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1.
Rogalewicz F Bourcier S Hoppilliard Y 《Rapid communications in mass spectrometry : RCM》2005,19(6):743-751
As part of a research program on neurotransmitters in a biological fluid, the fragmentations characterising catecholamines protonated under electrospray ionisation (ESI) conditions, under low collision energy in a triple-quadrupole mass spectrometer, were investigated. The decompositions of protonated noradrenaline (VH) and normetanephrine (VIH) were studied. Both precursor ions eliminate first H2O at very low collision energy, and the fragmentations of [MH-H2O]+ occur at higher collision energy. The breakdown graphs of [MH-H2O]+ ions, with collision energy varying from 0-40 eV in the laboratory frame, are presented. [VIH-H2O]+ ions lose competitively NH3 and CH3OH. For [VH-H2O]+ the loss of NH3 is dominant while H2O is eliminated at very low abundance at all collision energies. All of these secondary fragmentations are followed at higher collision energies by elimination of CO. These fragmentations are interpreted by means of ab initio calculations up to the B3LYP/6-311+G(2d,2p) level of theory. The elimination of H2O requires first the isomerisation of N-protonated forms, chosen as energy references, to O-protonated forms. The isomerisation barriers are calculated to be lower than 81 kJ/mol above the N-protonated forms. The elimination of NH3 from [MH-H2O]+ requires first the migration, via a cyclisation, of the amine function from the linear chain to the aromatic ring in order to prevent the formation of unstable disubstituted carbocations in the ring. The barriers associated with the loss of NH3 are located 220 and 233 kJ/mol above VH and 219 kJ/mol above VIH. The energy barrier for the loss of ROH is located 236 and 228 kJ/mol above VH and VIH, respectively. The absence of ions corresponding to [VH-2H2O]+ is due to a parasitic mechanism with an activation barrier lower than 236 kJ/mol that leads to a stable species unable to fragment, thus preventing the second loss of H2O. Losses of CO following the secondary fragmentations involve activation barriers higher than 330 kJ/mol. 相似文献
2.
Henri-Edouard Audier Marcel Fetizon Yannik Henry Thierry Prange 《Journal of mass spectrometry : JMS》1976,11(10):1047-1055
The fragmentation mechanisms of oxazole have been studied in detail on using various experimental techniques (refocusing of metastable ions, deuteration, AP measurements) and by theoretical calculations. 相似文献
3.
Guy Bouchoux Yannik Hoppiiliard Pascale Jaudon 《Journal of mass spectrometry : JMS》1987,22(2):98-102
Dissociative ionization of 1,2-epoxy n-alkanes gives rise to abundant [C4H7O]+ ions of structure [CH3OCHCHCH2]+. This conclusion is drawn from metastable ion analysis and from collisional activation spectra. This fragmentation involves the C? C ring opening and a 1,4-H migration leading to the corresponding enol ether [CH3OCHCHCH2R]+. precursor of [CH3OCHCHCH2]+ fragment. The same isomerization scheme applies to 1,2-epoxy methyl substituted alkanes and 2,3-epoxy n-alkanes. 相似文献
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5.
Stphane Bouchonnet Yannik Hoppilliard Agns Maret 《Journal of mass spectrometry : JMS》1993,28(9):963-969
Isomeric di- and trifunctional aromatic amines are easily differentiated on the basis of their plasma desorption (PD) mass spectra. Six series of aromatic amines were studied in the positive-ion mode. In each series, the differences observed in the PD mass spectra allow each isomer to be characterized. In the formation of molecular ions, these differences proceed from the competition between electron impact ionization and protonation. Several chemoselective or regioselective reactions such as hydrogenation, hydration, dimerization and some fragmentations also allow isomeric aromatic amines to be differentiated. 相似文献
6.
