155 research outputs found
Synthesis and application of pinene-pyridine derivatives in asymmetric catalysis
The research described herein focuses on the synthesis of chiral pinene-pyridine derivatives, and their application in asymmetric catalysis. Both transition metal catalysed and organocatalytic transformations were investigated.
Chiral pyridine-phosphines based on α-pinene were synthesised and applied as efficient P,N-ligands for the enantioselective palladium(II)-catalysed Baeyer-Villiger oxidation of prochiral 3-substituted cyclobutanones to furnish chiral γ-butyrolactones in up to 81% ee. Complexes of these ligands with iridium can also promote asymmetric hydrogenation of olefins in up to 83% ee.
Novel N,Nâ-dioxides were synthesised from α-pinene and a range of 2-pyridine-acetophenones by employing Kröhnke annulation reaction as the key cyclisation step. Although poor enantioselectivity was achieved (up to 12% ee), high reactivity of the catalysts is, however, promising
Structure et résilience des réseaux trophiques benthiques de l'Arctique canadien et de la mer des Tchouktches
RĂSUMĂ: Les changements climatiques actuels sont Ă lâorigine de nombreuses modifications dans lâocĂ©an Arctique, telles quâune augmentation de la tempĂ©rature des eaux de surface, une augmentation des apports fluviaux, une rĂ©duction dans la couverture de glace de mer, des changements de composition des espĂšces ou des changements dans la phĂ©nologie et lâintensitĂ© de la production primaire. Ces changements pourraient ĂȘtre Ă lâorigine de modifications dans la structure et le fonctionnement des rĂ©seaux trophiques benthiques. Il est nĂ©cessaire aujourdâhui de dĂ©crire la structure et la rĂ©silience de rĂ©seaux trophiques benthiques de ces rĂ©gions pour Ă©valuer lâimpact des changements climatiques sur celles-ci. Cette Ă©tude a pour objectifs de dĂ©crire la structure et la rĂ©silience des rĂ©seaux trophiques benthiques de lâArctique canadien (polynie des eaux du Nord, archipel canadien, golfe dâAmundsen, mer de Beaufort) et de la mer des Tchouktches par une approche isotopique, et dâĂ©valuer lâimportance des algues de glace pour ces rĂ©seaux trophiques, Ă lâaide du biomarqueur dâalgues de glace IP25 (Ice Proxy 25). Pour atteindre ces deux objectifs, nous avons collectĂ© des Ă©chantillons de matiĂšre particulaire en suspension, de sĂ©diments de surface, et de faune benthique de juillet Ă octobre 2014, Ă bord du NGCC Amundsen. Les valeurs en ÎŽ13C mesurĂ©es dans les sĂ©diments de la polynie des eaux du Nord, de lâarchipel canadien et de la mer des Tchoukches, traduisent une origine marine de la matiĂšre organique. La mer de Beaufort et le golfe dâAmundsen sont quant Ă eux caractĂ©risĂ©s par des apports terrigĂšnes et des apports mixtes (terrigĂšnes et marins) respectivement.
Ces diffĂ©rences dans lâorigine de matiĂšre organique se retrouvent dans les signatures isotopiques des organismes et dans la structure des rĂ©seaux trophiques : la mer de Beaufort se distingue des autres rĂ©gions par des signatures appauvries en 13C chez les consommateurs et par de nombreux organismes avec de hauts niveaux trophiques. La faible sĂ©paration trophique et la forte redondance trophique suggĂšrent que la polynie des eaux du Nord et lâarchipel canadien semblent ĂȘtre les rĂ©gions avec la plus grande possibilitĂ© de rĂ©silience face Ă des changements environnementaux. Nous avons mis en Ă©vidence la prĂ©sence du marqueur dâalgue de glace IP25 chez les organismes appartenant Ă tous les niveaux trophiques. Les plus fortes concentrations en IP25 ont Ă©tĂ© retrouvĂ©es chez les dĂ©posivores de surface. Les algues de glace semblent ĂȘtre une source de xv nourriture importante pour les organismes de lâarchipel canadien, oĂč les plus fortes concentrations en biomarqueurs dâalgues de glace ont Ă©tĂ© retrouvĂ©es (en particulier chez les dĂ©posivores et les prĂ©dateurs) et pour la polynie des eaux du Nord oĂč les signatures en carbone des organismes indiquent une assimilation dâalgues de glace. -- Mot(s) clĂ©(s) en français : Benthos, structure trophique, rĂ©silience, algues de glace, biomarqueur IP25, isotopes stables, Arctique Canadien, Mer des Tchouktches. -- ABSTRACT: Ongoing climate change is causing rapid changes in the Arctic Ocean, such as higher water temperatures, increased fluvial run-off, reduced sea-ice cover, change in species composition, change in the timing and intensity of primary production. Those changes will give rise to severe ecosystem changes propagating in benthic food web through all trophic levels. There is a need to establish benthic food web structure and resilience baseline