scholarly journals STUDIES ON THE CORNEA. II. THE FINE STRUCTURE OF DESCEMET'S MEMBRANE

1956 ◽  
Vol 2 (4) ◽  
pp. 243-252 ◽  
Author(s):  
Marie A. Jakus
Keyword(s):  
Fine Structure ◽  
Chick Embryo ◽  
Average Distance ◽  
Membrane Surface ◽  
Two Dimensional ◽  
X Ray Diffraction ◽  
X Ray ◽  
Dimensional Array ◽  
Descemet's Membrane ◽  
Descemet’S Membrane

Descemet's membrane, previously thought to be "structureless," has been found to be characterized by a fine structure of great regularity. Sections perpendicular to the plane of the membrane surface appeared to be cross-striated, with narrow dark bands separated by wide light bands traversed by fine filaments. Tangential sections showed a two-dimensional array of dark nodes and thin internodal filaments which connected each node with the six others around it to form a hexagonal figure. The average distance between nodes, and between the dark bands in transverse sections, was about 1070 A; the width of the nodes was about 270 A; and the width of the connecting filaments was less than 100 A. This pattern has been found in all species of Descemet's membrane so far examined, although it appeared to be better developed in some forms than in others. So far as is known, it has not been observed in any other type of tissue. The differentiation of Descemet's membrane has been followed in the chick embryo. It appeared late and developed slowly but showed the characteristic fine structure from the time it could be clearly identified. The evidence for placing Descemet's membrane in the collagen class of proteins is strongly supplemented by the results obtained from x-ray diffraction examination by Rougvie and Bear.

CRAFS: a model to analyze two-dimensional X-ray diffraction patterns of plant cellulose

2013 ◽  
Vol 46 (4) ◽  
pp. 1196-1210 ◽  
Author(s):  
Rafael P. Oliveira ◽  
Carlos Driemeier
Keyword(s):  
Fine Structure ◽  
Higher Plants ◽  
Rietveld Method ◽  
Renewable Resource ◽  
Two Dimensional ◽  
X Ray Diffraction ◽  
X Ray ◽  
Peak Broadening ◽  
Cellulose Iβ ◽  
Diffraction Patterns

Cellulose from higher plants is a vast renewable resource organized as crystals. Analysis of these crystals by X-ray diffraction poses very specific challenges, including ubiquitous crystallite texture and substantial overlapping of diffraction peaks. In this article, a tailor-made model named Cellulose Rietveld Analysis for Fine Structure (CRAFS) is developed to analyze two-dimensional X-ray diffraction patterns from raw and processed plant cellulose. One-dimensional powder diffractograms are analyzable as a particular case. The CRAFS model considers cellulose Iβ crystal structure, fibrillar crystal shape, paracrystalline peak broadening, pseudo-Voigt peak profiles, harmonic crystallite orientation distribution function and diffraction in fiber geometry. Formulated on the basis of the Rietveld method, CRAFS is presently written in the MATLAB computing language. A set of meaningful coefficients are output from each analyzed pattern. To exemplify model applicability, representative samples are analyzed, bringing some general insights and evidencing the model's potential for systematic parameterization of the fine structure of raw and processed plant celluloses.

scholarly journals In vitro crystallization of ribosomes from chick embryos.

1982 ◽  
Vol 95 (2) ◽  
pp. 648-653 ◽  
Author(s):  
R A Milligan ◽  
P N Unwin
Keyword(s):  
Chick Embryo ◽  
Ribosomal Subunit ◽  
Chick Embryos ◽  
Two Dimensional ◽  
Large Ribosomal Subunit ◽  
X Ray Diffraction ◽  
X Ray ◽  
Full Complement ◽  
Polymorphic Forms

A new two-dimensional ribosome crystal, having the tetragonal space group P42(1)2 (a = 593 A), has been grown from ribosome tetramers extracted from hypothermic chick embryos. It is of particular interest because of its larger size (up to 3 x 3 micron2) and greater stability compared to other related polymorphic forms, and because it can easily be grown in large amounts. X-ray diffraction shows the order in the crystal to extend to a resolution of at least 60 A. The crystalline ribosomes appear to contain a full complement of small and large ribosomal subunit proteins and an additional four proteins not characteristic of chick embryo polysomes.

scholarly journals Crystal structure of the [(THF)Cs(μ-η5:η5-Cp′)3Yb] n oligomer

2020 ◽  
Vol 76 (7) ◽  
pp. 1131-1135
Author(s):  
Daniel N. Huh ◽  
Joseph W. Ziller ◽  
William J. Evans
Keyword(s):  
Crystal Structure ◽  
Electron Configuration ◽  
Two Dimensional ◽  
X Ray Diffraction ◽  
Coordination Environment ◽  
X Ray ◽  
Dimensional Array

