Portail HAL ENSCP
Not a member yet
9647 research outputs found
Sort by
Composition-Encoded Control of Amphiphilicity and Nanoscale Rigidity in Poly(isobutyl cyanoacrylate)/Poly(butylene oxide)-statpolyglycidol Nanospheres and Nanoellipsoids
No full textTuning the interfacial hydrophobicity and morphology of polymeric nanomaterials remains a central challenge for controlling their structural, mechanical, and biological properties. Here, we introduce poly(isobutyl cyanoacrylate)/(poly(butylene oxide)-stat-polyglycidol) (PIBCA/(PBO-stat-PG)) nanospheres (NSs) and nanoellipsoids (NEs) as a chemically defined platform for decoupling hydrophobic balance, internal architecture, and morphology within a single system. Statistical copolymers with variable butylene oxide (BO) and glycidol (G) content provide precise modulation of amphiphilicity while maintaining water solubility and stability under in situ polymerization conditions. Across the BO:G gradient, multimodal analyses (TEM, cryo-TEM, DLS, AFM, SAXS, SLS, ITC) reveal a continuous transition from hydrated, deformable G-rich NSs to compact, lamellar BO-rich structures with reduced hydration and enhanced rigidity. SAXS and AFM jointly establish that BO-induced hydrophobic interactions drive internal densification and structural ordering. Mechanical stretching of embedded NSs yielded NEs with modest aspect ratios (1.6-1.9), compared with previous reports on PIBCA/Chitosan NEs. ITC experiments showed a correlation between the aspect ratio and the strength of interaction between PVA and the copolymers. The combined results demonstrate that copolymer architecture alone can encode interfacial structure and mechanical response without altering size or charge. This work establishes PIBCA/(PBO-stat-PG) as a predictive, composition-tunable model for probing how nanoscale amphiphilicity and rigidity govern morphological stability and mechanical behavior in polymeric nanomaterials
Insights Into the Exchange of N ‐Heterocyclic Carbene Ligands on Gold Nanoparticles: Necessity of Oxygen
No full textInternational audienceGold nanoparticles (AuNPs) stabilized by N ‐heterocyclic carbenes (NHCs) represent robust alternatives to thiol‐protected counterparts owing to the NHCs’ strong Au-C bonds that provide enhanced stability. While NHC‐capped AuNPs with a single type of carbene have been reported many times, strategies to introduce multiple NHC ligands on the same nanoparticle remain unexplored. Here, we investigate NHC‐for‐NHC ligand exchange on AuNPs stabilized either by benzimidazol‐2‐ylidene or by mesoionic triazolylidene scaffolds, employing an in situ generated free carbene route. Prior to ligand exchange, the formation and stability of the studied NHCs from the corresponding azolium salts were examined and characterized by NMR spectroscopy. In situ NMR studies of the exchange reaction showed no evidence of ligand substitution under argon, the conventional atmosphere for free NHC intermediates. Although no exchange was detected by NMR, X‐ray photoelectron spectroscopy (XPS) analysis of the purified AuNPs revealed that ligand substitution had in fact occurred. Further investigation indicated that oxygen plays a key role in promoting the exchange, and that its involvement is also associated with oxidation of the gold core and the formation of NHC‐Au(I) complexes. Taken together, our results highlight the complexity of NHC‐for‐NHC exchange on AuNPs by the free carbene route and point to the need for alternative strategies to achieve controlled ligand substitution
Electronic structure origins of radical character in triangular fused acenes: sextet stabilization vs. antiaromaticity release
No full textInternational audienceOpen-shell hydrocarbons are of great interest in molecular materials, yet their electronic structures remain challenging to describe. Here we investigate triangular acenes, formed by fusing three identical linear acenes through cyclobutadiene linkers into a threefold symmetric framework. Using density functional and multiconfigurational methods, we show that triangular acenes display a stronger radical character than their linear counterparts, which increases with molecular size. Analysis of singlet–triplet gaps, unpaired electron numbers, and NICS(1) aromaticity indices reveals that this behavior arises from two cooperative effects: Clar's sextet stabilization and the release of cyclobutadiene antiaromaticity. Fractional occupation densities further indicate a redistribution of unpaired electrons from cyclobutadiene units in smaller molecules to the acene cores in larger systems. These results establish triangular acenes as a distinct class of multiradicaloid hydrocarbons, offering new insights for the design of open-shell π-conjugated materials
Step Toward Cationic RAFT Polymerization of Less Reactive Monomers: Dithiobenzoates Bearing Electron-Withdrawing Groups as Chain-Transfer Agents
No full textInternational audienceHere, we report a new strategy for the cationic RAFT polymerization of less reactive monomers such as pmethylstyrene and styrene. This strategy implies that the addition of electron-withdrawing substituents into the stabilizing group of cumyl dithiobenzoate results in a decrease in the stability of cationic intermediates, thus facilitating their fragmentation and cationic RAFT polymerization. Particularly, it was demonstrated that both cumyl dithiobenzoate and cumyl dithiobenzoate with a trifluoromethyl substituent in the Z-group activated by a small amount of SnCl4 induced living cationic RAFT polymerization of p-methoxystyrene, affording polymers with molecular weights up to 80,000 and 30,000 g mol -1 , respectively. In contrast to the unsubstituted counterpart, cumyl dithiobenzoate with a trifluoromethyl substituent in the Z-group was also an efficient chain transfer agent for conducting the living cationic RAFT polymerization of p-methylstyrene, giving polymers with Mn up to 10,000 g mol -1 and moderate dispersity (Đ= 1.3-1.8), while polymerization is terminated at incomplete conversion when cumyl dithiobenzoate was used. Cumyl dithiobenzoate with a trifluoromethyl substituent in conjunction with SnCl4 also induced cationic RAFT polymerization of styrene, affording well-defined polystyrenes with Mn up to 5,000 g mol -1 . Finally, the block copolymers of p-methylstyrene with styrene and methyl methacrylate were successfully synthesized via mechanistic transformation from cationic to radical RAFT polymerization
