HAL Portal ESPCI (Ecole Supérieure de Physique et de Chimie Industrielles)
Not a member yet
13939 research outputs found
Sort by
Commutation multi-étape de l'état de spin avec rupture de symétrie et photocommutation ON/OFF dans un complexe de fer (II)
No full textInternational audienceIn recent world advancement and the quest for smart multi-functional material, stimuli-responsive molecular bistable systems offer unique opportunities to explore their applicability in molecular switches, data storage, and sensing technologies. Multi-stimuli responsive stepwise Spin Crossover (SCO) systems stand tall in this area. While the effects of external stimuli, particularly thermal variations and photoirradiation on the magneto-structural properties of SCO systems have been extensively studied, the area of pressure-modulated stepwise spin crossover and its associated magneto-structural changes remains lesser explored. Herein, we report a mononuclear iron(II) complex containing tetradentate macrocyclic ligand with -diimine-based bidentate coligand, [Fe(L)(bik*)](BPh4)2 (1) (L = N,N'-di-iso-propyl-2,11-diaza[3,3](2,6)pyridinophane and bik* = bis(1-ethyl-1H-imidazol-2-yl)ketone)) undergoing a reversible stepwise thermo-induced spin-state switching with the presence of three spin-states HS, LS, and an ordered HS-LS with the exciting re-entrant symmetry breaking during the spin-state switching process. The influence of external pressure on the structure and magnetic response is thoroughly studied, where the pressure-induced modification in the intermolecular interactions leads to enhanced cooperativity and a hysteretic stepwise spin state switching. The versatility of the systems is further explored where 1 displays a reversible ON/OFF photo-switching between a photo-induced paramagnetic metastable HS and diamagnetic LS states under light irradiations at low temperatures along with light-induced excited spin state trapping (LIESST).Grâce aux progrès récents et à la quête de matériaux multifonctionnels intelligents, les systèmes moléculaires bistables sensibles aux stimuli offrent des opportunités uniques pour explorer leur applicabilité aux commutateurs moléculaires, au stockage de données et aux technologies de détection. Les systèmes à croisement de spin (SCO) multi-étape et multi-stimuli sont particulièrement performants dans ce domaine. Si les effets des stimuli externes, notamment les variations thermiques et la photo-irradiation sur les propriétés magnéto-structurales des systèmes SCO ont été largement étudiés, le croisement de spin multi-étape modulé par la pression et les modifications magnéto-structurales associées restent moins explorés. Ici, nous décrivons la commutation d'état de spin thermo-induite multi- étapes et réversible avec la présence de trois états de spin HS, LS et un HS-LS et avec la rupture de symétrie rentrante pendant le processus de commutation d'état de spin d'un complexe mononucléaire de fer(II) coordonné par un ligand macrocyclique tétradentent et par un coligand bidentent à base de -diimine, [Fe(L)(bik*)](BPh4)2 (1) (L = N,N'-di-iso-propyl-2,11-diaza[3,3](2,6)pyridinophane et bik* = bis(1-éthyl-1H-imidazol-2-yl)cétone)). L'influence de la pression externe sur la structure et la réponse magnétique est étudiée en profondeur, où la modification induite par la pression dans les interactions intermoléculaires conduit à une coopérativité améliorée et à une commutation d'état de spin par étapes hystérétique. La polyvalence des systèmes est explorée plus en détail lorsque 1 présente une photo-commutation ON/OFF réversible entre un état HS métastable paramagnétique photo-induit et un état LS diamagnétique sous irradiations lumineuses à basse température ainsi qu'un piégeage d'état de spin excité induit par la lumière (LIESST)
In‐Situ Constructing Eosin Y Sensitized Cs<sub>2</sub>PtSnCl<sub>6</sub> Perovskites for Enhanced Photocatalytic Hydrogen Evolution
No full textInternational audienceVacancy‐ordered Cs2SnX6 perovskites, with low‐toxicity and high stability, have emerged as promising photocatalysts for hydrogen evolution reaction (HER). However, most Cs2SnX6 and derivatives have low catalytic activity mainly due to their insufficient light utilization efficiency. Herein, a simple in situ method is introduced to sensitize Cs2PtSnCl6 with Eosin Y (EY), forming EY‐Cs2PtSnCl6 for HER in aqueous solution. Various characterizations indicate that the EY is immobilized onto the Cs2PtSnCl6 during the synthesis process. The EY‐Cs2PtSnCl6 displayed extended light absorption range and efficient charge transfer from EY to Cs2PtSnCl 6 . The resulting EY‐Cs2PtSnCl6 material exhibits high HER rate of 17.6 mmol g−1 h−1, ≈1760 folds than that of the pristine Cs2PtSnCl6. This work demonstrates an effective method to construct dye‐sensitized perovskites and highlights the importance of interaction between dye and perovskite. It provides useful guidance for the design of new perovskite‐based photocatalysts and it will advance the development of perovskites for solar energy conversion into renewable fuels
