HAL Portal ESPCI (Ecole Supérieure de Physique et de Chimie Industrielles)
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Transforming Nanocrystals into Superhard Boron Carbide Nanostructures
No full textInternational audienceBoron carbide (B4+δC) possesses a large potential as structural material owing to its lightness, refractory character and outstanding mechanical properties. However, its large-scale industrialization is set back by its tendency to amorphize when subjected to an external stress. In the present work, we design a path towards nanostructured boron carbide with greatly enhanced hardness and resistance to amorphization. The reaction pathway consists of triggering an isomorphic transformation of covalent nanocrystals of Na1-xB5-xC1+x (x = 0.18) produced in molten salts. The resulting 10 nm B4.1C nanocrystals exhibit a four-fold decrease of size compared to previous works. Solid-state 11B and 13C NMR coupled to DFT reveal that the boron carbide nanocrystals are made of a complex mixture of atomic configurations, which are located at the covalent structural chains between B11C icosahedral building units. These nanocrystals are combined with a spark plasma sintering-derived method operated at high pressure. This yields full densification while maintaining particle size. The nanoscaled grains and high density of grain boundaries provide the resulting nanostructured bodies with significantly enhanced hardness and resistance to amorphization, thus delivering a superhard material
Tuning the Resistance of a VO2 Junction by Focused Laser Beam and Atomic Force Microscopy
No full textInternational audienceAbstract Vanadium Dioxide (VO 2 ) is a material that exhibits a phase transition from an insulating state to a metallic state at ≈68 °C. During a temperature cycle consisting of warming followed by cooling, the resistivity of VO 2 changes by several orders of magnitude over the course of the hysteresis loop. Using a focused laser beam (λ = 532 nm), it is shown that it is possible to optically generate micron‐sized metallic patterns within the insulating phase of a VO 2 planar junction which can be used to tune, on demand, the resistance of the VO 2 junction. A resistor network simulation is used to characterize the resulting resistance drops in the devices. These patterns persist while the base temperature is held constant within the hysteretic region while being easily removed totally by simply lowering the base temperature. Surprisingly, it is also observed that the pattern can be partially erased using an atomic force microscope (AFM) tip on the submicron scale. This erasing process can be qualitatively explained by the temperature difference between the VO 2 surface and the tip which acts as a local cooler. This optical and AFM resistive fine‐tuning offers the possibility of creating controllable synaptic weights between room‐temperature VO 2 neuristors
Synthesis, evaluation and mechanistic insights of novel IMPDH inhibitors targeting ESKAPEE bacteria
No full textInternational audienceAntimicrobial resistance poses a significant threat to global health, necessitating the development of novel therapeutic agents with unique mechanisms of action. Inosine 5′-monophosphate dehydrogenase (IMPDH), an essential enzyme in guanine nucleotide biosynthesis, is a promising target for the discovery of new antimicrobial agents. High-throughput screening studies have previously identified several urea-based leads as potential inhibitors, although many of these are characterised by reduced chemical stability. In this work, we describe the design and synthesis of a series of heteroaryl-susbtituted analogues and the evaluation of their inhibitory potency against IMPDHs. Our screening targets ESKAPEE pathogens, including Pseudomonas aeruginosa, Staphylococcus aureus and Escherichia coli. Several analogues with submicromolar inhibitory potency are identified and show no inhibitory potency on human IMPDH nor cytotoxic effects on human cells. Kinetic studies revealed that these molecules act as noncompetitive inhibitors with respect to the substrates and ligand virtual docking simulations provided insights into the binding interactions at the interface of the NAD+ and IMP binding sites on IMPDH
Counterintuitive Viscoelasticity of Supramolecular Polymer Networks Driven by Coassembly with Water Molecules
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High-contrast and high-speed multimodal imaging platform: the adaptive optics-confocal rolling slit ophthalmoscope (AO-CRSO)
No full textInternational audienceAdaptive optics imaging techniques are invaluable for cellular-level retina visualization. While AO Flood illumination ophthalmoscopes provide distortion-free, high-speed images, they lack contrast. On the other hand, AO scanning laser ophthalmoscopes offer highly contrasted images due to point by point illumination and spatial filtering but suffer from low pixel throughput and distortion artifacts. Our recent advancements, using a DMD integrated AO-FIO, show that we can illuminate and capture multiple spatially separated zones, achieving contrast close to the one of a confocal microscope. Our theoretical framework emphasizes that each zone must be smaller than 100 µm in both directions or smaller than 10 µm in only one direction to minimize the diffuse light component. Building upon these results, we developed a cutting-edge confocal rolling slit ophthalmoscope, able to achieve brightfield contrast similar to a confocal ophthalmoscope, along with phase contrast images. We utilize a classical sCMOS camera with a rolling shutter synchronized with the line source scanning of the field of view. The system makes use of all the incident photons that can be collected, whether singly, multiply scattered or absorbed. Easy digital switching between the darkfield and brightfield, as well as modification of the size and offset of the detection aperture, enhances the adaptability and versatility of this multimodal imaging system, allowing for fine-tuning of imaging modalities and comprehensive exploration of the retina.</div
Spontaneous formation of polymeric nanoribbons in water driven by π‐π interactions
