I X-rays, X-ray Diffraction, and Structure Factors

In recent years powder X-ray diffraction has proven to be a valuable alternative to single-crystal X-ray diffraction for determining electron-density distributions in high-symmetry inorganic materials, including subtle deformation in the core electron density. This was made possible by performing diffraction measurements in vacuum using high-energy X-rays at a synchrotron-radiation facility. Here we present a new version of our custom-built in-vacuum powder diffractometer with the sample-to-detector distance increased by a factor of four. In practice this is found to give a reduction in instrumental peak broadening by approximately a factor of three and a large improvement in signal-to-background ratio compared to the previous instrument. Structure factors of silicon at room temperature are extracted using a combined multipole–Rietveld procedure and compared withab initiocalculations and the results from the previous diffractometer. Despite some remaining issues regarding peak asymmetry, the new diffractometer yields structure factors of comparable accuracy to the previous diffractometer at low angles and improved accuracy at high angles. The high quality of the structure factors is further assessed by modelling of core electron deformation with results in good agreement with previous investigations.

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Isomorphous replacement in electron diffraction of wet crystals of rat hemoglobin

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100075968 ◽

1983 ◽

Vol 41 ◽

pp. 446-447

Author(s):

William F. Tivol ◽

Murray Vernon King ◽

D. F. Parsons

Keyword(s):

Electron Diffraction ◽

Heavy Atom ◽

Isomorphous Substitution ◽

X Ray Diffraction ◽

Salt Solutions ◽

X Ray ◽

Isomorphous Replacement ◽

Structure Factors ◽

Diffraction Structure ◽

The Mean

Feasibility of isomorphous substitution in electron diffraction is supported by a calculation of the mean alteration of the electron-diffraction structure factors for hemoglobin crystals caused by substituting two mercury atoms per molecule, following Green, Ingram & Perutz, but with allowance for the proportionality of f to Z3/4 for electron diffraction. This yields a mean net change in F of 12.5%, as contrasted with 22.8% for x-ray diffraction.Use of the hydration chamber in electron diffraction opens prospects for examining many proteins that yield only very thin crystals not suitable for x-ray diffraction. Examination in the wet state avoids treatments that could cause translocation of the heavy-atom labels or distortion of the crystal. Combined with low-fluence techniques, it enables study of the protein in a state as close to native as possible.We have undertaken a study of crystals of rat hemoglobin by electron diffraction in the wet state. Rat hemoglobin offers a certain advantage for hydration-chamber work over other hemoglobins in that it can be crystallized from distilled water instead of salt solutions.

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X-ray diffraction properties of curved crystal diffractors

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100133308 ◽

1992 ◽

Vol 50 (2) ◽

pp. 1734-1735

Author(s):

W. Z. Chang ◽

D. B. Wittry

Keyword(s):

Diffraction Theory ◽

X Rays ◽

Diffraction Image ◽

X Ray Diffraction ◽

Rocking Curve ◽

X Ray ◽

Bent Crystal ◽

Diffraction Geometry ◽

Crystal Parameter ◽

Quantitative Procedure

Since Du Mond and Kirkpatrick first discussed the principle of a bent crystal spectrograph in 1930, curved single crystals have been widely utilized as spectrometric monochromators as well as diffractors for focusing x rays diverging from a point. Curved crystal diffraction theory predicts that the diffraction parameters - the rocking curve width w, and the peak reflection coefficient r of curved crystals will certainly deviate from those of their flat form. Due to a lack of curved crystal parameter data in current literature and the need for optimizing the choice of diffraction geometry and crystal materials for various applications, we have continued the investigation of our technique presented at the last conference. In the present abstract, we describe a more rigorous and quantitative procedure for measuring the parameters of curved crystals.The diffraction image of a singly bent crystal under study can be obtained by using the Johann geometry with an x-ray point source.

