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61.
Chafia Bennaceur Carlos Afonso Sandra Alves Anne Bossée Jean-Claude Tabet 《Journal of the American Society for Mass Spectrometry》2013,24(8):1260-1270
Structural elucidation and distinction of isomeric neurotoxic agents remain a challenge. Tandem mass spectrometry can be used for this purpose in particular if a “diagnostic” product ion is observed. Different vibrational activation methods were investigated to enhance formation of diagnostic ions through consecutive processes from O,O-dialkyl alkylphosphonates. Resonant and non-resonant collisional activation and infrared multiphoton dissociation (IRMPD) were used with different mass spectrometers: a hybrid quadrupole Fourier transform ion cyclotron resonance (Qh-FTICR) and a hybrid linear ion trap-Orbitrap (LTQ/Orbitrap). Double resonance (DR) experiments, in ion cyclotron resonance (ICR) cell, were used for unambiguous determination of direct intermediate yielding diagnostic ions. From protonated n-propyl and isopropyl O-O-dialkyl-phosphonates, a diagnostic m/z 83 ion characterizes the isopropyl isomer. This ion is produced through consecutive dissociation processes. Conditions to favor its formation and observation using different activation methods were investigated. It was shown that with the LTQ, consecutive experimental steps of isolation/activation with modified trapping conditions limiting the low mass cut off (LMCO) effect were required, whereas with FT-ICR by CID and IRMPD the diagnostic ion detection was provided only by one activation step. Among the different investigated activation methods it was shown that by using low-pressure conditions or using non-resonant methods, efficient and fast differentiation of isomeric neurotoxic agents was obtained. This work constitutes a unique comparison of different activation modes for distinction of isomers showing the instrumental dependence characteristic of the consecutive processes. New insights in the dissociation pathways were obtained based on double-resonance IRMPD experiments using a FT-ICR instrument with limitation at low mass values.
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62.
In the course of current work on the conformational analysis of cis-hydrindanones1, we required 5α, 13α, 14α and 5α, 13β, 14β-androstan-16-one 5 and 10 the C and D rings of which provide rigid models of the two conformations of cis-hydrindan-2-one. 相似文献
63.
Dr. Frederik Schleife Dr. Clément Bonnot Dr. Jean-Claude Chambron Dr. Martin Börner Prof. Dr. Berthold Kersting 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(21):e202104255
The syntheses and properties of expanded 4-tert-butyl-mercaptocalix[4]arenes, in which the methylene linkers are replaced by −CH2NRCH2− or −CH2NRCH2− and −CH2NRCH2CH2CH2NRCH2− units, are described. The new macrocycles were obtained in a step-wise manner, utilizing fully protected, i. e. S-alkylated, derivatives of the oxidation-sensitive thiophenols in the cyclisation steps. Reductive cleavage of the macrobicyclic or macrotricyclic intermediates ( 6 , 7 , 11 ) afforded the free thiophenols (H4 8 , H4 9 , and H4 12 ) in preparative yields as their hydrochloride salts. The protected proligands can exist in two conformations, resembling the “cone” and “1,3-alternate” conformations found for the parent calix[4]arenes. The free macrocycles do not show conformational isomerism, but are readily oxidized forming intramolecular disulfide linkages. Preliminary complexation experiments show that these expanded mercaptocalixarenes can serve as supporting ligands for tetranuclear thiolato clusters. 相似文献
64.
The structural rules which govern the epitaxial crystallisation of polymers - and especially polyolefins - on organic substrates are established. Illustrative examples involve isotactic and syndiotactic polypropylenes and poly( l-butene). Investigation of the film structure by electron microscopy, electron diffraction and atomic force microscopy reveals some unprecedented features, including in particular the selection of the contact plane according to the chirality of its constituent helices, and direct observation of both right and left hands of polyolefin helices. 相似文献
65.
66.
