Low-angle X-ray diffraction patterns of collagen

1956 ◽  
Vol 235 (1201) ◽  
pp. 189-201 ◽  
Keyword(s):  
Electron Microscopy ◽  
Density Distribution ◽  
Electron Density ◽  
Electron Micrographs ◽  
Electron Density Distribution ◽  
X Ray Diffraction ◽  
Collagen Fibres ◽  
X Ray ◽  
Diffraction Patterns ◽  
Different Sources

Measurements have been made of the intensities of up to 25 orders of the low-angle X-ray diffraction patterns of wet and dry collagen fibres from three different sources. From these data Patterson functions have been plotted, and using these curves, and the known results of electron microscopy as guides in making initial assumptions about the electron density distribution in collagen fibres, satisfactory interpretations of the diffraction patterns of wet and dry fibres have been reached. These results show that the conspicuous periodic raised bands seen in electron micrographs of metal-shadowed fibres change in length on wetting the fibres, while the regions between them are but little affected, and it is concluded that these bands are highly disordered regions in dry fibres, becoming more orderly on hydration, while the interbands are always well ordered. Some evidence has also been obtained for the existence of an axial periodicity of about 32·8 Å.

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.

scholarly journals An electron microscopic and optical diffraction analysis of the structure of Limulus telson muscle thick filaments.

1982 ◽  
Vol 92 (2) ◽  
pp. 443-451 ◽  
Author(s):  
R W Kensler ◽  
R J Levine
Keyword(s):  
Electron Microscopy ◽  
Diffraction Analysis ◽  
Electron Micrographs ◽  
Optical Diffraction ◽  
X Ray Diffraction ◽  
Electron Microscopic ◽  
X Ray ◽  
Thick Filaments ◽  
Diffraction Patterns ◽  
Cross Bridges

Long, thick filaments (greater than 4.0 micrometer) rapidly and gently isolated from fresh, unstimulated Limulus muscle by an improved procedure have been examined by electron microscopy and optical diffraction. Images of negatively stained filaments appear highly periodic with a well-preserved myosin cross-bridge array. Optical diffraction patterns of the electron micrographs show a wealth of detail and are consistent with a myosin helical repeat of 43.8 nm, similar to that observed by x-ray diffraction. Analysis of the optical diffraction patterns, in conjunction with the appearance in electron micrographs of the filaments, supports a model for the filament in which the myosin cross-bridges are arranged on a four-stranded helix, with 12 cross-bridges per turn or each helix, thus giving an axial repeat every third level of cross-bridges (43.8 nm).

Electron density distribution of Ba1-xKxBiO3 (x = 0.43) by ultra-short-wavelength x-ray diffraction

2002 ◽  
Vol 14 (22) ◽  
pp. 5477-5484 ◽  
Author(s):  
Yasuhiko Takahashi ◽  
Xioali Ji ◽  
Taichiro Nishio ◽  
Hiromoto Uwe ◽  
Ken-ichi Ohshima
Keyword(s):  
Density Distribution ◽  
Electron Density ◽  
Short Wavelength ◽  
Electron Density Distribution ◽  
X Ray Diffraction ◽  
X Ray

Electron Density Distribution in LiB3O5 at 293 K

1997 ◽  
Vol 53 (6) ◽  
pp. 870-879 ◽  
Author(s):  
C. Le Hénaff ◽  
N. K. Hansen ◽  
J. Protas ◽  
G. Marnier
Keyword(s):  
Density Distribution ◽  
Electron Density ◽  
Electron Density Distribution ◽  
X Ray Diffraction ◽  
X Ray ◽  
Hartree Fock ◽  
Density Maps ◽  
Symmetry Constraints ◽  
Net Charges ◽  
Good Agreement

The electron density distribution in lithium triborate LiB3O5 has been studied at room temperature by X-ray diffraction using Ag K \alpha radiation up to 1.02 Å−1 [1439 unique reflections with I > 3\sigma(I)]. Conventional refinements with a free-atom model yield R(F) = 0.0223, wR(F) = 0.0299, S = 1.632. Atom charge refinements show that the lithium should be considered a monovalent ion. Multipolar refinements were undertaken up to fourth order, imposing local non-crystallographic symmetry constraints in order to avoid phase problems leading to meaningless multipole populations due to the non-centrosymmetry of the structure (space group: Pn a21). The residual indices decreased to: R(F) = 0.0147, wR(F) = 0.0193, S = 1.106. The net charges are in good agreement with what can be expected in borate chemistry. Deformation density maps are analysed in terms of \sigma and \pi bonding. The experimental electron distribution in the p z orbitals of triangular B atoms and surrounding O atoms has been analysed by introducing idealized hybridized states. In parallel, the electron density has been determined from ab initio Hartree–Fock calculations on fragments of the structure. Agreement with the X-ray determination is very good and confirms the nature of bonding in the crystal. The amount of transfer of \pi electrons from the oxygen to the triangular B atoms is estimated to be 0.22 electrons by theory.

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