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Cu K (cu + k)
Selected AbstractsPreparation, structure, and optical properties of chiral sulfoxides and disulfoxide with a trithiole ringHETEROATOM CHEMISTRY, Issue 1 2003Takeshi Kimura Optically active 4,9-diethyl[1,4]-dithiino[5,6- f]benzo[1,2,3]trithiole 5-oxide (3) and 4,9-diethyl[1,4]dithiino[5,6- f]benzo[1,2,3]trithiole 5,8-dioxide (4) were obtained by the asymmetric oxidation of 6,11-diethyl[1,4]dithiino[5,6- h]benzo[1,2,3,4,5]pentathiepin (1). The reaction was accompanied by desulfurization and ring-contraction reactions of the pentathiepin ring. Similarly, optically active 4,8-diethyl[1,3]dithiolo[4,5- f]benzo[1,2,3]trithiole 5-oxide (7) was produced by the analogous asymmetric oxidation of 6,10-diethyl[1,3]dithiolo[4,5- h]benzo[1,2,3,4,5]pentathiepin (2). The specific rotations of 3, 4, and 7 were measured in chloroform, and their optical purity was verified by 1H NMR with a shift reagent [Eu(hfc)3]. The structures of 4 and 7 were determined by X-ray crystallography using Cu K, radiation, and the absolute configuration of the sulfinyl group was examined based on the Flack parameter, which revealed that 4 has an RR configuration, while 7 has an S configuration. The circular dichroism spectra of 3, 4, and 7 were measured in chloroform. © 2003 Wiley Periodicals, Inc. Heteroatom Chem 14:88,94, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10104 [source] Polarization switching in BaTiO3 thin films measured by X-ray diffraction exploiting anomalous dispersionJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 2 2004S. J. Van Reeuwijk Films of BaTiO3 ranging from 20,nm to 300,nm in thickness were grown with pulsed laser deposition on Nb:SrTiO3. The quality of the layers was investigated using atomic force microscopy, X-ray reflectivity and X-ray diffraction. Both the micrographs and the X-ray reflectivity spectra indicate a smooth surface of the layers. The X-ray diffraction profiles measured using synchrotron radiation show features characteristic for highly crystalline thin films. The application of an external electric field parallel to the c axis changes an hkl reflection of BaTiO3 to an hk reflection. Due to the anomalous dispersion, the intensities of these two reflections are not equal and the atomic displacements can be determined from the intensity differences. The electric field-induced intensity changes can be as large as a few percent, which makes data collection from a 100,nm film using Cu K, radiation from an X-ray tube feasible. The ,I/I values of a number of reflections from the 20 and 50,nm films were measured using synchrotron radiation. The observed ,I/I values were in good agreement with the intensity changes expected for polarization switching in the bulk. [source] Performance of a confocal multilayer X-ray opticJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 1 2002J. Kusz In recent years, several companies have developed the technique of arranging two multilayer mirrors in confocal optics for monochromatizing X-rays. In this study, a focusing device of Osmic Inc., with a source-to-focus distance of 1005,mm, has been used. The goal was to measure the homogeneity of the beam, the cross section at various distances from the focus and the efficiency of the optic when it is operated with vacuum and with air in the beam path. A small crystal sphere set at various distances is used to compare the intensities and the widths of reflections with those of a flat graphite monochromator. In a standard diffraction experiment (crystal size 0.25,mm), the gain factor with respect to graphite is roughly ten at a position where the beam plateau is 0.5,mm. The suppression of the Cu K, radiation and of higher harmonics of K, is very good. [source] Kinematical two-dimensional multiple-diffraction intensity profiles.JOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 6 2000Application to, radiation, scans obtained with Cu K Expressions for the calculation of multiple-diffraction patterns observed in ,,, scans of Bragg reflections are derived within the framework of the kinematical theory, taking into account the divergence and wavelength-spread of the incident beam as well as the mosaicity of the crystal sample. The theoretical results can be applied to X-ray tube radiation as well as synchrotron radiation experiments. A 189.9° experimental