealing significantly decreases the stacking fault density.
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    Sol phase and sol–gel transition in SnO2 colloidal suspensions (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 33 (2000), S. 609-613 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The effect of concentration on the structure of SnO2 colloids in aqueous suspension, on their spatial correlation and on the gelation process was studied by small angle x-ray scattering (SAXS). The shape of the experimental SAXS curves varies with suspension concentration. For diluted suspensions ([SnO2] ≤ 0.13 mol L−1), SAXS results indicate the presence of colloidal fractal aggregates with an internal correlation length ξ ∼ 20 Å, without any noticeable spatial correlation between them. This suggests that the aggregates are spatially arranged without any significant interaction like in ideal gas structures. For higher concentrations ([SnO2] = 0.16, 0.32, and 0.64 mol L−1), the colloidal aggregates are larger (ξ = 24 Å) and exhibit a certain degree of spatial correlation between them. The pair correlation function corresponding to the sol with the highest concentration (0.92 mol L−1) reveals a rather strong short range order between aggregates, characteristic of a fluid-like structure, with an average nearest-neighbor distance between aggregates d1 = 125 Å and an average second-neighbor distance d2 = 283 Å. The pair distribution function remains essentially invariant during the sol-gel transition, suggesting that gelation involves the formation of a few points of connection between the aggregates resulting in a gel network constituted by essentially linear chains of clusters.
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    Small-angle neutron scattering study of nanophase zirconia in a reverse micelle synthesis (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 33 (2000), S. 628-631 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Nanophase zirconia particles are synthesized by mixing two reverse micelle solutions containing the precursor salt ZrOCl2 and the base NH4OH. The primary reverse micelle solution consists of AOT, toluene and water. The reverse micelle structure of four solutions as a function of w (the molar ratio of [water]/[AOT]) is characterized by small-angle neutron scattering at room temperature. With the addition of ZrOCl2 and NH4OH into the water pools, the reverse micelle sizes decrease as compared to those in the D2O/AOT/C6D5CD3 primary system. The mixed microemulsions contain reverse micelle sizes that fall between the values of the premixed solutions. All the reverse micelles exhibit uniform size and spherical shape. The effect of concentration of inorganic salt precursor in the water pools on the reverse micelle structure is also studied.
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    Scaling properties in the structure of new complex materials (porphyrins and dendritic polymer systems) (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 33 (2000), S. 632-636 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Small angle light and X-ray scattering and scaling concepts are used to explore the intra- and inter-molecular structure of two different classes of new materials: dendritic polymer and porphyrins systems. Whereas porphyrins in water are characterized, depending on their concentration and ionic strength, by the built-up of extended clusters, dendrimers or ''starburst polymers'' display an internal self-similar structure.
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    Polymer bristles: a SANS study (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 33 (2000), S. 664-668 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: We report the results of a SANS study into the structure of the adsorbed layers formed at the interface in a dilute perfluorodecalinin-water emulsion by five short chain diblock copolymers of oxyethylene (OE) and oxybutylene (OB). The results are discussed in the context of the Marques-Joanny-Leibler scaling description of block copolymer adsorption from selective solvents. The volume fraction profiles are best described by parabolic and, to a lesser extent, Gaussian functional forms. On increasing the temperature the buoy segments of one copolymer were found to contract toward the surface, giving rise to profiles that were more block-like in accordance with the mean-field predictions of Wijmans and Zhulina.
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    Non-self-similar aggregation of methylcellulose (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 33 (2000), S. 669-672 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Aggregation of methylcellulose in aqueous dilute solution is studied by light and small angle neutron scattering. For temperature T〈293.15K, the free chains adopt a swollen conformation. For T〉313.15K, a slow aggregation kinetics occurs. At qRg〈1, the association number is found to vary as Rg3. However at qRg〉1, the scattered intensity decreases as q−(1〈d≤1.3) depending on the temperature. At even higher q, one observes a local compaction as aggregation proceeds, as revealed by a more and more pronounced Porod's behaviour. Results are discussed in terms of non self-similar growing aggregates, having neither a rod-like nor a dense structure.
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    Ternary mixture of a homopolymer blend and diblock copolymer studied near the Lifshitz composition by small-angle neutron scattering (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 33 (2000), S. 686-689 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A ternary mixture of two homopolymers and the corresponding diblock copolymer represents a good model system to study critical phenomena near the mean field predicted Lifshitz point. The structure factor of concentration fluctuations is in this regime of the phase diagram described by a formula which independently accounts for the peak-position q*, the scattering intensity at q*, S(q*), and the forward scattering, S(0). The susceptibility, which is given by the maximum value of either S(0) or S(q*), shows markedly renormalized critical behavior with critical exponents significant larger than the 3d-Ising value relevant for simple binary blends.
