Yuki Miyazaki
Okayama University
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Featured researches published by Yuki Miyazaki.
Catalysis Science & Technology | 2014
Chihiro Maeda; Yuki Miyazaki; Tadashi Ema
Chemical fixation of carbon dioxide (CO2), which is an inexpensive and renewable carbon source, is becoming more and more important. The development of both new reactions and new catalysts is needed to overcome the kinetic and thermodynamic stability of CO2. Organic and metal catalysts with unique and excellent activity and selectivity have been developed for various chemical conversions of CO2. In this perspective, we provide an overview of the recent progress in this field, classifying it into several categories, where each research is concisely summarized one by one using a single reaction scheme, a representative catalyst structure, and/or a catalytic cycle.
Chemical Communications | 2012
Tadashi Ema; Yuki Miyazaki; Shohei Koyama; Yuya Yano; Takashi Sakai
We have developed a very active bifunctional porphyrin catalyst showing a high turnover number (TON = 103,000) for the synthesis of cyclic carbonates from CO(2) and epoxides under solvent-free conditions.
Journal of the American Chemical Society | 2014
Tadashi Ema; Yuki Miyazaki; Junta Shimonishi; Chihiro Maeda; Jun-ya Hasegawa
We prepared bifunctional Mg(II) porphyrin catalysts 1 for the solvent-free synthesis of cyclic carbonates from epoxides and CO2. The activities of 1d, 1h, and 1i, which have Br(-), Cl(-), and I(-) counteranions, respectively, increased in the order 1i < 1h < 1d. Catalysts 1d and 1j-m, which bear four tetraalkylammonium bromide groups with different alkyl chain lengths, showed comparable but slightly different activities. Based on the excellent catalyst 1d, we synthesized Mg(II) porphyrin 1o with eight tetraalkylammonium bromide groups, which showed even higher catalytic activity (turnover number, 138,000; turnover frequency, 19,000 h(-1)). The catalytic mechanism was studied by using 1d. The yields were nearly constant at initial CO2 pressures in the 1-6 MPa range, suggesting that CO2 was not involved in the rate-determining step in this pressure range. No reaction proceeded in supercritical CO2, probably because the epoxide (into which the catalyst dissolved) dissolved in and was diluted by the supercritical CO2. Experiments with (18)O-labeled CO2 and D-labeled epoxide suggested that the catalytic cycle involved initial nucleophilic attack of Br(-) on the less hindered side of the epoxide to generate an oxyanion, which underwent CO2 insertion to afford a CO2 adduct; subsequent intramolecular ring closure formed the cyclic carbonate and regenerated the catalyst. Density functional theory calculations gave results consistent with the experimental results, revealing that the quaternary ammonium cation underwent conformational changes that stabilized various anionic species generated during the catalytic cycle. The high activity of 1d and 1o was due to the cooperative action of the Mg(II) and Br(-) and a conformational change (induced-fit) of the quaternary ammonium cation.
Green Chemistry | 2013
Tadashi Ema; Yuki Miyazaki; Tomoya Taniguchi; Jun Takada
Metalloporphyrins were immobilized on biogenous iron oxide (BIO) produced by iron-oxidizing bacteria, Leptothrix ochracea. These organic–inorganic hybrid materials were used as immobilized catalysts for the synthesis of cyclic carbonates from epoxides and CO2 under solvent-free conditions. ZnII porphyrin immobilized via four tetraalkylammonium bromide groups showed high catalytic activity and reusability at a catalyst loading of 0.1 mol%. The product was obtained in 99% yield after nine times reuse, and the substrate scope was broad.
Organic Letters | 2009
Tadashi Ema; Yoshitaka Oue; Kumiko Akihara; Yuki Miyazaki; Takashi Sakai
Bicyclic tertiary alcohols 1 bearing quaternary stereocenters at the two adjacent bridgehead positions were synthesized with high stereoselectivity via the intramolecular crossed benzoin reactions catalyzed by NHC organocatalysts.
Green Chemistry | 2011
Tadashi Ema; Yuki Miyazaki; Izumi Kozuki; Takashi Sakai; Hideki Hashimoto; Jun Takada
Iron-oxidizing bacteria, Leptothrix ochracea, produce biogenous iron oxide (BIO), while the heat treatment of BIO gives its magnetized material (m-BIO). In this study, they were chemically modified with silane coupling agents to give organic–inorganic hybrid materials, which were then used as immobilization supports for enzymes. BIO-M, which was prepared by modifying BIO with 3-methacryloxypropyltrimethoxysilane, was found to be the best immobilization support. The immobilized lipases showed remarkably high catalytic activity; for example, Burkholderia cepacialipase (BCL) immobilized on BIO-M showed a turnover frequency of 33 000 h−1 for 1-phenylethanol (1a). m-BIO-M, which was prepared by modifying m-BIO with 3-methacryloxypropyltrimethoxysilane, was also used as an immobilization support. Although the lipases immobilized on m-BIO-M showed lower catalytic activity than those immobilized on BIO-M, the former could be separated and reused easily by using a magnet. These immobilized enzymes could be recycled at least five times and are environmentally benign biocatalysts.
Journal of Medical Virology | 2017
Yuki Miyazaki; Hikaru Namba; Sadayoshi Torigoe; Masahiro Watanabe; Nobuko Yamashita; Hirohito Ogawa; Tsuneo Morishima; Masao Yamada
The amounts of the DNAs of human herpesviruses‐6 (HHV‐6) and ‐7 (HHV‐7) in saliva samples were monitored during the acute and convalescent phases of exanthem subitum (ES) to elucidate the kinetics of virus shedding after ES. A total of 247 saliva samples were collected from 17 children (5 males and 12 females: 8–31 months old at onset). The monitoring period ranged from 152 to 721 days after onset, and in 15 children it was longer than 1 year. Among the 17 cases, 16 were attributed to HHV‐6B, while a single case was attributed to HHV‐7. Detection rates and average amounts of HHV‐6 DNA in saliva samples after ES attributed to HHV‐6B were low in the acute phase, increased to the maximum in the convalescent phase at 3–7 months, and then decreased. In addition, to investigate the source of infection, saliva samples from the older siblings (age 3–9 years) and parents of ES patients and children with a history of ES were also examined. The detection rate of HHV‐6 DNA in saliva samples from 3‐ to 9‐year‐old children was significantly higher than the rate in adult saliva samples. Taken together, these findings suggest that the saliva of children in the convalescent phase of ES might be a more likely source of HHV‐6 infection than that of adults. J. Med. Virol. 89:696–702, 2017.
Carbon | 2009
Kazuma Gotoh; Koji Kawabata; Eiji Fujii; Kunimitsu Morishige; Taro Kinumoto; Yuki Miyazaki; Hiroyuki Ishida
Organic and Biomolecular Chemistry | 2010
Takashi Sakai; Yuki Miyazaki; Ai Murakami; Noriko Sakamoto; Tadashi Ema; Hideki Hashimoto; Mitsuaki Furutani; Makoto Nakanishi; Tatsuo Fujii; Jun Takada
Archive | 2012
Tadashi Ema; Takashi Sakai; Yuki Miyazaki