scholarly journals Structures of pseudo-decagonal approximants in Al−Co−Ni

2012 ◽  
Vol 370 (1969) ◽  
pp. 2949-2959 ◽  
Author(s):  
Sven Hovmöller ◽  
Linus Hovmöller Zou ◽  
Xiaodong Zou ◽  
Benjamin Grushko
Keyword(s):  
High Resolution Electron Microscopy ◽  
Limited Information ◽  
X Ray ◽  
X Ray Crystallography ◽  
Resolution Electron ◽  
Cell Dimensions ◽  
Diffraction Patterns ◽  
Quasi Crystals ◽  
Unit Cell Dimensions ◽  
Microscopy Images

Quasi-crystals shocked the crystallographic world when they were reported in 1984. We now know that they are not a rare exception, and can be found in many alloy systems. One of the richer systems for quasi-crystals and their approximants is Al−Co−Ni. A large series of pseudo-decagonal (PD) approximants have been found. Only two of them, PD4 and PD8, have been solved by X-ray crystallography. We report here the structures of PD1, PD2, PD3 and PD5, solved from the limited information that is provided by electron diffraction patterns, unit cell dimensions and high-resolution electron microscopy images.

Structure of Nd10W22O81 from high-resolution electron microscopy and X-ray powder diffraction

2001 ◽  
Vol 57 (1) ◽  
pp. 13-19 ◽  
Author(s):  
Carl Grenthe ◽  
Antonietta Guagliardi ◽  
Margareta Sundberg ◽  
Per-Erik Werner
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
Powder Diffraction ◽  
High Resolution Electron Microscopy ◽  
X Ray ◽  
Transmission Electron ◽  
Resolution Electron ◽  
Cell Dimensions ◽  
New Type ◽  
Unit Cell Dimensions

The crystal structure of Nd10W22O81, neodymium tungstate, has been determined using a combination of high-resolution transmission electron microscopy and X-ray powder diffraction methods. The unit-cell dimensions determined from X-ray data are a  =  3.8613 (1), b  =  35.9431 (1), c  =  21.8900 (1) Å, V = 3038.05 Å3, Z  =  2, space group Pbcm. The structure is built up of pentagonal columns (PCs) connected to ReO3-type fragments consisting of three octahedra, thus forming W9O32 units. These units form `pillars' along a. These `pillars' are joined by pairs of tilted octahedra (W2O11 groups) to form corrugated layers perpendicular to b. The Nd atoms are located in the space between these layers and form the only link between them. Interstitial O atoms are located between two of the Nd atoms. The formula Nd10W22O81 can thus be alternatively given as Nd5W11O39 + x (x ≃ 1.5), where x represents the interstitial O atoms. Nd10W22O81 is a new type of PC structure.

HREM Studies of Some Phases in the ZrO2-Nb2O5 System

1990 ◽  
Vol 48 (1) ◽  
pp. 40-41
Author(s):  
Margareta Sundberg ◽  
Bengt-Olov Marinder
Keyword(s):  
Electron Diffraction ◽  
High Resolution Electron Microscopy ◽  
Structure Type ◽  
X Ray ◽  
Resolution Electron ◽  
Commensurate Phase ◽  
Crystal Fragment ◽  
Diffraction Patterns ◽  
Unit Cell Dimensions ◽  
Block Structures

High resolution electron microscopy and x ray powder diffraction techniques were used to study samples of various compositions in the Nb2O5-rich part of the ZrO2-Nb2O5 system at 1500°C. A large number of fragments were also characterized by electron diffraction in combination with EDS analysis. Some HREM results concerning block structures formed in the above region have previously been reported.The x ray powder pattern of a ZrO2.9Nb2O5 sample indicated a phase isotypic with T-Nb2O5. The micrograph in Fig. 1, of a thin crystal fragment from that sample, illustrates a phase related to the UVO5 (m=2) structure type. The electron diffraction patterns showed an ordered commensurate phase (m=8) with unit cell dimensions similar to those reported for T-Nb2O5 and Ta30W2O81. The structure models of these two compounds are rather similar and differ mainly in the oxygen content.

Electron microscopy of rabbit FC crystals

1983 ◽  
Vol 41 ◽  
pp. 730-731
Author(s):  
Robert A. Grant ◽  
Laura L. Degn ◽  
Wah Chiu ◽  
John Robinson
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
High Resolution Electron Microscopy ◽  
Molecular Replacement ◽  
X Ray ◽  
X Ray Crystallography ◽  
Resolution Electron ◽  
Replacement Technique ◽  
Hydrated Crystal ◽  
Molecular Structure Analysis

Proteolytic digestion of the immunoglobulin IgG with papain cleaves the molecule into an antigen binding fragment, Fab, and a compliment binding fragment, Fc. Structures of intact immunoglobulin, Fab and Fc from various sources have been solved by X-ray crystallography. Rabbit Fc can be crystallized as thin platelets suitable for high resolution electron microscopy. The structure of rabbit Fc can be expected to be similar to the known structure of human Fc, making it an ideal specimen for comparing the X-ray and electron crystallographic techniques and for the application of the molecular replacement technique to electron crystallography. Thin protein crystals embedded in ice diffract to high resolution. A low resolution image of a frozen, hydrated crystal can be expected to have a better contrast than a glucose embedded crystal due to the larger density difference between protein and ice compared to protein and glucose. For these reasons we are using an ice embedding technique to prepare the rabbit Fc crystals for molecular structure analysis by electron microscopy.

