Isomorphous replacement in electron diffraction of wet crystals of rat hemoglobin

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.

X-Ray Investigations on Molten Cu-Sb Alloys

1994 ◽  
Vol 49 (4-5) ◽  
pp. 530-534 ◽  
Author(s):  
Th. Halm ◽  
H. Neumann ◽  
W. Hoyer
Keyword(s):  
Electronic Properties ◽  
Structure Factor ◽  
Correlation Functions ◽  
Pair Correlation ◽  
Model Structure ◽  
X Ray Diffraction ◽  
X Ray ◽  
Structure Factors ◽  
Diffraction Structure ◽  
Eutectic Concentration

Abstract Using X-ray diffraction, structure factors and pair correlation functions of several molten Cu-Sb alloys and pure antimony were determined and compared with published structural, thermodynamic and electronic properties. The eutectic concentration Cu37Sb63 was investigated in dependence on temperature, and a model structure factor was calculated applying a segregation model.

scholarly journals Mean Square Vibration Amplitudes in Zinc

1977 ◽  
Vol 30 (1) ◽  
pp. 105 ◽  
Author(s):  
DW Field
Keyword(s):  
Single Crystal ◽  
Debye Temperature ◽  
Mean Square ◽  
X Ray Diffraction ◽  
Zinc Single Crystal ◽  
X Ray ◽  
Structure Factors ◽  
Principal Directions ◽  
The Mean ◽  
Integrated Intensities

The structure factors of 98 independent reflections have been determined by measurement of the integrated intensities for X-ray diffraction from a zinc single crystal at 295 K. The mean square vibration amplitudes found for the two principal directions are' compared with 'other recent measurements. The X-ray Debye temperature determined from the data' is 207 � 3 K at 295 K.

scholarly journals Preliminary X-ray diffraction analysis of CfaA, a molecular chaperone essential for the assembly of CFA/I fimbriae of human enterotoxigenicEscherichia coli

2014 ◽  
Vol 70 (2) ◽  
pp. 196-199
Author(s):  
Rui Bao ◽  
Lothar Esser ◽  
Steven Poole ◽  
Annette McVeigh ◽  
Yu-xing Chen ◽  
...  
Keyword(s):  
Tertiary Structure ◽  
Heavy Atom ◽  
Diffusion Method ◽  
Anomalous Scattering ◽  
X Ray Diffraction ◽  
X Ray ◽  
Cell Parameters ◽  
Colonization Factor ◽  
Isomorphous Replacement ◽  
Periplasmic Chaperone

Understanding of pilus bioassembly in Gram-negative bacteria stems mainly from studies of P pili and type 1 fimbriae of uropathogenicEscherichia coli, which are mediated by the classic chaperone–usher pathway (CUP). However, CFA/I fimbriae, a class 5 fimbria and intestinal colonization factor for enterotoxigenicE. coli(ETEC), are proposed to assembleviathe alternate chaperone pathway (ACP). Both CUP and ACP fimbrial bioassembly pathways require the function of a periplasmic chaperone, but their corresponding proteins share very low similarity in primary sequence. Here, the crystallization of the CFA/I periplasmic chaperone CfaA by the hanging-drop vapor-diffusion method is reported. X-ray diffraction data sets were collected from a native CfaA crystal to 2 Å resolution and to 1.8 and 2.8 Å resolution, respectively, from a lead and a platinum derivative. These crystals displayed the symmetry of space groupC2, with unit-cell parametersa= 103.6,b= 28.68,c= 90.60 Å, β = 119.7°. Initial phases were derived from multiple isomorphous replacement with anomalous scattering experiments using the data from the platinum and lead derivatives. This resulted in an interpretable electron-density map showing one CfaA molecule in an asymmetric unit. Sequence assignments were aided by anomalous signals from the heavy-atom derivatives. Refinement of the atomic model of CfaA is ongoing, which is expected to further understanding of the essential aspects and allowable variations in tertiary structure of the greater family of chaperones involved in chaperone–usher mediated bioassembly.

The Molecular Structure and Hydrogen Bond Geometry in Liquid Formamide: Electron, Neutron, and X-Ray Diffraction Studies

1983 ◽  
Vol 38 (2) ◽  
pp. 231-236 ◽  
Author(s):  
E. Kálmán ◽  
I. Serke ◽  
G. Pálinkás ◽  
M. D. Zeidler ◽  
F. J. Wiesmann ◽  
...  
Keyword(s):  
Molecular Structure ◽  
Hydrogen Bond ◽  
Electron Diffraction ◽  
Diffraction Data ◽  
Free Molecule ◽  
X Ray Diffraction ◽  
X Ray ◽  
The Mean ◽  
Diffraction Patterns ◽  
Good Agreement

Abstract Electron, neutron and X-ray diffraction patterns of liquid formamide have been measured at a temperature of 25 °C. Analysis of the diffraction data yields the molecular structure and the average geometry of the hydrogen bond. The molecular parameters obtained from liquid diffraction experiments are in good agreement with those from gas electron diffraction for the free molecule. The mean O…N and O…H hydrogen bond distances are 2.9 Å and 1.9 Å, respectively. Four H-bonds per molecule are found on the average. The deviation of the H-bonds from the linearity is estimated.

