429 research outputs found
Influence of Phosphoramidites in Copper-Catalyzed Conjugate Borylation Reaction
Copper(I) has become the preferred metal to catalyze the ÎČ-boration of α,ÎČ-unsaturated carbonyl compounds, and now we demonstrate that easily accessible monodentate chiral ligands, such as phosphoramidites and phosphites, can be convenient alternative ligands to induce asymmetry in the enantioselective version of this reaction, particularly in the ÎČ-boration of α,ÎČ-unsaturated imines.
Extracting non-linear integrate-and-fire models from experimental data using dynamic I - V curves
The dynamic I-V curve method was recently introduced for the efficient experimental generation of reduced neuron models. The method extracts the response properties of a neuron while it is subject to a naturalistic stimulus that mimics in vivo-like fluctuating synaptic drive. The resulting history-dependent, transmembrane current is then projected onto a one-dimensional current-voltage relation that provides the basis for a tractable non-linear integrate-and-fire model. An attractive feature of the method is that it can be used in spike-triggered mode to quantify the distinct patterns of post-spike refractoriness seen in different classes of cortical neuron. The method is first illustrated using a conductance-based model and is then applied experimentally to generate reduced models of cortical layer-5 pyramidal cells and interneurons, in injected-current and injected- conductance protocols. The resulting low-dimensional neuron modelsâof the refractory exponential integrate-and-fire typeâprovide highly accurate predictions for spike-times. The method therefore provides a useful tool for the construction of tractable models and rapid experimental classification of cortical neuron
Soluble iron nanoparticles as cheap and environmentally benign alkene and alkyne hydrogenation catalysts
Soluble iron nanoparticles as cheap and environmentally benign alkene and alkyne hydrogenation catalysts
Soluble iron nanoparticles as cheap and environmentally benign alkene and alkyne hydrogenation catalysts
La mer dâIroise : une singularitĂ© dans lâapprovisionnement en silex des hommes du PalĂ©olithique breton
LâĂ©tude des prĂ©lĂšvements rĂ©alisĂ©s en mer dâIroise montre que cette rĂ©gion, contrairement au reste de la marge continentale bretonne, semble dĂ©pourvue de cordons littoraux anciens sous le niveau des plus hautes mers actuelles. Cette particularitĂ© rĂ©sulte de la densitĂ© des anciennes riviĂšres, reconnues grĂące Ă leurs palĂ©o-vallĂ©es, qui ont provoquĂ© un fort effet de chasse et au dĂ©capage des sĂ©diments dĂ©posĂ©s lors de chaque rĂ©gression importante de la mer. Par ailleurs, lors des pĂ©riodes transgressives, la distance importante qui existe entre les sources de silex et les cordons de galets cĂŽtiers actuels a provoquĂ© un important tri granulomĂ©trique. De telle façon que ce cordon ne livre que des galets de petite taille, Ă lâexception toutefois de rares rognons plus massifs dâorigine glacielle, qui sont arrivĂ©s plus tard et dont lâorigine est inconnue. Cette configuration particuliĂšre se reflĂšte dans la lithologie et la dimension de lâoutillage lithique des premiers habitants qui vivaient en bordure de lâIroise (PalĂ©olithique infĂ©rieur). Ceux-ci Ă©taient moins favorisĂ©s que ceux qui occupaient les rivages de la Baie dâAudierne (Menez-Dregan). Toutefois, Ă dĂ©faut de silex, ils pouvaient disposer, en relative abondance et Ă peu de distance, dâautres matĂ©riaux tels que les quartzites de la presquâĂźle de Crozon ou les grĂšs Ă©ocĂšnes de la vallĂ©e du Juch (Kervouster). Mais, ici encore, il semble quâils aient prĂ©fĂ©rĂ© le silex et privilĂ©giĂ© un approvisionnement local.Study of the sediments sampled in the Iroise Sea shows that this particular area, contrary to the other shelves surrounding Brittany, does not display any boulder bar. This particularity results from the strong flushing developed by the local braided rivers which were running on the shelf during each regression of the sea. On the other hand, the long distance which exists between the source of the flints and the present remains of the coastal boulder bar, was large enough to be responsible for a strong granulometric selection of the boulders during each transgressive episodes. It is the reason why the actual coastal boulder bar is almost only made of small sized boulders. Some associated rare and bigger elements were deposited by ice rafts during a more recent period of time. This particular environment is well expressed in the lithology and size of the lithic tools. The first inhabitants living along the Iroise sea shore (Lower Palaeolithic) were rather less favoured than those living close to the Audierne Bay (Menez Dregan) and were often forced to use different types of rocks, such as the PaleozoĂŻc or Eocene sandstones of the valley of Le Juch (Kervouster), to replace the missing flints. But even in this case, it seems that they preferred flints to another kind of rocks and favoured a local supply
A detailed study of the diastereoselective catalytic hydrogenation of 6-hydroxytetrahydroisoquinoline-(3R)-carboxylic ester intermediates
A key step towards a highly-selective antagonist of ionotropic glutamate receptors entails the diastereoselective arene hydrogenation of an enantiopure tetrahydroisoquinoline. An extensive screen using parallel reactors was conducted and led to the discovery of several Pd/C catalysts giving high yield and improved diastereoselectivity from 75 : 25 to 95 : 5. A detailed kinetic study of the best system was performed and supports the reduction occuring in two-steps.
