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851.
852.
Toshiki Nishiura Takehiro Ohta Takashi Ogura Jun Nakazawa Masaya Okamura Shiro Hikichi 《Molecules (Basel, Switzerland)》2022,27(19)
Conversion from superoxide (O2−) to hydroperoxide (OOH−) on the metal center of oxygenases and oxidases is recognized to be a key step to generating an active species for substrate oxidation. In this study, reactivity of cobalt(III)-superoxido complexes supported by facially-capping tridentate tris(3,5-dimethyl-4-X-pyrazolyl)hydroborate ([HB(pzMe2,X)3]−; TpMe2,X) and bidentate bis(1-methyl-imidazolyl)methylborate ([B(ImN-Me)2Me(Y)]−; LY) ligands toward H-atom donating reagent (2-hydroxy-2-azaadamantane; AZADOL) has been explored. The oxygenation of the cobalt(II) precursors give the corresponding cobalt(III)-superoxido complexes, and the following reaction with AZADOL yield the hydroperoxido species as has been characterized by spectroscopy (UV-vis, resonance Raman, EPR). The reaction of the cobalt(III)-superoxido species and a reducing reagent ([CoII(C5H5)2]; cobaltocene) with proton (trifluoroacetic acid; TFA) also yields the corresponding cobalt(III)-hydroperoxido species. Kinetic analyses of the formation rates of the cobalt(III)-hydroperoxido complexes reveal that second-order rate constants depend on the structural and electronic properties of the cobalt-supporting chelating ligands. An electron-withdrawing ligand opposite to the superoxide accelerates the hydrogen atom transfer (HAT) reaction from AZADOL due to an increase in the electrophilicity of the superoxide ligand. Shielding the cobalt center by the alkyl group on the boron center of bis(imidazolyl)borate ligands hinders the approaching of AZADOL to the superoxide, although the steric effect is insignificant. 相似文献
853.
New liquid-crystalline polyesters and paramagnetic vanadyl complex were prepared as host polymer and guest complex. Melt-drawn fibers were made from the blend of host polymer and guest complex at the mesophase temperature. ESR spectra of the melt-drawn fibers indicated that the base of pyramidal vanadyl complex is completely oriented parallel to the fiber axis. 相似文献
854.
Prof. Dr. Toshikazu Takata Prof. Dr. Koji Yamamoto Kazuki Higuchi Dr. Masahiro Ogawa Ayumi Kawasaki Shunya Mizuno Hikaru Iwasaki Masaki Nagashima Prof. Dr. Yoshihiro Hayashi Prof. Dr. Susumu Kawauchi Prof. Dr. Kazuko Nakazono Prof. Dr. Yasuhito Koyama 《Angewandte Chemie (International ed. in English)》2023,62(24):e202303494
Post-synthesis modification of polymers streamlines the synthesis of functionalized polymers, but is often incomplete due to the negative polymer effects. Developing efficient polymer reactions in artificial systems thus represents a long-standing objective in the fields of polymer and material science. Here, we show unprecedented macrocycle-metal-complex-catalyzed systems for efficient polymer reaction that result in 100 % transformation of the main chain functional groups presumably via a processive mode reaction. The complete polymer reactions were confirmed in not only intramolecular reaction (hydroamination) but also intermolecular reaction (hydrosilylation) by using Pd- and Pt-macrocycle-catalyzed systems. The most fascinating feature of the both reactions is that higher-molecular-weight polymers reach completion faster. Various studies suggested that the reactions occur in the catalyst cavity via the formation of a supramolecular complex between the macrocycle catalyst and polymer substrate like pseudorotaxane, which should be of characteristic of the efficient polymer reactions progressing in a processive mode. 相似文献
855.
Dr. Hikaru Saito Dr. Hiromasa Sato Taisuke Higashi Prof. Toshiki Sugimoto 《Angewandte Chemie (International ed. in English)》2023,62(33):e202306058
Environmentally sustainable and selective conversion of methane to valuable chemicals under ambient conditions is pivotal for the development of next-generation photocatalytic technology. However, due to the lack of microscopic knowledge about non-thermal methane conversion, controlling and modulating photocatalytic oxidation processes driven by photogenerated holes remain a challenge. Here, we report novel function of metal cocatalysts to accept photogenerated holes and dominate selectivity of methane oxidation, which is clearly beyond the conventional concept in photocatalysis that the metal cocatalysts loaded on the surfaces of semiconductor photocatalysts mostly capture photogenerated electrons and dominate reduction reactions exclusively. The novel photocatalytic role of metal cocatalysts was verified by operando molecular spectroscopy combined with real-time mass spectrometry for metal-loaded Ga2O3 model photocatalysts under methane and water vapor at ambient temperature and pressure. Our concept of metal cocatalysts that work as active sites for both photocatalytic oxidation and reduction provides a new understanding of photocatalysis and a solid basis for controlling non-thermal redox reactions by metal-cocatalyst engineering. 相似文献
856.
