Search

Interactions of a protein with a solid–liquid or a liquid–liquid interface may destabilize its conformation and hence result in a loss of biological activity. We propose here a method for the immobilization of proteins at an electrified liquid–liquid interface. Cytochrome c (Cyt c) is encapsulated in a silica matrix through an electrochemical process at an electrified liquid–liquid interface. Silica condensation is triggered by the interfacial transfer of cationic surfactant, cetyltrimethylammonium, at the lower end of the interfacial potential window. Cyt c is then adsorbed on the previously electrodeposited silica layer, when the interfacial potential, Δowϕ, is at the positive end of the potential window. By cycling of the potential window back and forth, silica electrodeposition and Cyt c adsorption occur sequentially as demonstrated by in situ UV–vis absorbance spectroscopy. After collection from the liquid–liquid interface, the Cyt c–silica matrix is characterized ex situ by UV–vis diffuse reflectance spectroscopy, confocal Raman microscopy, and fluorescence microscopy, showing that the protein maintained its tertiary structure during the encapsulation process. The absence of denaturation is further confirmed in situ by the absence of electrocatalytic activity toward O2 (observed in the case of Cyt c denaturation). This method of protein encapsulation may be used for other proteins (e.g., Fe–S cluster oxidoreductases, copper-containing reductases, pyrroloquinoline quinone-containing enzymes, or flavoproteins) in the development of biphasic bioelectrosynthesis or bioelectrocatalysis applications.

International audience; Controlled formation of cocrystals is an important objective in drug development. Here, cocrystallisation of caffeine and 1-hydroxy-2-naphthoic acid was investigated at the interface between two immiscible electrolyte solutions under chemical polarisation. In this way, selective cocrystallisation was achieved, as verified by X-ray diffraction and Raman spectroscopy. Positive interfacial potentials favoured the formation of one polymorphic form of caffeine:1-hydroxy-2-naphthoic acid cocrystal. This approach to electrochemically controlled cocrystallisation opens up new possibilities for drug development. The search for innovative crystallisation methods is a subject of constant interest as most drugs appear as crystalline forms whose polymorphs may have different toxicity, hygroscopicity or physical and chemical stability. 1-3 An additional issue encountered in drug development is the low stability in humid environments

The cocrystals of two reagents of mismatch solubility, hydrophilic caffeine and lipophilic 1-hydroxy-2-naphthoic acid, were obtained at a water-oil interface. 1 By analysing the product collected at the phase interface by X-ray diffraction and Raman spectroscopy, we confirmed that we obtained the molecular cocrystals of caffeine and 1-hydroxy-2-naphthoic acid, free of starting reagents and solvents. Polarisation of the interface allowed the electrochemical control of the cocrystallisation process: for non-polarised interfaces, a mixture of phase I and II cocrystals were obtained, whereas cocrystals of phase I were formed when a high interfacial potential was applied. The difference between the polymorphs obtained in the absence or in the presence of interfacial polarisation is attributed to the different cocrystallisation mechanisms. In the absence of interfacial polarisation, caffeine and 1-hydroxy-2-naphthoic acid are cocrystallising through an interfacial process. When the interface is positively polarised, cationic form of caffeine is transferred to the organic phase, the complex with naphthoic acid is formed and the proton is released. The pH increased after cocrystallisation, suggesting that the liberated H+ remained in the organic phase. On the contrary, in the absence of polarisation or in the case of low interfacial potential the protons are remaining in the aqueous phase what resulted in a decrease in pH after cocrystallisation process. We demonstrated an indirect evidence of the transfer of caffeine upon chemical polarization of the interface. We observed almost no deposits in the organic phase by analysing it with a scanning electron microscope. We investigated here the mechanism behind the formation of cocrystals by using the polarized interface between two immiscible electrolyte solutions (ITIES).2 For the purpose of this study, the two solutions have been placed in contact3 : one being an aqueous solution of caffeine, as a model drug substance, and the second being organic solution of 1-hydroxy-2-naphthoic acid (cocrystal component) and the salt inducing the suitable imposed potential difference. The formation of the caffeine: 1-hydroxy-2-naphthoic acid complex was studied by changing the salts present in the aqueous phase, the chemical compounds imposing potential in organic phase, varying the organic solvents and the temperature at the liquid-liquid interface. The cocrystals collected at the interface were analysed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and low frequency Raman spectroscopy. We studied the proportions of polymorphic phases as a function of changing conditions. To understand the mechanism behind the caffeine transfer and the formation of different forms of polymorphic crystals at the water-oil interface, Electrochemical Noise Experiments4 have been carried out. A four-electrode system was used to apply zero volts between the working electrode and the counter electrode and then measuring the current and the potential versus the reference electrode. Such a setup allows the measurement of potential and current as the function of time simultaneously. We could thus follow the phenomena that are taking place at the interface. The measurements were carried out by varying the cations (tetraalkylammoniums, Li+, K+) in aqueous and organic phase as well as the anions (derivatives of tetrakis(phenyl-borate) in organic phase). The experimental results were supported by theoretical equations and applied to the system containing caffeine. This novel strategy of cocrystallization, was followed by the investigation of other coformers (3-hydroxy-2-naphthoic acid) and drugs (cocrystals of ketoprofen with amino acids and carboxylic acids) in order to validate the method. Such an electrocrystallization process at the ITIES will open new opportunities for the formation of drugs cocrystals. M. Kaliszczak et al., CrystEngComm (2022) doi: 10.1039/D1CE01281A. Z. Samec, Pure Appl. Chem., 76, 2147–2180 (2004). S. J. Diez et al., Cryst. Growth Des., 18, 3263–3268 (2018). I. B. Obot, I. B. Onyeachu, A. Zeino, and S. A. Umoren, J. Adhes. Sci. Technol., 33, 1453–1496 (2019).

