Castany P.,INSA Rennes |
Ramarolahy A.,INSA Rennes |
Prima F.,CNRS Paris Research Institute of Chemistry |
Laheurte P.,CNRS Study of Microstructures, Mechanics and Material Sciences lab |
And 2 more authors.
Acta Materialia | Year: 2015
Mechanisms of superelasticity were investigated by in situ cyclic tensile tests performed under synchrotron X-ray radiation on Ti-24Nb-0.5N and Ti-24Nb-0.5O compositions of metastable β titanium alloys. Analyses of diffraction patterns acquired under load and after unloading for each cycle were used to determine the characteristics of the potential mechanisms of deformation in both alloys. The Ti-24Nb-0.5N alloy exhibits the conventional behavior of superelastic β titanium alloys. Synchrotron X-ray diffraction (SXRD) experiments proved that superelasticity is exclusively due to the occurrence of a stress-induced martensitic (SIM) transformation from the β phase to the α″ phase. The evolution of volume fraction of α″ martensite corresponds exactly to the variation of the recovery strain of the cyclic tensile curve. Conversely, the Ti-24Nb-0.5O alloy displays a non-conventional behavior. SXRD experiments showed a huge ability of the β phase to deform elastically until 2.1%. Surprisingly, a reversible SIM transformation also occurs in this alloy but starts after 1% of applied strain that corresponds to the yield point of the stress-strain curve. Although the SIM transformation occurs, the β phase simultaneously continues to deform elastically. The superelasticity of this alloy is unexpectedly due to a combination of a high elastic deformability of the β phase and a reversible SIM transformation. In both alloys, the lattice parameters of the α″ martensite evolve similarly in accordance with the initial texture of the β phase and the crystallography of the transformation. © 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Leydier F.,French Institute of Petroleum |
Leydier F.,CNRS Paris Research Institute of Chemistry |
Chizallet C.,French Institute of Petroleum |
Costa D.,CNRS Paris Research Institute of Chemistry |
Raybaud P.,French Institute of Petroleum
Journal of Catalysis | Year: 2015
Amorphous silica-aluminas (ASA) are prominent solids for their acidic properties. They are of first interest in catalysis, in particular for cracking reactions. Their relative acidity as compared to zeolites is a long-lasting general issue, driven by the limited knowledge of the surface structure of ASA, due to their amorphous nature. In the present contribution, thanks to a first principles approach based on our original ASA surface model, and on the study of a model mordenite zeolite (MOR), we propose a rational explanation for this feature. We compare by density functional theory calculations the ability of ASA and MOR to generate carbenium species from isobutene, versus π-complexes and alkoxide species. On ASA, carbenium species can be formed on pseudo-bridging silanols (PBS) only and are much less stable than in MOR. Then, we investigate the cracking pathway of a model alkene, 2,4,4-trimethyl-2-pentene (DIB), by quantifying the stability of relevant intermediates of carbocationic and alkoxide natures. The carbocationic pathway is favored in MOR, whereas on ASA, this pathway is strongly activated. By contrast, the PBS on ASA initiate preferentially a tertiary alkoxide route, or possibly a combined carbocationic/alkoxy route. Finally, the i-butene desorption step is also limiting in MOR due to the confinement effect induced by the zeolite pores. As a result, the higher cracking reactivity of zeolites as compared to ASA is mainly attributed to the favored nature of the carbenium route, stabilized by higher electrostatic confinement effect. © 2015 Elsevier Inc. All rights reserved.
Yang Y.,CNRS Chemistry Institute of Rennes |
Castany P.,CNRS Chemistry Institute of Rennes |
Cornen M.,CNRS Chemistry Institute of Rennes |
Prima F.,CNRS Paris Research Institute of Chemistry |
And 3 more authors.
