Enantioselective Organocatalytic Four-Atom Ring Expansion of Cyclobutanones: Synthesis of Benzazocinones

International audienceAn enantioselective Michael addition-four-atom ring expansion cascade reaction involving cyclobutanones activated by a N-aryl secondary amide group and ortho-amino nitrostyrenes has been developed for the preparation of functionalized eight-membered benzolactams using bifunc-tional aminocatalysts. Taking advantage of the secondary amide activating group, the eight-membered cyclic products could be further rearranged into their six-membered isomers having a glutarimide core under base catalysis conditions without erosion of optical purity, featuring an overall ring expansion-ring contraction strategy

Effect of mixed-phase cloud on the chemical budget of trace gases: A modeling approach

International audienceA multiphase cloud chemistry model coupling a detailed chemical reactivity mechanism in gas phase and aqueous phase to a cloud parcel model with a two-moment microphysical scheme has been extended to include ice phase processes. This newly developed model is used to study the influence of the ice phase on HCOOH, HNO3, H2O2 and CH2O in a mixed-phase cloud. Microphysical processes are describing the interactions between the water vapor phase, the liquid phase (cloud and rain water) and the ice phase (pristine ice, snow and graupel) in the cloud and for soluble chemical species, their transfer by mixed-phase microphysical processes has been included. In addition to microphysical transfer between iced hydrometeors, the probable two main processes incorporating soluble chemical species in iced hydrometeors are the retention in ice phase as riming or freezing occurs and the burial in the ice crystal as the crystal grows by vapor diffusion. The model is applied to a cloud event describing a moderate precipitating mixed-phase cloud forming in a continental air mass in winter. The main features of the cloud are described and the evolution of key chemical species as function of time and temperature is discussed. Sensitivity tests are performed: a run without ice to highlight the influence of ice phase on the chemical gas phase composition of the cloud, a run without burial showing that it is a negligible process, a run assuming full retention in ice for all species and a run varying the ice crystal shapes. A detailed analysis of the microphysical rates and chemical rates linked to retention and burial effects show that for this cloud event, the effect of the ice phase on gas phase composition is driven by riming of cloud droplets onto graupels, which leads to retention or not of soluble chemical species in the ice phase. Finally, the impact of crystal geometry on the efficiency of collection is studied together with its impact on the riming of cloud droplets on graupels and also on the retention of chemical species in ice phase

An Organocatalytic Two-atom Ring Expansion Approach to Optically Active Glutarimides

International audienceAn original two-step organocatalytic syn- thesis of optically active glutarimides from 2- oxocyclobutane carboxamides is described featuring an isothiourea-catalyzed two-atom ring-expansive rearrangement

Modelling paralytic shellfish toxins (PST) accumulation in Crassostrea gigas by using Dynamic Energy Budgets (DEB)

As other filter-feeders, Crassostrea gigas can concentrate paralytic shellfish toxins (PST) by consuming dinoflagellate phytoplankton species like Alexandrium minutum. Intake of PST in oyster tissues mainly results from feeding processes, i.e. clearance rate, pre-ingestive sorting and ingestion that are directly influenced by environmental conditions (trophic sources, temperature). This study aimed to develop a mechanistic model coupling the kinetics of PST accumulation and bioenergetics in C. gigas based on Dynamic Energy Budget (DEB) theory. For the first time, the Synthesizing Units (SU) concept was applied to formalize the feeding preference of oysters between non-toxic and toxic microalgae. Toxin intake and accumulation were both dependent on the physiological status of oysters. The accumulation was modelled through the dynamics of two toxin compartments: (1) a compartment of ingested but non-assimilated toxins, with labile toxins within the digestive gland eliminated via faeces production; (2) a compartment of assimilated toxins with a rapid detoxification rate (within a few days). Firstly, the DEB-PST model was calibrated using data from two laboratory experiments where oysters have been exposed to A. minutum. Secondly, it was validated using data from another laboratory experiment and from three field surveys carried out in the Bay of Brest (France) from 2012 to 2014. To account for the variability in PST content of A. minutum cells, the saxitoxin (STX) amount per energy units in a toxic algae (ρPST) was adjusted for each dataset. Additionally, the effects of PST on the oyster bioenergetics were calibrated during the first laboratory experiment. However, these effects were shown to depend on the strain of A. minutum. Results of this study could be of great importance for monitoring agencies and decision makers to identify risky conditions (e.g. production areas, seawater temperature), to properly assess detoxification step (e.g. duration, modalities) before any commercialization or to improve predictions regarding closing of shellfish areas