Structure of Sputtered Amorphous Zr-Hf-Si Alloys

1999 ◽  
Vol 54 (12) ◽  
pp. 699-703
Author(s):  
A. Pojtinger ◽  
P. Lamparter ◽  
S. Steeb
Keyword(s):  
Amorphous Alloys ◽  
Short Range ◽  
Pair Correlation ◽  
Isomorphous Substitution ◽  
X Ray Diffraction ◽  
Partial Functions ◽  
X Ray ◽  
Structure Factors ◽  
Reverse Monte Carlo Simulation ◽  
Total Structure

Abstract Amorphous (Zr,Hf)37Si63 alloys were produced by sputtering. Their total structure factors were determined by X-ray diffraction. Using the methods of isomorphous substitution and Reverse Monte Carlo simulation, the partial pair correlation functions were obtained. The results were compared with the partial functions of amorphous Ti40Si60. In the amorphous alloys under investigation the transition metal -metalloid correlation dominates the short range order.

Bonding charge densities of Al and Cu determined by electron diffraction

1989 ◽  
Vol 47 ◽  
pp. 492-493
Author(s):  
A.G. Fox ◽  
M.A. Tabbernor ◽  
R.M. Fisher
Keyword(s):  
Electron Diffraction ◽  
Form Factors ◽  
Critical Voltage ◽  
X Ray Diffraction ◽  
Small Magnitude ◽  
X Ray ◽  
Charge Densities ◽  
Density Maps ◽  
Structure Factors ◽  
Atomic Scattering

As discussed by Zuo et al, the small magnitude of the energy which determines a crystal's structure has long provided a severe challenge for both theoreticians and experimentalists who have attempted to accurately calculate and measure the crystal structure factors of many materials. In particular the f.c.c. elements copper and aluminum have received considerable attention both theoretically and experimentally, where attempts have been made to accurately measure the atomic scattering (form) factors by a variety of means other than the traditionally inaccurate X-ray diffraction methods. Smart and Humphreys recognized that the accuracy of the low-angle form factors of Cu and Al determined by the critical voltage effect (Vc) in electron diffraction should be good enough to give bonding information about these two elements. Unfortunately, they failed to analyze the problem of the higher angle form factors correctly, and thus produced erroneous deformation charge density maps.

Predicting some Effects of Lattice Vibrations on Proton Scattering Patterns

1970 ◽  
Vol 14 ◽  
pp. 1-10
Author(s):  
C. S. Barrett
Keyword(s):  
Temperature Factor ◽  
Lattice Vibrations ◽  
Proton Scattering ◽  
Mean Square ◽  
X Ray Diffraction ◽  
X Ray ◽  
Structure Factors ◽  
Integrated Intensity ◽  
The Mean ◽  
Thermal Vibrations

AbstractA method of predicting the approximate relative intensities of lines in proton blocking patterns recently proposed, which is based on summing the squares of structure factors for the various orders of reflection of a plane, is found to predict certain effects of lattice vibrations on the lines in some recently reported patterns. The mean square amplitude of vibration enters the calculations through a Debye-Waller temperature factor like that used in X-ray diffraction. When patterns are compared for groups of crystals that are nearly identical except for this temperature factor, the qualitative predictions by this method agree with the observations. If it is also arbitrarily assumed that the integrated intensity dip at a spot where lines intersect is approximated by summing the calculated Integrated intensity dips for all of the lines crossing at the spot, one has a simple and convenient method of predicting relative spot intensities. Such calculations have been successful in establishing the order of decreasing intensity for most of the spots along a given line, with several different kinds of crystals. This method also serves to predict qualitatively how prominent the spots appear relative to the lines, in general, in patterns of crystals that differ appreciably only in the amplitude of the thermal vibrations.

scholarly journals Structural and magnetic characterization of maghemites prepared from Al-substituted magnetites

2013 ◽  
Vol 37 (6) ◽  
pp. 1569-1575 ◽  
Author(s):  
Marcelo Augusto Batista ◽  
Antonio Carlos Saraiva da Costa ◽  
Jerry Marshal Bigham ◽  
Andrea Paesano Junior ◽  
Graciele Berndt ◽  
...  
Keyword(s):  
Magnetic Hyperfine Field ◽  
Isomorphous Substitution ◽  
X Ray Diffraction ◽  
Hyperfine Parameters ◽  
X Ray ◽  
Al Substitution ◽  
Diffraction Peaks ◽  
The Mean ◽  
Fe Substitution

Synthetic aluminum-substituted maghemites were characterized by total chemical analysis, powder X-ray diffraction (XRD), Mössbauer spectroscopy (ME), and vibrating sample magnetometry (VSM). The aim was to determine the structural, magnetic, and hyperfine properties of γ-Fe2-xAl xO3 as the Al concentration is varied. The XRD results of the synthetic products were indexed exclusively as maghemite. Increasing Al for Fe substitution decreased the mean crystalline dimension and shifted all diffraction peaks to higher º2θ angles. The a0 dimension of the cubic unit cell decreased with increasing Al according to the equation a o = 0.8385 - 3.63 x 10-5 Al (R²= 0.94). Most Mössbauer spectra were composed of one sextet, but at the highest substitution rate of 142.5 mmol mol-1 Al, both a doublet and sextet were obtained at 300 K. All hyperfine parameters from the sub-spectra were consistent with high-spin Fe3+ (0.2 a 0.7 mms-1) and suggested a strong superparamagnetic component associated with the doublet. The magnetic hyperfine field of the sextets decreased with the amount of Al-substitution [Bhf (T) = 49.751 - 0.1202Al; R² = 0.94] while the linewidth increased linearly. The saturation magnetization also decreased with increasing isomorphous substitution.

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