The green compound poly[(tetrahydrofuran)tris[μ-η5:η5-1-(trimethylsilyl)cyclopentadienyl]caesium(I)ytterbium(II)], [CsYb(C8H13Si)3(C4H8O)] n or [(THF)Cs(μ-η5:η5-Cp′)3YbII] n was synthesized by reduction of a red THF solution of (C5H4SiMe3)3YbIII with excess Cs metal and identified by X-ray diffraction. The compound crystallizes as a two-dimensional array of hexagons with alternating CsI and YbII ions at the vertices and cyclopentadienyl groups bridging each edge. This, based off the six-electron cyclopentadienyl rings occupying three coordination positions, gives a formally nine-coordinate tris(cyclopentadienyl) coordination environment to Yb and the Cs is ten-coordinate due to the three cyclopentadienyl rings and a coordinated molecule of THF. The complex comprises layers of Cs3Yb3 hexagons with THF ligands and Me3Si groups in between the layers. The Yb—C metrical parameters are consistent with a 4f 14 YbII electron configuration.

Tubulin structure at intermediate resolution

1995 ◽  
Vol 53 ◽  
pp. 852-853
Author(s):  
K. H. Downing ◽  
S. G. Wolf ◽  
E. Nogales
Keyword(s):  
High Resolution ◽  
Structural Data ◽  
Therapeutic Drug ◽  
Zinc Ions ◽  
Two Dimensional ◽  
X Ray Diffraction ◽  
X Ray ◽  
Negative Stain ◽  
Functional Mechanisms ◽  
Tubulin Structure

Microtubules are involved in a host of critical cell activities, many of which involve transport of organelles through the cell. Different sets of microtubules appear to form during the cell cycle for different functions. Knowledge of the structure of tubulin will be necessary in order to understand the various functional mechanisms of microtubule assemble, disassembly, and interaction with other molecules, but tubulin has so far resisted crystallization for x-ray diffraction studies. Fortuitously, in the presence of zinc ions, tubulin also forms two-dimensional, crystalline sheets that are ideally suited for study by electron microscopy. We have refined procedures for forming the sheets and preparing them for EM, and have been able to obtain high-resolution structural data that sheds light on the formation and stabilization of microtubules, and even the interaction with a therapeutic drug.Tubulin sheets had been extensively studied in negative stain, demonstrating that the same protofilament structure was formed in the sheets and microtubules. For high resolution studies, we have found that the sheets embedded in either glucose or tannin diffract to around 3 Å.

Synthesis and Structure of a Clathrated Two-Dimensional Metal-Organic Framework: [Cd(4,4'-bpy)2(H2O)2](ClO4)2·(L)2·H2O (L = Bis(1-pyrazinylethylidene)hydrazine)

2008 ◽  
Vol 73 (1) ◽  
pp. 24-31
Author(s):  
Dayu Wu ◽  
Genhua Wu ◽  
Wei Huang ◽  
Zhuqing Wang
Keyword(s):  
Metal Organic Framework ◽  
Channel Structure ◽  
Two Dimensional ◽  
X Ray Diffraction ◽  
Guest Molecules ◽  
X Ray ◽  
Square Planar ◽  
Metal Organic ◽  
Aqueous Meoh ◽  
Organic Framework

The compound [Cd(4,4'-bpy)2(H2O)2](ClO4)2·(L)2 was obtained by the reaction of Cd(ClO4)2, bis(1-pyrazinylethylidene)hydrazine (L) and 4,4'-bipyridine in aqueous MeOH. Single-crystal X-ray diffraction has revealed its two-dimensional metal-organic framework. The 2-D layers superpose on each other, giving a channel structure. The square planar grids consist of two pairs of shared edges with Cd(II) ion and a 4,4'-bipyridine molecule each vertex and side, respectively. The square cavity has a dimension of 11.817 × 11.781 Å. Two guest molecules of bis(1-pyrazinylethylidene)hydrazine are clathrated in every hydrophobic host cavity, being further stabilized by π-π stacking and hydrogen bonding. The results suggest that the hydrazine molecules present in the network serve as structure-directing templates in the formation of crystal structures.

scholarly journals Diethylstilbestrol Modifies the Structure of Model Membranes and Is Localized Close to the First Carbons of the Fatty Acyl Chains

Biomolecules ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 220
Author(s):  
Alessio Ausili ◽  
Inés Rodríguez-González ◽  
Alejandro Torrecillas ◽  
José A. Teruel ◽  
Juan C. Gómez-Fernández
Keyword(s):  
Membrane Surface ◽  
Water Layer ◽  
Fatty Acyl ◽  
31P Nmr Spectroscopy ◽  
Relaxation Rates ◽  
X Ray Diffraction ◽  
Scanning Calorimetry ◽  
X Ray ◽  
Acyl Chains ◽  
Dynamics Simulations