Nonlinear characterization of Ca5(BO3)3F (CBF) for third harmonic generation at 355 nm
No full textInternational audienc
Photopolymerized three-dimensional fiber arrays mimicking the extracellular matrix for the study of immune cell migration
No full textMicrofabricated systems offer a powerful means to dissect how local physical cues regulate cell migration and mechanics by providing precise control over geometry, stiffness, and dimensionality. Such control is especially valuable for studying immune cell behavior, as these dynamic cells constantly integrate physical and chemical information. Two-photon polymerization (TPP) has emerged as a versatile tool for fabricating 3D microscaffolds that replicate essential extracellular matrix (ECM) features with submicron precision, high control over geometry, and tunable mechanical properties. Here, we provide a detailed protocol for the use of TPPfabricated 3D fiber scaffolds to study the impact of local microtopography on leukocyte migration and force generation, with a focus on neutrophils, T cells and dendritic cells. The chapter outlines scaffold design, fabrication, cell preparation and seeding, imaging, and quantitative analysis workflows for cell tracking and traction force measurements. This methodology provides a robust framework for probing how specific ECM parameters govern leukocyte motility and force generation, linking migration strategies to physiologically relevant microarchitectures.</div
CrystalNets: A web app for topology determination of crystalline structures
No full textInternational audienceBecause topology plays a key role in many chemical and physical properties of materials, identification of topology from crystalline structures is a common and important task in materials science. We present here a new web application, CrystalNets, whose user-friendly interface allows scientists to identify and visualize the topology of crystals from their atomic structure in CIF format. The software has a lot of options to customize its features, such as detection of bonding, choice of clustering model, type of materials (inorganic, hybrid, etc). It has a default mode with powerful heuristics, and allows the user to easily visualize and check the topology detected against the full structure. We also improved the underlying CrystalNets.jl Julia library, including a systematic algorithm to handle the complex case of unstable nets
Synthesis, Characterization, and Evaluation of Chelators for Radium-223
No full textInternational audienceThe stable coordination of radium-223 ( 223 Ra) for targeted alpha therapy remains elusive. Herein, seventeen chelators were investigated for the complexation of 223 Ra, of which thirteen have previously not been reported. MacroPa was used as a reference and control for the studies, and by a process of systematic modifications to this chelator and a range of other chelator scaffolds, a library of structurally related compounds was obtained, each differing from another by a single functional group or change in the backbone. The radiolabelling of each chelator was assessed by radio-thin layer chromatography to determine radiochemical conversion. Fourteen of the synthesized chelators provided quantitative coordination of 223 Ra at room temperature and neutral pH (or close to). The stability of these complexes in human serum at 37 °C was analyzed using radio-size exclusion chromatography where results corresponding to [ 223 Ra][Ra(MacroMePhos)] were encouraging. However, radio-thin layer chromatography analysis of the 'small molecule' fractions revealed the presence of free 223 Ra, indicating instability within 1 h. In fact, even [ 223 Ra][Ra(MacroPa)] dissociated within 1 h, albeit at higher dilutions. Overall, this work shows that the search for a suitable 223 Rachelator for applications in radiopharmaceuticals still requires significant attention and effort.</div
Internal structure of random polydisperse foams in steady state
No full textInternational audienceThe interplay between the foam structure and the liquid fraction, which has been established theoretically, is difficult to access experimentally due to foam aging. Here, we use small-angle neutron scattering coupled with optical imaging to investigate the structure of foams under stationary conditions where the liquid fraction remains constant over time. Through forced drainage, i.e., by injecting the foaming solution at a low flow rate above the foams, the coalescence and coarsening of polyhedral bubbles are suppressed. At the nanoscale, the thin film thickness and specific surface area of the films and Plateau borders swell and reach constant values during forced drainage. Although foam is by nature a non-equilibrium system, the low drainage flow rates considered place the structure in a steady state. Under these conditions, theoretical models based on Kelvin cells for monodisperse foams enable to predict the structure of our foams, despite being polydisperse, as long as they are in a steady state obtained in forced drainage
Revisiting irreversible capacity in lignin-derived hard carbons for sodium-ion batteries: The dominant role of surface functional groups over surface area
No full textInternational audienceHard carbons are promising materials as anode for sodium-ion batteries due to their good reversible capacities and the huge diversity of bio-based precursors available for their synthesis. Nevertheless, their low initial coulombic efficiency (ICE), often below 80% for bio-based hard carbons, is one of the main challenges for their commercial applications. In this work, the surface of lignin-based hard carbons is modified with a thin layer of soft carbon obtained from petroleum pitch. Soft carbon is known to have rich sp2-hybridized domains, with very few heteroatoms, leading to a surface with less defects. After pyrolysis at different temperatures (900 °C to 1400 °C), hard carbon materials were coated using an impregnation coating method. Structural, textural and surface analyses were carried out to understand the impact of soft carbon coating on the electrochemical performance. The composite carbon initially pyrolyzed at 1200 °C exhibited the best performance, achieving a reversible capacity of 310 mAh.g−1, and an excellent initial coulombic efficiency of 89%. Notably, this ICE is among the highest reported for lignin-based hard carbons, which highlights the effectiveness of surface engineering in enhancing their electrochemical properties for sodium-ion batteries