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Nucleophilic Initiation of Episulfide Anionic Ring-Opening Polymerization by Amino Acids and Oligopeptides
No full textInternational audiencePeptide–polymer conjugates are promising molecules because they combine the biological functionality of peptides with the versatile properties of polymers, enabling applications in drug delivery, biomaterials, and nanomedicine with enhanced stability, biocompatibility, and tailored functionalities. Until now, the grafting-to approach has been the predominant strategy for synthesizing these biohybrids. By comparison, grafting-from techniques are relatively less diverse. Mainly, radical grafting-from techniques have also been developed, but they present a number of limitations, including a limited variety of polymerizable monomers and the introduction of nonbiodegradable polymer chains. The AROP-based grafting-from strategy offers a promising, yet still underexplored, route for synthesizing peptide–polymer conjugates bearing heteroatom-containing polymer side chains. We report an original AROP grafting-from strategy using primary amines as attachment sites, N-acetyl homocysteine thiolactone as a linker, and propylene sulfide as a monomer. The grafting-from technique was optimized using various protected and unprotected amino acids as model scaffolds. In addition, the regioselective functionalization of primary amine lateral substituents of lysine residues over chain-end amines was demonstrated. The method was then extended to dipeptides and tripeptides. Surprisingly, the grafting-from polymerization was demonstrated to also occur in a controlled manner using oligopeptide initiators bearing unprotected terminal carboxylic acid end-groups. Furthermore, this technique was applied to the introduction of polythioether grafts on the KLVFF peptide sequence (Lys-Leu-Val-Phe-Phe), which is a key recognition motif found in the amyloid-β (Aβ) protein, a protein strongly associated with Alzheimer’s disease
Multi-scale models for a better understanding of the carbon electrode / electrolyte interface and their applications in the field of supercapacitors
No full textInternational audienceIon adsorption and dynamics in porous carbons are crucial for many technologies, such as energy storage and desalination. Progress in the development of novel systems is hampered by our lack of understanding of the microscopic mechanisms that determine their behaviour and performance. The key issue is that phenomena on the atomistic scale have consequences on macroscopic length and timescales. In particular, the effects of ionic confinement and diffusion are crucial for device performance, yet experiments that probe properties related to local structure and diffusion are challenging and difficult to interpret without a parallel modelling approach. I will present a multi-scale approach designed to bridge the gap between molecular simulations (corresponding to length scales of a few nanometers) and experiments (here length scales of a few micrometers). The mesoscopic models developed, versatile and very computationnally efficient, allow one to predict useful quantities, such as NMR spectra, tortuosities, and quantities of adsorbed ions, for electrolyte species adsorbed in disordered porous carbons. I will show how this approach can be used to gain insights into the structure of porous carbons [1][2] and simulate in situ NMR spectra of electrolyte ions adsorbed into carbon electrodes maintained at a given potential difference [3]. The simulation of electrolyte species adsorbed in nanoporous carbons is especially relevant for electrochemical double layer capacitors (also called supercapacitors), energy storage systems in which the energy is stored at the carbon-electrolyte interface. Recently, major improvements in the code implementation have allowed us to reach even larger scales (several hundreds of nanometers), allowing for the simulation of carbon particles with different sizes and full supercapacitors [4]
Sub-Kelvin Spectral Hole Burning in Eu:YSO for Laser Frequency Stabilisation
No full textInternational audienceAs basic building blocks for quantum devices, ultra-stable lasers have a profound impact on various fields. Longer laser coherence times enhance the performance of quantum sensors, computers, communications, and optical clocks. Although optical lattice clocks have accomplished significant high-precision measurements, they often fall short of their quantum projection noise limits due to dead times during atom preparation: the instability in the laser frequency introduces stochastic fluctuations during the interrogation of atomic transitions (Dick effect). High-resolution optical clock comparisons are crucial for evaluating their accuracy and could lead to a redefinition of the SI second based on optical transitions [1].However, the most common technique for achieving ultra-stable lasers, the Pound-Drever-Hall method with Fabry-Perot cavities, faces thermal noise limitations of the cavities. To overcome these constraints, alternative methods such as Spectral Hole Burning (SHB) in rare-earth-doped crystals (REICs) have been explored. Indeed, REICs experience inhomogeneous broadening due to local lattice distortions caused by the size difference between dopant and host ions. An SHB protocol, which creates narrow spectral features through selective depletion of specific dopant ion populations using narrow-linewidth lasers, allows to overcome the inhomogeneous broadening and fully exploit the coherence of rare-earth ions. At cryogenic temperatures, Eu:YSO crystal exhibit persistent Spectral Holes a few kHz narrow and with a lifetime up to 10 h, at 4 K [2], making it a high-precision frequency reference, ideal for intermediate-timescale sensing.We report recent experimental progress on SHB in Eu:YSO