The grazing-angle X-ray standing wave（GAXSW）method for model-independent and atomic-scale determination of in-plane structures and X-ray reciprocal-space mapping（XRSM）at a sample angular position for quick structural estimation are discussed. The both have been developed for analysis of a nanoscale structure such as an adsorbed surface system and a buried nanoscale structure. They are synchrotron-based X-ray diffraction techniques, which use monochromatic parallel hard X-rays incident at a small angle close to the critical angle for total-external reflection. GAXSW's are dynamically formed by the interference of an incident, a specularly reflected, and a specularly diffracted beam above a sample surface. A Bragg condition is satisfied on lattice planes perpendicular to the surface. The author describes in-plane structural analyses of a surface system and a thin film. Outcomes of XRSM are briefly summarized for nanoscale structures of a surface, buried interfaces, and a thin film. In particular, results of nanoscale wires are mentioned.
Single crystals of Li4+xTi5O12 were prepared by means of electrochemical Li-ion intercalation technique using parent Li4Ti5O12 single crystals. The obtained Li4+xTi5O12（x＝1.35）crystallizes in the cubic spinel-related type structre, space group Fd3m, and lattice parameters of a＝8.346（3）Å and V＝581.3（5）Å3. The Li-ion intercalated sites were successfully determined by single crystal X-ray diffraction. From the result, because of the structural restriction of the spinel structure, unfortunately, the theoretical capacity was revealed to be 175 mAh/g. New material Li2Ti6O13 with rectangular tunnels was synthesized by Na+/Li+ ion-exchange method as one of the negative electrode material having a high capacity than Li4Ti5O12. The Li2Ti6O13 as determined the precise crystal structure by powder neutron diffraction and evaluated reversible Li insertion/extraction reaction.
Poly（［R］-3-hydroxybutyrate）（P（3HB））and its copolymers are accumulated by a wide variety of microorganisms as intracellular carbon and energy materials, and are extensively studied as biodegradable and biocompatible thermoplastics. Recently, we succeeded in obtaining strong fibers and films by new drawing techniques from microbial polyesters produced by both wild-type and recombinant bacteria. The improvement of mechanical properties of fibers and films is due not only to the orientation of molecular chains but also to the generation of a planar zigzag conformation. The structure of strong fiber with tensile strength of over 1.0 GPa was analyzed by micro-beam X-ray diffraction and X-ray micro-tomography with synchrotron radiation. The strong fibers and films were completely degraded in environment or by extracellular PHB depolymerases. In this article, I present the processing, mechanical properties, highly ordered structure and biodegradability of strong fibers and films produced from microbial polyesters.
To characterize the role of cysteine residues on the structure, function and stability of JNK1, we prepared and evaluated the wild-type JNK1 and seven cysteine-deficient JNK1 proteins. The solvent exposed cysteine residues did not influence biological function and mutating these residues raised the thermal stability because of newly formed hydrogen bonds and of higher hydration as speculated by the mutant structures. The surface cysteine involved in the molecular-surface hydrophobic pocket did not affect biological function; although a moderate thermal destabilization was observed. Cysteines in the loosely-assembled hydrophobic environment moderately contributed to thermal stability and the mutations of these cysteines had negligible effect on enzyme activity. The other cysteines are involved in the tightly-filled hydrophobic core and mutation of these residues conferred the adverse effects on the thermal stability and enzyme activity.
Skeletal muscle contraction is regulated mainly by Ca2+ binding to the thin actin filaments in a sarcomere, but the participation of the thick myosin filament in the regulatory mechanism has remained to be clarified. The lattice sampling-free intensities of the myosin layer lines in the X-ray diffraction patterns from live resting higher vertebrate striated muscles with a full thick-thin filament overlap were analyzed. Atomic modeling of the myosin filament was performed, revealing the head-head interactions of myosin crossbridges, which are in common among various resting striated muscles. The head-head interactions are primarily electrostatic and the converter domain is responsible for their interactions. The results indicate that multiple head-head interactions of myosin crossbridges stabilize the resting myosin structure and play a role in the regulatory function also in the thin filament-regulated muscles.
Proteins, sophisticated biological macromolecules, are being expected to use a wide variety of applications in the fields of industry, drug discovery and so on. However, it is now limited due to their structural instability. We first achieved to enclose the protein ubiquitin within the precisely-structured artificial capsules utilizing self-assembly process. This molecule is quite stable in various physicochemical environments. Moreover, to prove the existence of the flexible protein structure within the capsule, we developed a crystallographic method using histogram analysis of MEM electron-density（H-MED）. This method might be useful to identify flexible structures which are difficult to construct atomic models.
Fullerene with encapsulated lithium cation, Li+@C60, can be regarded as an alkaline cation owing to the spherical shape and positively charged Li+ cation. We present the crystal structure and phase transition of a rock-salt-type Li+@C60 crystal that consists of the freely rotating Li+@C60 cations and orientationally disordered PF6− anions at 400 K. The orientations of the C60 cages and PF6− anions are perfectly ordered below TC＝370 K, whereas the Li+ cations are thermally hopping within the cages even at 155 K. A gradual localization of the Li+ cations at polar two positions in each C60 below 100 K and a negative thermal expansion of the static C60 are demonstrated.
Clostridium perfringens enterotoxin（CPE）is a cause of food poisoning and is considered a pore-forming toxin which damages target cells by disrupting the selective permeability of the plasma membrane. We determined the crystal structure of the full-length CPE at 2.0 Å. The overall structure of CPE displays an elongated shape, composed of three distinct domains, D1, D2, and D3. In this structure, the pore-forming domain（Val81〜Ile106）of CPE has alternating pattern of polar and hydrophobic residues and forms α-helix. This characteristic sequence is frequently observed in β pore-forming toxin families as typified by α-hemolysin. These results indicate that CPE behaves as β pore-forming toxins.