Results of the first European Source Apportionment intercomparison for Receptor and Chemical Transport Models

In this study, the performance of the source apportionment model applications were evaluated by comparing the model results provided by 44 participants adopting a methodology based on performance indicators: z-scores and RMSEu, with pre-established acceptability criteria. Involving models based on completely different and independent input data, such as receptor models (RMs) and chemical transport models (CTMs), provided a unique opportunity to cross-validate them. In addition, comparing the modelled source chemical profiles, with those measured directly at the source contributed to corroborate the chemical profile of the tested model results. The most used RM was EPA- PMF5. RMs showed very good performance for the overall dataset (91% of z-scores accepted) and more difficulties are observed with SCE time series (72% of RMSEu accepted). Industry resulted the most problematic source for RMs due to the high variability among participants. Also the results obtained with CTMs were quite comparable to their ensemble reference using all models for the overall average (>92% of successful z-scores) while the comparability of the time series is more problematic (between 58% and 77% of the candidates’ RMSEu are accepted). In the CTM models a gap was observed between the sum of source contributions and the gravimetric PM10 mass likely due to PM underestimation in the base case. Interestingly, when only the tagged species CTM results were used in the reference, the differences between the two CTM approaches (brute force and tagged species) were evident. In this case the percentage of candidates passing the z-score and RMSEu tests were only 50% and 86%, respectively. CTMs showed good comparability with RMs for the overall dataset (83% of the z-scores accepted), more differences were observed when dealing with the time series of the single source categories. In this case the share of successful RMSEu was in the range 25% - 34%.JRC.C.5-Air and Climat

TRY plant trait database – enhanced coverage and open access

Plant traits - the morphological, anatomical, physiological, biochemical and phenological characteristics of plants - determine how plants respond to environmental factors, affect other trophic levels, and influence ecosystem properties and their benefits and detriments to people. Plant trait data thus represent the basis for a vast area of research spanning from evolutionary biology, community and functional ecology, to biodiversity conservation, ecosystem and landscape management, restoration, biogeography and earth system modelling. Since its foundation in 2007, the TRY database of plant traits has grown continuously. It now provides unprecedented data coverage under an open access data policy and is the main plant trait database used by the research community worldwide. Increasingly, the TRY database also supports new frontiers of trait‐based plant research, including the identification of data gaps and the subsequent mobilization or measurement of new data. To support this development, in this article we evaluate the extent of the trait data compiled in TRY and analyse emerging patterns of data coverage and representativeness. Best species coverage is achieved for categorical traits - almost complete coverage for ‘plant growth form’. However, most traits relevant for ecology and vegetation modelling are characterized by continuous intraspecific variation and trait–environmental relationships. These traits have to be measured on individual plants in their respective environment. Despite unprecedented data coverage, we observe a humbling lack of completeness and representativeness of these continuous traits in many aspects. We, therefore, conclude that reducing data gaps and biases in the TRY database remains a key challenge and requires a coordinated approach to data mobilization and trait measurements. This can only be achieved in collaboration with other initiatives

Modelling of cloud physico-chemical processes : studies of the reactivity of organic matter