Tetsu Mitsumata Masashi Yuge Shinichi Morino Kenji Iwakura Kiyohito Koyama 《Macromolecular rapid communications》2002,23(17):1045-1048
The storage moduli, shear moduli and surface morphologies of poly(vinyl alcohol) (PVA) and alumina hybrid hydrogels were investigated. The storage moduli of hybrid hydrogels with higher alumina contents were found to be 1.5 times higher than those of PVA gels. This increase in modulus might be attributed to the cohesion of alumina to the PVA network.
857.
Yasuhiro Hayakawa Masahiko Ando Tadanobu Koyama Masashi Kumagawa Tetsuo Ozawa Miyuki Masaki Katsumi Takahashi 《Crystal Research and Technology》1996,31(5):567-575
InxGa1-xAs (x = 0.045) ternary bulk crystals were grown on GaAs seeds from an In–Ga–As solution by the temperature-difference method modified to rotate a growth ampoule. The effect of ampoule rotation on the profiles of the composition and the growth rate were investigated. The In compositional profiles were uniform irrespective of the ampoule rotation. On the other hand, the growth rate at the center of the crystal increased from 40 μm/h at 0 rpm to 55 μm/h at 100 rpm. The profile of growth rate changed from concave to convex toward the seed due to the ampoule rotation. Flow patterns and compositional profiles in the solution were simulated by solving four equations: Navier-Stokes, continuity, energy, and solute diffusion. The ampoule rotation enhanced the transportation of As component from the GaAs feed toward the seed at the central region in the solution. This led to the increase of the growth rate. 相似文献
858.
Prof. Dr. Shinji Harada Ryotaro Koyama Ryuya Masuda Prof. Dr. Shigeru Arai 《European journal of organic chemistry》2023,26(38):e202300747
A trichloromethylative olefin lactonization reaction using an iridium photoredox catalyst was developed. The reactions proceeded at room temperature for olefins with various substituents and substitution patterns, and a variety of lactones with a tetrasubstituted carbon and trichloromethyl group were obtained regio- and stereoselectively. The reaction mechanism was elucidated through isotope labeling experiments. The chemical properties of the lactones containing the trichloromethyl groups were investigated, and synthetic transformations of the product were realized. 相似文献
859.
Toshiki Fujii Prof. Dr. Takahiro Kusukawa Prof. Dr. Hiroaki Imoto Prof. Dr. Kensuke Naka 《Chemistry (Weinheim an der Bergstrasse, Germany)》2023,29(1):e202202572
In this study, pnictogen (Pn)-bridged diphenyl sulfones were synthesized as motifs for photoinduced dynamic rearrangement. The newly synthesized sulfones exhibited dual fluorescence at 298 K. Density functional theory calculations revealed that the longer-wavelength fluorescence was derived from the geometries after structural relaxation through photo-driven pnictogen bond formation between the O atom lone pair of the sulfonyl moiety and the antibonding orbital of the Pn−C bond. This is the first report on emission dynamics driven by pnictogen bond formation upon photoexcitation. 相似文献
860.
The treatment of N‐benzylideneaniline ( 1a ) with a half‐equivalent of lanthanum metal and a catalytic amount of iodine gave the reductive dimerization product of 1a , a vic‐diamine, in good yield. Various vic‐diamines were synthesized from aldimines in this manner in moderate to good yields. Our findings suggest that electrons of a zero‐valent lanthanum metal were efficiently utilized in this reductive dimerization. In the reaction of ketimines, however, a similar reductive dimerization did not take place, and the corresponding amines were formed as the sole products. © 2002 Wiley Periodicals, Inc. Heteroatom Chem 13:131–135, 2002; Published online in Wiley Interscience (www.interscience.wiley.com). DOI 10.1002/hc.10007 相似文献