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Abiotic Ribonucleoside Formation in Aqueous Microdroplets: Mechanistic Exploration, Acidity, and Electric Field Effects
No full textInternational audienceAbstract Aqueous microdroplets have been reported to dramatically increase the rate of chemical reactions. Proposed mechanisms for this acceleration include confinement effects upon droplet evaporation, and Brønsted acid or electric field catalysis at the air‐water interface. However, computational investigations indicate that the operation of these mechanisms is reaction‐dependent, with conclusive evidence for a role for electric field catalysis still lacking. Here, we present a computational investigation of the reported abiotic phosphorylation of ribose and the subsequent formation of ribonucleosides, focusing on acidity and oriented external electric field (OEEF) effects. The most plausible reaction mechanism identified involves the protonation of ribose, followed by carbocation formation and an S N 2 substitution step. Without an OEEF, all considered pathways are thermally inaccessible. However, in the presence of a significant OEEF, the S N 2‐based pathway, leading to the β ‐ribonucleoside isomer, becomes highly stabilized, reducing the energetic span to a thermally accessible 12–13 kcal/mol. Surprisingly, the OEEF‐mediated reaction closely mirrors the enzymatic mechanism of phosphorolysis via S N 2 substitution, including a pronounced anomeric selectivity. Our results support the hypothesis that some reactions in aqueous microdroplets are accelerated by electric fields and provide further evidence for the importance of electrostatic catalysis in biological systems, particularly for phosphorylase enzymes
Graph-Based Deep Learning Models for Thermodynamic Property Prediction: The Interplay between Target Definition, Data Distribution, Featurization, and Model Architecture
No full textInternational audienceIn this contribution, we examine the interplay between target definition, data distribution, featurization approaches, and model architectures on graph-based deep learning models for thermodynamic property prediction. Through consideration of five curated datasets, exhibiting diversity in elemental composition, multiplicity, charge state, and size, we examine the impact of each of these factors on model accuracy. We observe that target definition, i.e., using formation instead of atomization energy/enthalpy, is a decisive factor, and so is a careful selection of the featurization approach. Our attempts at directly modifying model architectures result in more modest, though not negligible, accuracy gains. Remarkably, we observe that molecule-level predictions tend to outperform atom-level increment predictions, in contrast to previous findings. Overall, this work paves the way toward the development of robust graph-based thermodynamic model architectures with more universal capabilities, i.e., architectures that can reach excellent accuracy across data sets and compound domains.</div
Unveiling the Reactivity of Li1+xAlxTi2–x(PO4)3 with Lithium Salts to Reduce Its Sintering Temperature
No full textInternational audienceNaSICON-type materials, such as Li1.3Al0.3Ti1.7(PO4)3 (LATP), are considered promising solid electrolytes due to their good total ionic conductivity of 10-4 S.cm-1 at room temperature and their stability at high potentials (4.1 V vs Li/Li+). However, decreasing their densification temperature is crucial for their integration into all-solid-state batteries (ASSBs). The minimum required heat treatment temperature for densification of LATP is 900 °C, which is incompatible with its integration in composite electrode of ASSBs due to reactivity with the positive electrode material (cathode). To lower this temperature, lithium salts are often proposed as sintering aids to promote liquid-phase sintering. However, the systematic formation of impurities, such as LiTiOPO4 and Li4P2O7, suggests that chemical reactivity plays a significant role in LATP densification. In this work, the chemical reactivity mechanism of lithium salts with LATP during densification and sintering was investigated. Various characterization techniques, including in situ and ex situ X-ray diffraction, TGA-DTA-MS, DSC, ex situ Raman and solid-state NMR spectroscopy (7Li, 27Al, 31P), were employed to elucidate the mechanism. The formation of intermediate decomposition products Li3PO4 and TiO2 is identified for the first time via the reactivity of the lithium salt with LATP prior to the melting temperature of the salt. These intermediates subsequently react with LATP at higher temperature, resulting in the formation of final impurities LiTiOPO4 and Li4P2O7. This unified mechanism provides important insights on the enhanced densification of LATP at lower temperatures with the use of Li salt sintering aids
Recent Progress and Applications of Asymmetric Hydrogenation and Transfer Hydrogenation through Dynamic Kinetic Resolution
No full textInternational audienceAbstract Given the growing demand for enantiomerically enriched compounds, the design of efficient, atom-economical, and sustainable synthetic strategies for the preparation of chiral alcohols and amines remains a critical objective in modern chemistry. This short, updated review highlights recent advances in homogeneous asymmetric catalysis employing transition-metal complexes in asymmetric hydrogenation (AH) and transfer hydrogenation (ATH) of ketones and imines under dynamic kinetic resolution (DKR) conditions to access these important building blocks. These methods enable the simultaneous formation of multiple stereogenic centers and have been significantly expanded through the development of novel catalytic systems and their application to previously unexplored classes of substrates
Nanoscale Mapping of Transition Metal Ordering in Individual LiNi0.5Mn1.5O4 Particles Using 4D-STEM ACOM Technique
