Gas permeability and n‐butane solubility of poly(1‐trimethylgermyl‐1‐propyne)

The gas permeability and n‐butane solubility in glassy poly(1‐trimethylgermyl‐1‐propyne) (PTMGP) are reported. As synthesized, the PTMGP product contains two fractions: (1) one that is insoluble in toluene and soluble only in carbon disulfide (the toluene‐insoluble polymer) and (2) one that is soluble in both toluene and carbon disulfide (the toluene‐soluble polymer). In as‐cast films, the gas permeability and n‐butane solubility are higher in films prepared from the toluene‐soluble polymer (particularly in those films cast from toluene) than in films prepared from the toluene‐insoluble polymer and increase to a maximum in both fractions after methanol conditioning. For example, in as‐cast films prepared from carbon disulfide, the oxygen permeability at 35 °C is 330 × 10^?10 cm³ (STP) cm/(cm² s cmHg) for the toluene‐soluble polymer and 73 × 10^?10 cm³ (STP) cm/(cm² s cmHg) for the toluene‐insoluble polymer. After these films are conditioned in methanol, the oxygen permeability increases to 5200 × 10^?10 cm³ (STP) cm/(cm² s cmHg) for the toluene‐soluble polymer and 6200 × 10^?10 cm³ (STP) cm/(cm² s cmHg) for the toluene‐insoluble polymer. The rankings of the fractional free volume and nonequilibrium excess free volume in the various PTMGP films are consistent with the measured gas permeability and n‐butane solubility values. Methanol conditioning increases gas permeability and n‐butane solubility of as‐cast PTMGP films, regardless of the polymer fraction type and casting solvent used, and minimizes the permeability and solubility differences between the various films (i.e., the permeability and solubility values of all conditioned PTMGP films are similar). © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2228–2236, 2002     

CP violation in t → W + b decays in two-Higgs doublet model

Due to the large mass of top quark, CP violation in the top-quark decay is sensitive to the interactions mediated by Higgs bosons. We consider CP violation in t → W ⁺ b decay by calculating consistently in unitary gauge the CP-violating up-down asymmetry of the leptons from W boson decays in t → W ⁺ b, defined by Grz?dkowski and Gunion, in the two-Higgs doublet model with CP-violating neutral sector. The asymmetry is shown to be at most of the order of (1–4) × 10^-4 for tan β = 1.0, where tan β is the ratio of vacuum expectation values for the two neutral Higgs bosons.     

Hartree–Fock and density functional theory calculations for the reaction mechanism of nitric oxide reductase cytochrome P450nor from Fusarium oxysporum

A reaction mechanism of a nitric oxide reductase, cytochrome P450nor (P450nor) from Fusarium oxysporum, was clarified by using Density functional theory and Hartree–Fock calculations. In this reaction mechanism, molecular orbital (MO) analysis revealed that the NO ligand dissociates from the heme iron immediately after one-electron reduction by NADH, and MO energy analysis revealed that NADH acts as a one-electron reducer, not as a two-electron reducer, and that NADH has a pivotal role different from other one-electron reducers. The role of NADH is to act as a double one-electron donor (i.e. one-electron transfer occurring twice) and to combine with the NO⁻ molecule by charge recombination reaction. Our quantum chemical calculations indicated that all reactions occurring in the heme pocket are too fast to become rate-limiting. Therefore, the rate-limiting steps in the proposed reaction mechanism are the process of capturing NO and NADH into the heme pocket and the process of expelling a product generated in the heme pocket. Kinetics of these processes was discussed based on large-amplitude vibration, which helps capturing and expelling processes in a widely opened heme pocket of P450nor. The reaction mechanism proposed here well explains published experimental data.     

Experimental study of heat and mass transfer from a horizontal cylinder in downward air-water mist flow with blockage effect

An experimental study was made on convective heat and mass transfer from a horizontal heated cylinder in a downward flow of air-water mist at a blockage ratio of 0.4. The measured local heat transfer coefficients agree fairly well with the authors' numerical solutions obtained previously for the front surface of a cylinder over the ranges mass flow ratio 0–4.5×10⁻², a temperature difference between the cylinder and air 10–43 K, gas Reynolds number (7.9–23)×10³, Rosin-Rammler size parameter 105–168 μm, and dispersion parameter 3.4–3.7. Heat transfer augmentation, two-pahse to single-phase of greater than 19 was attained at the forward stagnation point. For heat transfer in the rear part of the cylinder, an empirical formula is derived by taking into account the dimensionless governing variables, that is, coolant-feed and evaporation parameters.     

