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La dynamique de transition de phase étudiée par la microscopie optique cryogénique dans un matériau moléculaire commutable Fe₂Co₂ à transfert de charge
No full textInternational audienceUnderstanding the phase transition mechanism in switchable materials is crucial for optimizing their properties. In this study, we present the thermal electron transfer -coupled spin transition (ETCST) mechanism, revealed through the cryogenic optical microscopy (OM) measurements on a cyanide-bridged square complex: where Tp is tris(pyrazolyl)borate and vbik, bis(1vinylimidazolyl)ketone. A one-step thermal ETCST of 1•ClO4 is observed using conventional techniques such as single crystal X-ray diffraction (SC-XRD) and bulk sample magnetic measurements. The ETCST is cooperative, with quite different transition temperatures for the single crystal (T1/2↑ = 251.5 K for heating and T1/2↓ = 243.5 K) and the bulk sample (T1/2↑ = 273 K and T1/2↓ = 255 K). In contrast, the direct visualization of the thermal ETCST in the single crystal of 1•ClO4 through OM and the subsequent image analysis disclose, for the first time, a phase transition of unexpected complexity. The ETCST progresses in three steps along the a, b and c axes, respectively: i) Initially, strip domains form and rapidly extend along the a-axis. ii) These domains then gradually widen in the b-axis covering the entire ab layer. iii) The final step involves a layerby-layer extension of ETCST along the c-axis. Structural analysis of 1•ClO4 reveals that two types of intermolecular interactions govern the two preferential propagation directions of ETCST. The first type, mediated by ClO4⁻ anion, drives the rapid propagation of ETCST along the a axis, occurring so rapidly that the conventional methods like magnetometry and SC-XRD are unable to detect it. The second type, along the b axis, involves the π-π stackings of vbik ligands, which contribute to the slower ETCST propagation in this direction. This mechanistic insight into the anisotropic propagation patterns of ETCST in 1•ClO4 underscores the role of intermolecular interactions in modulating the dynamics of molecular switching.La compréhension du mécanisme de transition de phase dans les matériaux commutables est essentielle à l'optimisation de leurs propriétés. Dans cette étude, nous présentons le mécanisme de transition de spin couplée au transfert thermique d'électrons (ETCST), révélé par des mesures de microscopie optique cryogénique (MO) sur un complexe carré ponté par du cyanure : {[Fe(Tp)(CN)3]2[Co(vbik)2]2}·2ClO4·2CH2Cl2 (1·ClO4), où Tp est le tris(pyrazolyl)borate et vbik, la bis(1-vinylimidazolyl)cétone. Une ETCST thermique en une étape de 1·ClO4 est observée à l'aide de techniques conventionnelles telles que la diffraction des rayons X sur monocristal (SC-DRX) et les mesures magnétiques sur échantillon massif. L'ETCST est coopératif, avec des températures de transition très différentes pour le monocristal (T1/2↑ = 251,5 K pour le chauffage et T1/2↓ = 243,5 K) et l'échantillon en vrac (T1/2↑ = 273 K et T1/2↓ = 255 K). En revanche, la visualisation directe de l'ETCST thermique dans le monocristal de 1·ClO4 à travers OM et l'analyse d'image ultérieure révèlent, pour la première fois, une transition de phase d'une complexité inattendue. L'ETCST progresse en trois étapes le long des axes a, b et c, respectivement : i) Initialement, des domaines en bande se forment et s'étendent rapidement le long de l'axe a. ii) Ces domaines s'élargissent ensuite progressivement dans l'axe b couvrant toute la couche ab. iii) L'étape finale implique une extension couche par couche de l'ETCST le long de l'axe c. L'analyse structurale de 1·ClO4 révèle que deux types d'interactions intermoléculaires régissent les deux directions de propagation préférentielles de l'ETCST. Le premier type, médié par l'anion ClO4⁻, entraîne la propagation rapide de l'ETCST le long de l'axe a, se produisant si rapidement que les méthodes conventionnelles comme la magnétométrie et la SC-XRD sont incapables de la détecter. Le second type, le long de l'axe b, implique les empilements π–π des ligands vbik, qui contribuent à la propagation plus lente de l'ETCST dans cette direction. Cette compréhension mécaniste des schémas de propagation anisotropes de l'ETCST dans 1·ClO4 souligne le rôle des interactions intermoléculaires dans la modulation de la dynamique de la commutation moléculaire
L'évolution de la motilité de gouttes actives est capturée par un modèle de marche aléatoire auto-évitante.
