Conventional Monochromatic X-ray Research Articles

Large-view x-ray imaging for medical applications using the world’s only vertically polarized synchrotron radiation beam and a single asymmetric Si crystal

Objective. X-ray microangiography provides detailed information on the internal structure and function of a biological subject. Its ability to evaluate the microvasculature of small animals is useful for acquiring basic and clinical medical knowledge. The following three conditions are necessary to attain detailed knowledge of biological functions: (1) high temporal resolution with sufficient x-ray intensity, (2) high spatial resolution, and (3) a wide field of view. Because synchrotron radiation microangiography systems provide high sapatial resolution and high temporal resolution as a result of their high x-ray intensity, such systems have been developed at various synchrotron radiation facilities, starting with the photon factory, leading to numerous medical discoveries. However, the three aforementioned functions are incompatible with the use of synchrotron radiation because the x-ray intensity decreases when a wide field of view is obtained. To overcome these problems, we developed a new x-ray optical system for microangiography in rats using synchrotron radiation x-rays. Approach. Instead of using monochromatic synchrotron radiation x-rays with a conventional double-crystal monochromator, we used white synchrotron radiation x-rays and an asymmetric Si crystal to simultaneously monochromatize the beam and widen the field of view. Main results. The intensity profile and spatial resolution of the x-ray images were then evaluated. The proposed x-ray optics increased the x-ray intensity and beam width by factors of 1.3 and 2.7, respectively, compared with those of conventional monochromatic x-rays. In addition, in vivo studies on microangiography in rats were performed to confirm that the images had sufficient intensity, spatial resolution, and field of view. One of a series of images taken at 50 ms frame−1 was shown as an example. Significance. This x-ray optics provides sufficient x-ray intensity, high spatial resolution, and a wide field of view. This technique is expected providing new insights into the evaluation of the vascular system.

Circular polariscopic analysis of strains in a semi-insulating SiC wafer: Its high potential to complement the information obtained from monochromatic x-ray topography

We demonstrate that circular polariscopy is highly sensitive to strains in SiC wafers. In the monochromatic x-ray topographic analysis, which is regarded as a fundamental characterization method, the image information is disappeared in various areas: x-ray topography is not always suitable to evaluate wafer-size regions. Using circular polarizer plates, we apply the polariscopic analysis, which reveals the inhomogeneous strain distributed in the whole wafer region; namely, the circular polariscopic map has the high potential to complement the conventional monochromatic x-ray topograph. From the phonon-frequency shift observed in the Raman scattering spectra, the maximum stress is estimated to be ∼490 MPa. The crystal-plane distortion causing the strains is confirmed from the appearance of the forbidden reflections in the θ-2θ x-ray diffraction pattern.

Simple dose rate measurements for a very high synchrotron X-ray flux

Dose measurements based on methylene blue (MB) bleaching, widely used for ultraviolet light, can also be applied to X-rays including very high flux levels. This method has been tested by using both MB bleaching and Fricke dosimetry for a conventional monochromatic X-ray source and then for 'white-beam' synchrotron radiation. The results show that MB bleaching dosimetry can easily measure X-ray doses up to at least 10(5) Gy s(-1), as long as the MB concentration is sufficiently high. This condition can be verified from the deviations from linearity of the bleaching versus exposure time.

The use of Co2+for crystallization and structure determination, using a conventional monochromatic X-ray source, of flax rust avirulence protein

Metal-binding sites are ubiquitous in proteins and can be readily utilized for phasing. It is shown that a protein crystal structure can be solved using single-wavelength anomalous diffraction based on the anomalous signal of a cobalt ion measured on a conventional monochromatic X-ray source. The unique absorption edge of cobalt (1.61 A) is compatible with the Cu K alpha wavelength (1.54 A) commonly available in macromolecular crystallography laboratories. This approach was applied to the determination of the structure of Melampsora lini avirulence protein AvrL567-A, a protein with a novel fold from the fungal pathogen flax rust that induces plant disease resistance in flax plants. This approach using cobalt ions may be applicable to all cobalt-binding proteins and may be advantageous when synchrotron radiation is not readily available.

