In order to review the advantage as well as disadvantage of a neutron 4-circle diffractometer technique, several comparisons were shown such as X-ray and neutron, powder and single crystal, filmmethod and pulse counter methods, and so on. Recent progress of the crystal and magnetic structure analyses using neutron 4-circle diffractometer FONDER installed at JRR3M is discussed.
Neutron diffraction provides an experimental method of directly locating hydrogen atoms in proteins and nucleic acids, and the development of the neutron imaging plate (NIP) became a breakthrough event in neutron protein crystallography. A high resolution neutron diffractometers dedicated to biological macromolecules (BIX-3, BIX-4) with the NIP have been constructed at Japan Atomic Energy Research Institute. The detailed structure of the diffractometer and the systematic procedure of the neutron diffraction experiment from the crystallization of a large single crystal to the data collection and the data processing, and the future prospect of the neutron diffractometry in proteins will be presented.
Crystallographic studies on nucleic acid-nucleic acid, nucleic acid-protein and protein-protein interactions are reviewed. The studies contain base pairing, sequence-specific stability of Z-DNA structures, base recognition by ribonuclease T1, transcriptional factors-DNA interaction, G proteins and the effector protein recognition, and protein-protein interactions in intracellular signaling pathways.
Coenzyme B12 or adenosylcobalamin, commonly known as Vitamin B12, is one of the most complicated natural organic compounds involved in heteroatom elimination and carbonskeleton rearrangement reactions. Diol dehydratase is an adenosylcobalamin-dependant enzyme that catalyzes conversion from 1, 2-diol compounds to the corresponding aldehydes. Comparison of the structures of the enzyme of substrate-bound and substrate-free forms reveals the activation mechanism of adenosylcobalamin. Structural studies of chiral substrates imply that this enzyme catalyses each enantiomer with different mechanisms in the final step of the reaction.
Photo and thermal induced dynamic processes of organic molecules have been studied by focusing on intermolecular contacts and void spaces in crystals. On the photoisomerization of cobaloxime complex, the reaction rates were controlled by forming host-guest complexes. Volume of the void space around the reactive group, reaction cavity, was systematically changed by replacing the host molecules with retaining the isomorphic structure. On the first order phase transition of acylurea derivative crystal, the mechanism of the phase transition was clarified by a detailed temperature resolved single crystal diffraction method. The phase transition proceeds via two elementary processes, namely supramolecular and molecular processes.
Bloch wave degeneracies, which can be observed in high-energy electron diffraction, are summarized. Many beam dynamical theory and the symmetries of Bloch waves are described briefly for discussion of Bloch wave degeneracies. Conditions for degeneracy of Bloch waves are explained for the three-beam case. Degeneracies in the symmetric three beam case and non-systematic reflections case are shown. Critical voltage in systematic row of reflections is discussed.
We review our recent works on the positional disorder and diffusion path of oxide ions in Bi2O3, CeO2 and (La0.8Sr0.2) (Ga0.8Mg0.15Co0.05) O3-δ. These were studied through the nuclear density distribution obtained by a combined technique including a Rietveld refinement, a maximumentropy method (MEM) and MEM-based pattern fitting of the neutron powder diffraction data measured at high temperatures. Oxide ions in fluorite-type structured δ-Bi2O3 and CeO2 have a complicated disorder spreading over a wide area and shift to the ‹111› directions from the ideal fluorite site at higher temperatures. Diffusion path of oxide ions in (La0.8Sr0.2) (Ga0.8Mg0.15Co0.05) O3-δ perovskite is not along the straight line between the ideal positions, but exhibits an arc shape away from the B-site cation (Ga0.8Mg0.15Co0.05) .
We developed crystallization method of a protein molecule by laser irradiation, and call this process Laser Irradiated GrowtH Technique (LIGHT) . Effective crystallization was confirmed by applying a femtosecond laser. The crystallization period was shortened by LIGHT. Protein crystals were also obtained by LIGHT from normally uncrystallized conditions. These results indicate that laser irradiation generates crystal nuclei; protein crystals can then be grown from the nuclei that act as seeds in a supersaturated solution. We should optimize the laserirradiated condition to control the number of crystals and to obtain high-quality crystals because protein crystallization depends on the conditions.