Radiation-induced reduction-polymerization route for the synthesis of PEDOT conducting polymers

Synthesis of conducting poly(3,4-ethylenedioxythiophene), PEDOT, is achieved through an original reduction-polymerization route: γ-radiolysis of aqueous solutions containing EDOT monomers under N2 atmosphere. According to UV-vis absorption spectrophotometry and ATR-FTIR spectroscopy, reduction of EDOT is initiated by hydrated electrons produced by water radiolysis and leads to PEDOT polymers through coupling reactions. The morphology of PEDOT is characterized by Cryo- TEM microscopy in aqueous solution and by SEM after deposition. In an original way, high resolution AFM microscopy, coupled with infrared nanospectroscopy, is used to probe the local chemical composition of PEDOT nanostructures. The results demonstrate that spherical self-assembled PEDOT nanostructures are formed. TGA analysis and four point probe measurements demonstrate that thermal stability and electrical conductivity of PEDOT polymers obtained by the present original reduction-polymerization method are close to those of PEDOT we previously prepared by radiolysis according to an oxidation-polymerization route

Influx of nitrogen-rich material from the outer Solar System indicated by iron nitride in Ryugu samples

Large amounts of nitrogen compounds, such as ammonium salts, may be stored in icy bodies and comets, but the transport of these nitrogen-bearing solids into the near-Earth region is not well understood. Here, we report the discovery of iron nitride on magnetite grains from the surface of the near-Earth C-type carbonaceous asteroid Ryugu, suggesting inorganic nitrogen fixation. Micrometeoroid impacts and solar wind irradiation may have caused the selective loss of volatile species from major iron-bearing minerals to form the metallic iron. Iron nitride is a product of nitridation of the iron metal by impacts of micrometeoroids that have higher nitrogen contents than the CI chondrites. The impactors are probably primitive materials with origins in the nitrogen-rich reservoirs in the outer Solar System. Our observation implies that the amount of nitrogen available for planetary formation and prebiotic reactions in the inner Solar System is greater than previously recognized

Four‐dimensional‐STEM analysis of the phyllosilicate‐rich matrix of Ryugu samples

Ryugu asteroid grains brought back to the Earth by the Hayabusa2 space mission are pristine samples containing hydrated minerals and organic compounds. Here, we investigate the mineralogy of their phyllosilicate-rich matrix with four-dimensional scanning transmission electron microscopy (4D-STEM). We have identified and mapped the mineral phases at the nanometer scale (serpentine, smectite, pyrrhotite), observed the presence of Ni-bearing pyrrhotite, and identified the serpentine polymorph as lizardite, in agreement with the reported aqueous alteration history of Ryugu. Furthermore, we have mapped the d-spacings of smectite and observed a broad distribution of values, ranging from 1 to 2 nm, with an average d-spacing of 1.24 nm, indicating significant heterogeneity within the sample. Such d-spacing variability could be the result of either the presence of organic matter trapped in the interlayers or the influence of various geochemical conditions at the submicrometer scale, suggestive of a range of organic compounds and/or changes in smectite crystal chemistry

A dehydrated space-weathered skin cloaking the hydrated interior of Ryugu

Without a protective atmosphere, space-exposed surfaces of airless Solar System bodies gradually experience an alteration in composition, structure and optical properties through a collective process called space weathering. The return of samples from near-Earth asteroid (162173) Ryugu by Hayabusa2 provides the first opportunity for laboratory study of space-weathering signatures on the most abundant type of inner solar system body: a C-type asteroid, composed of materials largely unchanged since the formation of the Solar System. Weathered Ryugu grains show areas of surface amorphization and partial melting of phyllosilicates, in which reduction from Fe3+ to Fe2+ and dehydration developed. Space weathering probably contributed to dehydration by dehydroxylation of Ryugu surface phyllosilicates that had already lost interlayer water molecules and to weakening of the 2.7 µm hydroxyl (–OH) band in reflectance spectra. For C-type asteroids in general, this indicates that a weak 2.7 µm band can signify space-weathering-induced surface dehydration, rather than bulk volatile loss

