Infrared femtosecond laser pulse induced permanent reduction of Eu3+ to Eu2+ in a fluorozirconate glass

We report what is believed to be the first observation of permanent photoreduction of Eu(3+) to Eu(2+) in transparent and colorless Eu(3+) -doped fluorozirconate glass at room temperature, using an infrared femtosecond laser. Difference absorption and electron-spin-resonance spectra of the glass before and after laser irradiation showed that a portion of the Eu(3+) ions in the focused part of the laser inside the glass were reduced to Eu(2+) ions after laser irradiation. It is suggested that Eu(3+) ions act as electron-trapping centers, whereas active sites in the glass matrix act as hole-trapping centers, leading to the formation of Eu(2+) ions. The observed phenomenon is inferred to be useful in the fabrication of optical memory devices with high storage density and waveguide-type micro-optical devices.     

Characterization of BCN films synthesized by radiofrequency plasma enhanced chemical vapor deposition

Boron carbonitride (BCN) films have been synthesized on Si(1 0 0) substrate by radio frequency plasma enhanced chemical vapor deposition using tris-(dimethylamino)borane (TDMAB) as a precursor. The deposition was performed at the different RF powers of 400-800 W, at the working pressure of 2×10⁻¹ Torr. The formation of the sp²-bonded BCN phase was confirmed by Fourier transform infrared spectroscopy. X-ray photoelectron spectroscopy measurements showed that B atoms were bonded to C and N atoms to form the BCN atomic hybrid configurations with the chemical compositions of B₅₂C₁₂N₃₆ (sample 1; prepared at the RF power of 400 W), B₅₂C₁₀N₃₈ (sample 2; at 500 W) and B₄₆C₁₈N₃₆ (sample 3; at 800 W), respectively. Near-edge X-ray absorption fine structure (NEXAFS) measurements indicated that B atoms were bonded not only to N atoms but also to C atoms to form various configurations of sp²-BCN atomic hybrids. The polarization dependence of NEXAFS suggested that the predominant hybrid configuration of sp²-BCN films oriented in the direction perpendicular to the Si substrate.     

Thermal stability of ZnO thin film prepared by RF-magnetron sputtering evaluated by thermal desorption spectroscopy

Thermal stability of sputter deposited ZnO thin films was evaluated by thermal desorption spectroscopy (TDS). Desorption of Zn was mainly observed from the films deposited at low O₂/Ar gas ratio and low RF power. In contrast, O₂ desorption was mainly observed from the films deposited at high O₂/Ar gas ratio and high RF power. The amount of desorbed O₂ from the film increased with increasing the O₂/Ar gas flow ratio and the RF power. Furthermore, the desorption temperature of O₂ increased with increasing the RF power during the deposition. Thermal stability of the ZnO films was controlled not only by the O₂/Ar gas flow ratio, but also applied RF power to the target.     

Vacuum‐driven fluid manipulation by a piezoelectric diaphragm micropump for microfluidic droplet generation with a rapid system response time

Recently, we developed a convenient microfluidic droplet generation device based on vacuum‐driven fluid manipulation with a piezoelectric diaphragm micropump. In the present study built on our previous work, we investigate the influence of settings applied to the piezoelectric pump, such as peak‐to‐peak drive voltage (V_p‐p) and wave frequency, on droplet generation characteristics. Stepwise adjustments to the drive voltage in ±10‐V_p‐p increments over the range of 200?250 V_p‐p during droplet creation revealed that the droplet generation rate could be reproducibly controlled at a specific drive voltage. The droplet generation rate switched within <0.5 s after the input of a new voltage. Although the droplet generation rate depended on the drive voltage, this setting had almost no influence on droplet size. The frequency over the selected range (50?60 Hz) did not markedly influence the droplet generation rate or droplet size. We show that the current fluid manipulation system can be conveniently used for both droplet generation and for rapid droplet reading, which is required in many microfluidic‐based applications.     

Amphoteric poly(vinyl alcohol) gel as a force generator: Observation of microporous gel formation with cryo-SEM

Amphoteric PVA hydrogels were made from mixed aqueous solutions of poly(acrylic acid), poly(allylamine) hydrochloride and poly(vinyl alcohol) by repetitive freezing and thawing. The hydrogen bond induced gelation produced an elastic and tough microporous hydrogel which generated tension as high as 0.3MPa corresponding to the solvent exchange from water to acetone. In this paper we show the microscopic structure of hydrogels determined by means of cryo-SEM technique and X-ray analysis.     

