Composé inorganique

Résumé

Les composés inorganiques sont les composés chimiques (molécules, polymères mono-, bi- ou tridimensionnels…) étudiés en chimie inorganique. Très généralement, ce sont des composés qui intègrent d'une manière ou d'une autre, un ou plusieurs atomes métalliques dans leur structure. L'ensemble de ces composés est moins connu (environ un million décrits) que l'ensemble des composés organiques (environ sept millions connus), la chimie organométallique faisant en quelque sorte le partage entre composés organiques et inorganiques. D'après Joseph M. Hornback, la distinction entre composés inorganiques et organiques est un peu arbitraire ; par exemple, un composé contenant à la fois du carbone et un métal peut être considéré comme organique ou inorganique. Exemples L'eau, le dioxyde de carbone (composés covalents), ainsi que l'acide chlorhydrique (acide minéral), le chlorure de sodium et le cyanate d'ammonium (composés ioniques) sont des représentants simples. Tous les complexes, c

Source officielle

https://fr.wikipedia.org/wiki/Compos%C3%A9_inorganique

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Marine phytoplankton can regulate their stoichiometric composition in response to variations in the availability of nutrients, light and the pH of seawater. Varying elemental composition of photoautotrophs affects several important ecological and biogeochemical processes, e.g., primary and export production, nutrient cycling, calcification, and grazing. Here we compare two plankton ecosystem models that consider regulatory mechanisms of cellular carbon and nitrogen, driving the physiological acclimation of photoautotrophs. The Carbon:Nitrogen Regulated Ecosystem Model (CN-REcoM) and the optimality-based model (OBM) differ in their representation of phytoplankton dynamics, i.e. nutrient acquisition, synthesis of chlorophyll a, and growth. All other model compartments (zooplankton, detritus, dissolved inorganic and organic matter) and processes (grazing, aggregation, remineralisation) remain identical in both models. We assess the skills of the two models against data from an ocean acidification mesocosm experiment with three CO2 treatments. Neither model accounts for any carbon dioxide (CO2) effects explicitly. Instead, we assimilate data of the different CO2 treatments separately into the models. Thereby we aim at identifying optimal model parameter values that might correlate with differences in CO2 conditions. For the OBM, optimal parameter estimates of Q(min) (subsistence N:C ratio) and V-C(0) (maximum potential photosynthesis rate of photoautotrophs) turned out to be higher for mesocosms exposed to high CO2 compared to those with low CO2 concentrations. By contrast, a similar correlation is not observed for the CN-REcoM. A possible physiological interpretation of higher estimates of Q(min), and V-C(0) according to the OBM is that phytoplankton may experience environmental stress under more acidic conditions, and hence must invest more energy/resources for maintaining basic cellular functions. Our data assimilation reveals that the parameters of the OBM are better constrained by the data than those of the CN-REcoM. Furthermore, the OBM is better able than CN-REcoM to reproduce data that were not used for parameter optimization.

2019

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Computational modeling of the olfactory receptor Olfr73 suggests a molecular basis for low potency of olfactory receptor-activating compounds

Marc Brugarolas Campillos, Thamani Dahoun, Horst Pick, Horst Vogel, Shuguang Yuan

The mammalian olfactory system uses hundreds of specialized G-protein-coupled olfactory receptors (ORs) to discriminate a nearly unlimited number of odorants. Cognate agonists of most ORs have not yet been identified and potential non-olfactory processes mediated by ORs are unknown. Here, we used molecular modeling, fingerprint interaction analysis and molecular dynamics simulations to show that the binding pocket of the prototypical olfactory receptor Olfr73 is smaller, but more flexible, than binding pockets of typical non-olfactory G-protein-coupled receptors. We extended our modeling to virtual screening of a library of 1.6 million compounds against Olfr73. Our screen predicted 25 Olfr73 agonists beyond traditional odorants, of which 17 compounds, some with therapeutic potential, were validated in cell-based assays. Our modeling suggests a molecular basis for reduced interaction contacts between an odorant and its OR and thus the typical low potency of OR-activating compounds. These results provide a proof-of-principle for identifying novel therapeutic OR agonists.

Springer2019

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Le réarrangement [1,2] de Wittig

Frédéric Bailly

The importance of catalysis in chemistry has not to be proved anymore. Be it homogeneous or heterogeneous catalysis, the constant progresses observed in that field proves its obvious interest. The asymmetric homogeneous catalysis is a method of choice to synthesize chiral substances. Indeed, it allows the obtention of these compounds in an enantioselective way. During transition metal mediated catalytic asymmetric reactions, the chirality is induced by the presence of organic monodentate or bidentate chiral ligand, directly linked to the metal. Very good results were obtained in this kind of reaction with chiral ligands based on binaphthyl skeleton. Initially, this thesis work consisted in the study of the double [1,2] Wittig rearrangement of binaphthyl ethers. It was shown, for allyl carbanion, that only one diastereoisomer is formed during the rearrangement among the three possible one. This diastereoisomer has a C2 symmetry axis and the absolute configuration of the two new asymmetric centers created was assigned. On the other hand, for benzyl or benzhydril carbanions, the results are differents. For the former, the three possible diastereisomer are formed with the unsymmetrical one as the major compound. In the latter case, no rearrangement takes place and only starting material is recovered after neutralization of the reaction mixture. Then, the potential of double [1,2] Wittig rearrangements applied to allyl binaphthyl ethers was evaluate in order to synthesize homochiral compounds usable in asymmetric homogeneous catalysis. It was shown that this transformation could be used to give access to the enantiopur acid 1,1'-binaphtyl-2,2'-dicarboxylic which finds applications in the field of the asymmetric catalysis. The high diastereoselectivity observed during this double rearrangement allowed to develop the kinetic resolution of the binaphthyl skeleton by means of the asymmetric epoxidation according to the conditions described by K.B Sharpless and T Katsuki. Finally, taking profit of the high diastereoselectivity already mentioned, it was possible to elaborate out a new phosphorus ligand whose stereoinduction capacity was evaluated for catalytic asymmetric hydrosilylation.

EPFL2005

Chargement

Le réarrangement [1,2] de Wittig

Frédéric Bailly

EPFL2005

2019