Study of the biomolecules’ production by AFM-IR

Le sujet de thèse porte sur l’étude de l’accumulation de vésicules de TriAcylGlycérol (TAG) chez Streptomyces, une bactérie du sol filamenteuse utilisée dans l’industrie pour sa production d’antibiotiques. Le TAG est un précurseur direct du bio-diesel puisqu’il permet, suite à une transestérification, l’obtention de glycérol et de bio-diesel.L’objectif principal de la thèse est de regarder l’effet de la source de carbone présente dans le milieu nutritif sur la production de TAG par la bactérie lors d’études cinétiques afin de trouver des souches sur-productrices. Deux sources de carbone sont utilisés : Le glucose, source de carbone classique généralement utilisé en microbiologie, et le glycérol qui est un « déchet » de l’industrie. Afin de suivre le contenu lipidique, une première étude globale utilisant un spectrophotomètre infra-rouge (IR), nous a permis de suivre l’évolution de la production de TAG par la bactérie au sein de notre milieu de culture lors d’études cinétiques de 96h. Il a été montré, par exemple, que pour la souche sauvage S. lividans, la source de carbone introduite (glucose ou glycérol) n’a pas d’influence observable sur la production de TAG par la bactérie au cours de la cinétique. Cependant, la technique FTIR nous donne uniquement une information globale sur la production de TAG mais ne nous donne aucune indication sur l’évolution des vésicules à l’intérieur de la bactérie au cours du temps. C’est pourquoi une deuxième étude, plus locale, à l’aide d’un nanoIR, couplage entre un Microscope à Force Atomique (AFM) et un laser IR pulsé permet de localiser au sein de la bactérie les vésicules lipidiques. Cela permet d'observer la dynamique de production du TAG et d'obtenir des pistes sur le métabolisme de production par la bactérie.Streptomyces is a genus of Gram+ filamentous soil bacteria well known for their ability to produce antibiotics and other molecules useful as therapeutic or phytosanitary agents in medicine or agriculture. Under specific growth conditions some strains can store an excess of carbon into TriAcylGlycerols (TAGs), a direct Bio-diesel precursor. Streptomyces is thus an interesting canditate to generate bio-oils by fermentation. In this study, our goal is to evaluate, at the subcellular scale, the size/shape and localization of storage lipid inclusions in different Streptomyces strains (such as Streptomyces lividans (TK24), Streptomyces coelicolor (M145)…).In a previous study, the global TAGs content of those strains was easily and precisely quantified using infrared (IR) spectroscopy and thin layer chromatography revealing among other things that S. coelicolor has a very low TAGs content whereas S. lividans has an high TAG content. This was possible since TAG molecules show a specific response in the mid-infrared (IR) region, quite distinct from that of the other cellular constituants.Triacylglycerols posses several absorption bands in IR. In particular we can easily distinguish the band of the C=O stretching of the esters at 1741 cm-1 from the amide I band (protein signature) of the bacterium.For the study of the local repartition of TAG inside the cells, a combination of atomic force microscopy and infrared spectroscopy was employed in order to create sub-cellular chemical maps that allow label-free identification of TAG inclusions in Streptomyces cytoplasm using their specific absorption properties at 1741 cm-1. AFM-IR is a user-friendly benchtop technique that enables infrared spectroscopy with a spatial resolution well below conventional optical diffraction limits. It acquires IR absorption imaging with lateral resolution down to 100 nm.This technique coupled with classical FTIR measurements constitutes a powerful tool to study TAG metabolism in Streptomyces and can be easily used to control the rate of lipid accumulation during the fermentation process. Hence, the AFM-IR technique is likely to provide new insights into the constitution of the fatty inclusions and the role of TAGs in the morphological and metabolic differentiation processes that characterize Streptomyces developmental cell cycle

Chemical functional characterization of immature and mature coals at the nanoscale by atomic force microscopy-based infrared spectroscopy (AFM-IR)

International audienceUnderstanding the composition and molecular structure of kerogens and coals is a key issue in geochemistry, as these parameters control their chemical evolution and their by-products generated in sedimentary basins. As they are chemically heterogenous, investing their structure and composition at various spatial scales is essential and relies on a variety of micro-analytical tools. Conventional infrared (IR) microscopy has proven to be a powerful and promising approach to characterize these heterogeneous materials, but due to the diffraction limit, the spatial resolution cannot get below ~ 1 µm, and cannot measure individual submacerals, tiny mineral inclusions, and more generally cannot access to chemical variations at the nanometer scale. In contrast, atomic force microscopy coupled to infrared spectroscopy (AFM-IR) attains a much higher spatial resolution, down to tens of nanometers. In this paper, AFM-IR measurements were collected on three immature and mature coals, with mean-maximum vitrinite reflectance R0 of 0.33%, 1.16%, and 2.8%. Measurements were collected in both tapping and contact modes, on samples prepared as sulfur embedded ultrathin sections and pressed on diamond windows. These spectral data were compared to spectra collected with conventional micro-IR microscopy (μ-FTIR). Spectra with a high quality could be obtained, which point to chemical heterogeneity at the sub-micrometer scale, and they display similar bands than those observed in spectra collected by means of conventional micro-IR. The signal-to-noise ratio was better in spectra collected in contact mode compared to tapping mode. The spatial resolution was around ~ 100 nm in contact mode, while a resolution of at least 20 nm was achieved in tapping mode. Kaolinite was detected as a ~ 500 nm grain included in organic matter. These results show that sulfur embedded ultrathin sections are as a suitable sample preparation for AFM-IR. However, systematic differences are reported compared to spectra collected by conventional μ-FTIR, possibly due to an instrumental artifact that increases the absorption signal as the wavenumber is decreased. Similarly, systematic differences are observed between data collected in tapping and contact modes, along with a much broader chemical heterogeneity. These differences are not fully understood, and should be investigated further in future studies