Cu K,,,, scan of diamond is compared with the corresponding theoretical multiple-diffraction pattern. [source] Improvement of SAXS measurements on Kratky slit systems by Göbel mirrors and imaging-plate detectorsJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 3-2 2000Alexander Bergmann Laboratory X-ray sources emit a highly divergent beam. The Kratky compact camera is constructed to maximize the intensity in the sample using a slit collimation system. The performance of this camera can be further increased if the primary beam is collimated from a divergent into a parallel beam. A recently developed device for this purpose is the so-called `Göbel mirror'. This mirror is made of parabolically bent multilayers, designed to collimate divergent X-rays from laboratory X-ray sources into a parallel and monochromatic beam of high brilliance. Modification of the block collimation system in combination with a Göbel mirror leads to a different beam geometry, resulting in an intensity increase by a factor of about 10. The gain in intensity implicates the use of imaging-plate detectors, which have a wide linear range in intensity and allow the full use of the increased intensity. Hence the quality of the SAXS data is improved by the higher intensity primary beam, the much lower background due to the exclusive use of Cu K, radiation, and a detection unit which is linear in the measured intensity regime. All these advantages, such as intensity gain, lower background, better quality of the data, are demonstrated with some selected experimental results. [source] Use of Cr K, radiation to enhance the signal from anomalous scatterers including sulfurJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 3-2 2000Witek Kwiatkowski The anomalous signals from scatterers such as sulfur (S) and arsenic (As) were compared in diffraction data sets collected from an X-ray source with three different targets, Au, Cu and Cr, on a multi-target rotating anode. HIV-1 integrase crystals served as the test case for this study. The crystalline specimen of HIV-1 integrase contains in each protein molecule two As atoms, each covalently bound to a cysteine S atom, and two additional S atoms derived from methionine. It was found that the Cr K, radiation gave the clearest peaks in anomalous difference Fourier maps, although the signal-to-noise ratios of the anomalous signal for the Cu K, and Cr K, data were similar but better than that for Au L,. This result was in spite of the fourfold higher flux from the Cu anode versus the Cr anode. For all three X-ray wavelengths, anomalous difference Fourier maps calculated with bias-removed phases derived from the known atomic model revealed clear peaks at the two As sites. However, only in the map calculated using the Cr K, data were both peaks of the expected ellipsoidal shape, enveloping the As atom and the adjacent S atom. None of the S sites was apparent in difference maps calculated using the Au L, data. The ability to enhance the S-derived anomalous signal using Cr K, radiation has particularly useful applications in the structure determination of proteins, for example in resolving ambiguities in the chain tracing of a protein with numerous disulfide bonds and in assigning amino acid identities. Additionally, anomalous difference Patterson maps calculated from the Cr K, data were sufficiently clear to identify the As-related peaks. These results form the groundwork for in-house phase determination with the multi-wavelength anomalous diffraction method. [source] Electronic states in Cu2MnX (X = Al, In and Sn) Heusler alloy studied by XMCD and multiple scattering calculationsJOURNAL OF SYNCHROTRON RADIATION, Issue 2 2001Shigeaki Uemura X-ray magnetic circular dichroism (XMCD) has been measured at Mn and Cu K-edge in Cu2MnX (X = Al, In, and Sn) Heusler alloy. The Mn K -edge spectrum shows a dispersion-type profile and the Cu K -edge resembles the Mn spectrum, which suggests that polarization of the p unoccupied bands originates commonly in Mn 3d states. To reproduce the observed spectrum by full multiple scattering calculations, Madelung potential has been taken into account. Charge redistribution is an important factor for the electronic structure in Cu2MnX Heusler alloy. [source] Impact of Annealing on the Conductivity of Amorphous Carbon Films Incorporating Copper and Gold Nanoparticles Deposited by