A low X-ray background low temperature specimen stage for biological microanalysis in the TEM†

1982 â—½  
Vol 126 (3) â—½  
pp. 307-316 â—½  
Author(s):  
W. A. P. Nicholson â—½  
W. H. Biddlecombe â—½  
H. Y. Elder
Keyword(s):  
Low Temperature â—½  
X Ray â—½  
X Ray Background â—½  
Low X

scholarly journals Automated harvesting and processing of protein crystals through laser photoablation

2016 â—½  
Vol 72 (4) â—½  
pp. 454-466 â—½  
Author(s):  
Ulrich Zander â—½  
Guillaume Hoffmann â—½  
Irina Cornaciu â—½  
Jean-Pierre Marquette â—½  
Gergely Papp â—½  
...  
Keyword(s):  
Data Collection â—½  
Macromolecular Crystallography â—½  
X Ray Diffraction â—½  
X Ray â—½  
New Methods â—½  
Repeated Sample â—½  
Sample Recovery â—½  
Through Diffusion â—½  
X Ray Background â—½  
Low X

Currently, macromolecular crystallography projects often require the use of highly automated facilities for crystallization and X-ray data collection. However, crystal harvesting and processing largely depend on manual operations. Here, a series of new methods are presented based on the use of a low X-ray-background film as a crystallization support and a photoablation laser that enable the automation of major operations required for the preparation of crystals for X-ray diffraction experiments. In this approach, the controlled removal of the mother liquor before crystal mounting simplifies the cryocooling process, in many cases eliminating the use of cryoprotectant agents, while crystal-soaking experiments are performed through diffusion, precluding the need for repeated sample-recovery and transfer operations. Moreover, the high-precision laser enables new mounting strategies that are not accessible through other methods. This approach bridges an important gap in automation and can contribute to expanding the capabilities of modern macromolecular crystallography facilities.

High-resolution x-ray elemental images

1989 â—½  
Vol 47 â—½  
pp. 204-205
Author(s):  
C. E. Lyman â—½  
J. S. Hepburn â—½  
H. G. Stenger â—½  
J. R. Michael
Keyword(s):  
Electron Beam â—½  
Field Emission â—½  
X Ray â—½  
Electron Sources â—½  
Small Probe â—½  
Long Time â—½  
X Ray Background â—½  
Low X â—½  
Image Collection â—½  
Better Than

Field-emission electron sources and digital image collection techniques produce x-ray emission images of elemental distributions (maps) with far higher quality than those obtained by conventional x-ray dot mapping. Without a field-emission source the useful upper magnification of an x-ray image is only a few times 104X with the resolution rarely exceeding 100 nm. The images described below are routinely collected at 1,000,000x with a resolution of better than 5 nm. Such images are collected at quite low x-ray intensities and over long time periods compared to electron images. This means that the effects of x-ray background at each pixel and of image drift become important issues in the collection of meaningful images.The instrument used in this work was the Vacuum Generators HB-501 STEM equipped with a Link Systems LZ-5 windowless energy dispersive x-ray detector of 146 eV energy resolution. This instrument is equipped with a gun lens to provide several times more current in the small probe than the normal HB-501. The electron beam was 1.8 nm in diameter (FWHM) and the beam contained about 0.9 nA. The digital x-ray maps shown here were obtained with 128x128 pixels and 100 ms dwell time per pixel. With this small electron beam the image magnification should be at least 400,000x to allow the beam to fill each pixel and avoid underscanning (beam smaller than the pixel).

scholarly journals Low X-ray background measurements at the Underground Canfranc Laboratory

10.1051/eas/1253019 â—½  
2012 â—½  
Vol 53 â—½  
pp. 155-163 â—½  
Author(s):  
J. Galán â—½  
S. Aune â—½  
T. Dafni â—½  
G. Fanourakis â—½  
E. Ferrer-Ribas â—½  
...  
Keyword(s):  
X Ray â—½  
X Ray Background â—½  
Low X

scholarly journals In vacuoX-ray data collection from graphene-wrapped protein crystals

