Various transition-metal compound systems with intriguing characteristics have been investigated for the purpose of the comprehensive understanding of the crystal structures and the physical properties from macroscopic and microscopic viewpoints. For the vanadium oxides and polyanions, specifically Cu_xV₄O₁₁, Li_xV₃（P₂O₇）₃（PO₄）₂, Li_xV₂（PO₄）₃, Li_xVOPO₄, and LixVFPO4 that may be designed to serve as high-performance energy storage or thermoelectric device, the crystal structures, electronic properties, and spin dynamics are described on the basis of results of X-ray four-circle diffraction, electrical resistivity, thermoelectric power, magnetization, nuclear magnetic resonance, and electron paramagnetic resonance.

View full abstract

Multiferroic materials in which ferroelectricity is induced by magnetic ordering have been intensively investigated in the past decade. We performed magnetic and crystal structural studies on the typical multiferroic materials, MnWO₄ and RMnO₃（R＝Dy or Tb）and established that the spin supercurrent or the inverse effect of the Dzyaloshinskii-Moriya interaction is the origin of ferroelectricity in these materials by means of spin polarized neutron scattering and circularly-polarized X-ray diffraction. It is also shown that magnetic moments of rare-earth ions play an important role in incomprehensible electromagnetic effects in RMnO₃.

View full abstract

Characteristic behavior and physical properties associated with the vortex domain structure in multiferroic hexagonal manganites RMnO₃（R＝Y, and Ho）have been investigated mainly using transmission electron microscopy and high angle annular dark field scanning transmission electron microscopy. The insulating nature due to peculiar local structures is found at the vortex domain boundaries. In addition, unique 180° charged ferroelectric boundaries originated from the vortex domain formation are discovered, leading to selective boundary conduction related to bound charge screening.

View full abstract

Local structures of the rhombohedral, orthorhombic, and tetragonal phases of barium titanate （BaTiO₃）have been investigated using convergent-beam electron diffraction （CBED）. Nanometer sized rhombohedral structures have been found in both the orthorhombic and tetragonal phases. This indicates the existence of an order-disorder character in their phase transformations. The nanostructures in these phases are discussed in terms of an order-disorder model with off-centered Ti in the ［111］ directions. Spatial distributions of the nanostructures were examined by the combined use of the scanning transmission electron microscopy and convergent-beam electron diffraction methods （STEM-CBED method）. Two-dimensional structural fluctuations were successfully visualized in the tetragonal phase of BaTiO₃.

View full abstract

Li-ion rechargeable battery is one of the most desirable energy sources for electric vehicles, handy phone and other electric articles for daily use. The structure and disorder of the ion conductors are discussed by neutron scattering measurement. Typical structures of cathode, electrolyte and anode materials of Li-ion rechargeable battery are summarized first. The effect of isotope replacement in cathode material by neutron diffraction measurement is introduced. Static and dynamic disorders in materials are investigated from the analysis of diffuse scattering intensity. The correlation effects among thermal displacements of atoms are applied to estimate the force constants, phonon dispersion relations and specific heat. Neutron elastic and inelastic scattering method is very important to clarify the mechanism of the dynamics of ions.

View full abstract

Our modern confortable lifestyles are supported by advanced fibers and the application fields of the fibers have spread into not only clothing textiles but also industrial uses. The industry of the high strength fibers, which is a typical example of the advanced fiber, has concurrently been grown with the progress of the fiber science including crystallography of polymer crystals. The history of the high strength fibers shedding light on the technologies of molecular manipulation giving rise to the high strength fibers and the related crystallography are summarized in this article. Moreover, a new mechanism of the formation of the flow-induced super structure, “shish-kebab”, with regard to the key-structure of the high strength fibers is shown as a recent topic of flow-induced polymer crystallization.

View full abstract

Three-dimensional structure of an organic photocatalyst, 9-mesityl-10-methylacridinium ion, at a photoexcited state and photoinduced structural dynamics in tetrathiafulvalene-p-chloranil were directly observed by single crystal X-ray structure analysis. In diffraction data collection, a laser pump and X-ray probe （pump-probe） technique was applied. Drawing the Fourier maps using difference of observed structural factors between the laser-irradiated and the non-irradiated conditions presicely visualized electron densities corresponding to 1～2％ of photoexcited species in a crystal. The observed structural features of photoexcited molecules clearly reflected their photocatalitic or photoswitchable property.

View full abstract

DNA, which carries genetic information, is easily damaged by reactive oxygen species,UV radiation and chemical agents, and DNA integrity is maintained by various nucleic acid enzymes. We carried out X-ray crystallographic studies of two types of nucleic acid enzymes, oxidative nucleotide hydrolase MutT and translesion DNA polymerase η. In this review, I will describe the mechanism of high substrate specificity for oxidative nucleotides by E. coli MutT and the visualization of nucleotidyl transfer reaction by human DNA polymerase η.

View full abstract

Transthyretin（TTR）is a plasma protein associated with human amyloid diseases. The dissociation of the TTR tetramer is considered to be the rate-limiting step in amyloid fibril formation. The amyloid fibril formation by TTR is known to be promoted by acidic pH. In order reveal the molecular mechanisms of pH dependence of TTR amyloidogenesis, the neutron crystal structure of TTR was solved at 2.0 Å resolution using IBARAKI Biological Crystal Diffractometer. The neutron structure revealed that His88 was single protonated and involved in a large hydrogen-bond network consisted of Thr75, Trp79, Pro113 and water molecules. The double protonation of His88 by acidification breaks this hydrogen-bond network and causes the destabilization of the TTR tetramer. Furthuermore, the comparison with X-ray structure solved at pH 4.0 indicated that the protonation occurred to Asp74, His88 and Glu89 at pH 4.0. Our structural analysis reveals a wealth of information about the hydrogen bonds and the pH sensitivity in human TTR.

View full abstract

The RecQ family of DNA helicases play a key role in protecting the genome against deleterious changes. In humans, mutations in the members WRN （Werner syndrome protein） and BLM （Bloom syndrome protein） respectively lead to rare genetic diseases associated with accelerated aging and cancer predisposition. Recently we determined the 3D structures of human WRN and BLM including a crystal structure of the RecQ C-terminal （RQC） domain bound to a DNA duplex, the first structure of the RecQ-DNA complex. In the complex, the β-wing of the RQC winged-helix motif acts as a scalpel to induce unpairing of a Watson-Crick base pair, an explanation for the unique activities of RecQs toward recombination and repair intermediates such as Holliday junctions.

View full abstract