Chemical functional characterization of immature and mature coals at the nanoscale by atomic force microscopy-based infrared spectroscopy (AFM-IR)

International audienceUnderstanding the composition and molecular structure of kerogens and coals is a key issue in geochemistry, as these parameters control their chemical evolution and their by-products generated in sedimentary basins. As they are chemically heterogenous, investing their structure and composition at various spatial scales is essential and relies on a variety of micro-analytical tools. Conventional infrared (IR) microscopy has proven to be a powerful and promising approach to characterize these heterogeneous materials, but due to the diffraction limit, the spatial resolution cannot get below ~ 1 µm, and cannot measure individual submacerals, tiny mineral inclusions, and more generally cannot access to chemical variations at the nanometer scale. In contrast, atomic force microscopy coupled to infrared spectroscopy (AFM-IR) attains a much higher spatial resolution, down to tens of nanometers. In this paper, AFM-IR measurements were collected on three immature and mature coals, with mean-maximum vitrinite reflectance R0 of 0.33%, 1.16%, and 2.8%. Measurements were collected in both tapping and contact modes, on samples prepared as sulfur embedded ultrathin sections and pressed on diamond windows. These spectral data were compared to spectra collected with conventional micro-IR microscopy (μ-FTIR). Spectra with a high quality could be obtained, which point to chemical heterogeneity at the sub-micrometer scale, and they display similar bands than those observed in spectra collected by means of conventional micro-IR. The signal-to-noise ratio was better in spectra collected in contact mode compared to tapping mode. The spatial resolution was around ~ 100 nm in contact mode, while a resolution of at least 20 nm was achieved in tapping mode. Kaolinite was detected as a ~ 500 nm grain included in organic matter. These results show that sulfur embedded ultrathin sections are as a suitable sample preparation for AFM-IR. However, systematic differences are reported compared to spectra collected by conventional μ-FTIR, possibly due to an instrumental artifact that increases the absorption signal as the wavenumber is decreased. Similarly, systematic differences are observed between data collected in tapping and contact modes, along with a much broader chemical heterogeneity. These differences are not fully understood, and should be investigated further in future studies

Nanoscale mineralogy and organic structure in Orgueil (CI) and EET 92042 (CR) carbonaceous chondrites studied with AFM-IR spectroscopy

International audienceMeteorite matrices from primitive chondrites are an interplay of ingredients at the sub-µm scale, which requires analytical techniques with the nanometer spatial resolution to decipher the composition of individual components in their petrographic context. Infrared spectroscopy is an effective method that enables the probing of vibrations at the molecule atomic scale of organic and inorganic compounds but is often limited to a few micrometers in spatial resolution. To efficiently distinguish spectral signatures of the different constituents, we apply here nano-infrared spectroscopy (AFM-IR), based on the combination of infrared and atomic force microscopy, having a spatial resolution beyond the diffraction limits. Our study aims to characterize two chosen meteorite samples to investigate primitive material in terms of bulk chemistry (the CI chondrite Orgueil) and organic composition (the CR chondrite EET 92042). We confirm that this technique allows unmixing the IR signatures of organics and minerals to assess the variability of organic structure within these samples. We report an investigation of the impact of the widely used chemical HF/HCl (hydrogen fluoride/hydrochloric acid) extraction on the nature of refractory organics (insoluble organic matter [IOM]) and provide insights on the mineralogy of meteorite matrices from these two samples by comparing to reference (extra)terrestrial materials. These findings are discussed with a perspective toward understanding the impact of post-accretional aqueous alteration and thermal metamorphism on the composition of chondrites. Last, we highlight that the heterogeneity of organic matter within meteoritic materials extends down to the nanoscale, and by comparison with IOMs, oxygenated chemical groups are not affected by acid extractions

Revealing Lipid Body Formation and its Subcellular Reorganization in Oleaginous Microalgae Using Correlative Optical Microscopy and Infrared Nanospectroscopy Atomic Force Microscopy-Induced Resonance (AFM-IR)

International audienceThe purpose of this work is to develop an integrated imaging approach to characterize without labeling at the sub-cellular level the formation of lipid body droplets (LBs) in microalgae undergoing nitrogen starvation. First conventional optical microscopy approaches, gas chromatography, and turbidimetry measurements allowed to monitor the biomass and the total lipid content in the oleaginous microalgae Parachlorella kesslerii during the starvation process. Then a local analysis of the LBs was proposed using an innovative infrared nanospectroscopy technique called atomic force microscopy-based infrared spectroscopy (AFM-IR). This label-free technique assessed the formation of LBs and allowed to look into the LB composition thanks to the acquisition of local infrared spectra. Last correlative measurements using fluorescence microscopy and AFM-IR were performed to investigate the subcellular reorganization of LB and the chloroplasts