The synthetic estrogen diethylstilbestrol (DES) is used to treat metastatic carcinomas and prostate cancer. We studied its interaction with membranes and its localization to understand its mechanism of action and side-effects. We used differential scanning calorimetry (DSC) showing that DES fluidized the membrane and has poor solubility in DMPC (1,2-dimyristoyl-sn-glycero-3-phosphocholine) in the fluid state. Using small-angle X-ray diffraction (SAXD), it was observed that DES increased the thickness of the water layer between phospholipid membranes, indicating effects on the membrane surface. DSC, X-ray diffraction, and 31P-NMR spectroscopy were used to study the effect of DES on the Lα-to-HII phase transition, and it was observed that negative curvature of the membrane is promoted by DES, and this effect may be significant to understand its action on membrane enzymes. Using the 1H-NOESY-NMR-MAS technique, cross-relaxation rates for different protons of DES with POPC (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine) protons were calculated, suggesting that the most likely location of DES in the membrane is with the main axis parallel to the surface and close to the first carbons of the fatty acyl chains of POPC. Molecular dynamics simulations were in close agreements with the experimental results regarding the location of DES in phospholipids bilayers.

One Step Synthesis and Characterization of Zirconia-Graphene Composites

2012 ◽  
Vol 600 ◽  
pp. 174-177 ◽  
Author(s):  
Jian Fei Xia ◽  
Zong Hua Wang ◽  
Yan Zhi Xia ◽  
Fei Fei Zhang ◽  
Fu Qiang Zhu ◽  
...  
Keyword(s):  
Synthesis And Characterization ◽  
Two Dimensional ◽  
X Ray Diffraction ◽  
X Ray ◽  
Graphene Composite ◽  
Transmission Electron ◽  
One Step ◽  
Ft Ir ◽  
Xrd Techniques

Zirconia-graphene composite (ZrO2-G) has been successfully synthesized via decomposition of ZrOCl2•6H2O in a water-isopropanol system with dispersed graphene oxide (GO) utilizing Na2S as a precursor could enable the occurrence of the deposition of Zr4+ and the deoxygenation of GO at the same time. Transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD) techniques were used to characterize the samples. It was found that graphene were fully coated with ZrO2, and the ZrO2 existing in tetragonal phase, which resulted in the formation of two-dimensional composite.

Two-dimensional lanthanide(III) coordination polymers: solvothermal synthesis, crystal structure, and stability

2020 ◽  
Vol 0 (0) ◽  
Author(s):  
Runmei Ding ◽  
Zixin He ◽  
Meilin Wang ◽  
Danian Tian ◽  
Peipei Cen
Keyword(s):  
Crystal Structure ◽  
Coordination Polymers ◽  
Solvothermal Synthesis ◽  
Analysis Data ◽  
Water Stability ◽  
Two Dimensional ◽  
X Ray Diffraction ◽  
Triclinic Space Group ◽  
X Ray ◽  
Solvothermal Conditions

AbstractBased on 2-(4-pyridyl)-terephthalate (H2pta) and oxalate ligands, two new lanthanide-containing coordination polymers (CPs), [Tb(pta)(C2O4)0.5(H2O)2)]·2H2O (1) and [Sm(pta)(C2O4)0.5(H2O)2)]·2H2O (2), have been synthesized under solvothermal conditions. The structures of both 1 and 2 have been determined by single-crystal X-ray diffraction. Infrared, elemental analysis, powder X-ray diffraction and thermogravimetric analysis data are also presented. The crystals of 1 and 2 exhibit isostructural layer-like networks, crystallizing in the triclinic space group P$‾{1}$. The layers are further stabilized and associated into 3D architectures through hydrogen bonding. Remarkably, the CPs 1 and 2 exhibit excellent water stability and remarkable thermostability with thermal decomposition temperatures of more than 420 °C.

scholarly journals c-Perpendicular Orientation of Poly(ʟ-lactide) Films

Polymers ◽  
2021 ◽  
Vol 13 (10) ◽  
pp. 1572
Author(s):  
Baku Nagendra ◽  
Paola Rizzo ◽  
Christophe Daniel ◽  
Lucia Baldino ◽  
Gaetano Guerra
Keyword(s):  
Low Temperature ◽  
Film Plane ◽  
Wide Angle ◽  
Two Dimensional ◽  
X Ray Diffraction ◽  
Amorphous Films ◽  
High Transparency ◽  
X Ray ◽  
Crystalline Forms ◽  
Induced Crystallization

Poly(ʟ-lactide) (PLLA) films, even of high thickness, exhibiting co-crystalline and crystalline α phases with their chain axes preferentially perpendicular to the film plane (c⊥ orientation) have been obtained. This c⊥ orientation, unprecedented for PLLA films, can be achieved by the crystallization of amorphous films as induced by low-temperature sorption of molecules being suitable as guests of PLLA co-crystalline forms, such as N,N-dimethylformamide, cyclopentanone or 1,3-dioxolane. This kind of orientation is shown and quantified by two-dimensional wide-angle X-ray diffraction (2D-WAXD) patterns, as taken with the X-ray beam parallel to the film plane (EDGE patterns), which present all the hk0 arcs centered on the meridian. PLLA α-form films, as obtained by low-temperature guest-induced crystallization, also exhibit high transparency, being not far from those of the starting amorphous films.

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