HAL Portal ESPCI (Ecole Supérieure de Physique et de Chimie Industrielles)
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Développement de nouveaux ligands NHC chiraux pour la catalyse énantiosélective à l'or (I)
No full textThe control of chirality in molecules is an integral part of synthetic organic chemistry and remains a highly challenging task to this day. Placing a stereocenter into the molecular structure of a catalyst is a prominent strategy, giving chemists the ability to transfer the catalyst's chiral information onto a substrate molecule as part of the catalyzed reaction. Privileged structures for this approach are transition metal complexes, giving a wide range of possibilities in the design of a chiral ligand framework. This work focuses on the design of new ligands for enantioselective gold(I)-catalyzed transformations. The metal is exceptionally selective for the activation of unsaturated carbon carbon bonds while having a high tolerance for other types of functional groups, making it a powerful tool to build molecular complexity even in late-stage transformations. A main challenge is the unfavorable linear geometry of gold(I)'s coordination sphere, requiring intricate ligand structures to overcome the distance between chiral center and the substrate molecules. Recent studies have revealed the proficiency of cyclodextrin-based cavitands as ligands in efficient enantioselective gold(I) catalysis. The application of capped β cyclodextrin NHC ligands in enantioconvergent reactions was investigated in the first part of this work. In that body of research, their proficiency based on a cavity-driven catalysis was showcased in enantioselective cycloisomerization reactions of various 1,5 enyne substrates. In the second part, a new methodology featuring L-shaped NHC-ligands with and imidazopyridine core structure was developed. Utilizing a bifunctional strategy with multiple coordination sites, a family of new gold(I) complexes was synthesized in a chiral pool approach from amino acid alcohols. They employ an electronically tunable urea-group playing the role of both H-bond donor and acceptor, showcasing high efficiency and unprecedented reaction pathways in the enantioselective cycloisomerization of 1,6-enynols.In the third part, the newly developed catalysts were employed in the enanti-oselective dearomatization of naphthols and this methodology transferred onto phenols. New substrate classes were synthesized to investigate the impact of electronic effects on the reaction.Le contrôle de la chiralité dans les molécules fait partie intégrante de la chimie organique synthétique et reste une tâche très difficile à ce jour. Placer un stéréocentre dans la structure moléculaire d'un catalyseur est une méthode importante, donnant aux chimistes la possibilité de transférer l'information chirale du catalyseur sur une molécule substrat dans le cadre de la réaction catalysée. Les structures privilégiées pour cette approche sont les complexes de métaux de transition, offrant un large éventail de possibilités dans la conception d'une structure ligand chirale. Ce travail se concentre sur la conception de nouveaux ligands pour les transformations énantiosélectives catalysées par l'or (I). Le métal est exceptionnellement sélectif pour l'activation des liaisons carbone-carbone insaturées tout en ayant une tolérance élevée pour d'autres types de groupes fonctionnels, ce qui en fait un outil important pour créer une complexité moléculaire même dans les transformations à un stade avancé. L'un des principaux défis est la géométrie linéaire défavorable de la sphère de coordination de l'or (I), qui nécessite des structures ligand complexes pour surmonter la distance entre le centre chiral et les molécules substrates. Des études récentes ont révélé la compétence des cavités à base de cyclodextrine en tant que ligands dans une catalyse énantiosélective efficace de l'or (I). L'application de ligands NHC à base de β-cyclodextrine dans des réactions énantioconvergentes a été étudiée dans la première partie de ce travail. Dans ce corpus de recherche, leurs compétences basées sur une catalyse pilotée par cavité a été présentée dans des réactions de cycloisomérisation énantiosélective de divers substrats 1,5-ényne. Dans la deuxième partie, une nouvelle méthode mettant en avant des ligands NHC en forme de L avec une structure de noyau imidazopyridine a été développée. En utilisant une stratégie bifonctionnelle avec plusieurs sites de coordination, une famille de nouveaux complexes d'or (I) a été synthétisée dans une approche de chiral pool à partir d'alcools d'acides aminés. Ils utilisent un groupe urée modifiable électroniquement jouant à la fois le rôle de donneur et d'accepteur de liaison H, présentant une efficacité élevée et de nouvelles voies de réaction dans la cycloisomérisation énantiosélective des 1,6-énynols. Dans la troisième partie, les catalyseurs nouvellement développés ont été utilisés dans la désaromatisation énantiosélective des naphtols puis des phénols. De nouvelles classes de substrats ont été synthétisées pour étudier l´influence des effets électroniques sur la réaction