2015 â—½  
Vol 71 (10) â—½  
pp. 2079-2088 â—½  
Author(s):  
Anna J. Warren â—½  
Adam D. Crawshaw â—½  
Jose Trincao â—½  
Pierre Aller â—½  
Simon Alcock â—½  
...  
Keyword(s):  
Data Collection â—½  
Room Temperature â—½  
Protein Crystals â—½  
Quality Data â—½  
Liquid Jets â—½  
High Quality Data â—½  
X Ray â—½  
Serial Data â—½  
X Ray Background â—½  
Low X

The measurement of diffraction data from macromolecular crystal samples heldin vacuoholds the promise of a very low X-ray background and zero absorption of incident and scattered beams, leading to better data and the potential for accessing very long X-ray wavelengths (>3 Å) for native sulfur phasing. Maintaining the hydration of protein crystals under vacuum is achieved by the use of liquid jets, as with serial data collection at free-electron lasers, or is side-stepped by cryocooling the samples, as implemented at new synchrotron beamlines. Graphene has been shown to protect crystals from dehydration by creating an extremely thin layer that is impermeable to any exchanges with the environment. Furthermore, owing to its hydrophobicity, most of the aqueous solution surrounding the crystal is excluded during sample preparation, thus eliminating most of the background caused by liquid. Here, it is shown that high-quality data can be recorded at room temperature from graphene-wrapped protein crystals in a rough vacuum. Furthermore, it was observed that graphene protects crystals exposed to different relative humidities and a chemically harsh environment.

Low temperature x-ray microanalysis of frozen-hydrated tobacco leaves

1984 â—½  
Vol 42 â—½  
pp. 284-285
Author(s):  
S. Edith Taylor â—½  
Patrick Echlin â—½  
May McKoon â—½  
Thomas L. Hayes
Keyword(s):  
Low Temperature â—½  
Lemna Minor â—½  
Root Tips â—½  
Tobacco Leaves â—½  
X Ray â—½  
Whole Cells â—½  
Carbon Coated â—½  
The Right â—½  
Beam Currents â—½  
The University

Low temperature x-ray microanalysis (LTXM) of solid biological materials has been documented for Lemna minor L. root tips. This discussion will be limited to a demonstration of LTXM for measuring relative elemental distributions of P,S,Cl and K species within whole cells of tobacco leaves.Mature Wisconsin-38 tobacco was grown in the greenhouse at the University of California, Berkeley and picked daily from the mid-stalk position (leaf #9). The tissue was excised from the right of the mid rib and rapidly frozen in liquid nitrogen slush. It was then placed into an Amray biochamber and maintained at 103K. Fracture faces of the tissue were prepared and carbon-coated in the biochamber. The prepared sample was transferred from the biochamber to the Amray 1000A SEM equipped with a cold stage to maintain low temperatures at 103K. Analyses were performed using a tungsten source with accelerating voltages of 17.5 to 20 KV and beam currents from 1-2nA.

Bulk standards for low-temperature biological x-ray microanalysis

1984 â—½  
Vol 42 â—½  
pp. 282-283
Author(s):  
P. Echlin â—½  
M. McKoon â—½  
E.S. Taylor â—½  
C.E. Thomas â—½  
K.L. Maloney â—½  
...  
Keyword(s):  
Phase Separation â—½  
Low Temperature â—½  
Analytical Method â—½  
Salt Solutions â—½  
Absolute Concentration â—½  
Cooling Process â—½  
X Ray â—½  
The Absolute â—½  
Analytical Procedures â—½  
Electrical Conductors

Although sections of frozen salt solutions have been used as standards for x-ray microanalysis, such solutions are less useful when analysed in the bulk form. They are poor thermal and electrical conductors and severe phase separation occurs during the cooling process. Following a suggestion by Whitecross et al we have made up a series of salt solutions containing a small amount of graphite to improve the sample conductivity. In addition, we have incorporated a polymer to ensure the formation of microcrystalline ice and a consequent homogenity of salt dispersion within the frozen matrix. The mixtures have been used to standardize the analytical procedures applied to frozen hydrated bulk specimens based on the peak/background analytical method and to measure the absolute concentration of elements in developing roots.

