Acid Catalyzed Cyclization of Bis Silyl Diacylhydrazines: A New 1, 3, 4-Oxadiazole Synthesis

Diacylhydrazines are converted in good yields into 1,3,4-oxadiazoles with dichlorodimethyl-silane and trifluoromethane sulfonic acid.     

Structure and Dynamic of Three Indole Alkaloids from the Campylospermum Genus (Ochnaceae)

A new indole alkaloid, calanthumindole ( 4 ), and three known biflavonoids, amentoflavone, sequoiaflavone, and podoscarpusflavone B, were isolated from Campylospermum calanthum (Ochnaceae). Calanthumindole is a new indole alkaloid of the serotobenine family characterized by the presence of a C?C bond between atoms C(7′) and C(8′) of the furan ring. This is the first compound to have a fully unsaturated furan ring among the members of this family. The combination of NMR and DFT allowed the determination and comparison of the 3D structures and relevant conformational characteristics of serotobenine ( 1 ), flavumindole ( 2 ), and calanthumindole ( 4 ).     

Disilylated Compounds as Precursors of Heterocycles: A New and Easy Oxadiazole Synthesis

Silyl diacylhydtazines have been synthesized. When they are treated with 3 slight amount of a uariety of catalyst (nucleophiles, F, true or Lewis acids, Pd, Pt.), 1,3,4-oxadiazoles are obtained. This cyclization can be performed in one step by using hexamethyldisilazane or dimethyldichlorosilane as the silylation agent.     

Elementaranalyse auf nassem Wege

Ohne Zusammenfassung     

Laser-based measurements of gas-phase chemistry in non-equilibrium pulsed nanosecond discharges

Detailed experimental investigation of a non-equilibrium nanosecond pulsed discharge in premixed CH₄/air mixtures at atmospheric pressure has been carried out. The experiments demonstrated significant reductions in ignition delay and increased lean burn capability relative to conventional spark ignition. Advanced laser diagnostics have been used to identify the physical processes which lead to these improvements. The electron temperature and density properties were measured using laser Thomson scattering (LTS). Temperature measurements were performed using N₂ CARS thermometry to quantify the energy transfer in the gas mixture. Effect of the discharge on the local temperature shows the existence of the ignition of the gas mixture for equivalence ratio between 0.7 and 1.3. Fast development of a flame kernel is then observed. The experiment also shows that the flame can be sustained above the discharge due the repetitive ignition of the flame at the plasma repetition rate. Finally, OH and CH PLIF experiments were performed to confirm the large OH and CH streamer-induced production over the discharge volume. To cite this article: F. Grisch et al., C. R. Mecanique 337 (2009).     

Characterisation of cw Nd : YAG laser keyhole dynamics

The paper concerns laser–matter interaction characterisation. In this work, we use a rapid CCD camera located coaxially to the laser beam and we compare recorded images with those obtained by numerical modelling. Because images are difficult to understand, we compute thermal radiation emitted by a keyhole of fixed geometry and we adjust it trying to approach the camera record. The modelling treats radiative heat transfer within the keyhole and determines the sensor illumination map. By adjusting the geometrical characteristics of the hole, we seek to obtain the image that corresponds as well as possible to the realised experiment. Results are compared with other experimental methods simultaneously performed plume characterisation with an electric probe and spectrometric analysis. They show the existence of two distinct behaviours of the keyhole: a pseudo-steady state associated with regular and pseudo-constant keyhole shapes, low frequencies of electric current in the plume, and generally good welding results, and a highly dynamic mode associated with irregular and rapidly varying keyhole shapes, high frequencies in the plume current and generally poor welding results.     

Physically and Chemically Crosslinked Gelatin Gels

In this paper, we examine the rheological and the structural properties of different types of gelatin networks, physical, chemical and both. The physical gel is due to the formation of collagen type triple helices when cooling the solutions. Chemically crosslinked gels are obtained with a reagent, in our case the bis(vinylsulfonyl)methane (BVSM), kindly provided by Kodak Industrie (France). Each BVSM molecule provides two covalent bonds. The chemical reaction was followed by microcalorimetry (MicroDSC III from Setaram, Caluire, France). The relation between shear moduli and crosslinking for the three types of gels is discussed, in relation with theoretical models of randomly crosslinked systems.     

First Total Syntheses of Novel Non-Enzymatic Polyunsaturated Fatty Acid Metabolites and Their Identification in Edible Oils

Oxidative stress (OS) is an in vivo process leading to free radical overproduction, which triggers polyunsaturated fatty acid (PUFA) peroxidation resulting in the formation of racemic non-enzymatic oxygenated metabolites. As potential biomarkers of OS, their in vivo quantification is of great interest. However, since a large number of isomeric metabolites is formed in parallel, their quantification remains difficult without primary standards. Three new PUFA-metabolites, namely 18-F_3t-isoprostane (IsoP) from eicosapentaenoic acid (EPA), 20-F_4t-neuroprostane (NeuroP) from docosahexaenoic acid (DHA) and 20-F_3t-NeuroP from docosapentaenoic acid (DPA_n-3) were synthesized by two complementary synthetic strategies. The first one relied on a racemic approach to 18(RS)-18-F_3t-IsoP using an oxidative radical anion cyclization as a key step, whereas the second used an enzymatic deracemization of a bicyclo[3.3.0]octene intermediate obtained from cyclooctadiene to pursue an asymmetric synthesis. The synthesized metabolites were applied in targeted lipidomics to prove lipid peroxidation in edible oils of commercial nutraceuticals.     

Influence of irradiation defects on the properties of incommensurate insulators

This paper is a short review on experiments on the influence of radiation damage in incommensurate insulators. The main results are discussed on the basis of existing models.