THE REACTION OF TETRAMETHYLSILANE WITH BORON TRIBROMIDE

The reaction of tetramethylsilane with boron tribromide in deuterochloroform in ambient temperature or at 40°C led to bromotrimethylsilane (3) and to dibromomethylborane (4). Identity of products was confirmed by NMR spectroscopy. Analogical reaction carried out in 1,3-dichloropropane allowed to separate products of the reaction and to obtain them in 68% and 59% yields respectively.CNRS Franc

Émile Combes, vulgarisation et politique de la Préhistoire

Émile Combes, figure emblématique de la laïcité radicale et de la lutte anticléricale de la IIIe République a joué un rôle dans la vulgarisation d’une science naissante, la Préhistoire. Bien avant sa réussite en politique, simple médecin dans la petite ville de Pons, vers 1869, il a participé à « l’invention » de la préhistoire dans le département de la Charente-Inférieure. Émile Combes collecte des silex, publie des articles sur l’âge de la pierre taillée et utilise ses conférences de vulgarisation scientifique dans son combat anticlérical. Devenu un notable important dans son département, il défend une recherche préhistorique pratiquée par les instituteurs laïques contre les sociétés savantes conservatrices. Cependant son engagement national va l’éloigner de sa passion pour les temps antédiluviens.Émile Combes, symbol of the radical secularity and the anticlerical fight during the Third Républic took part in the popularization of the new science, Prehistory. Long before his political success, as doctor in the small town of Pons, towards 1869, he participated to the creation of prehistory in Charente-Inférieure. Émile Combes collects flints, publishes articles on the “Stone Age” and uses his scientist popularization conferences in his anticlerical action. Became an important personality of his department, he defends a prehistoric research used by secular primary school teachers against conservative learned societies. However his national commitment will keep him away from his passion for antedeluvian times

Improved Transparency-Nonlinearity Trade-Off with Boroxine-Based Octupolar Molecules

C. Katan present address: CNRS UMR6082 FOTON, INSA de Rennes, 20 avenue des Buttes de Coësmes, CS 70839, 35708 RENNES cedex 7, FranceInternational audienceOver the last two decades, a substantial effort has been devoted to the design of molecules with enhanced NLO responses. It has become increasingly clear over recent years that multipolar structures offer challenging possibilities in this respect. In particular, the octupolar framework provides an interesting route towards enhanced NLO responses and improved nonlinearity-transparency trade-off. In this perspective, we have implemented an innovative route based on octupolar structures derived from the boroxine ring. By grafting three electron-donating appendices on the electron-deficient boroxine core, octupolar quasi-planar molecules displaying markedly improved nonlinearity-transparency trade-off, as compared to the prototypical octupole (TATB) or the extensively studied triazine derivatives, were designed. This route indeed led to octupolar molecules showing (0) values (from calculations and solution measurements) larger than that of TIATB while remaining blue-shifted by nearly 100 nm and totally transparent in the visible region. Combined experimental and theoretical investigations reveal that this behavior is related to a periphery-to-core intramolecular charge transfer phenomenon in relation with the low-aromaticity and electron-withdrawing character of the boroxine ring. This study opens a new route for molecular engineering of transparent octupolar derivatives for NLO, including the design of effective materials for SHG in the visible-blue regio

Degradation state of organic matter in surface sediments from the Southern Beaufort Sea: a lipid approach

For the next decades significant climatic changes should occur in the Arctic zone. The expected destabilisation of permafrost and its consequences for hydrology and plant cover should increase the input of terrigenous carbon to coastal seas. Consequently, the relative importance of the fluxes of terrestrial and marine organic carbon to the seafloor will likely change, strongly impacting the preservation of organic carbon in Arctic marine sediments. Here, we investigated the lipid content of surface sediments collected on the Mackenzie basin in the Beaufort Sea. Particular attention was given to biotic and abiotic degradation products of sterols and monounsaturated fatty acids. By using sitosterol and campesterol degradation products as tracers of the degradation of terrestrial higher plant inputs and brassicasterol degradation products as tracers of degradation of phytoplanktonic organisms, it could be observed that autoxidation, photooxidation and biodegradation processes act much more intensively on higher plant debris than on phytoplanktonic organisms. Examination of oxidation products of monounsaturated fatty acids showed that photo- and autoxidation processes act more intensively on bacteria than on phytodetritus. Enhanced damages induced by singlet oxygen (transferred from senescent phytoplanktonic cells) in bacteria were attributed to the lack of an adapted antioxidant system in these microorganisms. The strong oxidative stress observed in the sampled sediments resulted in the production of significant amounts of epoxy acids and unusually high proportions of monounsaturated fatty acids with a <i>trans</i> double bond. The formation of epoxy acids was attributed to peroxygenases (enzymes playing a protective role against the deleterious effects of fatty acid hydroperoxides in vivo), while <i>cis/trans</i> isomerisation was probably induced by thiyl radicals produced during the reaction of thiols with hydroperoxides. Our results confirm the important role played by abiotic oxidative processes in the degradation of marine bacteria and do not support the generally expected refractory character of terrigenous material deposited in deltaic systems

Seasonal survey of the composition and degradation state of particulate organic matter in the Rhône River using lipid tracers