Dans l’atmosphère, la matière organique est omniprésente et joue un rôle important par son action sur le bilan radiatif de la Terre et par son impact sur la santé publique notamment dans les zones fortement polluées. A ce jour plus de 10000 Composés Organiques Volatils différents ont été identifiés dans l’atmosphère. Leurs propriétés physico-chimiques (solubilité, volatilité, réactivité, …) sont variées et mal documentées. Leur distribution est perturbée par la présence de nuage qui représente un milieu réactif. L’objectif de cette thèse est d’évaluer la contribution des processus physico-chimiques sur la redistribution des COV à partir d'études numériques via le modèle de processus M2C2 (Model of Multiphase Cloud Chemistry). Les résultats sur les processus microphysiques en phase mixte ont montré que la rétention des composés chimiques dans les cristaux de glace qui grossissent principalement par givrage des gouttelettes de nuage, est un processus important dans la redistribution des espèces en phase gazeuse, comme la forme des cristaux (complexe ou sphérique). Par ailleurs, une intensité du givrage plus élevée entraîne un dégazage des composés chimiques dissous dans l’eau liquide nuageuse plus important et réparti sur une gamme de températures plus faibles dans le cas des cristaux complexes. La chimie en phase aqueuse du modèle M2C2 a été confrontée et calibrée avec des mesures effectuées lors d’expériences d’irradiations d’échantillons d’eau synthétique (i.e. de composition chimique connue). Ce travail a mis en évidence la complexité du système HxOy/fer et les incertitudes associées, notamment en présence de matière organique. Ces premières études ont montré la nécessité, dans le cas considéré, de prendre en compte la photolyse du complexe fer/oxalate à un seul ligand Fe(C2O4)+ et d'étudier expérimentalement la formation de complexes fer – acide formique en détail. Cette thèse aborde le développement de la chimie en phase aqueuse dans M2C2 en ajoutant les voies d’oxydation des composés organiques à deux atomes de carbone à partir de données expérimentales et d'analogie mécanistiques. Ce nouveau mécanisme a été testé sur un ensemble de scénarios académiques (urbain, rural et marin). Les résultats montrent, dans le cas d’un scénario urbain, que les COV influent sur l’évolution temporelle du radical hydroxyle en phase aqueuse à travers une modification importante de ses sources et de ses puits ; notamment par la présence de nouveaux complexes organiques avec le fer. Les alcools, transférés en phase aqueuse ne contribuent que très faiblement, par oxydation, aux aldéhydes dissous. Les aldéhydes sont issus principalement de la phase gazeuse. Enfin, les acides carboxyliques en phase aqueuse sont produits par oxydation des aldéhydes à un taux du même ordre de grandeur que celui de leur transfert de masse.Organic matter is ubiquitous in the atmosphere and plays a key role on both Earth radiative budget and public health particularly in high pollution level areas. Up to now around 10000 different VOCs (Volatil Organic Compounds) were identified. Their physical and chemical properties (solubility, volatility, reactivity …) are highly variables and not fully documented. Their distribution is perturbed by cloud droplet which represents a reactive media. The aim of this thesis is to evaluate the physical and chemical processes contribution on VOCs distribution from numerical studies using the M2C2 (Model of Multiphase Cloud Chemistry) model. A detailed analysis of the microphysical rates and chemical rates linked to retention and burial effects show that for a moderate precipitating mixed-phase-cloud, the effect of the ice phase on gas phase composition is driven by riming of cloud droplets onto graupels, which leads to retention or not of soluble chemical species in the ice phase. Finally, the impact of crystal geometry on the efficiency of collection is studied together with its impact on the riming of cloud droplets on graupels and also on the retention of chemical species in ice phase. Numerical chemical outputs from M2C2 model were compared with experimental data that consisted of a time evolution of the concentrations of the target species. The chemical mechanism in the model describing the "oxidative engine" of the HxOy/iron chemical system was consistent with laboratory measurements. Thus, the degradation of the carboxylic acids evaluated was closely reproduced by the model. However, photolysis of the Fe(C2O4)+ complex needs to be considered in cloud chemistry models for polluted conditions (i.e., acidic pH) to correctly reproduce oxalic acid degradation. We also show that iron and formic acid lead to a stable complex whose photoreactivity has currently not been investigated. This thesis proposes the development of a new cloud chemical mechanism considering oxidative pathways of VOCs with 2-carbon atoms from experimental data and mechanism analogies. This new mechanism is tested using academic scenarios (urban, remote and marine). Results show that VOCs modify the sources and sinks of hydroxyl radical through the formation of new iron organic complexes in the case of urban scenario. In aqueous phase, alcohols concentrations are mainly drive by mass transfer and are not a significant source for aldehydes which are mostly produced in gaseous phase. Carboxylic acids are formed by aldehydes oxidation with a rate as a same order than their mass transfer

Modélisation des processus physico-chimiques nuageux : études de la réactivité de la matière organique

