Integrated Chemical Process: Convenient Synthesis of Enantiopure 2‐Hydroxymethyl‐1,4‐benzodioxane Derivatives under Iterative Catalysis of CsF

One‐pot processes to enantiopure 2‐hydroxymethyl‐1,4‐benzodioxane derivatives have been established under catalysis of CsF. A sequence of O‐alkylation of catechols with enantiopure 3‐chloro‐1,2‐propanediol, tosylation of the alcohol, deprotection of the benzyl ether, and intramolecular etherification can be integrated. The O‐alkylation is also feasible with enantiopure oxiranes. All reactions, except debenzylation, are catalyzed by a single catalyst, CsF. The hydrogenative deprotection of the benzyl ether with Pd‐C is compatible with the CsF‐catalyzed reactions. The integrated protocols give rise not only to compaction of the whole processes but also to increases in overall yields.     

A practical study of semiconducting glaze for insulators

Semiconducting glaze insulators show excellent electrical performance under contaminated conditions. In order to mass‐produce this type of insulator, it is first necessary to determine the kind of materials that have such semiconducting properties and to decide on an optimum resistivity of the semiconducting glaze from a practical manufacturing standpoint. This paper describes the results of a series of investigations into the macroscopic surface resistivity needed to develop the expected superior electrical characteristics of these insulators, and the optimum distribution of volume resistivity of the glaze over the actual insulator surface, among others. The chemical composition of the glaze ingredients and the manufacturing conditions are critical for realizing the resultant glaze characteristics. © 2000 Scripta Technica, Electr Eng Jpn, 131(1): 10–18, 2000     

Preparation of ultrafine particles of silicon base intermetallic compound by arc plasma method

The purpose of this paper was to prepare ultrafine particles of Si-based intermetallic compounds, TiSi₂, MoSi₂ and VSi₂, by an arc plasma method with hydrogen addition. The properties of the prepared particles were affected by the vapor pressure ratio (Ti/Si, V/Si: 10⁻¹; Mo/Si: 10⁻³) of the constituent metals. The vaporization and condensation rates of the constituent metals should be controlled to prepare intermetallic compound particles in the case of large different vapor pressures. The vaporization rate can be controlled by H₂ concentration in the arc; for example, an increase in H₂ concentration leads to an increase in Ti fraction in the prepared particles in a Si---Ti system. The preparation of ultrafine particles of TiSi₂ was most successful from the 60-wt.% Ti raw material with the 50%-H₂ arc. MoSi₂ particles were prepared from the 85-wt.% Mo raw material with the 50%-H₂ arc. A single phase of VSi₂ particles was prepared successfully from the 60-wt.% V raw material with the 50%-H₂ arc. Another purpose was to investigate the mechanism of vaporization enhancement of particular metals from a metal mixture by hydrogen in arc plasmas. The vaporization enhancement was mainly attributed to the formation of intermediate products such as hydride and/or activity modification by hydrogen in molten metals.     

Docosahexaenoic Acid Suppresses Oxidative Stress-Induced Autophagy and Cell Death via the AMPK-Dependent Signaling Pathway in Immortalized Fischer Rat Schwann Cells 1

Autophagy is the process by which intracellular components are degraded by lysosomes. It is also activated by oxidative stress; hence, autophagy is thought to be closely related to oxidative stress, one of the major causes of diabetic neuropathy. We previously reported that docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) induced antioxidant enzymes and protected Schwann cells from oxidative stress. However, the relationship between autophagy and oxidative stress-induced cell death in diabetic neuropathy has not been elucidated. Treatment with tert-butyl hydroperoxide (tBHP) decreased the cell survival rate, as measured by an MTT assay in immortalized Fischer rat Schwann cells 1 (IFRS1). A DHA pretreatment significantly prevented tBHP-induced cytotoxicity. tBHP increased autophagy, which was revealed by the ratio of the initiation markers, AMP-activated protein kinase, and UNC51-like kinase phosphorylation. Conversely, the DHA pretreatment suppressed excessive tBHP-induced autophagy signaling. Autophagosomes induced by tBHP in IFRS1 cells were decreased to control levels by the DHA pretreatment whereas autolysosomes were only partially decreased. These results suggest that DHA attenuated excessive autophagy induced by oxidative stress in Schwann cells and may be useful to prevent or reduce cell death in vitro. However, its potentiality to treat diabetic neuropathy must be validated in in vivo studies.     

GAS CHROMATOGRAPHIC STUDIES ON VOLATILE ALCOHOLS AND ESTERS OF BEER*

A method is presented for concentrating volatile alcohols and esters from beer by distillation, and analysing six alcohols and ten esters in the distillate simultaneously by gas chromatography. Using this method, the composition of volatile alcohols and esters in different types of beer was analysed and the characteristic patterns of aroma of these beers were demonstrated. Further, the formation of the volatile fraction during fermentation was investigated and it was concluded that the formation of volatile alcohols is completed by the end of the primary fermentation period and does not occur in the lagering tank. On the other hand, ester formation continues from the middle stage of primary fermentation to the initial stage of after-fermentation.     