Description, An electrified aqueous-organic interface modulates the conformational plasticity of the protein cytochrome c., Programmed cell death via apoptosis is a natural defence against excessive cell division, crucial for fetal development to maintenance of homeostasis and elimination of precancerous and senescent cells. Here, we demonstrate an electrified liquid biointerface that replicates the molecular machinery of the inner mitochondrial membrane at the onset of apoptosis. By mimicking in vivo cytochrome c (Cyt c) interactions with cell membranes, our platform allows us to modulate the conformational plasticity of the protein by simply varying the electrochemical environment at an aqueous-organic interface. We observe interfacial electron transfer between an organic electron donor decamethylferrocene and O2, electrocatalyzed by Cyt c. This interfacial reaction requires partial Cyt c unfolding, mimicking Cyt c in vivo peroxidase activity. As proof of concept, we use our electrified liquid biointerface to identify drug molecules, such as bifonazole, that can potentially down-regulate Cyt c and protect against uncontrolled neuronal cell death in neurodegenerative disorders.

International audience; Extraordinary properties of graphenic materials no longer need to be demonstrated. Nitrogen doping has been known to broaden the graphene application fields, especially for catalysis purposes. The present work reports a solvothermal-based process for the synthesis of a nitrogen-doped graphenic foam with up to 2.6 at.% nitrogen, exhibiting the inherent properties of graphenic materials with high textural properties and surface areas as high as 2243 m².g-1. This study aims to give a better understanding of the influence of the pyrolysis treatment on the properties of the produced material for optimization of the synthesis in view to fuel cell applications. Several cross-linked techniques such as transmission electron microscopy, thermogravimetric analysis, Raman spectroscopy, nitrogen physisorption at 77 K and X-ray photoelectron spectroscopy have been employed to give a complete, precise characterization of the elaborated N-doped graphenic foams, leading to optimized conditions for the pyrolysis step. Pyrolysis at 850 °C has been found to allow the best compromise in terms of purity, homogeneity and crystallinity, with high fractions of pyrrolic, pyridinic and graphitic N-substitution that are known to greatly enhance the material catalytic properties. An oxidative degradation process was also evidenced for temperatures above 875 °C, leading to far lower graphene amounts.