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Highlights in the history of X-ray topography1

Zeitschrift für Kristallographie - Crystalline Materials ◽

10.1524/zkri.1995.210.6.394 ◽

1995 ◽

Vol 210 (6) ◽

Author(s):

A. R. Lang

Keyword(s):

Magnetic Domain ◽

Diffraction Theory ◽

Dislocation Loops ◽

X Ray Diffraction ◽

X Ray ◽

Domain Structures ◽

Structure Factors ◽

History Of ◽

Dislocation Sources ◽

Non Destructive

AbstractX-ray topography provides a non-destructive method of mapping point-by-point variations in orientation and reflecting power within crystals. The discovery, made by several workers independently, that in nearly perfect crystals it was possible to detect individual dislocations by X-ray diffraction contrast started an epoch of rapid exploitation of X-ray topography as a new, general method for assessing crystal perfection. Another discovery, that of X-ray Pendellösung, led to important theoretical developments in X-ray diffraction theory and to a new and precise method for measuring structure factors on an absolute scale. Other highlights picked out for mention are studies of Frank-Read dislocation sources, the discovery of long dislocation helices and lines of coaxial dislocation loops in aluminium, of internal magnetic domain structures in Fe-3 wt.% Si, and of stacking faults in silicon and natural diamonds.

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Investigation of the phase shift in X-ray forward diffraction using an X-ray interferometer

Journal of Synchrotron Radiation ◽

10.1107/s0909049597015525 ◽

1998 ◽

Vol 5 (3) ◽

pp. 967-968 ◽

Cited By ~ 1

Author(s):

Keiichi Hirano ◽

Atsushi Momose

Keyword(s):

Phase Shift ◽

Silicon Crystal ◽

Dynamical Theory ◽

Perfect Crystal ◽

X Rays ◽

X Ray Diffraction ◽

X Ray ◽

Bragg Geometry

The phase shift of forward-diffracted X-rays by a perfect crystal is discussed on the basis of the dynamical theory of X-ray diffraction. By means of a triple Laue-case X-ray interferometer, the phase shift of forward-diffracted X-rays by a silicon crystal in the Bragg geometry was investigated.

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X-ray crystal structure of a malonate-semialdehyde dehydrogenase fromPseudomonassp. strain AAC

Acta Crystallographica Section F Structural Biology Communications ◽

10.1107/s2053230x16020008 ◽

2017 ◽

Vol 73 (1) ◽

pp. 24-28 ◽

Cited By ~ 1

Author(s):

Matthew Wilding ◽

Colin Scott ◽

Thomas S. Peat ◽

Janet Newman

Keyword(s):

Crystal Structure ◽

Search Model ◽

Molecular Replacement ◽

X Rays ◽

X Ray Diffraction ◽

Acetyl Coa ◽

Space Group ◽

X Ray ◽

Semialdehyde Dehydrogenase

The NAD-dependent malonate-semialdehyde dehydrogenase KES23460 fromPseudomonassp. strain AAC makes up half of a bicistronic operon responsible for β-alanine catabolism to produce acetyl-CoA. The KES23460 protein has been heterologously expressed, purified and used to generate crystals suitable for X-ray diffraction studies. The crystals belonged to space groupP212121and diffracted X-rays to beyond 3 Å resolution using the microfocus beamline of the Australian Synchrotron. The structure was solved using molecular replacement, with a monomer from PDB entry 4zz7 as the search model.

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Electronic Excitations and Radiation Damage in Macromolecular Crystallography

Crystals ◽

10.3390/cryst8070273 ◽

2018 ◽

Vol 8 (7) ◽

pp. 273 ◽

Cited By ~ 1

Author(s):

José Brandão-Neto ◽

Leonardo Bernasconi

Keyword(s):

Chemical Information ◽

X Rays ◽

Electronic Excitations ◽

Macromolecular Crystallography ◽

X Ray Diffraction ◽

X Ray ◽

Atomic Structures ◽

Successful Approach ◽

Structural Research

Macromolecular crystallography at cryogenic temperatures has so far provided the majority of the experimental evidence that underpins the determination of the atomic structures of proteins and other biomolecular assemblies by means of single crystal X-ray diffraction experiments. One of the core limitations of the current methods is that crystal samples degrade as they are subject to X-rays, and two broad groups of effects are observed: global and specific damage. While the currently successful approach is to operate outside the range where global damage is observed, specific damage is not well understood and may lead to poor interpretation of the chemistry and biology of the system under study. In this work, we present a phenomenological model in which specific damage is understood as the result of a single process, the steady excitation of crystal electrons caused by X-ray absorption, which acts as a trigger for the bulk effects that manifest themselves in the form of global damage and obscure the interpretation of chemical information from XFEL and synchrotron structural research.

