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Smart electrode surfaces by electrolyte immobilization for electrocatalytic CO 2 conversion
No full textInternational audienceThe activity and selectivity of molecular catalysts for the electrochemical CO2 reduction reaction (CO2RR) are influenced by the induced electric field at the electrode/electrolyte interface. We present here a novel electrolyte immobilization method to control the electric field at this interface by positively charging the electrode surface with an imidazolium cation organic layer, which significantly favors CO2 conversion to formate, suppresses hydrogen evolution reaction, and diminishes the operating cell voltage. Those results are well supported by our previous DFT calculations studying the mechanistic role of imidazolium cations in solution for CO2 reduction to formate catalyzed by a model molecular catalyst. This smart electrode surface concept based on covalent grafting of imidazolium on a carbon electrode is successfully scaled up for operating at industrially relevant conditions (100 mA cm–2) on an imidazolium-modified carbon-based gas diffusion electrode using a flow cell configuration, where the CO2 conversion to formate process takes place in acidic aqueous solution to avoid carbonate formation and is catalyzed by a model molecular Rh complex in solution. The formate production rate reaches a maximum of 4.6 gHCOO– m–2 min–1 after accumulating a total of 9000 C of charge circulated on the same electrode. Constant formate production and no significant microscopic changes on the imidazolium-modified cathode in consecutive long-term CO2 electrolysis confirmed the high stability of the imidazolium organic layer under operating conditions for CO2RR
Postglacial flooding and Holocene climate shifts in the Persian Gulf
No full textInternational audiencePostglacial flooding of the Persian Gulf (PG) was important in shaping human history and driving landscape changes in the region. However, there is a paucity of data regarding the postglacial transgression. The position of the PG at the edge of major synoptic systems of the Indian Ocean Summer Monsoon (IOSM) and Mid‐latitude Westerlies (MLW) makes the environment particularly sensitive to Holocene climate shifts. To investigate the timing of the flooding and to detect the impacts of significant climate shifts on the regional environment during the Holocene, a multiproxy study was conducted on three short sediment cores from two deep sites in the PG. Sedimentological, palynological and geochemical analyses were performed on the cores. The results show that inundation of the western part of the PG that started from ca. 11.5 ka bp continued with successive prominent phases of transgression centered on 10.4 and 9.2 ka cal bp , and definitive marine conditions were established around 8.8 ka cal bp. The IOSM was the dominant system in the region until about 9 to ~6.3 ka cal bp. After that time, the intensity of the IOSM declined, as MLW dominated the region after ~6.3 ka cal bp. These climatic shifts induced significant changes in regional vegetation and hydrology, and possibly triggered socio‐cultural transformations
Untangling bacterial DNA topoisomerases functions
No full textInternational audienceTopoisomerases are the main enzymes capable of resolving the topological constraints imposed by DNA transactions such as transcription or replication. All bacteria possess topoisomerases of different types. Although, bacteria with circular replicons should encounter similar DNA topology issues, the distribution of topoisomerases varies from one bacterium to another, suggesting polymorphic functioning. Recently, several proteins restricting, enhancing or modifying the activity of topoisomerases were discovered opening the way to new area of understanding DNA topology management during the bacterial cell cycle. In this review, we discuss the distribution of topoisomerases across the bacterial phylum and current knowledge on the interplay between the different topoisomerase to maintain topological homeostasis
Châtelperronian cultural diversity at its western limits: shell beads and pigments from La Roche-à-Pierrot, Saint-Césaire (France).
