Structural studies using multiple powder profiles were described with two examples. An algorithm for determining the element-selective charge density is developed using multi-wavelength anomalous synchrotron X-ray powder diffraction data. The method is employed in order to resolve the disordered structure of Yttrium in Y@C82(C6H5CH3). Systematic structural studies of 24 different kinds of endohedral metallofullerenes, MxC2n(M = La, Y, Sc, Lu, Ti, Eu, Er, Hf, Sc3N ; 34 ≤ n ≤ 43), as 1 : 1 cocrystals with solvent toluene molecules have been carried out. It is found that the volume for one fullerene and one toluene molecule depends linearly on the number of carbon atoms in the fullerene cage. The linear dependence found in the present study provides a metallofullerene diagnostics diagram that may have universal importance for structural characterization of the so-called cluster endohedral fullerenes.
G protein coupled receptors (GPCR) are involved in a wide variety of physiological functions, and thus are the targets for most of today's medicine. Here we report the raising of a monoclonalantibody against human adenosine A2A receptor that works as strong inverse agonist, and describe the crystal structure of the receptor in complex with the antibody fragment. The structure reveals that the antibody specifically recognizes the intracellular surface of thereceptor in an inactivated state so as to inhibit the structural changes to the active conformation. Our results suggest a new strategy to modulate the activity of GPCR.
The Tup1-Cyc8 complex acts as a corepressor for members of multiple families of transcription factors. Although its physiological functions have been extensively studied, it remained unclear how the corepressor assembles, and how the assembly involves in the molecular functions. Here, we report the crystal structure of N-terminal domain of Tup1, which is essential for its self-assembly and interaction with Cyc8. The N-terminal domain of Tup1 tetramerizes to form a novel antiparallel four-helix bundle, and is organized as a dimer of dimers. Coiled-coil interactions stabilize each dimer together, and mutagenesis study confirmed that the hydrophobic residues responsible for the association of the protomers as dimers are required for transcriptional repression. We confirmed the functional and structural importance of the hydrophobic residues by further X-ray crystallography.
Cd2Os2O7 shows a metal-insulator transition at 227 K with magnetic ordering in an undistorted pyrochlore lattice, but its magnetic structure and the origin of the transition are not yet uncovered. We observed commensurate magnetic peaks by resonant X-ray scattering experiments on a high-quality single crystal. A noncollinear all-in/all-out spin arrangement on the Os tetrahedra is proposed on the bases of the experimental results and the irreducible representation analysis.
Quantitative reciprocal-space analyses of magnetic fine structures in magnetic artificial lattices of patterned elements and chiral helimagnets have been performed by means of small-angle electron scattering (SAES) technique. Lorentz deflection due to magnetic moments and Bragg diffraction due to lattice periodicity are simultaneously recorded at an angle of the order of 1×10−6 rad using long-distance camera length more than 100 m. The present SAES technique,together with TEM real-space imaging method such as in-situ Lorentz microscopy, is very powerful in analyzing electromagnetic fields in nano-scaled materials. The existence of both chiral helimagnetic order and chiral soliton lattice in a chiral helimagnet CrNb3S6 has been successfully verified using the present methods.
Strongly interacting electrons can exhibit novel collective phases, among which the electronic nematic phases are perhaps the most surprising as they spontaneously break rotational symmetry of the underlying crystal lattice. Our highly sensitive magnetic torque measurements under in-plane field rotation in iron-based superconductors BaFe2(As1-xPx)2 provide evidence for the electronic nematic ordering below a characteristic temperature T*. High-resolution crystal-structure analysis by using synchrotron X-ray reveals small but finite orhthorhobic distortionbelow T* and the orthorhombicity shows a big jump at a lower temperature Ts. The results imply an electronic origin of rotational symmetry breaking, whose relation to superconductivityis discussed.
Through the combined studies of temperature- and pressure-dependent dielectric permittivity and X-ray diffraction, ferroelectric cocrystals of phenazine with anilic acid have been characterized by the interplay between the successive structural transformations and solid-state acid-base (proton transfer) reactions. Ferroelectric domain-wall motions associated with local proton rearrangement and collective proton relay have been revealed by the piezoresponse force microscopy.
A successful example of visualization of quantitative structure-property relationship, relation between the anomalous distribution/dynamics of the guest atom “rattling” and the reduction of thermal conductivity in type-I clathrates, is introduced. We found that the area governed by the weakly bounded guest atom in the cage can be extracted using trace of electrostaticpotential local-minimum (EPLM). The area normalized by the size of guest atom, rattling factor, corresponds to degree of rattling, and thermal conductivity decreases with an increase of the rattling factor. The electrostatic potential distribution analysis will be a powerful tool to visualize quantitative structure-property relationship in many kinds of materials in which the novel properties originate from polarization, uneven distribution of electrons etc.
Piezoelectric materials have been used in a wide range of fields such as information communication, electric appliances, medical equipments, and automobiles, and will continue to be essential electronic device materials for people's lives. Although it is technically difficult to develop a high-performance lead-free piezoelectric ceramics, the author and coworkers have been examined the capability of alkali niobate piezoelectric ceramics. This article introduces our recent study about crystal growth and ferroelectric domain evaluation for (Li,Na,K)NbO3. The importance of basic study on the domain structure is also emphasized to reach the next R&D stage toward future industrialization.