Synthesis, structure determination from powder diffraction data and thermal behaviour of titanium(IV) oxalate [Ti 2O 3(H 2O) 2](C 2O 4)·H 2O

A titanium(IV) oxalate, [Ti 2O 3(H 2O) 2](C 2O 4)·H 2O, has been synthesised in a polycrystalline form in the course of the study of precursors of PZT type oxides. Its crystal structure has been solved ab initio from powder diffraction data collected with conventional monochromatic X-rays. The symmetry is orthorhombic, space group Cmca, with cell dimensions a=15.494(2) Å, b=10.491(1) Å, c=9.700(1) Å and Z=8. The structure consists of inorganic corrugated layers of corner-sharing TiO 6 octahedra, which form infinite TiOTi connections, linked together by the oxalate anions. The titanium environment is discussed with regard to bond-valence calculations. The thermal behaviour of this compound has been studied by temperature-dependent X-ray diffraction and thermal analyses. In the course of the dehydration process, the partially dehydrated phase [Ti 2O 3(H 2O) 2](C 2O 4) has been isolated and its structure has been solved from in situ X-ray powder diffraction data. Its crystal structure determination has shown that the framework of the precursor is preserved. The complete decomposition scheme into anatase is also described.

A device for the high-pressure oxygenation of protein crystals

A system has been developed for subjecting protein crystals to hyperbaric pressures of oxygen gas in order to promote enzymatic reaction. Crystals of an oxygenase or oxidase enzyme are grown anaerobically by hanging drop vapor diffusion, under crystallization conditions modified to eliminate combustible materials such as plastic coverslips and grease. The crystalline enzyme:substrate complex can then be exposed to oxygen gas at pressures up to 60 bar using a custom-built device or “bomb.” In this way, reaction is initiated synchronously throughout the crystal and subsequent flash freezing allows the trapping of enzyme:product complexes in high occupancy. These complexes can then be structurally characterized by conventional monochromatic X-ray crystallography. The bomb is furnished from naval brass and lubricated with Fomblin RT15 perfluorinated polyether grease in order to ensure compatibility with the highly oxidizing environment.

The crystal structure of 3-methyluracil from X-ray powder diffraction data

The crystal structure of 3-methyluracil has been determined ab initio by conventional monochromatic X-ray powder diffraction data. The crystal data are: orthorombic, a=6.6294(1), b=13.1816(3), c=6.53938(9) (Å), V=571.45(3) (Å 3), space group Pbnm, Z=8. The structure was solved by direct methods and the final Rietveld refinement converged to R p=0.0398, R wp=0.0528, R Bragg=0.0294. The crystal structure exhibits endless chains of planar molecules, connected via head-to-tail N–H⋯O hydrogen bonds.

Synthesis, Structure Determination from Powder Diffraction Data, and Thermal Behavior of Lead Zirconium Oxalate Hydrate Pb2Zr(C2O4)4·nH2O (3 < n < 9)

A new mixed lead zirconium oxalate, Pb2Zr(C2O4)4·nH2O (3 < n < 9), has been prepared from precipitation of a nitric solution of lead and zirconium cations by an oxalic solution at 345 K. The crystal structure of Pb2Zr(C2O4)4·6H2O has been determined ab initio from powder diffraction data collected with conventional monochromatic X-rays. The symmetry is monoclinic, space group C2/c (No. 15), cell dimensions a = 9.537(1) Å, b = 29.622(3) Å, c = 8.9398(9) Å, β = 121.19(4)°, and Z = 4. The complex three-dimensional structure is built from 8-fold-coordinated zirconium atoms and 9-fold- and 8-fold-coordinated lead atoms linked by oxalate groups. Only one water molecule has been found free in the structure. The dehydration is reversible, and the cell parameters vary between the composition limits without a major change of the crystal structure framework. A thermodynamical study has demonstrated the zeolitic nature of the water molecules. The enthalpy, ΔrH, and entropy, ΔrS, of the dehydration reaction have been determined as a function of the number of zeolitic water molecules. The complete decomposition scheme of the anhydrous phase Pb2Zr(C2O4)4 into PbZrO3 and finally ZrO2, studied from temperature-dependent X-ray powder diffraction and thermogravimetric analysis, is carefully described.

