Electroreductive block copolymerization of dichlorosilanes in the presence of disilane additives

The electroreductive polymerization of dichloromethylphenylsilane in the presence of triphenylsilyl group‐containing disilanes such as hexaphenyldisilane followed by the electroreductive termination with chlorotriphenylsilane afforded triphenylsilyl group‐terminated polymethylphenylsilane in 15–32% yield. The isolated polymethylphenylsilane (M_n = 3350 g mol^?1, M_w/M_n = 1.4) was found to react as a macroinitiator to copolymerize with dibutyldichlorosilane under electroreductive conditions producing the corresponding block copolymer (M_n = 4730 g mol^?1, M_w/M_n = 1.2) in 38% yield. The ratio of monomer units (? MeSiPh? to? BuSiBu? ) of the copolymer was determined to be 75:25 using ¹H NMR analysis, which was in good agreement with the calculated ratio (74:26) on the assumption that molecular weight of the macroinitiator was not changed. The block structure of the resulting copolymer, poly(methylphenylsilane)‐block‐poly(dibutylsilane), was also confirmed by comparing its ¹H NMR and UV absorption spectra with those of polymethylphenylsilane, polydibutylsilane and a statistical copolymer prepared by electroreductive polymerization of dichloromethylphenylsilane with dibutyldichlorosilane. This method is applicable to the preparation of other types of macroinitiator such as triphenylsilyl group‐terminated polydibutylsilane, and polydibutylsilane‐block‐polymethylphenylsilane was also obtained using this macroinitiator. Copyright © 2011 Society of Chemical Industry     

N.m.r. study of egg yolk lecithin in aromatic solvents. Magnetic nonequivalence in the methylene protons of the fatty acyl chains

¹H and ¹³C n.m.r. chemical shifts and also spin-lattice relaxation times of phospholipids, mainly egg yolk lecithin, were measured in organic solvents, especially aromatic solvents. The use of aromatic solvents promotes the difference in the magnetic shielding environment of the internal methylene protons of the fatty acyl chains and as a result, a doublet peak for the methylene groups was observed in the solvents, especially mesitylene. The ¹H and ¹³C n.m.r. T₁ measurements indicate the remarkable gradient in the motional freedom along the fatty acyl chains as well as the marked decrease in the motional freedom of the polar head group and also, the high-field component of the doublet peak for internal methylene protons has a shorter T₁ value than the low-field component. Thus, it was concluded that the low-field component in the doublet comes from the methylene protons located relatively in the neighbourhood of the carbonyl groups and the high-field component the methylene protons located relatively in the neighbourhood of the terminal methyl groups of the fatty acyl chains.     

Improving the gas recovery and separation efficiency of a hydrate-based gas separation

Efficient gas recovery and separation in a hydrate-based system was investigated for a model gaseous mixture of R22 and nitrogen. The formed hydrate settled in the recovery vessel; excess water was recycled and the hydrate was subsequently decomposed by releasing pressure from the vessel. The gas uptake rate of R22 gas from the vapor phase and the gas recovery rate from the hydrate were determined from hydrate formation and decomposition, respectively. The gas recovery rate of R22 gas gradually increased with time. On the contrary, the nitrogen gas recovery rate was a maximum in the initial stage of hydrate decomposition. A high separation factor (S.F.) was achieved by first separating the N₂-rich gas generated during initial hydrate decomposition. An efficient hydrate-based gas separation and recovery process is proposed.     

Synthesis and Initial Characterization of a Selective,Pseudo-irreversible Inhibitor of Human Butyrylcholinesterase as PET Tracer

The enzyme butyrylcholinesterase (BChE) represents a promising target for imaging probes to potentially enable early diagnosis of neurodegenerative diseases like Alzheimer's disease (AD) and to monitor disease progression in some forms of cancer. In this study, we present the design, facile synthesis, in vitro and preliminary ex vivo and in vivo evaluation of a morpholine-based, selective inhibitor of human BChE as a positron emission tomography (PET) tracer with a pseudo-irreversible binding mode. We demonstrate a novel protecting group strategy for ¹⁸F radiolabeling of carbamate precursors and show that the inhibitory potency as well as kinetic properties of our unlabeled reference compound were retained in comparison to the parent compound. In particular, the prolonged duration of enzyme inhibition of such a morpholinocarbamate motivated us to design a PET tracer, possibly enabling a precise mapping of BChE distribution.     

Thermal Stability,Optical Transmittance,and Refractive Index Dispersion of La2O3–Nb2O5–Al2O3 Glasses

La₂O₃–Nb₂O₅–Al₂O₃ high‐refractive‐index glasses were fabricated by containerless processing, and the glass‐forming region was determined. The thermal stability, density, optical transmittance, and the refractive index dispersion of these glasses were investigated. All the glasses were colorless and transparent in the visible to near infrared (NIR) region and had high refractive index with low wavelength dispersion. Some of these glasses were found to have significantly high glass‐forming ability. These results indicate that the ternary glasses are suitable for optical applications in the visible to NIR region. The effects of the substitution of Al₂O₃ for Nb₂O₅ on optical properties were discussed on the basis of the Drude–Voigt equation. It was suggested that the substitution of Al₂O₃ for Nb₂O₅ increased the molecular density and suppressed a decrease in the refractive index, even when both the average oscillator strength and inherent absorption wavelength decreased in La₂O₃–Nb₂O₅–Al₂O₃ glasses. These results are helpful for designing new optical glasses controlled to have a higher refractive index and lower wavelength dispersion.     

