scholarly journals On the Consistency of QCBED Structure Factor Measurements for TiO2 (Rutile)

2003 ◽  
Vol 9 (5) ◽  
pp. 457-467 ◽  
Author(s):  
Bin Jiang ◽  
Jian-Min Zuo ◽  
Jesper Friis ◽  
John C.H. Spence
Keyword(s):  
Structure Factor ◽  
Bragg Reflection ◽  
Surface Oxidation ◽  
Ccd Camera ◽  
Order Structure ◽  
X Ray ◽  
X Ray Crystallography ◽  
Order Of Magnitude ◽  
Factor Measurement ◽  
Bond Charge

The same Bragg reflection in TiO2 from 12 different (CBED) patterns (from different crystals, orientations, and thicknesses) are analyzed quantitatively to evaluate the consistency of the quantitative CBED method for bond-charge mapping. The standard deviation in the resulting distribution of derived X-ray structure factors is found to be an order of magnitude smaller than that in conventional X-ray work, and the standard error (0.026% for FX(110)) is slightly better than obtained by the X-ray Pendellösung method applied to silicon. This is sufficiently accurate to distinguish between atomic, covalent, and ionic models of bonding. We describe the importance of extracting experimental parameters from CCD camera characterization, and of surface oxidation and crystal shape. The current experiments show that the QCBED method is now a robust and powerful tool for low-order structure factor measurement, which does not suffer from the large extinction (multiple scattering) errors that occur in inorganic X-ray crystallography, and may be applied to nanocrystals. Our results will be used to understand the role of d-electrons in the chemical bonding of TiO2.

scholarly journals Where is crystallography going?

2018 ◽  
Vol 74 (2) ◽  
pp. 152-166 ◽  
Author(s):  
Jonathan M. Grimes ◽  
David R. Hall ◽  
Alun W. Ashton ◽  
Gwyndaf Evans ◽  
Robin L. Owen ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Synchrotron Radiation ◽  
Electron Diffraction ◽  
Recombinant Proteins ◽  
Free Electron Lasers ◽  
Macromolecular Crystallography ◽  
Signal To Noise ◽  
X Ray ◽  
X Ray Crystallography ◽  
Order Of Magnitude

Macromolecular crystallography (MX) has been a motor for biology for over half a century and this continues apace. A series of revolutions, including the production of recombinant proteins and cryo-crystallography, have meant that MX has repeatedly reinvented itself to dramatically increase its reach. Over the last 30 years synchrotron radiation has nucleated a succession of advances, ranging from detectors to optics and automation. These advances, in turn, open up opportunities. For instance, a further order of magnitude could perhaps be gained in signal to noise for general synchrotron experiments. In addition, X-ray free-electron lasers offer to capture fragments of reciprocal space without radiation damage, and open up the subpicosecond regime of protein dynamics and activity. But electrons have recently stolen the limelight: so is X-ray crystallography in rude health, or will imaging methods, especially single-particle electron microscopy, render it obsolete for the most interesting biology, whilst electron diffraction enables structure determination from even the smallest crystals? We will lay out some information to help you decide.

scholarly journals Ortho-Phenylene-Based Macrocyclic Hydrocarbons Assembled Using Olefin Metathesis

2020 ◽  
Author(s):  
Viraj kirinda ◽  
Briana Schrage ◽  
Christopher Ziegler ◽  
Scott Hartley
Keyword(s):  
Nmr Spectroscopy ◽  
Ab Initio Calculations ◽  
Ab Initio ◽  
Olefin Metathesis ◽  
Secondary Structures ◽  
Higher Order ◽  
Order Structure ◽  
X Ray ◽  
X Ray Crystallography ◽  
Simple Strategy

While many foldamer systems reliably fold into well-defined secondary structures, higher order structure remains a challenge. A simple strategy for the organization of folded subunits in space is to link them together within a macrocycle. Previous work has shown that o-phenylenes can be co-assembled with rod-shaped linkers into twisted macrocycles, showing an interesting synergy between folding and thermodynamically controlled macrocyclization. In these systems the foldamer units were largely decoupled from each other both conformationally and electronically. Here, we show that hydrocarbon macrocycles, with very short ethenylene linkers, can be assembled from o-phenylenes using olefin metathesis. Characterization by NMR spectroscopy, X-ray crystallography, and ab initio calculations shows that the products are approximately triangular [3+3] macrocycles with helical o-phenylene corners in a heterochiral configuration. Their photophysics are dominated by the 4,4′-diphenylstilbene moieties, the longest conjugated segments, with further conjugation broken by the twisting of the o-phenylenes.

