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排序方式: 共有1346条查询结果,搜索用时 15 毫秒
941.
942.
Dr. Shunpei Hitosugi Prof. Kei Ohkubo Yuki Kawashima Dr. Taisuke Matsuno Sho Kamata Kosuke Nakamura Hirohiko Kono Dr. Sota Sato Prof. Shunichi Fukuzumi Prof. Hiroyuki Isobe 《化学:亚洲杂志》2015,10(11):2404-2410
The energetics and photodynamics of carbonaceous molecular bearings with discrete molecular structures were investigated. A series of supramolecular bearings comprising belt‐persistent tubular cycloarylene and fullerene molecules accepted photonic stimuli to afford charge‐separated species via a photoinduced electron transfer process. The energy conversion processes associated with the photoexcitation, however, differed depending on the molecular structure. A π‐lengthened tubular molecule allowed for the emergence of an intermediary triplet excited state at the bearing, which should lead to an energy conversion to thermal energy. On the other hand, low‐lying charge‐separated species induced by an endohedral lithium ion in fullerene enabled back electron transfer processes to occur without involving triplet excited species. The structure–photodynamics relationship was analyzed in terms of the Marcus theory to reveal a large electronic coupling in this dynamic supramolecular system. 相似文献
943.
Modulation of Benzene or Naphthalene Binding to Palladium Cluster Sites by the Backside‐Ligand Effect
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Yuki Ishikawa Seita Kimura Kohei Takase Koji Yamamoto Dr. Yuki Kurashige Prof. Takeshi Yanai Prof. Tetsuro Murahashi 《Angewandte Chemie (International ed. in English)》2015,54(8):2482-2486
The backside‐ligand modulation strategy to enhance the substrate binding property of Pd clusters is reported. The benzene or naphthalene binding ability of Pd3 or Pd4 clusters is enhanced significantly by the backside cyclooctatetraene ligand, leading to the formation of the first solution‐stable benzene‐ or naphthalene Pd clusters. The present results imply that the ligand design of the metal clusters, especially for the backside ligand of the metal cluster site, is crucial to acquire a desired reactivity of metal clusters. 相似文献
944.
Time‐Resolved Crystallography of the Reaction Intermediate of Nitrile Hydratase: Revealing a Role for the Cysteinesulfenic Acid Ligand as a Catalytic Nucleophile
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Dr. Yasuaki Yamanaka Dr. Yuki Kato Dr. Koichi Hashimoto Dr. Keisuke Iida Prof. Kazuo Nagasawa Dr. Hiroshi Nakayama Dr. Naoshi Dohmae Prof. Keiichi Noguchi Prof. Takumi Noguchi Prof. Masafumi Yohda Prof. Masafumi Odaka 《Angewandte Chemie (International ed. in English)》2015,54(37):10763-10767
The reaction mechanism of nitrile hydratase (NHase) was investigated using time‐resolved crystallography of the mutant NHase, in which βArg56, strictly conserved and hydrogen bonded to the two post‐translationally oxidized cysteine ligands, was replaced by lysine, and pivalonitrile was the substrate. The crystal structures of the reaction intermediates were determined at high resolution (1.2–1.3 Å). In combination with FTIR analyses of NHase following hydration in H218O, we propose that the metal‐coordinated substrate is nucleophilically attacked by the O(SO?) atom of αCys114‐SO?, followed by nucleophilic attack of the S(SO?) atom by a βArg56‐activated water molecule to release the product amide and regenerate αCys114‐SO?. 相似文献
945.
Multicolor Fluorescence Writing Based on Host–Guest Interactions and Force‐Induced Fluorescence‐Color Memory
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Dr. Yuki Matsunaga Prof. Jye‐Shane Yang 《Angewandte Chemie (International ed. in English)》2015,54(27):7985-7989
A new strategy is reported for multicolor fluorescence writing on thin solid films with mechanical forces. This concept is illustrated by the use of a green‐fluorescent pentiptycene derivative 1 , which forms variably colored fluorescent exciplexes: a change from yellow to red was observed with anilines, and fluorescence quenching (a change to black) occurred in the presence of benzoquinone. Mechanical forces, such as grinding and shearing, induced a crystalline‐to‐amorphous phase transition in both the pristine and guest‐adsorbed solids that led to a change in the fluorescence color (mechanofluorochromism) and a memory of the resulting color. Fluorescence drawings of five or more colors were created on glass or paper and could be readily erased by exposure to air and dichloromethane fumes. The structural and mechanistic aspects of the observations are also discussed. 相似文献
946.
