MnTaO2N: Polar LiNbO3‐type Oxynitride with a Helical Spin Order

The synthesis, structure, and magnetic properties of a polar and magnetic oxynitride MnTaO₂N are reported. High‐pressure synthesis at 6 GPa and 1400 °C allows for the stabilization of a high‐density structure containing middle‐to‐late transition metals. Synchrotron X‐ray and neutron diffraction studies revealed that MnTaO₂N adopts the LiNbO₃‐type structure, with a random distribution of O^2? and N^3? anions. MnTaO₂N with an “orbital‐inactive” Mn²⁺ ion (d⁵; S=5/2) exhibits a nontrivial helical spin order at 25 K with a propagation vector of [0,0,δ] (δ≈0.3), which is different from the conventional G‐type order observed in other orbital‐inactive perovskite oxides and LiNbO₃‐type oxides. This result suggests the presence of strong frustration because of the heavily tilted MnO₄N₂ octahedral network combined with the mixed O^2?/N^3? species that results in a distribution of (super)‐superexchange interactions.     

Thermal behaviour under pressure of the thermotropic cubic mesogen 4'- n -alkoxy-3'-nitrobiphenyl-4-carboxylic acids

The thermal behaviour of members of a homologous series which exhibits the optically isotropic cubic phase, the 4'- n -alkoxy-3'-nitrobiphenyl-4-carboxylic acids having alkoxy chains containing 16, 20 and 22 carbon atoms (referred to as ANBC-16, -20 and -22, respectively) was investigated under pressures up to 200-400 MPa by high pressure differential thermal analysis. In the phase diagram of ANBC-16 obtained on heating, a triple point was estimated at 54 ±1 MPa and 205 ±1°C for the SmC, Cub and SmA phases. It was found that the X phase is formed on cooling under all pressures, while appearing on heating at high pressures above about 54 MPa. Thus the X phase appears monotropically between the SmA and Cub phases in the low pressure region and enantiotropically between the SmA and SmC phases under higher pressures. It is strongly suggested that the X phase is a columnar mesophase. For ANBC-20 and -22, the cubic phase tends to be destabilized with increasing pressure. The temperature region of the cubic phase of ANBC-20 becomes narrower with increasing pressure and a triple point for the SmC, Cub and I phases is estimated to be at about 309 MPa. On the other hand, the cubic phase of ANBC-22 is still observed at the highest pressure examined.     

Effect of sorbed molecules on the resistivity of alkali metal-graphite intercalation compounds

Alkali metal-graphite intercalation compounds with the composition of MC₂₄ (M=K, Rb, Cs) were prepared by heating a mixture of MC₈ (saturated compound) and graphite sheet (Grafoil) at 350-450 °C. The resistivity perpendicular to the layer planes (ρ_c) of the resulting compounds was determined by the two-terminal method. The anisotropy factor of the resistivity, (ρ_c/ρ_a), of KC₂₄ prepared from Grafoil was ∼130, being about 1/6-1/10 in magnitude compared with that of KC₂₄ prepared from highly oriented pyrolytic graphite. The resistivity change during sorption of hydrogen (at 90 K), ethylene (at 194 K) and acetylene (at 194 K) was determined. The resistivity of MC₂₄ increased with increase of the sorbed amount of H₂. The magnitude of the increase was in the order KC₂₄>RbC₂₄>CsC₂₄. This resistivity increase was considered to be due to the expansion along c-direction which reduces the charge-transfer interaction between the carbon layers and potassium ions, resulting in the decrease of the density of the conduction electron. The resistivity of MC₂₄ increased extensively during sorption of C₂H₄ and C₂H₂. It was discussed in connection with the in-plane structural transition and chemical interaction between alkali metal ions and sorbed molecules.     

Phase behaviour of three homologues of the discotic hexa-n-alkoxyanthraquinones under pressure

The phase transition behaviour of three homologous discotic mesogens, the hexa-n-alkoxyanthraquinones HOAQ(n), n indicating the number of carbon atoms in the alkoxy group, was investigated under hydrostatic pressures up to 500 MPa using a high pressure differential thermal analyser. The T vs. P phase diagrams of HOAQ(6), HOAQ(8) and HOAQ(9) were constructed for solution- (Cr₀) and melt-crystallized (Cr₁) samples of the compounds. HOAQ(6) shows the reversible Cr₀-rectangular columnar phase (Col_r)-hexagonal columnar phase (Col_h)-isotropic liquid (I) phase sequence at atmospheric pressure. The stable Col_r phase of HOAQ(6) has a decreased temperature range with increasing pressure and then the Col_r phase disappears under pressures above about 350 MPa; instead the Cr₀-Col_h-I phase sequence is exhibited. For HOAQ(8), the solution-grown sample exhibits the stable Cr₀-Col_h-I phase sequence at atmospheric pressure. Applying pressure to the solution-grown sample induces the formation of the stable Col_r phase in the pressure region between 10 and 350 MPa, leading to the Cr₀-Col_r-Col_h-I phase sequence. The pressure-induced Col_r phase disappears under higher pressures. The melt-cooled sample of HOAQ(8) shows the formation of the metastable crystal (Cr₁), unknown mesophase (X) and Col_r phases at lower temperatures under atmospheric pressure, and exhibits the reversible Cr₁-X-Col_r-Col_h-I phase sequence on subsequent thermal cycles. The metastable phase sequence was observed under pressures up to 100 MPa, but the phase transitions were too small to be detected under higher pressures. In HOAQ(9) the stable Cr₀-Col_h-I phase sequence is observed at all pressures, while the melt-cooled sample shows the metastable Cr₁-Col_r-Col_h-I phase sequence under pressures up to 300 MPa. The metastable Col_r phase disappears under higher pressures.     

