Diastereoselective Synthesis of Novel Aza-diketopiperazines via a Domino Cyclohydrocarbonylation/Addition Process

Herein, we report an unprecedented, short and diastereo-selective synthesis of newly reported aza-diketopiperazine (aza-DKP) scaffolds starting from amino acids. The strategy is based on a Rh(I)-catalyzed hydroformylative cyclohydrocarbonylation of allyl-substituted aza-DKP, followed by a diastereoselective functionalization of the platform. This methodology allows the synthesis of novel bicyclic and tricyclic aza-DKP scaffolds incorporating six- or seven-membered rings, with potential applications in medicinal chemistry

A step-economical multicomponent synthesis of 3D-shaped aza-diketopiperazines and their drug-like chemical space analysis

A rapid and atom economical multicomponent synthesis of complex aza-diketopiperazines (aza-DKPs) driven by Rh(I)-catalyzed hydroformylation of alkenylsemicarbazides is described. Combined with catalytic amounts of acid and the presence of nucleophilic species, this unprecedented multicomponent reaction (MCR) enabled the formation of six bonds and a controlled stereocenter from simple substrates. The efficacy of the strategy was demonstrated with a series of various allyl-substituted semicarbazides and nucleophiles leading to the preparation of 3D-shaped bicyclic aza-DKPs. Moreover, an analysis of their 3D molecular descriptors and “drug-likeness” properties highlights not only their originality in the chemical space of aza-heterocycles but also their great potential for medicinal chemistry

A rockslide-generated tsunami in a Greenland fjord rang Earth for 9 days

Climate change is increasingly predisposing polar regions to large landslides. Tsunamigenic landslides have occurred recently in Greenland (Kalaallit Nunaat), but none have been reported from the eastern fjords. In September 2023, we detected the start of a 9-day-long, global 10.88-millihertz (92-second) monochromatic very-long-period (VLP) seismic signal, originating from East Greenland. In this study, we demonstrate how this event started with a glacial thinning–induced rock-ice avalanche of 25 × 106 cubic meters plunging into Dickson Fjord, triggering a 200-meter-high tsunami. Simulations show that the tsunami stabilized into a 7-meter-high long-duration seiche with a frequency (11.45 millihertz) and slow amplitude decay that were nearly identical to the seismic signal. An oscillating, fjord-transverse single force with a maximum amplitude of 5 × 1011 newtons reproduced the seismic amplitudes and their radiation pattern relative to the fjord, demonstrating how a seiche directly caused the 9-day-long seismic signal. Our findings highlight how climate change is causing cascading, hazardous feedbacks between the cryosphere, hydrosphere, and lithosphere.acceptedVersio

Chemical kinetics in an atmospheric pressure helium plasma containing humidity

Atmospheric pressure plasmas are sources of biologically active oxygen and nitrogen species, which makes them potentially suitable for the use as biomedical devices. Here, experiments and simulations are combined to investigate the formation of the key reactive oxygen species, atomic oxygen (O) and hydroxyl radicals (OH), in a radio-frequency driven atmospheric pressure plasma jet operated in humidified helium. Vacuum ultra-violet high-resolution Fourier-transform absorption spectroscopy and ultra-violet broad-band absorption spectroscopy are used to measure absolute densities of O and OH. These densities increase with increasing H 2 O content in the feed gas, and approach saturation values at higher admixtures on the order of 3 × 10 14 cm −3 for OH and 3 × 10 13 cm −3 for O. Experimental results are used to benchmark densities obtained from zero-dimensional plasma chemical kinetics simulations, which reveal the dominant formation pathways. At low humidity content, O is formed from OH + by proton transfer to H 2 O, which also initiates the formation of large cluster ions. At higher humidity content, O is created by reactions between OH radicals, and lost by recombination with OH. OH is produced mainly from H 2 O + by proton transfer to H 2 O and by electron impact dissociation of H 2 O. It is lost by reactions with other OH molecules to form either H 2 O + O or H 2 O 2 . Formation pathways change as a function of humidity content and position in the plasma channel. The understanding of the chemical kinetics of O and OH gained in this work will help in the development of plasma tailoring strategies to optimise their densities in applications

