Absolute structure of shoreaketone: a rotational isomeric resveratrol tetramer in Dipterocarpaceaeous plants

A rotational isomeric shoreaketone (1), identified as a skeletal member of resveratrol tetramers, was isolated from three species of Dipterocarpaceaeous plants: Shorea uliginosa, Shorea hemsleyana, and Vateria indica. The structure was elucidated by spectroscopic analysis including NMR experiments and their absolute configurations determined based on circular dichroism data. Shoreaketone has 10 asymmetric carbons and a framework of fused heptacyclic ring system including a spiro ring and an α,β-unsaturated carbonyl group that has not been reported in any other natural product. NMR experiments using shoreaketone indicate the presence of two conformers due to restricted rotation of a C–C bond in solution. The complex stereochemistry is due to its skeleton, 10 asymmetric carbons, and a chiral axis. The conformations of rotational isomeric stilbenoid were studied by variable-temperature NMR, ROESY, a skeletal conversion. The coexistence of two conformers for shoreaketone (1) was confirmed to be 1a and 1b, in which the diaryl-dihydrobenzofuran moiety (unit 1B) is extended below or above the plane of the cyclopentane ring (unit 1A), respectively.     

Two novel blue pigments with ellagitannin moiety, rosacyanins A1 and A2, isolated from the petals of Rosa hybrida

Two novel blue pigments, rosacyanins A1 and A2, were isolated from the petals of Rosa hybrida cv. ‘M'me. Violet’. Their structures were elucidated on the basis of high-resolution Fourier transform ion cyclotron resonance mass spectroscopy (HR-FT-ICR-MS), FABMS/MS/MS, ¹H, ¹³C and two-dimensional NMR. The molecular formulas of rosacyanin A1 (1) and A2 (2) are C₅₆H₃₇O₃₁ and C₆₃H₄₁O₃₅, respectively. The structures of rosacyanins A1 and A2 consisted of a common chromophore containing cyanidin with a galloyl group link between positions 4 and 5 of the hydroxyl group of the flavylium nucleus and tellimagrandins (1 or 2). These pigments in which anthocyanidin nuclei linked to ellagitannin through an ether bond are the first compounds isolated from natural sources.     

Electronic structures of Pt-Co and Pt-Ru alloys for CO-tolerant anode catalysts in polymer electrolyte fuel cells studied by EC-XPS

CO tolerance at pure Pt, Pt-Co, and Pt-Ru alloys was investigated by X-ray photoelectron spectroscopy combined with an electrochemical cell (EC-XPS) in order to discover a hint for designing higher performance anode catalysts. After the electrochemical stabilization and/or CO adsorption, these electrodes were immediately transferred to the XPS chamber without exposure to air to avoid contamination of the surfaces. It was revealed that alloying with Co or Ru modified the electronic structures of Pt atoms, resulting in a positive core level (CL) shift of Pt 4f(7/2) which could weaken the Pt-CO interaction. For the Pt-Co alloy electrode, the Pt 4f(7/2) CL shift remained after the electrochemical stabilization despite Co dissolution and formation of a Pt skin layer. Changes in surface core level shifts (DeltaSCLSs) induced by CO adsorption were evaluated and related to the CO adsorption energy. The values of DeltaSCLS at these alloys were smaller than that of pure Pt, indicating that Ru and Co are effective elements to weaken the bond strength of Pt-CO.     

Facile synthesis of highly congested 1,2-diphosphinobenzenes from bis(phosphine)boronium salts

[Structure: see text] Bis(phosphine)boronium salts 3a-c were designed and prepared as key building blocks for the synthesis of highly congested diphosphinobenzenes. The preparation of sterically hindered ortho-phenylene-bridged diphosphines 1a-c was achieved by the reaction of the bis(phosphine)boronium salts 3a-c with difluorobenzenechromium complex 2 and subsequent removal of the BH2 group. The steric nature of diphosphine 1a was revealed in single-crystal X-ray analysis of its Rh complex.     

