X-Ray crystallographic determination of molecular geometry for bis(imidotetramethyldithiodiphosphino-SS)-iron(II), a structural model for the iron–sulphur core of rubredoxin

1970 ◽  
Vol 0 (11) ◽  
pp. 703b-704 ◽  
Author(s):  
Melvyn R. Churchill ◽  
John Wormald
Keyword(s):  
Structural Model ◽  
Molecular Geometry ◽  
X Ray

scholarly journals X-RAY DETERMINATION OF THE STRUCTURE OF ANHYDROUS DIPHENYLCYCLOPROPENONE. VARIATIONS OF THE MOLECULAR GEOMETRY DUE TO HYDROGEN BONDING

1974 ◽  
Vol 3 (6) ◽  
pp. 639-642 ◽  
Author(s):  
Harumichi Tsukada ◽  
Hirotaka Shimanouchi ◽  
Yoshio Sasada
Keyword(s):  
Hydrogen Bonding ◽  
Molecular Geometry ◽  
X Ray

Structure determination of the stable anhydrous phase of α-lactose from X-ray powder diffraction

2005 ◽  
Vol 61 (2) ◽  
pp. 185-191 ◽  
Author(s):  
Cyril Platteau ◽  
Jacques Lefebvre ◽  
Frederic Affouard ◽  
Jean-François Willart ◽  
Patrick Derollez ◽  
...  
Keyword(s):  
Powder Diffraction ◽  
Room Temperature ◽  
Structural Model ◽  
Hydroxyl Groups ◽  
Rietveld Refinements ◽  
X Ray ◽  
Hydrogen Bond Networks ◽  
Monte Carlo Simulated Annealing ◽  
Annealing Method

The stable anhydrous form of α-lactose has been obtained by the dehydration of α-lactose monohydrate in methanol. An X-ray powder diffraction pattern was recorded at room temperature with a laboratory diffractometer equipped with an INEL curved sensitive detector CPS120. The starting structural model of this form was found by a Monte-Carlo simulated annealing method. The structure was obtained through Rietveld refinements and the minimization of crystalline energy for the localization of the H atoms of the hydroxyl groups. Soft restraints were applied to bond lengths and angles. Networks of O—H...O hydrogen bonds account for the crystalline cohesion. A comparison is made between the hydrogen-bond networks of this form and those of the monohydrate and hygroscopic anhydrous forms of α-lactose.

Six pyrimidonium salts: determination of their crystal structures and studies of their prototropic behaviour in solution

1984 ◽  
Vol 62 (6) ◽  
pp. 1194-1202 ◽  
Author(s):  
Thomas W. S. Lee ◽  
Steven J. Rettig ◽  
Ross Stewart ◽  
James Trotter
Keyword(s):  
Hydrogen Exchange ◽  
Molecular Geometry ◽  
High Reactivity ◽  
Methyl Groups ◽  
Contributing Factors ◽  
X Ray ◽  
X Ray Crystallography ◽  
Reactive Compound ◽  
Chloride Salts

Six methyl-substituted 2-pyrimidonium chloride salts have been prepared and the rates of hydrogen exchange of their reactive methyl groups (at the 4- and 6-positions) have been determined in DCl/D2O solution. Adjacent methyl groups, whether on nitrogen or carbon, activate the exchanging centres, whereas more distant methyl groups have a deactivating effect. The molecular geometry of the salts has been determined by X-ray crystallography with the view to determining whether the presence of strain in the pyrimidonium ring can account for the activating effect of adjacent methyl. The most reactive compound, the 1,5,6-trimethylpyrimidonium chloride, has a geometry that is consistent with high reactivity, viz. a non-planar ring and short H … H intermethyl distance. However, the 1,4,5,6-tetramethyl compound, which also is non-planar and has an extremely short 5-6 intermethyl distance (1.99 Å), is not highly reactive; that is, the heightened strain is unable to overcome the deactivating inductive effect of the additional methyl group. We conclude that deviations from ring planarity and short intermethyl distances are insufficient to account for the activation produced by adjacent methyl though they appear to be contributing factors to this effect.

scholarly journals Serial crystallography onin vivogrown microcrystals using synchrotron radiation

