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71.
Mesylate derivatives of 3-aryl-3-hydroxy-beta-lactams and thiolactams react in DMSO-d(6) by first-order processes to give alcohol products. Substituent effect studies implicate carbocation intermediates (ion-pairs) that are captured by DMSO-d(6) to give transient oxosulfonium ions. Rapid reaction of the oxosulfonium ions with trace amounts of water leads to the alcohol product and regenerates DMSO-d(6). H(2)(17)O labeling studies show that (17)O is incorporated into the DMSO. The mesylate derivatives of endo- and exo-2-hydroxy-2-phenylbicyclo[2.2.1]heptan-3-one also react in DMSO-d(6) to give the alcohol products. Ion-pair intermediates that capture DMSO giving unstable oxosulfonium ions are again proposed. Exo-2-phenyl-endo-bicyclo[2.2.1]heptyl trifluoroacetate readily eliminates trifluoroacetic acid in DMSO-d(6) via a cationic mechanism involving loss of the endo-trifluoroacetate leaving group as well as an exo-hydrogen. The O-methyl oxime derivative of alpha-chloro-alpha,alpha-diphenylacetophenone reacts in DMSO-d(6) to give 1-methoxy-2,3-diphenylindole, a product derived from cyclization of a cationic intermediate. A common ion rate suppression provides further evidence for a cationic mechanism. The triflate derivative of pivaloin reacts by a cationic mechanism in DMSO-d(6) to give rearranged products. The rate is even faster than in highly ionizing solvents such as trifluoroethanol or trifluoroacetic acid. 1-Adamantyl mesylate reacts in DMSO-d(6) by a first-order process (Y(OMs) = -4.00) to give a long-lived oxosulfonium ion, 1-Ad-OS(CD(3))(2)(+), which can be characterized spectroscopically. This oxosulfonium ion reacts only slowly with water at elevated temperatures to give 1-adamantanol. DMSO is therefore a viable solvent for k(s), k(C), and k(Delta) cationic processes. 相似文献
72.
Arbia Khemiri Bertrand Naudin Xavier Franck Philippe Chan Tchi Song Thierry Jouenne Pascal Cosette 《Analytical and bioanalytical chemistry》2013,405(30):9835-9842
In prokaryote organisms, N-glycosylation of proteins is often correlated to cell–cell recognition and extracellular events. Those glycoproteins are potential targets for infection control. To date, many surface-glycosylated proteins from bacterial pathogens have been described. However, N-linked Pseudomonas surface-associated glycoproteins remain underexplored. We report a combined enrichment and labeling strategy to identify major glycoproteins on the outside of microorganisms. More precisely, bacteria were exposed to a mix of biotinylated lectins able to bind with glycoproteins. The latter were then recovered by avidin beads, digested with trypsin, and submitted to mass spectrometry. The targeted mixture of glycoproteins was additionally deglycosylated in the presence of H2 18O to incorporate 18O during PNGase F treatment and were also analyzed using mass spectrometry. This approach allowed us to identify a few tens of potential N-glycoproteins, among which flagellin FliC was the most abundant. To detect the possible sites of FliC modifications, a de novo sequencing step was also performed to discriminate between spontaneous deamidation and N-glycan loss. This approach led to the proposal of three potential N-glycosylated sites on the primary sequence of FliC: N26, N69, and N439, with two of these three asparagines belonging to an N-X-(S/T) consensus sequence. These observations suggest that flagellin FliC is a heterogeneous protein mixture containing both O- and N-glycoforms. Figure
Analytical scenario developed for bacterial glycoprotein enrichment. This strategy includes three main steps: (1) exposure of Pseudomonas aeruginosa cells to a mixture of biotinylated lectins [wheat germ agglutinin (WGA) and concanavalin A (ConA)]; (2) enrichment of N-glycoproteins by elution with avidin beads; and (3) mass spectrometry (MS) identification and characterization of intact and deglycosylated peptides before and after H2 18O PNGase F enzymatic treatment, respectively 相似文献
73.
74.