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    SAXS studies on Kynar-based membranes for fuel cells (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 33 (2000), S. 723-726 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The structure of the styrene grafted and sulfonated poly(vinylidenefluoride-co-hexafluoropropylene) was studied by small angle x-ray scattering, SAXS. The starting material is lamellar and the grafting and sulfonation processes and the hexafluoropropylene, HFP, contents affected the lamellar period. The SAXS intensity curve of the sulfonated membranes also included an ionic peak which arises from the ionic aggregates. The effects of the humidy and metal ion neutralization on the ionic aggregates were studied.
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    Small-angle X-ray scattering from semi-dilute solutions of poly(N-isopropylacrylamide) in aqueous acetonitrile solutions (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 33 (2000), S. 731-734 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Interaction parameters of poly(N-isopropylacrylamide) in acetonitrile–water mixed solvent were determined by using small-angle X-ray scattering. Small-angle X-ray scattering measurements were carried out in conditions of the semi-dilute poor solvent regime and just below the lower critical solution temperature. From concentration dependence of the correlation length, the binary and ternary cluster integrals were determined. The contribution of the segment–segment interactions to the entropy Sint and the enthalpy Hint has been calculated from the temperature dependence of these cluster integrals. It has been found that both values are positive. On addition of a small amount of acetonitrile into aqueous solution of poly(N-isopropylacrylamide), Sint and Hint increase with increasing acetonitrile content. Upon further addition of acetonitrile, these values decreased.
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    Small-angle neutron scattering from poly(NIPA-co-AMPS) gels (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 33 (2000), S. 735-739 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The microstructure of the poly(N-isopropylacrylamide-co-acrylamido-2-methyl-1-propane sulphonic acid) gel, poly(NIPA-co-AMPS), was investigated as a function of temperature and cross-link density using the small angle neutron scattering technique. The sample temperature was varied in the range 30 to 55C. Two different behaviours of poly(NIPA-co-AMPS) gels were observed. At low temperature (30C), the magnitude of the scattered intensity increased with cross-link density suggesting that additional cross-links introduced more inhomogeneities in the gel network. At high temperatures the trend was reversed; that is the lower cross-link density, the higher the scattered intensity. Therefore, the role of cross-links at high temperature was to suppress microphase separation. The fitting of the experimental data with the Rabin and Panyukov theory indicated qualitative agreement.
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    Morphology of Ni-base superalloys via very small-angle neutron scattering technique (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 33 (2000), S. 847-850 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Very small-angle neutron scattering (VSANS) was used to develop a nondestructive inspecting technique for predicting the residual life time of turbine blades made from single crystal Ni-base superalloy. The VSANS curves, obtained from single crystalline CMSX-4 samples with the various degrees of damage, clearly show the first order peak of the lamellar structure created by a sequence of γ and γ' phases in this material. The peak shifts in the direction of lower scattering vector magnitudes when the creep damage increases, which reflects a corresponding increase of the period of the lamellar structure. According to the VSANS data, the interphase distance in the samples increases gradually (but does not grow rapidly) with increasing creep damage when the latter is 〈 54% of the creep leading to rupture. Thus, the interphase distance is a sensitive parameter which can be used to describe the morphological changes in Ni-base superalloys related to creep damage. The results are consistent with those obtained from scanning electron microscopy.
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    Phase behavior of blends of linear and branched polyethylenes on micron length scales via ultra-small angle neutron scattering (USANS) (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 33 (2000), S. 843-846 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: SANS experiments on blends of linear, high density (HD) and long chain branched, low density (LD) polyethylenes indicate that these systems form a one-phase mixture in the melt. However, the maximum spatial resolution of pinhole cameras is ∼103Å and it has therefore been suggested that data might also be interpreted as arising from a bi-phasic melt with large a particle size (∼1µm), because most of the scattering from the different phases would not be resolved. We have addressed this hypothesis by means of USANS experiments, which confirm that HDPE/LDPE blends are homogenous in the melt on length scales up to 20µm. We have also studied blends of HDPE and short-chain branched linear low density polyethylenes (LLDPEs), which phase separate when the branch content is sufficiently high. LLDPEs prepared with Ziegler-Natta catalysts exhibit a wide distribution of compositions, and may therefore be thought of as a "blend" of different species. When the composition distribution is broad enough, a fraction of highly branched chains may phase separate on µm-length scales, and USANS has also been used to quantify this phenomenon.
