Phosphoenolpyruvate carboxylase (PEPC) and ribulose 1, 5-bisphosphate carboxylase/oxygenase (Rubisco) play pivotal roles in CO2 fixation. Both of the enzymes are involved in photosynthetic efficiency of plants. Here, we report the crystal structures of PEPC and Rubisco; the inactivated Escherichia coli PEPC complexed with L-aspartate, the activated maize PEPC complexed with a sulfate, the Chlamydomonas Rubisco complexed with transition state analogue, and Galdieria Rubisco complexed with a sulfate. X-ray crystallographic analysis and site-directed mutagenesis studies revealed the allosteric regulation and the reaction mechanism of PEPC. The crystallographic studies on Rubisco provided detailed understanding of activity and regulation in Rubisco.
The understanding of crystal and chain structure evolution during the processing is one of the most essential information for the design of polymer with better processability and physical properties. For this purpose, X-ray and neutron scatterings are very powerful tools. In this paper, focusing on the deformation behavior of isotactic polypropylene (iPP) under external field, we introduce 1) application of microbeam SAXS-WAXS to the observation of iPP spherulite deformation process and 2) application of SANS for clarifying the role of each molecular weight component (low, medium and high molecular weight component) on shish-kebab structure formation of iPP.
Hard magnetic properties of FePd nanoparticles originate from their L10-type tetragonal ordered structure with high magnetocrystalline anisotropy energy. In order to know correlations among the long-range order (LRO) parameter (S), the particle size and the anisotropy energy, we employed a new technique to determine LRO parameter of single L10-FePd nanoparticle using nanobeam electron diffraction (NBD) . The LRO parameter was determined by quantitative analysis of NBD intensities recorded on imaging plates together with intensity calculations considering the multiple scattering of electrons. In taking NBD patterns, hh0 systematic reflections were excited using a transmission electron microscope with a field emission gun operated at 300 kV. Specimen thickness was evaluated by electron holography. The obtained order parameters of individual nanoparticles larger than 8 nm are almost around the mean LRO parameter (S=0.79) determined by selected area electron diffraction. In contrast, the parameters gradually decrease as the particle size decreases below 8 nm (S=0.60-0.73) . The low degree of order in very small particles is responsible for the coercivity (anisotropy energy) decrease of the L10 nanoparticles in smaller sized region. Experimental conditions required for NBD analysis are presented in detail and the possible experimental errors of the determined LRO parameters are discussed.
The electronic and magnetic structure of La1-xSrxCoO3 (0.0≤x≤0.6) has been studied by X-ray magnetic circular dichroism (XMCD) at the Co K absorption edge. A negative XMCD peak was clearly observed for pure LaCoO3 at E=7.719 keV within the threshold region, suggesting the existence of the intermediate-spin state of Co3+. A positive XMCD peak at E=7.723 keV was assigned to Co4+, having the double-exchange interaction between Co3+ and Co4+. In order to verify the origin of XMCD, the electronic structure of ground and is core-hole states was calculated by a DV-Xα Hartree-Fock-Slater method, using several cluster models up to the fifth neighbor shell. The first-principles calculations well reproduced the experimental XMCD spectra, where a hybridization of Co 3d, 4p and O 2p orbits stabilizes a magnetic state of La1-xSrxCoO3.
PbTiO3 nanoislands were grown on Pt-covered SiO2/Si and SrTiO3 substrates by self assembly using metalorganic chemical vapor deposition (MOCVD) . Square-, triangular-prism- and pyramidal-shaped nanoislands with orderly in-plane direction were fabricated on Pt/SrTiO3 (001), (101) and (111) substrates, respectively, demonstrating structural control using epitaxial relationships. The size dependence of crystalline and domain structures was influenced by the experience of the phase transition from paraelectric to ferroelectric phase in the cooling process after MOCVD growth of nanoislands. Piezoresponse force microscopy revealed that the piezoelectric constant was dependent on not the width but the height in PbTiO3 (001) nanoislands with heights below 10 nm, suggesting intrinsic size effects. The minimum size of PbTiO3 (001) nanoislands showing ferroelectricity was 1.2 nm in height and 27 nm in width.
Surface Plasmon on metallic nano-structures has been studied by Electron Beam Induced Light Emission method. A focused electron beam in a transmission electron microscope can excite a surface plasmon polariton (SPP) at any position on a metallic nano-structure as a point source. The excited SPP is converted into light via nano-structures, and the emission intensity depends on beam position, photon energy, and emission angle.