Atomic structure of YB56 studied by digital high-resolution electron microscopy and electron diffraction

2001 ◽  
Vol 16 (1) ◽  
pp. 101-107 ◽  
Author(s):  
Takeo Oku ◽  
Jan-Olov Bovin ◽  
Iwami Higashi ◽  
Takaho Tanaka ◽  
Yoshio Ishizawa
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
Electron Diffraction ◽  
High Resolution Electron Microscopy ◽  
Charge Coupled Device ◽  
X Ray ◽  
Resolution Electron ◽  
High Resolution Images ◽  
Diffraction Patterns ◽  
Simulated Images

Atomic positions for Y atoms were determined by using high-resolution electron microscopy and electron diffraction. A slow-scan charge-coupled device camera which had high linearity and electron sensitivity was used to record high-resolution images and electron diffraction patterns digitally. Crystallographic image processing was applied for image analysis, which provided more accurate, averaged Y atom positions. In addition, atomic disordering positions in YB56 were detected from the differential images between observed and simulated images based on x-ray data, which were B24 clusters around the Y-holes. The present work indicates that the structure analysis combined with digital high-resolution electron microscopy, electron diffraction, and differential images is useful for the evaluation of atomic positions and disordering in the boron-based crystals.

scholarly journals The crystal structures of two polyamides (‘nylons’)

1947 ◽  
Vol 189 (1016) ◽  
pp. 39-68 ◽  
Keyword(s):  
Crystal Structures ◽  
Unit Cell ◽  
Chain Molecule ◽  
X Ray Diffraction ◽  
X Ray ◽  
Cell Dimensions ◽  
C Fibre ◽  
Diffraction Patterns ◽  
Unit Cell Dimensions ◽  
Crystalline Forms

Detailed interpretations of the X -ray diffraction patterns of fibres and sheets of 66 and 6.10 polyamides (polyhexam ethylene adipamide and sebacamide respectively) are proposed. The crystal structures of the two substances are completely analogous. Fibres of these two polyam ides usually contain two different crystalline forms, α and β, which are different packings of geometrically similar molecules; most fibres consist chiefly of the α form. In the case of the 66 polymer, fibres have been obtained in which there is no detectable proportion of the β form. Unit cell dimensions and the indices of reflexions for the α form were determined by trial, using normal fibre photographs, and were checked by using doubly oriented sheets set at different angles to the X -ray beam. The unit cell of the a form is triclinic, with a — 4·9 A, b = 5·4 A, c (fibre axis) = 17·2A, α = 48 1/2º, β = 77º, γ = 63 1/2º for the 66 polymer; a = 4·95A, b = 5·4A, c (fibre axes) = 22·4A, α = 49º, β = 76 1/2º, γ = 63 1/2º for the 6.10 polymer. One chain molecule passes through the cell in both cases. Atomic coordinates in occrystals were determined by interpretation of the relative intensities of the reflexions. The chains are planar or very nearly so; the oxygen atoms appear to lie a little off the plane of the chain. The molecules are linked by hydrogen bonds between C = 0 and NH groups, to form sheets. A simple packing of these sheets of molecules gives the α arrangement.

scholarly journals Helicobacter pylori Csd4 is a peptidoglycan metallocarboxypeptidase

2014 ◽  
Vol 70 (a1) ◽  
pp. C442-C442
Author(s):  
Anson Chan ◽  
Yanjie Liu ◽  
Kris Blair ◽  
Emilisa Frirdich ◽  
Erin Gaynor ◽  
...  
Keyword(s):  
Helicobacter Pylori ◽  
Cell Shape ◽  
Diaminopimelic Acid ◽  
Specific Substrate ◽  
Substrate Molecule ◽  
X Ray ◽  
X Ray Crystallography ◽  
Cell Dimensions ◽  
Peptidoglycan Structure ◽  
Unit Cell Dimensions

The bacterial cell wall is a polymeric structure that determines the overall shape of the cell and undergoes constant remodelling during cell growth, requiring enzymes that cleave the existing peptidoglycan structure. Csd4 is an enzyme important for cell shape as deleting it in Helicobacter pylori causes the helical-shaped cells to become rod-like. Csd4 is a zinc carboxypeptidase that can cleave the tripeptide moiety found in peptidoglycan (i.e. L-Ala-γ-D-Glu-m-DAP) to release meso-diaminopimelic acid (mDAP). Structures of Csd4 were solved by X-ray crystallography up to 1.75 Å resolution in space group P212121 with zinc and substrate/product bound and contain the same unit cell dimensions. Csd4 is a monomeric enzyme with three domains: an N-terminal M14-family carboxypeptidase domain followed by two smaller domains likely important in protein-protein or protein-peptidoglycan interactions. Key interactions are observed between the protein and substrate in the active site, supporting specific substrate recognition by Csd4. A water or hydroxide molecule, which is required for catalytic activity, is also observed bound to the zinc and is poised to interact with the substrate molecule upon activation.