International audience; A novel concept is introduced for signal amplification in electrochemical sensing: the electrooligomerisation stripping voltammetry, which has been applied here to the improved detection of the isoproturon herbicide in spring waters as a proof-of-principle. It involves a potentiostatic accumulation step onto a glassy carbon electrode (at +1.5 V vs Ag/AgCl reference electrode for 300 s) leading to the formation of an oligomeric film, which is then detected by cathodic stripping square wave voltammetry (SWV). The presence and composition of the film are confirmed by confocal Raman spectroscopy. Its characterisation by cyclic voltammetry demonstrates the reversible nature of the electrodeposited material, confirming its interest for sensitive detection by SWV. Adding a mesoporous silica membrane with vertically oriented nanochannels further enhances the sensitivity of the sensor, exhibiting a linear response in the 10-100 µM concentration range. This effect was even more interesting for real media analysis thanks to the permselective properties of such nanoporous coating in rejecting interferences and/or surface fouling agents. The method should be applicable to other analytes that are usually not detectable by conventional accumulation/stripping voltammetry.

peer-reviewed The full text of this article will not be available in ULIR until the embargo expires on the 06/03/2021 One of the many evolved functions of photosynthetic organisms is to synthesize light harvesting nanostructures from photoactive molecules such as porphyrins. Engineering synthetic analogues with optimized molecular order necessary for the efficient capture and harvest of light energy remains challenging. Here, we address this challenge by reporting the self-assembly of zinc(II) meso-tetrakis(4-carboxyphenyl)porphyrins into films of highly ordered nanostructures. The self-assembly process takes place selectively at the interface between two immiscible liquids (water|organic solvent), with kinetically stable interfacial nanostructures formed only at pH values close to the pKa of the carboxyphenyl groups. Molecular dynamics simulations suggest that the assembly process is driven by an interplay between the hydrophobicity gradient at the interface and hydrogen bonding in the formed nanostructure. Ex situ XRD analysis and in situ UV/vis and steady state fluorescence indicates the formation of chlathrate type nanostructures that retain the emission properties of their monomeric constituents. The self-assembly method presented here avoids the use of acidic conditions, additives such as surfactants and external stimuli, offering an alternative for the realization of light-harvesting antennas in artificial photosynthesis technologies.

A living material was formed by self-assembly of bacterial cells ( Shewanella oneidensis MR-1 or Pseudomonas fluorescens ) with carbon nanotubes in the presence of cytochrome c from a bovine heart with the goal to mimic electroactive biofilms. The role of cytochrome c on self-assembly, cell viability and extracellular electron transfer was studied. Scanning electron microscopy and dynamic light scattering experiments highlighted its role on the self-assembly of bacteria‑carbon nanotube aggregates within only 2 h in solution. The deposition of these aggregates on glassy carbon surfaces led to a homogenous composite film in which the bacteria were embedded in a carbon nanotube network. A comparable cell density of 1 cell μm − 2 was achieved in the presence or in the absence of cytochrome c , but this protein allowed maintaining a higher bacterial viability. Electrochemical characterization demonstrated the role of cytochrome c on electron transfer reactions, leading to a current density of up to 300 μA cm − 2 in the presence of 50 mM formate when a porous carbon felt electrode is used as support for the biocomposite.

One of many evolved functions of biological cell membranes is to induce and regulate self-assembly of photoactive molecules into efficient light harvesting nanomaterials. Synthetic molecular assemblies at soft interfaces exhibit macroscale long-range order and so provide routes to biomimetic analogues that minimise concentration quenching. Here, we report the facile assembly of free-standing layered crystalline films of zinc(II) meso-tetrakis(4-carboxyphenyl)porphyrin nanostructures that exhibit significant photocurrents in situ at an electrified liquid | liquid interface. This methodology does not require acidic conditions, specialised amphiphilic porphyrins, or the use of additives or external stimuli. The assembly process is driven by an interplay between the hydrophobicity gradient at an immiscible aqueous | organic interface and optimised hydrogen bonding in the formed nanostructure. Highly-ordered interfacial nanostructures may provide a new paradigm for realisation of light-harvesting antennae in artificial photosynthetic technologies.

