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261.
The rate constant for abstraction of hydrogen from isobutane by methyl radicals has been re-examined making use of new measurements at temperatures above 660 K. Most of the data over the temperature range 300–855 K can be accommodated by the following values for the rate constants for abstraction from primary and tertiary hydrogen atoms: This activation energy for abstraction of the tertiary hydrogen atom in isobutane is essentially the same as expressed in a previous evaluation, which considered data only below 500 K, but the magnitude of the rate constant is about 0.25 log units greater. 相似文献
262.
263.
Replacement of the 2-keto group of readily available di(endo-3-camphoryl) diselenide with oxime or O-benzoyloxime substituents, followed by conversion into the corresponding selenenyl triflates, produced highly effective chiral selenium electrophiles for the asymmetric oxyselenenylation of alkenes in the presence of methanol. 相似文献
264.
(+/-)-Bakkenolide A was prepared in five steps from ethyl 4-benzyloxyacetoacetate by sequential alkylations with tiglyl bromide nd cis-5-bromo-1,3-pentadiene, followed by an intramolecular Diels-Alder reaction as the key step. The known 7-epibakkenolide A and novel 10-epi- and 7,10-diepibakkenolide A stereoisomers were obtained as minor byproducts. 相似文献
265.
Determination of f(s)/f(d) for 7 TeV pp collisions and measurement of the B0→D-K+ branching fraction
Aaij R Adeva B Adinolfi M Adrover C Affolder A Ajaltouni Z Albrecht J Alessio F Alexander M Alkhazov G Alvarez Cartelle P Alves AA Amato S Amhis Y Amoraal J Anderson J Appleby RB Gutierrez OA Arrabito L Artamonov A Artuso M Aslanides E Auriemma G Bachmann S Back JJ Bailey DS Balagura V Baldini W Barlow RJ Barschel C Barsuk S Barter W Bates A Bauer C Bauer T Bay A Bediaga I Belous K Belyaev I Ben-Haim E Benayoun M Bencivenni G Benson S Benton J Bernet R Bettler MO van Beuzekom M Bien A Bifani S 《Physical review letters》2011,107(21):211801
The relative abundance of the three decay modes B(0)→D(-)K(+), B(0)→D(-)π(+), and B(s)(0)→D(s)(-)π(+) produced in 7 TeV pp collisions at the LHC is determined from data corresponding to an integrated luminosity of 35 pb(-1). The branching fraction of B(0)→D(-)K(+) is found to be B(B(0)→D(-)K(+)) = (2.01 ± 0.18(stat) ± 0.14(syst)) × 10(-4). The ratio of fragmentation fractions f(s)/f(d) is determined through the relative abundance of B(s)(0)→D(s)(-)π(+) to B(0)→D(-)K(+) and B(0)→D(-)π(+), leading to f(s)/f(d) = 0.253 ± 0.017 ± 0.017 ± 0.020, where the uncertainties are statistical, systematic, and theoretical, respectively. 相似文献
266.
Conformationally restricted naphthalene peri-diselenides function as glutathione peroxidase mimetics with superior catalytic activity to that displayed by typical acyclic diaryl diselenides. Their activity was increased by electron-donating methoxy substituents, while a further 100-fold increase was observed with the corresponding ditelluride. 相似文献
267.
Arpesella C Back HO Balata M Bellini G Benziger J Bonetti S Brigatti A Caccianiga B Cadonati L Calaprice F Carraro C Cecchet G Chavarria A Chen M Dalnoki-Veress F D'Angelo D de Bari A de Bellefon A de Kerret H Derbin A Deutsch M di Credico A di Pietro G Eisenstein R Elisei F Etenko A Fernholz R Fomenko K Ford R Franco D Freudiger B Galbiati C Gatti F Gazzana S Giammarchi M Giugni D Goeger-Neff M Goldbrunner T Goretti A Grieb C Hagner C Hampel W Harding E Hardy S Hartman FX Hertrich T Heusser G 《Physical review letters》2008,101(9):091302
We report the direct measurement of the 7Be solar neutrino signal rate performed with the Borexino detector at the Laboratori Nazionali del Gran Sasso. The interaction rate of the 0.862 MeV 7Be neutrinos is 49+/-3stat+/-4syst counts/(day.100 ton). The hypothesis of no oscillation for 7Be solar neutrinos is inconsistent with our measurement at the 4sigma C.L. Our result is the first direct measurement of the survival probability for solar nu(e) in the transition region between matter-enhanced and vacuum-driven oscillations. The measurement improves the experimental determination of the flux of 7Be, pp, and CNO solar nu(e), and the limit on the effective neutrino magnetic moment using solar neutrinos. 相似文献
268.
269.
Andrew J. Devine Dr. Alice E. Parnell Dr. Catherine R. Back Dr. Nicholas R. Lees Dr. Samuel T. Johns Ainul Z. Zulkepli Rob Barringer Dr. Katja Zorn Dr. James E. M. Stach Prof. Matthew P. Crump Prof. Martin A. Hayes Dr. Marc W. van der Kamp Prof. Paul R. Race Prof. Christine L. Willis 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2023,135(3):e202213053
Abyssomicin C and its atropisomer are potent inhibitors of bacterial folate metabolism. They possess complex polycyclic structures, and their biosynthesis has been shown to involve several unusual enzymatic transformations. Using a combination of synthesis and in vitro assays we reveal that AbyV, a cytochrome P450 enzyme from the aby gene cluster, catalyses a key late-stage epoxidation required for the installation of the characteristic ether-bridged core of abyssomicin C. The X-ray crystal structure of AbyV has been determined, which in combination with molecular dynamics simulations provides a structural framework for our functional data. This work demonstrates the power of combining selective carbon-13 labelling with NMR spectroscopy as a sensitive tool to interrogate enzyme-catalysed reactions in vitro with no need for purification. 相似文献