Electron Microscopy of Alcohol Oxidase Crystals from Pichia Pastoris

1990 ◽  
Vol 48 (1) ◽  
pp. 108-109
Author(s):  
Janet Vonck ◽  
Ernst F.J. van Bruggen
Keyword(s):  
Pichia Pastoris ◽  
Hansenula Polymorpha ◽  
Alcohol Oxidase ◽  
Unit Cell ◽  
Electron Microscopic ◽  
X Ray ◽  
X Ray Crystallography ◽  
Cell Dimensions ◽  
Microscopic Studies ◽  
Unit Cell Dimensions

Several yeast species are able to grow on methanol. When they are grown in a methanol-restricted culture, their peroxisomes contain large crystalline inclusions, consisting of alcohol oxidase (AOX). A monomer of AOX has a molecular weight of ca. 74,000. Inside the peroxisome, AOX occurs as octamers.Electron microscopic studies of AOX from Hansenula polymorpha have revealed that the eight subunits are slightly elongated and form two layers of four, which are twisted relative to each other. The molecule measures ca. 12 nm in all directions.Recently, crystals suitable for x-ray diffraction have been formed of AOX from Pichia pastoris . The space group is P21, with unit cell dimensions a=157.3Å, b=171.45Å, c=231.6Å, β=94°. These dimensions indicate that the unit cell contains four octamers, too much to solve by x-ray crystallography alone. Therefore, we have started an EM study of the crystals, to get information about the organization of the molecules in the crystal lattice.

Structure and Conformation of Photosynthetic Pigments and Related Compounds, 8 [1]Molecular Structure of an Iron(III) Chlorophyll Derivative-Chloro(phytochlorinato methyl ester)iron(III)

1995 ◽  
Vol 50 (1) ◽  
pp. 139-146 ◽  
Author(s):  
Mathias O. Senge ◽  
Karin Ruhlandt-Senge ◽  
Kevin M. Smith
Keyword(s):  
Molecular Structure ◽  
Crystal And Molecular Structure ◽  
Axial Ligand ◽  
Monoclinic Space Group ◽  
X Ray ◽  
X Ray Crystallography ◽  
Chlorophyll Derivative ◽  
Cell Dimensions ◽  
Unit Cell Dimensions ◽  
Related Compounds

The crystal and molecular structure of chloro(methyl phytochlorinato)iron(III), 4, have been determined by single crystal X-ray crystallography to obtain further information on the conformation of metallochlorins related to chlorophyll. The compound crystallized with two independent molecules mainly distinguished by the orientation of the axial ligand. The macrocycles show significant deviations from planarity larger than those observed in corresponding magnesium(II) complexes. The overall type of distortion is similar to those found in chlorophyllides. Compound 4 crystallized in the monoclinic space group P21 (MoKa,λ = 0.71063 A) with unit cell dimensions a = 12.035(6) Å, b = 13.396(8) Å, c = 19.04(2), b = 97.51(2) Å, Z = 4, V = 3043(4) Å3. The structure was refined to an R-value of 0.075 on the basis of 3974 reflections with I > 3.0σ(Ι) (130 Κ).

X-ray powder diffraction pattern for lactitol and lactitol monohydrate

1994 ◽  
Vol 9 (3) ◽  
pp. 213-216 ◽  
Author(s):  
J. Valkonen ◽  
P. Perkkalainen ◽  
I. Pitkänen ◽  
H. Rautiainen
Keyword(s):  
Powder Diffraction ◽  
Least Squares Method ◽  
Unit Cell ◽  
Unit Cell Parameters ◽  
Space Group ◽  
X Ray ◽  
Cell Parameters ◽  
Cell Dimensions ◽  
Diffraction Patterns ◽  
Unit Cell Dimensions

Diffraction patterns were recorded, and unit cell dimensions refined by the least-squares method, for lactitol and lactitol monohydrate. Refined unit cell parameters for lactitol are: a =7.622(1) Å, b = 10.764(2) Å, c = 9.375(1) Å, β= 108.25(1)° in space group P21, and those for lactitol monohydrate a =7.844(1) Å, b = 12.673(2) Å, c = 15.942(2) Å in space group P212121.

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