Organic matter is ubiquitous in the atmosphere and plays a key role on both Earth radiative budget and public health particularly in high pollution level areas. Up to now around 10000 different VOCs (Volatil Organic Compounds) were identified. Their physical and chemical properties (solubility, volatility, reactivity …) are highly variables and not fully documented. Their distribution is perturbed by cloud droplet which represents a reactive media. The aim of this thesis is to evaluate the physical and chemical processes contribution on VOCs distribution from numerical studies using the M2C2 (Model of Multiphase Cloud Chemistry) model. A detailed analysis of the microphysical rates and chemical rates linked to retention and burial effects show that for a moderate precipitating mixed-phase-cloud, the effect of the ice phase on gas phase composition is driven by riming of cloud droplets onto graupels, which leads to retention or not of soluble chemical species in the ice phase. Finally, the impact of crystal geometry on the efficiency of collection is studied together with its impact on the riming of cloud droplets on graupels and also on the retention of chemical species in ice phase. Numerical chemical outputs from M2C2 model were compared with experimental data that consisted of a time evolution of the concentrations of the target species. The chemical mechanism in the model describing the "oxidative engine" of the HxOy/iron chemical system was consistent with laboratory measurements. Thus, the degradation of the carboxylic acids evaluated was closely reproduced by the model. However, photolysis of the Fe(C2O4)+ complex needs to be considered in cloud chemistry models for polluted conditions (i.e., acidic pH) to correctly reproduce oxalic acid degradation. We also show that iron and formic acid lead to a stable complex whose photoreactivity has currently not been investigated. This thesis proposes the development of a new cloud chemical mechanism considering oxidative pathways of VOCs with 2-carbon atoms from experimental data and mechanism analogies. This new mechanism is tested using academic scenarios (urban, remote and marine). Results show that VOCs modify the sources and sinks of hydroxyl radical through the formation of new iron organic complexes in the case of urban scenario. In aqueous phase, alcohols concentrations are mainly drive by mass transfer and are not a significant source for aldehydes which are mostly produced in gaseous phase. Carboxylic acids are formed by aldehydes oxidation with a rate as a same order than their mass transfer.Dans l’atmosphère, la matière organique est omniprésente et joue un rôle important par son action sur le bilan radiatif de la Terre et par son impact sur la santé publique notamment dans les zones fortement polluées. A ce jour plus de 10000 Composés Organiques Volatils différents ont été identifiés dans l’atmosphère. Leurs propriétés physico-chimiques (solubilité, volatilité, réactivité, …) sont variées et mal documentées. Leur distribution est perturbée par la présence de nuage qui représente un milieu réactif. L’objectif de cette thèse est d’évaluer la contribution des processus physico-chimiques sur la redistribution des COV à partir d'études numériques via le modèle de processus M2C2 (Model of Multiphase Cloud Chemistry). Les résultats sur les processus microphysiques en phase mixte ont montré que la rétention des composés chimiques dans les cristaux de glace qui grossissent principalement par givrage des gouttelettes de nuage, est un processus important dans la redistribution des espèces en phase gazeuse, comme la forme des cristaux (complexe ou sphérique). Par ailleurs, une intensité du givrage plus élevée entraîne un dégazage des composés chimiques dissous dans l’eau liquide nuageuse plus important et réparti sur une gamme de températures plus faibles dans le cas des cristaux complexes. La chimie en phase aqueuse du modèle M2C2 a été confrontée et calibrée avec des mesures effectuées lors d’expériences d’irradiations d’échantillons d’eau synthétique (i.e. de composition chimique connue). Ce travail a mis en évidence la complexité du système HxOy/fer et les incertitudes associées, notamment en présence de matière organique. Ces premières études ont montré la nécessité, dans le cas considéré, de prendre en compte la photolyse du complexe fer/oxalate à un seul ligand Fe(C2O4)+ et d'étudier expérimentalement la formation de complexes fer – acide formique en détail. Cette thèse aborde le développement de la chimie en phase aqueuse dans M2C2 en ajoutant les voies d’oxydation des composés organiques à deux atomes de carbone à partir de données expérimentales et d'analogie mécanistiques. Ce nouveau mécanisme a été testé sur un ensemble de scénarios académiques (urbain, rural et marin). Les résultats montrent, dans le cas d’un scénario urbain, que les COV influent sur l’évolution temporelle du radical hydroxyle en phase aqueuse à travers une modification importante de ses sources et de ses puits ; notamment par la présence de nouveaux complexes organiques avec le fer. Les alcools, transférés en phase aqueuse ne contribuent que très faiblement, par oxydation, aux aldéhydes dissous. Les aldéhydes sont issus principalement de la phase gazeuse. Enfin, les acides carboxyliques en phase aqueuse sont produits par oxydation des aldéhydes à un taux du même ordre de grandeur que celui de leur transfert de masse

Modélisation des processus physico-chimiques nuageux (études de la réactivité de la matière organique)