No full textInternational audienceIn living matter, concentration gradients of nutrients carve the motility of microorganisms in a heterogeneous environment. Here, we use swimming droplets as a model system to study how swimmer-trail interactions guide locomotion. Combining experiments and theory, we show that our non-Markovian droplet model quantitatively captures droplet motility. The two fit parameters provide the first estimate of the effective temperature arising from hydrodynamic flows and the coupling strength of the propulsion force. This framework is general and explains memory effects, droplet hovering, and enhanced collective motion
Les astrocytes du VLPO, acteurs clés de la régulation du sommeil: published in Médecine du Sommeil, Volume 21, Issue 4, 2024, p. 198-206
No full textInternational audienceAstrocytes are glial cells of the central nervous system, whose role in brain physiology is increasingly well understood. Recently, their involvement in sleep regulation, particularly through the regulation of extracellular adenosine levels, has been extensively studied. This purine plays a central role in sleep regulation, especially in the ventrolateral preoptic nucleus (VLPO), a key brain region involved in the promotion of slow-wave sleep. By combining in situ enzymatic quantification of adenosine levels, infrared videomicroscopy measurements of vascular reactivity, and patch-clamp recordings of neuronal activity, it has been demonstrated that these VLPO astrocytes adjust extracellular adenosine levels in response to available glucose, prostaglandin D2 (PGD2) levels, and circadian timing.Extracellular adenosine activates A2A receptors located on endothelial cells of blood vessels and sleep-promoting neurons of the VLPO, simultaneously adjusting the increase in blood flow to neuronal activity. This ensures the necessary energy supply for neuronal activation, thereby allowing optimal activation of the VLPO and promoting sleep. This gliocentric mechanism is also integrative, adapting the adenosinergic response to circadian timing, with a greater impact when sleep pressure is high compared to when it is low. Thus, VLPO astrocytes do not merely provide structural support to neurons but also play a dynamic and integrative role in the regulation of vigilance states.Les astrocytes sont des cellules gliales du système nerveux central, dont le rôle dans la physiologie cérébrale est de mieux en mieux compris. Récemment, leur implication dans la régulation du sommeil, notamment via la régulation des taux extracellulaires d’adénosine a été particulièrement étudiée. Cette purine joue en effet un rôle central dans la régulation du sommeil, en particulier au niveau du noyau préoptique ventrolatéral (VLPO), une région clé du cerveau impliquée dans la promotion du sommeil lent. En combinant des quantifications enzymatiques in situ des taux d’adénosine, des mesures en vidéomicroscopie infra rouge de la réactivité vasculaire, ainsi que des enregistrements en patch-clamp de l’activité neuronale, il a été démontré que ces astrocytes du VLPO ajustent les taux d’adénosine extracellulaires en réponse du glucose disponible, des taux de prostaglandine D2 (PGD2) et du moment circadien. L’adénosine extracellulaire active les récepteurs A2A situés au niveau des cellules endothéliales des vaisseaux sanguins et des neurones promoteurs du sommeil du VLPO, afin d’ajuster simultanément l’augmentation du flux sanguin à l'activité neuronale. Ainsi, l’apport énergétique nécessaire à l’activation neuronale est assuré, ce qui permet ainsi une activation optimale du VLPO et le sommeil. Ce mécanisme gliocentrique est également intégratif, adaptant la réponse adénosinergique au moment circadien, plus important quand la pression de sommeil est élevée, que lorsqu’elle est faible.Les astrocytes du VLPO ne se contentent donc pas de soutenir structurellement les neurones, mais jouent également un rôle dynamique et intégratif dans la régulation des états de vigilance
Balancing limited resources in actin network competition