IUCrJ ◽  
2014 ◽  
Vol 1 (2) ◽  
pp. 87-94 ◽  
Author(s):  
Cornelius Gati ◽  
Gleb Bourenkov ◽  
Marco Klinge ◽  
Dirk Rehders ◽  
Francesco Stellato ◽  
...  
Keyword(s):  
Structural Model ◽  
Array Detector ◽  
Biological Macromolecules ◽  
Data Set ◽  
X Ray ◽  
Pixel Array ◽  
Structure Determinations ◽  
Serial Crystallography ◽  
Serial Femtosecond Crystallography

Crystal structure determinations of biological macromolecules are limited by the availability of sufficiently sized crystals and by the fact that crystal quality deteriorates during data collection owing to radiation damage. Exploiting a micrometre-sized X-ray beam, high-precision diffractometry and shutterless data acquisition with a pixel-array detector, a strategy for collecting data from many micrometre-sized crystals presented to an X-ray beam in a vitrified suspension is demonstrated. By combining diffraction data from 80Trypanosoma bruceiprocathepsin B crystals with an average volume of 9 µm3, a complete data set to 3.0 Å resolution has been assembled. The data allowed the refinement of a structural model that is consistent with that previously obtained using free-electron laser radiation, providing mutual validation. Further improvements of the serial synchrotron crystallography technique and its combination with serial femtosecond crystallography are discussed that may allow the determination of high-resolution structures of micrometre-sized crystals.

Structure determination of the silver carboxylate dimer [Ag(O2C20H39)]2, silver arachidate, using powder X-ray diffraction methods

2012 ◽  
Vol 27 (2) ◽  
pp. 99-103 ◽  
Author(s):  
Peter W. Stephens ◽  
James A. Kaduk ◽  
Thomas N. Blanton ◽  
David R. Whitcomb ◽  
Scott T. Misture ◽  
...  
Keyword(s):  
Density Functional ◽  
Structural Model ◽  
X Ray Diffraction ◽  
Triclinic Space Group ◽  
One Dimensional ◽  
X Ray ◽  
Cell Dimensions ◽  
Silver Carboxylate ◽  
Pseudo Potential

High-resolution powder X-ray diffraction and density functional plane wave pseudo-potential techniques have been used to obtain an optimized structural model of silver arachidate, [Ag(O2C(CH2)18CH3]2. The unit cell is triclinic, space group P-1 with cell dimensions of a = 4.1519(10) Å, b = 4.7055(10) Å, c = 53.555(4) Å, α = 89.473(15)°, β = 87.617(5)° and γ = 76.329(5)°. The structure is characterized by an 8-membered ring dimer of Ag atoms and carboxyl groups joined by four-member Ag–O rings with fully extended zigzag side chains, giving rise to one-dimensional chains along the b-axis.

Structure determination of L-arabinitol by powder X-ray diffraction

2012 ◽  
Vol 68 (4) ◽  
pp. 407-411 ◽  
Author(s):  
Patrick Derollez ◽  
Yannick Guinet ◽  
Frédéric Affouard ◽  
Florence Danède ◽  
Laurent Carpentier ◽  
...  
Keyword(s):  
Structural Model ◽  
Interatomic Bond ◽  
Hydroxyl Groups ◽  
X Ray Diffraction ◽  
Rietveld Refinements ◽  
X Ray ◽  
Monte Carlo Simulated Annealing ◽  
Diffraction Patterns ◽  
Annealing Method

Powder X-ray diffraction patterns of the commercial phase of L-arabinitol were recorded with a laboratory diffractometer. The starting structural model was found by a Monte-Carlo simulated annealing method. The final structure was obtained through Rietveld refinements with soft restraints on the interatomic bond lengths and bond angles. H atoms of hydroxyl groups were localized by minimization of the crystalline energy. The cell is triclinic with the space group P1 and contains two molecules. The crystalline cohesion is achieved by an important network of O—H...O hydrogen bonds.

Direct re-determination of the modulated lamellar ‘ripple’ phase of hydrated lecithin

1998 ◽  
Vol 213 (7-8) ◽  
Author(s):  
D. L. Dorset ◽  
C. J. Gilmore
Keyword(s):  
Maximum Entropy ◽  
Structural Model ◽  
Direct Methods ◽  
Basis Set ◽  
X Ray ◽  
Using Data ◽  
Ripple Phase ◽  
Successive Phase ◽  
New Phase

AbstractThe structure of the ripple phase in hydrated lecithin (DMPC) was determined by direct methods using data collected in an earlier synchrotron X-ray study. When the Sayre-Hughes equation or maximum entropy and like-lihood were used to determine phases of a basis set, recognizable features of the bilayer profile could be identified. The subsequent refinement, based on permutation of successive phase clusters, allowed a correct structural model to be visualized directly, by imposing the continuity of the directly-identified bilayer as a basis of accepting new phase terms.

