Maëva Almeida, Daniel Dudzinski, Catherine Amiel, Jean-Michel Guigner,Sylvain Prévost, Clémence Le Coeur and Fabrice Cousin
Here, we describe the behavior of mixtures of stearic acid (SA) and its hydroxylated counterpart 12-hydroxystearic acid (12-HSA) in aqueous mixtures at room temperature as a function of the 12-HSA/SA mole ratio R. The morphologies of the self-assembled aggregates are obtained through a multi-structural approach that combines confocal and cryo-TEM microscopies with small-angle neutron scattering (SANS) and wide-angle X-ray scattering (WAXS) measurements, coupled with rheology measurements. Fatty acids are solubilized by an excess of ethanolamine counterions, so that their heads are negatively charged. A clear trend towards partitioning between the two types of fatty acids is observed, presumably driven by the favorable formation of a H-bond network between hydroxyl OH function on the 12th carbon. For all R, the self-assembled structures are locally lamellar, with bilayers composed of crystallized and strongly interdigitated fatty acids. At high R, multilamellar tubes are formed. The doping via a low amount of SA molecules slightly modifies the dimensions of the tubes and decreases the bilayer rigidity. The solutions have a gel-like behavior. At intermediate R, tubes coexist in solution with helical ribbons. At low R, local partitioning also occurs, and the architecture of the self-assemblies associates the two morphologies of the pure fatty acids systems: they are faceted objects with planar domains enriched in SA molecules, capped with curved domains enriched in 12-HSA molecules. The rigidity of the bilayers is strongly increased, as well their storage modulus. The solutions remain, however, viscous fluids in this regime.
Simeon Minic, Burkhard Annighöfer, Milos Milcic, François Maignen, Annie Brûlet, Sophie Combet
Apomyoglobin (apoMb), a model protein in biochemistry, exhibits a strong propensity to bind various ligands, which makes it a good candidate as a carrier of bioactive hydrophobic drugs. The stability of its hydrophobic pocket determines its potential as a carrier of bioactive compounds. High pressure (HP) is a potent tool for studying protein stability, revealing the specific role of hydrophobic cavities in unfolding. We probed the effects of biliverdin (BV) binding and its complex with Zn2+ ions on the structure and HP stability of apoMb. CD spectroscopy and SAXS measurements revealed that BV and BV-Zn2+ complexes make the apoMb structure more compact with higher α-helical content. We performed in situ HP measurements of apoMb intrinsic fluorescence to demonstrate the ability of BV to stabilise apoMb structure at HP conditions. Furthermore, the presence of Zn2+ within the apoMb-BV complex significantly enhances the BV stabilisation effect. In situ visible absorption study of BV chromophore confirmed the ability of Zn2+ to increase the stability of apoMb-BV complex under HP: the onset of complex dissociation is shifted by ∼100 MPa in presence of Zn2+. By combining HP-fluorescence and HP-visible absorption spectroscopy, our strategy highlights the crucial role of tetrapyrrole-metal complexes in stabilising apoMb hydrophobic pocket.
Somia Haouache, Yu Chen, Clara Jimenez-Saelices, Fabrice Cousin, Pan Chen, Yoshiharu Nishiyama, François Jerome, and Isabelle Capron
Nanocelluloses can be used to stabilize oil–water surfaces, forming so-called Pickering emulsions. In this work, we compare the organization of native and mercerized cellulose nanocrystals (CNC-I and CNC-II) adsorbed on the surface of hexadecane droplets dispersed in water at different CNC concentrations. Both types of CNCs have an elongated particle morphology and form a layer strongly adsorbed at the interface. However, while the layer thickness formed with CNC-I is independent of the concentration at 7 nm, CNC-II forms a layer ranging from 9 to 14 nm thick with increasing concentration, as determined using small-angle neutron scattering with contrast-matched experiments. Molecular dynamics (MD) simulations showed a preferred interacting crystallographic plane for both crystalline allomorphs that exposes the CH groups (100 and 010) and is therefore considered hydrophobic. Furthermore, this study suggests that whatever the allomorph, the migration of CNCs to the oil–water interface is spontaneous and irreversible and is driven by both enthalpic and entropic processes.