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    XIth International Conference on Small-Angle Scattering (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 33 (2000), S. 1-1 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Use of Cr Kα radiation to enhance the signal from anomalous scatterers including sulfur (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 33 (2000), S. 876-881 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The anomalous signals from scatterers such as sulfur (S) and arsenic (As) were compared in diffraction data sets collected from an X-ray source with three different targets, Au, Cu and Cr, on a multi-target rotating anode. HIV-1 integrase crystals served as the test case for this study. The crystalline specimen of HIV-1 integrase contains in each protein molecule two As atoms, each covalently bound to a cysteine S atom, and two additional S atoms derived from methionine. It was found that the Cr Kα radiation gave the clearest peaks in anomalous difference Fourier maps, although the signal-to-noise ratios of the anomalous signal for the Cu Kα and Cr Kα data were similar but better than that for Au Lα. This result was in spite of the fourfold higher flux from the Cu anode versus the Cr anode. For all three X-ray wavelengths, anomalous difference Fourier maps calculated with bias-removed phases derived from the known atomic model revealed clear peaks at the two As sites. However, only in the map calculated using the Cr Kα data were both peaks of the expected ellipsoidal shape, enveloping the As atom and the adjacent S atom. None of the S sites was apparent in difference maps calculated using the Au Lα data. The ability to enhance the S-derived anomalous signal using Cr Kα radiation has particularly useful applications in the structure determination of proteins, for example in resolving ambiguities in the chain tracing of a protein with numerous disulfide bonds and in assigning amino acid identities. Additionally, anomalous difference Patterson maps calculated from the Cr Kα data were sufficiently clear to identify the As-related peaks. These results form the groundwork for in-house phase determination with the multi-wavelength anomalous diffraction method.
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    Approximate calculation of multiple-diffraction patterns based on Renninger's kinematical `simplest approach' (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 33 (2000), S. 921-927 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Analytical expressions for the absolute change of the primary reflection intensity due to multiple diffraction are given in the kinematical approach. It is shown that satisfactory agreement between experiment and theory can be obtained for a mosaic crystal (diamond) as well as for a perfect crystal (silicon) even in the case of strong reflections.
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    Biological Crystallography goes online (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 56 (2000), S. 1-1 
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    ISSN: 1399-0047
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
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    Guidelines for the deposition and release of macromolecular coordinate and experimental data (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 56 (2000), S. 2-2 
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    ISSN: 1399-0047
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
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    The three-dimensional structure of a Trichoderma reesei β-mannanase from glycoside hydrolase family 5 (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 56 (2000), S. 3-13 
    Details
    ISSN: 1399-0047
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The crystal structure of the catalytic core domain of β-mannanase from the fungus Trichoderma reesei has been determined at a resolution of 1.5 Å. The structure was solved using the anomalous scattering from a single non-isomorphous platinum complex with two heavy-metal sites in space group P21. The map computed with the experimental phases was enhanced by the application of an automated model building and refinement procedure using the amplitudes and experimental phases as observations. This approach is expected to be of more general application. The structure of the native enzyme and complexes with Tris–HCl and mannobiose are also reported: the mannobiose binds in subsites +1 and +2. The structure is briefly compared with that of the homologous β-mannanase from the bacterium Thermomonospora fusca.
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    RSPS version 4.0: a semi-interactive vector-search program for solving heavy-atom derivatives (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 56 (2000), S. 42-47 
    Details
    ISSN: 1399-0047
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: A program for inspection and interpretation of the Patterson function is described. The program is mainly intended for finding heavy-atom positions from difference Patterson maps, but may also be used to locate molecules with non-crystallographic symmetry when the local axis is nearly parallel to a crystallographic symmetry axis. Options are available for vector-based methods to locate heavy-atom sites, for finding sets from a list of possible heavy-atom positions and for checking of potential solutions. Both crystallographic and non-crystallographic symmetry may be used, either independently or in conjunction.
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    Structure of a new neurotoxin from the scorpion Buthus martensii Karsch at 1.76 Å (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 56 (2000), S. 25-33 
    Details
    ISSN: 1399-0047
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: A new neurotoxin BmK M2, toxic to both mammals and insects, with the strongest toxicity in the BmK toxin series, has been purified from the Chinese scorpion Buthus martensii Karsch and crystallized with MPD at pH 7.5. The crystals are orthorhombic, belonging to space group P212121, with unit-cell parameters a = 36.64, b = 36.95, c = 37.23 Å. The structure was solved by molecular replacement and refined to R = 0.186 for all reflections to a resolution of 1.76 Å. The whole sequence (64 residues) of BmK M2 was determined by crystallographic analysis based on high-resolution data and the homologous model of BmK M8. The refined BmK M2 structure shows a non-proline cis peptide bond between Pro9 and His10 which enables the C-terminal segment to adopt a conformation different to that of the weak toxin BmK M8. Recently, a mutation analysis had suggested that both the tenth residue and the C-terminus play key roles in receptor binding. Therefore, these features may be related to the binding selectivity of the group III α-like toxins. The charge changes of residues 8, 10, 18, 28, 55 and 59 from neutral or negative to positive or neutral, which leads to a positive electrostatic potential surface, may be responsible for the high toxicity of BmK M2.