crystals at specific sub-K dilution temperature setpoints that cancel the thermal sensitivity of the hole frequency [3]. The latest recorded performances on our experiment reach a fractional frequency stability of 4.10-16 at 1 s [4], which is close to the perfomance of our reference cavity at LTE. Therefore, a second SHB setup is needed for our future stability comparisons. On one front, we rationalize our SHB protocol and investigate new optimal burning parameters as well as test various doping concentrations to achieve the narrowest possible spectral holes on both setups. On another, we continue to further improving the laser frequency lock onto spectral holes, by cancelling as many systematic noise sources as possible. We provide the performances of our Michelson interferometer to reject frequency noise induced on light propagation to the crystal and by the cryostat acoustic vibrations. In addition, we explore a group delay measurement technique via phase modulation to enhance the precision on the pointing of the center of spectral holes. This should help removing slow frequency drifts due to asymmetric burning of the hole while it is probed by the laser
Unraveling Nickel Dissolution Kinetics in Sulfuric Acid via Element-Resolved Electrochemical Impedance Spectroscopy
No full textInternational audienceDissolution of transition metals in acidic environments central to corrosion and electrocatalysis, yet decoupling the kinetics of individual electrochemical steps remains a longstanding challenge. We introduce a combined atomic emission spectroelectrochemistry -electrochemical impedance spectroscopy (AESEC-EIS) method enabling real-time, element-specific quantification of metal dissolution while simultaneously resolving interfacial impedance. Using nickel in deaerated sulfuric acid as a model system, we construct the first element-resolved Nyquist and Bode plots for an actively dissolving metal. The results reveal a Ni dissolution mechanism involving adsorbed intermediates acting as precursors to soluble Ni(II). A second anodic peak, induced by prior cathodic potential sweep, reflects surface modification. Kinetic modeling and EIS simulations confirm that surface-mediated pathway dominates under cathodic activation, whereas passivating route involving NiO formation prevails otherwise. AESEC-EIS offers a robust approach to decompose interfacial electrochemical kinetics and to elucidate metal dissolution mechanisms relevant to corrosion and electrocatalysis
Unsupervised multi-clustering and decision-making strategies for 4D-STEM orientation mapping
No full textInternational audienceThis study presents a novel integration of unsupervised learning and decision-making strategies for the advanced analysis of 4D-STEM datasets, with a focus on non-negative matrix factorization (NMF) as the primary clustering method. Our approach introduces a systematic framework to determine the optimal number of components (k) required for robust and interpretable orientation mapping. By leveraging the K-component loss method and Image Quality Assessment (IQA) metrics, we effectively balance reconstruction fidelity and model complexity. Additionally, we highlight the critical role of dataset preprocessing in improving clustering stability and accuracy. Furthermore, our spatial weight matrix analysis provides insights into overlapping regions within the dataset by employing threshold-based visualization, facilitating a detailed understanding of cluster interactions. The results demonstrate the potential of combining NMF with advanced IQA metrics and preprocessing techniques for reliable orientation mapping and structural analysis in 4D-STEM datasets, paving the way for future applications in multi-dimensional material characterization
An untargeted data mining strategy for extracting chemical exposome signatures from LC-HRMS data: Application to meconium for early-life exposure assessment
No full textInternational audienceExposome research has expanded rapidly in recent years, driven by advances in analytical techniques such as liquid chromatography-high-resolution mass spectrometry (LC-HRMS), which enable broad and sensitive chemical coverage. Targeted methods focus on known compounds, while untargeted metabolomic approaches provide a more holistic view and may reveal exposure biomarkers, but they are not specifically designed to detect exogenous chemicals. Identifying relevant exposure markers within the vast and complex datasets generated by untargeted LC-HRMS data remains a significant analytical and computational challenge, requiring innovative data mining strategies. Results: We developed a novel untargeted data mining strategy to extract exogenous chemical signatures from complex LC-HRMS datasets. The approach integrates isotopic signature enrichment (ISE), biotransformationinformed feature selection and an "exposure rate" metric. When applied to meconium data from the EDEN cohort, the strategy led to a six-fold reduction in the number of features by retaining only those exhibiting valid carbon isotope patterns. Mass defect plots revealed signatures of suspect monohalogenated species and putative conjugated and non-conjugated metabolites in a specific region. Incorporating ISE results into the chemical formula prediction significantly reduced the number of candidates, improving annotation efficiency. In utero exposure to xenobiotics was supported by the detection of known exposure markers such as acetaminophen, caffeine and nicotine. These results demonstrate the method's potential to uncover exposomic signals in complex biological matrices. Significance: This study presents a novel data mining strategy that reduces the complexity of untargeted LC-HRMS data by retaining chemically reliable features based on isotopic signatures. As a proof of concept, this strategy enables the detection of specific chemical signatures and exogenous compounds without prior knowledge. Its adaptability to various biological matrices and its compatibility with different high-resolution mass spectrometry platforms make this strategy a valuable tool for exposome research and early-life exposure assessment
