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DEVELOPMENT OF THE INTCAL DATABASE
No full textInternational audienceABSTRACT The IntCal family of radiocarbon ( 14 C) calibration curves is based on research spanning more than three decades. The IntCal group have collated the 14 C and calendar age data (mostly derived from primary publications with other types of data and meta-data) and, since 2010, made them available for other sorts of analysis through an open-access database. This has ensured transparency in terms of the data used in the construction of the ratified calibration curves. As the IntCal database expands, work is underway to facilitate best practice for new data submissions, make more of the associated metadata available in a structured form, and help those wishing to process the data with programming languages such as R, Python, and MATLAB. The data and metadata are complex because of the range of different types of archives. A restructured interface, based on the “IntChron” open-access data model, includes tools which allow the data to be plotted and compared without the need for export. The intention is to include complementary information which can be used alongside the main 14 C series to provide new insights into the global carbon cycle, as well as facilitating access to the data for other research applications. Overall, this work aims to streamline the generation of new calibration curves
Mechanisms and timing of carbonaceous chondrite delivery to the Earth
No full textInternational audienceThe nucleosynthetic isotope signatures of meteorites and the bulk silicate Earth (BSE) indicate that Earth consists of a mixture of "carbonaceous" (CC) and "non-carbonaceous" (NC) materials. We show that the fraction of CC material recorded in the isotopic composition of the BSE varies for different elements, and depends on the element's tendency to partition into metal and its volatility. The observed behavior indicates that the majority of material accreted to the Earth was NC-dominated, but that CC-dominated material enriched in moderately volatile elements by a factor of similar to 10 was delivered during the last similar to 2-10% of Earth's accretion. The late delivery of CC material to Earth contrasts with dynamical evidence for the early implantation of CC objects into the inner solar system during the growth and migration of the giant planets. This, together with the NC-dominated nature of both Earth's late veneer and bulk Mars, suggests that material scattered inwards had the bulk of its mass concentrated in a few, large CC embryos rather than in smaller planetesimals. We propose that Earth accreted a few of these CC embryos while Mars did not, and that at least one of the CC embryos impacted Earth relatively late (when accretion was 90-98% complete). This scenario is consistent with the subsequent Moon-forming impact of a large NC body, as long as this impact did not re-homogenize the entire Earth's mantle
Tidally driven remelting around 4.35 billion years ago indicates the Moon is old
No full textInternational audienceThe last giant impact on Earth is thought to have formed the Moon. The timing of this event can be determined by dating the different rocks assumed to have crystallized from the lunar magma ocean (LMO). This has led to a wide range of estimates for the age of the Moon between 4.35 and 4.51 billion years ago (Ga), depending on whether ages for lunar whole-rock samples or individual zircon grains are used. Here we argue that the frequent occurrence of approximately 4.35-Ga ages among lunar rocks and a spike in zircon ages at about the same time is indicative of a remelting event driven by the Moon’s orbital evolution rather than the original crystallization of the LMO. We show that during passage through the Laplace plane transition, the Moon experienced sufficient tidal heating and melting to reset the formation ages of most lunar samples, while retaining an earlier frozen-in shape and rare, earlier-formed zircons. This paradigm reconciles existing discrepancies in estimates for the crystallization time of the LMO, and permits formation of the Moon within a few tens of million years of Solar System formation, consistent with dynamical models of terrestrial planet formation. Remelting of the Moon also explains the lower number of lunar impact basins than expected, and allows metal from planetesimals accreted to the Moon after its formation to be removed to the lunar core, explaining the apparent deficit of such materials in the Moon compared with Earth