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    The 2.0 Å structure of bovine interferon-γ; assessment of the structural differences between species (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 56 (2000), S. 14-24 
    Details
    ISSN: 1399-0047
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The structure of bovine interferon-γ (IFN-γ) was determined by multiple isomorphous replacement at 2.0 Å resolution. Bovine IFN-γ crystallizes in two related crystal forms. Crystal form 1 diffracts to 2.9 Å resolution and is reproducible and stable to derivatization. Crystal form 2 diffracts to 2.0 Å resolution, but shows significant non-isomorphism from crystal to crystal. The previously determined structures of several different species of INF-γ were either at too low a resolution [human, 1hig; Ealick et al. (1991), Science, 252, 698–702] or were too inaccurate [bovine, 1rfb; Samudzi & Rubin (1993), Acta Cryst. D49(6), 505–512; rabbit, 2rig; Samudzi et al. (1991), J. Biol. Chem. 266(32), 21791–21797] for the structure to be solved by molecular replacement. The structure was solved in crystal form 1 using two derivatives produced by chemically modifying two free cysteine residues that were introduced by site-directed mutagenesis (Ser30Cys, Asn59Cys). After model building and refinement, the final R value was 21.8% (Rfree = 30.9%) for all data in the resolution range 8.0–2.9 Å. The crystal form 1 structure was then used as a molecular-replacement model for crystal form 2 data collected from a flash-cooled crystal. Subsequent model building and refinement, using all data in the resolution range 15.0–2.0 Å, gave an R value of 19.7% and an Rfree of 27.5%. Pairwise comparison of Cα positions of bovine IFN-γ (BOV) and the previously determined 1rfb and 2rig structures indicated some significant differences in the models (r.m.s.d. values for BOV to 1rfb, 4.3 Å; BOV to 2rig, 4.0 Å). An assessment of the quality of the structures was made using the 3D–1D algorithm [Eisenberg et al. (1992), Faraday Discuss. 93, 25–34]. The resulting statistical scoring indicated that BOV was consistent with expected criteria for a 2.0 Å structure, whereas both 1rfb and 2rig fell below acceptable criteria.
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    1.35 and 2.07 Å resolution structures of the red abalone sperm lysin monomer and dimer reveal features involved in receptor binding (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 56 (2000), S. 34-41 
    Details
    ISSN: 1399-0047
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abalone sperm use lysin to make a hole in the egg's protective vitelline envelope (VE). When released from sperm, lysin first binds to the VE receptor for lysin (VERL) then dissolves the VE by a non-enzymatic mechanism. The structures of the monomeric and dimeric forms of Haliotis rufescens (red abalone) lysin, previously solved at 1.90 and 2.75 Å, respectively, have now been refined to 1.35 and 2.07 Å, respectively. The monomeric form of lysin was refined using previously obtained crystallization conditions, while the dimer was solved in a new crystal form with four molecules (two dimers) per asymmetric unit. These high-resolution structures reveal alternate residue conformations, enabling a thorough analysis of the conserved residues contributing to the amphipathic nature of lysin. The availability of five independent high-resolution copies of lysin permits comparisons leading to insights on the local flexibility of lysin and alternative conformations of the hypervariable N-terminus, thought to be involved in species-specific receptor recognition. The new analysis led to the discovery of the basic nature of a cleft formed upon dimerization and a patch of basic residues in the dimer interface. Identification of these features was not possible at lower resolution. In light of this new information, a model explaining the binding of sperm lysin to egg VERL and the subsequent dissolution of the egg VE is proposed.
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    Real-time swelling-series method improves the accuracy of lamellar neutron-diffraction data (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 56 (2000), S. 48-54 
    Details
    ISSN: 1399-0047
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Neutron-diffraction data were collected from stacked bilayers of 1,2-dioleoyl-sn-glycero-phosphocholine under conditions of increasing relative humidity at both 0 and 8.06% 2H2O. Over the period of data collection, the d-repeat of both swelling-series samples increased. Each family of structure factors, representing each of the five orders of diffraction, are shown to lie on smooth curves, allowing structure factors of intermediate d-repeat to be determined. In the case of the 8.06% 2H2O data, but not the 0% 2H2O data, all observed structure factors lie on a single continuous transform. 8.06% 2H2O has a net neutron-scattering density of zero; its use in neutron-diffraction experiments presents a novel application of the so-called `minus fluid' approach, without mathematical manipulation. The data are used to demonstrate the increased accuracy inherent in this real-time swelling-series approach. A quantitative analysis of errors caused by differences in d-repeat in difference subtractions is presented.
