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721.
Takayuki Serizawa Yoshitaka Numajiri Takayuki Doi Takashi Takahashi 《Tetrahedron letters》2009,50(26):3408-3410
The stereoselective one-pot three-component coupling reaction was accomplished by 1,4-addition of the protected cyanohydrin ether 9f to cyclohexenone 10g and subsequent addition of the resulting enolate to formaldehyde in high yield for the formation of the AC ring system of taxanes. We found that the bulky substituents at the 10-position in the A ring prevent the desired 1,4-addition. Similarly, the bulky trialkylsiloxy groups at the 4-position in the C ring prevent the 1,4-addition and electron-donating alkoxy groups at the same position induce the undesired retro-Michael reaction. 相似文献
722.
Shigeo Sato Koji Omori Sawa Araki Yohei Takahashi Kazuaki Wagatsuma 《Surface and interface analysis : SIA》2009,41(6):496-501
Nitriding phenomena that occur on the surfaces of pure Fe and Fe? Cr alloy (16 wt% Cr) samples were investigated. An Ar + N2 mixture‐gas glow‐discharge plasma was used so that surface nitriding could occur on a clean surface etched by Ar+ ion sputtering. In addition, the metal substrates were kept at a low temperature to suppress the diffusion of nitrogen. These plasma‐nitriding conditions enabled us to characterize the surface reaction between nitrogen radicals and the metal substrates. The emission characteristics of the band heads of the nitrogen molecule ion (N2+) and nitrogen molecule from the glow‐discharge plasma suggest that the active nitrogen molecule is probably the major nitriding reactant. AES and angle‐resolved XPS were used to characterize the thickness of the nitride layer and the concentration of elements and chemical species in the nitride layer. The thickness of the nitride layer did not depend on the metal substrate type. An oxide layer with a thickness of a few nanometers was formed on the top of the nitride layer during the nitriding process. The oxide layer consisted of several species of Nx‐Fey‐O, NO+, and NO2?. In the Fe? Cr alloy sample, these oxide species could be reduced because chromium is preferentially nitrided. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
723.
Photocyclization of 2,4,6-triethylbenzophenones (TEBPs) into (E)- or (Z)-benzocyclobutenols ((E)- or (Z)-CBs) is E-selective in solution. By contrast, upon solid-state photolysis, TEBP-3,4-diCl and especially TEBP-4-t-Bu gave (Z)-CB relative to (E)-CB with a much higher proportion than that in solution. For TEBP-4-t-Bu, the most major product in the solid state is an indanol derivative (Inol) (E/Z/Inol=1:3.9:10.3 at 9% conversion). On the basis of the X-ray crystallographic analysis, Inol and (Z)-CB are both topochemical products. Notably, the relative proportion of (E)-CB increased with increased conversion, namely with increased disruption of the crystal lattice. The DFT calculation of highly hindered 2,6-diisopropylbenzophenone (DIBP) was also conducted. These results in conjunction with the previous results on 2,4,6-triisopropylbenzophenones (TIBPs) indicate that CB is formed either via trans-enol followed by its conrotatory ring-closure (paths a and d) or through direct cyclization of biradical (BR) (path b) as shown in Scheme 1. Normally the former route is faster. However, in the crystalline state or in the case of sterically hindered phenyl ketones, path b tends to be adopted. 相似文献
724.
Hitomi Kitagawa Ryosuke Kitagawa Masamichi Yamanaka Kenji Kobayashi 《Tetrahedron》2009,65(35):7234-914
Tetra(4-pyridyl)-cavitand 1 and tetrakis(4-hydroxyphenyl)-cavitand 2 self-assemble into a heterodimeric capsule 1·2 via four PhOH?pyridyl hydrogen bonds in CDCl3, wherein one molecule of 1,4-disubstituted-benzene as a guest is encapsulated to form a ternary complex, guest@(1·2). The X-ray crystallographic analysis of (methyl p-ethoxybenzoate)@(1·2) confirmed that the methyl ester and ethoxy groups of the encapsulated guest are oriented to the cavity ends of the 1 and 2 units, respectively. The scope and limitation of guest encapsulation in 1·2, including guest-binding selectivity and orientational isomeric selectivity, are described from the viewpoint of size complementarity and CH-π, CH-halogen, and halogen-π interactions between guest and the cavity of 1·2. 相似文献
725.
