Infra-red imaging of bulk water and water-solid interfaces under stable and metastable conditions.

International audienceSuperheated water has been studied by infrared spectroscopy to examine whether the special ability of liquid water to undergo such metastable state corresponds to the development of peculiar inter-molecular networking under tension. As the best technique to superheat water is to trap the liquid inside micro-cavities in solids (the so-called ―fluid inclusions‖), the role of the water-solid interfaces to stabilize the adjoining liquid is also explored with the same infra-red micro-spectroscopy tool. The key signal is the intra- molecular OH stretching band, sensitive to the networking in the probed material. The sample of choice is liquid water occluded inside quartz cavity of micrometric size, synthetized in laboratory from pure quartz and milli-Q water. The stretching band of the superheated water shows no significant spectral difference with that of a bulk ―normal‖ water, which means that the molecular properties of the superheating liquid is quite similar to those of the stable bulk liquid. Liquid water is readily ―superheatable‖ but retains its ―normality‖ under these special conditions. Additionally, this result establishes a firm ground to justify that the properties of the former are predicted extrapolating the usual (though empirical) equation of state of the latter. The infra-red signals of the water-solid interfaces are more complex. The water-solid interfaces blue-shift the signal, affecting differently the three sub-bands of the OH-stretching. This effect was unexpected since the micro-IR spectroscopy probes volume beyond of what is classicaly assigned for the interfacial properties. In addition, the interfacial signature is clearer under superheating than with the saturation conditions, which offers an interesting (and unexpected) way to interpret the special stability of the occluded metastable water. These encouraging results give confidence on the potentialities of the high-resolution micro-spectroscopy to get insights into the molecular basis of macroscopic properties

Preferred metabolic pathway of bovine muscle fibre revealed by synchrotron–deep ultraviolet fluorescence imaging

International audienceThe different bovine muscle fibre types I, IIA and IIX are characterised by their preferred metabolic pathway, either oxidative (I, IIA) or glycolytic (IIX), and their contraction speed, either slow-twitch (I) or fast-twitch (IIA, IIX). These physiological specificities are associated with variations in intracellular composition and their fluorescence spectra signatures. We hypothesised that these slight differences in autofluorescence responses could be used to discriminate the muscle fibre types by fluorescence imaging. Serial histological cross-sections of beef longissimus dorsi were performed: the start set was used to identify the metabolic and contractile type of muscle fibres by both immunohistoenzymology and immunohistofluorescence, and the following set was used to acquire synchrotron–deep ultraviolet (UV) autofluorescence images after excitation in the UV range (275 nm and 315 nm). This strategy made it possible to explore the label-free autofluorescence of muscle cells previously subtyped by histochemistry. Glycolytic cells (IIX) showed more intense fluorescence than oxidative cells (I and IIA) with near-90 % accuracy. This discrimination is more specifically assigned to the fluorescence of nicotinamide adenine dinucleotide. UV autofluorescence was unable to discriminate contractile type

Investigations by AFM of Ageing Mechanisms in PLA-Flax Fibre Composites during Garden Composting.

PLA-flax non-woven composites are promising materials, coupling high performance and possible degradation at their end of life. To explore their ageing mechanisms during garden composting, microstructural investigations were carried out through scanning electron microscopy (SEM) and atomic force microscopy (AFM). We observe that flax fibres preferentially degrade 'inwards' from the edge to the core of the composite. In addition, progressive erosion of the cell walls occurs within the fibres themselves, 'outwards' from the central lumen to the periphery primary wall. This preferential degradation is reflected in the decrease in indentation modulus from around 23 GPa for fibres located in the preserved core of the composite to 3-4 GPa for the remaining outer-most cell wall crowns located at the edge of the sample that is in contact with the compost. Ageing of the PLA matrix is less drastic with a relatively stable indentation modulus. Nevertheless, a change in the PLA morphology, a significant decrease in its roughness and increase of porosity, can be observed towards the edge of the sample, in comparison to the core. This work highlights the important role of intrinsic fibre porosity, called lumen, which is suspected to be a major variable of the compost ageing process, providing pathways of entry for moisture and microorganisms that are involved in cell wall degradation

Extracorporeal Membrane Oxygenation for Severe Acute Respiratory Distress Syndrome associated with COVID-19: An Emulated Target Trial Analysis.

RATIONALE: Whether COVID patients may benefit from extracorporeal membrane oxygenation (ECMO) compared with conventional invasive mechanical ventilation (IMV) remains unknown. OBJECTIVES: To estimate the effect of ECMO on 90-Day mortality vs IMV only Methods: Among 4,244 critically ill adult patients with COVID-19 included in a multicenter cohort study, we emulated a target trial comparing the treatment strategies of initiating ECMO vs. no ECMO within 7 days of IMV in patients with severe acute respiratory distress syndrome (PaO2/FiO2 <80 or PaCO2 ≥60 mmHg). We controlled for confounding using a multivariable Cox model based on predefined variables. MAIN RESULTS: 1,235 patients met the full eligibility criteria for the emulated trial, among whom 164 patients initiated ECMO. The ECMO strategy had a higher survival probability at Day-7 from the onset of eligibility criteria (87% vs 83%, risk difference: 4%, 95% CI 0;9%) which decreased during follow-up (survival at Day-90: 63% vs 65%, risk difference: -2%, 95% CI -10;5%). However, ECMO was associated with higher survival when performed in high-volume ECMO centers or in regions where a specific ECMO network organization was set up to handle high demand, and when initiated within the first 4 days of MV and in profoundly hypoxemic patients. CONCLUSIONS: In an emulated trial based on a nationwide COVID-19 cohort, we found differential survival over time of an ECMO compared with a no-ECMO strategy. However, ECMO was consistently associated with better outcomes when performed in high-volume centers and in regions with ECMO capacities specifically organized to handle high demand. This article is open access and distributed under the terms of the Creative Commons Attribution Non-Commercial No Derivatives License 4.0 (http://creativecommons.org/licenses/by-nc-nd/4.0/)

