The large angle technique and lattice defect identifications

The history of the Convergent Beam Electron Diffraction (CBED) is shortly introduced. Symmetry determinations[1] of crystals or the point groups and space groups of 3, 4, 5 and 6 dimensional crystals, and crystal structure analysis including the determination of charge density distribution and potential distribution of a crystal are briefly reviewed.[2] Then, the large angle CBED (LACBED) technique is described.[3] Applications of the LACBED technique to the determinations of the Burgers vector of a dislocation, the shift vector at a stacking fault, the precise orientation difference of a twin domain and the strain of an advanced multi-layer material are reviewed.

Study of nanoscale local structures of ferroelectric barium titanate using CBED

It is well known that BaTiO3 undergoes successive phase transformations from the cubic paraelectric phase to three ferroelectric phases: tetragonal, orthorhombic and rhombohedral ones. Coexistence of the displacive and order-disorder characters in the phase transformations of BaTiO3 was pointed out from many experiments and theories. However, local structures related to the order-disorder character were discovered neither in crystal structure analyses using neutron and X-ray diffraction nor by TEM observations. In the present study, the convergent-beam electron diffraction (CBED) method was applied to examine nanometer-scale local structures of BaTiO3. Rhombohedral nanostructures were observed in the orthorhombic and tetragonal phases of BaTiO3 using CBED [1]. It was found that the symmetry of the orthorhombic phase is formed as the average of two rhombohedral variants with different polarizations, and that of the tetragonal phase is formed as the average of four rhombohedral variants. These results indicate an order-disorder character in their phase transformations. Similar results were obtained in the ferroelectric orthorhombic phase of KNbO3 [2], while it was found that the ferroelectric tetragonal phase of PbTiO3 does not have such rhombohedral nanostructures. We also proposed a combined use of STEM and CBED methods (STEM-CBED method) to observe the nanostructures of polarizations [3]. Using the method, two-dimensional distribution of the rhombohedral nanostructures, or nanoscale fluctuations of the polarization clusters, were successfully visualized in the tetragonal phase of BaTiO3.

Structural and thermal analyses of a hydrolysis compound of thalidomide

Thalidomide (TD) is a historically famous chiral drug. After prescription as a safe hypnotic, TD was suspected of contributing to teratogenicity, resulting in prohibition of the use of TD. TD and its derivatives, however, have attracted a renewed attention since their therapeutic effects for Hansen's disease and multiple myeloma were demonstrated. Meanwhile TD has been known to suffer from spontaneous hydrolysis with complicated pathways, leading to the production of various metabolites of TD. Therefore, we are now facing the difficulty in specifying the compounds which cause desired and/or adverse effects in the drug mechanism of TD. In a previous study, pure hydrolytic products of TD were synthesized and assayed for production-inhibitory activity of TNF-α, a kind of cytokine that induces inflammation. This study has showed that some products, especially α-(2-carboxybenzamido)glutarimide (CBG), exhibit high potency for the inhibition of TNF-α production compared to original TD. The hydrolytic products of TD thus are found to greatly attribute to the pharmacological effect of TD. For comprehending effects of the hydrolytic products, it is much significant to perform physicochemical analysis of them because their properties are deeply related to molecular stability and interaction with receptor proteins. In this study, we thus aim to investigate the physicochemical properties of CBG employing X-ray crystal structural analysis and thermal analyses. Single crystals of racemic and enantiomeric CBG were grown by solvent evaporation methods. On the crystallization, we chose alcoholic solvents such as methanol and ethanol. Surprisingly, crystals grown from the CBG solutions have indicated the same crystal structure of TD with high reproducibility. This unique result is likely to represent dehydration of CBG in non-aqueous solvents, which has not been reported so far. The detailed mechanism is under investigation.

Optical properties of chiral photomechanical salicylideneaniline crystal

Mechanical motion caused by UV/VIS radiation onto bulk materials is called a photomechanical effect. In other words, the photomechanical effect is a type of energy conversion systems. Recently, a mechanical bending of photochromic diarylethene crystals was reported, and the molecular-scale motion was found to produce the macroscale bending of the crystals (Kobatake et al., 2007). Subsequently, several photomechanical crystals have been reported to provide promising opportunities for artificial molecular machinery. The mechanism of the conversion of light energy to mechanical energy, however, has not quantitatively been understood. In photomechanical effect, microscale structural change and stress should be involved with optical properties of anisotropy and chirality; linear birefringence (LB), linear dichroism (LD), circular dichroism (CD) and optical rotatory power (ORP). CD and ORP in a chiral anisotropic crystal are extremely difficult to be measured owing exclusively to the contribution of strong linear anisotropy. The High Accuracy Universal Polarimeter generalized by our group (G-HAUP) enables us to measure LB, LD, CD, and ORP simultaneously and quantitatively (Tanaka et al., 2012). The purpose of our study is to investigate the relationship between microscale structural change or stress induced by UV/VIS radiation and the four optical properties. We synthesized chiral N-3,5-di-tert-butylsalicylidene-1-phenylethylamine photochromic crystal, as shown in Scheme 1, because the mechanism of photomechanical effect in this crystal has been revealed qualitatively by analyzing single-crystal structure under UV/VIS radiation (Koshima et al., 2013). The LB, LD, CD, and ORP spectra in the direction perpendicular to (001) were successfully measured under VIS radiation. Furthermore, LD spectrum was found to change by UV radiation in 30mW/cm². These results could contribute to an elucidation of the mechanism of photomechanical effect quantitatively.