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    Effects of microgravity on the crystal quality of a collagen-like polypeptide (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 56 (2000), S. 55-61 
    Details
    ISSN: 1399-0047
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: (Pro-Pro-Gly)10 is one of the most widely studied collagen polypeptide models. Microgravity crystal growth of (Pro-Pro-Gly)10 was carried out in the Advanced Protein Crystallization Facility aboard the Space Shuttle Discovery during the STS-95 mission. Crystals were successfully grown in all experiments, using both dialysis and free-interface diffusion methods. The quality of the microgravity-grown crystals and of ground-grown counterparts was assessed by X-ray synchrotron diffraction. Microgravity-grown crystals exhibited a significant improvement in terms of dimensions and resolution limit. As previously reported, crystals were orthorhombic, space group P212121. However, the diffraction pattern showed weak reflections, never previously measured, that were consistent with new unit-cell parameters a = 26.9, b = 26.4, c = 182.5 Å. This allowed the derivation of a new model for the arrangement of the triple-helical molecules in the crystals.
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    Crystallization and preliminary X-ray diffraction studies of human epidermal growth factor (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 56 (2000), S. 62-63 
    Details
    ISSN: 1399-0047
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Human epidermal growth factor (hEGF), a 6.2 kDa protein of 53 amino acids with three internal disulfide bridges, has been crystallized by the hanging-drop method. hEGF crystallizes in space group P3121 (or P3221) using MgCl2 as precipitant, with unit-cell parameters a = b = 61.4, c = 87.0 Å. Another type of crystal, obtained using NaCl as precipitant, belongs to a tetragonal point group and has unit-cell dimensions a = b = 102.5, c = 166.6 Å. The trigonal crystals with the smaller unit cell diffract X-rays better and a native data set from a single crystal has been collected to 3.0 Å resolution.
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    Crystallization and preliminary X-ray diffraction studies on the N-utilizing substance-B (NusB) from Mycobacterium tuberculosis (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 56 (2000), S. 64-66 
    Details
    ISSN: 1399-0047
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: N-utilizing substance B (NusB) is a protein which forms part of a complex assembly in transcriptional antitermination in Mycobacterium tuberculosis. It forms a heterodimer with the product of the NusE gene (identical to the ribosomal protein S10) and mediates the process of transcriptional antitermination by forming the core complex with the nut site of the ribosomal RNA along with other protein factors. NusB has been cloned and overexpressed in Escherichia coli and crystallized using the hanging-drop vapour-diffusion method. The space group is P212121, with unit-cell parameters a = 46.6, b = 64.2, c = 90.1 Å. A native data set complete to 1.6 Å resolution has been collected from a single crystal.
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    Crystallization and preliminary X-ray analyses of catabolite control protein A, free and in complex with its DNA-binding site (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 56 (2000), S. 67-69 
    Details
    ISSN: 1399-0047
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The catabolite control protein (CcpA) from Bacillus megaterium is a member of the bacterial repressor protein family GalR/LacI. CcpA with an N-terminal His-tag was used for crystallization. Crystals of free CcpA and of CcpA in complex with the putative operator sequence (catabolite responsive elements, CRE) were obtained by vapour-diffusion techniques at 291 K using the hanging-drop method. CcpA crystals grown in the presence of polyethylene glycol 8000 belong to the hexagonal space group P6122 or P6522, with unit-cell parameters a = 74.4, c = 238.8 Å. These crystals diffract X-rays to 2.55 Å resolution and contain one monomer of the homodimeric protein per asymmetric unit. Crystals of the CcpA–CRE complex were obtained with ammonium sulfate as precipitant and belong to the tetragonal space group I4122, with unit-cell parameters a = 125, c = 400 Å and one complex per asymmetric unit. Although these co-crystals grew to a sufficient size, X-ray diffraction was limited to 8 Å resolution.
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    Crystallization and preliminary diffraction studies of a truncated form of a novel protease from spores of Bacillus megaterium (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 56 (2000), S. 70-72 
    Details
    ISSN: 1399-0047
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: During germination of spores of Bacillus species, a novel protease termed GPR initiates the degradation of a group of small acid-soluble spore proteins which protect the dormant spore's DNA from damage. Trypsin digestion of the zymogen of B. megaterium GPR removes ∼15 kDa from the C-terminal end of the 46 kDa zymogen subunit, leaving a 30 kDa subunit. Single crystals of this truncated form of GPR have been obtained by the vapor-diffusion method using PEG 4000 as a precipitating agent. The crystals belong to the monoclinic space group P21, with unit-cell parameters a = 67.99, b = 105.34, c = 108.63 Å, β = 95.68°. The cryofrozen crystals diffract X-rays to about 3.3 Å using synchrotron radiation.