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Correlating Substrate Reactivity at Electrified Interfaces with the Electrolyte Structure in Synthetically Relevant Organic Solvent/Water Mixtures
No full textInternational audienceOptimizing electrosynthetic reactions requires fine tuning of a vast chemical space, including charge transfer at electrocatalyst/electrode surfaces, engineering of mass transport limitations and complex interactions of reactants and products with their environment. Hybrid electrolytes, in which supporting salt ions and substrates are dissolved in a binary mixture of organic solvent and water, represent a new piece to this complex puzzle, as they offer a unique opportunity to harness water as the oxygen or proton source in electrosynthesis. In this work, we demonstrate that modulating water-organic solvent interactions drastically impacts the solvation properties of hybrid electrolytes. Combining various spectroscopies with synchrotron small-angle X-ray scattering (SAXS) and force field-based molecular dynamics (MD) simulations, we show that the size and composition of aqueous domains forming in hybrid electrolytes can be controlled. We demonstrate that water is more reactive for the hydrogen evolution reaction (HER) in aqueous domains than when strongly interacting with solvent molecules, which originates from a change in reaction kinetics rather than from a thermodynamic effect. We exemplify novel opportunities arising from this new knowledge for optimizing electrosynthetic reactions in hybrid electrolytes. For reactions proceeding first via the activation of water, fine tuning of aqueous domains impacts the kinetics and potentially the selectivity of the reaction. Instead, for organic substrates reacting prior to water, aqueous domains have no impact on reaction kinetics, while selectivity may be affected. We believe that such fine comprehension of solvation properties of hybrid electrolytes can be transposed to numerous electrosynthetic reactions
Integrating ZooMS and zooarchaeology to assess the Châtelperronian and carnivore occupations at Cassenade (Dordogne, France)
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Can ZooMS Help Assess Species Abundance in Highly Fragmented Bone Assemblages? Integrating Morphological and Proteomic Identifications for the Calculation of an Adjusted ZooMS-eNISP
No full textInternational audienceZooarchaeology by Mass Spectrometry (ZooMS) is a rapid, low-cost, collagen-based method for the taxonomic identification of animal tissues. It is now increasingly applied to bone fragments from archeological contexts, creating large taxonomic datasets. How to integrate these ZooMS identifications within general zooarchaeological theoretical frameworks, such as estimates of species abundance and taxonomic richness, remains problematic. Past large-scale ZooMS analyses of Eurasian Paleolithic faunal assemblages have shown a general trend towards an increased representation of large ungulates (mainly Bos/Bison) in the ZooMS fraction, often coupled with a decrease in medium-sized taxa (e.g., reindeer). Here we propose several hypotheses to explain these identification discrepancies, involving identification biases and differential fragmentation patterns across various taxa, and test them using the case study of the Paleolithic site of Cassenade.At the Châtelperronian site of Cassenade (France), nearly all bone fragments larger than 20mm (n=1,119) have been identified to taxa, either through comparative morphology (n=364) or ZooMS (n=755). Each of these fragments was weighed and measured, creating a unique database to explore the relation between fragmentation and identification. Analysis shows that fragment size and mass distributions are distinct across taxa if only bones identified by morphology are considered, but, somehow counter-intuitively, extremely similar across taxa of various body sizes when all their bones are integrated. In particular, the bones of larger ungulates tend to be broken into a higher number of fragments, inducing an over-representation of larger taxa in ZooMS-NISP. Our dataset also shows that sorting long-bone shaft fragments by body size classes should be seen by zooarchaeologists as a process that, in addition to being prone to risks of misidentification, provides highly biased information of little use for estimating species abundance. To overcome this issue, we propose the calculation of an adjusted equivalent ZooMS NISP (ZooMS-eNISP) by dividing, for each taxon, the total ZooMS mass of identified bones (g) by the mean mass of morphologically identified bones for that taxon (g/NISP). The advantage of this method is that it considers site-specific characteristics of the faunal assemblage, notably bone preservation, which is especially important in Paleolithic contexts. Finally, we propose that ZooMS-eNISP, despite its limits, can facilitate the integration of both identification methods to produce a more refined picture of patterns of species representation, site formation, and human behavior at an archaeological site.</p
