Stereoselective Syntheses of all the Possible Stereoisomers of Coronafacic Acid

An efficient and stereoselective syntheses of all the possible stereoisomers of coronafacic acid (CFA) has been developed. The stereochemistries of C3a and C7a were controlled in a diastereoselective Diels-Alder type cycloaddition using a chiral auxiliary. CFA and 6-epi-CFA were synthesized by hydrogenation of a common intermediate. During the synthesis of 6-epi-CFA, we established that its cis-fused configuration is important for the introduction of C4-C5 double bond by dehydration. This report is the first practical synthesis of both 6-epi-CFA, and its enantiomer.     

Temporal analysis of products (TAP) study on oxygen storage properties over Pt−Rh/CeO2 catalyst

The oxygen storage capacity of CeO₂, Ce_0.9Pr_0.1O₂, Pt?Rh/CeO₂ and Pt?Rh/Ce_0.9Pr_0.1O₂ was investigated by conventional GC pulse method and transient pulse techniques. It is shown that incorporation of PrO_y into CeO₂ matrix strongly promotes oxygen storage capacity (OSC) measured using the transient pulse technique. The improvement of OSC at low temperature is observed in Pt?Rh loaded onto CeO₂ and Ce?Pr catalysts.     

The annealing behavior of hydrogen implanted into Al-1.5 at.% Si alloy

We have studied effects of added elements as well as defects on trap-sites of hydrogen in metals. For the purpose, we observed depth profiles and thermal behaviors of hydrogen implanted into Al-1.5 at.% Si alloy samples in an implantation-temperature range of liquid nitrogen temperature (LNT) to 373 K at different doses. The results were compared with those for pure aluminum samples. It was found that hydrogen is trapped as molecules in grain boundaries of Al/Si.     

A SYNTHETIC ROUTE TO 3-METHYLTHIO-2-ALKANONES STARTING FROM 3-ALKYL-2,4-PENTANEDIONES

Abstract

An efficient preparation of a 3-methylthio-2-alkanone (1) has been realized by the reaction of a 3-alkyl-2,4-pentanedione (8) with one mol-equiv of S-methyl methanethiosulfonate (4) in the presence of excess EtONa in EtOH. Furthermore, treatment of 8 with 4 and K₂CO₃ in refluxing acetone, followed by addition of MeOH and heating the resulting mixture, gave 1 in a high yield. These methods were applied to synthesis of pseudoionone.     

Effect of the protonation level of poly(o-phenylenediamine) (PoPD) on the ac impedance of humidity-sensitive PoPD/poly(vinyl alcohol) composite film

A composite film consisting of poly(o-phenylenediamine) (PoPD) and poly(vinyl alcohol) (PVA) has been prepared, and the effect of the protonation level of PoPD on the response of the composite to humidity been investigated by ac impedance measurements. The electrochemical system of the PoPD/PVA composite in a humid atmosphere is represented by an electrochemical equivalent circuit containing film (R_film, C_film), Warburg (W) and interfacial (R_ct, C_dl) impedance. R_film was increased with decreasing protonation level of the PoPD in relative humidity regions higher than 40%, but it was almost independent of the protonation level in humidity regions lower than this percentage.     

Ion chromatographic system with a novel switching suppression device

Ion chromatography (IC) has been a powerful tool for measuring ionic species in environmental samples such as tap, river and drain waters. Suppressor modules (membrane and disposable column types) have been used for reducing the background of a baseline. A new type of suppressor device, which has a suppressor resin and switching valve was developed. Fresh ionic resin is introduced into a groove for each analysis to perform the suppression of the working eluent. The eluent composition for obtaining higher sensitivity and better resolutions among ionic species and carbonate ion was also investigated. Although carbonate buffers are used for ion separation in general, the separation of carbonate ion from other ions was not achieved. A borate eluent resulted in good resolutions and higher sensitivity. A new column was also developed for obtaining higher column efficiency and resolution. The optimization of anion separation using a new IC system (IC-2001) that consists of a new suppressor device, an anion-exchange column (TSKgel SuperIC-Anion, 150x4.6 mm), an autosampler, a conductivity cell and a pump in a compact module is described.     

Piled-lamellae structure in polyethylene film and its deformation

The fine structure of polyethylene film has been investigated by using a high-resolution scanning electron microscope equipped with a field emission source. The original film surface of a-axis-oriented blown polyethylene film and the surface of a necked region formed by drawing the film in the machine direction were observed. High magnification electron micrographs indicate that the basic unit of internal texture of this film consists of piled-lamellae units, each pile containing three to ten lamellar crystal sheets. The piled-lamellae unit acts as one body and does not separate into single lamellae during deformation. Many tie fibrils are formed between adjacent piled-lamellae units, when the film is drawn in the machine direction. Although little attention has been given to this mechanism, it is important in deformation. This fact seems to be reflected in different shapes of the stress-strain curves of films drawn the machine direction and perpendicular to it.     

Infrared spectroscopic studies of polymer transitions. III. Effects of sodium ion on glass transitions in styrene-based ionomers

The glass transition in styrene-based ionomers was investigated by means of infrared spectroscopy and differential scanning calorimetry (DSC). Transition temperatures were determined from the temperature dependence of the peak absorbances of the 1700 and 1745 cm^?1 bands. These transition temperatures agreed with glass transition temperatures (T_g) determined by DSC. With increasing degree of ionization, T_g and the enthalpy ΔH of the residual intermolecular hydrogen bonding increased. The values of T_g obtained were analyzed by the theory of Fox and Loshaek for the effect of crosslinks. It is concluded that sodium ions probably from ionic domains and act as crosslinks to reinforce the residual hydrogen bonding and may increase T_g. The absorbance at 1560 cm^?1 (ν_COO^?) did not change at T_g. This suggests that the glass transition observed here is not due to the onset of the mobility in ionic domains, as has been proposed for ethylene-based ionomers on the basis of dielectric measurements.     

Localization-dependent photoluminescence spectrum of biexcitons in semiconductor quantum wires

We study exciton and biexciton spectra in disordered semiconductor quantum wires by means of nanophotoluminescence spectroscopy. We demonstrate a close link between the exciton localization length along the wire and the occurrence of a biexciton spectral line. The biexciton signature appears only if the corresponding exciton state extends over more than a few tens of nanometers. We also measure a nonmonotonous variation of the biexciton binding energy with decreasing exciton localization length. This behavior is quantitatively well reproduced by the solution of the single-band Schr?dinger equation of the four-particle problem in a one-dimensional confining potential.