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151.
Geoffrey C. Kite Nigel C. Veitch 《Rapid communications in mass spectrometry : RCM》2011,25(18):2579-2590
Flavonoid O‐glycosides are a ubiquitous and important group of plant natural products in which a wide variety of sugars are O‐linked to an aglycone. Determining the identity of the sugars, and the manner in which they are linked, by mass spectrometry alone is challenging. To improve the identification of common O‐linked di‐ and trisaccharides when analysing mixtures of flavonoid O‐glycosides by liquid chromatography/mass spectrometry (LC/MS), the fragmentation of electrosprayed sodium adducts in an ion trap mass spectrometer was investigated. The sodium adducts [M + Na]+ of kaempferol 3‐O‐glycosides generated sodiated glycosyl groups by the neutral loss of kaempferol. The product ion spectra of these sodiated glycosyl groups differed between four isomeric kaempferol 3‐O‐rhamnosylhexosides and four isomeric kaempferol 3‐O‐glucosylhexosides in which the primary hexose was either glucose or galactose and bore the terminal glucose or rhamnose at either C‐2 or C‐6. Fragmentation of sodiated glycosyl groups from linear O‐triglucosides and branched O‐glucosyl‐(1 → 2)‐[rhamnosyl‐(1 → 6)]‐hexosides produced sodiated disaccharide residues, and the product ion spectra of these ions assisted the identification of the complete sugar. The product ion spectra of the sodiated glycosyl groups were consistent among flavonoid O‐glycosides differing in the position at which the sugar was O‐linked to the aglycone, and the nature of the aglycone. The abundance of sodiated species was enhanced by application of a pre‐trap collision voltage, without the need to dope with salt, allowing automated LC/MS methods to be used to identify the glycosyl groups of common flavonoid O‐glycosides, such as rutinosides, robinobiosides, neohesperidosides, gentiobiosides and sophorosides. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
152.
153.
In this paper, we report 30 THz measurements of ammonia in its excited, ν2 = 1, inversion state. These measurements include transition frequencies and pressure shifts (where significant enough to be observed). Included in the data are two forbidden and three ro-inversion transitions, as well as 18 transitions never directly measured before. The measurements were made with an all-solid-state, diode-laser, difference-frequency spectrometer. Using an innovative laser-frequency locking scheme, this spectrometer provided accurately determined and continuously tuned THz-frequencies without requiring accurate knowledge of the absolute laser frequencies. The details of the spectrometer’s frequency calibration is discussed. A global analysis of NH3 based on the available ground state, ν2 = 1 state, and ν2-band transitions was carried out, and the resulting set of recommended molecular effective-Hamiltonian parameters for ammonia is presented. In addition, calculated center frequencies and intensities for all possible transitions up to J = 20 between rotation, inversion, and vibration levels in the ground and ν2 = 1 states are included as supplementary material. 相似文献
154.
Coleman and Korté have restated and defended an earlier attempt to refute the traditional thesis of the conventionality of simultaneity within special relativity. Here we argue their attempt still fails and respond to criticisms of a paper in which we addressed the inadequacies of their earlier paper. The spatial criterion they use to argue for standard synchronization throughout an inertial frame is merely a definition and provides no demonstration that a unique distant simultaneity relation exists in nature. 相似文献
155.
The kinetics of elementary gas phase reactions involved in the oxidation of reduced sulfur species, H2S, CS2, OCS, CH3SH, CH3SCH3, and CH3SSCH3, to SO2 (or other products) are reviewed. The reactions with OH and NO3 which are the processes that initiate the degradation of the above compounds have been evaluated. Reactions of key intermediates, HS, HSO, CH3S, and CH3SO, are discussed. Whenever possible, recommendations for the rate coefficients are made and the need for further work indicated. The review has been carried out with the atmospheric chemistry in mind by looking at the laboratory based kinetics data. This review also provides information that will help model the Earth's sulfur cycle. 相似文献
156.
Edelmann GF Lingevitch JF Gaumond CF Fromm DM Calvo DC 《The Journal of the Acoustical Society of America》2007,122(5):2706-2714
This paper investigates the application of time-reversal techniques to the detection and ensonification of a target of interest. The focusing method is based on a generalization of time-reversal operator techniques. A subrank time-reversal operator is derived and implemented using a discrete set of transmission beams to ensonify a region of interest. In a dynamic ocean simulation, target focusing using a subrank matrix is shown to be superior to using a full-rank matrix, specifically when the subrank matrix is captured in a period shorter than the coherence time of the modeled environment. Backscatter from the point target was propagated to a vertical 64-element source-receiver array and processed to form the sub-rank time-reversal operator matrix. The eigenvector corresponding to the strongest eigenvalue of the time-reversal operator was shown to focus energy on the target in simulation. Modeled results will be augmented by a limited at-sea experiment conducted on the New Jersey shelf in April-May 2004 measured low-frequency backscattered signal from an artificial target (echo repeater). 相似文献
157.
