The structure of bacterial flagella: the packing of the polypeptide chains within a flagellum

1961 ◽  
Vol 260 (1303) ◽  
pp. 558-573 ◽  
Keyword(s):  
Point Of View ◽  
X Ray Diffraction ◽  
Detailed Structure ◽  
Satisfactory Explanation ◽  
X Ray ◽  
Bacterial Flagella ◽  
Diffraction Patterns ◽  
Polypeptide Chains ◽  
Ray Patterns ◽  
Single Flagellum

The X-ray diffraction patterns from specimens of bacterial flagella taken by Astbury, Weibull and others consist essentially of three sets of reflexions, two sets on the meridian and one set on the equator. The equatorial set gives information on the packing arrange-merit of the polypeptide chains within a single flagellum. This paper is concerned with the interpretation in terms of a physical model of the equatorial diffraction from flagella from Proteus vulgaris for which the published diffraction data are most detailed. The polypeptide chains are all assumed to be in the α -helical form though the meridional diffraction gives some indication that a smaller ‘cross- β ’ component may also be present. The separation (121 Å) between the flagella in the X-ray specimens is inferred from the spacings of the equatorial reflexions and two alternative models (model I and model II) for the detailed structure of a flagellum are inferred from the intensity data. The structures proposed are similar in outline but differ in detail and postulate that a flagellum is composed of a number of identical interwoven filaments which themselves comprise a limited number of α -helices in a centred hexagonal or pseudo-hexagonal array. In model I the flagella are assumed to be in contact in the X-ray specimens and the structure comprises three filaments of diameter 56 Å each containing 19 single α -helices. In model II the flagella are not in contact and each of the seven filaments of diameter 33 Å contains seven α -helices; the diameter of the flagellum on this model is about 100 Å. The equatorial X-ray patterns from the two models are calculated in detail including effects due to the packing of the flagella within an X-ray specimen, for comparison with the observed diffraction. Both calculated patterns give a satisfactory explanation of the spacings of the observed reflexions and show reasonable agreement with the experimental intensities. The relative merits of the two models are discussed from the diffraction point of view and in conjunction with available data from electron microscopy. The diffraction pattern from model II is in better agreement with the experimental results than the pattern from model I but the latter agreement may be improved if the hexagonal packing of the α -helices within a filament is slightly modified; a cylindrical lattice is considered from this point of view. It is concluded that, at the present time, there is insufficient evidence to differentiate between the two models of a flagellum presented.

scholarly journals Anomalous reflexions in X-ray patterns

1941 ◽  
Vol 179 (976) ◽  
pp. 1-7 ◽  
Keyword(s):  
Simple Theory ◽  
Monochromatic Radiation ◽  
X Ray Diffraction ◽  
Satisfactory Explanation ◽  
Characteristic Radiation ◽  
X Ray ◽  
Diffraction Patterns ◽  
Ray Patterns

The presence on X-ray diffraction patterns of anomalous reflexions, that is to say, reflexions which cannot be accounted for by the simple theory of diffraction, is almost a commonplace. Many of these effects are no doubt to be ascribed to imperfections in the specimen, strains, etc., but even after these have been taken into account there remain streaks and spots for which there is no satisfactory explanation. The observation of effects of the type considered here is by no means novel; Friedrich (1913) recorded them as radial streaks running through the Laue spots in a photograph of KCl. The extra spots are generally very weak compared with the normal Laue reflexions and indeed may not be observed at all unless the photographs are somewhat over-exposed. They are most easily observed on Laue photographs taken with a tube emitting a characteristic radiation such as the K radiation of Cu or Ag, and their study will be greatly facilitated by the use of powerful sources of monochromatic radiation.

