Laboratoire Léon Brillouin

UMR12 CEA-CNRS, Bât. 563 CEA Saclay

91191 Gif sur Yvette Cedex, France

+33-169085241 llb-sec@cea.fr

BD diffusons les neutrons

Faits marquants scientifiques 2019

19 juillet 2019

The response of a position-sensitive Li-glass scintillator detector to alpha-particles from a collimated 241Am source scanned across the face of the detector has been measured. Scintillation light was read out by an 8x8 pixel multi-anode photomultiplier and the signal amplitude for each pixel has been recorded for every position on a scan. The pixel signal is strongly dependent on position and in general several pixels will register a signal (a hit) above a given threshold. The effect of this threshold on hit multiplicity is studied, with a view to optimize the single-hit efficiency of the detector.

https://doi.org/10.1016/j.nima.2019.03.014

 

04 mai 2019

B. Annighöfer , A. Hélary, A. Brulet, A. Colas de la Noue, C. Loupiac and S. Combet
Review of Scientific Instruments 90 (2019) 025106

Abstract :

We report on a high pressure (HP) cell designed for the determination of the structure of molecular solutions by small-angle neutron scattering (SANS). The HP cell is fitted up with two thick metallic windows that make the device very resistant under hydrostatic pressures up to 600 MPa (or 6 kbar). The metallic windows are removable, offering the possibility to adapt the HP cell to a given study with the pressure desired on an appropriate spatial range to study the structure of various molecular solutions by SANS. In this context, we report the absorption, transmission, and scattering properties of different metallic windows. Finally, we describe, as a proof of principle, the solution structure changes of myoglobin, a small globular protein.

https://doi.org/10.1063/1.5051765

11 mars 2019

Dans la catégorie "Appui direct à la recherche", l'équipe technique "Petits angles" du Laboratoire Léon Brillouin (LLB, UMR 12 CEA/DRF-CNRS/InP ) est distingué en 2019 d'un "Cristal"* du CNRS.

L'équipe, avec Annie Brulet, Patrice Permingeat, Gaston Exil, William Josse, Sylvain Désert, Pascal Lavie, Fabien Prunes du groupe "INFRA" et Marc Detrez, Arnaud Helary, Sébastien Gautrot du groupe MMB, conçoit, construit et met en œuvre des spectromètres de diffusion de neutrons aux petits angles**, et possède un savoir-faire de très haut niveau lui permettant de proposer à la communauté des instruments au meilleur niveau mondial.

(**) Voir en particulier les spectromètres du LLB : G51-PA20 et G23-PAXY.


(*) En 2018, le CNRS décerne une nouvelle distinction "le Cristal collectif", qui récompense des équipes d'ingénieurs, chercheurs et techniciens pour leur projet collectif innovant ou technique remarquable. Ce prix qui sera remis tous les ans, vient enrichir les "Talents du CNRS" (médailles du CNRS et projets ERC). Les projets lauréats du "Cristal collectif" concernent tant l’accompagnement que l’appui direct à la recherche et réunissent des compétences pluridisciplinaires.

22 septembre 2019

Daniela Russo, Maya Dimova Lambreva, Christiane Alba Simionesco, Pierre Sebban,and Giuseppina Rea

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.

DOI : https://doi.org/10.1016/j.bpj.2019.03.029

 

18 septembre 2019
Des chercheurs de l’I2BC@Saclay et de l’UMR NIMBE, en collaboration avec le Laboratoire Léon Brillouin (LLB), ont analysé la structure de la couronne composée de deux protéines modèles adsorbées sur des nanoparticules de silice, en utilisant la technique de diffusion des neutrons aux petits angles. Ils montrent que les structures formées sont de véritables nanoassemblages contrôlés, dans lesquels les protéines conservent leur forme.

 

20 juin 2019

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

30 mai 2019

"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.