for future comparison and to understand the impact of climate change in those various benthic food-webs. We also need a thorough study of the role of ice algae for the benthic food webs on a large scale. The objectives of this study were to describe the structure and the resilience of the benthic food-web of the Canadian Arctic and the Chukchi Sea (North Water Polynya, Canadian Archipelago, Amundsen Gulf, Beaufort Sea, Chukchi Sea), using stable carbon and nitrogen isotope analyses and to evaluate the importance of sea-ice algae in the benthic food-web using the Sea ice biomarkerIP25 (âIce Proxy 25â). To reach these objectives, we collected suspended particulate organic matter, surface sediments and zoobenthic samples from July to October 2014 aboard the CCGS Amundsen. Values in ÎŽ13C in the sediment were indicative of a marine origin of the organic matter in the North Water Polynya, Canadian Archipelago and the Chukchi Sea. The Beaufort Sea was characterized by terrestrial input, and the Amundsen Gulf was characterized by a mix between terrestrial and marine input. Those differences in the origin of organic matter were mirrored in consumer isotopic signatures in all the regions. The Beaufort Sea differed from the other regions regarding the trophic structure.
The high trophic redundancy and the low trophic separation of the North Water Polynya and the Canadian Archipelago suggest those regions have the higher potential of resilience facing environmental changes. We highlight transfer of ice algae across the different trophic levels. The biomarker IP25 was detectable in all the trophic guilds, and the higher concentrations were found in the surface deposit feeder. Ice algae seem to be an important food source for the Canadian Archipelago food web, were the higher concentration in IP25 were found and for the North Water Polynya, where the carbon stable isotopic signatures indicate ice algae assimilation. -- Mot(s) clé(s) en anglais : Benthos, trophic structure, resilience, ice-algae, IP25 biomarker, stable isotopes, Canadian arctic, Chukchi Sea
Southern Ocean food-webs and climate change: A short review and future directions
Food-webs are a critical feature of ecosystems and help us understand how communities will respond to climate change. The Southern Ocean is facing rapid and accelerating changes due to climate change. Though having evolved in an isolated and somewhat extreme environment, Southern Ocean biodiversity and food-webs are among the most vulnerable. Here, we review 1) current knowledge on Southern Ocean food-webs; 2) methods to study food-webs; 3) assessment of current and future impacts of climate change on Southern Ocean food-webs; 4) knowledge gaps; and 5) the role of Early Career Researchers (ECRs) in future studies. Most knowledge on Southern Ocean food-webs come from the pelagic environment, both at macro- and microbial levels. Modelling and diet studies of individual species are major contributors to the food-web knowledge. These studies revealed a short food-web, predominantly sustained by Antarctic Krill (Euphausia superba). Additionally, alternative pathways exist, involving other krill species, fish, and squid, which play equally important roles in connecting primary producers with top predators. Advantages and disadvantages of several techniques used to study Southern Ocean food-webs were identified, from the classical analyses of stomach contents, scats, or boluses to the most recent approaches such as metabarcoding and trophic-biomarkers. Observations show that climate change can impact the food-web in different ways. As an example, changes to smaller phytoplankton species can lengthen the food-web, increasing assimilation losses and/or changing nutrient cycles. Future studies need to focus on the benthic-dominated food-webs and the benthopelagic coupling. Furthermore, research during the winter season and below the ice-shelves is needed as these areas may play a crucial role in the functioning of this ecosystem. ECRs can play a significant role in advancing the study of Southern Ocean food-webs due to their willingness for interdisciplinary collaboration and proficiency in employing various methodologies, contributing to the construction of high-resolution food-webs.</jats:p
Fast and Efficient Postsynthetic DNA Labeling in Cells by Means of Strain-Promoted Sydnone-Alkyne Cycloadditions
Fast and efficient: DNA strands, modified with the novel bioorthogonal reporters sydnones, undergo fast and efficient labeling with cyclooctynes and have the potential to become essential tools for imaging DNA and possibly RNA in cells.