Measurement of small structure factors by the critical-voltage effect in HEED: The superlattice reflections in β'nial, β'CoAl and γtial

1992 ◽  
Vol 50 (2) ◽  
pp. 1174-1175
Author(s):  
Alan G. Fox ◽  
Mark A. Tabbernor
Keyword(s):  
Structure Factor ◽  
High Energy ◽  
Critical Voltage ◽  
Intermetallic Alloys ◽  
Rocking Curve ◽  
X Ray ◽  
Structure Factors ◽  
Factor Measurement ◽  
Small Structure ◽  
Convergent Beam

The systematic critical voltage effect, Vc, in high energy electron diffraction has been used for some time to accurately measure low-angle x-ray structure factor structure factor amplitudes (see e.g. 1). It has a significant advantage over other methods for accurate structure factor measurement, such as systematic convergent beam rocking curve or x-ray Pendellösung techniques, in that it is capable of measuring very small structure factors such as the 222 ‘forbidden’ reflections in Si and Ge (see e.g. 2). In the present work the potential of the systematic Vc method for measuring small structure factor amplitudes and average Debye-Waller factors in the intermetallic alloys NiAl, CoAl and TiAl will be demonstrated.The structure factors, F, for ordered stoichiometric B2 alloys comprising A and B atoms such as Ni (Co)Al are given by

One Order of Magnitude Increase of Triplet State Lifetime Observed in Deprotonated Form Selenium Substituted Uracil

2021 ◽  
Author(s):  
Peipei Jin ◽  
Xueli Wang ◽  
Haifeng Pan ◽  
Jinquan Chen
Keyword(s):  
Nucleic Acids ◽  
Triplet State ◽  
Deprotonated Form ◽  
X Ray ◽  
X Ray Crystallography ◽  
Wide Range ◽  
Order Of Magnitude ◽  
Medical Therapies ◽  
Magnitude Increase

Selenium nucleic acids possess unique properties and have been demonstrated to have a wide range of applications such as DNA X-ray crystallography and novel medical therapies. Yet, as a heavy...

Extinction in X-ray crystallography

1947 ◽  
Vol 28 (196) ◽  
pp. 14-25 ◽  
Author(s):  
Kathleen Lonsdale
Keyword(s):  
Single Crystals ◽  
Bragg Reflection ◽  
X Rays ◽  
Transmitted Beam ◽  
X Ray ◽  
X Ray Crystallography

Extinction is the increase in absorption that is to be expected when Bragg reflection of X-rays takes place in single crystals, and the corresponding decrease in intensity of reflection observed.The increase of absorption was directly observed in 1914 in two ways. Using the ionization spectrometer, W. H. Bragg found that the amount of radiation transmitted by a crystal section was notably decreased when the transmitted beam had suffered reflection from a set of crystal planes.

Signal to noise considerations for single crystal femtosecond time resolved crystallography of the Photoactive Yellow Protein

2014 ◽  
Vol 171 ◽  
pp. 439-455 ◽  
Author(s):  
Jasper J. van Thor ◽  
Mark M. Warren ◽  
Craig N. Lincoln ◽  
Matthieu Chollet ◽  
Henrik Till Lemke ◽  
...  
Keyword(s):  
Single Crystal ◽  
Structure Factor ◽  
Bragg Reflection ◽  
Threshold Concentration ◽  
Photoactive Yellow Protein ◽  
Signal To Noise ◽  
Time Resolved ◽  
X Ray ◽  
Mosaic Spread ◽  
Rotation Method