Harumi Sato Rumi Murakami Katsuhito Mori Yuriko Ando Isao Takahashi Isao Noda Yukihiro Ozaki 《Vibrational Spectroscopy》2009,51(1):132-135
Infrared reflection–absorption (IR-RAS) and transmission spectra were measured for poly(3-hydroxybutyrate) (PHB) thin films to explore its specific crystal structure in the surface region. As IR-RAS is sensitive to the vibration mode of perpendicular orientation of the surface, differences between IR-RAS and transmission spectra indicate an orientation of the lamella structure in the surface of PHB thin films. The relative intensity of the crystalline CO stretching band in the IR-RAS spectrum is significantly weaker than that in the transmission spectrum. It may be concluded that the transient dipole moment of the CO stretching mode of the crystalline state is not oriented perpendicular but nearly parallel to the substrate surface. On the other hand, the relative intensity of the band at 3009 cm−1 due to the C–H stretching mode of the C–HOC hydrogen bonding is similar between the IR-RAS and transmission spectra, suggesting that the C–H bond is oriented neither perpendicular nor parallel to the substrate surface but in an intermediate direction. Since the CO group of the C–HOC hydrogen bonding is oriented nearly parallel to the surface and its C–H group is in the intermediate direction, it is very likely that the C–HOC hydrogen bonding has a somewhat bent structure. These results are in good agreement with our previous conclusion that the C–HOC hydrogen bonding of PHB exists along the a-axis (not the b-axis) between the CH3 group of one helix and the CO group of another helix. 相似文献
726.
Miho Tanaka Kazuya Takahashi Tatsuya Urabe Tomohiro Oikawa Masao Nemoto Hideki Nagashima 《Rapid communications in mass spectrometry : RCM》2009,23(5):698-704
Silica, represented by SiO2, is the general name for the compounds composed of Si, O and H with their derivative complexes. Silica forms various chemical species in aquatic solutions, such as a monomer (Si(OH)3O−), dimer (Si2(OH)5O), and others. These species are known to vary in their relative abundances in solution depending on the chemical and physical conditions. Silica species dissolved in seawater have been examined by fast-atom bombardment mass spectrometry (FAB-MS) to elucidate the behavior of silica and its circulation as a novel tracer reflecting the chemical and physical conditions of seawater and the bioactivity of diatoms, which take up silica. In the seawater of Tokyo Bay, silica species such as [Si(OH)2O2Na]− ([monomer–Na]−), [Si2(OH)5O2]− ([dimer]−), [Si2(OH)4O3Na]− ([dimer–Na]−), [Si4(OH)7O5]− ([cyclic tetramer]−), [Si4(OH)6O6Na]− ([cyclic tetramer–Na]−), [Si4(OH)9O4]− ([linear tetramer]−) and [Si4(OH)8O5Na]− ([linear tetramer–Na]−) were observed and assigned by FAB-MS. To investigate the suitability of silica species as a tracer, the relative peak intensity ratios of silica species observed in the mass spectra, i.e. the profiles of the ratio of the linear tetramer to the cyclic tetramer (m/z 329/311) and the ratio of the dimer to the cyclic tetramer (m/z 173/311) against depth, were examined to determine the annual changes and reproducibility of the depth profiles. In particular, the depth profile of the relative ratio of the linear tetramer to the cyclic tetramer, 329/311, exhibits critical changes depending on the seawater budget. These changes in the relative ratios were identified by an experiment involving a simple sodium chloride solution system. Our measurement is expected to elucidate the dynamics of silica and its role as ‘food’ for diatoms, and we showed that speciation using mass spectrometry is a powerful tool for examining elemental behavior in nature and environmental changes. Our results suggest that a silica tracer is useful for investigating the behavior of seawater in small coastal regions and the uptake of silica by diatoms. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
727.
Degradation of imidazolium ionic liquid, [bmim+][TFSA−] and iodide solution of [bmim+][TFSA−] by UV-laser irradiation has been studied through ground-state absorption and transient absorption spectroscopy. We found that excited state [bmim+]* undergoes degradation efficiently. 相似文献
728.