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    Crystallization and preliminary X-ray diffraction studies of cytochrome c6 from Porphyra yezoensis (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 56 (2000), S. 79-80 
    Details
    ISSN: 1399-0047
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Cytochrome c6 from the red alga Porphyra yezoensis has been purified and crystallized by the sitting-drop vapour-diffusion method. Two different crystal forms, tetragonal and orthorhombic, were obtained. The tetragonal crystals belong to space group P41212 or P43212, with unit-cell dimensions a = 49.33 (2), c = 83.70 (10) Å. The orthorhombic crystals belong to space group P212121, with unit-cell dimensions a = 46.74 (2), b = 49.42 (1), c = 37.11 (1) Å. Absorption spectra of the crystals showed that the tetragonal form was oxidized and the orthorhombic form was reduced.
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    Toxoplasma gondii adenosine kinase: expression, purification, characterization, crystallization and preliminary crystallographic analysis (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 56 (2000), S. 76-78 
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    ISSN: 1399-0047
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The obligate intracellular protozoan parasite Toxoplasma gondii depends on the purine-salvage pathway for its purine supply. Unlike its mammalian hosts, T. gondii salvages purine precursors predominantly via adenosine kinase, the enzyme that phosphorylates adenosine to adenosine monophosphate (AMP). The cDNA encoding T. gondii adenosine kinase was subcloned and expressed in Escherichia coli. The recombinant protein was active in an in vitro enzyme assay over a broad pH range. It required a divalent cation for activity. The enzyme was inactivated by the addition of 1 µM mercuric chloride. The inactivation could be reversed by a reducing agent. The active recombinant protein was crystallized using sodium sulfate as precipitant at pH 8.0. The crystals diffract to 1.8 Å and belong to the monoclinic space group P21, with unit-cell parameters a = 47.5, b = 68.9, c = 57.0 Å, β = 100.3°. The calculated Vm based on one molecule per asymmetric unit is 2.38 Å3 Da−1.
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    Lactate dehydrogenase from the hyperthermophilic archaeon Methanococcus jannaschii: overexpression, crystallization and preliminary X-ray analysis (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 56 (2000), S. 81-83 
    Details
    ISSN: 1399-0047
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: L(+)-Lactate dehydrogenase (LDH) is a key enzyme in anaerobic metabolism which converts pyruvate to lactate. LDH from the hyperthermophilic archaebacterium Methanococcus jannaschii has been overexpressed in Escherichia coli and crystallized in two crystal forms at 297 K using 2-methyl-2,4-pentanediol as precipitant. Type I crystals grew rapidly and diffracted to at least 2.8 Å Bragg spacing upon exposure to Cu Kα X-rays. X-ray diffraction data to 2.9 Å have been collected from a native crystal. The type I crystal is tetragonal, belonging to the space group P42212, with unit-cell parameters a = b = 99.74, c = 170.00 Å. The asymmetric unit contains two LDH subunits, with a corresponding crystal volume per protein mass (Vm) of 3.05 Å3 Da−1 and a solvent content of 59.7%. Type II crystals, which grew more slowly, diffracted to at least 1.8 Å Bragg spacing upon exposure to Cu Kα X-rays. X-ray diffraction data to 1.9 Å have been collected from a native crystal. The type II crystal is orthorhombic, belonging to the space group P21212, with unit-cell parameters a = 47.65, b = 125.10, c = 58.08 Å. The asymmetric unit contains a single LDH subunit, with a corresponding crystal volume per protein mass (Vm) of 2.50 Å3 Da−1 and a solvent content of 50.8%. Therefore, the type II crystal is more suitable for high-resolution structure determination than the type I crystal.
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    Crystallization and preliminary X-ray analysis of recombinant full-length human m-calpain (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 56 (2000), S. 73-75 
    Details
    ISSN: 1399-0047
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: m-Calpain constitutes the prototype of the superfamily of neutral calcium-activated cysteine proteinases. It is a heterodimer consisting of an 80 and a 30 kDa subunit. Recombinant full-length human m-calpain has been crystallized using macro-seeding techniques and vapour-diffusion methods. Two different monoclinic crystal forms (space group P21) were obtained from a solution containing polyethylene glycol (MW = 10 000) as a pecipitating agent. Complete data sets have been collected to 2.3 and 3.0 Å resolution using cryo-cooling conditions and synchrotron radiation. The unit-cell parameters are a = 64.86, b = 133.97, c = 78.00 Å, β = 102.43° and a = 51.80, b = 171.36, c = 64.66 Å, β = 94.78°, respectively. The Vm values indicate that there is one heterodimer in each asymmetric unit.
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    Crystallization and preliminary crystallographic studies of ribosome recycling factor from Escherichia coli (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 56 (2000), S. 84-85 
    Details
    ISSN: 1399-0047
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Ribosome recycling factor (RRF) catalyzes the disassembly of a termination complex during the final stage of protein synthesis. RRF from Escherichia coli has been crystallized with PEG 400 as precipitant at 287 K. The crystal belongs to the trigonal space group P3121 (or P3221), with unit-cell parameters a = b = 48.08, c = 141.67 Å. Native data were collected from a frozen crystal to a resolution of 3.0 Å on a Cu Kα rotating-anode X-ray source.