No full textThe electrochemical performance of the spinel LiNi0.5Mn1.5O4, a high-voltage positive electrode material for Li-ion batteries, is influenced by the transition metal arrangement in the octahedral network, leading to disordered (Fd m S.G.) and ordered3 (P4332 S.G.) structures. However, widely used techniques lack the spatial resolution necessary to elucidate the ordering phenomenon at the particle scale. Using the 4D-STEM technique, we present the first direct observation of ordering distribution in individual LiNi0.5Mn1.5O4 particles with nanometric spatial resolution. We propose a quantification method for the local degree of ordering based on the ratio of ordered to disordered spinel lattices along the particle thickness extracted from electron diffraction spot intensities. In an ordered spinel LiNi0.5Mn1.5O4, the transition metal ordering is consistently observed throughout the primary particle. However, the extent of ordering in the spinel phase depends on its distribution at the particle scale, a factor influenced by the annealing conditions. The 4D-STEM analysis elucidates the boundary between highly-ordered and low-ordered LiNi0.5Mn1.5O4 particles
Organic interlayers for hole transfer in MA-free mixed PB/SN halide perovskites for all-perovskite tandem solar cells
No full textInternational audienceThe efficiency of mixed lead–tin perovskite solar cells has increased rapidly, thanks to efficient passivation strategies of bulk and interfacial defects. For example, this occurs at the hole-transport layer and the perovskite interface. Here, we compare the self-assembled monolayers and multilayers (SAMs), [2-(9H-carbazol-9-yl)ethyl]phosphonic acid (2PACz) and methylphosphonic acid (MPA), to a PEDOT:PSS layer at the rear interface of a MA-free narrow band gap perovskite in single-junction (SJ) and all-perovskite tandem solar cells. PEDOT:PSS-based devices show the best power conversion efficiency of 14% in SJ and 17.2% in all-perovskite tandem architecture. By using photoluminescence and ultraviolet photoelectron spectroscopy, we show that this behavior is due to better energy alignment at the PEDOT:PSS/PK than the SAM/PK interface. However, SAMs also show lower nonradiative recombination rates at this interface. The results identify the limits of the effectiveness of 2PACz and MPA in mixed lead–tin MA-free perovskite solar cells and confirm the need for other SAMs with improved energy-level alignment while maintaining their passivating properties
Self-regulating and self-oscillating metal-organic framework hybrid plasmonic metasurfaces
No full textInternational audienceMetal-organic frameworks (MOFs) offer remarkable chemical versatility, structural diversity, and, in some cases, stimuli-responsiveness. In the latter case, they typically rely on external inputs to trigger these changes. In contrast, living systems possess the ability to internally self-regulate and autonomously adapt their properties without external intervention, utilizing internal feedback mechanisms. To fill this gap, we develop a MOF-based metasurface that exhibits autonomous optical self-regulation, dynamically adjusting light absorption in response to varying incident light intensity. This device integrates colloidal MOFs with a plasmonic metasurface to create a thermo-optical negative feedback mechanism based on vapor sorption in and out of the colloidal MOF device. The self-regulation process is dynamic, leading each MOF/antenna unit to exhibit self-oscillatory behavior in the presence of a constant external energy input, analogous to a light-fueled nanoscale steam engine. This proof-of-concept highlights the potential of harnessing MOFs and sorption processes for designing metasurfaces for adaptable optical applications. It also represents a first step toward the design of materials integrating feedback mechanisms and internal clocks paving the way for a new generation of porous materials with life-like autonomy
Multiscale Porous Carbon Monoliths Obtained through Si(HIPE) Chemical Vapor Infiltration and Their Electrochemical Behavior
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An innovative method of XRF signal isolation in bi-layered systems for characterizing red rock art
No full textInternational audienceThe in-situ and non-destructive elemental characterization of coloring matter used in parietal art or mobile art is an approach both technically challenging and valuable to better understand prehistoric ornated sites or objects. Portable X-Ray Fluorescence spectrometry (pXRF) is currently the main method used to analyze such coloring matter as they are primarily of inorganic nature. The complexity of the data obtained in such environment makes it often difficult to interpret. Advanced data treatment procedures of pXRF spectra are required to correctly separate the signal of the coloring matter from that of its substrate. This article presents such a procedure, particularly well-suited for studying red coloring matters in-situ. Our approach consists in calculating a thickness estimator of the coloring matter, smoothing the data with a specific procedure and extrapolating the obtained element intensities to an infinitely thick coloring matter layer. This procedure was applied on simulated and mock-up samples as well as archaeological data acquired in-situ at the Font-de-Gaume cave in Dordogne, France, with Paleolithic cave art. The results display the strong potential of the improved data evaluation procedure as it was possible to distinguish different coloring matters including red ones in each case presented
CABLE SOLAR : A Tethered Airborne Platform Dedicated To Solar Cell Characterization
No full textInternational audienceA Tethered Airborne Platform Dedicated To Solar Cell Characterization is presented that could be used ultimately as an Aerostat for Solar Power GenerationPV prototype, electronics for data acquisition and intregration on aerostat were tested with success. The first results are promising and could be associated witha simulation part (LAAS collaboration :https://hal.science/hal-04730979