04 mai 2019

B. Annighöfer , A. Hélary, A. Brulet, A. Colas de la Noue, C. Loupiac and S. Combet
Review of Scientific Instruments 90 (2019) 025106

Abstract :

We report on a high pressure (HP) cell designed for the determination of the structure of molecular solutions by small-angle neutron scattering (SANS). The HP cell is fitted up with two thick metallic windows that make the device very resistant under hydrostatic pressures up to 600 MPa (or 6 kbar). The metallic windows are removable, offering the possibility to adapt the HP cell to a given study with the pressure desired on an appropriate spatial range to study the structure of various molecular solutions by SANS. In this context, we report the absorption, transmission, and scattering properties of different metallic windows. Finally, we describe, as a proof of principle, the solution structure changes of myoglobin, a small globular protein.

https://doi.org/10.1063/1.5051765

21 avril 2019

Les membranes d’oxyde d’aluminium nanoporeuses sont des systèmes modèles permettant d’étudier le comportement de la matière sous confinement. Leurs utilisations pour des études de nano-moulage, de microfluidique ou en biologie sont ainsi nombreuses. Une équipe du laboratoire PHENIX (Université Pierre et Marie Curie) et du laboratoire Léon Brillouin (IRAMIS, CEA Saclay) ont étudié in-situ l’adsorption de polymères chargés dans ces matériaux modèles par une approche combinant la réflectivité de neutrons et la microscopie électronique.

01 avril 2019

Andrés Marcoleta, Frank Wien, Véronique Arluison, Rosalba Lagos, Rafael Giraldo
Bacterial Amyloids (2019)

Amyloids are supramolecular protein assemblies based on fibrillar arrangements of β‐sheets that were first found as linked to neurodegenerative and systemic human diseases. However, there is now overwhelming evidence on alternative roles of amyloids as functional assemblies and as epigenetic determinants of beneficial traits, both in Fungi and Metazoa. Bacteria also use amyloids as functional devices, mainly as extracellular scaffolds in biofilms, but there is increasing evidence for functional roles of amyloids in the bacterial cytosol, and these have enabled to engineer minimal models of a ‘generic’ amyloid disease. Amyloids are thus key players in the physiology of bacteria and versatile building blocks in synthetic biology.

 

21 décembre 2019

M. Ruminy, S. Guitteny, J. Robert, L.-P. Regnault, M. Boehm, P. Steffens, H. Mutka, J. Ollivier, U. Stuhr, J. S. White, B. Roessli, L. Bovo, C. Decorse, M. K. Haas, R. J. Cava, I. Mirebeau, M. Kenzelmann, S. Petit, and T. Fennell

Tb2Ti2O7 presents an ongoing conundrum in the study of rare-earth pyrochlores. Despite the expectation that it should be the prototypical unfrustrated noncollinear Ising antiferromagnet on the pyrochlore lattice, it presents a puzzling correlated state that persists to the lowest temperatures. Effects which can reintroduce frustration or fluctuations are therefore sought, and quadrupolar operators have been implicated. One consequence of strong quadrupolar effects is the possible coupling of magnetic and lattice degrees of freedom, and it has previously been shown that a hybrid magnetoelastic mode with both magnetic and phononic character is formed in Tb2Ti2O7 by the interaction of a crystal field excitation with a transverse-acoustic phonon. Here, using polarized and unpolarized inelastic neutron scattering, we present a detailed characterization of the magnetic and phononic branches of this magnetoelastic mode, particularly with respect to their composition, the anisotropy of any magnetic fluctuations, and also the temperature dependence of the different types of fluctuation that are involved. We also examine the dispersion relations of the exciton branches that develop from the crystal field excitation in the same temperature regime that the coupled mode appears, and find three quasidispersionless branches where four are expected, each with a distinctive structure factor indicating that they are nonetheless cooperative excitations. We interpret the overall structure of the spectrum as containing four branches, one hybridized with the phonons and gaining a strong dispersion, and three remaining dispersionless.

https ://doi.org/10.1103/PhysRevB.99.224431

25 novembre 2019

A. S. Sukhanov, Praveen Vir, A. S. Cameron, H. C. Wu, N. Martin, S. Mühlbauer, A. Heinemann, H. D. Yang, C. Felser, and D. S. Inosov