Guérandel C Vernex-Loset L Krier G De Lanève M Guillot X Pierre C Muller JF 《Talanta》2011,84(1):133-140
Enhancing the flowing properties of fresh concrete is a crucial step for cement based materials users. This is done by adding polymeric admixtures. Such additives have enabled to improve final mechanicals properties and the development of new materials like high performance or self compacting concrete. Like this, the superplasticizers are used in almost cement based materials, in particular for concrete structures that can have a potential interaction with drinking water. It is then essential to have suitable detection techniques to assess whether these organic compounds are dissolved in water after a leaching process or not. The main constituent of the last generation superplasticizer is a PolyCarboxylate-Ester copolymer (PCE), in addition this organic admixture contains polyethylene oxide (free PEO) which constitutes a synthesis residue. Numerous analytical methods are available to characterize superplasticizer content. Although these techniques work well, they do not bring suitable detection threshold to analyze superplasticizer traces in solution with high mineral content such as leachates of hardened cement based materials formulated with superplasticizers. Moreover those techniques do not enable to distinguish free PEO from PCE in the superplasticizer.Here we discuss two highly sensitive analytical methods based on mass spectrometry suitable to perform a rapid detection of superplasticizer compounds traces in CEM I cement paste leachates: MALDI-TOF mass spectrometry, is used to determine the free PEO content in the leachate. However, industrial copolymers (such as PCE) are characterized by high molecular weight and polymolecular index. These two parameters lead to limitation concerning analysis of copolymers by MALDI-TOFMS. In this study, we demonstrate how pyrolysis and a Thermally assisted Hydrolysis/Methylation coupled with a triple-quadrupole mass spectrometer, provides good results for the detection of PCE copolymer traces in CEM I cement paste leachates. 相似文献
75.
Dr. Samuel Oger Damien Schapman Dr. Romain Mougeot Dr. Stéphane Leleu Dr. Noëlle Lascoux Dr. Patrice Baldeck Dr. Magalie Bénard Dr. Thibault Gallavardin Dr. Ludovic Galas Dr. Xavier Franck 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(46):10954-10964
Epicocconone 1 is a natural chromophore isolated from the fungus Epicoccum nigrum that has shown applications in proteomics and fluorescent microscopy thanks to its unique pro-fluorescence properties. The modification of the skeleton of the natural product by replacing the triene side chain by a fluorenyl scaffold can noticeably increase the fluorophore's absorption coefficient. The synthesis of the analogues of the natural product has been made possible by the use of a palladium-catalyzed carbonylation reaction, allowing the construction of the β-keto-dioxinone key intermediate. Two-photon absorption cross-section measurements of the fluorenyl epicocconone analogues show a structure dependency with values ranging from 60 to 280 GM and live cell imaging show intense staining of intracellular vesicle-like structures around the nucleus. 相似文献
76.
Léo Birbaum Dr. Laurent Gillard Prof. Hélène Gérard Prof. Hassan Oulyadi Dr. Guillaume Vincent Prof. Xavier Moreau Dr. Michael De Paolis Prof. Isabelle Chataigner 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(60):13688-13693
3-Nitroindoles are easily reacted with highly substituted γ-allenoates in the presence of a commercially available phosphine catalyst. For instance, allenoates derived from biomolecules such as amino and deoxycholic acids are combined for the first time with 3-nitroindole. The corresponding dearomatized (3+2) tricyclic cycloadducts are obtained as α-regioisomers exclusively. DFT computations shed light on this multi-step reaction mechanism and on the selectivities observed in the sequence. 相似文献
77.
78.
Yinqiang Xia Vahid Adibnia Renliang Huang Frederic Murschel Jimmy Faivre Guojun Xie Mateusz Olszewski Gregory DeCrescenzo Wei Qi Zhimin He Rongxin Su Krzysztof Matyjaszewski Xavier Banquy 《Angewandte Chemie (International ed. in English)》2019,58(5):1308-1314
Demand for long‐lasting antifouling surfaces has steered the development of accessible, novel, biocompatible and environmentally friendly materials. Inspired by lubricin (LUB), a component of mammalian synovial fluid with excellent antifouling properties, three block polymers offering stability, efficacy, and ease of use were designed. The bottlebrush‐structured polymers adsorbed strongly on silica surfaces in less than 10 minutes by a simple drop casting or online exposure method and were extremely stable in high‐salinity solutions and across a wide pH range. Antifouling properties against proteins and bacteria were evaluated with different techniques and ultralow fouling properties demonstrated. With serum albumin and lysozyme adsorption <0.2 ng cm?2, the polymers were 50 and 25 times more effective than LUB and known ultralow fouling coatings. The antifouling properties were also tested under MPa compression pressures by direct force measurements using surface forces apparatus. The findings suggest that these polymers are among the most robust and efficient antifouling agents currently known. 相似文献
79.
Justum Y Gatti F Lauvergnat D Nauts A Chapuisat X 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2002,58(4):649-661
For high values of the quantum number of the total angular momentum J (up to J = 20), quantum mechanical eigenstates (eigenvalues and eigenfunctions) are calculated by the method of Gatti et al. (J. Mol. Spectrosc. 181 (1997) 403) for the bending deformations of HCN and CNH. In particular, we have examined the l-type resonances in highly excited rovibrational states within the framework of a one-dimensional model, i.e. along the reaction pathway for the isomerization reaction HCN/CNH. The potential energy surface used is that of Bowman et al. (J. Chem. Phys. 99 (1993) 308). 相似文献
80.