Synchrotron radiation (SR) is an extremely useful X-ray source for protein crystallography. It is high brilliance, high intensity and small divergence white X-ray source, which enables us to collect high resolution diffraction data of biological macromolecular crystals with large cell dimensions. Furthermore, wavelength tunability of SR is essential for the phase determination by multiwavelength anomalous diffraction (MAD) method, which has a possibility of the direct phase determination of metal proteins, selenomethionyl proteins and proteins with single isomorphous derivative of poor isomorphism. MAD method is applied for the structure determination of cytochrome c-553 from Desulfovibrio vulgaris Miyazaki F strain.
9-Hydroxyphenalenones exhibit a dynamical disorder due to a tautomeric process or a reorientational motion in the solid state depending on the crystal environment. Both 5-methyl and 5-bromo derivatives undergo a rapid tautomerization in crystals along the symmetrical double-well potential of the hydrogen bond. While the tautomerization of 5-methyl derivative was quenched at 41K due to the antiferroelectric phase transition, 5-bromo derivative does not show any transition down to 4K, because the antiferroelectric transition is suppressed due to the “quantum fluctuation” caused by the tunnelling effect on the proton transfer along the hydrogen bond. On the other hand, the unique dielectric behavior of 9-hydroxyphenalenone in phase II was interpreted in terms of the motion of the domain walls between left-and right-directed molecules based on the reorientational motion in crystals.
Diene is one of the most basic organic substrate including two carbon-carbon double bonds in its chain skeleton. Four π-electrons in its double bonds interact with metal atoms in various modes of bonding. Especially with early transition metals diene interact in unique fashion of bonding. These variety of bonding characteristics between diene and early transition metals reflect versatile utility of this type of complexes as the important reagents for new organic syntheses. This paper reviews the interaction of diene with early transition metals from the structure chemical point of view.
Polarized infrared absorption spectrum of an optically anisotropic crystal was formulated under Fourier transform polarized infrared microspectroscopy. The formulation of the spectrum requests us to set the optically anisotropic crystal at its extinction position under an IR polarizing microscope. Under this experimental constraint, pleochroic distribution of absorbance due to OH dipoles was also formulated for the purpose of determining the orientation of the OH dipole in an optically anisotropic crystal. The formulation was applied to determine the orientations of the OH dipoles in topaz and quartz. The OH dipoles in topaz predominantly lies in the (010) plane and inclined 27° from the c-axis. The OH dipoles in quartz lie almost perpendicular to the c-axis.
High resolution transmission electron microscopes nowadays achieve a point resolution beyond 0.2nm so that structural information can be visualized at the atomic scale. However, since the images are strongly influenced by dynamical electron scattering and imaging parameters such as defocus and spherical aberration, it is still difficult to determine the structure directly from the images without a priori knowledge. Some recent technological developments have possibilities to solve this problem. A novel approach based on defocus-modulation image processing allows us to correct spherical aberration, leading to marked improvement of the resolution and direct retrieval of structural information from the processed images.
A novel X-ray diffraction method for liquids using an imaging plate area detector has been successfully applied to constant-density measurements of water at high temperatures and high pressures covering the supercrital state. The radial distribution functions have shown that the local tetrahedral ice-like structure of water is ruptured above 416K and that the short-range O-O interactions at -2.9Å still exist by -40% to the coordination number of 3.9, however, with large fluctuation and distorted hydrogen bonding in dense supercritical water at 649K.