排序方式: 共有113条查询结果,搜索用时 15 毫秒
31.
Allouch A Roubaud V Lauricella R Bouteiller JC Tuccio B 《Organic & biomolecular chemistry》2003,1(3):593-598
The synthesis of two new nitrones, N-benzylidene-1,1-bis(ethoxycarbonyl)ethylamine N-oxide (DEEPN) and N-[(1-oxidopyridin-1-ium-4-yl)methylidene]-1-ethoxycarbonyl-1- methylethylamine N-oxide (EPPyON), is described. Measurement of their n-octanol-phosphate buffer partition coefficient permitted evaluation of their lipophilicity. Their capacity to act as spin trapping agents was investigated in aqueous media. Although these nitrones were unsuitable for detecting hydroxyl radical, they efficiently trapped various carbon- and oxygen-centred radicals, including superoxide, in aqueous media. The half-lives of their superoxide adducts were determined at pH 5.8 and 7.2. At neutral pH, the superoxide spin adduct of DEEPN was found to be as persistent as that of 5-diethoxyphosphoryl-5-methyl-3,4-dihydropyrrole N-oxide (DEPMPO). Consequently, DEEPN was believed to be an efficient trap for superoxide detection in aqueous media. 相似文献
32.
Wang MZ Lee YJ Abe K Abe K Abe T Aihara H Akatsu M Asano Y Aso T Aushev T Bakich AM Ban Y Banas E Bay A Behera PK Bizjak I Bondar A Bozek A Bracko M Browder TE Casey BC Chang MC Chang P Chao Y Chen KF Cheon BG Chistov R Choi Y Choi YK Drutskoy A Eidelman S Eiges V Fukunaga C Gabyshev N Garmash A Gershon T Golob B Guo R Hagner C Hara T Hazumi M Hojo T Hokuue T Hoshi Y Hou WS Hsiung YB Huang HC Igaki T Igarashi Y Iijima T Inami K Ishikawa A Itoh R Iwasaki H Iwasaki Y Jang HK Kang JH Kang JS 《Physical review letters》2003,90(20):201802
We report the first observation of the charmless hyperonic B decay, B0-->pLambda(pi)(-), using a 78 fb(-1) data sample recorded on the Upsilon(4S) resonance with the Belle detector at KEKB. The measured branching fraction is B(B0-->pLambda(pi)(-))=(3.97(+1.00)(-0.80)+/-0.56)x10(-6). Searches for B0-->pLambda(K)- and pSigma(0)pi(-) yield no significant signals and we set 90% confidence-level upper limits of B(B0-->pLambda(K)-)<8.2x10(-7) and B(B0-->pSigma(0)pi(-))<3.8x10(-6). 相似文献
33.
Schwanda C Abe K Abe K Abe T Adachi I Aihara H Akatsu M Asano Y Aushev T Bahinipati S Bakich AM Ban Y Banas E Bay A Bizjak I Bondar A Bozek A Bracko M Browder TE Chang MC Chao Y Cheon BG Choi Y Choi YK Chuvikov A Cole S Danilov M Dash M Dong LY Drutskoy A Eidelman S Eiges V Gabyshev N Gershon T Gokhroo G Golob B Hazumi M Higuchi I Hinz L Hokuue T Hoshi Y Hou WS Huang HC Iijima T Inami K Ishikawa A Itoh R Iwasaki H Iwasaki M Kang JH Kang JS Kapusta P Katayama N Kawai H Kichimi H Kim HJ 《Physical review letters》2004,93(13):131803
We have searched for the decay B+-->omegal(+)nu (l=e or mu) in 78 fb(-1) of Upsilon(4S) data (85x10(6)BB events) accumulated with the Belle detector. The final state is fully reconstructed using the omega decay into pi(+)pi(-)pi(0), combined with detector hermeticity to estimate the neutrino momentum. A signal of 414+/-125 events is found in the data, corresponding to a branching fraction of (1.3+/-0.4+/-0.2+/-0.3)x10(-4), where the first two errors are statistical and systematic, respectively. The third error reflects the estimated form-factor uncertainty. 相似文献
34.
Filhol JS Saint-Lager MC De Santis M Dolle P Simon D Baudoing-Savois R Bertolini JC Sautet P 《Physical review letters》2002,89(14):146106
The structure of a four monolayer deposit of Pd on Ni(110) has been determined by a combination of x-ray diffraction experiments and density-functional theory calculations. This Pd film presents, after annealing at 500 K, a (Nx2) reconstruction associated with a large enhancement of its catalytic activity. The N superstructure, along the dense [11;0] direction, comes from periodic edge dislocations initiated by a vacancy in the first Pd layer. In the perpendicular direction, the doubling of the period originates in a pairing-buckling displacement of the rows. This study evidences a new Pd atoms arrangement with quasi-four-fold hollow sites on the surface, which could play an important role in the exceptional catalytic activity. 相似文献
35.
