Magnetic and dielectric study of Bi2CuO4

Magnetic and dielectric properties have been investigated for Bi₂CuO₄, which has the same chemical formula as that of the parent materials of cuprate superconductors R₂CuO₄ (R: rare earths). Magnetization measurements show the antiferromagnetic transition of the Cu²⁺ spins at ～42 K, as reported previously. Dielectric measurements for the frequencies of 1 kHz to 1 MHz show that the dielectric constants are 100–500 at room temperature. The dielectric dispersion reveals that the dielectric response lacks spatial coherence, a property which indicates the possible existence of phase separation as suggested for La₂CuO₄. The imaginary part of dielectric response gives the activation energy of 0.22 eV, suggesting that the dielectric response is governed by the electron hopping between the Cu ions.     

Local structures and transport properties of K ions in a hollandite superstructure KxMg(8 + x)/3Sb(16 − x)/3O16

Possible local structures of K ions in the tunnel of a hollandite superstructure K_xMg_(8 + x)/3Sb_{(16 − x)/3}O₁₆ (x ≈ 1.76) were presented, and the validity of the models was confirmed by the structure refinement using single-crystal X-ray diffraction data. Additional constraint conditions were introduced in refinements so that the average structure obtained from the refinement is consistent with assumed microscopic pictures. Joint-probability density functions were calculated for specific K ions concerning the hopping process between neighboring cavities, and converted to the one-particle potentials. Three types of the energy barrier for the hopping process were seen, which were uniformly reduced applying the anharmonic atomic displacement parameters.     

A morphometric approach for the accurate solvation thermodynamics of proteins and ligands

We have developed a versatile method for calculating solvation thermodynamic quantities for molecules, starting from their atomic coordinates. The contribution of each atom to the thermodynamic quantities is estimated as a linear combination of four fundamental geometric measures of the atomic species, which are defined by Hadwiger's theorem, and the coefficients reflecting their solvation properties. This treatment enables us to calculate the solvation free energy with high accuracy despite of the limited computational load. The method can readily be applied to macromolecules in an all‐atom molecular model, allowing the stability of these molecules' structures in solution to be evaluated. © 2013 Wiley Periodicals, Inc.     

Unique inclusion behaviour of 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetraaminothiacalix[4]-arene towards small organic molecules

Tetraaminothiacalixarene 3, bearing four amino groups instead of the hydroxy groups of p-tert-butylthiacalix[4]arene 2, exhibits inclusion properties different from those of compound 2 towards small organic molecules upon crystallisation from neat solvents or guest solutions. X-ray crystallographic analyses reveal that nitromethane and acetonitrile are included into the cone-shaped cavity of compound 3, as is often seen in inclusion crystals of compound 2, whereas dichloromethane occupies a space between two distal benzene rings of compound 3, adopting a 1,3-alternate conformation. Acetic acid, which forms a dimer, fills a pore surrounded by four host molecules with a pinched cone conformation. Furthermore, guest-free crystals of compound 3 with a 1,3-alternate conformation absorb acetonitrile to give inclusion crystals with the same crystal structure as that obtained by the crystallisation. Thus, compound 3 flexibly changes its conformation according to the structures of guest compounds.     

Relationship between particle size and radiocesium in fluvial suspended sediment related to the Fukushima Daiichi Nuclear Power Plant accident

We collected fluvial suspended sediments in Fukushima after the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident and analyzed the ¹³⁷Cs concentration in bulk and size-fractioned samples to investigate the particle-size-dependent distribution of radiocesium. The ¹³⁷Cs concentration in bulk suspended sediments decreased from August to December 2011, possibly reflecting a decrease of radiocesium concentration in its source materials. Smaller particles had higher radiocesium concentrations, reflecting larger specific surface areas. Silt- and sand-size fractions occupied more than 95 % of the total ¹³⁷Cs in the suspended sediments. The contribution of clay-size fractions, which had the highest ¹³⁷Cs concentration, was quite small because of their low frequency. A line of the data showed that the particle size distribution of radiocesium was essential to evaluate the migration and distribution of radiocesium in river systems where radiocesium is mainly present as particulate form after the FDNPP accident.     