No full textInternational audienceA simple method was developed to produce polymeric nanoribbons and other nanostructures in water. This approach incorporates a perylene diimide (PDI) functionalized by hydrophilic triethylene glycol (TEG) as a hydrophobic supramolecular structure directing unit (SSDU) into the core of hydrophilic poly(N,N‐dimethylacrylamide) (PDMAc) chains using RAFT polymerization. All PDI‐functional polymers dissolved spontaneously in water, forming different nanostructures depending on the degree of polymerization (DPn): nanoribbons and nanocylinders for DPn = 14 and 22, and spheres for DPn > 50 as determined by cryo‐TEM and SAXS analyses. UV‐VIS absorption spectroscopy was used to monitor the evolution of the PDI absorption signal upon dissolution. In solid form, all polymers show a H‐aggregate absorption signature, but upon dissolution in water, the shortest DPn forming nanoribbons evolved to show HJ‐aggregate absorption signals. Over time, the J‐aggregate band increased in intensity, while cryo‐TEM monitoring evidenced an increase in the nanoribbon’s width. Heating the nanoribbons above 60 °C, triggered a morphological transition from nanoribbons to nanocylinders, due to the disappearance of J‐aggregates, while H‐aggregates were maintained. The study shows that the TEG‐PDI is a powerful SSDU to promote 2D or 1D self‐assembly of polymers depending on DPn through simple dissolution in water
Tailored functional monolayers made from mesoionic carbenes
No full textInternational audienceSignificant progress has been made over the last decades in surface functionalization of coinage metals using thiols and more recently N-heterocyclic carbenes. As shown in this work, mesoionic carbenes (MICs) provide straightforward access to a novel class of surface ligands including electroactive ones and thus materials. Importantly, MICs are easily accessed from triazolium salts (TS) onto which functional groups may be attached with little synthetic effort. Here, we present a library of TS that were further converted, in situ, into MICs and grafted onto gold surfaces. The modified surfaces were thoroughly characterized by advanced spectroscopic methods such as XPS, infrared and Tip-Enhanced Raman Spectroscopy. Through cyclic voltammetry at 100 Vs-1, we could evaluate the surfacic concentration of the grafted molecules for electroactive MICs. We also prepared mixed MIC/thiol self-assembled monolayers, which opens the route to multifunctional surfaces
Multilamellar Nanovectors composed of Microbial Glycolipid-Polylysine Complexes for Drug Encapsulation
No full textInternational audienceThis study addresses the potential use of single-glucose microbial amphiphiles as phospholipid-free drug carriers. Microbial amphiphiles, also known as biosurfactants, are molecules obtained from the fermentation of bacteria, fungi or yeast and largely studied for their antimicrobial, cleaning or anti-pollution potential. However, recent understanding of their self-assembly properties combined to their interactions with macromolecules suggest broader potential applications, one being the phospholipid-free conception of drugs. In this study, we want to demonstrate that this class of bio-based molecules can be directly used to design colloidally-stable vesicular carriers for hydrophobic drugs, without employing phospholipid supports, and that the actives can be delivered to human cells. In this study, multilamellar wall vesicles (MLWVs) have been synthesised using a microbial glycolipid amphiphile and poly-L-lysine, held together by electrostatic attractive interactions. Curcumin, a highly lipophilic molecule, was used as natural drug model to evaluate the present colloidal system as potential nanocarrier. The cell uptake of the curcumin-loaded nanocarriers was significantly higher for HeLa cells (50 %) compared to Normal Human Dermal Fibroblasts (35 %) and to THP-1 derived macrophages (20 %). The cytotoxic effect of delivered curcumin or other pharmaceuticals (Doxorubicin, Docetaxel, Paclitaxel) was higher in HeLa cells as the cell viability was reduced by 50 %
Unlocking Metal-Ligand Cooperative Catalytic Photochemical Benzene Carbonylation: A Mechanistic Approach
No full textInternational audienceA key challenge in green synthesis is the catalytic transformation of renewable substrates at high atom and energy efficiency, with minimal energy input (∆G≈0). Non-thermal pathways, i.e., electrochemical and photochemical, can be used to leverage renewable energy resources to drive chemical processes at well-defined energy input and efficiency. Within this context, photochemical benzene carbonylation to produce benzaldehyde is a particularly interesting, albeit challenging, process that combines unfavorable thermodynamics (∆G° = 1.7 kcal/mol) and the breaking of strong C-H bonds (113.5 kcal/mol) with full atom efficiency and the use of renewable starting materials. Herein, we present a mechanistic study of photochemical benzene carbonylation catalyzed by a rhodium-based pincer complex that is capable of metal-ligand cooperation. The catalytic cycle, comprising both thermal and non-thermal steps, was probed by NMR spectroscopy, UV-visible spectroscopy and spectrophotochemistry, and density functional theory calculations. This investigation provided us with a detailed understanding of the reaction mechanism, allowing us to unlock the catalytic reactivity of the Rh-pincer complex, which represents the first example of a metal-ligand cooperative system for benzene carbonylation, exhibiting excellent selectivity
Static Bell test in pilot-wave hydrodynamics
No full textInternational audienceSince its discovery in 2005, the hydrodynamic pilot-wave system has provided a concrete macroscopic realization of wave-particle duality and concomitant classical analogs of a growing number of quantum effects. The question naturally arises as to how closely particleparticle correlations achieved with this classical system can mimic those arising on the quantum scale. We here introduce a new platform for addressing this question, a numerical model of cooperative tunneling in a bipartite pilot-wave hydrodynamic system. We execute a static Bell test, in which the system geometry is fixed and the two subsystems are coupled through the intervening wave field. This wave-mediated coupling is not congruent with the assumptions made in deriving Bell's inequality, and so allows one to rationalize the reported violations. Nevertheless, these violations are elusive, and arise only in a limited corner of parameter space