Generation of laser plasma X-rays and experiments of picosecond time-resolved X-rays diffraction are reviewed. Ultrashort pulsed X-rays are generated by focusing femtosecond laser beam onto metal targets at power density above 1016 W/cm2. Dynamics of phase transition and shock-wave propagation in condensed matter can be investigated by the picosecond time-resolved X-ray diffraction using a pump-probe technique.
Photo-induced motion of an adsorbed atom on a single crystal surface is observed by time-resolved two-photon photoemission. Application of ultrashort pulse may reveal electronic and structual dynamic behavior of condensed matter and its surface.
Solitoic mechanism concerning the intermolecular proton transfer in a one-dimensional (1D) hydrogen-boned chain has been theoretically proposed. Recently, (pseudo) 1D hydrogen-bonded crystals composed of squaric acid derivatives were prepared and their hydrogen-bonded scheme was elucidated by low temperature X-ray crystallography. A characteristic temperature- and frequency-dependent dielectric response exhibited by the hydrogen-bonded crystal of bisquaric acid was interpreted by the solitonic migration of ionic defects generated by the local proton transfer between bisquaric acid molecules. The dielectric response observed in a hydrated crystal of bis (squaric acid) biphenyl turned out to be even more pronounced. The dielectric behavior was relationarized by a collective proton-relay along the hybrid hydrogenbonded 1D-chain composed of deprotonated squarate ions and partially protonated water molecules. These experimental results are expected to provide a clue to understand the active proton transport observed in a hydrogen-bonded channel composed of water pools and amino acid residues in membrane proteins.
When organic radicals form assemblies, the molecules suffer either a ferromagnetic or an antiferromagnetic intermoelcular interaction. Although most of organic radicals exhibit the antiferromagnetic ones, there has been a dramatic development in the research of organic ferromagnetism based on the ferromagnetic intermolecular interaction. An important character of the organic radical crystals is the low-dimensionality, reflecting the anisotropic π orbitals. Such crystals have provided excellent models of one-dimensional magnets of Heisenberg spin. It is notable that they occasionally exhibit unusual phase transitions caused by the fact that their structures easily allow lattice modification along the stacking direction. In this report we describe the magneto-structural correlation in the iodide salts of p-N alkylpyridinium nitronylnitroxides (alkyl = methyl, ethyl, propyl, and butyl) which show an interesting change in magnetism from antiferromagnetic to ferromagnetic with the extension of the N-alkyl chain. We also report an unusual first order phase transition in a thiazyl radical, TTTA. The transition occurs between a paramagnetic high-temperature phase and a diamagnetic low-temperature phase with a surprisingly wide hysteresis loop in the vicinity of room temperature.
Reversible change in color of substances with variation of the temperature is known as thermochromism and has attracted much interest from chemist for a long time. Salicylideneanilines belong to a class of the most popular compounds that show thermochromism in the solid state. We recently succeeded for the first time in the observation of the crystal structure change associated with the thermochromism and in the determination of the structure of the colored form. Furthermore, we discovered that salicylideneanilines are generally thermochromic in the fluid solution of a saturated hydrocarbon solvent, although it has been believed that salicylideneanilines are thermochromic only in the solid state. Our study revealed that the association of the molecules plays an essential role in the thermochromism.
We have discovered the first case of enantiomeric resolution by simple recrystallization of a series of racemic crystals, although in principle this sort of enantiomeric resolution was believed to be impossible for more than a century since the mechanical resolution of enantiomeric conglomerates by Pasteur and the discovery of“Preferential Crystallization”technique by Gernetz. We have referred to this new phenomenon of enantiomeric resolution as“Preferential Enrichment”in the mother liquor. By means of X-ray crystallographic analysis and construction of the binary melting point phase diagram, it has been found that the racemic crystals of the compounds, which show Preferential Enrichment, can be classified into a highly or fairly ordered mixed crystal composed of the two enantiomers. By comparison of the presumed enantiomeric association mode in solution with the enantiomeric arrangement in the crystal, we propose a mechanism of the polymorphic transition during crystallization closely associated with Preferential Enrichment.
The living organism is a complex system consisting of numerous biological machineries. Biological machinery is defined as a functional unit responsible for particular biological activity and may be classified into two types. The first type refers to a stable assembly of macromolecules, like ATP synthase, ribosome, etc. This kind of machinery may be crystallized and its whole structure determined by the X-ray crystallography. The second type does not form such stable assembly, but by the concerted action of individual macromolecules, the system as a whole performs a complex biological function, like various metabolic pathways. The development of protein crystallography in recent years makes it possible to determine the three-dimensional structure of the biological machineries of both types. Three-dimensional structure determination of biological machinery has opened a new era in the field of structural biology.