The cubic chiral helimagnets with the P213 space group represent a group of compounds in which the stable skyrmion-lattice state is experimentally observed. The key parameter that controls the energy landscape of such systems and determines the emergence of a topologically nontrivial magnetic structure is the Dzyaloshinskii-Moriya interaction (DMI). Chemical substitution is recognized as a convenient instrument to tune the DMI in real materials and has been successfully utilized in studies of a number of chiral magnets, such as MnSi, FeGe, MnGe, and others. In our study, we applied small-angle neutron scattering to investigate how chemical substitution influences the skyrmionic properties of an insulating helimagnet Cu2OSeO3 when Cu ions are replaced by either Zn or Ni. Our results demonstrate that the DMI is enhanced in the Ni-substituted compounds (Cu,Ni)2OSeO3, but weakened in (Cu,Zn)2OSeO3. The observed changes in the DMI strength are reflected in the magnitude of the spin-spiral propagation vector and the temperature stability of the skyrmion phase.

https://doi.org/10.1103/PhysRevB.100.184408

23 octobre 2019

N. Martin, I. Mirebeau, C. Franz, G. Chaboussant, L. N. Fomicheva, and A. V. Tsvyashchenko

We study the helimagnetic ground state of the MnGe cubic alloy using small-angle neutron scattering and a high-resolution method, the so-called MIEZE spectroscopy. Upon cooling below the Néel temperature TN = 170(5) K, we observe the proliferation of long-wavelength gapless spin fluctuations, concomitant with a continuous evolution of the helical correlation length. These fluctuations disappear at Tcom = 32(5) K when the helical period becomes commensurate with the lattice. We propose to describe this intermediate phase as a soliton lattice, promoting nonlinear collective modes, or phasons, over a large temperature interval. We discuss the possible relevance of our results to the previously observed magnetotransport anomalies.

https://doi.org/10.1103/PhysRevB.99.100402

25 septembre 2019

La physique de la matière condensée repose sur quelques concepts fondateurs, comme le paradigme de Néel (avec sa description des ordres magnétiques classiques), la théorie des liquides de Fermi (avec le concept de quasi-particule), et la théorie de Landau des transitions de phases (mettant en exergue le concept de brisure spontanée de symétrie). Toutefois, de nouvelles découvertes bouleversent ces dogmes, mettant en lumière le rôle des fortes corrélations entre quasi-particules, la découverte de transitions de phase topologiques, ou l’observation de nouveaux états de la matière.

Ce sont par exemple les liquides ou glaces de spin, les états de boucle de courant dans certains oxydes, ou la description de nouvelles transitions de phase, sans symétrie brisée, mettant en jeu le confinement/déconfinement d’objets topologiques comme les vortex. Ceci suscite et motive toujours plus avant l’étude de la matière et des "matériaux quantiques", pour acquérir de nouvelles connaissances fondamentales et en tirer le meilleur parti pour des applications diverses. Ces nouveaux états de la matière se rencontrent dans des conditions ultimes et notamment aux très basses températures, dans la gamme du milliKelvin (mK).

Dans cette optique, et pour accompagner cette recherche, notre équipe du LLB responsable de l’opération du diffractomètre de neutrons G4-1 (LLB-Orphée) a fait l’acquisition d’un nouvel appareil permettant de réaliser des mesures de diffraction des neutrons jusqu’à des températures ultra-basses (40 mK).

 

 

25 janvier 2019

M. Deutsch, W. Peng, P. Foury-Leylekian, V. Balédent, S. Chattopadhyay, M. T. Fernandez-Diaz, T. C. Hansen, A. Forget, D. Colson, M. Greenblatt, M.-B. Lepetit, S. Petit, and I. Mirebeau

The magnetic structure of TbMn2O5 and DyMn2O5 multiferroics has been studied by high-pressure neutron diffraction in a large pressure range up to 6.6 GPa. In both cases, we observe a pressure-induced commensurate magnetic phase with propagation vector ( 1/2 0 1/2 ), growing with pressure at the expense of the ambient pressure phases. Being previously observed in YMn2O5 and PrMn2O5, this phase is most likely a generic feature of the RMn2O5 multiferroic family. A simple model is proposed to explain qualitatively the emergence of this pressure-induced phase. Differences between TbMn2O5 and DyMn2O5 behaviors at ambient and low pressures provide clues on the interaction scheme.

DOI : http://dx.doi.org/10.1103/PhysRevB.98.024408


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