Synthesis of Branched Ribo‐Polysaccharides with Defined Structures by Ring‐Opening Polymerization of 1,4‐Anhydro Ribo‐Disaccharide Monomer

Ring‐opening polymerization of a new 1,4‐anhydro‐disaccharide monomer, 1,4‐anhydro‐2‐O‐benzyl‐3‐O‐(2,3,4,6‐tetra‐O‐benzyl‐β‐D ‐galactopyranosyl)‐α‐D ‐ribopyranose, which was prepared by the glycosylation of 1,4‐anhydro‐2‐O‐benzyl‐α‐D ‐ribopyranose with 2,3,4,6‐tetra‐O‐acetyl‐1‐O‐trichloroacetimidoyl‐α‐D ‐galactopyranose, was performed for the first time with boron trifluoride etherate to give stereoregular branched ribofuranans having high molecular weights of M̄_n = 43.0×10³ and positive specific rotation of [α]_D²⁵ = +25.1 deg·dm^–1· g^–1·cm³. The repalcement of the benzyl group by a hydroxyl group gave stereoregular 1,5‐α‐D ‐ribofuranans having a β‐D ‐galactopyranose branch in every repeating unit. The copolymerization of the ribo‐disaccharide monomer with 1,4‐anhydro‐2,3‐di‐O‐benzyl‐α‐D ‐ribopyranose was also carried out to afford stereoregular 1,5‐α‐D ‐ribofuranans having randomly distributed galactopyranose branches on the main chain.     

Microstructure of Highly Syndiotactic “Living” Poly(propylene)s Produced from a Titanium Complex with Chelating Fluorine‐Containing Phenoxyimine Ligands (an FI Catalyst)

Highly syndiotactic “living” poly(propylene)s were synthesized at 25°C using a bis[N‐(3‐tert‐butylsalicylidene)‐2,3,4,5,6‐pentafluoroanilinato]titanium (IV) dichloride/MAO catalyst system, and microstructures of the polymer were analyzed by means of ¹³C NMR spectroscopy. The syndiotactic poly(propylene) contains isobutyl, isopentyl and propyl end groups, suggesting that the living polymerization of propylene was initiated via 1,2‐insertion, followed by 2,1‐insertion as the principal mode of polymerization. Pentad distribution analysis revealed that the syndiospecific polymerization proceeds under chain‐end control.     

An explicit time-domain finite element method for room acoustics simulations: Comparison of the performance with implicit methods

This paper presents the applicability of an explicit time-domain finite element method (TD-FEM) using a dispersion reduction technique called modified integration rules (MIR) on room acoustics simulations with a frequency-independent finite impedance boundary. First, a dispersion error analysis and a stability analysis are performed to derive the dispersion relation and the stability condition of the present explicit TD-FEM for three-dimensional room acoustics simulations with an infinite impedance boundary. Secondly, the accuracy and efficiency of the explicit TD-FEM are presented by comparing with implicit TD-FEM using MIR through room acoustics simulations in a rectangular room with infinite impedance boundaries. Thirdly, the stability condition of the explicit TD-FEM is investigated numerically in the case with finite impedance boundaries. Finally, the performance of the explicit TD-FEM in room acoustics simulations with finite impedance boundaries is demonstrated in a comparison with the implicit TD-FEM. Although the stability of the present explicit TD-FEM is dependent on the impedance values given at boundaries, the explicit TD-FEM is computationally more efficient than the implicit method from the perspective of computational time for acoustics simulations of a room with larger impedance values at boundaries.     

A plasmonic photocatalyst consisting of silver nanoparticles embedded in titanium dioxide

Titanium dioxide (TiO2) displays photocatalytic behavior under near-ultraviolet (UV) illumination. In another scientific field, it is well understood that the excitation of localized plasmon polaritons on the surface of silver (Ag) nanoparticles (NPs) causes a tremendous increase of the near-field amplitude at well-defined wavelengths in the near UV. The exact resonance wavelength depends on the shape and the dielectric environment of the NPs. We expected that the photocatalytic behavior of TiO2 would be greatly boosted if it gets assisted by the enhanced near-field amplitudes of localized surface plasmon (LSP). Here we show that this is true indeed. We named this new phenomenon "plasmonic photocatalysis". The key to enable plasmonic photocatalysis is to deposit TiO2 on a NP comprising an Ag core covered with a silica (SiO2) shell to prevent oxidation of Ag by direct contact with TiO2. The most appropriate diameter for Ag NPs and thickness for the SiO2 shell giving rise to LSP in the near UV were estimated from Mie scattering theory. Upon implementing a device that took these design considerations into account, the measured photocatalytic activity under near UV illumination of such a plasmonic photocatalyst, monitored by decomposition of methylene blue, was enhanced by a factor of 7. The enhancement of the photocatalytic activity increases with a decreased thickness of the SiO2 shell. The plasmonic photocatalysis will be of use as a high performance photocatalyst in nearly all current applications but will be of particular importance for applications in locations of minimal light exposure.     

Mechanical interaction between cellulose microfibrils and matrix substances in wood cell walls induced by repeated wet-and-dry treatment

We measured the lattice spacing of the cellulose in sugi (Cryptomeria japonica D. Don) and hinoki (Chamaecyparis obtusa Endl.) cell walls under wet and dry conditions. We gave all specimens repeated wet-and-dry treatments and tried to induce substantial changes in the microstructure of the wood cell wall. Macroscopic dimensions, measured using a micrometer, showed well-known behaviors, that is, shrinkage by drying and swelling by wetting, which were unaffected after the repeated wet-and-dry treatments in both longitudinal and tangential directions. On the other hand, lattice spacing, measured using an X-ray diffractometer, showed different results. In particular, d ₂₀₀ lattice spacing expanded considerably with drying in the early stages of repeated wet-and-dry treatments. The d ₂₀₀ lattice spacing in the dried specimen then became gradually smaller in the later stages, whereas no such dynamic change was observed in d ₀₀₄ lattice spacing throughout the repeated wet-and-dry treatments. Once the d ₂₀₀ lattice spacing in the dried specimen had become smaller after giving wet-and-dry treatments, it did not recover, even after soaking in distilled water for 1 month. These results suggest that repeated drying and re-swelling caused structural changes in the wood cell wall, specifically an interfacial separation between cellulose microfibrils and matrix substances.     

Development of xanthene dyes containing arylacetylenes: The role of acetylene linker and substituents on the aryl group

Fluorescent dyes possessing a variety of arylacetylenes at the 9-position of a xanthene skeleton were synthesized and their optical properties were investigated. The π system effectively expanded over the xanthene skeleton and the aryl group through the triple bond. Starting from the emission wavelength (λ_em) of 9-methyl xanthene 20 in basic DMSO solution at 536?nm, the emission wavelengths gradually shifted to the red region for methylacetylene 17 (λ_em?=?600?nm), phenylacetylene 5 (λ_em?=?636?nm), and p-CF₃-phenylacetylene 11 (λ_em?=?660?nm). On the basis of these data, we estimated the substituent effects for the red shift on the emission wavelength and rationally explained the results by DFT calculations. Furthermore, potential applicability of these fluorescent dyes to cell staining was exemplified.