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144.
Tino Gumann Helmut Schwarz Daniel Stahl Jean-Claude Tabet 《Helvetica chimica acta》1981,64(8):2782-2790
The molecular ions from three isomeric cyclanones isomerize to the ethyl-2-cyclohexanone ion prior to C2H4 elimination. With D- and 18O-labelled compounds it is shown by Mass Analyzed Ion Kinetic Energy Spectroscopy (MIKES.) that both isomerization and C2H4 loss are specific processes. By high resolution collisional activation spectra it is shown that the resultant fragment ion [C6H10O]\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{+ \atop \dot{}} $\end{document} (m/z = 98) differs in structure from the cyclohexanone molecular ion. 相似文献
145.
Da Silva MV Perlat MC Tabet JC Giorgi G Salvini L Ponticelli F 《Journal of the American Society for Mass Spectrometry》2003,14(8):851-861
Ion trap mass spectrometry has been used to structurally characterize and differentiate positional and stereo isomers of arylglycosides having potential antioxidant properties. The use of the self-ionization (SI) technique has allowed to evidence a strong reactivity of fragment ions produced from dissociations of the molecular ion towards the molecules introduced into the trap. Specific structural effects due to positional isomers and anomers have been also envisaged through the occurrence of bimolecular processes inside the ion trap analyzer. Under self-ionization conditions, even-electron ions are produced. The charge is retained on the sugar moiety, in agreement with its proton affinity higher than that of the substituted phenol moiety. Most of the fragmentation pathways involve elimination of acetic acid that protects the hydroxylic groups of the glycoside. SI also produces adduct ions, likely as covalent species, having higher m/z values than the molecular ion. The reaction site is mainly the double bond present in the pyranosidic ring. Even if some fragment ions have lost the initial stereochemistry, their formation can be related to the structure of the parent neutrals introduced into the cell. Collision-induced dissociation (CID) experiments, carried out on ions formed by ion-molecule reactions, have allowed to obtain further information on gas phase ion structures. The study of mass-selected ion-molecule reactions and their kinetics have evidenced a spectacularly different reactivity of the ion at m/z 111 towards the two anomers 2alpha and 2beta, with the latter showing a much more pronounced reactivity. The approach developed in this work revealed to be an useful tool in structural characterization, as well as in stereo and regiochemical differentiation of arylglycosides. 相似文献
146.
Tino Gumann Raymond Houriet Daniel Stahl Jean-Claude Tabet Nikolaus Heinrich Helmut Schwarz 《Journal of mass spectrometry : JMS》1983,18(5):215-218
The [C6H9]+ ions produced either via unimolecular H2O loss from 13 [C6H11O]+ precursors or direct protonation of 1,3- and 1,4-cyclohexadiene have identical collisional activation mass spectra. The kinetic energy release data for the process [C6H11O]+→[C6H9]++H2O are also very similar (on average T0.5=24 meV) irrespective of the constitution of the precursor. From the proton affinities of 1,3-cyclohexadiene (PA=837.2 kJ mol?1) using ion cyclotron resonance mass spectrometry the heat of formation of the [C6H9]+ ion is determined to 804.6 kJ mol?1. This value taken together with the results of molecular orbital calculations (MNDO) and the structure indicative losses of CH3. and C2H4 upon collisional activation suggest that the [C6H9]+ ion has the structure of the 1-methylcyclopentenylium ion f and not that of the slightly less stable cyclohexenylium ion g. The generator of an easily interconverting system of isomeric [C6H9]+ ions is unlikely to be due to the high barrier separating the various isomers. 相似文献
147.
Jankowski CK Allain F Dozol JF Virelizier H Tabet JC Moulin C Lamouroux C 《Rapid communications in mass spectrometry : RCM》2003,17(12):1247-1255
The extraction of (135)Cs from high activity waste arising from reprocessing of spent fuel can be achieved by using calix[4]arene crown compounds. The radiolytic degradation of calix[4]arene crowns as well as their solvent, o-nitrophenyloctyl ether (NPOE), was studied using electrospray ionization mass spectrometry (ESI-MS) (that formed Cs(+) or Na(+) adducts) in nitric acid, as well as by chemical ionization tandem mass spectrometry (MS/MS) experiments. The structures of major degradation products were identified with MS and specifically labelled nitric acid. Although NPOE and calix[4]arene crowns alone are relatively stable, under simulated conditions resembling the real industrial processes involving radiolysis in the presence of nitric acid, several products resulting from nitration and oxidation were observed. 相似文献
148.