Seco‐Tremulanes from Cultures of the Basidiomycete Flavodon flavus BCC 17421

A new seco‐tremulane, 11,12‐epoxy‐5,6‐secotremula‐1,6(13)‐dien‐5,12‐olide ( 1 ), was isolated together with the known compounds, conocenolides A ( 2 ) and B ( 3 ), tremulenediol A ( 4 ), tremulenolide A ( 5 ), and two lanostane triterpenoids, trametenolic acid B ( 6 ), and pinicolic acid A ( 7 ), from cultures of the basidiomycete Flavodon flavus BCC 17421. Interconversion of conocenolides A/B was demonstrated. Compound 1 exhibited weak cytotoxic activities, whereas tremulenediol A showed antiplasmodial activity (IC₅₀ 8.6 μg/ml). Pinicolic acid A exhibited activity against herpes simplex virus type‐1 (IC₅₀ 15 μg/ml) as well as cytotoxic activities.     

Photoinduced Charge‐Transfer State of 4‐Carbazolyl‐3‐(trifluoromethyl)benzoic Acid: Photophysical Property and Application to Reduction of Carbon−Halogen Bonds as a Sensitizer

The photoinduced persistent intramolecular charge‐transfer state of 4‐carbazolyl‐3‐(trifluoromethyl)benzoic acid was confirmed. It showed a higher catalytic activity in terms of yield and selectivity in the photochemical reduction of alkyl halides compared to the parent carbazole. Even unactivated primary alkyl bromides could be reduced by this photocatalyst. The high catalytic activity is rationalized by considering the slower backward single‐electron transfer owing to the spatial separation of the donor and acceptor subunits.     

Preparation of Silicalite-1 Within Macroporous Silica Glass

Microcrystalline silicalite-1 was formed on the inner surface of macroporus silica glasses prepared by the sol-gel process. By heating a homogeneous precursor solution at 100°C under a hydrothermal condition, 2–5 m of plate-like particles of silicalite-1 were deposited. With an increase of mixing time of the precursor solution, the number of silicalite-1 particles increased, accompanied by the relative decrease of the particle size. Depending on the temperature and the duration of the heat-treatment of the macroporous silica, the amount of deposited silicalite-1 varied. Below 1000°C, the amount increased with the heat-treatment temperature, as a result of the competition between the precipitation of silicalite-1 and the dissolution of silica from the macroporous silica glass under a strongly basic condition. On the other hand, above 1000°C the amount of deposited silicalite-1 decreased in accordance with the decrease of the macropore diameter by the heat-treatment, because of the limited transport of the dissolved silicate species through the smaller macropores.     

Fragmentation reaction via an ipso-attack in the multistep synthesis of regioselectively functionalized Calix

The acid-catalyzed convergent synthesis of a calix[8]arene containing a regioselectively functionalized upper rim has been investigated through the isolation and identification of cyclic and acyclic byproducts. Theoretical calculations demonstrated that the synthetic process involves two types of reaction mechanisms, one of which leads to the favorably constructed framework, while the other causes undesirable fragmentation via ipso-substitution. A possible rationale is proposed to explain the overall reaction pathways which derive the calix[8]arene along with the byproducts.     

A theoretical study of catalytic hydration reactions of ethylene

The hydration reaction of ethylene, C₂H₄+H₂O → C₂H₅OH, catalyzed by oxoacids (H₃PO₄, H₂SO₄, and HClO₄) and metal cations (B³⁺, Al³⁺, Sc³⁺, Ga³⁺, La³⁺, Be²⁺, Mg²⁺, Ca²⁺, Zn²⁺, and Sr²⁺) are studied systematically by density functional theory with a BLYP functional. The reaction profiles of the main reaction and some side reactions, such as ester formation, dimerization of ethylene, and dehydrogenation of ethanol, have been determined with a variety of catalysts. In each case, the intermediate states, the transition states, and their energetics are calculated. Metal cations react more efficiently for the main reaction than oxoacids, but they also make the dehydrogenation reaction active. While the dimerization reaction is strongly affected by the acidity of the catalyst, both the acidity and basicity of the catalyst are important for the dehydrogenation reaction. Efficient formation of ethanol from ethylene over a catalyst is suggested. © 2000 John Wiley & Sons, Inc. J Comput Chem 21: 1292–1304, 2000