Programmed cell death via apoptosis is a natural defence against excessive cell division, crucial at all stages of life from foetal development to maintenance of homeostasis and elimination of precancerous and senescent cells. In this presentation, an electrified liquid|liquid bio-interface is demonstrated that replicates the molecular machinery of the inner mitochondrial membrane at the onset of apoptosis. By mimicking in vivo cytochrome c (Cyt c) interactions with cell membranes, our platform allows us to modulate the conformational plasticity of the protein by simply varying the electrochemical environment at an aqueous|organic interface. Our experimental findings supported by molecular modelling show that adsorption, orientation, restructuring, and pro-apoptotic peroxidase activity of Cyt c can all be precisely manipulated. Remarkably, we observe interfacial electron transfer between an organic electron donor decamethylferrocene and O2, electrocatalysed by Cyt c. This interfacial reaction requires partial Cyt c unfolding, mimicking Cyt c in vivo peroxidase activity. Our electrified liquid|liquid bio-interface motivates development of biomimetic electrochemical platforms to identify drug molecules that can potentially downregulate Cyt c and protect against uncontrolled neuronal cell death in Alzheimer’s and other neurodegenerative diseases. As proof-of-concept, we demonstrate that bifonazole, predicted to target the heme pocket, inhibits the electrocatalytic activity of Cyt c and switches off O2 reduction. Figure 1

International audience; Single-walled carbon nanotubes (SWCNTs) were functionalized by ferrocene through ethyleneglycol chains of different lengths (FcETGn) and the functionalized SWCNTs (f-SWCNTs) were characterized by different complementary analytical techniques. In particular, high-resolution scanning electron transmission microscopy (HRSTEM) and electron energy loss spectroscopy (EELS) analyses support that the outer tubes of the carbon-nanotube bundles were covalently grafted with FcETGn groups. This result confirms that the electrocatalytic effect observed during the oxidation of the reduced form of nicotinamide adenine dinucleotide (NADH) co-factor by the f-SWCNTs is due to the presence of grafted ferrocene derivatives playing the role of a mediator. This work clearly proves that residual impurities present in our SWCNT sample (below 5 wt. %) play no role in the electrocatalytic oxidation of NADH. Moreover, molecular dynamic simulations confirm the essential role of the PEG linker in the efficiency of the bioelectrochemical device in water, due to the favorable interaction between the ETG units and water molecules that prevents π-stacking of the ferrocene unit on the surface of the CNTs. This system can be applied to biosensing, as exemplified for glucose detection. The well-controlled and well-characterized functionalization of essentially clean SWCNTs enabled us to establish the maximum level of impurity content, below which the f-SWCNT intrinsic electrochemical activity is not jeopardized.

International audience; Ca-Fe layered double hydroxide (LDH) intercalated with chloride and nitrate ions has been synthesized with varying Ca-II:Fe-III molar ratios of the initial solution. Phase pure LDH is observed with Ca-II:Fe-III molar ratio of 2:1 and a mixture of LDH and Ca(OH)(2) is formed for Ca-II:Fe-III molar ratios higher than 2:1. Vibrational spectroscopies (Raman and IR) were used successfully to understand the interaction between the cationic and anionic sheets. The Raman bands positions at lower frequencies (150-600 cm(-1)) are intimately correlated to the nature of the divalent and trivalent ions but also to the nature of the anions. Indeed, a shift of similar to 9 cm(-1) is observed for the Raman double bands situated in the 300-400 cm(-1) region when comparing Raman spectra of CaFe-LDH containing either nitrate or chloride ions. Two types of nitrate environments are observed namely free (non-hydrogen bonded) nitrate and nitrate hydrogen bonded to the interlayer water or to the `brucite-like' hydroxyl surface. Multiple types of water structure are observed and would result from different hydrogen bond structures. Water bending modes are identified at 1645 cm(-1) greater than the one observed for LDH intercalated with chloride anions (1618 cm(-1)), indicating that the water is strongly hydrogen bonded to the nitrate anions.