Dans l atmosphère, la matière organique est omniprésente et joue un rôle important par son action sur le bilan radiatif de la Terre et par son impact sur la santé publique notamment dans les zones fortement polluées. A ce jour plus de 10000 Composés Organiques Volatils différents ont été identifiés dans l atmosphère. Leurs propriétés physico-chimiques (solubilité, volatilité, réactivité, ) sont variées et mal documentées. Leur distribution est perturbée par la présence de nuage qui représente un milieu réactif. L objectif de cette thèse est d évaluer la contribution des processus physico-chimiques sur la redistribution des COV à partir d'études numériques via le modèle de processus M2C2 (Model of Multiphase Cloud Chemistry). Les résultats sur les processus microphysiques en phase mixte ont montré que la rétention des composés chimiques dans les cristaux de glace qui grossissent principalement par givrage des gouttelettes de nuage, est un processus important dans la redistribution des espèces en phase gazeuse, comme la forme des cristaux (complexe ou sphérique). Par ailleurs, une intensité du givrage plus élevée entraîne un dégazage des composés chimiques dissous dans l eau liquide nuageuse plus important et réparti sur une gamme de températures plus faibles dans le cas des cristaux complexes. La chimie en phase aqueuse du modèle M2C2 a été confrontée et calibrée avec des mesures effectuées lors d expériences d irradiations d échantillons d eau synthétique (i.e. de composition chimique connue). Ce travail a mis en évidence la complexité du système HxOy/fer et les incertitudes associées, notamment en présence de matière organique. Ces premières études ont montré la nécessité, dans le cas considéré, de prendre en compte la photolyse du complexe fer/oxalate à un seul ligand Fe(C2O4)+ et d'étudier expérimentalement la formation de complexes fer acide formique en détail. Cette thèse aborde le développement de la chimie en phase aqueuse dans M2C2 en ajoutant les voies d oxydation des composés organiques à deux atomes de carbone à partir de données expérimentales et d'analogie mécanistiques. Ce nouveau mécanisme a été testé sur un ensemble de scénarios académiques (urbain, rural et marin). Les résultats montrent, dans le cas d un scénario urbain, que les COV influent sur l évolution temporelle du radical hydroxyle en phase aqueuse à travers une modification importante de ses sources et de ses puits ; notamment par la présence de nouveaux complexes organiques avec le fer. Les alcools, transférés en phase aqueuse ne contribuent que très faiblement, par oxydation, aux aldéhydes dissous. Les aldéhydes sont issus principalement de la phase gazeuse. Enfin, les acides carboxyliques en phase aqueuse sont produits par oxydation des aldéhydes à un taux du même ordre de grandeur que celui de leur transfert de masse.Organic matter is ubiquitous in the atmosphere and plays a key role on both Earth radiative budget and public health particularly in high pollution level areas. Up to now around 10000 different VOCs (Volatil Organic Compounds) were identified. Their physical and chemical properties (solubility, volatility, reactivity ) are highly variables and not fully documented. Their distribution is perturbed by cloud droplet which represents a reactive media. The aim of this thesis is to evaluate the physical and chemical processes contribution on VOCs distribution from numerical studies using the M2C2 (Model of Multiphase Cloud Chemistry) model. A detailed analysis of the microphysical rates and chemical rates linked to retention and burial effects show that for a moderate precipitating mixed-phase-cloud, the effect of the ice phase on gas phase composition is driven by riming of cloud droplets onto graupels, which leads to retention or not of soluble chemical species in the ice phase. Finally, the impact of crystal geometry on the efficiency of collection is studied together with its impact on the riming of cloud droplets on graupels and also on the retention of chemical species in ice phase. Numerical chemical outputs from M2C2 model were compared with experimental data that consisted of a time evolution of the concentrations of the target species. The chemical mechanism in the model describing the "oxidative engine" of the HxOy/iron chemical system was consistent with laboratory measurements. Thus, the degradation of the carboxylic acids evaluated was closely reproduced by the model. However, photolysis of the Fe(C2O4)+ complex needs to be considered in cloud chemistry models for polluted conditions (i.e., acidic pH) to correctly reproduce oxalic acid degradation. We also show that iron and formic acid lead to a stable complex whose photoreactivity has currently not been investigated. This thesis proposes the development of a new cloud chemical mechanism considering oxidative pathways of VOCs with 2-carbon atoms from experimental data and mechanism analogies. This new mechanism is tested using academic scenarios (urban, remote and marine). Results show that VOCs modify the sources and sinks of hydroxyl radical through the formation of new iron organic complexes in the case of urban scenario. In aqueous phase, alcohols concentrations are mainly drive by mass transfer and are not a significant source for aldehydes which are mostly produced in gaseous phase. Carboxylic acids are formed by aldehydes oxidation with a rate as a same order than their mass transfer.CLERMONT FD-Bib.électronique (631139902) / SudocSudocFranceF

Enantiospecific Generation and Trapping Reactions of Aryne Atropisomers

Enantioenriched aryne atropisomers having a biaryl stereogenic axis vicinal to the reactive triple bond are demonstrated to exist. These reaction intermediates are easily produced in situ and can undergo the standard aryne cycloaddition chemistry in an enantiospecific manner. Notably, the aryne atropisomers herein have allowed the practical syntheses of a small nanographene as well as some triptycene and anthracene derivatives that embed stereogenic axes of controlled absolute configurations