Mise en évidence des modifications métaboliques induites par l'accumulation de lipides dans la levure S. cerevisiae par sFTIR sur cellules uniques

L'utilisation combinée du faisceau synchrotron de la ligne SMIS et d'hémisphère en ZnSe nous a permis d'obtenir des spectres FTIR sur cellules uniques. Nos résultats ont révélé une hétérogénéité du métabolisme cellulaire au sein d'une population issue d'une même souche. Nous avons également observé de fortes modifications entre souches ayant une capacité variable de stockage des lipides neutres.The combination of SMIS beamline synchrotron radiation and ZnSe hemisphere led us to obtain single-cell FTIR spectra. Our results revealed cell metabolism heterogeneity in a population coming from a single clone. We also observed clear modi bc0 d82cations bet bc0 c59een strains exhibiting various capacities in neutral lipid storage

Thermodynamic properties of interfacial water from its infrared signatures

International audienceWater liquid trapped in quartz micro-cavities is probed by infrared micro-spectroscopy to explore the influence of the solid/liquid and liquid/air interfaces on water thermodynamics. The sample is infraredly mapped with a 3x3 µm micro-beam allowed by the brilliance of synchrotron radiation source (SOLEIL, SMIS beamline) at 2.5 µm xy interval. It appears that the intramolecular OH-stretching band is changing as a function of its proximity to the interfaces. To refine these variations, the band is decomposed into Gaussian components, evidencing that water is interface-printed even at micrometric distance to the wall and/or to the bubble with the closest layer to the interface marked by a dangling-OH effect. Then, these vibrational changes are converted into Gibbs free energy, which range from 35 J.mol-1 4.5 µm away from the interface, to 1 kJ.mol-1 at about 1 µm

Tracking hidden organic carbon in rocks using chemometrics and hyperspectral imaging

Abstract Finding traces of life or organic components of prebiotic interest in the rock record is an appealing goal for numerous fields in Earth and space sciences. However, this is often hampered by the scarceness and highly heterogeneous distribution of organic compounds within rocks. We assess here an innovative analytical strategy combining Synchrotron radiation-based Fourier-Transform Infrared microspectroscopy (S-FTIR) and multivariate analysis techniques to track and characterize organic compounds at the pore level in complex oceanic rocks. S-FTIR hyperspectral images are analysed individually or as multiple image combinations (multiset analysis) using Principal Component Analyses (PCA) and Multivariate Curve Resolution – Alternating Least Squares (MCR-ALS). This approach allows extracting simultaneously pure organic and mineral spectral signatures and determining their spatial distributions and relationships. MCR-ALS analysis provides resolved S-FTIR signatures of 8 pure mineral and organic components showing the close association at a micrometric scale of organic compounds and secondary clays formed during rock alteration and known to catalyse organic synthesis. These results highlights the potential of the serpentinizing oceanic lithosphere to generate and preserve organic compounds of abiotic origin, in favour of the hydrothermal theory for the origin of life

Rétroactions Porosité - Réactivité

International audienceLa structure des milieux poreux est de première importance lorsqu’on étudie les propriétés de transport, avec un intérêt dirigé versla taille des pores et la topologie 3d. Les propriétés réactives ont également des liens très forts avec la structure, et même la micro-structure, notamment la géométrie et la composition locales, les états de surface, des phases dissoutes et solides. Dans cette contribution, nous nous intéressons aux relations spécifiquement entre taille et réactivité, pour déterminer quelle est l’échelle dimensionnelle où les propriétésde l’eau porale changent. Trois situations contrastées sont étudiées : (1) l’eau est abritée dans un pore de grande taille (plusieurs dizaines de microns) ; (2) l’eau liquide est confinée entre deux surfaces de silice ; (3) une épaisseur d’eau entre 0.5 et quelques micromètres est déposée sur une surface. Deux types d’échantillons abritent ces situations : une inclusion fluide de quartz, c’est -à-dire une vacuole fermée au cœur même du solide, contenant soit seulement de l’eau liquide, soit un mélange biphasique eau-air; des canaux de nano-fluidique, à base de silicium monocristallin, dont la hauteur varie entre 5 et 100 nm. Des mesures infra-rouges ont été menées sur cette eau piégée, et les signaux enregistrés sont examinés en fonction de la hauteur de canaux ou de l’éloignement à l’interface.Ces mesures sont ensuite converties en propriétés thermodynamiques en champ moyen et les prédictions en termes de transitions de phase calculées par simulation thermodynamique

Evolution of the ultrastructure and polysaccharide composition of flax fibres over time: When history meets science

International audienceFlax fibres have been used by humans for approximately 10,000 years. With time, the geographic area of production and cultivation has changed, as have the applications of flax fibres; from clothing to sails and paintings from antiquity, to automotive, fashion, and design applications in the contemporary era. The degradation process of flax fibres is the same for both ancient and modern objects made from this polysaccharidic material. This review, focusing on the cultural heritage field, after a brief description of flax plants and fibres, retraces the history of their use through Europe and the Near East, and discusses the evolution of extraction methods with human progress. Furthermore, the most important mechanisms of flax fibre degradation and the characterisation techniques currently in use are described. This study highlights the constructive interchange between engineering and cultural heritage that can be realised through a continuous comparison of antiquity and the contemporary era