The conformation of alkyl cyclohexanones and terpenic ketones. Interpretation for the ‘alkylketone effect’ based on the CH/π(CO) hydrogen bond

Ab initio MO calculations were carried out, at the MP2/6-311++G(d,p)//MP2/6-311G(d,p) level, to investigate the Gibbs free energy of the conformational isomers of 2-alkyl, 3-alkyl, and 4-alkyl cyclohexanones. The calculation gave results consistent with the general trend experimentally found. The genesis of stabilization of the axial conformers in 2- and 3-alkyl cyclohexanones, as compared to the structurally corresponding cyclohexane derivatives, was sought in the context of the attractive CH/π(CO) hydrogen bond. In support of this hypothesis, short nonbonded distances have been noted between CHs in the alkyl group and the carbonyl carbon in the relevant axial conformers. Calculations were also carried out to study the conformational energies of several terpenic ketones. For isomenthone, more than a half molecular fraction (ca. 55%) has been suggested to be in the isopropyl-axial conformation, while for isocarvomenthone ca. 77% has been suggested to be in the axial-isopropyl conformation; this is consistent with bibliographic experimental data. A crystallographic database search has provided results compatible with this conclusion. We suggest that the relative stability of the axial alkyl substituent, often observed in terpenic and steroidal ketones is rationalized in terms of an attractive molecular force, the CH/π(CO) hydrogen bond.     

High-throughput assay of nitric oxide metabolites in human plasma without deproteinization by lab-on-a-chip electrophoresis using a zwitterionic additive

In order to develop a high-throughput assay for nitric oxide metabolites, nitrite (NO2-) and nitrate (NO3-), in biological fluids, we have investigated the simultaneous determination of them using an electrophoretic lab-on-a-chip (microchip capillary electrophoresis, MCE) technique. In this study, in order to establish an MCE assay process without deproteinization, the addition of a zwitterionic additive into the running buffer to reduce the adsorption of protein onto the surface of channel was investigated. Initially, some zwitterionic additives were investigated by making a comparison of relative standard deviations (RSDs) of the migration times for NO2(-) and NO3(-) on capillary electrophoresis. From the results of our comparison of the RSD values, 2% (w/w) N-cyclohexyl-2-aminoethanesulfonic acid (CHES) was selected. As a result of the application of the running buffer with CHES to the MCE process, the complete separation of NO2(-) and NO3(-) in human plasma without deproteinization was achieved within 1 min. Since the RSD values of the positions of the peaks were less than 2.3%, beneficial reduction effects on MCE were suggested. When we used an internal standard method in order to correct the injection volume, the RSDs of the peak heights and areas were less than 10%, and the correlation coefficients of spiked calibration curves ranging from 0 to 350 microM were 0.999 and 0.997 for NO2(-) and NO3(-), respectively. The limits of detection (S/N=3) were 53 microM for NO2(-) and 41 microM for NO3(-). Moreover, the correlation coefficients in excess of 0.99 between the MCE method and a conventional Griess method were achieved for both NO2(-) and NO3(-). Consequently, the possibility of establishing a high-throughput assay process was obtained by utilizing 2% (w/w) CHES to reduce protein adsorption.     

Identification of two types of exchangeable sites for monovalent copper ions exchanged in MFI-type zeolite

Three different approaches have been used to characterize the state of exchanged copper ions in copper-ion-exchanged MFI (CuMFI) samples. (1) Two types of an ion-exchangeable site with different adsorption properties for N(2) or CO molecules were identified depending on the pre-treatment temperature (723 or 873 K) of a sample prepared by using an aqueous solution of CuCl(2). (2) The state of the active sites formed by the evacuation of a sample at 873 K that had been prepared using a mixture solution of aqueous NH(4)CH(3)COO and Cu(CH(3)COO)(2) was analysed utilizing both (13)C(18)O and (12)C(16)O to identify the two types of active adsorption sites for CO molecules. (3) CuMFI samples prepared by the ion-exchange method employing anhydrous CuCH(3)COO showed a surprising adsorption feature characterized by a single IR band occurring at 2159 cm(-1) due to the adsorbed CO molecules, but there was no corresponding IR band due to adsorbed N(2) molecules. A successful preparation of CuMFI, in which the monovalent copper ions exclusively occupied another one of the two types of ion-exchangeable sites, was also carried out utilizing the solid-ion exchange method using Cu(CH(3)COO)(2).H(2)O. This site exhibits an IR band occurring at 2151 cm(-1) for CO molecules and also acts as an active site for N(2) molecules. These experimental data correlate, and clearly indicate that there are at least two types of exchangeable sites for copper ions in MFI-type zeolites.     

Ogawa’s nipponium and its re-assignment to rhenium

Foundations of Chemistry - We re-examine the history of the element “nipponium” discovered by a Japanese chemist Masataka Ogawa in 1908. Since 1996 H.K. Yoshihara has made extensive...     

Pochonins K-P: new radicicol analogues from Pochonia chlamydosporia var. chlamydosporia and their WNT-5A expression inhibitory activities

WNT-5A, a secretory glycoprotein, is related to the proliferation of dermal papilla cells. To develop a hair-growth stimulant, we have been searching for an inhibitor of WNT-5A expression, and have identified an active compound, radicicol (1), and isolated six new radicicol analogues, pochonins K-P (2-7), together with ten known radicicol analogues, including monorden analogue-1 (8), pochonin E (9), and pochonin F (10), from a culture broth of the fungus Pochonia chlamydosporia TF-0480. This report describes the structural elucidation of 2-7, determination of the stereochemistries of 8-10, and their biological activities against WNT-5A.