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A Combination Method of Charge Density Measurement in Hard Materials Using Accurate, Quantitative Electron and X-ray Diffraction: The α-Al2O3 Case

Microscopy and Microanalysis ◽

10.1017/s1431927603030356 ◽

2003 ◽

Vol 9 (5) ◽

pp. 419-427 ◽

Cited By ~ 10

Author(s):

Victor A. Streltsov ◽

Philip N.H. Nakashima ◽

Andrew W.S. Johnson

Keyword(s):

Charge Density ◽

Multiple Scattering ◽

Density Measurement ◽

Bloch Wave ◽

Combination Method ◽

X Ray Diffraction ◽

X Ray ◽

Hard Materials ◽

Structure Factors ◽

Free Data

Current X-ray diffraction techniques intended for “ideally imperfect” specimens provide structure factors only on a relative scale and ever-present multiple scattering in strong low-angle Bragg reflections is difficult to correct. Multiple scattering is implicit in the quantitative convergent beam electron diffraction (QCBED) method, which provides absolutely scaled structure factors. Conventional single crystal X-ray diffraction has proved adequate in softer materials where crystal perfection is limited. In hard materials, the highly perfect nature of the crystals is often a difficulty, due to the inadequacy of the conventional corrections for multiple scattering (extinction corrections). The present study on α-Al2O3 exploits the complementarity of synchrotron X-ray measurements for weak and medium intensities and QCBED measurement of the strong low-angle reflections. Two-dimensional near zone axis QCBED data from different crystals at various accelerating voltages, thicknesses, and orientations have been matched using Bloch-wave and multislice methods. The reproducibility of QCBED data is better than 0.5%. The low-angle strong QCBED structure factors were combined with middle and high-angle extinction-free data from synchrotron X-ray diffraction measurements. Static deformation charge density maps for α-Al2O3 have been calculated from a multipole expansion model refined using the combined QCBED and X-ray data.

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Applications of High-Resolution Powder X-Ray Diffraction

Solid State Phenomena ◽

10.4028/www.scientific.net/ssp.130.7 ◽

2007 ◽

Vol 130 ◽

pp. 7-14 ◽

Cited By ~ 4

Author(s):

Andrew N. Fitch

Keyword(s):

High Resolution ◽

Synchrotron Radiation ◽

Powder Diffraction ◽

X Rays ◽

X Ray Diffraction ◽

Crystalline Materials ◽

X Ray ◽

Structural Characterisation ◽

Pdf Analysis

The highly-collimated, intense X-rays produced by a synchrotron radiation source can be harnessed to build high-resolution powder diffraction instruments with a wide variety of applications. The general advantages of using synchrotron radiation for powder diffraction are discussed and illustrated with reference to the structural characterisation of crystalline materials, atomic PDF analysis, in-situ and high-throughput studies where the structure is evolving between successive scans, and the measurement of residual strain in engineering components.

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Synchrotron Nano-Diffraction Study of Thermally Treated Asbestos Tremolite from Val d’Ala, Turin (Italy)

Minerals ◽

10.3390/min8080311 ◽

2018 ◽

Vol 8 (8) ◽

pp. 311 ◽

Cited By ~ 2

Author(s):

Carlotta Giacobbe ◽

Jonathan Wright ◽

Dario Di Giuseppe ◽

Alessandro Zoboli ◽

Mauro Zapparoli ◽

...

Keyword(s):

Crystal Structure ◽

Heat Treatment ◽

Risk Management ◽

Structure Analysis ◽

X Rays ◽

X Ray Diffraction ◽

X Ray ◽

Adverse Health Effects ◽

Nano Crystalline ◽

Original Fibre

Nowadays, due to the adverse health effects associated with exposure to asbestos, its removal and thermal inertization has become one of the most promising ways for reducing waste risk management. Despite all the advances in structure analysis of fibers and characterization, some problems still remain that are very hard to solve. One challenge is the structure analysis of natural micro- and nano-crystalline samples, which do not form crystals large enough for single-crystal X-ray diffraction (SC-XRD), and their analysis is often hampered by reflection overlap and the coexistence of multiple fibres linked together. In this paper, we have used nano-focused synchrotron X-rays to refine the crystal structure of a micrometric tremolite fibres from Val d’Ala, Turin (Italy) after various heat treatment. The structure of the original fibre and after heating to 800 °C show minor differences, while the fibre that was heated at 1000 °C is recrystallized into pyroxene phases and cristobalite.

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