Earliest modern human genomes constrain timing of Neanderthal admixture
No full textInternational audienceModern humans arrived in Europe more than 45,000 years ago, overlapping at least 5,000 years with Neanderthals 1–4 . Limited genomic data from these early modern humans have shown that at least two genetically distinct groups inhabited Europe, represented by Zlatý kůň, Czechia 3 and Bacho Kiro, Bulgaria 2 . Here we deepen our understanding of early modern humans by analysing one high-coverage genome and five low-coverage genomes from approximately 45,000-year-old remains from Ilsenhöhle in Ranis, Germany 4 , and a further high-coverage genome from Zlatý kůň. We show that distant familial relationships link the Ranis and Zlatý kůň individuals and that they were part of the same small, isolated population that represents the deepest known split from the Out-of-Africa lineage. Ranis genomes harbour Neanderthal segments that originate from a single admixture event shared with all non-Africans that we date to approximately 45,000–49,000 years ago. This implies that ancestors of all non-Africans sequenced so far resided in a common population at this time, and further suggests that modern human remains older than 50,000 years from outside Africa represent different non-African populations
Dynamical Correlations and Order in Magic-Angle Twisted Bilayer Graphene
No full textInternational audienceThe interplay of dynamical correlations and electronic ordering is pivotal in shaping phase diagrams of correlated quantum materials. In magic-angle twisted bilayer graphene, transport, thermodynamic, and spectroscopic experiments pinpoint a competition between distinct low-energy states with and without electronic order, as well as between localized and delocalized charge carriers. In this study, we utilize dynamical mean-field theory on the topological heavy fermion model of twisted bilayer graphene to investigate the emergence of electronic correlations and long-range order in the absence of strain. We contrast moment formation, Kondo screening, and ordering on a temperature basis and explain the nature of emergent correlated states based on three central phenomena: (i) the formation of local spin and valley isospin moments around 100 K, (ii) the ordering of the local isospin moments around 10 K preempting Kondo screening, and (iii) a cascadic redistribution of charge between localized and delocalized electronic states upon doping. At integer fillings, we find that low-energy spectral weight is depleted in the symmetric phase, while we find insulating states with gaps enhanced by exchange coupling in the zero-strain ordered phases. Doping away from integer filling results in distinct metallic states: a “bad metal” above the ordering temperature, where scattering off the disordered local moments suppresses electronic coherence, and a “good metal” in the ordered states with coherence of quasiparticles facilitated by isospin order. This finding reveals coherence from order as the microscopic mechanism behind the Pomeranchuk effect observed experimentally by Rozen [] and by Saito []. Upon doping, there is a periodic charge reshuffling between localized and delocalized electronic orbitals leading to cascades of doping-induced Lifshitz transitions, local spectral weight redistributions, and periodic variations of the electronic compressibility ranging from nearly incompressible to negative. Our findings highlight the essential role of charge transfer, hybridization, and ordering in shaping the electronic excitations and thermodynamic properties in twisted bilayer graphene and provide a unified understanding of the most puzzling aspects of scanning tunneling spectroscopy, transport, and compressibility experiments. Published by the American Physical Society 202
New insight on the impact of NOx on diethanolamine (DEA) degradation mechanisms.