Femtosecond time resolved pump–probe protein X-ray crystallography requires highly accurate measurements of the photoinduced structure factor amplitude differences. In the case of femtosecond photolysis of single P63crystals of the Photoactive Yellow Protein, it is shown that photochemical dynamics place a considerable restraint on the achievable time resolution due to the requirement to stretch and add second order dispersion in order to generate threshold concentration levels in the interaction region. Here, we report on using a ‘quasi-cw’ approach to use the rotation method with monochromatic radiation and 2 eV bandwidth at 9.465 keV at the Linac Coherent Light Source operated in SASE mode. A source of significant Bragg reflection intensity noise is identified from the combination of mode structure and jitter with very small mosaic spread of the crystals and very low convergence of the XFEL source. The accuracy with which the three dimensional reflection is approximated by the ‘quasi-cw’ rotation method with the pulsed source is modelled from the experimentally collected X-ray pulse intensities together with the measured rocking curves. This model is extended to predict merging statistics for recently demonstrated self seeded mode generated pulse train with improved stability, in addition to extrapolating to single crystal experiments with increased mosaic spread. The results show that the noise level can be adequately modelled in this manner, indicating that the large intensity fluctuations dominate the merged signal-to-noise (I/σI) value. Furthermore, these results predict that using the self seeded mode together with more mosaic crystals, sufficient accuracy may be obtained in order to resolve typical photoinduced structure factor amplitude differences, as taken from representative synchrotron results.

scholarly journals Structure factor measurement in TiAl and silicon

1995 ◽  
Vol 53 ◽  
pp. 150-151
Author(s):  
S. Swaminathan ◽  
J. M. Wiezorek ◽  
I. P. Jones ◽  
N. J. Zaluzec ◽  
D. M. Maher ◽  
...  
Keyword(s):  
Electron Diffraction ◽  
Structure Factor ◽  
Diffraction Theory ◽  
Bloch Wave ◽  
Order Structure ◽  
Electron Charge Density ◽  
Energy Filtering ◽  
Structure Factors ◽  
Factor Measurement ◽  
Theoretical Pattern

The accurate measurement of low order structure factors is required for the determination of the electron charge density distribution in crystals. In this work the energy-filtered convergent beam electron diffraction (CBED) rocking curve method has been used for accurate structure factor measurements. This CBED method for structure factor refinement involves matching of the experimental CBED intensities to those calculated using dynamical electron diffraction theory. The CBED experiments were conducted with a Philips EM420 Transmission Electron Microscope coupled with a custom built energy-filtering attachment enabling single electron counting. The theoretical pattern matching was performed using FORTRAN programs which were developed by Swaminathan. Initially the experimental plan involved an attempt to refine structure factors of TiAl by two dimensional Bloch wave calculations. The results of this project have been reported elsewhere. Subsequently it proved impossible to obtain results with sufficient precision for TiAl reproducibly, i.e. less than 0.1%, from samples of different thicknesses.

scholarly journals Ortho-Phenylene-Based Macrocyclic Hydrocarbons Assembled Using Olefin Metathesis

2020 ◽  
Author(s):  
Viraj kirinda ◽  
Briana Schrage ◽  
Christopher Ziegler ◽  
Scott Hartley
Keyword(s):  
Nmr Spectroscopy ◽  
Ab Initio Calculations ◽  
Ab Initio ◽  
Olefin Metathesis ◽  
Secondary Structures ◽  
Higher Order ◽  
Order Structure ◽  
X Ray ◽  
X Ray Crystallography ◽  
Simple Strategy

While many foldamer systems reliably fold into well-defined secondary structures, higher order structure remains a challenge. A simple strategy for the organization of folded subunits in space is to link them together within a macrocycle. Previous work has shown that o-phenylenes can be co-assembled with rod-shaped linkers into twisted macrocycles, showing an interesting synergy between folding and thermodynamically controlled macrocyclization. In these systems the foldamer units were largely decoupled from each other both conformationally and electronically. Here, we show that hydrocarbon macrocycles, with very short ethenylene linkers, can be assembled from o-phenylenes using olefin metathesis. Characterization by NMR spectroscopy, X-ray crystallography, and ab initio calculations shows that the products are approximately triangular [3+3] macrocycles with helical o-phenylene corners in a heterochiral configuration. Their photophysics are dominated by the 4,4′-diphenylstilbene moieties, the longest conjugated segments, with further conjugation broken by the twisting of the o-phenylenes.

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