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排序方式: 共有365条查询结果,搜索用时 31 毫秒
91.
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93.
M. A. Gashkov N. M. Zubarev O. V. Zubareva G. A. Mesyats I. V. Uimanov 《Journal of Experimental and Theoretical Physics》2016,122(4):776-786
The formation of microjets is studied during the extrusion of a melted metal by the plasma pressure from craters formed on a cathode in a burning vacuum arc. An analytic model of liquid-metal splashing that includes two stages is proposed. At the first stage, the liquid motion has the axial symmetry and a liquid-metal wall surrounding the crater is formed. At the second stage, the axial symmetry is broken due to the development of the Plateau–Rayleigh instability in the upper part of the wall. The wall breakup process is shown to have a threshold. The minimal plasma pressure and the minimal electric current flowing through the crater required for obtaining the liquid-metal splashing regime are found. The basic spatial and temporal characteristics of the jet formation process are found using the analytic model. 相似文献
94.
Budnik BA Tsybin YO Håkansson P Zubarev RA 《Journal of mass spectrometry : JMS》2002,37(11):1141-1144
Ionization energies (IE) of [M + zH](z+) (z+) electrospray-produced polypeptides were determined by electron ionization in a Penning cell of 4.7 and 9.4 T Fourier transform mass spectrometers. For z = 1+ and substance P, the found IE value of 11.0 +/- 0.4 eV is in agreement with that obtained earlier for ions generated with matrix-assisted laser desorption/ionization. For higher z, the following values were found: 11.7 +/- 0.3 eV for 2+ of [Arg-8]-vasopressin, 11.1 +/- 0.6 eV for 2+ of substance P, 12.2 +/- 0.7 eV for 2+ of renin substrate, 13.3 +/- 0.4 eV for 3+ of B-chain of insulin and 14.6 +/- 0.6 eV for 4+ and 15.1 +/- 0.4 eV for 5+ of melittin. It was found that 90% of existing IE data on polypeptides in the 1.0-3.5 kDa mass range are described with 相似文献
95.
Vladislav A. Ksenofontov Tamara V. Vasina Yuri E. Zubarev Leonid M. Kustov 《Reaction Kinetics and Catalysis Letters》2003,80(2):329-335
Cyclohexane and methylcyclopentane isomerization were carried out under mild conditions using an ionic liquid consisting of
n-butylpyridinium chloride and aluminum chloride as catalyst. The ionic liquid showed reasonably high catalytic activity in
both reactions with a selectivity to corresponding products of 100%. In the case of cyclohexane isomerization, the thermodynamic
equilibrium methylcyclopentane ⇌cyclohexane was almost achieved. For the reaction of cyclohexane isomerization, the kinetic
study was performed, and the rate constants and the activation energy of the process were determined.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
96.
Olsen JV Haselmann KF Nielsen ML Budnik BA Nielsen PE Zubarev RA 《Rapid communications in mass spectrometry : RCM》2001,15(12):969-974
Electron capture dissociation (ECD) in Fourier transform ion cyclotron resonance mass spectrometry coupled with electrospray ionization enhances the sequence elucidation of peptide nucleic acids compared with conventional low-energy collisionally activated dissociation (CAD). Examples are shown where ECD produced complete or extensive sequence coverage in PNAs six to ten nucleobases long. However, facile base losses from the reduced species and low abundances of backbone ECD fragments presented a significant problem. This was rationalized through the lower degree of charge solvation on the backbone compared to polypeptides. Combination of both CAD and ECD data is advantageous, as these techniques produce cleavages at different sites. 相似文献
97.
Budnik BA Jensen KB Jørgensen TJ Haase A Zubarev RA 《Rapid communications in mass spectrometry : RCM》2000,14(7):578-584
A 2.94 microm Er:YAG laser was used together with a commercial Fourier transform mass spectrometer to study labile biomolecules. The combination has shown superior performance over conventional 337 nm ultraviolet matrix-assisted laser desorption/ionization (UV-MALDI) Fourier transform mass spectrometry (FTMS), especially for the analysis of peptides with post-translational modifications. With succinic acid as a matrix, the sensitivity of the single-shot analysis was increased by an order of magnitude to the low femtomole level, with significantly less fragmentation observed. Intact molecular ions of a range of O-glycosylated and sulfated peptides were detected. Urea was found to induce even less fragmentation, although at the expense of the total ion yield. Molecular ions of a noncovalent complex (vancomycin + diacetyl-L-Lys-D-Ala-D-Ala) have been observed for the first time in MALDI-FTMS. 2.94 microm infrared (IR) MALDI also produced abundant molecular ions of a range of nonbiological samples, including C60 and C70 fullerenes as well as dimetal coordination complexes. 相似文献
98.
McLafferty FW Horn DM Breuker K Ge Y Lewis MA Cerda B Zubarev RA Carpenter BK 《Journal of the American Society for Mass Spectrometry》2001,12(3):245-249
Fourier-transform ion cyclotron resonance instrumentation is uniquely applicable to an unusual new ion chemistry, electron capture dissociation (ECD). This causes nonergodic dissociation of far larger molecules (42 kDa) than previously observed (<1 kDa), with the resulting unimolecular ion chemistry also unique because it involves radical site reactions for similarly larger ions. ECD is highly complementary to the well known energetic methods for multiply charged ion dissociation, providing much more extensive protein sequence information, including the direct identification of N- versus C-terminal fragment ions. Because ECD only excites the molecule near the cleavage site, accompanying rearrangements are minimized. Counterintuitively, cleavage of backbone covalent bonds of protein ions is favored over that of noncovalent bonds; larger (>10 kDa) ions give far more extensive ECD if they are first thermally activated. This high specificity for covalent bond cleavage also makes ECD promising for studying the secondary and tertiary structure of gaseous protein ions caused by noncovalent bonding. 相似文献
99.
V. Yu. Zubarev R. E. Trifonov V. V. Poborchii V. A. Ostrovskii 《Chemistry of Heterocyclic Compounds》2006,42(4):469-474
α,ω-Ditetrazol-5-ylalkanes with 1 to 5 methylene groups in the alkyl fragment display the properties of dibasic heterocyclic
NH acids with pKa values lying in the range 3.4–6.1. The pKa values of these compounds are in a linear dependence on the values of the dielectric permeability of the medium, on the chemical
shifts of the signals of the endocyclic carbon atom, and of the carbon atom of the α-methylene group in the 13C NMR spectra.
__________
Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 535–541, April. 2006. 相似文献
100.