Facile synthesis of platinum nanoparticle-containing porous carbons,and their application to amperometric glucose biosensing

This study describes the facile synthesis of platinum nanoparticle-containing porous carbons (Pt/C) by carbonization of freeze-dried agarose gels containing potassium tetrachloroplatinate under a nitrogen atmosphere at 800 °C. By adjusting the ratio between agarose and platinate in the freeze-dried gels, the Pt content in the final Pt/C products could be systematically varied from 0–10 wt.%. Transmission electron microscopy, inductively coupled plasma atomic emission spectrometry, X-ray photoelectron spectroscopy, Raman spectroscopy, and nitrogen physisorption measurements revealed that the Pt/C materials obtained by this method possess high surface areas (350–500 m² g⁻¹), narrow Pt nanoparticle size distributions (6 ± 3 nm) and nanocrystalline graphite –like carbon character. By immobilization of glucose oxidase on the surface of a 4 wt.% Pt/C electrocatalyst prepared by this route, a very sensitive amperometric glucose biosensor was obtained (response time <2 min, sensitivity 1.9 mA M⁻¹; and a linear response with glucose concentration up to 10 mM). The simplicity and versatility of the described synthetic method suggests its application to the preparation of carbon supported noble metal catalysts including palladium/C and gold/C.

This study describes the facile synthesis of platinum nanoparticle-containing porous carbons (Pt/C) by carbonization of freeze-dried agarose gels containing potassium tetrachloroplatinate. The Pt/C materials exhibited excellent electrocatalytic activities, as demonstrated by their successful integration into amperometric glucose biosensor

     

Liquid crystal gels cross-linked with 1,3,5-tris-(ω-methacryloyloxyalkyloxy)benzenes

A mixture of ω-(4-cyanobiphenyl-4′-yloxy)alkyl methacrylate and 1,3,5-tris-(ω-methacryloyloxyalkyloxy)benzene was heated to 200 °C at 5–10 °C/min. A large, broad exothermic transition peak was observed by differential scanning calorimetry during the first heating process. The transition indicated the formation of a networked polymer, which was then immersed for 24 h in various nematic liquid crystals, such as 4-cyano-4′-pentylbiphenyl, to give liquid crystal gels. The networked polymers and their corresponding liquid crystal gels exhibited different liquid crystal-isotropic transitions. The swelling behaviors of the liquid crystal gels were compared with those of gels cross-linked with 1,6-hexanediol dimethacrylate, trimethylpropane trimethacrylate, and pentaerythritol tetraacetate. The characteristics of liquid crystal gels cross-linked with 1,3,5-tris-(ω-methacryloyloxyalkyloxy)benzenes were studied.     

Functionalization of mesoporous silica membrane with a Schiff base fluorophore for Cu(II) ion sensing

A Schiff base (SB) immobilized hybrid mesoporous silica membrane (SB-HMM) was prepared by immobilizing a Schiff base onto the pore surface of mesoporous silica (pore size=3.1 nm) embedded in the pores of a porous anodic alumina membrane. In contrast to the non-fluorescent analogous SB molecule in homogeneous solutions, SB-HMM exhibited intense fluorescence due to emission enhancement caused by aggregation of SB groups on the pore surface. The high quantum efficiency of the surface SB groups allows SB-HMM to function as a fluorescent sensor for Cu(II) ions in an aqueous solution with good sensitivity, selectivity and reproducibility. Under the optimal conditions described, the linear ranges of fluorescence intensity for Cu(II) are 1.2-13.8(M (R(2)=0.993) and 19.4-60 (R(2)=0.992) (M. The limit of detection for Cu(II) is 0.8 μM on basis of the definition by IUPAC (C(LOD)=3.3S(b)/m).     

Integral stereocontrolled synthesis of a spiro-norlignan, sequosempervirin A: revision of absolute configuration

A novel synthetic path to sequosempervirin A was established by employing a samarium diiodide promoted intramolecular Barbier-type reaction of the lactonic iodide, in which the key structural feature, a spiro[4.5]decane ring system, could be constructed by controlling the stereochemistry of the hydroxyl group at the 8-position. The absolute configuration of natural sequosempervirin A was revised to be 4S based on this synthesis.