Infrared spectroscopic study of the YPO4-YCrO4 system

1985 ◽  
Vol 50 (10) ◽  
pp. 2139-2145
Author(s):  
Alexander Muck ◽  
Eva Šantavá ◽  
Bohumil Hájek
Keyword(s):  
Spectroscopic Study ◽  
Infrared Spectra ◽  
Point Of View ◽  
Mixed Crystals ◽  
Crystal Symmetry ◽  
Infrared Spectroscopic Study ◽  
X Ray Diffraction ◽  
X Ray ◽  
Infrared Spectroscopic ◽  
Diffraction Patterns

The infrared spectra and powder X-ray diffraction patterns of polycrystalline YPO4-YCrO4 samples are studied from the point of view of their crystal symmetry. Mixed crystals of the D4h19 symmetry are formed over the region of 0-30 mol.% YPO4 in YCrO4. The Td → D2d → D2 or C2v(GS eff) correlation is appropriate for both PO43- and CrO43- anions.

Algorithms for the calculation of X-ray diffraction patterns from finite element data

2010 ◽  
Vol 43 (6) ◽  
pp. 1287-1299 ◽  
Author(s):  
E. Wintersberger ◽  
D. Kriegner ◽  
N. Hrauda ◽  
J. Stangl ◽  
G. Bauer
Keyword(s):  
Finite Element ◽  
Three Dimensional ◽  
Point Of View ◽  
X Ray Diffraction ◽  
Displacement Fields ◽  
X Ray ◽  
Si Substrates ◽  
Diffraction Patterns ◽  
Simulation Point ◽  
Ccd Detectors

A set of algorithms is presented for the calculation of X-ray diffraction patterns from strained nanostructures. Their development was triggered by novel developments in the recording of scattered intensity distributions as well as in simulation practice. The increasing use of two-dimensional CCD detectors in X-ray diffraction experiments, with which three-dimensional reciprocal-space maps can be recorded in a reasonably short time, requires efficient simulation programs to compute one-, two- and three-dimensional intensity distributions. From the simulation point of view, the finite element method (FEM) has become the standard tool for calculation of the strain and displacement fields in nanostructures. Therefore, X-ray diffraction simulation programs must be able to handle FEM data properly. The algorithms presented here make use of the deformation fields calculated on a mesh, which are directly imported into the calculation of diffraction patterns. To demonstrate the application of the developed algorithms, they were applied to several examples such as diffraction data from a dislocated quantum dot, from a periodic array of dislocations in a PbSe epilayer grown on a PbTe pseudosubstrate, and from ripple structures at the surface of SiGe layers deposited on miscut Si substrates.

The Effect of Al on Phase Stability and Oxidation Behavior in Ternary Nb-Ti-Si Alloys

2014 ◽  
Vol 556-562 ◽  
pp. 310-313
Author(s):  
Yong Jun Jiang
Keyword(s):  
Room Temperature ◽  
Oxidation Behavior ◽  
Point Of View ◽  
Transition Elements ◽  
X Ray Diffraction ◽  
X Ray ◽  
Room Temperature Ductility ◽  
Oxidation Properties ◽  
Diffraction Patterns ◽  
And Control

In this paper, we report a significant improvement in mechanical and oxidation properties of near eutectic Nb–Si alloys by the addition of aluminum (Al) and control of microstructural length scale. Thus in order to develop new alloys, we have to choose proper alloying elements keeping all the above issues in mind. Among the non-transition elements such as Al, Ga, Ge, Sn, and Al is most attractive from the point of view of enhancing the oxidation resistance and room temperature ductility due to substitution of Si with metallic Al . Al forms oxides which are even more thermodynamically stable than Si and Nb based oxides. Al is also soluble in Nb to a greater degree in conjunction with other refractory elementsFig.1 The figure shows composite X-ray diffraction patterns of each sample exposed to air for one hour in a TGA furnace at above mention temperatures.

Thermal decomposition of magnesium sesquicarbide

1983 ◽  
Vol 48 (7) ◽  
pp. 1963-1968 ◽  
Author(s):  
Bohumil Hájek ◽  
Pavel Karen ◽  
Vlastimil Brožek
Keyword(s):  
Thermal Decomposition ◽  
Kinetic Data ◽  
Arrhenius Equation ◽  
Kinetic Equations ◽  
Decomposition Reaction ◽  
Point Of View ◽  
X Ray Diffraction ◽  
X Ray ◽  
Diffraction Patterns ◽  
Thermal Stability Of