Acta Materialia | Year: 2015
In this work, the martensitic transformation occurring in the superelastic Ti-24Nb-4Zr-8Sn alloy was investigated by tensile tests, in situ synchrotron X-ray diffraction (SXRD) and dynamic mechanical analysis (DMA). The SXRD results clearly showed the diffraction peaks related to the α″ and β phases and their evolution, under loading and unloading conditions, have highlighted the reversible stress-induced martensitic (SIM) transformation. Consequently, a three step deformation sequence was established from both SXRD analysis and tensile test characterization. On the other hand, the characteristic temperatures related to the martensitic transformation under different applied stresses have been determined from the storage modulus and the damping curves by DMA analysis. Very good accordance concerning the critical stress inducing the martensitic transformation was obtained by comparing the results obtained from SXRD, DMA and tensile tests. © 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Coffinet S.,CNRS Transfers and Interactions in Hydrosystems and Soils |
Huguet A.,CNRS Transfers and Interactions in Hydrosystems and Soils |
Williamson D.,IRD Montpellier |
Fosse C.,CNRS Paris Research Institute of Chemistry |
Derenne S.,CNRS Transfers and Interactions in Hydrosystems and Soils
Organic Geochemistry | Year: 2014
Glycerol dialkyl glycerol tetraethers (GDGTs) are membrane lipids of high molecular weight and include the isoprenoid GDGTs (iGDGTs) produced by Archaea and the branched GDGTs (brGDGTs) produced by unknown bacteria. Several indices have been developed to describe the relationship between GDGT distribution and environmental parameters: the TEX86 (tetraether index of tetraethers consisting of 86 carbons), based on the relative abundances of iGDGTs, and the MBT (methylation index of branched tetraethers) and CBT (cyclisation ratio of branched tetraethers), based on the relative abundance of brGDGTs. For soils, most studies have focused only on the relationship between brGDGT distribution and environmental parameters, without examining the iGDGT distribution. We have analysed both brGDGT and iGDGT distributions and determined GDGT-derived proxies along an altitudinal transect at Mt. Rungwe, Tanzania. MBT/CBT-derived temperature values were found to correlate linearly with altitude (R2 0.75), as observed before for the other altitudinal transects investigated. The MBT/CBT-derived temperature lapse rate along Mt. Rungwe (0.7°C/100m) was similar to the in situ measured one and was consistent with results obtained previously for an altitudinal gradient in the same region at higher altitude. This confirms the robustness of the MBT/CBT as a paleoelevation proxy in East Africa. In addition, a linear correlation (R2 0.50) between TEX86 and altitude was observed, likely reflecting the effect of the adiabatic cooling of air with altitude on iGDGT distribution. This suggests that TEX86 might be used to track temperature change in terrestrial settings, in addition to the MBT/CBT indices. © 2014 Elsevier Ltd.
Costa D.,CNRS Paris Research Institute of Chemistry |
Pradier C.-M.,CNRS Surface Science Lab |
Tielens F.,CNRS Laboratory of Condensed Matter Chemistry, Paris |
Savio L.,National Research Council Italy
Surface Science Reports | Year: 2015
Understanding the bio-physical-chemical interactions at nanostructured biointerfaces and the assembly mechanisms of so-called hybrid nano-composites is nowadays a key issue for nanoscience in view of the many possible applications foreseen. The contribution of surface science in this field is noteworthy since, using a bottom-up approach, it allows the investigation of the fundamental processes at the basis of complex interfacial phenomena and thus it helps to unravel the elementary mechanisms governing them. Nowadays it is well demonstrated that a wide variety of different molecular assemblies can form upon adsorption of small biomolecules at surfaces. The geometry of such self-organized structures can often be tuned by a careful control of the experimental conditions during the deposition process. Indeed an impressive number of studies exists (both experimental and - to a lesser extent - theoretical), which demonstrates the ability of molecular self-assembly to create different structural motifs in a more or less predictable manner, by tuning the molecular building blocks as well as the metallic substrate. In this frame, amino acids and small peptides at surfaces are key, basic, systems to be studied. The amino acids structure is simple enough to serve as a model for the chemisorption of biofunctional molecules, but their adsorption at surfaces has applications in surface functionalization, in enantiospecific catalysis, biosensing, shape control of nanoparticles or in emerging fields such as "green" corrosion inhibition. In this paper we review the most recent advances in this field. We shall start from the adsorption of amino acids at metal surfaces and we will evolve then in the direction of more complex systems, in the light of the latest improvements of surface science techniques and of computational methods. On one side, we will focus on amino acids adsorption at oxide surfaces, on the other on peptide adsorption both at metal and oxide substrates. Particular attention will be drawn to the added value provided by the combination of several experimental surface science techniques and to the precious contribution of advanced complementary computational methods to resolve the details of systems of increased complexity. Finally, some hints on experiments performed in presence of water and then characterized in UHV and on the related theoretical work will be presented. This is a further step towards a better approximation of real biological systems. However, since the methods employed are often not typical of surface science, this topic is not developed in detail. © 2015 Elsevier B.V. All rights reserved.