Françoise Maugé Jean-Paul Gallas Jean-Claude Lavalley Guido Busca Gianguido Ramis Vincenzo Lorenzelli 《Mikrochimica acta》1988,95(1-6):57-61
In the far IR region at low molybdenum loadings, Mo-SiO2 catalysts present a pseudomolybdate or a polymolybdate species, while bulk-like MoO3 appears at loadings close to the geometrical monolayer coverage. W-SiO2 and V-SiO2 spectra show bands close to those observed on the corresponding bulk oxides.In the case of TiO2, Al2O3, ZrO2 supported catalysts, a band is observed near 1000 cm–1 which is assigned to the Mo=O stretching vibration of coordinatively unsaturated Mo
n+ ions showing a stronger interaction with the support than one observed on silica. 相似文献
67.
Noncovalent complexes of DNA and Hoechst 33258 were investigated by ESI-FT/ICR MS in various activation modes (collision-induced dissociation (CID), sustained off-resonance irradiation collision-induced dissociation (SORI-CID), infrared multiphoton dissociation (IRMPD) and electron detachment dissociation (EDD)). The binding selectivity of Hoechst 33258 was confirmed by the comparative study of its noncovalent association with different DNA sequences. The CID spectra of [ds + HO - 5H](5-) obtained with a linear hexapole ion trap resulted in unzipping of the strands. This outcome is a clue to the drug-binding mode, shading light on the localization of the binding sites of Hoechst 33258 to the DNA sequence. The IRMPD and SORI-CID experiments mainly gave DNA backbone cleavages and internal fragment ions. From this result, information on the localization of the binding sites of Hoechst 33258 in the DNA sequence was obtained. No sodium cationization was observed on the DNA sequence ions although they were present on fragmentation of the duplex, indicating that the backbone cleavages were generated from the single strand associated with the Hoechst 33258 where the number of alkali cation is restricted. Under electron detachment (ED) conditions, multiple EDs were achieved for the [ds + HO - 5H](5-) ion without any significant dissociation. The presence of drug appears to enhance the stability of the multiply charged system. It was proposed that the studied noncovalent complex involved the formation of zwitterions and consequently strong salt-bridge interactions between DNA and drug. 相似文献
68.
范宇航 孙丽萍 霍丽华 赵辉 Jean-Marc Bassat Aline Rougier Sbastien Fourcade Jean-Claude Grenier 《无机化学学报》2013,29(18)
采用EDTA-柠檬酸法合成了中温固体氧化物燃料电池阴极材料Sr1.5La0.5Mn1-xCoxO4(SLMCOx),并利用粉末X射线衍射(XRD)、X射线光电子能谱(XPS)以及电化学交流阻抗谱(EIS)进行表征。结果表明,该材料与Ce0.9Gd0.1O1.95(CGO)在1 200℃烧结12 h不发生化学反应。随着Co掺入量的增加,氧化物中Mn3+和Co2+含量增多,晶格氧含量降低,晶格畸变率增大。交流阻抗谱(EIS)测试结果显示,钴的掺杂明显降低电极的极化电阻,其中Sr1.5La0.5Mn0.7Co0.3O4阴极在700℃空气中的极化电阻为0.62 Ω·cm2,明显小于Sr1.5La0.5MnO4阴极在750℃的极化电阻(1.5 Ω·cm2),表明钴掺杂的Sr1.5La0.5Mn1-xCoxO4是一种潜在的IT-SOFC阴极材料。 相似文献
69.
70.
Jean-Claude Petit 《Accreditation and quality assurance》1999,4(11):458-462
An appropriate Quality approach in fundamental research should have its roots in the very principles of the "scientific method".
Quality and fundamental research could thus reconcile at the condition, on the one hand, that Quality practioners understand
and take into account the reality of the "science in action" and, on the other hand, that scientists improve their awareness
of the new deal which is being made between science, technology and society as well as of the actual issues of Quality. A
modern Quality approach, well adapted to this specific activity, should help both scientists, decision-makers and the public
face the issues concerning the role of science in society in the future. In this context, I specify a number of practical
proposals concerning, in particular, the adaptation of the requirements of the quality approach to the type of research, the
distinction between the three major steps of a research programme (i.e. quality of the objective, the process and the results)
and the encouragement of experience feedback.
Received: 8 March 1998 / Accepted: 8 December 1998 相似文献