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26 citations found for Seki,

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Acta Cryst. (2011). A67, C622
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Acta Cryst. (2014). A70, C155
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Langmuir-Blodgett (LB) films containing azobenzene undergo reversible structural change under light irradiation because of trans-to-cis or cis-to-trans transformations of azobenzene molecules. Such films are a candidate for molecular machines. Time resolved measurements of specular X-ray reflectivity (XRR) curves were carried out for polymer specimens of azobenzene-containing polyvinil alcohol (6Az10-PVA) monolayer LB films on quartz substrates during light (365 nm or 436 nm) irradiation (1 mW/cm2). Measurements were performed with a time-resolution of 10 s using an X-ray reflectometer [1, 2], which can simultaneously measure the whole XRR curves with no need to rotate the specimen, detector or monochromator crystal. Profiles of XRR curves changed as a function of the elapsed time after initiation of the light irradiation reflecting the structural change of the film. Despite of a common belief that the photo-induced structural change occurs directly between the initial and final states, we found an evidence of the existence of the intermediate third structure. We also found that the time needed for changes in XRR curves was several times longer than for optical absorption spectroscopy (OAS) spectra reported with the same irradiation power. Details of such changes of XRR curves and structures of the film will be discussed and compared with the changes of OAS spectra. An XRR curve for the intermediate state of the 6Az10-PVA monolayer LB film specimen separated from the XRR curves measured under 365 nm light irradiation is shown in the figure together with curves for the initial and final states of the same specimen.

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Angle-resolved UV photoelectron spectra (ARUPS) were measured for thin films of perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) deposited on cleaved MoS2 surfaces. The take-off angle ([theta]) dependence of the photoelectron intensity of the highest [pi] band showed a sharp maximum at [theta] = 32-34°. A spectral feature of the binding energy at ~8.9 eV, which is believed to originate from a [pi] state, showed a remarkably different [theta] dependence from that of the [pi] band. A quantitative analysis of the observed [theta] dependencies clearly indicates that (a) the feature at ~8.9 eV originates from the oxygen 2p non-bonding states and (b) the molecules lie flat on the substrate surface.

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Attempts to produce high-quality protein from the MTB genome using the established pET expression system in E. coli are shown. The difficulties encountered at each stage are assessed and the need for alternative purification methodologies are suggested.

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The crystal structure of the mouse UNC5H2 death domain at 2.1 Å resolution is reported. The UNC5H2 death domain is a dimer in the crystal and in solution.

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A change in the higher-order structure of the oligomeric protein is directly detectable by a small-angle scattering method. A SAXS study of the denaturation process of the chaperonin protein GroEL showed that the disappearance of the quaternary structure can be monitored by the Kratky plot of the scattered intensities.


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Acta Cryst. (2014). A70, C91
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It is commonly accepted that the definition of quasicrystal should include a rotational symmetry forbidden in periodic crystals. On the other hand, the quasicrystal with a conventional point group is theoretically possible [1,2]. In a rapidly-solidified Mg-Al alloy, intriguing electron diffraction patterns (EDPs) were reported, which show a cubic symmetry with aperiodic arrays of Bragg reflections [2]. In the present work, we investigate the detailed structure of the rapidly-solidified Mg-Al phase based on direct structure observations using STEM. In a rapidly-solidified Mg-61 at.% Al alloy, 2-fold, 3-fold, and 4-fold EDPs are obtained (Fig. a), which shows that the structure has the cubic point group. However, the relevant diffraction spots are arranged aperiodically. Especially in the 2-fold EDP, a high density of the spots is observed, and the corresponding HADDF-STEM image shows several remarkable features (Fig. b). Two length scales, L and S, can be definitely observed, and they are arranged quasiperiodically along the 3-fold axis. Their arrangement can be well described by the hyperspace crystallography; a physical space tilted by the angle [theta] , where tan[theta] ~ 1.4, successfully generates the observed quasiperiodic pattern. Simulated EDPs from a simple model without detailed atomic decoration reproduces fairly well the experimental patterns. Further analysis of the images reveals that the present quasiperiodic structure has similar local structure to the stable [beta]-Mg2Al3 phase; two lengths correspond to L and S may be reasonably defined. The quasicrystal with a cubic symmetry is unambiguously determined for the first time, based on a direct structural observation. The present results strongly suggest that the noncrystallographic rotational symmetry is not an essential factor to form the quasiperiodic structure, raising a very fundamental, universal question on the physical origin of a long-range order of condensed matters.

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The structure of a copper(II) complex cation of a reinforced chiral 14-membered aza-macrocycle, namely, chloro[(2S,13S)-2,13-diisobutyl-1,4,8,12,-tetraazabicyclo[10.2.2]tetradecane- [kappa]4N]copper(II), which crystallizes as a perchlorate hydrate, [CuCl(C20H42N4)]ClO4.H2O, has been determined. The copper(II) cation lies in the macrocyclic cavity coordinated in a square-pyramidal manner with the four N atoms of the aza-macrocycle, with chloride anion in an apical position.