No full textInternational audienceAmine degradation presents a significant challenge in post-combustion CO2 capture processes. While oxidative and thermal degradation pathways have been extensively studied, the impact of NOx-induced degradation remains relatively underexplored. Nitrosamines and nitramines are the primary degradation products formed through the reaction of amines with NOx; however, the mechanisms underlying their formation are not well understood, with various pathways proposed in the literature. In this study, the experimental degradation of diethanolamine (DEA) in the presence of NOx species (NO, NO2, and their mixtures) was systematically investigated using specialized reactors. The effects of temperature on nitrosamine and nitramine formation were investigated. The degraded solutions were analyzed using Gas chromatography (GC-MS/FID) and ion chromatography (IC), coupled with a comprehensive mass balance assessment. The results obtained did not align with the proposed mechanism for nitrosamine formation by NO2 gas. The stoichiometric ratio between nitrosamine and nitrate salt was found to be 3.6, rather than the expected 1. Our results suggested the possibility of alternative pathways for nitrosamine formation by NO2 gas. No impact of temperature on nitrosamine formation was observed, except at 130 °C, where a high amount of nitrosamine was formed. In contrast, nitramine formation was directly influenced by temperature, with no nitramine formed at 130 °C. This highlights the need for further investigation to refine the understanding of NOx-induced degradation pathways and their impact on amine-based CO2 capture
Reduction of cortical pulling at mitotic entry facilitates aster centration
No full textInternational audienceABSTRACT Equal cell division relies upon astral microtubule-based centering mechanisms, yet how the interplay between mitotic entry, cortical force generation and long astral microtubules leads to symmetric cell division is not resolved. We report that a cortically located sperm aster displaying long astral microtubules that penetrate the whole zygote does not undergo centration until mitotic entry. At mitotic entry, we find that microtubule-based cortical pulling is lost. Quantitative measurements of cortical pulling and cytoplasmic pulling together with physical simulations suggested that a wavelike loss of cortical pulling at mitotic entry leads to aster centration based on cytoplasmic pulling. Cortical actin is lost from the cortex at mitotic entry coincident with a fall in cortical tension from ∼300pN/µm to ∼100pN/µm. Following the loss of cortical force generators at mitotic entry, long microtubule-based cytoplasmic pulling is sufficient to displace the aster towards the cell center. These data reveal how mitotic aster centration is coordinated with mitotic entry in chordate zygotes
A Palm Space Approach to Non-Linear Hawkes Processes
No full textInternational audienceA Hawkes process on is a point process whose intensity function at time is a functional of its past activity before time . It is defined by its activation function and its memory function . In this paper, the Hawkes property is expressed as an operator on the sub-space of non-negative sequences associated to distances between its points. By using the classical correspondence between a stationary point process and its Palm measure, we establish a characterization of the corresponding Palm measure as an invariant distribution of a Markovian kernel. We prove that if is continuous and its growth rate is at most linear with a rate below some constant, then there exists a stationary Hawkes point process. The classical Lipschitz condition of the literature for an unbounded function is relaxed. Our proofs rely on a combination of coupling methods, monotonicity properties of linear Hawkes processes and classical results on Palm distributions. An investigation of the Hawkes process starting from the null measure on , the empty state, plays also an important role. The linear case of Hawkes and Oakes is revisited at this occasion. If the memory function is an exponential function, under a weak condition it is shown that there exists a stationary Hawkes point process. In this case, its Palm measure is expressed in terms of the invariant distribution of a one-dimensional Harris ergodic Markov chain. When the activation function is a polynomial with degree , there does not exist a stationary Hawkes process and if the Hawkes process starts from the empty state, a scaling result for the accumulation of its points is obtained
A virally encoded tRNA neutralizes the PARIS antiviral defence system
No full textInternational audienceViruses compete with each other for limited cellular resources, and some deliver defence mechanisms that protect the host from competing genetic parasites1. The phage antirestriction induced system (PARIS) is a defence system, often encoded in viral genomes, that is composed of a 55 kDa ABC ATPase (AriA) and a 35 kDa TOPRIM nuclease (AriB)2. However, the mechanism by which AriA and AriB function in phage defence is unknown. Here we show that AriA and AriB assemble into a 425 kDa supramolecular immune complex. We use cryo-electron microscopy to determine the structure of this complex, thereby explaining how six molecules of AriA assemble into a propeller-shaped scaffold that coordinates three subunits of AriB. ATP-dependent detection of foreign proteins triggers the release of AriB, which assembles into a homodimeric nuclease that blocks infection by cleaving host lysine transfer RNA. Phage T5 subverts PARIS immunity through expression of a lysine transfer RNA variant that is not cleaved by PARIS, thereby restoring viral infection. Collectively, these data explain how AriA functions as an ATP-dependent sensor that detects viral proteins and activates the AriB toxin. PARIS is one of an emerging set of immune systems that form macromolecular complexes for the recognition of foreign proteins, rather than foreign nucleic acids3
