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Kazushige Hori Mina Tamura Keita Tani Nagatoshi Nishiwaki Masahiro Ariga Yasuo Tohda 《Tetrahedron letters》2006,47(18):3115-3118
Asymmetric epoxidation of (E)-chalcone with alkaline hydrogen peroxide by novel chiral phase-transfer catalysts (chiral PTCs) with quaternary ammonium salts of azacrown ether proceeded in high yield and good enantioselectivity. Remarkably, this reaction depended on the length of the carbon chain on the nitrogen atom with the chiral PTCs and on the bulk of the base. 相似文献
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Dr. Keita Nakanishi Dr. Geoffrey J. T. Cooper Dr. Laurie J. Points Dr. Leanne G. Bloor Prof. Masaaki Ohba Prof. Leroy Cronin 《Angewandte Chemie (International ed. in English)》2018,57(40):13066-13070
Inorganic chemical cells (iCHELLs) are compartment structures consisting of polyoxometalates (POMs) and cations, offering structured and confined reaction spaces bounded by membranes. We have constructed a system capable of efficient anisotropic and hierarchical photo‐induced electron transfer across the iCHELL membrane. Mimicking photosynthesis, our system uses proton gradients between the compartment and the bulk to drive efficient conversion of light into chemical energy, producing hydrogen upon irradiation. This illustrates the power of the iCHELL approach for catalysis, where the structure, compartmentalisation and variation in possible components could be utilised to approach a wide range of reactions. 相似文献
315.
Photoliquefiable Ionic Crystals: A Phase Crossover Approach for Photon Energy Storage Materials with Functional Multiplicity 下载免费PDF全文
Keita Ishiba Dr. Masa‐aki Morikawa Chie Chikara Dr. Teppei Yamada Katsunori Iwase Mika Kawakita Prof. Dr. Nobuo Kimizuka 《Angewandte Chemie (International ed. in English)》2015,54(5):1532-1536
Ionic crystals (ICs) of the azobenzene derivatives show photoinduced IC–ionic liquid (IL) phase transition (photoliquefaction) upon UV‐irradiation, and the resulting cis‐azobenzene ILs are reversibly photocrystallized by illumination with visible light. The photoliquefaction of ICs is accompanied by a significant increase in ionic conductivity at ambient temperature. The photoliquefaction also brings the azobenzene ICs further significance as photon energy storage materials. The cis‐IL shows thermally induced crystallization to the trans‐IC phase. This transition is accompanied by exothermic peaks with a total ΔH of 97.1 kJ mol?1, which is almost double the conformational energy stored in cis‐azobenzene chromophores. Thus, the integration of photoresponsive ILs and self‐assembly pushes the limit of solar thermal batteries. 相似文献
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Baba K Ono H Itoh E Itoh S Noda K Usui T Ishihara K Inamo M Takagi HD Asano T 《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(20):5328-5333
Thermal Z to E isomerization reactions of azobenzene and 4-dimethylamino-4'-nitroazobenzene were examined in three ionic liquids of general formula 1-R-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (R = butyl, pentyl, and hexyl). The first-order rate constants and activation energies for the reactions of azobenzene measured in these ionic liquids were consistent with those measured in ordinary organic solvents, which indicated that the slow isomerization through the inversion mechanism with a nonpolar transition state was little influenced by the solvent properties, such as the viscosity and dielectric constant, of ionic liquids. On the other hand, the rate constants and the corresponding frequency factors of the Arrhenius plot were significantly reduced for the isomerization of 4-dimethylamino-4'-nitroazobenzene in ionic liquids compared with those for the isomerization in ordinary organic molecular solvents with similar dielectric properties. Although these ionic liquids are viscous, the apparent viscosity dependence of the rate constant could not be explained either by the Kramers-Grote-Hynes model or by the Agmon-Hopfield model for solution reactions. It is proposed that the positive and the negative charge centers of a highly polar rotational transition state are stabilized by the surrounding anions and cations, respectively, and that the ions must be rearranged so as to form highly ordered solvation shells around the charge centers of the reactant in the transition state. This requirement for the orderly solvation in the transition state results in unusually small frequency factors of 10(4)-10(7) s(-1). 相似文献
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Keita Yamada Ryota Hattori Yuji Ito Hiroki Shibata Naohiro Yoshida 《Isotopes in environmental and health studies》2013,49(3):392-399
Isotopic signatures of atmospheric methanol and acetaldehyde have the potential to improve our ability to quantitatively assess their importance in atmospheric chemistry. However, isotopic measurements of atmospheric methanol and acetaldehyde and their individual source and sink processes have been limited. In this study, we examined gas chromatography-isotope ratio mass spectrometry combined with headspace solid-phase microextraction to measure the carbon isotope ratios of methanol and acetaldehyde in air samples. The method enabled us to determine carbon isotope ratios with a precision (1 standard deviation) of±0.6 ‰ for 20 ml of air sample containing more than 3 ppm of methanol and±0.7 ‰ for 20 ml of air sample containing more than 2 ppm of acetaldehyde. Moreover, the applicability of this method to determine isotope ratios of methanol and acetaldehyde emitted from detached plant leaves was demonstrated. 相似文献
318.
The development of efficient methods for stereocontrolled synthesis of polyol derivatives has been of continuing interest for the synthetic community. We describe herein tandem olefin cross‐metathesis/hemiacetalization/intramolecular oxa‐Michael addition of allylic/homoallylic alcohols, α,β‐unsaturated ketones, and aldehydes, which enabled the synthesis of syn‐1,2‐ and syn‐1,3‐diol derivatives in a step‐economical manner. A series of differentially protected polyol derivatives could be obtained in subsequent transformations via chemoselective/regioselective cleavage of the acetal moiety of the tandem reaction products. 相似文献
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