Dr. Shuji Yamashita Dr. Akito Naruko Yuki Nakazawa Dr. Le Zhao Prof. Dr. Yujiro Hayashi Prof. Dr. Masahiro Hirama 《Angewandte Chemie (International ed. in English)》2015,54(29):8538-8541
Limonoids are highly oxygenated C13α‐triterpenes and common secondary metabolites. Several hundred congeners have been isolated to date. The first total synthesis of (±)‐limonin, the flagship congener of the limonoids, is now reported and features 1) a tandem radical cyclization generating the BCD ring system with the C13α configuration that is essential to the limonoids and a Robinson annulation to construct the limonoid androstane framework, 2) a singlet‐oxygen cycloaddition and a Baeyer–Villiger oxidation to synthesize the highly oxidized D ring, and 3) a Suárez reaction to construct the unique AA′ ring system. 相似文献
947.
Shusuke Yamanaka Yuki Mitsuta Mitsutaka Okumura Kizashi Yamaguchi Haruki Nakamura 《Molecular physics》2015,113(3-4):336-341
We here formulate and implement linear response function (LRF) of the Mayer bond order (MBO), which is expected to be a new indicator to describe intrinsic chemical reactivity of molecules. We calculate LRFs of the MBOs of para-substituted benzoic acids, and compare the results with the Hammett substituent constants and computational results of acid dissociation constants that were previously reported. The results are discussed from the viewpoint of the applicability of LRF of the MBO to estimate the relative reactivity of the substituted benzoic acids. 相似文献
948.
One‐Pot Halogen Dance/Negishi Coupling of Dibromothiophenes for Regiocontrolled Synthesis of Multiply Arylated Thiophenes
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Prof. Dr. Kentaro Okano Kazuhiro Sunahara Yoshiki Yamane Yuki Hayashi Prof. Dr. Atsunori Mori 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(46):16450-16454
One‐pot halogen dance/Negishi cross‐coupling of readily available 2,5‐dibromothiophenes is described. A lithium diisopropylamide (LDA)‐mediated halogen dance reaction resulted in the formation of thermodynamically stable α‐lithiodibromothiophenes, which were transmetalated with ZnCl2 and subjected to Negishi cross‐coupling to provide the corresponding arylated dibromothiophenes in one pot. The resultant β‐bromo group was much less reactive than the remaining α‐bromo group, which was used in a one‐pot double Suzuki–Miyaura cross‐coupling, enabling facile synthesis of multiply arylated thiophenes. 相似文献
949.
Yuki Hirai Hitoshi Tamiaki Shigenori Kashimura Yoshitaka Saga 《Photochemistry and photobiology》2009,85(5):1140-1146
Demetalation kinetics of bacteriochlorophylls (BChls) c, d and e from green sulfur photosynthetic bacteria were studied under weakly acidic conditions. Demetalation rate constants of BChl e possessing a formyl group at the 7-position were significantly smaller than those of BChls c and d , which had a methyl group at this position. The activation energy of demetalation of 31 R -8,12-diethyl([E,E])-BChl e was 1.5-times larger than that of 31 R -[E,E]-BChl c . 15 N-labeled 31 R -[E,E]-BChls c and e were purified from cells of green sulfur bacteria grown in a medium containing 15 NH4 Cl, and their 15 N NMR spectra were measured. The chemical shifts of N21 , N22 and N23 atoms of 31 R -[E,E]-BChl e were lower-field shifted than those of 31 R -[E,E]-BChl c , respectively, and especially the difference in chemical shifts of N22 was significantly large. These results suggest that the electron-withdrawing formyl group at the 7-position of BChl e affected an electronic state of the chlorin macrocycle and caused BChl e to be more tolerant for removal of the central magnesium compared with BChls c and d . 相似文献
950.
Ryoichi Hirayama Yoshitaka Matsumoto Yuki Kase Miho Noguchi Koichi Ando Atsushi Ito Ryuichi Okayasu Yoshiya Furusawa 《Radiation Physics and Chemistry》2009,78(12):1175-1178
The contribution of OH radical-mediated indirect action by particle beams under hypoxic irradiation condition was investigated by using a radical scavenger. V79 cells were irradiated with 150 MeV/nucleon helium ions at an LET of 2.2 keV/μm in the presence or absence of DMSO, and their colony survivals were determined. The contribution of indirect action to cell killing under hypoxic condition was estimated to be 52±9%. We conclude that OH radical-mediated indirect action still has a half in total contribution on cell killing under hypoxic condition. 相似文献