The Birth and Initial Exploitation of X-ray Diffraction

2020 ◽  
pp. 17-40
Author(s):  
John Meurig Thomas
Keyword(s):  
Molecular Weight ◽  
High Resolution ◽  
Density Distribution ◽  
Chemical Bonding ◽  
Interatomic Distance ◽  
Electron Density Distribution ◽  
Simple Explanation ◽  
X Ray Diffraction ◽  
X Ray ◽  
High Resolution Microscopy

A non-mathematical account of the discovery of X-ray diffraction by von Laue and its use as a new kind of high-resolution microscopy by W. L. Bragg is given. There follows a simple explanation of how the electron densities in various regions of any molecule that can be crystallized can be retrieved from its X-ray diffraction pattern. Also, it is explained how the molecular weight of the molecule can be determined from straightforward measurements of the diffraction and the density of the crystal. The identity of the elements in a crystal, as well as the nature of the chemical bonding between them, may also be derived from measurement of the electron density distribution within it. The importance of Bragg’s Law, relating X-ray pattern to interatomic distance, is demonstrated, and initial applications of it by Bragg and Pauling are given.

Insight into the Electron Density Distribution in an O,N-Heterocyclic Stannylene by High-Resolution X-ray Diffraction Analysis

2019 ◽  
Vol 2019 (6) ◽  
pp. 875-884 ◽  
Author(s):  
Maxim G. Chegerev ◽  
Alexandr V. Piskunov ◽  
Kseniya V. Tsys ◽  
Andrey G. Starikov ◽  
Klaus Jurkschat ◽  
...  
Keyword(s):  
High Resolution ◽  
Density Distribution ◽  
Diffraction Analysis ◽  
Electron Density ◽  
Electron Density Distribution ◽  
X Ray Diffraction ◽  
X Ray ◽  
Insight Into

Electron density distribution and Madelung potential in α-spodumene, LiAl(SiO3)2, from two-wavelength high-resolution X-ray diffraction data

1999 ◽  
Vol 55 (3) ◽  
pp. 273-284 ◽  
Author(s):  
Sandrine Kuntzinger ◽  
Nour Eddine Ghermani
Keyword(s):  
High Resolution ◽  
Density Distribution ◽  
Electron Density ◽  
Electron Density Distribution ◽  
Data Sets ◽  
X Ray Diffraction ◽  
Net Charge ◽  
X Ray ◽  
Madelung Potential ◽  
Net Charges

The electron density distribution in α-spodumene, LiAl(SiO3)2, was derived from high-resolution X-ray diffraction experiments. The results obtained from both Mo Kα- and Ag Kα-wavelength data sets are reported. The features of the Si—O and Al—O bonds are related to the geometrical parameters of the Si—O—Al and Si—O—Si bridges on the one hand and to the O...Li+ interaction on the other. Kappa refinements against the two data sets yielded almost the same net charges for the Si (+1.8 e) and O (−1.0 e) atoms in spodumene. However, the Al net charge obtained from the Ag Kα data (+1.9 e) is larger than the net charge derived from the Mo Kα data (+1.5 e). This difference correlates with a more contracted Al valence shell revealed by the shorter X-ray wavelength (κ = 1.4 for the Ag Kα data set). The derived net charges were used to calculate the Madelung potential at the spodumene atomic sites. The electrostatic energy for the chemical formula LiAl(SiO3)2 was −8.60 e2 Å−1 (−123.84 eV) from the net charges derived from the Ag Kα data and −6.97 e2 Å−1 (−100.37 eV) from the net charges derived from the Mo Kα data.

Distribution and Topology of the Electron Density in an Aluminosilicate Compound from High-Resolution X-ray Diffraction Data: the Case of Scolecite

1998 ◽  
Vol 54 (6) ◽  
pp. 819-833 ◽  
Author(s):  
S. Kuntzinger ◽  
N. E. Ghermani ◽  
Y. Dusausoy ◽  
C. Lecomte
Keyword(s):  
High Resolution ◽  
Density Distribution ◽  
Electron Density ◽  
Critical Points ◽  
Diffraction Data ◽  
Electron Density Distribution ◽  
X Ray Diffraction ◽  
X Ray ◽  
And Topology ◽  
Experimental Electron Density

The experimental electron density distribution in scolecite, CaAl2Si3O10.3H2O, has been derived from single-crystal high-resolution Ag Kα X-ray diffraction data. A statistical method based on the prediction matrix has been used to discuss the estimation of the valence populations (P val) in the kappa least-squares refinements. The densities on the Si—O—Si and Si—O—Al bridges have been characterized using the topology of the electron density through its Laplacian at the bond critical points. The Si—O and Al—O bond features are related to the atomic environment and to the Si—O—T geometries (T = Si, Al).

scholarly journals High-resolution neutron and X-ray diffraction room-temperature studies of an H-FABP–oleic acid complex: study of the internal water cluster and ligand binding by a transferred multipolar electron-density distribution

IUCrJ ◽  
2016 ◽  
Vol 3 (2) ◽  
pp. 115-126 ◽  
Author(s):  
E. I. Howard ◽  
B. Guillot ◽  
M. P. Blakeley ◽  
M. Haertlein ◽  
M. Moulin ◽  
...  
Keyword(s):  
Oleic Acid ◽  
Fatty Acid ◽  
High Resolution ◽  
Density Distribution ◽  
Electron Density ◽  
Electron Density Distribution ◽  
Room Temperature ◽  
Water Molecules ◽  
X Ray

Crystal diffraction data of heart fatty acid binding protein (H-FABP) in complex with oleic acid were measured at room temperature with high-resolution X-ray and neutron protein crystallography (0.98 and 1.90 Å resolution, respectively). These data provided very detailed information about the cluster of water molecules and the bound oleic acid in the H-FABP large internal cavity. The jointly refined X-ray/neutron structure of H-FABP was complemented by a transferred multipolar electron-density distribution using the parameters of the ELMAMII library. The resulting electron density allowed a precise determination of the electrostatic potential in the fatty acid (FA) binding pocket. Bader's quantum theory of atoms in molecules was then used to study interactions involving the internal water molecules, the FA and the protein. This approach showed H...H contacts of the FA with highly conserved hydrophobic residues known to play a role in the stabilization of long-chain FAs in the binding cavity. The determination of water hydrogen (deuterium) positions allowed the analysis of the orientation and electrostatic properties of the water molecules in the very ordered cluster. As a result, a significant alignment of the permanent dipoles of the water molecules with the protein electrostatic field was observed. This can be related to the dielectric properties of hydration layers around proteins, where the shielding of electrostatic interactions depends directly on the rotational degrees of freedom of the water molecules in the interface.

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