HAL Portal ESPCI (Ecole Supérieure de Physique et de Chimie Industrielles)
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Palladium‐Catalyzed/Mn(OAc) 3 ‐Mediated 1,2‐Diazidation and 1,2‐Acetoxy/Hydroxylation of N ‐Allyl Sulfonamides
No full textInternational audiencePalladium‐catalyzed conditions for diazidation or acetoxy/hydroxylation of N ‐allyl sulfonamides by using Pd(OAc) 2 as the catalyst combined with Mn(OAc) 3 ⋅ 2H 2 O have been developed. The 1,2‐diazidation reaction of the carbon‐carbon double bond occurs in mild conditions ( i. e . NaN 3 as azide source in THF at room temperature), whereas the 1,2‐acetoxy/hydroxylation requires an excess of Mn(OAc) 3 ⋅ 2H 2 O. The well‐known ability of this reagent to act through single‐electron transfer (SET) makes plausible a radical mechanism involving high valent palladium complexes
Design of Bright Chemogenetic Reporters Based on the Combined Engineering of Fluorogenic Molecular Rotors and of the HaloTag Protein
No full textInternational audienceThe combination of fluorogenic probes (fluorogens) and self‐labeling protein tags represent a promising tool for imaging biological processes with high specificity but it requires the adequation between the fluorogen and its target to ensure a good activation of its fluorescence. In this work, we report a strategy to develop molecular rotors that specifically target HaloTag with a strong enhancement of their fluorescence. The divergent design facilitates the diversification of the structures to tune the photophysical and cellular properties. Four bright fluorogens with emissions ranging from green to red were identified and applied in wash‐free live cell imaging experiments with good contrast and selectivity. A HaloTag mutant adapted from previous literature reports was also tested and shown to further improve the brightness and reaction rate of the most promising fluorogen of the series both in vitro and in cells. This work opens new possibilities to develop bright chemogenetic reporters with diverse photophysical and biological properties by exploring a potentially large chemical space of simple dipolar fluorophores in combination with protein engineering
Site‐Selective Radical Aromatic C–H Functionalization of Alloxazine and Flavin through Ground‐State Single Electron Transfer
No full textInternational audienceFlavins and their alloxazine isomers are key chemical scaffolds for bioinspired electron transfer strategies. Their properties can be fine-tuned by functional groups, which must be introduced at an early stage of the synthesis as their aromatic ring is inert towards post-functionalization. We show that the introduction of a remote metal-binding redox site on alloxazine and flavin activates their aromatic ring towards direct C–H functionalization. Mechanistic studies are consistent with a synthetic sequence involving ground state single electron transfer (SET) with an electrophilic source followed by radical-radical coupling. This unprecedented reactivity opens new opportunities in molecular editing of flavins by direct aromatic post-functionalization and the utility of the method is demonstrated with the site-selective C6 functionalization of alloxazine and flavin with a CF3 group, Br or Cl, that can be further elaborated into OH and aryl for chemical diversification
Vectorial phase retrieval in super-resolution polarization microscopy
No full textInternational audienceIn single-molecule orientation localization microscopy, valuable information about the orientation and longitudinal position of each molecule is often encoded in the shape of the point spread function (PSF). Yet, this shape can be significantly affected by aberrations and other imperfections in the imaging system, leading to an erroneous estimation of the measured parameters. A basic solution is to model the aberrations as a scalar mask in the pupil plane that is characterized through phase retrieval algorithms. However, this approach is not suitable for cases involving polarization-dependent aberrations, introduced either through unintentional anisotropy in the elements or by using birefringent masks for PSF shaping. Here, this problem is addressed by introducing a fully vectorial model in which the polarization aberrations are represented via a spatially dependent Jones matrix, commonly used to describe polarization-dependent elements. It is then shown that these aberrations can be characterized by a set of PSF measurements at varying focal planes and for various polarization projections. This PZ-stack of PSFs, which contains diversity in both phase and polarization projection, is used in a phase retrieval algorithm based on nonlinear optimization to determine the aberrations. This methodology is demonstrated with numerical simulations and experimental measurements. The PY PSF STACK software developed for modeling and characterization is made freely available
Chiroptical properties of semiconducting nanoplatelets functionalized by tartrate derivatives
No full textInternational audienceInducing chirality in semiconductor nanoparticles is a recent trend motivated by the possible applications in circularly polarized light emission, spintronics, or stereoselective synthesis. However, the previous reports on CdSe nanoplatelets (NPLs) exclusively rely on cysteine or its derivatives as chiral ligands to induce optical activity. Here, we show a strong induction of chirality with derivatives of tartaric acid obtained by a single-step synthesis. The ligand exchange procedure in organic solvent was optimized for five-monolayer (5 ML) NPLs but can also be performed on 4 ML, 3 ML, and 2 ML. We show that the features of the CD spectra change with structural modification of the ligands and that these chiral ligands interact mainly with the first light-hole (lh1) band rather than the first heavy-hole (hh1) band, contrary to cysteine. This result suggests that chiroptical properties could be used to probe CdSe nanoplatelets' surface ligands
