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21.
V. M. Aulchenko M. N. Achasov S. E. Baru K. I. Beloborodov A. V. Berdyugin A. G. Bogdanchikov A. V. Bozhenok A. D. Bukin D. A. Bukin A. V. Vasilev V. B. Golubev T. V. Dimova V. P. Druzhinin V. N. Ivanchenko I. A. Koop A. A. Korol S. V. Koshuba A. P. Lysenko A. V. Otboev E. V. Pakhtusova A. A. Salnikov S. I. Serednyakov V. A. Sidorov Z. K. Silagadze V. V. Shary Yu. M. Shatunov 《Journal of Experimental and Theoretical Physics》2003,97(1):24-33
The process e + e ? → η′γ, η′ → η π0π0, η → γγ is investigated by an SND detector in experiment on a VEPP-2M equipment with colliding electron-positron beams. The analysis of experimental data yields a value of B(? → η′γ)=(6.7 ?4.2 +5.0 ±1.5)×10?5 for the decay probability. Taking into account a previous measurement of this quantity by an SND detector in the decay channel η′ → π+π?η, one finally obtains B(?→η ′γ)=(6.7 ?2.4 +2.8 ±0.8)×10?5. 相似文献
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Vincent Larraillet Aleksey Vorobyev Claire Brunet Jér?me Lemoine Yury O. Tsybin Rodolphe Antoine Philippe Dugourd 《Journal of the American Society for Mass Spectrometry》2010,21(4):670-680
We compare product-ion mass spectra produced by electron detachment dissociation (EDD) and electron photodetachment dissociation
(EPD) of multi-deprotonated peptides on a Fourier transform and a linear ion trap mass spectrometer, respectively. Both methods,
EDD and EPD, involve the electron emission-induced formation of a radical oxidized species from a multi-deprotonated precursor
peptide. Product-ion mass spectra display mainly fragment ions resulting from backbone cleavages of Cα-C bond ruptures yielding a and x ions. Fragment ions originating from N-Cα backbone bond cleavages are also observed, in particular by EPD. Although EDD and EPD methods involve the generation of a
charge-reduced radical anion intermediate by electron emission, the product ion abundance distributions are drastically different.
Both processes seem to be triggered by the location and the recombination of radicals (both neutral and cation radicals).
Therefore, EPD product ions are predominantly formed near tryptophan and histidine residues, whereas in EDD the negative charge
solvation sites on the backbone seem to be the most favorable for the nearby bond dissociation. 相似文献
25.
Kuznetsov AE Geletii YV Hill CL Musaev DG 《The journal of physical chemistry. A》2010,114(43):11417-11424
To probe photoinduced water oxidation catalyzed by the Mn?O?L? cubane clusters, we have computationally studied the mechanism and controlling factors of the O? formation from the [Mn?O?L?] catalyst, 6. It was demonstrated that dissociation of an L = H?PO?? ligand from 6 facilitates the direct O-O bond formation that proceeds with a 28.3 (33.4) kcal/mol rate-determining energy barrier at the transition state TS1. This step (the O-O single bond formation) of the reaction is a two-electron oxidation/reduction process, during which two oxo ligands are transformed into to μ2:η2-O?2? unit, and two ("distal") Mn centers are reduced from the 4+ to the 3+ oxidation state. Next two-electron oxidation/reduction occurs by "dancing" of the resulted O?2? fragment between the Mn1 and Mn2/Mn(2')-centers, keeping its strong coordination to the Mn(1')-center. As a result of this four-electron oxidation/reduction process Mn centers of the Mn?-core of I transform from {Mn1(III)-Mn(1')(III)-Mn2(IV)-Mn(2')(IV)} to {Mn1(II)-Mn(1')(II)-Mn2(III)-Mn(2')(III)} in IV. In other words, upon O? formation in cationic complex [Mn?O?L?](+), I, all four Mn-centers are reduced by one electron each. The overall reaction I → TS1 → II → III → TS2 → IV → TS3 → V → VI + O? is found to be exothermic by 15.4 (10.5) kcal/mol. We analyze the lowest spin states and geometries of all reactants, intermediates, transition states, and products of the targeted reaction. 相似文献
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Aleksey A. Goldberg Aleksey V. Shastin Valentine G. Nenajdenko 《Journal of fluorine chemistry》2010,131(3):384-5688
CF3CFBr2 was employed in catalytic olefination reactions of aromatic aldehydes. In situ prepared hydrazones of aldehydes were transformed to β-fluoro-β-(trifluoromethyl)styrenes by reaction with CF3CFBr2 under CuCl catalysis. Based on this reaction, a novel stereoselective approach towards β-fluoro-β-(trifluoromethyl)styrenes was elaborated. Nucleophilic vinylic substitution of fluorine by secondary amines, thiolates and alkoxides in β-fluoro-β-(trifluoromethyl)styrenes was also tested. 相似文献
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Alexander Yu. Rulev Igor A. Ushakov Evgeniy V. Kondrashov Vasiliy M. Muzalevskiy Aleksey V. Shastin Valentine G. Nenajdenko 《Journal of fluorine chemistry》2011,132(11):945-950
The key steps of the reactions of nitrogen nucleophiles with β-halogen-β-trifluoromethylstyrenes have been studied by 19F and 1H NMR monitoring and quantum-chemical calculations. In contrast to the mechanism proposed earlier for nucleophilic vinylic substitution of captodative carbonyl-bearing haloalkenes, this reaction proceeds via either E–Ad or Ad–E sequence depending on the nature of aromatic substituents of the parent styrenes. 相似文献
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The gauge cell Monte Carlo method is extended to calculations of the incremental chemical potentials and free energies of linear chain molecules. The method was applied to chains of Lennard-Jones beads with stiff harmonic bonds up to 500 monomers in length. We show that the suggested method quantitatively reproduces the modified Widom particle insertion method of Kumar et al. [S. K. Kumar, I. Szleifer, and A. Z. Panagiotopoulos, Phys. Rev. Lett. 66(22), 2935 (1991)], and is by an order of magnitude more efficient for long chains in terms of the computational time required for the same accuracy of chemical potential calculations. The chain increment ansatz, which suggests that the incremental chemical potential is independent of the chain length, was tested at different temperatures. We confirmed that the ansatz holds only for coils above the θ temperature. Special attention is paid to the effects of the magnitude of adsorption potential and temperature on the behavior of single chains in confinements that are comparable in size with the free chain radius of gyration. At sufficiently low temperatures, the dependence of the incremental chemical potential on the chain length in wetting pores is superficially similar to a capillary condensation isotherm, reflecting monolayer formation following by pore volume filling, as the chain length increases. We find that the incremental gauge cell method is an accurate and efficient technique for calculations of the free energies of chain molecules in bulk systems and nanoconfinements alike. The suggested method may find practical applications, such as modeling polymer partitioning on porous substrates and dynamics of chain translocation into nanopores. 相似文献