Crystal Structure and Thermal Behavior of La(H2O)2M(C2O4)2·H2O (M=K, NH4) Studied by Powder X-Ray Diffraction

The crystal structure of La(H2O)2K(C2O4)2·H2O has been solved ab initio from powder diffraction data collected with conventional monochromatic X-rays. The symmetry is monoclinic, space group C2/m, cell dimensions a=22.033(1) Å, b=7.6003(5) Å, c=6.6418(4) Å, β=103.814(6)°, V=1080.05(8) Å3, Z=4. Since a disorder of one oxalate group is observed with all possible monoclinic space groups, it has been found convenient to describe the crystal structure in a triclinic subcell. The disorder problem is thoroughly discussed with respect to the powder diffraction data available for this material. From this description the compound exhibits a layered-type structure, which could explain reported cation-exchange properties. The layers are formed by four-membered rings [La(C2O4)]4. The potassium atom and two of the three water molecules are located between the layers. The third water molecule lies on the layer in tunnels with a diamond-shaped cross section. The lanthanum atom is tenfold-coordinated in a distorted bicapped square antiprism and the potassium atom is eightfold-coordinated in a dodecahedron. The crystal structure of La(H2O)2(NH4)(C2O4)2·H2O is isostructural with that of La(H2O)2K(C2O4)2·H2O [a=22.130(4) Å, b=7.774(1) Å, c=6.655(2) Å, β=105.28(2)°, V=1104.4(3) Å3]. The thermal decomposition of these two precursors has been carried out by means of temperature-dependent X-ray diffraction and TG-DSC. The dehydration leads to anhydrous phases, which are amorphous and poorly crystalline for the potassium and ammonium compounds, respectively. Amorphous LaK(C2O4)2 crystallizes at 260°C. Its symmetry is monoclinic with the cell dimensions a=5.687(3) Å, b=15.241(5) Å, c=9.017(4) Å, β=92.82(3)°. At higher temperature, the decomposition of LaK(C2O4)2 yields La2O2CO3 (Type-Ia), La2O2CO3 (Type-II), and pure La2O3, successively. La(NH4)(C2O4)2 leads to La2O2CO3 (Type-II) and, finally, La2O3.

Ab Initio Structure Determination of New Mixed Zirconium Hydroxide Nitrates ZrM(OH)2(NO3)3 (M=K, Rb) from X-Ray Powder Diffraction Data

Two new mixed zirconium hydroxide nitrates ZrM(OH)2(NO3)3 (M=K, Rb) have been synthesized through a wet chemical process. The two crystal structures have been solved ab initio from powder diffraction data collected with conventional monochromatic X-rays. ZrK(OH)2(NO3)3 crystallizes with a monoclinic symmetry [a=16.569(3) Å, b=5.791(1) Å, c=9.813(2) Å, β=90.17(2)°, P21/n, Z=4) and ZrRb(OH)2(NO3)3 with an orthorhombic symmetry [a=10.126(3) Å, b=16.492(3) Å, c=5.855(2) Å, Pbcn, Z=4]. The heavy atoms have been located from an interpretation of Patterson functions. The coordinates of the remaining light atoms have been determined from successive three-dimensional Fourier maps. The final Rietveld refinement indicators were RF=0.042, Rp=0.077 (M=K) and RF=0.064, Rp=0.115 (M=Rb). Like the structures of α-Zr(OH)2(NO3)2·1.65H2O and β-Zr(OH)2(NO3)2·H2O, the structures of the mixed basic zirconium nitrates are built from edge-sharing ZrO8 polyhedra to form infinite neutral zigzag chains of chemical composition [Zr(OH)4/2(NO3)2]n. The main difference with respect to the hydrated phases is the nature of the cohesion in the structures based on ionic contacts involving intercalated K+ or Rb+ and NO−3 species in the mixed compounds and on a complex hydrogen-bonding network in the hydrated phases. The crystal chemistry of the zirconium hydroxide nitrates is discussed and three structure types are identified.