Collective Long-Lived Zero-Quantum Coherences in Aliphatic Chains
No full textInternational audienceIn nuclear magnetic resonance, long-lived coherences constitute a class of zero-quantum (ZQ) coherences that have lifetimes that can be longer than the relaxation lifetimes T2 of transverse magnetization. So far, such coherences have been observed in systems with two coupled spins with spin quantum numbers I = 1/2, where a term S0T0+T0S0 in the density operator corresponds to a coherent superposition between the singlet S0 and the central triplet T0 state. Here, we report on the excitation and detection of collective long-lived coherences in AA'MM'XX' spin systems in molecules containing a chain of at least three methylene (-CH2-) groups. Several variants of excitation by polychromatic spin-lock induced crossing (poly-SLIC) are introduced that can excite a non-uniform distribution of the amplitudes of terms such as S0S0T0S0S0T0, S0T0S0S0T0S0, and T0S0S0T0S0S0. Once the radio frequency fields are switched off, these are not eigenstates, leading to ZQ precession involving all six protons, a process that can be understood as a propagation of spin order along the chain of CH2 groups before the reconversion into observable magnetization by a second poly-SLIC pulse that can be applied to any one or several of the CH2 groups. In the resulting 2D spectra, the ω2 domain shows SQ spectra with the chemical shifts of the CH2 groups irradiated during the reconversion, while the ω1 dimension shows ZQ signals in absorption mode with linewidths on the order of 0.1 Hz that are not affected by the inhomogeneity of the static magnetic field but can be broadened by chemical exchange as occurs in drug screening. The ZQ frequencies are primarily determined by differences ΔJ between vicinal J-couplings
Rhéologie non-linéaire de gels polymères à associations modulables
No full textWe propose a new yield stress fluid concept using functional associative polymers consisting of a polyelectrolyte backbone bearing -CnH2n+1 alkyl-terminated side chains. At basic pH, the backbone is soluble and the hydrophobic groups associate to form micelles that connect the macromolecules in a transient network. We establish a link between the linear and non-linear rheological properties of the solutions and the hydrophobicity of the alkyl chains. For n = 32, solutions show a sol-gel transition between viscoelastic liquid and yield stress fluids at very low concentrations. Viscoelastic properties are studied in detail by varying concentration and temperature. Using an original particle-tracking microvelocimetry setup implemented on a commercial rheometer, we show that solution flow in the yield stress fluid regime is accompanied by remarkable structuring that combines time-dependent transient shear banding and wall slip. Once the stationary state is reached, the Herschel-Bulkley law for yield stress fluids describes the relationship between stress and shear rate. For n = 16 and 20, the solutions remain viscoelastic liquids throughout the studied range of concentration. Viscoelastic moduli variations can be superimposed to obtain master curves by multiplying the frequency by a coefficient that depends on the hydrophobicity of the polymer. Modulus variations are then described over 13 frequency decades by the sticky Rouse model. These results provide guidelines for the rational formulation of varnishes and paints.Nous proposons un nouveau concept de fluide à seuil d’écoulement qui utilise des polymères associatifs fonctionnels constitués d’un squelette polyélectrolyte portant des chaînes latérales terminées par un groupement alkyle –CnH2n+1. A pH basique, le squelette est soluble et les groupements hydrophobes s’associent et forment des micelles qui connectent les macromolécules en un réseau transitoire. Nous établissons un lien entre les propriétés rhéologiques linéaires et non linéaires des solutions et l’hydrophobie des chaînes alkyles. Pour n = 32, les solutions présentent à très faible concentration une transition de type sol-gel entre des liquides viscoélastiques et des fluides à seuil d’écoulement. Les propriétés viscoélastiques sont étudiées en détail en faisant varier la concentration et la température. Grâce à un montage original de microvélocimétrie par suivi de particules implanté sur un rhéomètre commercial, nous montrons que l’écoulement des solutions dans le régime de fluide à seuil s’accompagne d’une structuration remarquable qui combine des bandes de cisaillement transitoires dépendantes du temps et du glissement aux parois. Une fois atteint l’état stationnaire, la loi de Herschel-Bulkley pour les fluides à seuil décrit la relation entre la contrainte et le taux de cisaillement. Pour n = 16 et 20, les solutions restent des liquides viscoélastiques dans tout le domaine de concentration étudié. Il est possible de superposer les variations des modules viscoélastiques et d’obtenir des courbes maîtresses en multipliant la fréquence par un coefficient qui dépend de l’hydrophobie du polymère. Les variations des modules sont alors décrites sur 13 décades de fréquence par le modèle de Rouse associatif. Ces résultats fournissent des guides pour la formulation rationnelle de vernis et peintures
Odd Viscosity Suppresses Intermittency in Direct Turbulent Cascades