Pulsed Dual Cathodic ArcPLASMA PROCESSES AND POLYMERS, Issue S1 2009Jose Luis Endrino Abstract The influence of annealing in argon at 300,°C on the conductivity, phase stability and electronic structure of hydrogen-free amorphous carbon (a-C) films containing copper (a-C:Cu) and gold (a-C:Au) nanoclusters was investigated. The motivation of this work is twofold: (1) to study the thermal stability of a-C:Cu and a-C:Au films and (2) to point out the relevance of X-ray absorption near edge structure (XANES) technique to study the structural evolution of metal-doped a-C nanocomposites. The films were produced at room temperature using a selective-bias pulsed dual-cathode arc deposition technique. Compositional analysis was performed with secondary neutral mass spectroscopy whereas grazing incidence X-ray diffraction (GIXRD) was used to monitor phase transformation and identify the dispersion or agglomeration of the crystallites within the carbon matrix. XANES spectra at the C-K was used to investigate the effect of annealing in argon on the electronic structure of the a-C matrix, while Cu K and Au L-edges were investigated on a-C:Cu and a-C:Au samples, respectively, to study the nanocluster evolution. XANES showed that the a-C host matrix increased its graphitic character and that stress was relieved upon annealing. No relevant changes were observed in the Au arrangements in a-C:Au films. In the case of the a-C:Cu samples, the Cu-K XANES spectra indicated the formation of Cu2O crystals which correlated well with GIXRD spectra and the decrease in conductivity. [source] Lagoden dimethylformamide hemisolvate dihydrate: absolute configuration, dipolar interactions and hydrogen-bonding interactionsACTA CRYSTALLOGRAPHICA SECTION C, Issue 10 2009Barbara Wicher Lagoden (L·3H2O, where L is Na+·C20H33O6,; sodium 3,,16,18-trihydroxy-8,13- epi -9,13-epoxylabdan-15-oate trihydrate) is widely used as an effective haemostatic agent. It has been crystallized from dimethylformamide (DMF) as sodium 3,,16,18-trihydroxy-8,13- epi -9,13-epoxylabdan-15-oate dimethylformamide hemisolvate dihydrate, Na+·C20H33O6,·0.5C3H7NO·2H2O or L2·DMF·4H2O, and the asymmetric unit contains two of the latter formulation. The four symmetry-independent Na+ cations and lagoden anions, one DMF molecule and six of the eight symmetry-independent water molecules assemble into a one-dimensional polymeric structure via dipolar and hydrogen-bonding interactions. The lagoden anions coordinate to the Na+ cations via the carboxylate groups and the two primary hydroxy groups, whereas the secondary OH groups are solely involved in hydrogen bonding. Two of the four symmetry-independent lagoden anions act in a chelating mode, forming seven-membered chelate rings. The absolute structure, based on anomalous dispersion data collected at 130,K with Cu K, radiation, confirms an inverted configuration at chiral centres C8 and C13 (labdane numbering) relative to the labdane skeleton. [source] Absolute structures and conformations of the spongian diterpenes spongia-13(16),14-dien-3-one, epispongiadiol and spongiadiolACTA CRYSTALLOGRAPHICA SECTION C, Issue 4 2009Ken W. L. Yong The absolute configurations of spongia-13(16),14-dien-3-one [systematic name: (3bR,5aR,9aR,9bR)-3b,6,6,9a-tetramethyl-4,5,5a,6,8,9,9a,9b,10,11-decahydrophenanthro[1,2- c]furan-7(3bH)-one], C20H28O2, (I), epispongiadiol [systematic name: (3bR,5aR,6S,7R,9aR,9bR)-7-hydroxy-6-hydroxymethyl-3b,6,9a-trimethyl-3b,5,5a,6,7,9,9a,9b,10,11-decahydrophenanthro[1,2- c]furan-8(4H)-one], C20H28O4, (II), and spongiadiol [systematic name: (3bR,5aR,6S,7S,9aR,9bR)-7-hydroxy-6-hydroxymethyl-3b,6,9a-trimethyl-3b,5,5a,6,7,9,9a,9b,10,11-decahydrophenanthro[1,2- c]furan-8(4H)-one], C20H28O4, (III), were assigned by analysis of anomalous dispersion data collected at 130,K with Cu K, radiation. Compounds (II) and (III) are epimers. The equatorial 3-hydroxyl group on the cyclohexanone ring (A) of (II) is syn with respect to the 4-hydroxymethyl group, leading to a chair conformation. In contrast, isomer (III), where the 3-hydroxyl group is anti to the 4-hydroxymethyl group, is conformationally disordered between a major chair conformer where the OH group is axial and a minor boat conformer where it is equatorial. In compound (I), a carbonyl group is present at position 3 and ring A adopts a distorted-boat conformation. [source] | ||||||||||