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    Crystallization and preliminary X-ray analysis of a bacteriophage T4 primase fragment (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 56 (2000), S. 95-97 
    Details
    ISSN: 1399-0047
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The primase from bacteriophage T4 is a single-stranded DNA-dependent RNA polymerase that is one of the seven proteins that constitute the DNA-replication machinery of bacteriophage T4. In an attempt to crystallize the protein, a number of variants were generated. One such construct, which includes the C-terminal region (residues 196–340), gave four different crystal forms which diffract in the 3.5–6.0 Å resolution range.
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    Crystallization and preliminary X-ray diffraction analysis of the NAD-dependent non-phosphorylating GAPDH of the hyperthermophilic archaeon Thermoproteus tenax (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 56 (2000), S. 89-91 
    Details
    ISSN: 1399-0047
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Recombinant non-phosphorylating NAD+-dependent glyceraldehyde-3-phosphate dehydrogenase (GAPN) of the hyperthermophilic crenarchaeote Thermoproteus tenax has been overexpressed, purified and crystallized using the hanging-drop vapour-diffusion technique. Crystals of different habits were obtained from several precipitant solutions (salts and polyethylene glycols). Preliminary X-ray analysis was performed with crystals grown in ammonium formate, which belonged to the primitive hexagonal space group P622, and had unit-cell parameters a = b = 184.8, c = 133.0 Å, γ = 120°. Assuming a molecular weight of 55 kDa, a Matthews parameter of 3.3 Å3 Da−1 is calculated assuming two molecules per asymmetric unit. The diffraction limit of these crystals is 2.5 Å resolution.
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    Crystallization and preliminary X-ray analysis of the catalytic core of the alkylhydroperoxide reductase component AhpF from Escherichia coli (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 56 (2000), S. 92-94 
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    ISSN: 1399-0047
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Alkylhydroperoxide reductases (AhpR, E.C. 1.6.4.x) are essential for the oxygen tolerance of aerobic organisms, converting otherwise toxic hydroperoxides of lipids or nucleic acids to their corresponding alcohols. The AhpF component (521 amino-acid residues, 56.2 kDa) belongs to the family of pyridine nucleotide–disulfide oxidoreductases and channels electrons from NAD(P)H via a series of disulfides towards the AhpC component, which finally reduces the hydroperoxide substrates. Crystals of the proteolytically truncated AhpF component (residues Asn208–Ala521) of the alkyl hydroperoxide reductase from Escherichia coli were grown under oxidizing conditions. The crystals belong to space group P3221, with unit-cell parameters a = 60.4, c = 171.8 Å. X-ray diffraction data were collected to 1.9 Å resolution using synchrotron radiation. A molecular-replacement solution was found using the structure of thioredoxin reductase from Arabidopsis thaliana as a search model.
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    URL: http://dx.doi.org/10.1107/S0907444999014146
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    Crystallization of the NADP-dependent β-keto acyl-carrier protein reductase from Brassica napus (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 56 (2000), S. 86-88 
    Details
    ISSN: 1399-0047
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The NADP-dependent β-keto acyl-carrier protein reductase (BKR) from Brassica napus has been crystallized by the hanging-drop vapour-diffusion method using polyethylene glycol of average molecular weight 1500 as the precipitant. The crystals belong to the hexagonal space group P6422, with unit-cell parameters a = b = 129.9, c = 93.1 Å, α = β = 90, γ = 120°. Calculated values for Vm, the use of rotation and translation functions and consideration of the packing suggest that the asymmetric unit contains a monomer. The crystals diffract to beyond 2.8 Å resolution and are more amenable to X-ray diffraction analysis than those reported previously for the Escherichia coli enzyme. The structure determination of B. napus BKR will provide important insights into the catalytic mechanism of the enzyme and into the evolution of the fatty-acid elongation cycle by comparisons with the other oxidoreductase of the pathway, enoyl acyl-carrier protein reductase (ENR).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0907444999013918
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  • 93
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    Preliminary X-ray crystallographic analysis of a plant defence protein, the polygalacturonase-inhibiting protein from Phaseolus vulgaris (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 56 (2000), S. 98-100 
    Details
    ISSN: 1399-0047
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: A leucine-rich repeat plant protein involved in resistance to pathogens, a polygalacturonase-inhibiting protein (PGIP-1) from Phaseolus vulgaris, has been crystallized and preliminary X-ray characterization has been performed. The protein contains ten repeats of a short (24 amino-acid) leucine-rich repeat motif. Single crystals of the protein were grown from vapour-diffusion experiments using PEG 2K monomethylether as precipitant; these crystals diffract to at least 2.3 Å resolution. The space group is P21, with two molecules of PGIP-1 in the asymmetric unit; the crystals contain approximately 38% solvent.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0907444999014316
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  • 94
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    Crystallization of type I chloramphenicol acetyltransferase: an approach based on the concept of ionic strength reducers (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 56 (2000), S. 101-103 