The structure of Mg2C3 and the course of its decomposition were studied. The powder X-ray diffraction patterns were analyzed to obtain the lattice parameters for hexagonal Mg2C3, a = 743.4 ± 0.5 pm, c = 1 056.4 ± 1.6 pm. Thermal decomposition data were obtained for temperatures 670-740 °C and pressure 130 Pa; they could be fitted satisfactorily by kinetic equations for various processes, including the 1 st order decomposition reaction, and so the controlling phenomenon of the reaction cannot be deduced based on the kinetic data. The 1 st order rate constants and reaction halflives were evaluated for various temperatures and approximated by the Arrhenius equation to calculate the parameters AA = 1.97 . 1014 s-1, EA = 333 kJ mol-1. The conditions of synthesis of Mg2C3 are discussed from the point of view of the choice of a suitable hydrocarbon for the reaction with magnesium. The thermal stability of the sesquicarbide increases with increasing pressure; it could be formed from dicarbide and sustained even at a temperature of 1 450 °C by applying a pressure as high as 6 GPa.

Structure and X-ray reference diffraction patterns of (Ba6−xSrx)R2Co4O15 (x = 1, 2) (R = lanthanides)

2013 ◽  
Vol 28 (3) ◽  
pp. 212-221 ◽  
Author(s):  
W. Wong-Ng ◽  
G. Liu ◽  
Y.G. Yan ◽  
J.A. Kaduk
Keyword(s):  
General Structure ◽  
Unit Cell ◽  
X Ray Diffraction ◽  
Unit Cell Parameters ◽  
Powder Diffraction File ◽  
Coordination Environment ◽  
X Ray ◽  
Cell Parameters ◽  
Diffraction Patterns ◽  
Ray Patterns

The structure and X-ray patterns of two series of barium lanthanide cobaltates, namely, Ba4Sr2R2Co4O15 (R = La, Nd, Sm, Eu, Gd, and Dy), and Ba5SrR2Co4O15 (R = La, Nd, Sm, Eu, and Gd) have been determined. These compounds crystallize in the space group P63mc; the unit-cell parameters of Ba4Sr2R2Co4O15 (R from La to Dy) decrease from a = 11.6128(2) Å to 11. 5266(9) Å, c = 6.869 03(11) to 6. 7630(5) Å, and V = 802.23(3) Å3 to 778.17(15) Å3, respectively. In the Ba5SrR2Co4O15 series (R = La to Gd), the unit-cell parameters decrease from a = 11.735 44(14) Å to 11.619 79(12) Å, c = 6.942 89 (14) Å to 6.836 52(8) Å, and V = 828.08(3) Å3 to 799.40(2) Å3. In the general structure of (Ba6−xSrx)R2Co4O15, there are four Co ions per formula unit occupying one CoO6 octahedral and three CoO4 tetrahedral units. Through corner-sharing of these polyhedra, a larger Co4O15 unit is formed. Sr2+ ions adopt both octahedral and 8-fold coordination environment. R3+ ions adopt 8-fold coordination (mixed site with Sr), while the larger Ba2+ ions assume both 10- and 11-fold coordination environments. The samples were found to be insulators. X-ray diffraction patterns of these samples have been determined and submitted to the Powder Diffraction File (PDF).

scholarly journals EFFECT OF VARIOUS PRETREATMENTS ON X-RAY DIFFRACTION PATTERNS OF CLAY FRACTIONS OF PODZOLIC B HORIZONS

1981 ◽  
Vol 61 (2) ◽  
pp. 311-316 ◽  
Author(s):  
C. WANG ◽  
H. KODAMA ◽  
N. M. MILES
Keyword(s):  
Amorphous Material ◽  
Clay Sample ◽  
X Ray Diffraction ◽  
X Ray ◽  
Freeze Dried ◽  
Amorphous Si ◽  
Chemical Pretreatments ◽  
Diffraction Patterns ◽  
Ray Patterns ◽  
Identification And Quantification