Synthesis and structural analysis of the plutonium peroxide-based complexes

Dans le cadre de l’amélioration de la voie d’élaboration du combustible nucléaire recyclé et du multirecyclage du plutonium, la coconversion U-Pu représente une alternative potentielle au procédé actuel de mélange mécanique des poudres d’oxyde d’uranium et de plutonium. Par rapport aux voies carbonées de coconversion, la voie peroxyde présente l’avantage, entre autres, de conduire à l’absence de carbone résiduel dans la poudre d’oxydes. Cependant, les connaissances actuelles sur les peroxydes de plutonium sont partielles et fragmentées, constituant un frein au développement technologique de la conversion du plutonium et à la coconversion U-Pu par voie peroxyde. Ainsi, l’évaluation de la faisabilité d’un tel procédé nécessite une consolidation préalable des connaissances des propriétés physico-chimiques des peroxydes de plutonium.La première partie de ce travail a donc été consacrée à la caractérisation des complexes solubles et des sels de peroxyde de plutonium. Les coefficients d’extinction molaires des complexes solubles ont été estimés afin de quantifier les fuites en plutonium lors des expériences de synthèse par précipitation. Les conditions opératoires permettant l’obtention d’un rendement de précipitation quantitatif et d’une poudre de bonne filtrabilité ont été déterminées. En outre, une base de données nouvelles sur les propriétés de sels de peroxyde de plutonium a été établie à partir des caractérisations effectuées.En seconde partie, des synthèses réalisées avec les systèmes mixtes U-Pu et U-Th ont abouti à l’obtention d’un mélange de peroxyde d’uranyle et de sel de peroxyde d’actinide +IV. Les conditions opératoires permettant l’obtention de rendements très élevés pour l’uranium et le plutonium ainsi qu’une poudre précipitée de bonne filtrabilité ont été déterminées. Par la suite, le traitement thermique du précipité a conduit à l’obtention d’une poudre d’oxydes avec une bonne aptitude à la fabrication de pastille frittée, ce qui a permis de démontrer la faisabilité de la coconversion U-Pu à l’échelle du laboratoire.In the framework of the improvement of the reused nuclear fuel manufacturing and the Pu multirecycling, U-Pu coconversion represent a potential alternative to the current mixing process of uranium and plutonium oxide powders. Compared to carbon-based U-Pu coconversion processes, the peroxide process has the advantage of, among others, leading to the absence of residual carbon in oxide powder. However, the current knowledge of plutonium peroxide is incomplete and scattered, hindering the plutonium conversion and U-Pu coconversion technological developments. Thus, the evaluation of the feasibility of this process requires a preliminary strengthening of the knowledge of plutonium peroxide physico-chemical properties. The first part of this work has been dedicated to the characterization of plutonium peroxide soluble complexes and salts. Molar extinction coefficient of soluble complexes have been estimated in order to quantify the plutonium loss in precipitation experiments. The experimental conditions enabling very high yield of precipitation of Pu and an easy-filterable powder have been determined. Moreover, a new database of plutonium peroxide salt properties has been established from the characterizations obtained. In the second part, syntheses carried out with mixed systems such as U-Pu and U-Th have led to obtaining a mix of uranyl peroxide and +IV actinide peroxide salt. The experimental conditions enabling very high yields for uranium and for plutonium and an easy-filterable powder have been determined. Then, thermal treatment of the precipitate has led to obtaining an oxide powder with a good ability to the manufacturing of sintered oxide pellet and which enables to demonstrate the feasibility of U-Pu conversion process at the laboratory scale

Investigation of Plutonium(IV) peroxide-based complexes, syntheses and structural characterization

International audienc

Synthèse et caractérisation structurale de complexes de plutonium à base de ligands peroxyde et peroxo-oxalate

National audienc

Synthèse et caractérisation structurale de complexes de plutonium à base de ligands peroxyde

National audienc

Peroxide co-conversion as an original route for mixed (U,Pu)O2 pellet fabrication.

International audienceMOx pellets (UO2-PuO2) with high PuO2 content (above 15 wt.% Pu) are regarded as promising nuclear fuel for Sodium cooled Fast nuclear Reactor. Standard pellet fabrication is based on powder metallurgy processes (grinding, pressing and sintering) using typical UO2 and PuO2 powders. The object of the present study is to examine, at the laboratory scale, an alternative route based on powder co-precipitation in peroxo-nitric media. The precipitated solids were found to be composed of uranyl peroxide (studtite) and Pu(IV) peroxo-nitrate. The ratio between these two compounds fully followed the actinide ions ratio of the feed solution. The oxide conversion, carried out under reducing conditions, yields fine powder with high specific area. As expected, the obtained oxide powder granulometry appears to be mainly bimodal, namely at 650nm and 7µm, and with some 55µm-sized coarse particles resulting from physical aggregation. The green pellet, obtained by uniaxial pressing of the raw powder, was sintered at 1700°C for 4 hours in Ar + H2 (5%) + 200 ppm H2O with a heating ramp of 2°C.min-1. The constant water concentration in the furnace was ensured by monitoring the oxygen partial pressure during all the sintering cycles. The obtained pellet exhibits a relative density equal to 95 ± 1 %. The porosity of 5 % was confirmed by optical image analysis performed on pellet polished cross-section, showing 1mm long cracks throughout the pellet oriented in a perpendicular fashion of the pressing direction. The grain size distribution appears monomodal centered at about 8 µm (Equivalent Circular Diameter). EPMA analyses confirm the homogenous actinide distribution. More surprisingly, XRD and µ-Raman analyses indicate the formation of a single phase (U,Pu)O2 solid-solution with a fluorite structure and low defect concentration. The presentation will focus on the structural and microstructural characterizations of the sintered pellet

Coprecipitation of actinide peroxide salts in the U-Th and U-Pu systems and their thermal decomposition

International audienceThe uranium and plutonium co-conversion process constitutes a continuous subject of interest for MOx fuel fabrication. Among the various routes considered, chemical coprecipitation by the salt effect has been widely investigated regarding its simplicity of integration between the partitioning and purification steps of the PUREX process, and the straightforward recovery of precursors that are easily converted into oxide phases by thermal decomposition. The present study focuses on the coprecipitation behavior of U–Th and U–Pu actinide peroxide mixed systems by examining the precipitation yields and settling properties for nitric acidity in the range of 1 to 3 M and hydrogen peroxide concentration in the range of 4.5 to 7 M. The precipitated solids have been characterized by powder XRD, IR and Raman spectroscopy, laser granulometry and SEM-EDS analyses revealing the synthesis of studtite and actinide(IV) peroxo-nitrates as aggregated particles. The actinide solid phases are uniformly distributed within the filtered cakes. The precursor thermal decomposition results in the formation of oxide phases at low temperature according to a sequential release of water molecules, peroxide ligands and nitrate ions. The calcination step has a limited effect on the morphology of the powders which remain highly divided. The high precipitation rate of actinides makes this chemical route potentially interesting as a co-precipitation process