Cahiez G.,CNRS Paris Research Institute of Chemistry |
Moyeux A.,CNRS Paris Research Institute of Chemistry |
Moyeux A.,University of Paris 13 |
Cossy J.,CNRS Chemistry, Biology and Innovation Laboratory
Advanced Synthesis and Catalysis | Year: 2015
Grignard reagents are probably the best organometallics to develop large-scale eco-friendly cross-couplings compatible with the requirements of sustainable development. This account aims to highlight some reactions having an interesting industrial potential and gives the personal point of view of the authors on some attractive fields of research in this area. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Arcadi A.,University of L'Aquila |
Pietropaolo E.,University of L'Aquila |
Alvino A.,University of Rome La Sapienza |
Michelet V.,CNRS Paris Research Institute of Chemistry
Beilstein Journal of Organic Chemistry | Year: 2014
The scope and limitations of gold-catalyzed tandem cycloisomerization/ fluorination reactions of unprotected 2-alkynylanilines to have access to 3,3-difluoro-2-aryl-3H-indoles and 3-fluoro-2-arylindoles are described. An unprecedented aminoauration/oxidation/ fluorination cascade reaction of 2-alkynylanilines bearing a linear alkyl group on the terminal triple bond is reported. © 2014 Arcadi et al; licensee Beilstein-Institut.
Pradal A.,CNRS Paris Research Institute of Chemistry |
Gladiali S.,University of Sassari |
Michelet V.,CNRS Paris Research Institute of Chemistry |
Toullec P.Y.,CNRS Paris Research Institute of Chemistry
Chemistry - A European Journal | Year: 2014
A straightforward methodology for the synthesis of libraries of chiral tris-ligated cationic platinum complexes and their in situ evaluation as asymmetric carbophilic catalysts in a model domino hydroarylation/cyclization reaction of a 1,6-enyne was developed. A catalyst-generation process based on a combination of a monodentate and a bidentate phosphorus ligand allowed the formation of 108 chiral complexes. One-pot screening of the stereoinduction obtained with this library in a test domino addition/cyclization reaction validated this approach and stressed the key role played by the monodentate ligand partner in obtaining high enantioselectivities. In the case of two challenging substrate/nucleophile combinations, the combinatorial approach resulted in a significant gain in enantioselectivity. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Maldiney T.,CNRS Health Technology, Chemistry and Biology Unit |
Bessiere A.,CNRS Paris Research Institute of Chemistry |
Seguin J.,CNRS Health Technology, Chemistry and Biology Unit |
Teston E.,CNRS Health Technology, Chemistry and Biology Unit |
And 8 more authors.
Nature Materials | Year: 2014
Optical imaging for biological applications requires more sensitive tools. Near-infrared persistent luminescence nanoparticles enable highly sensitive in vivo optical detection and complete avoidance of tissue autofluorescence. However, the actual generation of persistent luminescence nanoparticles necessitates ex vivo activation before systemic administration, which prevents long-term imaging in living animals. Here, we introduce a new generation of optical nanoprobes, based on chromium-doped zinc gallate, whose persistent luminescence can be activated in vivo through living tissues using highly penetrating low-energy red photons. Surface functionalization of this photonic probe can be adjusted to favour multiple biomedical applications such as tumour targeting. Notably, we show that cells can endocytose these nanoparticles in vitro and that, after intravenous injection, we can track labelled cells in vivo and follow their biodistribution by a simple whole animal optical detection, opening new perspectives for cell therapy research and for a variety of diagnosis applications. © 2014 Macmillan Publishers Limited. All rights reserved.
Vakarin E.V.,CNRS Paris Research Institute of Chemistry |
Badiali J.P.,CNRS Paris Research Institute of Chemistry
Journal of Physics: Conference Series | Year: 2015
A procedure of the minimization of the maximum entropy with respect to an external driving force μ, is proposed. In application to coupled dynamic-stochastic systems such an approach allows one to reduce the uncertainty in estimating the dynamic counterpart (a probe or a model) parameters. In its turn this permits to estimate an optimal driving path giving a maximal information on the probability distribution f(x|μ) of the stochastic counterpart with a given probe/model θ(μ|x). It is found that the functional form of the model should be similar to the observed/measured one θ(μ), while the minimum uncertainty is reached when the distribution becomes independent of the driving μ. © Published under licence by IOP Publishing Ltd.