Sydnones are highly stable mesoionic 1,3-dipoles that react with cyclooctynes through strain-promoted sydnone-alkyne cycloaddition (SPSAC). Although sydnones have been shown to be valuable bioorthogonal chemical reporters for the labeling of proteins and complex glycans, nucleic acids have not yet been tagged by SPSAC. Evaluation of SPSAC kinetics with model substrates showed fast reactions with cyclooctyne probes (up to k=0.59â
Mâs), and two different sydnones were effectively incorporated into both 2â-deoxyuridines at position 5, and 7-deaza-2â-deoxyadenosines at position 7. These modified nucleosides were synthetically incorporated into single-stranded DNAs, which were successfully postsynthetically labeled with cyclooctyne probes both inâ
vitro and in cells. These results show that sydnones are versatile bioorthogonal tags and have the premise to become essential tools for tracking DNA and potentially RNA in living cells
Southern Ocean food-webs and climate change:A short review and future directions
Food-webs are a critical feature of ecosystems and help us understand how communities will respond to climate change. The Southern Ocean is facing rapid and accelerating changes due to climate change. Though having evolved in an isolated and somewhat extreme environment, Southern Ocean biodiversity and food-webs are among the most vulnerable. Here, we review 1) current knowledge on Southern Ocean food-webs; 2) methods to study food-webs; 3) assessment of current and future impacts of climate change on Southern Ocean food-webs; 4) knowledge gaps; and 5) the role of Early Career Researchers (ECRs) in future studies. Most knowledge on Southern Ocean food-webs come from the pelagic environment, both at macro- and microbial levels. Modelling and diet studies of individual species are major contributors to the food-web knowledge. These studies revealed a short food-web, predominantly sustained by Antarctic Krill (Euphausia superba). Additionally, alternative pathways exist, involving other krill species, fish, and squid, which play equally important roles in connecting primary producers with top predators. Advantages and disadvantages of several techniques used to study Southern Ocean food-webs were identified, from the classical analyses of stomach contents, scats, or boluses to the most recent approaches such as metabarcoding and trophic-biomarkers. Observations show that climate change can impact the food-web in different ways. As an example, changes to smaller phytoplankton species can lengthen the food-web, increasing assimilation losses and/or changing nutrient cycles. Future studies need to focus on the benthic-dominated food-webs and the benthopelagic coupling. Furthermore, research during the winter season and below the ice-shelves is needed as these areas may play a crucial role in the functioning of this ecosystem. ECRs can play a significant role in advancing the study of Southern Ocean food-webs due to their willingness for interdisciplinary collaboration and proficiency in employing various methodologies, contributing to the construction of high-resolution food-webs
Structure et résilience des réseaux trophiques benthiques de l'Arctique canadien et de la mer des Tchouktches
RĂSUMĂ: Les changements climatiques actuels sont Ă lâorigine de nombreuses modifications dans lâocĂ©an Arctique, telles quâune augmentation de la tempĂ©rature des eaux de surface, une augmentation des apports fluviaux, une rĂ©duction dans la couverture de glace de mer, des changements de composition des espĂšces ou des changements dans la phĂ©nologie et lâintensitĂ© de la production primaire. Ces changements pourraient ĂȘtre Ă lâorigine de modifications dans la structure et le fonctionnement des rĂ©seaux trophiques benthiques. Il est nĂ©cessaire aujourdâhui de dĂ©crire la structure et la rĂ©silience de rĂ©seaux trophiques benthiques de ces rĂ©gions pour Ă©valuer lâimpact des changements climatiques sur celles-ci. Cette Ă©tude a pour objectifs de dĂ©crire la structure et la rĂ©silience des rĂ©seaux trophiques benthiques de lâArctique canadien (polynie des eaux du Nord, archipel canadien, golfe dâAmundsen, mer de Beaufort) et de la mer des Tchouktches par une approche isotopique, et dâĂ©valuer lâimportance des algues de glace pour ces rĂ©seaux trophiques, Ă lâaide du biomarqueur dâalgues de glace IP25 (Ice Proxy 25). Pour atteindre ces deux objectifs, nous avons collectĂ© des Ă©chantillons de matiĂšre particulaire en suspension, de sĂ©diments de surface, et de faune benthique de juillet Ă octobre 2014, Ă bord du NGCC Amundsen. Les valeurs en ÎŽ13C mesurĂ©es dans les sĂ©diments de la polynie des eaux du Nord, de lâarchipel canadien et de la mer des Tchoukches, traduisent une origine marine de la matiĂšre organique. La mer de Beaufort et le golfe dâAmundsen sont quant Ă eux caractĂ©risĂ©s par des apports terrigĂšnes et des apports mixtes (terrigĂšnes et marins) respectivement.