The objective of this study was to compare the effects of various pretreatments on the X-ray identification and quantification of clay-sized minerals from some podzolic B horizons. After soil samples were treated with H2O2 to remove organic matter, clay fractions were dispersed, separated, and freeze-dried. A portion of each clay sample was subjected to the following pretreatments: ultrasonic bath, extraction by citrate-dithionite, extraction by 0.5 N NaOH, and extraction by Tiron. Oriented slides were used for identification and quantification of clay minerals after each pretreatment. The X-ray patterns for ultrasonically dispersed samples were used as a basis for evaluating the effectiveness of the three chemical pretreatments. Tiron pretreatment was found to be the most suitable method for removal of amorphous material from clay separates of podzolic B horizons. The traditional citrate-dithionite method was not effective in removing amorphous Si from clays. The 0.5 N NaOH method is not recommended because it resulted in significant destruction of phyllosilicates and it was not effective in removing amorphous Fe.

scholarly journals The dissociation of chicken erythrocyte deoxyribonucleoprotein and some properties of its partial nucleoproteins

1970 ◽  
Vol 120 (4) ◽  
pp. 859-871 ◽  
Author(s):  
K. Murray ◽  
E. M. Bradbury ◽  
C. Crane-Robinson ◽  
R. M. Stephens ◽  
A. J. Haydon ◽  
...  
Keyword(s):  
Sodium Chloride ◽  
Double Helix ◽  
Sedimentation Coefficient ◽  
X Ray Diffraction ◽  
Histone Fraction ◽  
X Ray ◽  
Coil Structure ◽  
Diffraction Patterns ◽  
Fraction I ◽  
Polypeptide Chains

Histones were completely dissociated from their native complex with DNA in 2.0m-sodium chloride. Histone fractions IIb, V and I were dissociated in 1.2m-sodium chloride, fractions V and I in 0.7m-sodium chloride and fraction I in 0.45m-sodium chloride. Repeated extraction of partial dRNP (deoxyribonucleoprotein) preparations with sodium chloride of the same concentration as that from which they were prepared resulted in release of histones that previously had remained associated with the DNA of the complex. Gradual removal of histones from dRNP was paralleled by an improvement in solubility, a decrease in wavelength of the u.v.-absorption minimum, and a fall in sedimentation coefficient of the remaining partial dRNP. X-ray diffraction patterns of partial dRNP preparations showed that removal of histone fractions I and V from dRNP did not destroy the super-coil structure of the dRNP, but further removal of histones did. Infrared spectra of partial dRNP preparations showed that in native dRNP histone fraction I was present in the form of extended, isolated polypeptide chains, and that the other histone fractions probably contain a helical component that lies roughly parallel to the polynucleotide chains in the double helix and an extended polypeptide component that is more nearly parallel to the DNA helix axis. An analysis of the sedimentation of partial dRNP preparations on sucrose gradients showed that native dRNP consists of DNA molecules each complexed with histone fractions of all types.

Structural Studies of the Vulcanization of Rubber under Stretch

1940 ◽  
Vol 13 (2) ◽  
pp. 243-248
Author(s):  
E. A. Hauser ◽  
I. N. Smith
Keyword(s):  
Point Of View ◽  
Chemical Bonds ◽  
Structural Studies ◽  
X Ray Diffraction ◽  
Satisfactory Explanation ◽  
Specific Chemical ◽  
X Ray ◽  
Vulcanized Rubber ◽  
Modern Methods ◽  
Definite Proof

Abstract Just one hundred years have passed since the changes were discovered which rubber undergoes when mixed with sulfur and heated. Although “vulcanization”, as this reaction and the changes subsequent thereto have been termed, must be considered the most important development in the rubber industry, we are still far from being in a position to offer a fully satisfactory explanation for this phenomenon. Nevertheless we have been able to improve our concept of these changes by the application of such modern methods of research as x-ray diffraction, and recent attempts to shed more light on the phenomenon from a strictly chemical point of view also have been successful. The outstanding results of the latter work are the definite proof that the changes in physical properties, which become noticeable during vulcanization, show no correlation with the amount of combined sulfur or with the total loss in unsaturation. The experiments offered no direct experimental evidence as to the existence of specific chemical bonds or linkages in vulcanized rubber. However, it could be definitely ascertained that chemical reactions involving the double bonds of the hydrocarbon and its combination with the vulcanizing agent, in one way or another, are necessary to produce a vulcanized structure responsible for the observed changes in properties.

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