Apport de la gĂ©ologie marine Ă la dĂ©termination des sources de matiĂšres premiĂšres au palĂ©olithique dans le massif armoricain : origine possible du silex utilisĂ© sur les stations palĂ©olithique infĂ©rieur de MenezâDregan (Plouhinec, FinistĂšre, France). Implications palĂ©oclimatiques et palĂ©oenvironnementales
Le silex nâest pas prĂ©sent dans le sousâsol armoricain. Sa mise en Ćuvre au PalĂ©olithique est principalement liĂ©e Ă la collecte de galets marins prĂ©levĂ©s dans les cordons littoraux Ă diffĂ©rents niveaux. Toutefois, dans la couche 5dâ de MenezâDregan1, apparaissent des Ă©clats de silex dont le cortex ne porte pas trace dâun transport important. Lâexploitation des minutes de dragages et carottages au large de la Baie dâAudierne montre que, pour une part, le matĂ©riau qui a servi Ă la taille de lâoutillage rĂ©coltĂ© au niveau 5dâ de Menez Dregan peut provenir dâun estran situĂ© vers â40 m et localisĂ© Ă une distance de 5 Ă 10 km de la cĂŽte actuelle lors dâune phase de rĂ©gression marine associĂ©e Ă un dĂ©but de dĂ©gradation climatique. Ces rĂ©sultats sont en remarquable concordance avec ceux de la palĂ©obotanique (anthracologie). Ceci nous donne des indications palĂ©ogĂ©ographiques et palĂ©oenvironnementales importantes pour la connaissance des occupations palĂ©olithiques Ă lâOuest de la Bretagne.There is no flint in the armorican terrain. Its use during Palaeolithic is mainly dependent from the gathering of marine pebbles taken along the old shorelines located at different levels. However, at MenezâDregan1 layer 5dâ, flint flakes do not show the cortex aspect which witness for a long transport. Analysis of dredging and coring samples made off Baie dâAudierne shows that, part of the raw material used to make the tools from MenezâDregan1 layer 5dâ may come from an old shore located at about â40 m depth and at a distance of 5 to 10 km from the actual coast, which developed during a marine regression phase associated with the beginning of a climatic deterioration. These results are in strong concordance with those of paleobotany (anthracology). They provide paleoâgeographic and paleoenvironmental informations for a better knowledge of the Palaeolithic presence in Western Brittany
Rapid Identification of a Scalable Catalyst for the Asymmetric Hydrogenation of a Sterically Demanding Aryl Enamide
High throughput screening was used to find a cost-effective and scalable catalyst for the asymmetric hydrogenation of a sterically demanding enamide as an intermediate towards a new potent melanocortin receptor agonist useful in the treatment of obesity. Lessons drawn from the testing of a first library of 96 chiral monodentate phosphoramidites led to the design of a second focused library of 16 chiral ligands, allowing the discovery of a new efficient catalyst. This catalyst was based on rhodium and a bulky monodentate phosphite ligand. The catalyst was scaled up and used in the kilogram production of the desired bulky chiral amide
Nonsupervised Ranking of Different Segmentation Approaches: Application to the Estimation of the Left Ventricular Ejection Fraction From Cardiac Cine MRI Sequences
International audienceA statistical methodology is proposed to rank several estimation methods of a relevant clinical parameter when no gold standard is available. Based on a regression without truth method, the proposed approach was applied to rank eightmethods without using any a priori information regarding the reliability of each method and its degree of automation. It was only based on a prior concerning the statistical distribution of the parameter of interest in the database. The ranking of the methods relies on figures of merit derived from the regression and computed using a bootstrap process. The methodology was applied to the estimation of the left ventricular ejection fraction derived from cardiac magnetic resonance images segmented using eight approaches with different degrees of automation: three segmentations were entirely manually performed and the others were variously automated. The ranking of methods was consistent with the expected performance of the estimation methods: the most accurate estimates of the ejection fraction were obtained using manual segmentations. The robustness of the ranking was demonstrated when at least three methods were compared. These results suggest that the proposed statistical approach might be helpful to assess the performance of estimation methods on clinical data for which no gold standard is available
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