Takafumi Kondoh Akira Asano Jinfeng Yang Kimihiro Norizawa Kenji Takahashi Mitsumasa Taguchi Ryuji Nagaishi Ryuzi Katoh Yoichi Yoshida 《Radiation Physics and Chemistry》2009,78(12):1157-1160
The spectra and kinetic behavior of solvated electrons (esol−) in alkyl ammonium ionic liquids (ILs), i.e. N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium bis(trifluoromethanesulfonyl)imide (DEMMA-TFSI), N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium tetrafluoroborate (DEMMA-BF4), N,N,N-trimethyl-N-propylammonium bis(trifluoromethanesulfonyl)imide (TMPA-TFSI), N-methyl-N-propylpiperidinium bis(trifluoromethanesulfonyl)imide (PP13-TFSI), N-methyl-N-propylpyrrolidinium bis(trifluoromethanesulfonyl)imide (P13-TFSI), and N-methyl-N-butylpyrrolidinium bis(trifluoromethanesulfonyl)imide (P14-TFSI) were investigated by the pulse radiolysis method. The esol− in each of the ammonium ILs has an absorption peak at 1100 nm, with molar absorption coefficients of 1.5–2.3×104 dm3 mol−1 cm−1. The esol− decayed by first order with a rate constant of 1.4–6.4×106 s−1. The reaction rate constant of the solvated electron with pyrene (Py) was 1.5–3.5×108 dm3 mol−1 s−1 in the various ILs. These values were about one order of magnitude higher than the diffusion-controlled limits calculated from measured viscosities. The radiolytic yields (G-value) of the esol− were 0.8–1.7×10−7 mol J−1. The formation rate constant of esol− in DEMMA-TFSI was 3.9×1010 s−1. The dry electron (edry−) in DEMMA-TFSI reacts with Py with a rate constant of 7.9×1011 dm3 mol−1 s−1, three orders of magnitude higher than that of the esol− reactions. The G-value of the esol− in the picosecond time region is 1.2×10−7 mol J−1. The capture of edry− by scavengers was found to be very fast in ILs. 相似文献
729.
Arata Aota Kazuma Mawatari Susumu Takahashi Teruki Matsumoto Kazuteru Kanda Ryo Anraku Akihide Hibara Manabu Tokeshi Takehiko Kitamori 《Mikrochimica acta》2009,164(3-4):249-255
Phase separation of gas–liquid and liquid–liquid microflows in microchannels were examined and characterized by interfacial pressure balance. We considered the conditions of the phase separation, where the phase separation requires a single phase flow in each output of the microchannel. As the interfacial pressure, we considered the pressure difference between the two phases due to pressure loss in each phase and the Laplace pressure generated by the interfacial tension at the interface between the separated phases. When the pressure difference between the two phases is balanced by the Laplace pressure, the contact line between the two phases is static. Since the contact angle characterizing the Laplace pressure is restricted to values between the advancing and receding contact angles, the Laplace pressure has a limit. When the pressure difference between the two phases exceeds the limiting Laplace pressure, one of the phases leaks into the output channel of the other phase, and the phase separation fails. In order to experimentally verify this physical picture, microchips were used having a width of 215 μm and a depth of 34 μm for the liquid–liquid microflows, a width of 100 μm and a depth of 45 μm for the gas–liquid microflows. The experimental results of the liquid–liquid microflows agreed well with the model whilst that of the gas–liquid microflows did not agree with the model because of the compressive properties of the gas phase and evaporation of the liquid phase. The model is useful for general liquid–liquid microflows in continuous flow chemical processing. 相似文献
730.
Naofumi Tsukada Makiko Wada Naoki Takahashi Yoshio Inoue 《Journal of organometallic chemistry》2009,694(9-10):1333-1338
Novel dinuclear palladium complexes having two isocyanide ligands were synthesized by using a binucleating ligand, N,N′-bis[2-(diphenylphsphino)phenyl]formamidinate (dpfam). The structure of [Pd2(μ-dpfam)(tert-BuNC)2]Cl was confirmed by X-ray analysis, showing that the Pd–Pd bond length of 2.5824(3) Å falls well within the range of those for known dipalladium complexes having the edge-sharing structure and two isocyanides coordinate to palladium in almost parallel and in close proximity. The dinuclear complex [Pd2(μ-dpfam)(tert-BuNC)2]PF6 served as catalyst for pyrrole formation from tert-butylisocyanide and various alkynes. 相似文献