Ab Initio Structure Determination and Dehydration Dynamics of YK(C2O4)2·4H2O Studied by X-ray Powder Diffraction

The crystal structure of YK(C2O4)2·4H2O has been solved ab initio from powder diffraction data collected with conventional monochromatic X-rays. The symmetry is tetragonal, space group I41/a (no. 88), cell dimensions a = 11.4612(8) A, c = 8.9040(8) A, Z = 4. The structure is built from chains of oxalate groups bridging 8-fold-coordinated yttrium atoms. The structure has an open framework exhibiting tunnels with square cross-sections, filled with zeolitic water molecules, and ellipsoidal cross-sections in which the potassium atoms are located. The hydrogen atoms have been localized, and their role on the precision of the bond lengths within the oxalate group has been demonstrated. The dehydration process is reversible and occurs with a pronounced anisotropic elastic property of the structure framework. The enthalpy, ΔrH, and entropy, ΔrS, of the dehydration reaction have been determined as a function of the number n of zeolitic water molecules. ΔrH decreases from 70.2 to 54.2 kJ mol-1 during the dehydratio...

Thermal Behavior of Zinc Phenylphosphonate and Structure Determination ofγ-Zn2P2O7from X-Ray Powder Diffraction Data

The thermal behavior of zinc phenylphosphonate has been studied by temperature-dependent X-ray powder diffraction and thermo-gravimetry in the temperature range 19–600°C. The different phases occurring during the decomposition have been identified, i.e., the anhydrous phase and the three successive polymorphic varieties of Zn2P2O7. The first one is amorphous,δ-Zn2P2O7is poorly crystalline, andγ-Zn2P2O7is a metastable phase. The last transforms into theβvariety at higher temperature. The crystal structure ofγ-Zn2P2O7has been solvedab initiofrom powder diffraction data collected with conventional monochromatic X-rays. The symmetry is orthorhombic with the cell dimensionsa=4.9504(5) Å,b=13.335(2) Å,c=16.482(3) Å, space groupPbcm,Z=8. The structure consists of infinite corrugated chains of ZnO5trigonal bipyramids, running along [001]. These chains are linked together by P2O7groups in the two other directions. The P2O4−7anions display low angles and an eclipsed conformation, contrary to theαandβphases.

Ab Initio Structure Determination from X-ray Powder Diffraction Data of Tetraaquabismuth(III) Triflate Obtained from the Nonahydrate

The thermal decomposition of nonaaquabismuth(III) triflate has been studied by thermogravimetric analysis, from which lower hydrates have been identified. The crystal structure of the tetraaquabismuth(III) triflate, Bi(H2O)4(OSO2CF3)3, has been solved ab initio from powder data collected with conventional monochromatic X-rays even though the asymmetric unit cell contains 29 atoms and 93 atomic coordinates to refine. The structure is built from discrete dimers in which the Bi atoms are 8-fold coordinated to four water molecules and four oxygen atoms belonging to three triflate groups. The structure differences with respect to that of the precursor are discussed.