No full textInternational audienceIn cells, multiple actin networks coexist in a dynamic manner. These networks compete for a common pool of actin monomers and actin-binding proteins. Interestingly, all of these networks manage to coexist despite the strong competition for resources. Moreover, the coexistence of networks with various strengths is key to cell adaptation to external changes. However, a comprehensive view of how these networks coexist in this competitive environment, where resources are limited, is still lacking. To address this question, we used a reconstituted system, in closed microwells, consisting of beads propelled by actin polymerization or micropatterns functionalized with lipids capable of initiating polymerization close to a membrane. This system enabled us to build dynamic actin architectures, competing for a limited pool of proteins, over a period of hours. We demonstrated the importance of protein turnover for the coexistence of actin networks, showing that it ensures resource distribution between weak and strong networks. However, when competition becomes too intense, turnover alone is insufficient, leading to a selection process that favors the strongest networks. Consequently, we emphasize the importance of competition strength, which is defined by the turnover rate, the amount of available protein, and the number of competing structures. More generally, this work illustrates how turnover allows biological populations with various competition strengths to coexist despite resource constraints
Investigating of the physico-chemistry dhiolated dextran derivatives
No full textInternational audienceThe study aimed to create redox-responsive dextran carriers for controlled hydrophobic molecule release using glutathione, a natural cellular reducing agent, by modifying dextran with a thiol derivative. Investigating the impact of different hydrophobic length on the molecular self-organization of polysaccharide derivatives into nanoparticles helped to understand their roles in this process. The study demonstrated that thiolated dextran particles can be used as emulsifier and can effectively encapsulated hydrophobic molecules like Nile red dye, with the disulfide linkage being cleaved by glutathione under physiological conditions for rapid release. Additionally, the dextran-based particles were found to be non-toxic to living cells
Reconstituted systems for studying the architecture and dynamics of actin networks.
No full textInternational audienceActin, a ubiquitous protein essential for numerous cellular functions, is found in all eukaryotes. Despite extensive research across molecular to organismal scales, fundamental questions persist regarding the regulation of dynamic actin architectures, their interaction with membranes, and their mechanical properties. Characterizing the factors governing these processes presents significant challenges. This review emphasizes the value of simplified, reconstituted systems in addressing these unresolved questions. We particularly highlight the critical importance of macroscopic, network-level reconstitutions for tackling these issues. We first describe the available methodological toolkit for (1) controlling actin polymerization spatiotemporally and (2) confining actin networks within closed environments to examine boundary constraint effects or the impact of limited component availability on network properties. We then review studies employing these reconstituted systems to investigate how actin architecture influences various processes and how dynamic actin structures are established and maintained. Further, we discuss how network-level reconstitutions have enhanced our understanding of actin networks' mechanical properties and their interaction with the lipid membranes. Throughout the review, we discuss future perspectives for each topic and explain how macroscale reconstitutions can provide deeper mechanistic insights into actin-related processes
An Alternative Method for Preparing Methyl 2-Ferrocenyl-2-oxo-acetate
No full textInternational audienceBecause of the continuous interest in ferrocene chemistry, there is a sustained demand for various ferrocenic building blocks, especially small molecules with useful chemical functional groups, sometimes containing multiple groups. Our interest in ferrocene ketoesters (ω-ferrocenyl-ω-ketoesters) was motivated by the synthesis of esters and subsequently alcohols of ferrociphenols. However, from a bibliographic survey, only one publication dated from 1964 reports the two-step synthesis (six-step synthesis from ferrocene) of methyl 2-ferrocenyl-2-oxoacetate, the simplest member of this family of compounds, with no further developments since. We hypothesized that a simpler method might exist, such as the Friedel-Crafts method. By focusing on our experiments to use aluminum trichloride as the catalyst, we managed to achieve the synthesis of FcCOCOOMe in a single step, albeit with a very low yield, regardless of reaction time, temperature, amount of aluminum chloride and reagents concentration. Nevertheless, considering the time saved, simplicity, and the use of less hazardous and less expensive reagents, this method offers certain advantages for synthesizing this building block