Crystallization of Manganese(V) Oxides by Hydroflux Synthesis: Control of Anisotropic Growth and Electrochemical Stability
No full textInternational audienceDespite intriguing optical, magnetic, and redox properties, inorganic materials containing pentavalent manganese (Mn V ) are rare and could never be designed as shape-controlled crystals, which limits the ability to tune properties. Herein, we explore alkali hydroxide mixtures with controlled water content, namely, hydrofluxes, to demonstrate phase, shape, and nanostruc-ture control of Mn(V) oxides. We demonstrate speciation among KSrMn V O 4 , Sr 5 (Mn V O 4 ) 3 OH, and SrMn IV O 3 with the water and strontium content and the nature of the alkali cation of the hydroxide salt. We then provide evidence of the key role of water in enabling shape and nanostructure control, which we relate to the preferential interaction of water with specific c rystal f acets o f the hydroxyapatite Sr 5 (Mn V O 4 ) 3 OH, and to the impact of water on precursor solubility in water-poor hydrofluxes. We then show that nanostructured Mn(V) hydroxyapatite possesses an acid-base redox stability window, enabling electrochemical operation in strongly oxidative conditions. By correlating the fundamental knowledge of hydrofluxes with crystallization mechanisms, this work sheds light on the possibilities offered by hydrofluxes for crystal shape, size, and property control.Manganese can be found in various oxidation states in solidstate materials from 0 to +7. 1 Despite its low stability and scarcity, pentavalent manganese(V) is the origin of important properties. It can be used to design colorful blue or green pigments. 2,3 Mn(V) compounds have been considered as laser materials 4 and also raise interest due to intriguing magnetic properties. 5,6 Mn(V) is also involved in the oxygen-evolving complex for the production of dioxygen during photosynthesis. 7,8 This suggests that Mn(V) compounds could find interest for use in water oxidation electrocatalysis provided that they can be used in conditions where the oxidation state and structural features are maintained. To date, the electrochemical properties of Mn(V) compounds, especially their pH-potential stability window, have not been evaluated, so the feasibility of using Mn(V) compounds for electrochemical applications remains an open question.Inorganic compounds containing pentavalent manganese (Mn V ) are scarce due to their low stability. 9 Currently reported manganese oxides built on Mn(V) are Ba</div
Zooarchaeology using mass spectrometry: an integrative approach to understanding subsistence behavior across the Middle-to-Upper Paleolithic transition in Europe
No full textInternational audienc
Defect-modulated ionic friction at hBN/water interfaces
No full textInternational audienceCharge transport at solid/liquid interfaces is vital to energy conversion, electrochemistry, and biological activities. These buried interfaces are the locus where continuum approaches break down, and molecular details become of utmost importance, with traditional ensemble-averaged studies giving an incomplete picture of the dynamics. Here, we build upon recently developed single-molecule microscopy optofluidic platform, to investigate the statistics of single charge transport at aqueous hexagonal Boron Nitride interfaces, demonstrating the microscopic origin of its non-Gaussian character and the control of transport by irradiation-induced surface defects. By increasing irradiation of the hBN crystals, we modulate the morphological distribution of adsorption sites, leading to a slow-down of interfacial charge transport, akin to an increasing frictional interaction. Charge hopping displacements feature exponentially-decaying arms, strongly departing from Gaussian distributions. 2D Brownian dynamics simulations evidence that these exponential tails originate from molecular jumps between trapping sites, allowing a consistent match between statistical distributions and the effective diffusion coefficient. Our study highlights the key yet overlooked role of defects in regulating interfacial charge transport, with relevance for energy applications
Self-Organization and Memory in a Disordered Solid Subject to Random Driving
No full textInternational audienc
Anomalous Softness in Amorphous Matter in the Reversible Plastic Regime