scholarly journals Method of determination of palladium concentration for C-Pd nanostructural films as a function of film thickness, roughness and topography

2014 ◽  
Vol 32 (2) ◽  
pp. 228-235
Author(s):  
Joanna Rymarczyk ◽  
Mirosław Kozłowski
Keyword(s):  
Film Thickness ◽  
Structural Model ◽  
Quartz Substrate ◽  
X Ray ◽  
Qualitative And Quantitative ◽  
Method Of Determination ◽  
Palladium Concentration ◽  
Quantitative Analyses ◽  
Model Film

AbstractIn this paper a method of determination of Pd in a carbon-palladium film (C-Pd film) deposited on a quartz substrate is presented. This method is based on energy dispersive X-ray spectroscopy (EDX) and all experiments were performed using a scanning electron microscope (SEM) equipped with EDX system. Qualitative and quantitative analyses were carried out for C-Pd films prepared by PVD method in different technological conditions. It was shown that results of the experiments depended on the structural model, film thickness and electron beam energy used for Pd content calculation.This method enabled us to conclude on the homogeneity of palladium distribution in the whole volume of carbonaceous matrix, depending on the parameters of PVD process. Additionally, these studies showed that a different palladium concentration in C-Pd films had a significant impact on their topography and morphology.

Bismuth on GaSb(110): Structural Determination of the 1×1 and 1×2 Phases by Surface X-Ray Diffraction

1998 ◽  
Vol 05 (05) ◽  
pp. 1043-1052 ◽  
Author(s):  
L. Lottermoser ◽  
T. Van Gemmeren ◽  
O. Bunk ◽  
R. L. Johnson ◽  
E. Landemark ◽  
...  
Keyword(s):  
Structural Model ◽  
Layer Structure ◽  
Zigzag Chain ◽  
X Ray Diffraction ◽  
Surface Geometry ◽  
X Ray ◽  
Reconstructed Surface ◽  
Thermal Stability Of ◽  
Good Agreement

The surface geometry of the 1×1 and 1×2 phases of bismuth on GaSb(110) has been determined using surface X-ray diffraction with synchrotron radiation. The bismuth atoms form zigzag chains along the [Formula: see text] direction of the substrate. For the 1×1 phase four different registries of the bismuth chains with respect to the GaSb(110) substrate are possible. It was found that only the epitaxial continued layer structure was in good agreement with the experimental data. In the 1×2 reconstruction every second zigzag chain in the uppermost substrate layer is missing. The reconstructed surface is terminated with a full monolayer of Bi atoms which also form zigzag chains. The Bi atoms in the chains bond alternately to the first and second layer substrate atoms and the Bi chains are inclined at 34° to the surface. This new structural model explains the higher thermal stability of the 1×2 phase compared to that of the 1×1 phase.

Crystal structure determination of the silver carboxylate dimer [Ag(O2C22H43)]2, silver behenate, using powder X-ray diffraction methods

2011 ◽  
Vol 26 (4) ◽  
pp. 313-320 ◽  
Author(s):  
Thomas N. Blanton ◽  
Manju Rajeswaran ◽  
Peter W. Stephens ◽  
David R. Whitcomb ◽  
Scott T. Misture ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Density Functional ◽  
Structural Model ◽  
X Ray Diffraction ◽  
Triclinic Space Group ◽  
X Ray ◽  
Cell Dimensions ◽  
Alkyl Side Chains ◽  
Silver Carboxylate

High-resolution powder X-ray diffraction has been used to determine the crystal structure of silver behenate, [Ag(O2C(CH2)20CH3]2. Using CASTEP density functional plane wave pseudopotential techniques to obtain an optimized structural model, Rietveld refinement of the structure gives Rwp = 8.66%. The unit cell is triclinic, space group P1, with cell dimensions of a = 4.1769(2) Å, b = 4.7218(2) Å, c = 58.3385(1) Å, α = 89.440(3)°, β = 89.634(3)°, γ = 75.854(1)°. The structure is characterized by an 8-membered ring dimer of Ag atoms and carboxyl groups with a fully extended all-trans configuration of the alkyl side chains. The dimers are joined by four-membered Ag-O rings creating a polymeric network, giving rise to one-dimensional chains along the b-axis. This structure is supported by EXAFS measurements of the local structure around the silver atoms and IR measurements.

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