Zr-Based MOF-545 Metal-Organic Framework Loaded with Highly Dispersed Small Size Ni Nanoparticles for CO2 Methanation
No full textInternational audienceWe report the use of Zr-based metal-organic frameworks (MOFs) MOF-545 and MOF-545(Cu) as supports to prepare catalysts with uniformly and highly dispersed Ni nanoparticles (NPs) for CO2 hydrogenation into CH4. In the first step, we studied the MOF support under catalytic conditions using operando diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, ex situ characterizations (PXRD, XPS, TEM, and EDX-element mapping), and DFT calculations. We showed that the high-temperature conditions undoubtedly confer a potential for catalytic functionality to the solids toward CH4 production, while no role of the Cu could be evidenced. The MOF was shown to be transformed into a catalytically active material, amorphized but still structured with dehydroxylated Zr-oxoclusters, in line with DFT calculations. In the second step, Ni@MOF-545 catalysts were prepared using either impregnation (IM) or double solvent (DS) methods, followed by a dry reduction (R) route under H2 to immobilize Ni NPs. The highest catalytic activity was obtained with the Ni@MOF-545 DS R catalyst (595 mmolCH4 gNi-1 h-1) with 100% CH4 selectivity and 60% CO2 conversion after ∼3 h. The higher catalytic activity of Ni@MOF-545 DS R is a result of much smaller (∼5 nm) and better dispersed Ni NPs than in the IM sample (20-40 nm), the latter exhibiting sintering. The advantages of the encapsulation of Ni NPs by the DS method and of the use of a MOF-545-based support are discussed, highlighting the interest of designing yet-unexplored Zr-based MOFs loaded with Ni NPs for CO2 hydrogenation
O “campo internacional” e suas especificidades: Reflexões a partir de uma pesquisa coletiva sobre a dimensão transnacional das eleições brasileiras de 2022
No full textInternational audienceWe present a collective reflection on research in the “international field”, understood as an opportunity to establish a direct relationship between the researcher and the subjects who carry out the practices under study, which allows observing changes in scale carried out by actors and processes of transnationalization. The article is based on a multimethod research project on transnational activism in France during the 2022 Brazilian presidential elections and offers a dialogue between International Relations and Sociology. The research was met by challenges related to the particularities of access to the field in a world divided into States and issues related to language, nationality and their impact on the researcher's relationship with the study population. We argue that multinational research teams can present ways to overcome these obstacles and that the State is responsible for building a more internationalized, plural and safe scientific field.Apresentamos uma reflexão coletiva sobre a pesquisa de “campo internacional”, entendida como uma oportunidade de estabelecimento de uma relação direta entre o pesquisador e os sujeitos que protagonizam as práticas em estudo, permitindo observar mudanças de escala efetuadas pelos atores e processos de transnacionalização. O artigo se baseia em uma pesquisa multimétodo sobre o ativismo transnacional na França durante o processo eleitoral brasileiro de 2022 e propõe um diálogo entre as Relações Internacionais e a Sociologia. A pesquisa foi marcada por desafios que são relacionados às particularidades do acesso ao campo em um mundo dividido em Estados e às questões relativas ao idioma, à nacionalidade e seus impactos na relação do pesquisador com a população em estudo. Argumentamos que as equipes multinacionais de pesquisa podem apresentar caminhos para a superação desses obstáculos e que o Estado é responsável pela construção de um campo científico mais internacionalizado, plural e seguro
Réécritures et registres linguistiques dans la Chine prémoderne : quelle approche conceptuelle ?
No full textNational audienceIn examining the production practices of literary texts in 17th-century China, we need to give the much-discussed notions of diglossia and intralingual translation their rightful place and topicality. Intralingual translation is linked to the traditional Chinese practice of commentary, and plays a decisive role in renewing the means by which knowledge is shared, a process of a political nature.L'examen des pratiques de production des textes littéraires dans la Chine du 17° siècle nous amène à donner toute leur place et leur actualité aux notions discutées de diglossie et de traduction intralinguale. Cette dernière est affine à la pratique, traditionnelle en Chine, du commentaire et joue un rôle décisif dans le renouvellement des moyens du partage du savoir, une démarche de nature politique