No full textInternational audienceWe study an elastoplastic model of an amorphous solid subject to athermal quasistatic cyclic shear strain. We focus on cycling amplitudes in the so-called reversible-plastic regime where, after a transient, the system locks into a hysteretic limit cycle and returns to the same microscopic configuration after one or more strain cycles. We show that the ground state energy of the terminal limit cycle decreases with increasing cycling amplitude. In analogy to an annealed alloy or an aged colloidal glass, one would expect the states with lower energy to be mechanically harder and to require larger stresses and strains to trigger microscopic rearrangements. However, we show the opposite result: the systems with lower energy cycled at higher strain amplitude are mechanically softer and begin to exhibit plastic rearrangements at smaller stresses and strains within the cycle. We explain this anomaly quantitatively in terms of Eshelby inclusion theory where an inclusion is subjected to a particular negative stress value after it undergoes a yielding event. These results point the way toward measurements to be conducted in experiments and particle-based computer simulations on cyclically sheared amorphous solids
Parallelization of Gillespie algorithm based on binary words
No full textWe present an improvement of the Gillespie Exact Stochastic Simulation Algorithm, which leverages a bitwise representation of variables to perform independent simulations in parallel. We show that the subsequent gain in computational yield is significant, and it may allow to perform simulations of non-well mixed chemical systems. We illustrate this idea with simulations of Frank model, originally introduced to explain the emergence of homochirality in prebiotic systems
A Dual Homeostatic Regulation of Dry Mass and Volume Defines a Target Density in Proliferating Mammalian Cells
No full textThe concentration of macromolecules, especially proteins, is vital for cellular function and is influenced not only by synthesis and degradation but also by the total cell volume. While we understand various growth regulation mechanisms, the coupling of dry mass and volume in growing mammalian cells remains unclear. Here we show that two independent mechanisms acting in single cells -one regulating volume through biophysical modulation and the other controlling protein biosynthesis-work together to maintain macromolecular dry mass density and restore it following perturbations. These mechanisms ensure that proliferating cells remain within a specific range around a target density, providing density homeostasis at the population level. Although the target density appears consistent across different cell types, it is disrupted around cell division, upon perturbations of growth pathways and in senescent cells. It may represent an optimal value for cellular processes, ensuring the efficiency of essential intracellular functions.</div
Unsupervised detection and fitness estimation of emerging SARS-CoV-2 variants. Application to wastewater samples (ANRS0160)
No full textInternational audienceRepeated waves of emerging variants during the SARS-CoV-2 pandemics have highlighted the urge of collecting longitudinal genomic data and developing statistical methods based on time series analyses for detecting new threatening lineages and estimating their fitness early in time. Most models study the evolution of the prevalence of particular lineages over time and require a prior classification of sequences into lineages which is prone to induce delays and biases. More recently, several authors studied the evolution of the prevalence of mutations over time with alternative clustering approaches, avoiding specific lineage classification. Most existing methods are either non parametric or unsuited to pooled data characterizing, for instance, wastewater samples. The analysis of wastewater samples has recently been pointed out as a valuable complementary approach to clinical sample analysis, however the pooled nature of the data involves specific statistical challenges. In this context, we propose an alternative unsupervised method for clustering mutations according to their frequency trajectory over time and estimating group fitness from time series of pooled mutation prevalence data. Our model is a mixture of observed count data and latent group assignment and we use the expectation-maximization algorithm for model selection and parameter estimation. The application of our method to time series of SARS-CoV-2 sequencing data collected from wastewater treatment plants in France from October 2020 to April 2021 shows its ability to agnostically group mutations in a consistent way with lineages B.1.160, Alpha, B.1.177, Beta, and with selection coefficient estimates per group in coherence with the viral dynamics in France reported by Nextstrain. Moreover, our method detected the Alpha variant as threatening as early as supervised methods (which track specific mutations over time) with the noticeable difference that, since unsupervised, it does not require any prior information on the set of mutations