In this lecture I explain basic concepts of small angle scattering and their application to structural analysis of polymer materials. The small angle scattering plays an important role to elucidate fundamental problems in polymer physics.
In spite of the vigorous efforts to understand the origin of large isotope effects observed in the phase transition temperature of hydrogen-bonded dielectrics, there are so far no show that the hydrogen bond plays an important role in phase transitions of these materials and the difference in the quantum behavior between proton and deuteron is responsible for the isotope effects.
Metastable phase, which has a lager value of Gibbs free energy than that of the stable phase, commonly occurs in nature against the thermodynamic regulation. Microtexture and microstructure of some metastable-phase minerals (opal-CT, marcasite and wurtzite) are studied by high-resolution transmission electron microscopy. Disordered stacking structures are commonly observed in the metastable phases. In the case of the opal-CT (Hosaka and Akase opal mines, Japan) and marcasite (Ikezuki, Japan), highly ordered domains appear around the domains with disordered stacking structure. Chocaya-Animas wurtzite crystals overgrow on the domains of disordered stackings of sphalerite and wurtzite, which were formed from ordered sphalerite.
Single crystal X-ray diffraction studies under virtually extinction-free conditions have been carried out using 10-micrometer-sized small crystals and the synchrotron radiation at the beamline 14A, Photon Factory, KEK. A case study for CaYAIO4 is described. Results were compared with those obtained by the conventional rotating-anode four-circle diffractometer using Ag Kα. It' was revealed that the extinction-correction included in the least-squares procedure sometimes causes serious artefacts in the deformation density maps and may lead to incorrect interpretation. Collection of virtually extinction-free diffraction data is indispensable for precise structure analyses to elucidate structures containing a lesser degree of disorder, as well as for charge density analyses.
Anomalous change of the mean square displacements (m.s.d.'s) of the octahedral site (B site) cation in magnetite (Fe3O4) was investigated by means of single crystal X-ray diffraction method and discussed with respect to an electron-phonon interaction. With change of temperature and cation deficit, m.s.d.'s of the B site cation of magnetite show unique trends. At lower temperatures the B site cation prefers to vibrate along , but this preference is reduced with temperature rise up to 630 K, above which the mean square displacement normal to  becomes dominant. This preference at lower temperature is also reduced with increasing cation deficit, in other words decreasing carrier population in the B-sublattice. In the MPMS measurements weakening of the electron-phonon interaction in the cation deficit one is apparently shown. From this point of view, these characteristic trends suggest relationship between the anisotropic temperature factor, particularly at lower temperatures, for the B site cation and the electron-phonon interaction possibly due to presence of charge carriers in the B-sublattice. The coordinate of oxygen remains nearly constant at x = 0.2549 (1) below approximately 600 K, but increases with increasing temperature above this temperature. This characteristic behavior of the oxygen coordinate with temperature indicates that the cation disordering over the tetrahedral (A) and octahedral (B) cation sites occurs above 600 K.
X-ray crystal structure of a catalytic-site mutant EQ208 [Glu2O8→Gln] of α-amylase from Bacillus subtilis complexed with maltopentaose (G5) has been determined at 2.5 Å resolution. The conformation around the third α- (1, 4) -glucosidic bond makes a sharp turn, allowing the substrate to fit into the L-shaped cleft of the active site. The amide nitrogen of G1n208 forms a hydrogen bond with the glucosidic oxygen in the scissile bond. The carboxyl group of Asp 176 has non-bonded contacts to the anomeric carbon atom and to the endocyclic oxygen atom. Thus, G1u208 may act as a proton donor and Asp176 may stabilize the oxocarbonium ion at the catalysis.
Bacteriorhodopsin, the sole protein in the purple membrane of Halobacterium salinarium, functions as a light-driven proton pump. To obtain it's three-dimensional crystal, we have developed a new crystallization method which does not involve any step of complete destruction of the membrane. First, purple membrane was incubated at high temperature with neutral detergent and ammonium sulfate so that the membrane was converted into uniformly sized spherical vesicles. Then the vesicles were condensed at low temperature, where fusion of the vesicles produced a hexagonal crystal which is made up of planar membranes. Structural analysis showed that the trimeric structure of bacteriorhodopsin was retained in the crystal. The native lipid bound to a specific site in the protein was suggested to play an important role in maintaining the higher-order structure of the membrane.