Molecular aspects of cell-penetrating peptides: key amino acids, membrane partners, and non-covalent interactions
No full textInternational audienceSince the early 1990s, there has been considerable interest in cell-penetrating peptides (CPPs) capable of transporting various types of molecules in cells. These CPPs are endowed with the ability to cross the cell membrane by endocytosis and by other, as yet poorly understood, translocation pathways. Translocation involves interactions of the peptide with plasma membrane components before it can contact, disrupt, and/or reorganize the lipid bilayer. The plasma membrane is complex in terms of molecular composition and structure. It separates the external environment from the cell interior and is composed of thousands of different lipids, proteins, and sulfated carbohydrates, all arranged in a complex and dynamic manner and at various length scales. Floating above the lipid bilayer, negatively charged proteoglycans and other polysaccharides form a viscous, anionic matrix layer surrounding animal cells, which CPPs have to go through to reach the lipid bilayer. Even though the thickness and structure of this glycocalyx are extremely variable in different cell types, CPPs can cross ubiquitously cell membranes. On the peptide side, CPPs are mostly short (less than 30 amino acids), positively charged sequences. Some have also primary or secondary amphipathic properties. Understanding CPP translocation pathways requires interdisciplinary approaches from physical chemistry to cell biology for identifying key amino acids in the peptide sequence and membrane components, and the interactions between the two involved in the different steps of the process. In the following synthetic review, we focus on these aspects
Pre-twins in Zr702 alloy enhance corrosion resistance in chloride and sulfuric acid electrolytes and strength
No full textInternational audienceThe influence of pre-twins on the corrosion behavior of Zr702 alloy was investigated through combined electrochemical and surface analysis techniques, including time-of-flight secondary ion mass spectrometry and X-ray photoelectron spectroscopy. The pre-twinned specimens exhibited increased pitting potential in 1 mol/L NaCl electrolyte. A significant reduction in corrosion current density was demonstrated in 0.05 mol/L H2SO4 electrolyte. Twin boundaries were found critical for promoting the formation of protective passive films. Furthermore, twinning induced orientation rotation, leading to more closely-packed plane {10−10} to be parallel to the sample surface, also contributed to the formation of protective passive films. In addition, pre-twins enhance the hardness and strength as a result of the high density of twin boundaries. These results may provide a new approach to improve the property of Zr alloy
Adaptive motility enables neutrophils to rapidly navigate confined capillaries
No full textAs the first responders of the immune system, neutrophils rapidly and abundantly reach inflamed tissues through blood capillaries. The diameter of capillaries can be as narrow as two microns, imposing considerable deformations on neutrophils. Notably, capillary obstruction due to neutrophil retention causes vascular dysfunction and contributes to the pathogenesis of several diseases. However, the cellular mechanisms that allow neutrophils to migrate into small capillaries and to avoid retention remain unknown. In this study, we demonstrate, both in vivo and in vitro , that capillary size does not influence neutrophil migration velocity. During migration into capillaries of different sizes, neutrophils maintain high speed, a phenomenon associated with a global actomyosin cytoskeleton rearrangement in response to confinement strength. In irregular capillaries, neutrophils rapidly adapt their cell contractility via the ROCK-MyoII pathway, which allows them to sustain their migration speed along the vessels despite changes in confinement. At the single cell level, inhibition of ROCK impairs actomyosin cytoskeleton rearrangement and reduces neutrophil migration speed within confined capillaries. At the collective level, ROCK inhibition hampers efficient neutrophil trafficking in a network of small capillaries, resulting in vessel obstruction. These findings reveal a unique capacity of neutrophils to rapidly and dynamically adapt their migration to the confinement strength of capillaries, an ability that might limit vascular dysfunction during inflammation
Design of a Novel Class of N-Heterocyclic Carbene Cycloplatinated Complexes Containing Pyrene Chromophores
No full textInternational audienceCycloplatinated complexes incorporating pyrene chromophores of the formulae (CˆC*)Pt(acac) (3, 4), (CˆC* = Pyrenyl-NHC, acac = acetylacetonate) were prepared and fully characterized. For comparison, two regioisomeric complexes were prepared following synthetic procedures developed by us. One isomer has the Pt(II) center attached to the 2-position of the pyrene chromophore, while the other regioisomer has the metal center attached at the 1-position of the organic chromophore. The molecular structures of 3 and 4 were ascertained by X-ray diffraction, and they prove the identity of the targeted compounds. Both complexes are emissive at room temperature in the red part of the spectrum in poly(methyl methacrylate) (PMMA), as well as at 77 K in 2-methyltetrahydrofuran (2-MeTHF). The regioisomer containing the Pt(II) at the 1-position shows enhanced emissive properties compared to the other regioisomer