Formation of Apatite Coatings on an Artificial Ligament Using a Plasma- and Precursor-Assisted Biomimetic Process

A plasma- and precursor-assisted biomimetic process utilizing plasma and alternate dipping treatments was applied to a Leed-Keio artificial ligament to produce a thin coating of apatite in a supersaturated calcium phosphate solution. Following plasma surface modification, the specimen was alternately dipped in calcium and phosphate ion solutions three times (alternate dipping treatment) to create a precoating containing amorphous calcium phosphate (ACP) which is an apatite precursor. To grow an apatite layer on the ACP precoating, the ACP-precoated specimen was immersed for 24 h in a simulated body fluid with ion concentrations approximately equal to those in human blood plasma. The plasma surface modification was necessary to create an adequate apatite coating and to improve the coating adhesion depending on the plasma power density. The apatite coating prepared using the optimized conditions formed a thin-film that covered the entire surface of the artificial ligament. The resulting apatite-coated artificial ligament should exhibit improved osseointegration within the bone tunnel and possesses great potential for use in ligament reconstructions.     

Desulfurization Reactions on Surfaces of Metal Carbides: Photoemission and Density–Functional Studies

High-resolution photoemission and density functional (DF) calculations were used to study the interaction of atomic sulfur and S-containing molecules with metal carbides in which the carbon/metal ratio varies from 0.5 to 1 (M₂C and MC, M = Ti, V or Mo). In these compounds, the C sites cannot be considered as simple spectators. They moderate the reactivity of the metal centers and provide bonding sites for adsorbates. For example, the adsorption of S on TiC(001) induces a large positive shift (1.0–1.3 eV) in the C 1s core level. DF calculations give a CTiTi hollow as the most stable site for the S adatoms. There is a correlation between the adsorption energy of S or thiophene and shifts in the centroid of the metal d band induced by metal–carbon bonding in the metal carbides. The M₂C and MC carbides have difficulty obeying Sabatier’s principle for being good HDS catalysts because some of them interact too strongly with the products (M₂C stoichiometry) and the others have problems dissociating the reactants (MC stoichiometry). The addition of small Au nanoparticles is an efficient way for enhancing the HDS activity of MC catalysts. In spite of the very poor desulfurization performance of TiC and MoC, the Au/TiC and Au/MoC systems display an HDS activity comparable or higher than that of conventional Ni/MoS _x catalysts. The Au nanoparticles probably increase the HDS activity of the metal carbides by enhancing the adsorption energy of thiophene and by helping in the dissociation of H₂ to produce the hydrogen necessary for the hydrogenolysis of C–S bonds and the removal of sulfur.     

Novel wet electrospinning system for fabrication of spongiform nanofiber 3-dimensional fabric

Electrospinning method is a simple and efficient method to fabricate the nanofiber non-woven mat from a rich variety of functional materials. However, it is difficult to control the 3-dimensional structure of nanofiber fabric via electrospinning method. On that point of view, novel wet electrospinning system was established for the 3-dimensional structure control of nanofiber fabric by combining electrospinning system and wet spinning system. Spongiform Poly (glycolic acid) (PGA) nanofiber 3-dimensional fabric controlling the fiber density was successfully formed with simplicity and cheapness using novel wet electrospinning system. Comparing with usual PGA nanofiber non-woven mat prepared by conventional electrospinning method, spongiform PGA nanofiber fabric had low apparent density and high porosity. The novel nanofiber fabrication system would be very useful for the structure control of the nanofiber fabric.     

Joint of silicon nitride and molybdenum with vanadium foil,and its high-temperature strength

Joints of silicon nitride and molybdenum with a vanadium interlayer were fabricated using a vacuum hot-pressing facility. The optimum joining conditions for producing a joint with the highest shear strength were found to be as follows: a temperature of 1328 K, a mechanical pressure of 20 MPa and a bonding time of 5.4 ks. The effect of test temperature on shear strength was also examined. The strength level was initially 118 MPa at room temperature and this level gradually decreased as the test temperature rose. At 973 K, the strength level was still 70 MPa. Observations of the interface by scanning electron microscopy (SEM) and electron probe X-ray microanalysis (EPMA) revealed that a layer of reaction product V₃Si formed at the silicon-nitride-vanadium interface.     

Reaction of poly(vinyl chloride) with ethylenediamine hydrotrisulphide and properties of the products

The chemical structure and the properties of the products of the reaction of poly(vinyl chloride) (PVC) with ethylenediamine hydrotrisulphide were investigated. PVC derivatives containing a polysulphide crosslinkage and a hydropolysulphide pendant (PSC-PVC) were obtained by the reaction of PVC with ethylenediamine hydrotrisulphide in ethylenediamine (EN) as well as in EN-diglyme, and EN-benzene at 20–50°C for 0.5–5h. The chemical structure of PSC-PVC was determined from crosslinking density before and after iodine oxidation and elemental analysis. Scission of polysulphide crosslinkage in PSC-PVC by some thiols was carried out in tetrahydrofuran-triethylamine solution at 30°C for 1–4h as well as in a hot roller mill at 125–180°C for 2–8 min. The former product was photocrosslinked under ultra-violet irradiation in air and the latter showed the properties of a plastic, a leather, and a rubber with increasing weight of dioctyl phthalate.