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Natural convection in a vertical channel. Part 2. Oblique solutions and global bifurcations in a spanwise-extended domain
No full textInternational audienceVertical thermal convection is a non-equilibrium system in which both buoyancy and shear forces play a role in driving the convective flow. Beyond the onset of convection, the driven dissipative system exhibits chaotic dynamics and turbulence. In a three-dimensional domain extended in both the vertical and the transverse dimensions, Gao et al. ( Phys. Rev. E , vol. 97, 2018, 053107) have observed a variety of convection patterns which are not described by linear stability analysis. We investigate the fully nonlinear dynamics of vertical convection using a dynamical-systems approach based on the Oberbeck–Boussinesq equations. We compute the invariant solutions of these equations and the bifurcations that are responsible for the creation and termination of various branches. We map out a sequence of local bifurcations from the laminar base state, including simultaneous bifurcations involving patterned steady states with different symmetries. This atypical phenomenon of multiple branches simultaneously bifurcating from a single parent branch is explained by the role of symmetry. In addition, two global bifurcations are identified: first, a homoclinic cycle from modulated transverse rolls and second, a heteroclinic cycle linking two symmetry-related diamond-roll patterns. These are confirmed by phase space projections as well as the functional form of the divergence of the period close to the bifurcation points. The heteroclinic orbit is shown to be robust and to result from a 1:2 mode interaction. The intricacy of this bifurcation diagram highlights the essential role played by dynamical systems theory and computation in hydrodynamic configurations
Comportements d'intercalation d'aluminium de composés de chaine pontée cyanido {[Fe(Tp)(CN) 3 ] 2 [M(H 2 O) 2 ]} dans un électrolyte liquide ionique
No full textInternational audienceAs the development of aluminum-ion batteries is still in its infancy, researchers are still dedicated to exploring suitable host materials and investigating their aluminum intercalation behaviours. Here, a series of cyanido-bridged chain compounds with the formula {[FeIII(Tp)(CN)3]2[MII(H2O)2]}n (M=Ni, Co, Mn, Zn, Cu) are studied as cathode electrodes for aluminum-ion batteries with [EMIm]Cl-AlCl3 (1-ethyl-3-methylimidazolium chloride-AlCl3) ionic liquid as electrolyte. The electrochemical properties suggested Fe3+/Fe2+ to be the redox-active couple during the aluminum intercalation and deintercalation processes of these compounds, and the observed maximum specific capacity obtained by Fe-Co compound is 200 mAh g−1 despite the rapid specific capacity fading. To gain a deeper understanding of the capacity decay suffered by these compounds, further investigation was conducted to explore the evolution of compounds during the electrochemical measurements. It has been attributed to the following reasons: 1. Thermodynamic instability results in the transformation/damage of two of the chain structures (for the Fe-Ni and Fe-Co compounds) during heat treatment on electrodes, a crucial step in electrod preparation; 2. The acidic nature of the electrolyte triggers the destruction of the chain structure, with the appearance of partial reduction of Fe3+ to Fe2+, and new interaction of cyano group with aluminum; 3. The high charge density of inserted Al ions makes the chain structure suffer structural damage during both the charging and discharging processes. The progressive accumulation of trapped intercalated ions hampers their involvement in the reaction, consequently decreasing electrochemical reversibility.Le développement des batteries aluminium-ion en étant encore à ses balbutiements, les chercheurs se consacrent toujours à l'exploration de matériaux hôtes appropriés et à l'étude de leurs comportements d'intercalation de l'aluminium. Ici, une série de composés à chaîne pontée cyanido de formule {[FeIII(Tp)(CN)3]2[MII(H2O)2]}n (M=Ni, Co, Mn, Zn, Cu) sont étudiés comme électrodes cathodiques pour les batteries aluminium-ion avec le liquide ionique [EMIm]Cl-AlCl3 (chlorure de 1-éthyl-3-méthylimidazolium-AlCl3) comme électrolyte. Les propriétés électrochimiques suggèrent que Fe3+/Fe2+ est le couple redox-actif pendant les processus d'intercalation et de désintercalation de l'aluminium de ces composés, et la capacité spécifique maximale observée obtenue par le composé Fe-Co est de 200 mAh g−1 malgré la diminution rapide de la capacité spécifique. Pour mieux comprendre la décroissance de capacité subie par ces composés, des recherches plus approfondies ont été menées pour explorer l'évolution des composés au cours des mesures électrochimiques. Français On l'attribue aux raisons suivantes : 1. L'instabilité thermodynamique entraîne la transformation/l'endommagement de deux des structures de chaîne (pour les composés Fe-Ni et Fe-Co) pendant le traitement thermique des électrodes, une étape cruciale dans la préparation des électrodes ; 2. La nature acide de l'électrolyte déclenche la destruction de la structure de la chaîne, avec l'apparition d'une réduction partielle de Fe3+ en Fe2+, et une nouvelle interaction du groupe cyano avec l'aluminium ; 3. La densité de charge élevée des ions Al insérés fait que la structure de la chaîne subit des dommages structurels pendant les processus de charge et de décharge. L'accumulation progressive d'ions intercalés piégés entrave leur implication dans la réaction, diminuant par conséquent la réversibilité électrochimique