Structural genomics is expected to supply a large number (tens of thousands) of protein structures in a high through-put manner. These structural data will accelerate scientific discovery in all fields of biological science, including human health and disease. The oldest structural genomics projects of the RIKEN Structural Genomics Initiative has two major goals: to determine mammalian, plant, and bacterial protein structures by X-ray crystallogra-phy and NMR spectroscopy and to perform functional analyses with the target proteins. The prediction of the polypeptide backbone conformation will be possible within several years.
The availability of the complete genome sequences of various organisms has presented a major challenge in structural bioinfoamtics: predicting the structure and function of the gene products, the proteins. Knowledge-based approaches, based on the conservation of protein sequence and structure during evolution, can offer realistic solutions to this daunting task. The paper discusses some of the basic principles behind these approaches, as well as recent advances in the methodologies and further challenges.
Recent interests on biominerals are related to expanded knowledges of biospheres and environmental problems in the Earth. Biominerals offer new materials for crystallographic study in the 21st century. The following unique properties and themes on biominerals are reviewed: types of biomineralization, mineral species of biominerals, evolution and crystals, magnetotactic bacteria and magnetite crystals, fine structures in biominerals and nanocrystalline to low-crystalline biominerals.
Physical chemistry of high level radioactive waste disposal were discussed by means of crystallography, crystal chemistry, and computer simulation method. The current status and problems were reviewed in terms of smectite, a kind of clay mineral, as the most important component of the engineering barrier system. Because of the poor crystallinity, the design and investigation of the clay minerals should be carried out using molecular simulation methods under the knowledge of chemical bonding. The molecular simulation method may be the essential approach for the design of the disposal combining with the homogenization analysis, a micro-macro mechanical treatment, and also further experimental investigations.
At the end of 20th century, we have to summarize a progress of clay crystallography in 20th century and mention what should be needed to make a breakthrough to clay application for environmental material science in new century. Clay crystallography in 20th century illustrated that clay is a crystalline material with some stacking disorder one-dimensionally. For our 21st century with continuous development, however, we have to understand the clay surface structure and charge distribution on the surface. If we understand those, it would be available to control the performance of clay materials with atomic scale.
Natural crystal samples such as Fe-rich pumpellyite occurring in low-grade metamorphic rocks are composed of very fine grains and the crystalline quality of each grain is quite low. The Weissenberg method combined with imaging plate and synchrotron radiation as an X-ray source was employed to determine the crystal structure with low crystalline quality.
Molecular dynamics (MD) simulation is used to predict the structure and elasticity of MgO, MgSiO3 perovskite, and the olivine, modified-spinel, and spinel forms of Mg2SiO4 at high temperatures and high pressures, found in the deep Earth. In order to take account of noncentral forces in crystals, the breathing shell model (BSM) is used for simulation, in which the repulsive radii of O ions are allowed to deform isotropically under the effects of other ions in the crystal. For each phase, the MD simulation with BSM is found to be very successful in reproducing accurately the observed structural and elastic properties over wide temperature and pressure ranges. We then apply MD simulation to predict the density and seismic velocity contrasts at the 410 km and 660 km discontinuities in the Earth's mantle, and compare the simulated results with seismologically observed data.
Recent status of high pressure and high temperature research under the condition of the Earth and planetary core are reviewed. Phase diagram of iron is important to investigate the core of terrestrial planets, but is still debated on the experimental results of both static and shock experiments. Hydrogen-helium system is major component of giant planets, which core condition are beyond the maximum pressure range achieved in laboratory. Future researches need a breakthrough in experimental technique and progress of theory and more observations for these planets.
Some materials exhibit a huge response to an applied field, the phenomenon being closely related to the mesoscopic hetero-phase fluctuation in materials. It has been revealed that the phenomenon is ubiquitous and is found in variety of materials such as martensitic alloys, dielectric relaxors, colossal magneto-resistance materials and so on. The response characteristics may be termed“super-susceptibility”. Examples of the phenomenon and the computer simulation using the time-dependent Ginzburg-Landau theory are reviewed.
I look back upon the past from a viewpoint how useful has been the crystallography for R&D of electronic devices and materials. They are semiconductor lasers, suicide and gate insulator SiO2 in LSI. Techniques and knowledge on crystallography have been very useful on lasers, but supplementary on SiO2. Now, we look in the face of the limits of the standard materials such as SiO2, Al and Si used for 30 years in Si-LSI. Then, we expect that new materials are the key to electronic devices on 21 century and it is very challenging century on many materials researchers.
Toward advanced information the oriented society, the creation of novel functional sensors and devices which can detect many kinds of information such as electric field, magnet field and light will become important to realize flexible information and transfer processes in human bodies. The transition metal oxides possess numerous functional properties, including ferroelectric-piezo-electric, photoactive, ferromagnetic, spin glass, and superconductive properties. By integrating these characteristics in function harmonized artificial lattices at atomic or molecular level, it is possible to create highly sensitive sensor materials for external field (super-five senses) and flexible information processing devices (brain type memory) . In this article, we describe how to create novel functional oxide superlattices and heterostructures as sensitive and multi-functional devices.