Faits marquants scientifiques 2024

Nina Královič-Kanjaková, Ali Asi Shirazi, Lukáš Hubčík, Mária Klacsová, Atoosa Keshavarzi, Juan Carlos Martínez, Sophie Combet, José Teixeira, and Daniela Uhríková

The use of an exogenous pulmonary surfactant (EPS) to deliver other relevant drugs to the lungs is a promising strategy for combined therapy. We evaluated the interaction of polymyxin B (PxB) with a clinically used EPS, the poractant alfa Curosurf (PSUR). The effect of PxB on the protein-free model system (MS) composed of four phospholipids (diC16:0PC/16:0–18:1PC/16:0–18:2PC/16:0–18:1PG) was examined in parallel to distinguish the specificity of the composition of PSUR. We used several experimental techniques (differential scanning calorimetry, small- and wide-angle X-ray scattering, small-angle neutron scattering, fluorescence spectroscopy, and electrophoretic light scattering) to characterize the binding of PxB to both EPS. Electrostatic interactions PxB–EPS are dominant. The results obtained support the concept of cationic PxB molecules lying on the surface of the PSUR bilayer, strengthening the multilamellar structure of PSUR as derived from SAXS and SANS. A protein-free MS mimics a natural EPS well but was found to be less resistant to penetration of PxB into the lipid bilayer. PxB does not affect the gel-to-fluid phase transition temperature, T_m, of PSUR, while T_m increased by ∼+ 2 °C in MS. The decrease of the thickness of the lipid bilayer (d_L) of PSUR upon PxB binding is negligible. The hydrophobic tail of the PxB molecule does not penetrate the bilayer as derived from SANS data analysis and changes in lateral pressure monitored by excimer fluorescence at two depths of the hydrophobic region of the bilayer. Changes in d_L of protein-free MS show a biphasic dependence on the adsorbed amount of PxB with a minimum close to the point of electroneutrality of the mixture. Our results do not discourage the concept of a combined treatment with PxB-enriched Curosurf. However, the amount of PxB must be carefully assessed (less than 5 wt % relative to the mass of the surfactant) to avoid inversion of the surface charge of the membrane

https://doi.org/10.1021/acs.langmuir.3c03746

On De Gennes narrowing of fluids confined at the molecular scale in nanoporous materials
Wanda Kellouai, Jean-Louis Barrat, Patrick Judeinstein, Marie Plazanet, Benoit Coasne, J. Chem. Phys. 160, 024113 (2024).

Beyond well-documented confinement and surface effects arising from the large internal surface and severely confining porosity of nanoporous hosts, the transport of nanoconfined fluids remains puzzling in many aspects. With striking examples such as memory, i.e., non-viscous effects, intermittent dynamics, and surface barriers, the dynamics of fluids in nanoconfinement challenge classical formalisms (e.g., random walk, viscous/advective transport)—especially for molecular pore sizes. In this context, while molecular frameworks such as intermittent Brownian motion, free volume theory, and surface diffusion are available to describe the self-diffusion of a molecularly confined fluid, a microscopic theory for collective diffusion (i.e., permeability), which characterizes the flow induced by a thermodynamic gradient, is lacking. Here, to fill this knowledge gap, we invoke the concept of “De Gennes narrowing,” which relates the wavevector-dependent collective diffusivity D₀(q) to the fluid structure factor S(q). First, using molecular simulation for a simple yet representative fluid confined in a prototypical solid (zeolite), we unravel an essential coupling between the wavevector-dependent collective diffusivity and the structural ordering imposed on the fluid by the crystalline nanoporous host. Second, despite this complex interplay with marked Bragg peaks in the fluid structure, the fluid collective dynamics is shown to be accurately described through De Gennes narrowing. Moreover, in contrast to the bulk fluid, the departure from De Gennes narrowing for the confined fluid in the macroscopic limit remains small as the fluid/solid interactions in severe confinement screen collective effects and, hence, weaken the wavevector dependence of collective transport.

Universality of q=1/2 orbital magnetism in the pseudogap phase of the high-Tc superconductor YBa₂Cu₃O_6+x
Dalila Bounoua, Yvan Sidis, Martin Boehm, Paul Steffens, Toshinao Loew, Lin Shan Guo, Jun Qian, Xin Yao, and Philippe Bourges, Phys. Rev. B 108 (2023) 214408.

Several decades of debate have centered around the nature of the enigmatic pseudogap state in high-temperature superconducting copper oxides. Recently, we reported polarized neutron diffraction measurements that suggested the existence of a magnetic texture bound to the pseudogap phase [Bounoua et al. Commun. Phys. 5, 268 (2022)]. Such a magnetic texture is likely to involve the spontaneous appearance of loop currents within the CuO2 unit cells, which give birth to complex correlated patterns. In the underdoped YBa2Cu3O6.6, the magnetic structure factor of such an orbital magnetic texture gives rise to two distinct magnetic responses at q=0 and q=1/2. As this pattern alters the lattice translation invariance, such a state of matter could contribute to an instability of the Fermi surface. Here, we report polarized neutron scattering measurements on a nearly optimally doped high-quality single crystal of YBa2Cu3O6.9 that exhibits the same q=1/2 magnetism and a weakly overdoped YBa2Cu3O7 sample where this signal is no longer sizable. The in-plane and out-of-plane magnetic neutron scattering intensities in YBa2Cu3O6.9 (at q=1/2) and YBa2Cu3O6.85 (at q=0), reported previously, display the same temperature-dependent hallmarks. The magnitudes of both q=0 and q=1/2 magnetic signals further exhibit the same trends upon doping in YBa2Cu3O6+x, confirming that they are likely intertwined.

https://doi.org/10.1103/PhysRevB.108.214408

M. Warburton, J.M. Ablett, J.-P. Rueff, P. Baroni, L. Paolasini, L. Noirez

We examine the influence at room temperature of the deposit of a water layer on the phonon dynamics of a solid. It is shown that the water wetting at the surface of an Alumina monocrystal has deep effects on acoustic phonons, propagating over several hundred µm distance and taking place on a relatively long time scale. The effect of the wetting at the boundary is two-fold: a hardening of both transverse and longitudinal acoustic phonons is observed as well as a relaxation of internal stresses. These acoustic phonon energy changes were observed by inelastic X-ray scattering up to 40 meV energy loss, allowing us to probe the solid at different depths from the surface.

https://doi.org/10.1016/j.molliq.2023.123342