Respective Roles of Electron-Phonon and Electron-Electron Interactions in the Transport and Quasiparticle Properties of SrVO 3
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Vers des CO2 réductases artificielles et des hydrogénases artificielles
No full textThe accumulation of carbon dioxide (CO2) from fossil fuel combustion drives climate change and the nonrenewable nature of the later, highlight need for sustainable energy and carbon source alternatives. CO2 can be captured and converted into valuable compounds like carbon monoxide (CO) and acid formic (HCOOH) through photochemical processes. Additionally, hydrogen from water reduction offers a promising clean fuel for a decarbonized economy. Thereby, photo-reduction of CO2 and water is a promising method to store renewable energy, such as solar power, by converting it into chemical energy. Inspired by natural enzymes that efficiently catalyze these reactions, but are difficult to produce, scientists are exploring artificial enzymology, which involves anchoring synthetic catalysts in proteins to expand the enzyme repertoire. In the same way, the objective of this thesis was to develop efficient and selective artificial enzymes based on non-noble metals to reduce CO2 or to evolve H2 via photocatalysis. The first chapter is a presentation of the artificial enzymes previously developed by the scientific community as photocatalyst for both the reduction of carbon dioxide and the reduction of protons to dihydrogen in aqueous environment. In a second chapter, we show how we have developed and characterized an artificial CO2 reductase resulting from the combination of a hemoprotein called the heme oxygenase with a cobalt protoporphyrin IX. The ensuing enzyme was able to reduce CO2 to CO with a turnover frequency value (TOF) of ~ 616h-1, a turnover number (TON) value of ~589, after 3h reaction, and a CO vs H2 selectivity of 72%. Photophysical experiments allowed to get insights into the reaction mechanism. Crystal structures of the enzyme in the presence and in the absence of the substrate in the active site were obtained. These results allowed us to build a rational site-directed mutagenesis strategy of residues at the vicinity of the cofactor with the objective to modulate the activity of the enzyme. In a third part we report the preparation of artificial metallo-enzymes based on the heme oxygenase scaffold in which metal-salophen complexes (metal= FeIII, CoII, MnIII and CrIII) were inserted. We show that the cobalt based constructs present a good activity for photoreduction of CO2 to CO reaching TON of 253 and TOF of 755h-1 after optimization of the photoreaction conditions. Furthermore, these constructs showed a 100% selectivity toward CO2 reduction. Site directed mutagenesis of residues in the active site of the protein were also performed to modulate the activity of the construct. Finally, in the last part of this manuscript, we describe the preparation and the complete biochemical and spectroscopic characterization of a small bacterial metalloprotein (12 kDa) called the orange protein (Orp). This protein of unknow function harbors a unique and linear Mo/Cu cluster ([S2MoS2CuS2MoS2]3−). Performing docking simulations and dynamic molecular studies we propose a structure of holo-Orp in which the negatively charged cluster is non covalently bound to a cavity containing positively charged lysine and arginine residues at the surface of the protein. While we were studying Orp as a potential artificial CO2 reductase in the presence of the well-known ruthenium-based photosensitizer ([Ru(bpy)3]2+]) and sodium ascorbate as a sacrificial electron donor, no CO2 reduction activity was observed but instead a high efficiency for proton reduction. After optimization of the photoreaction condition, holo-Orp reached a TON of 890 at 4 hours of reaction. A series of dinuclear [S2MS2M'S2MS2](4n)− clusters, with M = MoVI, WVI and M'(n+) = CuI, FeI, NiI, CoI , ZnII, CdII were assembled in Orp, leading to different M/M'-Orp versions which are shown to display catalytic activity, with the Mo/Fe-Orp catalyst giving a remarkable TON of 1150 after 2.5 hours reaction and TOF of 800 h-1. Finaly, DFT calculations allowed us to propose a mechanism of reaction.L'accumulation de CO2 due à la combustion des énergies fossiles contribuant au changement climatique et le caractère non renouvelable des énergies fossiles souligne le besoin d'alternatives durables en termes d'énergie et de source de Carbon utilisable dans l'industrie chimique. Le CO2 peut être transformé en composés utiles comme le monoxyde de Carbon et l'acide formique grâce à des