Synthesis of high surface area Al-containing mesoporous silica from calcined and acid leached kaolinites as the precursors

Al-containing mesoporous silicas were synthesized by hydrothermal treatment of microporous silica prepared by selectively acid leached metakaolinites with Si/Al = 3.9-92.5 mixed with a surfactant of cetyltrimethylammonium bromide (CTABr). The specific surface area of the products increased with higher surfactant/microporous silica (surf/Si) ratio and Si/Al ratio of the microporous silica, reaching about 1400 m2/g at CTABr/Si 0.1 and Si/Al 40. The XRD patterns of these products show a hexagonal (100) peak with the lattice parameter a0=4.2-4.3 nm and the N2 adsorption isotherms show steep increase of adsorption between relative pressure of 0.3 and 0.4. Hexagonal mesoporous microstructure is observed by high resolution TEM. The pore size distributions of the products show a sharp peak at 2.8 nm by the BJH method. The high specific surface area of the present mesoporous samples is attributed to the lower matrix density and surface roughness of mesopore wall. The highest specific surface area of the products reached up to 1420 m2/g and this value is apparently higher than those reported in hexagonal mesoporous silicas. A unique microporous structure of the starting material is thought to be related to achieve such a high specific surface area of the products.     

Preparation of sodium oleate/layered double hydroxide composites with acid-resistant properties

MgAlCO3 type layered double hydroxides (LDHs) with Mg/Al ratios ranging from 2 to 5 were synthesized by coprecipitation. Composites with sodium oleate/LDH were prepared by ion exchange and reconstruction of the LDH in sodium oleate solution. The amount of sodium oleate in the composites prepared by this reconstruction method was higher than that in samples prepared by the ion-exchange method. The basal spacings of the LDHs increased to 3.9 and 1.8 nm after synthesis of the composites, these spacings being in good agreement with models based on the assumption that the oleate ions are intercalated as bilayer and/or micelle structures, and as monolayers in the LDH interlayers, respectively. The number of sorbed oleate ions was higher than calculated from the anion-exchange capacities of the LDHs in most of the samples, increasing as the Mg/Al ratios of the LDHs were increased from 2 to 5. These results suggest that the oleate ions are present not only in the interlayers but also on the surfaces of the LDH particles. The acid-resistant properties of the composites were found to be much higher than for the pure LDHs. It is thus confirmed that the surfaces of the LDH particles in the composites are mostly covered with sorbed oleate ions and that the composites are good candidates as drug delivery materials.     

Evolution of two-step structural phase transition in Fe1+dTe detected by low-temperature x-ray diffraction

The low-temperature crystal structure of Fe_1.13Te, which exhibits an anomalous two-step magnetic transition, was clarified by the systematic x-ray diffraction measurements. It was found that two-step structural phase transition, tetragonal–orthorhombic–monoclinic, occurred correspondingly to the two-step magnetic transition. The detailed analysis of the profile at 5 K indicated the coexistence of the minor orthorhombic area inside the major, monoclinic lattice, which could explain the lower-shift (suppression) of the antiferromagnetic transition temperature in Fe_1.13Te and suggest a possibility of superconductivity at the domain boundary.     

A detection method of symmetry restoration process of attractor merging crisis

We propose a method to detect the approach to a specific unstable symmetric mediating solution, which characterises the symmetry restoration process close to a bifurcation point of an attractor merging crisis. This method captures a temporary restoration of the symmetry, and it does not require neither the exact parameter value of the bifurcation point nor the mediating solution. We study a forced XY model as an example and show that this method figures out the singularity caused by the approach from the asymmetric side of the crisis. An analysis of the repulsively coupled Stuart Landau system suggests the feasibility of this method even when the mediating solution is a symmetric torus.     

Synthesis of Hyperbranched Polysaccharide by Thermally Induced Cationic Polymerization of 1,6-Anhydrohexopyranose

The thermally induced cationic polymerizations of 1,6-anhydro-β-D -glucopyranose ( 1a ), 1,6-anhydro-β-D -mannopyranose ( 1b ) and 1,6-anhydro-β-D -galactopyranose ( 1c ) as a latent cyclic AB₄-type monomer were carried out using (S-2-butenyl)tetramethylenesulfonium hexafluoroantimonate ( 2 ) as an initiator. The solution polymerization in propylene carbonate proceeded without gelation to produce the water-soluble hyperbranched polysaccharides ( 3a-c ) with controlled molecular weights and narrow polydispersities. The degree of branching (DB), estimated by the methylation analysis of 3a-c , was in the range of 0.38 – 0.49. The thermally induced cationic polymerization of 1a-c using 2 is a facile method leading to a hyperbranched polysaccharide with a high DB value.