In the past decade, the number of publications dealing with 2D- and 3D-network structures in metal organic frameworks (MOF), porous coordination polymers (PCP), metal organic polyhedra (MOP) and zeolites has increased rapidly, owing to recent developments of methodologies of synthesis and X-ray structure analysis.“Topological symbol”is a useful method for describing and categorizing the net structures based on their structural features. Some topological symbols with different definitions were designed to describe a wide variety of the net structures. However, the definitions are quite complicated for understanding and using them correctly. Indeed, confusion and wrong applications of the topological symbols have been found in recent publications very often. Herein, the definitions of five kinds of topological symbols, Wells, Schläfli, vertex, point, and face descriptions, were summarized. “ToposPro”, a software for topological analysis, is also introduced.
Two topics on the recent structural studies of perovskite-type ferroelectrics under applied electric field are introduced. One is on the time-course measurement associated with the polarization reversal in a BaTiO3 single crystal capturing the change in lattice strain of millionths of a second. The other is on the electric field induced large lattice-strain in pseudocubic Bi(Mg1/2Ti1/2)O3-modified BaTiO3-BiFeO3 lead-free piezoelectric ceramics. Both experiments are carried out at SPring-8.
Crystal chirality, a label defining the handedness of a system without improper symmetry, has long been an intensive subject in a variety of research fields such as chemistry, biology, and solid-state physics. Its great importance in solid-state physics lies in the potential unique functionalities of chiral materials such as optical activity, piezoelectricity, and recently discovered unconventional magnetism and associated magneto-transport and magnetoelectric phenomena. An important step toward further development of the chirality research would be a quantification of chirality and a clarification of its relationship to physical properties. Here, we report the discovery of two novel chiral materials, A(TiO)Cu4(PO4)4 (A＝Ba, Sr), and the detailed characterization of their crystal and chiral domain structures. We identify that the chiral crystal structure of this system can be characterized by an antiferrorotative distortion of structural units, indicating that the rotation angle is a good quantitative measure of the chirality strength. Interestingly, the rotation angle and thus the chirality strength can be tuned by changing A site cations. We observe striking differences in the occurrence frequency of chiral domains in the two materials：weakly chiral Ba(TiO)Cu4(PO4)4 mostly hosts a multidomain state, while strongly chiral Sr(TiO)Cu4(PO4)4 predominantly shows monodomain state. On the basis of these results, we discuss the relationship between the chirality strength and the occurrence frequency of chiral domains in this system.
Soft matter generally shows a hierarchical structure both spatially and temporally. Time-resolved small-angle X-ray scattering is effective in revealing this spatio-temporal hierarchical structure of soft matters. Increase in X-ray brilliance and developments of X-ray detectors have contributed to improve the technique. Here recent progress in time-resolved small-angle X-ray scattering including X-ray photon correlation spectroscopy is briefly described.
ADP-Ribose pyrophosphatase (ADPRase) reaction was observed in crystalline-state at atomic resolutions around 1 Å. ADPRase achieves the general acid-base catalysis in the presence of divalent metal cations. Crystals of ADPRase alone, ADPRase-ADPR binary (ES-state) complex were prepared, and reaction intermediates were captured by the cryo-trapping after the soaking of MnCl2 into ES-state crystals. Just after two metal binding sites were successively occupied along with the soaking time, ADPR was hydrolyzed and reaction products were released, indicating the completion of the crystalline-state reaction. The key structures of ADPRase-ADPR-two Mn2+ ions complex revealed the various enzymatic phenomena including electrostatic, proximity and orientation effects and preferential binding for the transition states. The details of the metal assisting mechanism and the general base catalysis have been discussed.