Céline JAUDOIN, Isabelle GRILLO, Fabrice COUSIN, Maria GEHRKE, Malika OULDALI, Ana-Andreea ARTENI, Luc PICTON, Christophe RIHOUEY, Fanny SIMELIERE, Amélie BOCHOT, Florence AGNELY
Mixtures of hyaluronic acid (HA) with liposomes lead to hybrid colloid–polymer systems with a great interest in drug delivery. However, little is known about their microstructure. Small angle neutron scattering (SANS) is a valuable tool to characterize these systems in the semi-dilute entangled regime (1.5% HA) at high liposome concentration (80 mM lipids). The objective was to elucidate the influence of liposome surface (neutral, cationic, anionic or anionic PEGylated), drug encapsulation and HA concentration in a buffer mimicking biological fluids (37 °C). First, liposomes were characterized by SANS, cryo-electron microscopy, and dynamic light scattering and HA by SANS, size exclusion chromatography, and rheology. Secondly, HA-liposome mixtures were studied by SANS. In HA, liposomes kept their integrity. Anionic and PEGylated liposomes were in close contact within dense clusters with an amorphous organization. The center-to-center distance between liposomes corresponded to twice their diameter. A depletion mechanism could explain these findings. Encapsulation of a corticoid did not modify this organization. Cationic liposomes formed less dense aggregates and were better dispersed due to their complexation with HA. Liposome surface governed the interactions and microstructure of these hybrid systems.
Les clusters métalliques dans la gamme de 10-300 atomes (diamètre 1 à 2 nm) forment une classe spécifique de matériaux dont les propriétés dépendent fortement de leur taille en raison de la discrétisation de leurs niveaux d’énergie. Cette spécificité leur apporte des propriétés originales pouvant ouvrir de multiples applications dans des dispositifs électroniques, optiques ou catalytiques. Ces applications exigent cependant d’exploiter la réponse collective d'assemblages, avec une organisation contrôlée de ces clusters, dont le plus prometteur, bien que difficile à réaliser, requiert la formation de films minces organisés à grande échelle.
L'équipe du LLB en collaboration avec le Département de Chimie-Physique de Genève, a ainsi étudié la formation et le dépôt de films minces de nanoclusters d’or stabilisés par un thiolate (Au38-R), par la technique de Langmuir-Blodgett (LB), afin d'obtenir des films bien organisés à grande échelle. Les propriétés structurales des films déposés sont caractérisées par la réflectivité de rayons-X, et les propriétés mécaniques sont sondées quantitativement par une technique originale : la microscopie à force atomique bimodale, à double cantilevers de rigidité contrastée.
Anne-Sophie Robbes, Jacques Jestin, Florian Meneau, Florent Dalmas, François Boué, and Fabrice Cousin,
Macromolecules 2022, 55, 15, 6876–6889.
We present a combined detailed monitoring of the respective evolutions of the structure of fillers by SAXS and conformation of polymeric chains by SANS under uniaxial stretching at various elongation ratios in a nanocomposite made of spherical magnetic nanoparticles of γFe2O3 dispersed in a matrix of polystyrene (PS) chains. We can make the structure of fillers in the nanocomposite before stretching very anisotropic, as we demonstrated in reference (Macromolecules,2011,44(22), 8858–8865), thanks to the appliance of a magnetic field during the nanocomposite processing that induces the formation of nanoparticle chains aligned along the direction of the field, either parallel or perpendicular to the subsequent stretching. This gives rise to very anisotropic mechanical properties, and the structure of fillers evolves very differently. In the parallel case, there is a rupture of the chains of nanoparticles into smaller subunits that progressively align completely in the stretching direction. In the perpendicular case, the chains first rotate, to eventually reorient along the stretching direction, gradually breaking themselves. Finally, at a very large elongation rate (λ = 6), the organization of nanoparticles in both cases converge toward a common structure made of small chains of nanoparticles completely oriented along the stretching. The chain conformation is directly obtained by SANS as we probed samples containing 25% PSH/75% PSD chains, taking benefit from the fact that the neutron scattering length density of PSD is similar to the one of γFe2O3. Strikingly, the deformation of the polymer chains is the same as in the reference PS matrix without fillers, whatever stretching is parallel and perpendicular to the chains of nanoparticles at λ = 3. The chains scattering exhibit the typical features of those of the former studies of relaxation during or after stretching on pure melts, accounting for the relatively slow deformation rate, the distance from Tg (15 °C) their average masses, and their large polydispersity.