Ces diffĂ©rences dans lâorigine de matiĂšre organique se retrouvent dans les signatures isotopiques des organismes et dans la structure des rĂ©seaux trophiques : la mer de Beaufort se distingue des autres rĂ©gions par des signatures appauvries en 13C chez les consommateurs et par de nombreux organismes avec de hauts niveaux trophiques. La faible sĂ©paration trophique et la forte redondance trophique suggĂšrent que la polynie des eaux du Nord et lâarchipel canadien semblent ĂȘtre les rĂ©gions avec la plus grande possibilitĂ© de rĂ©silience face Ă des changements environnementaux. Nous avons mis en Ă©vidence la prĂ©sence du marqueur dâalgue de glace IP25 chez les organismes appartenant Ă tous les niveaux trophiques. Les plus fortes concentrations en IP25 ont Ă©tĂ© retrouvĂ©es chez les dĂ©posivores de surface. Les algues de glace semblent ĂȘtre une source de xv nourriture importante pour les organismes de lâarchipel canadien, oĂč les plus fortes concentrations en biomarqueurs dâalgues de glace ont Ă©tĂ© retrouvĂ©es (en particulier chez les dĂ©posivores et les prĂ©dateurs) et pour la polynie des eaux du Nord oĂč les signatures en carbone des organismes indiquent une assimilation dâalgues de glace. -- Mot(s) clĂ©(s) en français : Benthos, structure trophique, rĂ©silience, algues de glace, biomarqueur IP25, isotopes stables, Arctique Canadien, Mer des Tchouktches. -- ABSTRACT: Ongoing climate change is causing rapid changes in the Arctic Ocean, such as higher water temperatures, increased fluvial run-off, reduced sea-ice cover, change in species composition, change in the timing and intensity of primary production. Those changes will give rise to severe ecosystem changes propagating in benthic food web through all trophic levels. There is a need to establish benthic food web structure and resilience baseline for future comparison and to understand the impact of climate change in those various benthic food-webs. We also need a thorough study of the role of ice algae for the benthic food webs on a large scale. The objectives of this study were to describe the structure and the resilience of the benthic food-web of the Canadian Arctic and the Chukchi Sea (North Water Polynya, Canadian Archipelago, Amundsen Gulf, Beaufort Sea, Chukchi Sea), using stable carbon and nitrogen isotope analyses and to evaluate the importance of sea-ice algae in the benthic food-web using the Sea ice biomarkerIP25 (âIce Proxy 25â). To reach these objectives, we collected suspended particulate organic matter, surface sediments and zoobenthic samples from July to October 2014 aboard the CCGS Amundsen. Values in ÎŽ13C in the sediment were indicative of a marine origin of the organic matter in the North Water Polynya, Canadian Archipelago and the Chukchi Sea. The Beaufort Sea was characterized by terrestrial input, and the Amundsen Gulf was characterized by a mix between terrestrial and marine input. Those differences in the origin of organic matter were mirrored in consumer isotopic signatures in all the regions. The Beaufort Sea differed from the other regions regarding the trophic structure.
The high trophic redundancy and the low trophic separation of the North Water Polynya and the Canadian Archipelago suggest those regions have the higher potential of resilience facing environmental changes. We highlight transfer of ice algae across the different trophic levels. The biomarker IP25 was detectable in all the trophic guilds, and the higher concentrations were found in the surface deposit feeder. Ice algae seem to be an important food source for the Canadian Archipelago food web, were the higher concentration in IP25 were found and for the North Water Polynya, where the carbon stable isotopic signatures indicate ice algae assimilation. -- Mot(s) clé(s) en anglais : Benthos, trophic structure, resilience, ice-algae, IP25 biomarker, stable isotopes, Canadian arctic, Chukchi Sea
ChemInform Abstract: One-Pot Three-Step Synthesis of 1,2,3-Triazoles by Copper-Catalyzed Cycloaddition of Azides with Alkynes Formed by a Sonogashira Cross-Coupling and Desilylation.
De l'obésité à l'infection bactérienne via le diabÚte
LILLE2-BU Santé-Recherche (593502101) / SudocSudocFranceF
New cathode contacts for non transit-time limited InP TED's in the millimeter-wave range
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