procédés photochimiques. De plus, l'hydrogène issu de la réduction de l'eau est un carburant propre prometteur. Inspirés par les enzymes naturelles, les scientifiques explorent l'enzymologie artificielle pour créer des systèmes catalytiques en intégrant des catalyseurs synthétiques dans des protéines hôtes. L'objectif de cette thèse était de développer des enzymes artificielles efficaces et sélectives dont les cofacteurs seraient composés de métaux bon marché et abondants pour réduire le CO2 ou produire du H2 par photocatalyse. Le premier chapitre présente les enzymes artificielles utilisées comme photo catalyseurs pour la réduction du CO2 et des protons en H2 en milieu aqueux. Le deuxième chapitre décrit le développement et la caractérisation d'une réductase artificielle du CO2, issue de la combinaison d'une hémoprotéine, l'hème oxygénase, avec une protoporphyrine IX de cobalt. Cette enzyme artificielle s'est montrée active pour réduire le CO2 en CO atteignant une fréquence de rotation (TOF) d'environ 616 h-1, une valeur de rotation (TON) d'environ 589 après 3h de réaction, et une sélectivité de 72 % pour la production de CO par rapport à la génération de H2. Des expériences photo-physiques ont permises de mieux comprendre le mécanisme de la réaction. Nous avons obtenu aussi une structure cristalline de l'enzyme en présence et en absence du substrat dans le site actif. Ces résultats nous ont permis de mettre en place une stratégie de mutagenèse dirigée de résidus à proximité du cofacteur dans le but de moduler l'activité de l'enzyme. Dans une troisième partie de ce manuscrit, nous rapportons la préparation de metallo-enzymes artificielles basées sur la structure de l'hème oxygénase dans laquelle des salophènes métalliques (métal = FeIII, CoII, MnIII et CrIII) ont été insérés. Nous montrons que les dérivés à base de cobalt présentent une bonne activité pour la photo réduction du CO2 en monoxyde de carbone (CO), atteignant un TON de 253 et un TOF de 755 h-1. De plus, ces enzymes artificielles ont montré une sélectivité de 100% envers la réduction du CO2. Nous avons aussi conduit des études de mutagenèse dirigée des résidus dans le site actif de la protéine afin de moduler l'activité de cette dernière. Enfin, dans la dernière partie de ce manuscrit, nous décrirons la préparation et la caractérisation biochimique et spectroscopique complète d'une petite métalloprotéine bactérienne (12 kDa) appelée la protéine orange (Orp). Cette protéine contient un cluster unique et linéaire à base de molybdène et de cuivre ([S2MoS2CuS2MoS2]3−). En effectuant des simulations d'amarrage et des études de moléculaires dynamiques, nous avons proposé une structure de l'holo-Orp dans laquelle le cluster chargé négativement est lié de manière non covalente à une cavité contenant des lysines et des arginines chargées positivement à la surface de la protéine. Alors que l'Orp s'est révélée inactive pour la réduction du CO2 elle s'est cependant, l'Orp s'est montré efficace pour la réduction des protons. Après optimisation des conditions de photo réaction, l'holo-Orp a atteint un TON de 890 après 4h de réaction. De plus, sous avons reconstitué l'Orp avec une série de clusters dinucléaires [S2MS2M'S2MS2](4n)−, avec M = MoVI, WVI et M'(n+) = CuI, FeI, NiI, CoI, ZnII, CdII conduisant à différents dérivés M/M'-Orp qui se sont révélés actifs, le catalyseur Mo/Fe-Orp affichant un TON de 1150 après 2,5h de réaction et une fréquence de TOF de 800 h-1. Enfin, des calculs basés sur la théorie de la fonctionnelle de la densité nous ont permises de proposer un mécanisme de réaction
Sciences sociales par temps de crise: Leçon inaugurale prononcée au Collège de France le jeudi 30 mars 2023
No full textInternational audienceÉcologique, sanitaire, énergétique, économique, sociale, humanitaire, démocratique : les crises sont une composante essentielle du monde contemporain. Si les sciences sociales peuvent aider à les comprendre et à les résoudre, leur rôle est également d’interroger le langage de la crise, d’analyser l’écart ou la convergence entre la réalité et sa représentation : nommer ou taire une crise, l’exagérer ou la minimiser sont autant de procédés générateurs d’affects, de temporalités, d’omissions aux conséquences majeures qu’une pensée critique se doit de décrypter.S’appuyant à la fois sur les trajectoires de vie de figures célèbres des sciences humaines et sur des recherches conduites autour de faits éloquents du présent, cette leçon inaugurale, qui s’adresse à toute citoyenne et tout citoyen, pose les jalons d’une vaste réflexion éthique et politique dont l’époque ne cesse de démontrer la nécessité