International audienceLipid tracers including fatty acids, hydroxyacids, n-alkanols, sterols and triterpenoids were used to determine the origin and fate of suspended particulate organic matter (POM) collected in the Rhône River (France). This seasonal survey (April 2011 to May 2013) revealed a year-round strong terrestrial higher-plant contribution to the particulate organic matter (POM), with significant algal inputs observed in March and attributed to phytoplanktonic blooms likely dominated by diatoms. Major terrigenous contributors to our samples are gymnosperms, and more precisely their roots and stems, as evidenced by the presence of high proportions of ω-hydroxydocosanoic acid (a suberin biomarker). The high amounts of coprostanol detected clearly show that the Rhône River is significantly affected by sewage waters. Specific sterol degradation products were quantified and used to assess the part of biotic and abiotic degradation of POM within the river. Higher-plant-derived organic matter appears to be mainly affected by photo-oxidation and au-toxidation (free radical oxidation), while organic matter of mammal or human origin, evidenced by the presence of co-prostanol, is clearly more prone to bacterial degradation. Despite the involvement of an intense autoxidation-inducing ho-molytic cleavage of peroxy bonds, a significant proportion of hydroperoxides is still intact in higher plant debris. These compounds could affect the degradation of terrestrial material by inducing an intense autoxidation upon its arrival at sea

Lipoxygenase-induced autoxidative degradation of terrestrial particulate organic matter in estuaries: A widespread process enhanced at high and low latitude

International audienceThere exists a substantial amount of research on abiotic (e.g. photochemical) degradation pertaining to organic matter (OM) in the marine realm. While recent research has shown its importance in the degradation of terrestrial particulate OM (TPOM), the mechanisms involved in the induction of autoxidation in estuaries remain unclear. In this study, we propose for the first time the involvement of lipoxygenase (LOX) activity in the induction of autoxidation in mixed waters. The observation of unusual profiles of palmitoleic acid oxidation products and the presence of jasmonic acid in suspended particulate matter (SPM) collected close to the Rhône River, as well as in samples from the Mackenzie and Amazon rivers, is attributed to strong LOX activity. We show the role played by salinity in the induction of this LOX activity and provide an explanation for the differences in estuarine autoxidation level. At high latitude, lower temperatures and irradiance favor photooxidative damage to higher plant debris and, consequently, hydroperoxide production. High hydroperoxide content strongly contributes to LOX activation in mixed waters. The high resulting LOX activity enhances alkoxyl radical production and thus autoxidation. On the contrary, at low latitude, photooxidative effects are limited, and riverine autoxidation is favored. The higher hydroperoxide content of TPOM may, as a consequence, thereby also contribute to a high level of LOX activity and autoxidation in estuaries. In temperate zones, land and riverine photooxidative and autoxidative damage is limited, unlike estuaries where we observed significant LOX-induced and autox-idative damage.

Monitoring abiotic degradation in sinking versus suspended Arctic sea ice algae during a spring ice melt using specific lipid oxidation tracers

publisher: Elsevier articletitle: Monitoring abiotic degradation in sinking versus suspended Arctic sea ice algae during a spring ice melt using specific lipid oxidation tracers journaltitle: Organic Geochemistry articlelink: http://dx.doi.org/10.1016/j.orggeochem.2016.05.016 content_type: article copyright: © 2016 Elsevier Ltd. All rights reserved

Monitoring photo-oxidative and salinity-induced bacterial stress in the Canadian Arctic using specific lipid tracers

Publisher policy: author can archive post-print on open access repository after an embargo period of 18 months.Publisher's version/PDF cannot be used. Must link to publisher version with DOI. Author's post-print must be released with a Creative Commons Attribution Non-Commercial No Derivatives License

Evaluation of chemical diversity of biotinylated chiral 1,3-diamines as a catalytic moiety in artificial imine reductase

The possibility of obtaining an efficient artificial imine reductase was investigated by introducing a chiral cofactor into artificial metalloenzymes based on biotin-streptavidin technology. In particular, a chiral biotinylated 1,3-diamine ligand in coordination with iridium(III) complex was developed. Optimized chemogenetic studies afforded positive results in the stereoselective reduction of a cyclic imine, the salsolidine precursor, as a standard substrate with access to both enantiomers. Various factors such as pH, temperature, number of binding sites, and steric hindrance of the catalytic moiety have been proved to affect both efficiency and enantioselectivity, underlining the great flexibility of this system in comparison with the achiral system. Computational studies were also performed to explain how the metal configuration, in the proposed system, might affect the observed stereochemical outcome

Synthesis of Nitrogenated Heterocycles by Asymmetric Transfer Hydrogenation of N-(tert-Butylsulfinyl)haloimines

Highly optically enriched, protected, nitrogenated heterocycles with different ring sizes have been synthesized by a very efficient methodology consisting of the asymmetric transfer hydrogenation of N-(tert-butylsulfinyl)haloimines followed by treatment with a base to promote an intramolecular nucleophilic substitution process. N-Protected aziridines, pyrrolidines, piperidines, and azepanes bearing aromatic, heteroaromatic, and aliphatic substituents have been obtained in very high yields and diastereomeric ratios up to >99:1. The free heterocycles can be easily obtained by a simple and mild desulfinylation procedure. Both enantiomers of the free heterocycles can be prepared with the same good results by changing the absolute configuration of the sulfur atom of the sulfinyl group.This work was generously supported by the Spanish Ministerio de Ciencia e Innovación (MICINN; grant no. CONSOLIDER INGENIO 2010, CSD2007-00006, CTQ2007-65218 and CTQ2011-24151) and the Generalitat Valenciana (PROMETEO/2009/039 and FEDER). O.P. thanks the Spanish Ministerio de Educación for a predoctoral fellowship (grant no. AP-2008-00989)