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In the title compound, a distorted octahedral CoIII complex shows an orientational disorder such that the positions of the nitro and aqua ligands are exchanged. As a result, the averaged structure has an inversion centre at the Co atom.

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In the crystal structure of the title compound, [Co(C44H28N4)(NO2)]·C6H6, the CoIII atom has a distorted square-pyramidal coordination, with the nitro ligand at the apical position. The Co-N(nitro) bond distance is 1.880 (3) Å.

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In the crystal structure of the title compound, [Co(NO2)(C44H28N4)(H2O)]·CH2Cl2, the CoIII atom has a distorted octahedral coordination, with the water mol­ecule trans to the nitro ligand. The Co-N(nitro) and Co-O(aqua) bond distances are 1.863 (8) and 2.114 (8) Å, respectively. There is no intermolecular hydrogen bond involving the aqua ligand.

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In the crystal structure of the title compound, [Co(NO2)(C44H28N4)(C2H6O)], a distorted octahedral CoIII complex shows orientational disorder such that the positions of the nitro and ethanol ligands are exchanged. As a result, the averaged structure has an inversion center at the Co atom.

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The title compound, C19H18F2IO6P, prepared as a potential antiviral and anticancer agent from 3-methyl­salicyl­chloro­phosphane and 1-(2,4-di­fluoro-5-iodo­phenyl)-2-deoxy-[beta]-D-ribo­furan­ose, is one of a 1:1 mixture of two diastereomers. The diastereomers differ in their configuration, S or R, at the asymmetric phosphorus center. X-Ray crystallographic analysis of the title compound has determined the absolute configuration at the asymmetric P center to be S.

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Acta Cryst. (2014). A70, C387
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Incommensurate helical (or cycloidal) magnetic structure may have left- and right-wound states (helicity), which are in principle equally populated in a magnet with inversion symmetry. In addition, for a Heisenberg triangular antiferromagnet, clockwise and counter-clockwise rotations of the 120 degree spin structure provide another intriguing degree of freedom. Hence, a triangular magnet that has incommensurate helical ordering along the stacking direction will show intriguing interplay of the helicity (of the helical structure) and chirality (in the triangular plane). Such phenomenon is, however, rarely studied in the past since only one example, the Ba3NbFe3Si2O14 langathite, has been known to date [1]. In this work, we study MnSb2O6, which consists of distorted triangular lattice stacking along the c-axis [2,3]. MnSb2O6 belongs to the space group P321, and hence lacks inversion symmetry. Due to this fact, unique selection of the helicity and chirality may be expected. However, the earlier studies were carried out using unpolarized neutron diffraction with mostly the powder sample, and thus helicity and chirality selection cannot be concluded. Here, we have performed single-crystal diffraction experiment using polarized neutrons in addition to the unpolarized ones, and have succeeded in determination of the magnetic structure of MnSb2O6. The resulting magnetic structure is nearly cycloidal with the magnetic modulation vector q = (0, 0, 0.182) (see figure below). The spin rotation plane is, however, inclined from the ac-plane toward the b-axis for approximately 30 degrees. Polarization analysis indicates that both the helicity of the (nearly-) cycloidal structure and chirality of the in-plane 120 degree structure are uniquely selected. The 30 degree inclination from the ac-plane is a key finding of this work, allowing new kind of multiferroicity in this material.

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The periodic tricontinuous network structure (TNS) of symmetric isoprene-styrene-2-vinylpyridine triblock copolymers has been studied by small-angle X-ray scattering (SAXS). The observed SAXS profiles were compared with the calculated diffraction intensities based on the model electron density distributions constructed for a pair of surfaces parallel to the infinite periodic minimal surface.

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Acta Cryst. (2014). A70, C1547
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Magnetic skyrmion is a topologically stable particle-like object, which appears as nanometer-scale vortex-like spin texture in a chiral-lattice magnet [1]. In metallic materials (MnSi, FeGe, Fe1-xCoxSi etc), electrons moving through skyrmion spin texture gain a nontrivial quantum Berry phase, which provides topological force to the underlying spin texture and enables the current-induced manipulation of magnetic skyrmion [2]. Such electric controllability, in addition to the particle-like nature, is a promising advantage for potential spintronic device applications. Recently, we newly discovered that skyrmions appear also in an insulating chiral-lattice magnet Cu2OSeO3 [3]. We find that the skyrmions in insulator can magnetically induce electric polarization through the relativistic spin-orbit interaction, which implies possible manipulation of the skyrmion by external electric field without loss of joule heating. The present finding of multiferroic skyrmion may pave a new route toward the engineering of novel magnetoelectric devices with high energy efficiency. In this talk, our recent attempts to drive skyrmions by external field are also introduced.

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Acta Cryst. (2011). A67, C627-C628
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