Li Shi, Florent Carn, Arsen Goukassov, Eric Buhler, and François Boué

Mixing negatively charged polyelectrolyte (PEL) with positively charged gold nanoparticles (Au NPs) in aqueous solution results in electrostatics complexes of different shapes and compactness. Here, when complexing with a semirigid PEL hyaluronic acid (HA), we obtain crystals made of nanoparticles in a new region of the phase diagram, as evidenced by small-angle Xray scattering (SAXS). The Au NPs were initially well dispersed in solution; their size distribution is well controlled but does not need to be extremely narrow. The bacterial hyaluronic acid, polydispersed, is commercially available. Such rather simple materials and mixing preparation produce a highly ordered crystalline phase of electrostatic complexes. The details of the interactions between spherical nanoparticles and linear polymer chains remain to be investigated. In practice, it opens a completely new and unexpected method of complexation. It has high potential, in particular because one can take advantage of the versatility of Au NPs associated with the specificity of biopolymers, varied due to natural biodiversity.

https://dx.doi.org/10.1021/acs.langmuir.0c01064

Eni Kume, Patrick Baroni and Laurence Noirez, Scientific Reports 10 (2020) 13340.

Thermo-elasticity couples the deformation of an elastic (solid) body to its temperature and viceversa. It is a solid-like property. Highlighting such property in liquids is a paradigm shift: it requires long-range collective interactions that are not considered in current liquid descriptions. The present microthermal studies provide evidence for such solid-like correlations. It is shown that ordinary liquids emit a modulated thermal signal when applying a low frequency (Hz) mechanical shear stress. The liquid splits in several tenths microns wide hot and cold thermal bands, all varying synchronously and separately with the applied stress wave reaching a sizable amplitude of ± 0.2 °C. Thermomechanical coupling challenges fluid dynamics: it reveals that the liquid does not dissipate the energy of shear waves at low frequency, but converts it in non-uniform thermodynamic states. The dynamic thermal changes work in an adiabatic way supporting the hypothesis of the excitation of macroscopic elastic correlations whose range is limited to several tens of microns, in accordance with recent non-extensive theoretical models. The proof of thermomechanical coupling opens the way to a new generation of energy-efficient temperature converters.

Voir aussi en 2021 :

Identification of thermal response of mesoscopic liquids under mechanical excitation: from harmonic to nonharmonic thermal wave, Eni Kume and Laurence Noirez, J. Phys. Chem. B125(30)(2021) 8652.

de Oliveira-Silva, Rodrigo; Bélime, Agathe; Le Coeur, Clémence; Chennevière, Alexis; Helary, Arnaud; Cousin, Fabrice; Judeinstein, Patrick; Sakellariou, Dimitrios; Zanotti, Jean-Marc

In soft condensed matter, Small Angle Neutron Scattering (SANS) is a central tool to probe structures with characteristic sizes ranging from 1 to 100 nm. However, when used as a standalone technique, the dynamic properties of the sample are not accessible. Nuclear Magnetic Resonance (NMR) is a versatile technique which can easily probe dynamical information. Here, we report on the coupling of a low-field NMR system to a SANS instrument. We show that this original set-up makes it possible to obtain structural information and to simultaneously extract in situ on a same sample, long-range translational diffusion coefficient, T1T1 and T2T2 nuclear spin relaxation times. Such a feature is of major interest when a sample experiences a transient physical state or evolves rapidly. We illustrate the capabilities of alliancing these experimental methods by following the critical temperature-induced phase separation of a concentrated Poly(Methacrylic Acid) solution at its Lower Critical Solution Temperature. The characteristic size related to the domain growth of the polymer-rich phase of the gel is monitored by the evolution of the SANS spectra, while the dynamics of the sol phase (H₂O and polymer) is simultaneously characterized by NMR by measuring T1T1, T2T2 and the diffusion coefficient. Great care has been taken to design a cell able to optimize the thermalization of the sample and in particular its equilibration time. Details are given on the sample cell specifically designed and manufactured for these experiments. The acquisition time needed to reach good signal-to-noise ratios, for both NMR and SANS, match: it is of the order of one hour. Altogether, we show that in situ low-field NMR/SANS coupling the NMR is meaningful and is a promising experimental approach.