Michal Swierczewski, Fabrice Cousin, Ewa Banach, Arnulf Rosspeintner, Latevi Max Lawson Daku, Abolfazl Ziarati, Rania Kazan, Gunnar Jeschke, Raymond Azoulay, Lay-Theng Lee, Thomas Bürgi
A bidentate chiral dithiol (diBINAS) is utilised to bridge Au25 nanoclusters to form oligomers. Separation by size allows the isolation of fractions that are stable thanks to the bidentate nature of the linker. The structure of the products is elucidated by small-angle X-ray scattering and calculated using density functional theory. Additional structural details are studied by diffusion-ordered nuclear magnetic resonance spectroscopy, transmission electron microscopy and matrix-assisted laser desorption/ionization time of flight mass spectrometry. Significant changes in the optical properties are analysed by UV-Vis and fluorescence spectroscopies, with the latter demonstrating a strong emission enhancement. Furthermore, the emergent chiral characteristics are studied by circular dichroism. Due to the geometry constraints of the nanocluster assemblies, diBINAS can be regarded as a templating molecule, taking a step towards the directed self-assembly of metal clusters.
Florian Turbant, Jehan Waeytens, Camille Campidelli, Marianne Bombled, Denis Martinez, Axelle Grélard, Birgit Habenstein, Vincent Raussens, Marisela Velez, Frank Wien, Véronique Arluison
Hfq is a pleiotropic regulator that mediates several aspects of bacterial RNA metabolism. The protein notably regulates translation efficiency and RNA decay in Gram-negative bacteria, usually via its interaction with small regulatory RNAs. Previously, we showed that the Hfq C-terminal region forms an amyloid-like structure and that these fibrils interact with membranes. The immediate consequence of this interaction is a disruption of the membrane, but the effect on Hfq structure was unknown. To investigate details of the mechanism of interaction, the present work uses different in vitro biophysical approaches. We show that the Hfq C-terminal region influences membrane integrity and, conversely, that the membrane specifically affects the amyloid assembly. The reported effect of this bacterial master regulator on membrane integrity is discussed in light of the possible consequence on small regulatory RNA-based regulation.
Sophie Combet, Françoise Bonneté, Stéphanie Finet, Alexandre Pozza, Christelle Saade, Anne Martel, Alexandros Koutsioubas, Jean-Jacques Lacapère, Biochimie (2022) in press.
The translocator protein (TSPO) is a ubiquitous transmembrane protein of great pharmacological interest thanks to its high affinity to many drug ligands. The only high-resolution 3D-structure known for mammalian TSPO was obtained by NMR for the mouse mTSPO in DPC detergent only in presence of the high-affinity PK 11195 ligand. An atomic structure of free-ligand mTSPO is still missing to better understand the interaction of ligands with mTSPO and their effects on the protein conformation.
Les alliages à "haute entropie" forment une nouvelle classe de matériaux cristallins, qui se caractérise par des variations aléatoires dans la composition chimique de chaque maille, sans altérer l’ordre géométrique à longue distance. Constitués d'un mélange de type "solution solide" d'au moins 4 métaux, ces matériaux au désordre partiel (chimique) possèdent des propriétés thermiques qui relèvent à la fois des cristaux, avec des modes de vibrations thermiques (phonons) bien définis, et des verres, avec une longueur de propagation de ces phonons bien plus courte que celles des cristaux.
Ces cristaux chimiquement désordonnés présentent ainsi une faible conductivité thermique, qui pourrait être exploitée en thermoélectricité (conversion directe de chaleur en électricité par effet Seebeck).
Ellen Fogh, Bastian Klemke, Manfred Reehuis, Philippe Bourges, Christof Niedermayer, Sonja Holm-Dahlin, Oksana Zaharko, Jürg Schefer, Andreas B. Kristensen, Michael K. Sørensen, Sebastian Paeckel, Kasper S. Pedersen, Rasmus E. Hansen, Alexandre Pages, Kimmie K. Moerner, Giulia Meucci, Jian-Rui Soh, Alessandro Bombardi, David Vaknin, Henrik. M. Rønnow, Olav F. Syljuåsen, Niels B. Christensen and Rasmus Toft-Petersen
Control of magnetization and electric polarization is attractive in relation to tailoring materials for data storage and devices such as sensors or antennae. In magnetoelectric materials, these degrees of freedom are closely coupled, allowing polarization to be controlled by a magnetic ﬁeld, and magnetization by an electric ﬁeld, but the magnitude of the effect remains a challenge in the case of single-phase magnetoelectrics for applications. We demonstrate that the magnetoelectric properties of the mixed-anisotropy antiferromagnet LiNi1−xFexPO4 are profoundly affected by partial substitution of Ni2+ ions with Fe2+ on the transition metal site. This introduces random site-dependent single-ion anisotropy energies and causes a lowering of the magnetic symmetry of the system. In turn, magnetoelectric couplings that are symmetry-forbidden in the parent compounds, LiNiPO4 and LiFePO4, are unlocked and the dominant coupling is enhanced by almost two orders of magnitude. Our results demonstrate the potential of mixed-anisotropy magnets for tuning magnetoelectric properties.