Structure Determination of Uranium Halogenide Phosphates U XPO 4·2H 2O ( X=Cl, Br) from Powder Diffraction Data

The structure of the two isostructural uranium halogenide phosphates UClPO 4·2H 2O and UBrPO 4·2H 2O was determined from conventional monochromatic X-ray powder diffraction data. The crystal symmetry is tetragonal (space group I4/ m, Z=8) with lattice constants a=14.631(2) and c=6.662(1) Å for the chloride phase and a=14.7480(7) and c=6.6810(4) Å for the bromide compound. The structure solution was found from Patterson and Fourier syntheses and refinements by the Rietveld method (38 parameters, 760 reflections) converged to R F=0.03 for both examples. The configuration around uranium(IV) is derived from the typical pentagonal bipyramid formed by two water oxygen atoms, four phosphate oxygen atoms, and one halide atom. Due to steric considerations, the halide atom deviates from the pentagonal base, leading to a repulsion of the two apical oxygen atoms. The interatomic distances and angles are usual and agree with the values found from neutron diffraction in related compounds. The discrete U X 1O 6( X=Cl, Br) polyhedra are linked together by phosphate tetrahedra which are viewed as the unique bonding units in the structure. This arrangement results in a 3D network based on two kinds of tunnels along [001]. The widest tunnel contains the Xatoms, while half of the water molecules lie in the smallest tunnel.

Synthesis and structural study from X-ray powder diffraction of Pb0.5Th2(PO4)3

A new mixed lead thorium phosphate, Pb0.5Th2(PO4)3, has been isolated in the system PbO–ThO2–P2O5. Its crystal structure (monoclinic symmetry, a=17.459(1) Å, b=6.8451(4) Å, c=8.1438(5) Å, β=101.247(5)°, space group C2/c) has been determined from conventional monochromatic X-ray powder diffraction data. The structure is related to the MITh2(PO4)3 structure type. Lead atoms are located in the channels parallel to the c axis, out of the twofold axis for 0.97 Å, and are statistically distributed on a quarter of crystallographic positions. The thermal stability of this material is greater than that of the monazite-type compound PbTh(PO4)2.

Structure Determination of Two Polymorphic Phases of La(NO3)3· 4H2O from X-Ray Powder Diffraction

The structure of two polymorphic phases of lanthanum nitrate tetrahydrate, prepared from the thermal decomposition of the hexahydrate compound, have been determined from conventional monochromatic X-ray powder diffraction data. The α phase has a monoclinic unit cell with the parametersa= 6.7778(9) Å,b= 11.3673(1) Å,c= 6.5843(1) Å, β = 90.644(5)°, space groupP21/m. The β phase is orthorhombic with the unit cell parametersa= 11.834(1) Å,b= 12.973(1) Å,c= 13.531(1) Å, space groupPbca. For the α phase, atomic coordinates were found by interpretation of one Patterson and three difference Fourier maps, while for the β phase the starting model was the crystal structure of the related cerium compound. The structure models were refined by the Rietveld method. The structures consist of infinite chains along [001], built from 11-fold coordinated and 10-fold coordinated La atoms in the α and β phases, respectively, and linked by bridging nitrate groups. The cohesion of the structures is ensured by hydrogen bonds.

Structure determination of CuTh2(PO4)3

The crystal structure of CuTh 2 (PO 4 ) 3 , copper dithorium triphosphate, has been solved ab initio from conventional monochromatic X-ray powder diffraction and refined with neutron powder diffraction data. The symmetry is monoclinic, space group C2/c. The heavy-atom positions were found from a Patterson map calculated from integrated intensities extracted by whole-pattern fitting. Successive Fourier syntheses were used to locate the remaining atoms. The Th atoms and PO 4 groups exhibit an arrangement related to that found in the M I Th 2 (PT h ) 3 phases, with large sites in which the monovalent cations are located. In the title compound, these sites are elongated along a and shortened along b so that the Cu + ions, located on inversion centres, are linearly bonded to two phosphate groups with two short Cu-O distances of 1.828 A.