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排序方式: 共有311条查询结果,搜索用时 31 毫秒
1.
Chad R. Weisbrod Nathan K. Kaiser John E. P. Syka Lee Early Christopher Mullen Jean-Jacques Dunyach A. Michelle English Lissa C. Anderson Greg T. Blakney Jeffrey Shabanowitz Christopher L. Hendrickson Alan G. Marshall Donald F. Hunt 《Journal of the American Society for Mass Spectrometry》2017,28(9):1787-1795
High resolution mass spectrometry is a key technology for in-depth protein characterization. High-field Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) enables high-level interrogation of intact proteins in the most detail to date. However, an appropriate complement of fragmentation technologies must be paired with FTMS to provide comprehensive sequence coverage, as well as characterization of sequence variants, and post-translational modifications. Here we describe the integration of front-end electron transfer dissociation (FETD) with a custom-built 21 tesla FT-ICR mass spectrometer, which yields unprecedented sequence coverage for proteins ranging from 2.8 to 29 kDa, without the need for extensive spectral averaging (e.g., ~60% sequence coverage for apo-myoglobin with four averaged acquisitions). The system is equipped with a multipole storage device separate from the ETD reaction device, which allows accumulation of multiple ETD fragment ion fills. Consequently, an optimally large product ion population is accumulated prior to transfer to the ICR cell for mass analysis, which improves mass spectral signal-to-noise ratio, dynamic range, and scan rate. We find a linear relationship between protein molecular weight and minimum number of ETD reaction fills to achieve optimum sequence coverage, thereby enabling more efficient use of instrument data acquisition time. Finally, real-time scaling of the number of ETD reactions fills during method-based acquisition is shown, and the implications for LC-MS/MS top-down analysis are discussed. 相似文献
2.
The gas‐phase pyrolytic and oxidative chemistry of furans has received much attention recently because of their potential as platform chemicals and biofuels. Typically these compounds exhibit very strong ring carbon to H or CH3 bonds. 2‐Methoxyfuran had been reported to be exceptionally unstable in comparison to related substituted heterocycles in pyrolytic experiments. The origins of its reactivity are shown to be due to the very weak O–CH3, which at 189.5 ± 1.9 kJ mol?1 is some 200 kJ mol?1 weaker than C–H bonds in the molecule. We show that the reported reactivity is somewhat overestimated but that does not alter the fact that 2‐methoxyfuran is exceptionally unstable. It may prove to be a useful alternative to azomethane as a thermal source of methyl radicals. 相似文献
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5.
Zoltán Fodor Kieran HollandJulius Kuti Dániel NógrádiChris Schroeder 《Physics letters. [Part B]》2011,703(3):348-358
We report new results for a frequently discussed gauge theory with twelve fermion flavors in the fundamental representation of the SU(3) color gauge group. The model, controversial with respect to its conformality, is important in non-perturbative studies searching for a viable composite Higgs mechanism beyond the Standard Model (BSM). In comparison with earlier work, our new simulations apply larger volumes and probe deeper in fermion and pion masses toward the chiral limit. Investigating the controversy, we subject the model to opposite hypotheses with respect to the conformal window. In the first hypothesis, below the conformal window, we test chiral symmetry breaking (χSB) with its Goldstone spectrum, Fπ, the χSB condensate, and several composite hadron states as analytic functions of the fermion mass when varied in a limited range with our best effort to control finite volume effects. In the second test, for the alternate hypothesis inside the conformal window, we probe conformal behavior driven by a single anomalous mass dimension under the assumption of unbroken chiral symmetry at vanishing fermion mass. Our results at fixed gauge coupling, based on the assumptions of the two hypotheses we define, show low level of confidence in the conformal scenario with leading order scaling analysis. Relaxing the important assumption of leading mass-deformed conformality with its conformal finite size scaling would require added theoretical understanding of the scaling violation terms in the conformal analysis and a comprehensive test of its effects on the confidence level of the fits. Results for the running coupling, based on the force between static sources, and preliminary indications for the finite temperature transition are also presented. Staggered lattice fermions with stout-suppressed taste breaking are used throughout the simulations. 相似文献
6.