Structural analysis of polyacenic semiconductor (PAS) materials with Xenon NMR measurements

Structural analysis of the polyacenic semiconductor (PAS) material prepared by the pyrolysis of phenol-formaldehyde resin at relatively low temperature (680 °C) has been performed by applying ¹²⁹Xe nuclear magnetic resonance (NMR) measurements. One can obtain information on the microporous structure of the PAS material through adsorption of Xe atoms, since a ¹²⁹Xe nucleus is a very sensitive probe of its microscopic environment. All the introduced Xe atoms were adsorbed on the internal surface of the pure PAS sample, which indicated remarkably large surface area of the PAS material. The average pore size of the pure PAS sample has been determined to be 7.7 ± 1.6 Å from the pressure dependence of the Xe NMR chemical shift. In connection with the application of the PAS material to the electrode of the Li rechargeable battery, changes in the Xe NMR spectrum brought about by extrinsic additives such as binder, electrolyte solvent, and the doped Li have been investigated. In particular, it has been found that the Li-doping entirely prevents Xe atoms from entering into the micropores of the PAS material, probably due to adsorption of the solvent molecules on the internal surface of the micropores.     

Design and synthesis of zero–zero-birefringence polymers in a quaternary copolymerization system

We designed and synthesized quaternary copolymers of methyl methacrylate (MMA), 2,2,2-trifluoroethyl methacrylate (TFEMA), benzyl methacrylate (BzMA), and 3,3,5-trimethylcyclohexyl methacrylate (TMCHMA) and we investigated their birefringence, thermal properties, and other optical properties. When the copolymer composition was MMA/TFEMA/BzMA/TMCHMA = 50:38:8:4, 40:30:7:23, or 30:21:7:42 (wt%), a zero–zero-birefringence polymer that exhibited neither orientational nor photoelastic birefringence was obtained. We demonstrated that such zero–zero-birefringence polymers with a variety of compositions could be successfully prepared in the quaternary system by using the same compensation method as applied in ternary random copolymerization. We also demonstrated that the glass-transition temperature (T_g) and refractive index (n_D) of these copolymers could be controlled with high accuracy while retaining their zero–zero-birefringence property. We can therefore predict the type of birefringence, the T_g, and the n_D of a particular copolymer before polymerization. Zero–zero-birefringence polymers with the most appropriate characteristics can then be synthesized selectively by quaternary copolymerization.     

Preparation of bismuth nanowire encased in quartz template for Hall measurements using focused ion beam processing

ABSTRACT: Forming electrodes on opposite sides of an individual bismuth nanowire was attempted to prepare for Hall measurements. Although a 1-mm-long bismuth nanowire which is completely covered with a quartz template has been successfully fabricated to prevent oxidation, it is very difficult to attach Hall electrodes on the opposite sides of the nanowire due to the quartz covering. One side of the cylindrical quartz template was removed by polishing without exposure of the nanowire to the atmosphere; the thickness between the polished template surface and the nanowire was estimated to be several micrometers. Focused ion beam processing was successfully employed to expose both surfaces of the nanowire under high vacuum by removing part of the quartz template. A carbon thin film was then deposited in situ on the wire surface to fabricate an electrical contact on the bismuth nanowire sample. Furthermore, the energy dispersive X-ray analysis was performed to the area processed by focused ion beam, and the bismuth component of the nanowire was successfully detected. It was confirmed that the focused ion beam processing was applicable to attach electrodes to bismuth nanowire for Hall measurement.     

Disorders and oxygen vacancies in p-type Sn2B2O7 (B = Nb,Ta): Role of the B-site element

Sn₂Nb_2−xTa_xO₇ (x = 0.0–2.0) with pyrochlore structure is a promising material for p-type oxide semiconductors. A systematic study of its Nb/Ta ratio indicated that the hole–generation efficiency of the Nb end (Sn₂Nb₂O₇) was an order of magnitude lower than that of the Ta end (Sn₂Ta₂O₇). Although this occurs due to differences in oxygen-vacancy formation, the origins of the hole–generation efficiencies remain unclear due to limited information on local and global crystal-structure disorders in pyrochlore Sn₂Nb₂O₇ and Sn₂Ta₂O₇. In this study, the crystal structures of Sn₂B₂O₇ (B = Nb, Ta), composed of BO₆ octahedra and Sn₄O tetrahedra, were investigated using X-ray absorption spectroscopy and X-ray diffraction. A detailed investigation of the local and global crystal structures indicated a larger amount of disorder in the Sn₄O tetrahedra in Sn₂Nb₂O₇ compared to Sn₂Ta₂O₇; disorder in the BO₆ octahedra occurred only in Sn₂Ta₂O₇. This study indicates that an appropriate selection of the B-site element is vital for suppressing defect and disorder formation in Sn₄O tetrahedra and subsequently improving the hole–carrier–generation efficiency.