Material science is very important and interesting on our living-life and intelligent curiosity. Relationships between structure and function of target materials enable to more search and newly create the objects. The X-ray and synchrotron radiation are powerful tools to elucidate characteristics of the materials, furthermore the neutron is a best partner of X-rays to our purposes. This series will introduce the technique of neutron using, and its scientific development in terms of the probe of the neutron. The first is giving a lecture for the generation of the neutron from a reactor or an accelerator, and a new facility of a pulsed-neutron source with some instrumentation.
Researches of crystals consisting of IVth group element (C, Si, Ge and Sn) polyhedra are described. Fundamental concept for understanding the structure and the electronic properties of the polyhedral clusters and crystals is given. The different structure of the crystals of C and Si is emphasized focusing on van der Waals and covalent characters. Applications of cluster crystals colored by elemental isotopes are also demonstrated in connection to materials science and future electronic devices.
Proteins are encoded in genes in living organisms and play a wide variety of functions in life. X-ray crystallographic technique has provided a solid base for understanding their 3-D architecture. However, relatively little information has been extracted from these studies about their dynamics, because the 3-D structural information is essentially static. In order to understand the mechanistic details of how proteins function, it is crucial to know the dynamics of events that give rise to their designed functions. Recent progress in cryogenic techniques and/or time-resolved X-ray diffraction at synchrotron radiation facilities enables“watching”the collective motions of proteins that closely related to the protein functions. Here I review the instrumentations and feasibility of the protein dynamics research with protein crystallography.
The uniaxial strain method developed by us is a unique method to compress a crystalline sample along desired direction without involving Poisson's effect. This is one of the suitable methods to investigate the relationships between the crystal structure and electronic properties in“soft”organic conductors. Crystal structure analyses of the organic superconductor, α- (BEDTTTF) 2NH4Hg (SCN) 4, are presented as an example.
Hydrostatic pressure is a useful parameter to control protein crystallization. One can change the solubility of protein crystals quickly by changing pressure. Information about the hydration of the specific surfaces of protein molecules can be obtained from the pressure dependency of solubility. When a protein molecule is hydrophobic or when its molecular volume in a solution is significantly larger than that in a crystal, applying high pressure is expected to be an effective method to promote crystallization. Pressure also affects the growth kinetics of protein crystals. Dependency of a growth rate on a driving force for crystallization was measured on typical proteins and analyzed using a two-dimensional nucleation growth model of a poly-nuclei type. High-pressure effects on growth kinetics could be explained by changes in a surface free energy, an activation energy and an average distance between kinks. Common understanding, however, has not yet been obtained for growth kinetics.
The crystal and magnetic structures of an ordered double perovskite, Ca2FeReO6, were studied by high-resolution neutron powder diffraction as a function of the temperature from 7 K to 550 K. All of the diffraction data were precisely refined by the Rietveld method, and we confirmed a structural phase transition at around 140 K where the metal-insulator transition occurs from ferrimagnetic metal (FM) to ferrimagnetic insulator (FI) phases. At this temperature, there exists a change in the distortion direction of [ReO6] octahedra together with a spin reorientation, which strongly supports the occurrence of orbital ordering of the t2g electrons. FM and FI phases coexist in a narrow temperature range at around 140 K, which is typically seen in the first-order phase transition. A phase separation was not detected in our well-characterized sample.
Ab initio molecular orbital calculation is becoming a powerful tool for studying inter-molecular interactions in crystals. The effects of basis set and electron correlation and the performance of density functional methods are reviewed. Model chemistry calculations and classification of intermolecular interactions are briefly mentioned. Some examples of high-level ab initio computations of intermolecular interactions are also presented.