DOI

A. Theodoratou, L.-T. Lee, J. Oberdisse and A. Aubert-Pouëssel, Langmuir 35(20) (2019) 6620.

Abstract :

Nanofilms of about 2 nm thickness have been formed at the air–water interface using functionalized castor oil (ICO) with cross-linkable silylated groups. These hybrid films represent excellent candidates for replacing conventional polymeric materials in biomedical applications, but they need to be optimized in terms of biocompatibility, which is highly related to protein adsorption. Neutron reflectivity has been used to study the adsorption of two model proteins, bovine serum albumin and lysozyme, at the silylated oil (ICO)–water interface in the absence and presence of salt at physiologic ionic strength and pH and at different protein concentrations. These measurements are compared to adsorption at the air–water interface. While salt enhances adsorption by a similar degree at the air–water and oil–water interfaces, the impact of the oil film is significant with adsorption at the oil–water interface 3–4-fold higher compared to that at the air–water interface. Under these conditions, the concentration profiles of the adsorbed layers for both proteins indicate multilayer adsorption. The thickness of the outer layer (oil side) is close to the dimension of the minor axis of the protein molecule, ∼30 Å, suggesting a sideway orientation with the long axis parallel to the interface. The inner layer extends to 55–60 Å. Interestingly, in all cases, the composition of the oil film remains intact without significant protein penetration into the film. The optimal adsorption on these nanofilms, 1.7–2.0 mg·m^-2, is comparable to the results obtained recently on thick solid cross-linked films using a quartz crystal microbalance and atomic force microscopy, showing in particular that adsorption at these ICO film interfaces under standard physiological conditions is nonspecific. These results furnish useful information toward the elaboration of vegetable oil-based nanofilms in direct nanoscale applications or as precursor films in the fabrication of thicker macroscopic films for biomedical applications.

https://doi.org/10.1021/acs.langmuir.9b00186

"Dynamics properties of photosynthetic microorganisms probed by incoherent neutron scattering"
Daniela Russo, Maya Dimova Lambreva, Christiane Alba Simionesco, Pierre Sebban, and Giuseppina Rea
Biophysical Journal, 116 (9) (2019) 1759-1768

Studies on the dynamical properties of photosynthetic membranes of land plants and purple bacteria have been previously performed by neutron spectroscopy, revealing a tight coupling between specific photochemical reactions and macromolecular dynamics. Here, we probed the intrinsic dynamics of biotechnologically useful mutants of the green alga Chlamydomonas reinhardtii by incoherent neutron scattering coupled with prompt chlorophyll fluorescence experiments. We brought to light that single amino acid replacements in the plastoquinone (PQ)-binding niche of the photosystem II D1 protein impair electron transport (ET) efficiency between quinones and confer increased flexibility to the host membranes, expanding to the entire cells. Hence, a more flexible environment in the PQ-binding niche has been associated to a less efficient ET.Asimilar function/dynamics relationship was also demonstrated in Rhodobacter sphaeroides reaction centers having inhibited ET, indicating that flexibility at the quinones region plays a crucial role in evolutionarily distant organisms. Instead, a different functional/dynamical correlation was observed in algal mutants hosting a single amino acid replacement residing in a D1 domain far from the PQ-binding niche. Noteworthy, this mutant displayed the highest degree of flexibility, and besides having a nativelike ET efficiency in physiological conditions, it acquired novel, to our knowledge, phenotypic traits enabling it to preserve a high maximal quantum yield of photosystem II photochemistry in extreme habitats. Overall, in the nanosecond timescale, the degree of the observed flexibility is related to the mutation site; in the picosecond timescale, we highlighted the presence of a more pronounced dynamic heterogeneity in all mutants compared to the native cells, which could be related to a marked chemically heterogeneous environment.