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71.
Silva BV Violante FA Pinto AC Santos LS 《Rapid communications in mass spectrometry : RCM》2011,25(3):423-428
Using electrospray ionization (tandem) mass spectrometry (ESI-MS(/MS)) spectrometric experiments, the Sandmeyer reaction was monitored on-line, and key intermediates were intercepted and characterized for the first time. The mechanistic information provided by on-line ESI-MS(/MS) is in accordance with Sandmeyer's proposal, and was made possible by coupling a microreactor on-line to the ESI ion source, which allowed reactions to be screened from 0.7-2.0 s, identifying and characterizing all intermediates that were formed and consumed during the reaction. 相似文献
72.
Angelo Sala Kathleen Kayganich Joseph A. Zirrolli Robert C. Murphy 《Journal of the American Society for Mass Spectrometry》1991,2(4):314-321
The sulfidopeptide leukotrienes, leukotriene E4, (LTE4,) and its N-acetyl derivative and several ω? and β-oxidized metabolites of LTE4, have been analyzed by tandem mass spectrometry. [M?H]? ions were produced by continuous flow fast atom bombardment, and collision-induced dissociation of these ions was studied by using a triple quadrupole instrument. The product ion spectra obtained were characteristic of the structure of LTE4, and mechanisms of ion formation were investigated by using deuterated compounds. β-Elimination of the peptide portion of LTE4, by loss of CO2, and ethylene amine leaves the C-l carboxyl group ionized in the most abundant fragment ion for LTE4, and all metabolites. Tandem mass spectrometry of fast atom bombardment-generated anions from ω? and β-oxidized metabolites of LTE4, produced similar ions with only a minor influence of the third carboxyl group at the omega terminus evident. Tandem mass spectrometry was used to identify unequivocally the presence of unmodified LTE4, in a high performance liquid chromatography-purified fraction of urine from a normal healthy volunteer after infusion with LTE4. 相似文献
73.
Sayed Abdel-Khalek Angelo Plastino Abdel-Shafy Fahmy Obada 《Central European Journal of Physics》2011,9(6):1426-1433
The dynamics of the Buck and Sukumar model (B. Buck and C. V. Sukumar, Phys. Lett. A 81, 132 (1981)) is investigated using
different semi-classical information-theory tools. Their interplay reveals somewhat unexpected features. A new signature for
the classical-quantum barrier is encountered thereby. 相似文献
74.
Angelo Paci Dominique Guillaume Henri‐Philippe Husson 《Journal of heterocyclic chemistry》2001,38(5):1131-1134
Three analogs of the cytostatic drug ifosfamide incorporating 1‐methyl‐2‐chloroethyl side chains were designed and prepared as an attempt to obtain drugs of lower toxicity. 相似文献
75.
76.
Cyclic carbonate formation from carbon dioxide and oxiranes in tetrabutylammonium halides as solvents and catalysts 总被引:1,自引:0,他引:1
[reaction: see text] Epoxides dissolved in molten tetralkylammonium salts bearing halides as counterions are converted into cyclic carbonates under atmospheric pressure of carbon dioxide. The reaction rate depends on the nucleophilicity of the halide ion as well as the structure of the cation. 相似文献
77.
We investigate finite lattice approximations to the Wilson renormalization group in models of unconstrained spins. We discuss first the properties of the renormalization group transformation (RGT) that control the accuracy of this type of approximation and explain different methods and techniques to practically identify them. We also discuss how to determine the anomalous dimension of the field. We apply our considerations to a linear sigma model in two dimensions in the domain of attraction of the Ising fixed point using a Bell–Wilson RGT. We are able to identify optimal RGTs which allow accurate computations of quantities such as critical exponents, fixed-point couplings and eigenvectors with modest statistics. We finally discuss the advantages and limitations of this type of approach. 相似文献
78.
The mass spectrometric behaviour of 2-(2-pyridyl)-2,3-dihydroxy-5-phenyl-4-pentene has been studied with the aid of B/E, B2/E linked scans, exact mass measurements, collisionally activated dissociation mass-analysed ion kinetic energy spectra, and labelling experiments. The primary loss of water is proved to involve both hydroxylic hydrogens, thus suggesting the formation of an epoxidic radical ion and the presence of extensive skeletal rearrangements. 相似文献
79.
Tullio Carolina Angelo Clerici Dianella Coggiola Sergio Morrocchi 《Journal of heterocyclic chemistry》1981,18(7):1421-1423
Chemical evidence is given that the title photo-reactions proceed via hydrogen abstraction by the photo-excited base from the alcohol in neutral medium and via electron-transfer process between the photo-excited base and the alcohol in hydrochloric acid acidified medium. 相似文献
80.