DiCosmo F. Quesnel A. Misawa M. Tallevi S. G. 《Applied biochemistry and biotechnology》1987,14(2):101-106
The ammonium sulfate-precipitated fraction from mycelia and culture-filtrates and the crude, cell-free culture filtrates from
the growth medium of the fungiChrysosporium palmorum, Eurotium rubrum, Micromucor isabellina, andPythium aphanidermatum when aseptically added to cell suspensions ofCantharanthus roseus caused a rapid and dramatic increase in indole alkaloid biosynthesis. Up to 400 μg/L ajmalicine and 600 μg/L catharanthine
were detected in C.roseus cell suspension grown in the presence of theM. isabellina fungal culture filtrate for 3 d. Untreated cells produced only trace levels of ajmalicine and catharanthine per liter of
cell suspension after 15 d of culture. 相似文献
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Sophie Bourcier Yannik Hoppilliard 《Rapid communications in mass spectrometry : RCM》2009,23(1):93-103
This work presents the use of neutral losses (NL) for the identification of compounds related to the metabolism of tyrosine. The mass spectra of all the studied compounds, recorded at several collision energies, are compared. The fragmentation mechanism of protonated molecules, MH+, is explained by combining collision‐induced dissociation (CID) mass spectra and density functional theory (DFT) calculations. The results show that the first fragmentation is the elimination from MH+ of a neutral molecule including a functional group of the linear chain. Three primary neutral losses are observed: 17 u (NH3), 18 u (H2O) and 46 u (H2O+CO) characterizing amino, hydroxyl and carboxylic functions on the linear chain. The presence and abundance of ions corresponding to these losses are dependent on (i) the position of the functional group on the linear chain, (ii) the initial localisation of the protonating hydrogen, and (iii) the substitution of the aromatic ring. For compounds including a functional group on the benzylic carbon atom, the investigation of the other functions requires the knowledge of secondary fragmentations. Among these secondary fragmentations we have retained the loss of NH3 from [MH–18u]+ and the loss of ketene from [MH–17u]+. Experimentally these fragmentations are detected using losses of 35 u and 59/73 u. In other words, NL35 identifies hydroxy and amino compounds and NL 46 and/or NL59/73 identify carboxylic acids. The search for characteristic neutral losses is used for the analysis of compounds in a mixture and the analysis of biological fluid. We show that selective search of several neutral losses allows also the unambiguous differentiation of isomers and gives the opportunity to identify compounds in biological fluids. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
9.
Pierre Longevialle Guy Bouchoux Yannik Hoppilliard 《Journal of mass spectrometry : JMS》1990,25(10):527-536
Electron impact ionization of steroidal compounds with two diferently substituted functional groups (amide and amine) at remote positions leads to the interaction of these groups in ion-neutral complexes after the detachment of one of them. Two situations may be encountered, depending on which group is more easily detached from low-energy parent ions: (i) when the formation of the immonium ion is preferred, a very efficient proton transfer to the amide is observed leading to abundant [M? imine]+· and subsequent daughter ions; (ii) when the detachment of the amide is preferred, hydrogen exchanges occur with the amine group, and fragment ions may be observed resulting from the addition of both groups in a proton-bound structure. 相似文献
10.
Despite the technological importance of metal/Si multilayer structures in microelectronics, the interface reactions occurring during their preparation are not yet fully understood. In this work, the interface intermixing in Mo/Si multilayer coatings has been studied with respect to their preparation conditions. Various samples, prepared at room temperature with different Mo deposition rates (0.06–0.43?Å?s?1) and a constant Si rate, have been investigated by detailed TEM observations. Contrary to the Si-on-Mo interface where no evidence of chemical intermixing could be found, the Mo-on-Si interface presents a noticeable interface zone whose thickness was found to noticeably decrease (from 4.1 to 3.2?nm) when increasing the Mo deposition rate. Such intermixing phenomena correspond to diffusion mechanisms having coefficients ranging from 0.25?×?10?15 to 1.2?×?10?15?cm2?s?1 at room temperature. By assuming a diffusion mechanism mainly driven by Mo–Si atomic exchanges to minimize the surface energy, the diffusion dependence with Mo deposition rate has been successfully simulated using a cellular automaton. A refined simulation including Mo cluster formation is also proposed to explain the scenario leading to the full crystallization of Mo layers. 相似文献