I. V. Golosovsky, I. A. Kibalin, A. Gukasov, A. G. Roca, A. López-Ortega, M. Estrader, M. Vasilakaki, K. N. Trohidou, T. C. Hansen, I. Puente-Orench, E. Lelièvre-Berna, J. Nogués
Heterogeneous bi-magnetic nanostructured systems have had a sustained interest during the last decades owing to their unique magnetic properties and the wide range of derived potential applications. However, elucidating the details of their magnetic properties can be rather complex. Here, a comprehensive study of Fe3O4/Mn3O4 core/shell nanoparticles using polarized neutron powder diffraction, which allows disentangling the magnetic contributions of each of the components, is presented. The results show that while at low fields the Fe3O4 and Mn3O4 magnetic moments averaged over the unit cell are antiferromagnetically coupled, at high fields, they orient parallel to each other. This magnetic reorientation of the Mn3O4 shell moments is associated with a gradual evolution with the applied field of the local magnetic susceptibility from anisotropic to isotropic. Additionally, the magnetic coherence length of the Fe3O4 cores shows some unusual field dependence due to the competition between the antiferromagnetic interface interaction and the Zeeman energies. The results demonstrate the great potential of the quantitative analysis of polarized neutron powder diffraction for the study of complex multiphase magnetic materials.
|Le LLB et le SPEC s'équipent d'un four à image pour la croissance de monocristaux par la méthode de fusion de zone flottante. Cet équipement permettra de réaliser des monocristaux orientés de taille centimétrique et de haute pureté chimique, pour l’étude des matériaux quantiques (composés supraconducteurs, multiferroïques ou multifonctionnels...), jusqu’au magnétisme quantique dans des systèmes de basse dimension.|
Özge Azeri, Dennis Schönfeld, Bin Dai, Uwe Keiderling, Laurence Noirez and Michael Gradzielski
Block copolymers synthesized via Atom Transfer Radical Polymerization from alkyl acrylate and t-butyl acrylate and the subsequent hydrolysis of the t-butyl acrylate to acrylic acid were systematically varied with respect to their hydrophobic part by the variation in the alkyl chain length and the degree of polymerisation in this block. Depending on the architecture of the hydrophobic part, they had a more or less pronounced tendency to form copolymer micelles in an aqueous solution. They were employed for the preparation of IPECs by mixing the copolymer aggregates with the polycations polydiallyldimethylammonium chloride (PDADMAC) or q-chit. The IPEC structure as a function of the composition was investigated by Static Light and Small Angle Neutron Scattering. For weakly-associated block copolymers (short alkyl chain), complexation with polycation led to the formation of globular complexes, while already existing micelles (long alkyl chain) grew further in mass. In general, aggregates became larger upon the addition of further polycation, but this growth was much more pronounced for PDADMAC compared to q-chit, thereby leading to the formation of clusters of aggregates. Accordingly, the structure of such IPECs with a hydrophobic block depended largely on the type of complexing polyelectrolyte, which allowed for controlling the structural organisation via the molecular architecture of the two oppositely charged polyelectrolytes.
Eni Kume, Nicolas Martin, Peter Dunne, Patrick Baroni and Laurence Noirez
Molecules 2022, 27(22), 7829.
Mesoscopic shear elasticity has been revealed in ordinary liquids both experimentally by reinforcing the liquid/surface interfacial energy and theoretically by nonextensive models. The elastic effects are here examined in the frame of small molecules with strong electrostatic interactions such as room temperature ionic liquids [emim][Tf2N] and nitrate solutions exhibiting paramagnetic properties. We first show that these charged fluids also exhibit a nonzero lowfrequency shear elasticity at the submillimeter scale, highlighting their resistance to shear stress. A neutron scattering study completes the dynamic mechanical analysis of the paramagnetic nitrate solution, evidencing that the magnetic properties do not induce the formation of a structure in the solution. We conclude that the elastic correlations contained in liquids usually considered as viscous away from any phase transition contribute in an effective way to collective effects under external stress or mechanical and magnetic fields.