    Details
    ISSN: 1399-0047
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Chloramphenicol acetyltransferase (CAT) is responsible for bacterial resistance to chloramphenicol. It catalyzes inactivation of the antibiotic by acetyl-group transfer from acetyl CoA to one or both hydroxyl groups of chloramphenicol. Type I CAT possesses some unique properties which are not observed in other CAT variants. Type I CAT overexpressed in Escherichia coli was purified and crystals with a resolution limit of 2.22 Å have been obtained using a novel procedure which is based on the concept of `ionic strength reducers'. The crystals have the symmetry of space group P1 and unit-cell parameters a = 96.46, b = 113.86, c = 114.21 Å, α = 119.9, β = 94.1, γ = 98.6°. These dimensions are consistent with four to six trimers per unit cell, corresponding to a solvent fraction ranging from 65 to 47%.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S090744499901481X
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  • 95
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    Crystallization and preliminary crystallographic study of triple-helical DNA (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 56 (2000), S. 104-105 
    Details
    ISSN: 1399-0047
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Single crystals of d(CTCCTSCCGCGCG)·d(CGCGCGGAG) have been grown by the vapor-diffusion method using 2-methyl-2,4-pentanediol as a precipitant. The crystals are tetragonal, space group P42, with unit-cell parameters a = b = 53.8, c = 43.1 Å, and diffract to 1.8 Å resolution at a synchrotron X-ray beamline. In the crystal, the asymmetric unit contains one copy of the construct. The two halves of the structure are related by non-crystallographic twofold symmetry. These observations are consistent with the conclusion that the sequences of the 12-mer and 9-mer oligonucleotides form a duplex DNA at one end and a triplex DNA at the other end.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0907444999012895
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  • 96
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    Experiences and expectations of a novel X-ray microsource with focusing mirror. I. Erratum (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 56 (2000), S. 109-109 
    Details
    ISSN: 1399-0047
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The following are corrections to a paper by Bloomer & Arndt [(1999), Acta Cryst. D55, 1672–1680]. The entry in the second row of the IMAR column of Table 1(b) on page 1674 should read 6.6 and not 16.6. In Table 4 on page 1677 the source diameter should be given as 15 µm and not 15 mm, and the units for the diameter of the sample should be given as µm instead of mm.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0907444999015802
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  • 97
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    Crystallization of Helix pomatia agglutinin (HPA), a protein from the edible snail. Erratum (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 56 (2000), S. 109-109 
    Details
    ISSN: 1399-0047
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: One of the authors was omitted in the published version of the paper by Lisgarten et al. (1999) Acta Cryst. D55, 1903–1905. The full author list is given above.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0907444999015814
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  • 98
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    Optimization of the critical nuclear size for protein crystallization: a note (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 56 (2000), S. 106-108 
    Details
    ISSN: 1399-0047
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: It was observed that for some proteins the best crystals for X-ray diffraction have been obtained at supersaturation ratios of ca 2.5–3 (in experiments without seeding). It was then noticed that under certain conditions specific to the protein such values are close to a local minimum of the critical radius for nucleation. A relation between the two observations is proposed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0907444999013505
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  • 99
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    Notes for authors (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 56 (2000), S. 110-114 
    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/S0907444999014511
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  • 100
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    The porphobilinogen synthase family of metalloenzymes (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 56 (2000), S. 115-128 
    Details
    ISSN: 1399-0047
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The porphobilinogen synthase (PBGS) family of enzymes catalyzes the first common step in the biosynthesis of the essential tetrapyrroles such as chlorophyll and porphyrin. Although PBGSs are highly conserved at all four levels of protein structure, there is considerable diversity in the use of divalent cations for the catalytically essential and allosteric roles. Assumptions regarding commonalities among the PBGS proteins coupled with the diversity of usage of metal ions has led to a confused literature. The recent publication of crystal structures for three PBGS proteins coupled with more than 50 individual PBGS sequences allows an evaluation of these assumptions. This topical review focuses on the usage of metals by the PBGS family of proteins. It raises doubt concerning a dogma that there has been an evolutionary shift between ZnII and MgII at one or more of the divalent metal-binding sites. It also raises the possibility that there may be up to four specific divalent metal ion-binding sites, each serving a unique function that can be alternatively filled by amino acids in some of the PBGSs.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0907444999014894
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