The aminoacyl-tRNA decoding site (A-site) on the small ribosomal subunit is an RNA molecular switch guaranteeing high translation fidelity. Due to the similarity of the secondary structure of the A-site, it has long been believed that the functional characteristics and tertiary structure of the A-site molecular switch are basically conserved in three main cell types, bacteria, mitochondria and eukaryotic cytoplasm. However, these three cell types are noticeably different in their biological properties such as life cycle, genome size, structural component of ribosome and number of tRNA species. In our structural studies, we have shown how a small difference of nucleotide sequences affects the dynamics of the A-site molecular switches underlying the decoding mechanism adapted to their biological properties and environments. The observed structural insights into the decoding process allowed us to understand molecular mechanisms of non-syndromic hearing loss and toxicity mechanism of aminoglycoside antibiotics.

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The present paper is a brief review of our recent works on the crystal structures, structural disorders and ion-diffusion paths of various ionic and mixed conductors. Diffusion paths along the <100> directions are observed in the fluorite-type ionic conductors such as δ-Bi_1.4Yb_0.6O₃, Ce_0.93Y_0.07O_1.96, Y_0.785Ta_0.215O_1.715 and α-CuI. In the prerovskite-type and double-prerovskite-type conductors, the mobile oxide ions move along the <100> directions near the stable positions and along <110> around the midway of diffusion pathway. The cubic prerovskite-type and double-prerovskite-type conductors exhibit three- and two-dimensional networks of diffusion pathways, respectively. K₂NiF₄-type conductor has a two-dimensional network of diffusion pathway through interstitial oxide ions. The oxide ions in apatite-type conductors diffuse along the hexagonal c-axis. The diffusion paths of two lithium-ion conductors are also presented.

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The rare-earth iron oxides RFe₂O₄ (R = Y, Ho-Lu) have a rhombohedral crystal structure, consisting of an alternating stacking of triangular lattices of R, Fe and O ions. Recently, we have proposed that this system shows a new mechanism of ferroelectricity ; the ferroelectric state originates from a polar charge-ordered structure of Fe²⁺ and Fe³⁺ on a triangular lattice. In this article, a review is given on the details of this ferroelectricity, which were revealed by measurements of synchrotron X-ray diffraction and dielectric properties of one of the RFe₂O₄ oxides, LuFe₂O₄.

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Process of structure determination of liquid-crystalline superstructures formed in a mesogenic series, bis(n-alkoxybenzoyl)hydrazine[BABH(n) ; n, the number of carbon atoms in the alkoxy group], is described. The chain-length (n) dependence of relative diffraction intensities from the Ia3d phase resolves the phase problem, leading to the structural description that the molecular centers are on the rods forming two interpenetrating jungle gyms. Theoretical consideration on the stability of superstructures and systematic MEM analysis reveal the coexistence of two aggregation modes (rods forming an extending jungle gym and closed sheets forming spherical shells) for the Im3m phase.

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The lithium ion battery is the most advanced energy storage system, but the application has been limited to portable electronics devices due to cost and safety issues. State-of-the-art LiFePO₄ technology has now opened the door for lithium ion batteries to get into the large scale application as plug-in hybrid vehicles. Geometric information on the lithium diffusion is essential to understand the facile electrode reaction of Li_xFePO₄(0 < x < 1), but the previous approach has been limited to the computational prediction. Here, combining high-temperature powder neutron diffraction and the maximum entropy method, lithium distribution along [010] direction was clearly visualized.

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