L’effectivité du droit international face à l’urgence écologique
No full textInternational audienceLe droit international de l’environnement, souvent présenté comme un droit empreint de jeunesse, a en fait atteint une certaine maturité. Né dans la mouvance de la Conférence des Nations unies sur l’environnement humain qui s’est tenue à Stockholm en juin 1972, il s’est depuis considérablement développé au gré de l’adoption de nombreux accords et instruments de portée régionale et universelle. Les attentes sont maintenant tournées vers la nécessité d’un droit plus prescriptif, en complément d’un droit d’exhortation et d’incitation. Si des pas sont accomplis en matière de mise en œuvre des engagements, la protection de l’environnement fait face au défi de sa réalisation concrète, aussi nommée « effectivité », dans un contexte d’urgence écologique. De nouvelles approches s’esquissent pour répondre à cet enjeu, impliquant acteurs publics et privés. Cet ouvrage analyse ces développements, notamment l’évolution du contenu des normes et des standards, la judiciarisation de l’application du droit international de l’environnement ou encore la reconnaissance de droits à la nature
Therapeutic value of homeoprotein signaling pathways
No full textInternational audienceCell signaling based on homeoprotein transfer is a pathway with developmental and physiological functions. For a few transcription factors of this family, primarily ENGRAILED1, ENGRAILED2 and OTX2, their physiological functions have led to therapeutic strategies in animal models of human diseases, including Parkinson’s disease, amyotrophic lateral sclerosis, amblyopia and anxiety-related disorders. In mesencephalic dopaminergic neurons which degenerate in Parkinson’s disease, ENGRAILED1/2 have cell autonomous activities, but their transducing properties enables their use as therapeutic proteins. In contrast, in spinal alpha-motoneurons, which are lost in amyotrophic lateral sclerosis, ENGRAILED1 is supplied by V1 interneurons. Thus, its use as a therapeutic protein to protect alpha-motoneurons against degeneration mimics its normal non-cell autonomous neurotrophic activity. OTX2, synthesized and secreted by the choroid plexus, is transferred to parvalbumin interneurons and exerts regulatory functions controlling cerebral cortex plasticity. Understanding the latter OTX2 function has led to strategies for manipulating visual acuity and anxiety-like behavior in adult mice. In this review, we describe these cases and what is known about the involved molecular mechanisms. Because the transduction sequences are conserved in most of the few hundred homeoproteins, we argue how this family of molecules constitutes an important reservoir of physiological knowledge, with potential consequences in the search for new therapeutic strategies
Introduction: Northern Treasures: Lives and Deities — For a Critical History of the Northern Treasures 2
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Multi-analytical study of bone collagen for the radiocarbon dating of prehistoric archaeological sites.
No full textInternational audienceThe chronology of archaeological sites is often established through radiocarbon dating of collagen extracted from bones. However, these samples may contain external organic contaminants, which can artificially rejuvenate radiocarbon ages. To address this issue, several purification protocols have been developed in recent years, including compound-specific radiocarbon dating, which isolates hydroxyproline using preparative liquid chromatography-mass spectrometry (prep-LC/MS). However, these protocols are not systematically applied, and a deeper understanding of the molecular composition of archaeological collagen remains essential.This study explores a multi-analytical approach to characterizing collagen extracted from archaeological faunal bones, with the aim of improving radiocarbon dating accuracy. Pyrolysis coupled with gas chromatography-mass spectrometry (Py-GC/MS) was used to analyze protein-derived products, complemented by a metabolomic workflow. Principal Component Analysis (PCA) was employed to assess collagen quality, distinguishing between “High-Quality” and “Low-Quality” samples. Partial Least Squares-Discriminant Analysis (PLS-DA) identified discriminant chemical markers, indicating potential exogenous organic contamination in certain samples. These findings highlight the potential of multi-analytical approaches to inform the selection of purification protocols and enhance the reliability of radiocarbon dating