Self‐assembled silicon@silica metasurfaces with high‐quality resonances in the infrared
No full textInternational audience2D assemblies of resonant dielectric particles constitute promising materials for the next generation of photonic devices, thanks to their low optical losses and intense electromagnetic response. However, bottom‐up synthesis methods present many difficulties when targeting metasurface applications, particularly due to the high degree of positional disorder and the size dispersion of the resonant particles. This work presents the fabrication of core–shell silicon@silica particles with multipolar resonances in the visible and near‐infrared. These resonant particles are then assembled at an air–water interface into a semi‐ordered array with islands of crystallinity. The assembly is deposited on quartz and the optical properties are characterized with ellipsometry and optical microscopy. The effective medium of this material appears to display a magnetic resonance with a high‐quality factor at ≈945 nm, as demonstrated by a Lorentzian resonance in the permeability. Thus, this is the first bottom‐up synthesis of silicon particle assemblies known to generate optical magnetism, giving promise for the scalable production of high‐performance metasurfaces, in spite of the imperfections associated with bottom‐up fabrication
The interpeduncular nucleus blunts the rewarding effect of nicotine
No full textInternational audienceNicotine stimulates ventral tegmental area (VTA) dopaminergic neurons, producing a rewarding effect that drives tobacco consumption. The interpeduncular nucleus (IPN) is thought to become engaged at high nicotine doses to limit drug intake, but its response dynamics are unknown. We developed a chemogenetic approach using a "suicide" antagonist that selectively attaches to designer β4 nicotinic acetylcholine receptors (nAChRs) in genetically-modified mice, enabling sustained and pharmacologically-specific antagonism. Local infusion in the IPN revealed that nicotine, even at low doses, simultaneously activates and inhibits two distinct populations of IPN neurons, with β4-containing nAChRs mediating only the activation response. Blocking nicotine-induced IPN activation enhanced VTA responses and increased the drug's rewarding effect in a conditioned place preference paradigm. Moreover, optogenetic inhibition of IPN projections to the laterodorsal tegmental nucleus (LDTg) replicated these behavioral effects. Our findings indicate that the IPN acts as a regulatory brake on the nicotine reward circuit via the LDTg
Introduction of a Phosphine Group onto the Ferrocene Moiety in Ferrociphenol Opens Access to New Heterobimetallic Complexes with Anticancer Activity
No full textInternational audienceFerrocene analogs of biologically active compounds often exert favorable properties, as demonstrated by ferrocifens derived from the selective estrogen receptor modulator tamoxifen. This contribution reports an original approach to modify the structure of one of the first ferrocifens, namely ferrociphenol, by means of a diphenylphosphinyl moiety appended to the unsubstituted cyclopentadienyl ring of the ferrocene unit. The phosphine‐substituted ferrociphenol 1 is synthesized by two alternative routes and fully characterized including structure determination. Compound 1 is converted to the corresponding phosphonium salt 1 ·MeI and used to prepare a series of bimetallic (arene)metal and chloridogold(I) complexes. The biological evaluation reveals a relatively lower antiproliferative activity of the newly synthesized compounds compared to the parent ferrociphenol and [AuCl(FcPPh 2 ‐κ P )] (Fc = ferrocenyl) toward both tumorigenic and nontumorigenic cells. All the compounds exhibit complicated redox behavior due to chemical steps that follow the initial, ferrocene‐centered oxidation. Overall, the collected data indicate that the introduced phosphine substituent affects the redox and biological properties of the resulting compounds and, very likely, their mode of action