Micro X-Ray Diffraction Study of Polycrystalline MgB 2 Wire and Evaluation of Carbon Doping Effect Via Low-Temperature Sintering

2019 â—½  
Author(s):  
Minoru Maeda â—½  
Dipak Patel, Dr. â—½  
Hiroaki Kumakura, Dr. â—½  
Gen Nishijima, Dr. â—½  
Akiyoshi Matsumoto, Dr. â—½  
...  
Keyword(s):  
Low Temperature â—½  
Diffraction Study â—½  
Carbon Doping â—½  
Doping Effect â—½  
Low Temperature Sintering â—½  
X Ray Diffraction â—½  
X Ray

The Application of X-Ray Diffraction at Elevated Temperatures to Study the Mechanism of Formation of Sodium Tripolyphosphate

1961 â—½  
Vol 5 â—½  
pp. 276-284
Author(s):  
E. L. Moore â—½  
J. S. Metcalf
Keyword(s):  
High Temperature â—½  
Low Temperature â—½  
Amorphous Phase â—½  
Elevated Temperatures â—½  
Sodium Tripolyphosphate â—½  
X Ray Diffraction â—½  
Mechanism Of Formation â—½  
X Ray â—½  
Temperature Form â—½  
High Temperature Form

AbstractHigh-temperature X-ray diffraction techniques were employed to study the condensation reactions which occur when sodium orthophosphates are heated to 380°C. Crystalline Na4P2O7 and an amorphous phase were formed first from an equimolar mixture of Na2HPO4·NaH2PO4 and Na2HPO4 at temperatures above 150°C. Further heating resulted in the formation of Na5P3O10-I (high-temperature form) at the expense of the crystalline Na4P4O7 and amorphous phase. Crystalline Na5P3O10-II (low-temperature form) appears after Na5P3O10-I.Conditions which affect the yield of crystalline Na4P2O7 and amorphous phase as intermediates and their effect on the yield of Na5P3O10 are also presented.

scholarly journals Low Temperature Water-Gas Shift: Enhancing Stability through Optimizing Rb Loading on Pt/ZrO2

Catalysts â—½  
2021 â—½  
Vol 11 (2) â—½  
pp. 210
Author(s):  
Caleb Daniel Watson â—½  
Michela Martinelli â—½  
Donald Charles Cronauer â—½  
A. Jeremy Kropf â—½  
Gary Jacobs
Keyword(s):  
Low Temperature â—½  
Hydrogen Transfer â—½  
Water Gas Shift â—½  
Significant Shift â—½  
Catalyst Activation â—½  
X Ray â—½  
Temperature Programmed â—½  
Water Gas â—½  
X Ray Absorption â—½  
Temperature Water

Recent studies have shown that appropriate levels of alkali promotion can significantly improve the rate of low-temperature water gas shift (LT-WGS) on a range of catalysts. At sufficient loadings, the alkali metal can weaken the formate C–H bond and promote formate dehydrogenation, which is the proposed rate determining step in the formate associative mechanism. In a continuation of these studies, the effect of Rb promotion on Pt/ZrO2 is examined herein. Pt/ZrO2 catalysts were prepared with several different Rb loadings and characterized using temperature programmed reduction mass spectrometry (TPR-MS), temperature programmed desorption (TPD), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), an X-ray absorption near edge spectroscopy (XANES) difference procedure, extended X-ray absorption fine structure spectroscopy (EXAFS) fitting, TPR-EXAFS/XANES, and reactor testing. At loadings of 2.79% Rb or higher, a significant shift was seen in the formate ν(CH) band. The results showed that a Rb loading of 4.65%, significantly improves the rate of formate decomposition in the presence of steam via weakening the formate C–H bond. However, excessive rubidium loading led to the increase in stability of a second intermediate, carbonate and inhibited hydrogen transfer reactions on Pt through surface blocking and accelerated agglomeration during catalyst activation. Optimal catalytic performance was achieved with loadings in the range of 0.55–0.93% Rb, where the catalyst maintained high activity and exhibited higher stability in comparison with the unpromoted catalyst.

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