Species-dependent variation in the structure of the CK2α-apigenin complex

Ser/Thr kinase CK2, consisting of two catalytic α subunits and two regulatory β subunits, represents various cell fates such as proliferation and is a crucial target for cancer and glomerulonephritis therapies. To date, several planar compounds have been identified as ATP-competitive CK2-inhibitors including apigenin, a flavonoid inhibitor. We here determined the crystal structures of human CK2α complexed with apigenin and an ATP analogue (AMPPNP) at 2.3 and 2.5 Å resolution, respectively and investigated the species specificity in the molecular recognition by the structural comparisons of these complexes with each maize equivalent. The pairs of the superimposed structures reveal that apigenin binds to human and maize CK2α in the quite distinct manners. while AMPPNP binds to the both species in a similar manner. Together with the chemical calculations, we deduce that the alternation at the Leu45/Val45 position of CK2α largely contributes to the species-dependent variation in the apigenin binding mode although the discrepancy is unrelated to the structural conservation in the ATP binding mode.

Crystal Chemistry and Physics of Perovskites with Small Cations at the A Site

Synthesis, crystal chemistry, and physics of perovskites with small cations at the A site are an emerging field in perovskite science. Properties of ABO3 perovskites with small cations at the A site (A = Sc and In; B = transition metals) will be reported. ScBO3 and InBO3 perovskites extend the corresponding families of perovskites with A = Y, La-Lu, and Bi and exhibit larger structural distortions. As a result of large distortions, they show, in many cases, distinct structural and magnetic properties. It is manifested in B-site-ordered monoclinic structures of ScMnO3 [Inorg. Chem. 52 (2013) 9692] and `InMnO3' [Angew. Chem.: Inter. Ed. 49 (2010) 7723]; an unusual superstructure of ScRhO3 and InRhO3 [Inorg. Chem. 52 (2013) 12005]; two magnetic transitions in ScCrO3 and InCrO3 with very close transition temperatures [Chem. Mater. 24 (2012) 2197]; and antiferromagnetic ground states and multiferroic properties of Sc2NiMnO6 and In2NiMnO6 [Inorg. Chem. 52 (2013) 14108]. Features of such perovskites, such as, transition metal doping into the A site, (Sc1-xBx)BO3, will be discussed. Special attention will be given to new spin-driven multiferroics Sc2NiMnO6 and In2NiMnO6.

Determination of Chirality of the Chiral Space Groups with Two-fold Screw Axis

Crystals are classified according to their symmetry operations into 230 space groups. A two-fold screw axis, 2₁, a symmetry operation, is frequently found in the crystal, especially non-centrosymmetric organic crystals. The two-fold screw axis shows a chiral character when molecules in the crystal tilt against the screw axis as shown in Figure. The crystals belonging to a chiral space group with two-fold screw axis such as a P2₁ or P2₁2₁2₁ exhibit two different types with opposite chirality. However, although the two crystals are not identical in a molecular arrangement, we cannot distinguish them with the present notation of space group. Recently, the idea of determining the handedness of two-fold screw axis have been successfully proposed using hierarchical interpretation of the crystals.(I. Hisaki, T. Sasaki et al., 2012) Nevertheless, the issue on a notation to distinguish chiral crystals with two-fold screw axis still remains unsettled as far as we know. Therefore, we attempt to propose a novel notation for the crystals belonging to chiral space groups with two-fold screw axis. We focus on the relationship between the absolute structure and optical activity of the crystals. We have selected alanine crystals, which belong to P2₁2₁2₁, as model crystals to discuss the notation. We have determined the absolute structure of the alanine crystals by X-ray diffraction and have measured their optical activity with Generalized High Accuracy Universal Polarimeter (G-HAUP).(M. Tanaka, N. Nakamura et al., 2012) G-HAUP is an apparatus that can measure simultaneously the linear birefringence, linear dichroism, circular birefringence, i.e., optical activity, and circular dichroism in any solid material. These experimental results have successfully correlated the absolute structure to the optical activity of the alanine crystals.

Measurement of chiroptical properties of nickel sulfate hexahydrate with G-HAUP

A crystal, which belongs to a lower crystal system than cubic one, exhibits optical anisotropies. The optical anisotropies originate from the difference in refraction and absorption between orthogonally linearly polarized lights. When molecules forming a crystal are enantiomers with the same chirality or form helical structures with the same handedness, the crystal shows chiroptical properties, which originate from the difference in refraction and absorption between right and left circularly polarized lights. The four optical phenomena are called linear birefringence (LB), linear dichroism (LD), circular birefringence (CB) and circular dichroism (CD), respectively. It had been difficult to measure CB and CD in chiral crystals with optical anisotropies because the signals of the anisotropies are three or four orders of magnitude larger than those of chiroptical properties. The Generalized High Accuracy Universal Polarimeter (G-HAUP) [1] enables us to simultaneously measure LB, LD, CB and CD of any anisotropic crystal. Nickel sulfate (NS) is achiral in the solution state. However, in the crystalline state, it forms hexahydrate and exhibits chirality since molecules are put in helical arrangements. The NS crystal belongs to an enantiomorphous space group, P4₁2₁2 or P4₃2₁2. Many researchers have reported the optical properties of NS crystal because large and good-quality crystals are readily grown. However, we consider the LB, LD, CB and CD in NS crystal should be simultaneously and completely investigated. The purpose of this study is to obtain LB, LD, CB and CD along the a axis with G-HAUP and compare the CB and CD with the results along the c axis. We measured optical rotatory power (ORP) along the c axis with G-HAUP, which agrees with the previous results [2,3]. We then prepared for some samples with chirality and anisotropy. We measured LB, LD, CB and CD spectra, respectively and will demonstrate the relation between their optical properties and structures.