Jelassi J Grosz T Bako I Bellissent-Funel MC Dore JC Castricum HL Sridi-Dorbez R 《The Journal of chemical physics》2011,134(6):064509
Water confined in a sol-gel network has been characterized by x-ray and neutron diffraction for two samples of mesoporous silica: one with a hydrophilic character (a nonmodified one) and another with a hydrophobic character (a modified one with a methylated internal pore surface). The pore size has been previously characterized [J. Jelassi et al., Phys. Chem. Chem. Phys. 134, 1039 (2010)] to have a mean pore diameter of approximately 55 A?. The diffraction measurements presented in this paper have been made at room temperature [293 K] for a filling factor of 0.45, giving a mean thickness of 8-9 A? for the water layer. The results show that the local order of the confined water molecules in the intermediate region of 3-6 A? is significantly different from that of the bulk water and also for the two different environments. For the hydrophilic sample, the siloxyl groups at the surface modify the water structure through the effects of interfacial hydrogen-bonding, which influences the orientational configuration of local water molecules and creates a modified spatial arrangement in the pore. In the case of the hydrophobic sample, there is no specific interaction with the pore wall, which is primarily van der Waals type, and the water molecules at the interface are differently oriented to create a hydrogen-bonded network linked more directly to the rest of the water volume. In the present circumstances, the thickness of the water layer has a relatively small dimension so that the interpretation of the measured diffraction pattern is not as straightforward as for the bulk liquids, and it is necessary to consider the effects of diffraction-broadening from a distributed sample volume and also the contribution from cross-terms that remain after conducting a "wet-minus-dry" analysis procedure. These analytic difficulties are discussed in the context of the present measurements and compared with the work of other groups engaged in the study of water confined in different environments. The present results, again, emphasize the complexity influencing the properties of water in a confined geometry and the strong influence of surface interactions on its behavior. 相似文献
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37.
Attia J Rémita S Jonic S Lacaze E Fauré MC Larquet E Goldmann M 《Langmuir : the ACS journal of surfaces and colloids》2007,23(19):9523-9526
We combine the self-assembly properties of amphiphilic molecules with the radiolysis method to produce specific sizes and shapes of metallic nano-objects. Radiolysis is used to synthesize core--shell structures consisting of nanometric linoleate spherical micelles as the core and silver as the shell. The validity of the technique is asserted by cryoelectron microscopy, which is an adequate technique for low density contrasts and core--shell structures. The shells are found to be homogeneous with a size of a few nanometers. Images are used to bring forward the hypothesis of the fabrication process. 相似文献
38.
Paulin Nkolo Gérard Audran Paul Bremond Raphaël Bikanga Sylvain R.A. Marque Valérie Roubaud 《Tetrahedron》2017,73(23):3188-3201
Solvent effects in β-phosphorylated nitroxides show that nitrogen and phosphorus hyperfine coupling constants aN and aP, increase and decrease with increasing polarity, polarizity, and Hydrogen Bond Donor effects of solvents, respectively. In a series of articles, it was shown that the driving interaction controlling the change in aP is the maximization of the N+?—O– … ???+PO– dipole – dipole interaction. In this work, we show that the steric strain in spiro β-phosphorylated nitroxides affords the opposite trend for aP, that is, aP increases with increasing solvent properties features. 相似文献
39.
Matyja A Rozanska M Adachi I Aihara H Aulchenko V Aushev T Bahinipati S Bakich AM Balagura V Barberio E Bedny I Bhardwaj V Bitenc U Bondar A Bozek A Bracko M Brodzicka J Browder TE Chang MC Chang P Chen A Chen KF Cheon BG Chistov R Cho IS Choi Y Choi YK Dalseno J Dash M Eidelman S Fratina S Gabyshev N Golob B Ha H Haba J Hara T Hayasaka K Hazumi M Heffernan D Hokuue T Hoshi Y Hou WS Hyun HJ Iijima T Ikado K Inami K Ishikawa A Ishino H Itoh R Iwasaki Y Kaji H Kajiwara S Kang JH Katayama N 《Physical review letters》2007,99(19):191807
We report an observation of the decay B{0}-->D{*-}tau{+}nu{tau} in a data sample containing 535x10{6} BB pairs collected with the Belle detector at the KEKB asymmetric-energy e{+}e{-} collider. We find a signal with a significance of 5.2sigma and measure the branching fraction B(B{0}-->D{*-}tau{+}nu{tau})=(2.02{-0.37}{+0.40}(stat)+/-0.37(syst))%. This is the first observation of an exclusive B decay with a b-->ctaunu{tau} transition. 相似文献
40.
Mizuk R Abe K Adachi I Aihara H Anipko D Aulchenko V Aushev T Bakich AM Balagura V Barberio E Bay A Bedny I Belous K Bitenc U Bizjak I Blyth S Bondar A Bozek A Bracko M Brodzicka J Browder TE Chang MC Chen A Chen KF Chen WT Cheon BG Chistov R Choi Y Choi YK Cole S Dalseno J Danilov M Drutskoy A Eidelman S Epifanov D Fratina S Gabyshev N Garmash A Gershon T Gokhroo G Golob B Ha H Haba J Hayasaka K Hayashii H Hazumi M Heffernan D Hokuue T Hoshi Y Hou S Hou WS Iijima T Ikado K Imoto A Inami K 《Physical review letters》2007,98(26):262001
We report the results of several studies of the Lambda(c)(+)pi(+)pi(-)X final state in continuum e(+)e(-) annihilation data collected by the Belle detector. An analysis of angular distributions in Lambda(c)(2880)(+)-->Sigma(c)(2455)(0,++)pi(+,-) decays strongly favors a Lambda(c)(2880)(+) spin assignment of 5/2 over 3/2 or 1/2. We find evidence for Lambda(c)(2880)(+)-->Sigma(c)(2520)(0,++)pi(+,-) decay and measure the ratio of Lambda(c)(2880)(+) partial widths Gamma(Sigma(c)(2520)pi)/Gamma(Sigma(c)(2455)pi)=0.225+/-0.062+/-0.025. This value favors the Lambda(c)(2880)(+) spin-parity assignment of 5/2(+) over 5/2(-). We also report the first observation of Lambda(c)(2940)(+)-->Sigma(c)(2455)(0,++)pi(+,-) decay and measure Lambda(c)(2880)(+) and Lambda(c)(2940)(+) mass and width parameters. These studies are based on a 553 fb(-1) data sample collected at or near the Upsilon(4S) resonance at the KEKB collider. 相似文献