Screening acidic zeolites for catalytic fast pyrolysis of biomass and its components 总被引:2,自引:0,他引:2
David J. MihalcikCharles A. Mullen Akwasi A. Boateng 《Journal of Analytical and Applied Pyrolysis》2011,92(1):224-232
Zeolites have been shown to effectively promote cracking reactions during pyrolysis resulting in highly deoxygenated and hydrocarbon-rich compounds and stable pyrolysis oil product. Py/GC-MS was employed to study the catalytic fast pyrolysis of lignocellulosic biomass samples comprising oak, corn cob, corn stover, and switchgrass, as well as the fractional components of biomass, i.e., cellulose, hemicellulose, and lignin. Quantitative values of condensable vapors and relative compositions of the pyrolytic products including non-condensable gases (NCG's) and solid residues are presented to show how reaction products are affected by catalyst choice. While all catalysts decreased the oxygen-containing products in the condensable vapors, H-ZSM-5 was most effective at producing aromatic hydrocarbons from the pyrolytic vapors. We demonstrated how the Si/Al ratio of the catalysts plays a role in the deoxygenation of the vapors towards the pathway to aromatic hydrocarbons. 相似文献
7.
Alexander YavorskyyOksana Shvydkiv Kieran NolanNorbert Hoffmann Michael Oelgemöller 《Tetrahedron letters》2011,52(2):278-280
A novel continuous-flow photoreactor with parallel capillaries was constructed and successfully tested for the DMBP-sensitized addition of isopropanol to furanones. Complete conversions were achieved after a maximum of 10 min of irradiation with a single 350 nm lamp. The results were compared to analogous batch experiments using a conventional Rayonet chamber reactor equipped with 16 UVA lamps. The capillary tower generally showed higher space-time yields. 相似文献
8.
Joanne E. Stanley Anthony C. Swain Kieran C. Molloy David W. H. Rankin Heather E. Robertson Blair F. Johnston 《应用有机金属化学》2005,19(5):644-657
Perfluoroalkytin compounds R(4−n)Sn(Rf)n (R = Me, Et, Bu, Rf = C4F9, n = 1; R = Bu, Rf = C4F9, n = 2, 3; R = Bu, Rf = C6F13, n = 1) have been synthesized, characterized by 1H, 13C, 19F and 119Sn NMR, and evaluated as precursors for the atmospheric pressure chemical vapour deposition of fluorine‐doped SnO2 thin films. All precursors were sufficiently volatile in the range 84–136 °C and glass substrate temperatures of ca 550 °C to yield high‐quality films with ca 0.79–2.02% fluorine incorporation, save for Bu3SnC6F13, which incorporated <0.05% fluorine. Films were characterized by X‐ray diffraction, scanning electron microscopy, thickness, haze, emissivity, and sheet resistance. The fastest growth rates and highest quality films were obtained from Et3SnC4F9. An electron diffraction study of Me3SnC4F9 revealed four conformations, of which only the two of lowest abundance showed close F Sn contacts that could plausibly be associated with halogen transfer to tin, and in each case it was fluorine attached to either the γ‐ or δ‐carbon atoms of the Rf chain. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
9.
We discuss several enumerative results for irreducible polynomials of a given degree and pairs of relatively prime polynomials of given degrees in several variables over finite fields. Two notions of degree, the total degree and the vector degree, are considered. We show that the number of irreducibles can be computed recursively by degree and that the number of relatively prime pairs can be expressed in terms of the number of irreducibles. We also obtain asymptotic formulas for the number of irreducibles and the number of relatively prime pairs. The asymptotic formulas for the number of irreducibles generalize and improve several previous results by Carlitz, Cohen and Bodin. 相似文献
10.
J. M. Schwantes R. S. Addleman J. D. Davidson M. Douglas D. Meier O. D. Mullen M. Myjak M. E. Jones M. L. Woodring B. Johnson P. H. Santschi 《Journal of Radioanalytical and Nuclear Chemistry》2009,282(3):889-895
We are developing a medium-resolution autonomous in situ gamma detection system for marine and coastal waters. The system is designed to extract and preconcentrate isotopes of interest from natural waters prior to detection in order to eliminate signal attenuation of the gamma rays traveling through water and lower the overall background from the presence of naturally occurring radioactive isotopes (40K and U–Th series radionuclides). Filtration is used to preconcentrate target isotopes residing on suspended particles, while chemosorption is employed to preferentially extract truly dissolved components from the water column. Used filter and chemosorbent media will be counted autonomously using two LaBr3 detectors in a near 4-π configuration around the samples. A compact digital pulse processing system, developed in-house and capable of running in coincidence mode, is used to process the signal from the detectors to a small on-board computer. The entire system is extremely compact (9″ dia. × 30″ len.) and platform independent, but designed for initial deployment on a research buoy. A variety of commercial and in-house nano-porous chemosorbents have been selected, procured or produced, and these and filter and detector components have been tested. 相似文献