Jean-Claude Tabet Yves Tondeur Yutaka Hirano Annemarie Wegmann Pierre Tecon Carl Djerassi 《Journal of mass spectrometry : JMS》1984,19(10):473-481
The ammonia chemical ionization (CI/[NH4+]) mass spectra of a series of diastereomeric methyl and benzyl ethers derived from 3-hydroxy steroids (unsaturated in position 5 and saturated) have been studied. The adduct ions [M+NH4]+ and [MH]+ and the substitution product ions [M+NH4? ROH]+ (thereafter called [MsH]+) are characterized by an inversion in their relative stabilites in relation to their initial configuration. [M+NH4]α+ and [MH]α+ formed from the α-Δ5-steroid isomers are stabilized by the presence of a hydrogen bond which is not possible for the β-isomers. This stereochemical effect has also been observed in the mass analysed ion kinetic energy (MIKE) spectra of [M+NH4]+ and [MH]+. The MIKE spectra of [MsH]+ indicate that those issued from the β-isomers are more stable than the one originating from the α-isomers. This behavior is also observed in the first field free region (HV scan spectra) for [MH]+, [MsH]+ and [M+NH4]+ which are precursors of the ethylenic carbocations (base peak in the conventional CI/[NH4]+ spectra). Mechanisms, such as SN1 and SNi, have been ruled out for the formation of [MsH]+, but instead the data support an SN2 mechanism during the ion-molecule reaction between [M+NH4]+ and NH3. 相似文献
149.
Organic peroxides such as the cumene hydroperoxide I (M(r) = 152 u), the di-tert-butyl peroxide II (M(r) = 146 u) and the tert-butyl peroxybenzoate III (M(r) = 194 u) were analyzed by atmospheric pressure chemical ionization mass spectrometry using a water-methanol mixture as solvent with a low flow-rate of mobile phase and unusual conditions of the source temperature (< or =50 degrees C) and probe temperature (70-200 degrees C). The mass spectra of these compounds show the formation of (i) an [M + H](+) ion (m/z 153) for the hydroperoxide I, (ii) a stable adduct [M + CH(3)OH(2)](+) ion (m/z 179) for the dialkyl peroxide II and (iii) several protonated adduct species such as protonated molecules (m/z 195) and different protonated adduct ions (m/z 227, 389 and 421) for the peroxyester III. Tandem mass spectrometric experiments, exact mass measurements and theoretical calculations were performed for characterize these gas-phase ionic species. Using the double-well energy potential model illustrating a gas-phase bimolecular reaction, three important factors are taken into account to propose a qualitative interpretation of peroxide behavior toward the CH(3)OH(2) (+), i.e. thermochemical parameters (DeltaHdegrees(reaction)) and two kinetic factors such as the capture constant of the initial stable ion-dipole and the magnitude of the rate constant of proton transfer reaction into the loose proton bond cluster. 相似文献
150.
Delayed extraction experiments were undertaken to gain a better insight into the dynamic effects involved in the ion formation in UV matrix-assisted laser desorption/ionization. Part I1 was devoted to a 2,5-dihydroxybenzoic (2,5-DHB) matrix. The results clearly demonstrated the existence and the role of high-mass precursors corresponding to a non-covalent matrix-analyte association in ion formation. In this complementary study, ion flight time and abundance were studied as a function of the delay extraction time using the matrix alpha-cyano-4-hydroxycinnamic acid (HCCA). Under our instrumental conditions, where ejected ions experienced a low repulsing electric field before extraction, two main results were obtained: (i) two ion components are observed in the peak profiles depending on the repulsing field, a first, major component (I) similar to that observed for 2,5-DHB and a second, minor component (II) apparently triggered by the delayed extraction pulse, and (ii) ion time-of-flight variation vs delay time remained lower than that noted with 2,5-DHB matrix, indicating that the initial axial velocity is smaller. The initial kinetic energy of matrix and low molecular mass peptide ions for the component I is not high enough to overcome the repulsing potential in the delay time range (200-2200 ns) and we have to assume that ions have non-covalent clusters as precursors. Complete desolvation of these clusters-aggregates would be achieved through the extraction step. Simulations of the ion time-of-flight as a function of the delay time allow the determination of the average size of the precursors, typically 4500, 40000 and 50000 u for HCCA, ACTH 7-38 and bovine insulin quasi-molecular ion, respectively, assuming that the precursors are singly charged. The size of these ion precursors is greater than that of those generated for 2,5-DHB. For component II, ions are probably not solvated and they are directly desorbed from the target. Taking into account the results on HCCA and 2,5-DHB matrices and other results from the literature, a general model for ion formation based on clusters as ion precursors is proposed and discussed. 相似文献