Hollow giant lipid vesicles prepared by coaxially electrospraying solutions of phospholipid and degradable polyelectrolyte

Hollow giant lipid vesicles were prepared in a single step by coaxially electrospraying separate solutions of phospholipid and a degradable polyelectrolyte. We synthesized a hydrolytically degradable cationic polyelectrolyte, poly(β-amino esters) (PBAE), and employed it as a degradable microgel template to form giant vesicles. Droplets of the phospholipid solution and the degradable polyelectrolyte solution were electrosprayed from coaxial double needles into a receiving solution. The PBAE formed a microgel by crosslinking with multivalent anions in the receiving solution, and the phospholipids formed bilayers on the microgel. Hollow giant lipid vesicles were successfully obtained and the mean diameters were 7.6 μm (C.V. 58 %). Substrates (calcein, dextran, and polymeric microparticles) were successfully encapsulated in the giant vesicles. Microscopic observations of microparticle mobility inside a giant vesicle indicated the fluidity of its aqueous interior. Investigations using fluorescently labeled PBAE also suggested the degradation of PBAE, and the release of fluorescent PBAE fragments from the encapsulated microgel, to form hollow giant lipid vesicles.     

Synthesis of Cyclobakuchiols A,B, and C by Using Conformation‐Controlled Stereoselective Reactions

Cyclohexanone with the pMeOC₆H₄ and CH₂?C(Me) substituents at the C3 and C4‐positions was prepared from (+)‐β‐pinene and converted to the allylic picolinate by a Masamune–Wittig reaction followed by reduction and esterification. Allylic substitution of this picolinate with Me₂CuMgBr ? MgBr₂ in the presence of ZnI₂ proceeded with γ regio‐ and stereoselectively to afford the quaternary carbon center on the cyclohexane ring with the CH₂?CH and Me groups in axial and equatorial positions, respectively. This product was converted to cyclobakuchiol A by demethylation and to cyclobakuchiol C by epoxidation of the CH₂?C(Me) group. For the synthesis of cyclobakuchiol B, the enantiomer of the above cyclohexanone derived from (?)‐β‐pinene was converted to the cyclohexane‐carboxylate, and the derived enolate was subjected to the reaction with CH₂?CHSOPh followed by sulfoxide elimination to afford the intermediate with the quaternary carbon center with MeOC(?O) and CH₂?CH groups in axial and equatorial positions. The MeOC(?O) group was transformed to the Me group to complete the synthesis of cyclobakuchiol B.     

Substitutional disorder in Sr2−yEuyB2−2xSi2+3xAl2−xN8+x (x≃ 0.12, y≃ 0.10)

A novel nitride, Sr_2−yEu_yB_2−2xSi_2+3xAl_2−xN_8+x (x≃ 0.12, y≃ 0.10) (distrontium europium diboron disilicon dialuminium octanitride), with the space group P2c, was synthesized from Sr₃N₂, EuN, Si₃N₄, AlN and BN under nitrogen gas pressure. The structure consists of a host framework with Sr/Eu atoms accommodated in the cavities. The host framework is constructed by the linkage of MN₄ tetrahedra (M = Si, Al) and BN₃ triangles, and contains substitutional disorder described by the alternative occupation of B₂ or Si₂N on the (0, 0, z) axis. The B₂:Si₂N ratio contained in an entire crystal is about 9:1.     

A-site-ordered perovskites with intriguing physical properties

Recent findings on intriguing physical properties of new A-site-ordered perovskite structure oxides are reviewed. High-pressure and high-temperature conditions stabilize the square-coordinated Jahn-Teller Cu (2+) ions in the original 12-fold-coordinated positions of the perovskite structure. The special-ordered arrangement of the square-coordinated A'O 4 units that align perpendicularly to each other sets a characteristic structural framework, and the presence of Cu (2+) ions at the A' site and A'-B interactions play crucial roles for the diverse and intriguing physical properties.     

Neutron powder diffraction study of the crystal and magnetic structures of BiNiO3 at low temperature

The crystal and magnetic structures of the charge ordered perovskite BiNiO₃ have been studied at temperatures from 5 to 300 K using neutron diffraction. Rietveld analysis of the data shows that the structure remains triclinic (space group ) throughout the whole temperature range. Bond-valence sum calculations based on the Bi-O and Ni-O bond distances confirm that the charge distribution is Bi³⁺_0.5Bi⁵⁺_0.5Ni²⁺O₃ down to 5 K. The magnetic cell is identical to that of the triclinic superstructure and a G-type antiferromagnetic model gives a good fit to the magnetic intensities, with an ordered Ni²⁺ moment of 1.76(3) μ_B at 5 K. However, BiNiO₃ is ferrimagnetic due to the inexact cancellation of opposing, inequivalent moments in the low symmetry cell.