As an introduction of a lecture-series entitled by“Potential of synchrotron radiation as a probe and exciter”, a mechanism of synchrotron radiation is explained qualitatively with a time-scale squeezing factor. From the viewpoint of achieving highly brilliant synchrotron radiation, required performance for an electron beam and accelerator is reviewed. A limit of the third-generation synchrotron radiation source based on the stored beam in a storage ring is described and the direction of the next, i.e., the fourth-generation radiation source is also discussed.
The insertion devices (IDs) are instruments to produce highly brilliant synchrotron radiation (SR) to be installed in straight sections of a storage ring. Periodic magnetic fields are generated in the IDs mostly by permanent magnets, in which an electron moves along a sinusoidal orbit. The SR emitted at each period is superimposed coherently or incoherently, resulting in much higher brilliance than SR emitted at bending magnets. Characteristics of SR emitted from IDs are explained briefly to help the SR users utilize effectively the capability of SR.
The use of high-energy (E ≥ 50 keV) X-rays from SPring-8 allows us to perform X-ray diffraction experiments on disordered materials with the following advantages: high resolution in real space due to the wide range of scattering vector, small correction terms (particularly the absorption correction), and fast diffraction measurement with small amount of samples. Recently, high-energy X-ray diffraction data have been combined with neutron diffraction data from a pulsed neutron source to provide more detailed and reliable structural information than has hitherto been available. Furthermore, the use of reverse Monte Carlo modelling and PDF (pair distribution function) simulation based on high-energy X-ray diffraction data have succeeded in illustrating 3-dimensional structure of disordered materials and disorder in crystalline materials.
Glucokinase is a cytoplasmic enzyme that phosphorylates glucose and triggers glucose utilization and metabolism. Glucokinase expressed in liver and pancreas is thought to be the glucose sensor controlling plasma glucose levels. The role of glucokinase as a glucose sensor is due to its allosteric properties. In order to elucidate the molecular mechanism of glucose sensor, we analyzed the crystal structures of human glucokinase in both its active and inactive forms. Crystal structures suggest that the allosteric regulation of monomeric glucokinase obeys the“mnemonical mechanism”rather than the well-known concerted model.
Synthesis of optical active compounds from achiral or racemic materials is one of the most impressive studies in organic chemistry. Here we provide two new technique of generation of optical activity without anyl outside chiral source. One is the breaking of chiral symmetry of axially chiral materials via racemization-preferential crystallization method. Another involves the asymmetric reaction using the frozen chirality generated by chiral crystallization of achiral materials.
Much attention has been paid to the spin crossover process since the process is closely connected with the enzymatic pathways involving the heme proteins. The full picture of the spin crossover process is, however, not yet clarified. This paper describes our recent finding on the novel spin crossover process between S=3/2 and S=1/2 in highly saddled iron (III) porphyrin complex [Fe (OETPP) (Py) 2] ClO4, which was directly monitored by the crystallographic analysis at 298, 180, and 80 K.
Electron charge density distributions of perovskite-type dielectric oxides, PbTiO3 (ferroelectric), and PbZrO3 and PbHfO3 (antiferroelectric), have been investigated associated with the phase transitions, by analyzing high-energy synchrotron-radiation powder diffraction data by the maximum entropy method (MEM) /Rietveld method. Two distinctive structural features, that is, disordered Pb atom and anisotropic charge density distributions around O atom, are observed only in PbZrO3 and PbHfO3 in the cubic phase. These features can be a clue to understanding why PbZrO3 and PbHfO3 show antiferroelectric phase transition.