An approximate analytical solution is provided for one-dimensional, counter- current, spontaneous imbibition of a wetting
phase (water) into a semi-infinite porous medium. The solution is based on the assumption that a similarity solution exists
for the displacement process. This assumption, in turn, rests on the assumption that the set of relative permeability and
capillary pressures curves are unique functions of saturation and do not depend on the nature of the displacement. It further
rests on the assumption that the saturation at the imbibition face does not vary with time. It is demonstrated that the solution
is in agreement with results obtained from experiments and also numerical analyses of these experiments. The experiments utilize
cylindrical samples with the radial surface and one end-face sealed, and with counter-current imbibition occurring at the
open end-face. The stage of the experiment that is modeled by the present solution is the period before the imbibition front
contacts the sealed end-face. An important finding of the present analysis is that the pressure upstream of the advancing
invasion front is a constant. A second, improved solution is also presented; this solution is an iterative, series solution
of an integral-differential equation. It converges to a stable solution in very few terms. 相似文献
158.
Synthesis of an [(NHC)2Pd(SiMe3)2] Complex and Catalytic cis‐Bis(silyl)ations of Alkynes with Unactivated Disilanes 下载免费PDF全文
Melvyn B. Ansell Dr. Debbie E. Roberts Prof. F. Geoffrey N. Cloke Dr. Oscar Navarro Dr. John Spencer 《Angewandte Chemie (International ed. in English)》2015,54(19):5578-5582
The novel complex cis‐[(ITMe)2Pd(SiMe3)2 (ITMe=1,3,4,5‐tetramethylimidazol‐2‐ylidene) has been synthesized by mild oxidative cleavage of Me3SiSiMe3 using [(ITMe)2Pd0]. The use of this complex as precatalyst for the cis‐bis(silyl)ation of alkynes using unactivated disilanes is reported. 相似文献
159.
Dr. Aleksander Rebane Geoffrey Wicks Dr. Mikhail Drobizhev Dr. Thomas Cooper Aleksander Trummal Dr. Merle Uudsemaa 《Angewandte Chemie (International ed. in English)》2015,54(26):7582-7586
We present a new approach for determining the strength of the dipolar solute‐induced reaction field, along with the ground‐ and excited‐state electrostatic dipole moments and polarizability of a solvated chromophore, using exclusively one‐photon and two‐photon absorption measurements. We verify the approach on two benchmark chromophores N,N‐dimethyl‐6‐propionyl‐2‐naphthylamine (prodan) and coumarin 153 (C153) in a series of toluene/dimethyl sulfoxide (DMSO) mixtures and find that the experimental values show good quantitative agreement with literature and our quantum‐chemical calculations. Our results indicate that the reaction field varies in a surprisingly broad range, 0–107 V cm?1, and that at close proximity, on the order of the chromophore radius, the effective dielectric constant of the solute–solvent system displays a unique functional dependence on the bulk dielectric constant, offering new insight into the close‐range molecular interaction. 相似文献
160.
Insights into the Catalytic Activity of Nitridated Fibrous Silica (KCC‐1) Nanocatalysts from 15N and 29Si NMR Spectroscopy Enhanced by Dynamic Nuclear Polarization 下载免费PDF全文
Dr. Aany Sofia Lilly Thankamony Dr. Cédric Lion Dr. Frédérique Pourpoint Baljeet Singh Dr. Angel J. Perez Linde Dr. Diego Carnevale Prof. Geoffrey Bodenhausen Dr. Hervé Vezin Prof. Olivier Lafon Prof. Vivek Polshettiwar 《Angewandte Chemie (International ed. in English)》2015,54(7):2190-2193
Fibrous nanosilica (KCC‐1) oxynitrides are promising solid‐base catalysts. Paradoxically, when their nitrogen content increases, their catalytic activity decreases. This counterintuitive observation is explained here for the first time using 15N‐solid‐state NMR spectroscopy enhanced by dynamic nuclear polarization. 相似文献