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141.
Polyunsaturated fatty acids (PUFAs) are important constituents in all organisms. They fulfil many functions, ranging from modulating the structure of membranes to acting as precursors of physiologically important molecules, such as the prostaglandins, which for a long time were the most prominent cyclic PUFA metabolites. However, since the beginning of the 1990s a large variety of cyclic metabolites have been discovered that form under autoxidative conditions in vivo to a much larger extent than do prostaglandins. These compounds--isoprostanes, neuroprostanes, phytoprostanes, and isofurans--proved subsequently to be ubiquitous in nature. They display a wide range of biological activities, and isoprostanes have become the currently most reliable indicators of oxidative stress in humans. In a relatively short time, the structural variety, properties, and applications of the autoxidatively formed cyclic PUFA derivatives have been uncovered. 相似文献
142.
De Schutter DP Saison D Delvaux F Derdelinckx G Rock JM Neven H Delvaux FR 《Journal of chromatography. A》2008,1179(2):75-80
The aim of this study was to create a simple, solventless technique without derivatisation in order to analyze a broad range of volatiles in beer wort. A method was developed using headspace solid-phase microextraction coupled with gas chromatography and mass spectrometry. The procedure was optimised by selection of the appropriate fibre and optimisation of extraction temperature, extraction time, and salting-out. The detection limits were well below the actual wort concentrations of the selected volatiles, ranging from 12 ng/l for linalool to 0.53 microg/l for furfural. Moreover, the procedure showed a good linearity and was applied to the analysis of wort samples taken from a wort boiling process in an industrial brewery. 相似文献
143.
Navarro I Basset JF Hebbe S Major SM Werner T Howsham C Bräckow J Barrett AG 《Journal of the American Chemical Society》2008,130(31):10293-10298
Diketo-1,3-dioxin-2-ones underwent retro-Diels-Alder reaction on heating in toluene at 110 degrees C to generate alpha,gamma,-triketo-ketenes. These were trapped with alcohols to provide 2,4,6-triketocarboxylates, which were smoothly aromatized by sequential reaction with potassium carbonate and methanolic hydrogen chloride to give resorcylate esters. The reaction was applied in the total synthesis of the marine antifungal agents 15G256beta (1), 15G256iota (2), and 15G256pi (3) and the mycotoxin S-(-)-zearalenone (4). 相似文献
144.
Nardello-Rataj V Caron L Borde C Aubry JM 《Journal of the American Chemical Society》2008,130(45):14914-14915
A series of "Balanced Catalytic Surfactants" (BCS) [(Cn)2N(C1)2]2MoO4 (n = 8, 9, 10, 12) based on amphiphilic double-tailed quaternary ammonium with molybdate as a counterion has been developed for the dark singlet [4 + 2] cyclooxygenation of organic substrates in three-liquid-phase microemulsion systems. These cationic surfactants form three-liquid-phase microemulsion systems at room temperature in the presence of an appropriate organic solvent and water without addition of any cosurfactant or electrolyte. Comparative peroxidation of rubrene points out the specific advantages of these three-phase media over phase transfer catalysis in two phase systems and on conventional one-phase microemulsions based on sodium molybdate: (i) only three constituents, (ii) low amounts of surfactants, (iii) insensitivity to water dilution, (iv) fast separation of the three phases, (v) straightforward recovery of the product and the surfactant from the oil and microemulsion phases, respectively. The preparative peroxidation of alpha-terpinene and 1,4,5-trimethylnaphtalene was performed in the ternary systems [(C8)2N(C1)2]2MoO4/water/tert-butyl acetate or benzene. The reusability of the catalyst, the catalytic nature of the BCS, and the ability of the systems to oxidize poorly reactive substrates were demonstrated showing the broadness of the applicability of such systems. 相似文献
145.
Leduc AM Salameh A Soulivong D Chabanas M Basset JM Copéret C Solans-Monfort X Clot E Eisenstein O Böhm VP Röper M 《Journal of the American Chemical Society》2008,130(19):6288-6297
The surface complex [([triple bond]SiO)Re([triple bond]CtBu)(=CHtBu)(CH2tBu)] (1) is a highly efficient propene metathesis catalyst with high initial activities and a good productivity. However, it undergoes a fast deactivation process with time on stream, which is first order in active sites and ethene. Noteworthy, 1-butene and pentenes, unexpected products in the metathesis of propene, are formed as primary products, in large amount relative to Re (>1 equiv/Re), showing that their formation is not associated with the formation of inactive species. DFT calculations on molecular model systems show that byproduct formation and deactivation start by a beta-H transfer trans to the weak sigma-donor ligand (siloxy) at the metallacyclobutane intermediate having a square-based pyramid geometry. This key step has an energy barrier slightly higher than that calculated for olefin metathesis. After beta-H transfer, the most accessible pathway is the insertion of ethene in the Re-H bond. The resulting pentacoordinated trisperhydrocarbyl complex rearranges via either (1) alpha-H abstraction yielding the unexpected 1-butene byproduct and the regeneration of the catalyst or (2) beta-H abstraction leading to degrafting. These deactivation and byproduct formation pathways are in full agreement with the experimental data. 相似文献
146.
Souhir Boujday Romain Briandet Michèle Salmain Jean-Marie Herry Pierre-Guy Marnet Michel Gautier Claire-Marie Pradier 《Mikrochimica acta》2008,163(3-4):203-209
We describe the elaboration of ultra-sensitive immunosensors, to detect the bacterial pathogen Staphylococcus aureus. We utilized commercially available polyclonal anti-S. aureus antibody as receptor. Immunosensors were elaborated by building a self-assembled monolayer (SAM) of thiolamine onto planar gold-coated sensor chips. Then, Protein A was covalently linked to the thiolated SAM using glutaraldehyde as cross-linking agent. After a blocking step by Bovine Serum Albumin (BSA), the antibody was immobilized by affinity to Protein A. This step-by-step construction was monitored by Polarization Modulation Reflection Absorption Infrared Spectroscopy (PM-RAIRS) and Quartz Crystal Microbalance with Dissipation (QCM-D). In a first stage, the parameters of immunosensor elaboration were optimized using a model rabbit IgG. The accessibility of receptors and the homogeneity of their distribution were checked by PM-RAIRS, QCM-D, and by immuno-gold scanning electron microscopy. Then, the specific rabbit anti-S. aureus antibody was immobilized and the resulting sensing layer was applied to the detection of the pathogen target. Independent detection of bacteria immobilized on the sensors by fluorescent imaging allowed validation of the specificity of recognition toward the pathogen as well as a quantitative response of the sensor. Using PM-RAIRS as transducing technique allowed us to enhance sensitivity and reach a very competitive detection level (105 CFU mL?1). 相似文献
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