Déformation et fragmentation de bulles en turbulence
No full textFixed a bug in the chapters' table of contents.Through their contributions to mixing, gas and heat transfers and aerosol production, bubbles play a central role in many industrial and environmental contexts, characterized by inertial flows, possibly turbulent. Understanding the physical processes controlling the bubble size distribution (BSD) and its temporal evolution, is key to quantify these exchanges.In dilute environments, in which breakup dominates, the BSD is characterized by two power laws separated by a critical size.We first focus on the origin of this critical size.This size is known to be related to the Kolmogorov-Hinze scale, the size separating statistically stable, from unstable bubbles in turbulence.As a turbulent flow is characterized by large velocity and pressure fluctuations, this size is only defined in a statistical sense.We give here a new definition of this critical size, in terms of survival probability, which includes the residence time of bubbles within turbulent regions.To do so, we investigate numerically bubble deformations first in a model flow geometry and then in 3D homogeneous and isotropic turbulence (HIT).In both cases, we find that most of bubble deformation dynamics can be reproduced by a 1D model of the oblate-prolate mode.By extrapolating the deformation model obtained in turbulence to breaking bubbles, we deduce the probability of breaking and the evolution of the critical size in time.We then investigate the generation of sub-Hinze bubbles.While there is a consensus for the origin of the power-law scaling for the super-Hinze BSD, the sub-Hinze BSD remained to be understood.By running DNS of bubbles in turbulence, we identify that sub-Hinze bubbles come from the fracture of gas filaments produced during the deformations of super-Hinze bubbles.We characterize filament production in a model flow configuration, as well as filament splitting.We find that filament breaking under stretching universally produces a power-law distribution, which coincides with the one obtained below breaking waves. This mechanism explains the origin of the sub-Hinze BSD.La présence de bulles dans des écoulements contribuent à augmenter le mélange, ainsi que les échanges de matière et de chaleur entre les deux phases. Leur présence est ainsi primordiale dans un grand nombre de procédés industriels ainsi que dans des contextes environnementaux, caractérisés par des écoulements inertiels voire turbulents. Pour quantifier l'impact des bulles, il faut d'abord comprendre et modéliser leur distribution de taille, et son évolution temporelle. Dans des environements dilués, où l'évolution de la distribution est contrôlée par la fragmentation, la distribution présente deux lois de puissance séparées par une taille critique.Dans un premier temps, nous nous intéressons à l'origine de la taille critique.Celle-ci correspond à la limite entre les bulles stables et instables, appelée échelle de Kolmogorov-Hinze.Les écoulements turbulents étant intrinsèquement caractérisés par de larges fluctuations, à la fois de pression et de vitesse, cette taille critique reste mal définie.Ici, nous proposons une nouvelle définition, probabiliste, de cette limite, qui inclue le temps de résidence des bulles dans les zones turbulentes.Pour cela, nous étudions numériquement la déformation d'une bulle, d'abord dans une géométrie d'écoulement modèle puis dans un écoulement turbulent homogène isotrope.Dans les deux cas, nous montrons que la dynamique de déformation peut être reproduite par une dynamique 1D sur le mode de déformation oblate-prolate.En extrapolant la dynamique obtenue dans le cas turbulent à des bulles qui cassent, nous quantifions la probabilité de fracture en un temps donné et en déduisons l'évolution de la taille critique au cours du temps.Dans un second temps, nous nous intéressons à la génération de bulles sous l'échelle de Kolmogorov-Hinze.En effet, s'il y a un consensus sur l'origine de la distribution des bulles plus grandes que la taille critique, l'origine de la distribution pour les petites bulles restait à déterminer.Grâce à des simulations numériques directes, nous identifions que ces bulles proviennent de la rupture de filaments gazeux produits lors de la déformation de bulles plus grandes que l'échelle critique. Nous caractérisons ensuite la production et la fragmentation de ces filaments dans une géométrie d'écoulement modèle.Nous découvrons que la fragmentation de ligaments sous contrainte d'étirement conduit à une distribution de taille de bulles en loi de puissance qui coïncide avec la distribution sous l'échelle critique en turbulence
Digital One-Step Competitive Detection of a Small Molecule in Synthetic and Environmental Waters
No full textInternational audienceOptical methods for single-molecule analysis hold the promise of accurate, sensitive, and rapid detection of target molecules. Here, we demonstrate the efficiency of such an approach for the competitive detection of small molecules in water. Our biosensing method is based on a combination of a single-DNA biochip for the parallelization of tethered particle motion real-time measurements with antibodies and modified targets as molecular competitors. The antibodies are coupled to the particles tethered to the surface by along DNA bearing in its middle the molecular competitor bound to the antibodies. Competitive target binding leads to a detectable conformational change of the DNA tethers from looped to unlooped in proportions related to the target concentration. We thus managed to detect fluorescein, chosen as a model of a target molecule, in fresh water of various qualities, from solutions prepared with ultrapure water to more complex matrices such as river water and wastewater treatment plant effluent samples. Similar dose−response curves were obtained under these various conditions in a wide range of concentrations from nanomolar to micromolar with a limit of detection around 2nM