Single-walled carbon nanotubes (SWCNTs) have been dynamically (shock) compressed to 0.5 Mbar, above the limit of their structural integrity. Two distinct types of material are identified by high-re ...

International audience; Interfacial processes controlled by ion transfer voltammetry at the interface between two immiscible electrolyte solutions were studied by in situ Raman spectroscopy. Raman spectra of the interface between a 5 mM NaCl aqueous solution and 10 mM bis(triphenyl-phosphoranydieneammonium) tetrakis(4-chlorophenyl) borate in 1,2-dichloroethane were recorded at open circuit potential and at various interfacial potential differences. At open-circuit potential, Raman peaks assigned to vibrational modes of 1,2-dichloroethane are clearly visible and peaks of weak intensity are measured for the organic electrolyte ions. When a negative interfacial potential difference is applied, the intensity of the peaks of the cation of the organic electrolyte increases, confirming its transfer induced by the interfacial potential difference applied. The electrochemically assisted generation of mesoporous silica deposits was then followed by in situ confocal Raman spectroscopy. The condensation of mesoporous silica was controlled by the transfer of cetyltrimethylammonium (CTA(+)) ions to an aqueous phase containing hydrolysed silanes. The transfer of CTA(+) at the interface was monitored in situ by confocal Raman spectroscopy, and formation of silica was observed.

We report on a first study of single walled carbon nanotubes (SWCNTs) after application of dynamic (shock) compression. The experiments were conducted at 19 GPa and 36 GPa in a recovery assembly. For comparison, an experiment at a static pressure of 36 GPa was performed on the material from the same batch in a diamond anvil cell (DAC). After the high pressure treatment the samples were characterized by Raman spectroscopy and transmission electron microscopy (TEM). After exposure to 19 GPa of shock compression the CNT material exhibited substantial structural damage such as CNT wall disruption, opening of the tube along its axis (“unzipping”) and tube shortening (“cutting”). Dynamic compression to 36 GPa resulted in essentially complete CNT destruction whereas at least a fraction of the nanotubes was recovered after 36 GPa of static compression though severely damaged. The results of these shock wave experiments underline the prospect of using SWCNTs as reinforcing units in material WILEY-VCH Verlag GmbH &Co. KGaA, Weinheim)

International audience; To avoid the dissolution of steel in industrial pickling process, tetramine inhibitors are added to the pickling bath. This study is devoted to the understanding of the action mechanism of these inhibitors in hydrochloric and sulphuric baths on non-alloyed and alloyed steels. Pickling experiments and characterization with XPS, Raman and infrared spectroscopies have shown that inhibitors work only in acid media and leached out from the steel surfaces during the rinsing operation just after pickling. The effectiveness of inhibitors depends on the acid media and the temperature. Experimental data are consistent with a surface mechanism, i.e., the so-called "outer-sphere" adsorption.

The synthesis of single-walled carbon nanotubes (SWCNTs) with the narrowest possible diameter distribution is a challenging undertaking in carbon nanoscience, which can be overcome through the fabrication of monodisperse catalytic nanoparticles. A technique is presented here to approach the diameter control of SWCNTs using a chemisorbed nickel acetylacetonate monolayer at the surface of silica. We show by Fourier transform infrared spectroscopy and thermogravimetry coupled with mass spectroscopy that a monolayer of nickel acetylacetonate is anchored with the silanol groups at the surface of the substrate. After thermal decomposition, the nickel remains bonded with these silanol groups, resulting in a good dispersion of the nickel over the silica surface. Using this catalyst, SWCNTs with a narrow diameter distribution were synthesized at moderate temperature. This opens new perspectives for the fabrication of uniform-diameter carbon nanotubes.

International audience; The investigation of highly conformal thin films using Atomic Layer Deposition (ALD) is driven by a variety of applications in modern technologies. In particular, the emergence of 3D memory device architectures requires conformal materials with tuneable magnetic properties. Here, nanocomposites of carbon, cobalt and cobalt carbide are deposited by ALD using cobalt acetylacetonate with propanol as a reducing agent. Films were grown by varying the ALD deposition parameters including deposition temperature and propanol exposure time. The morphology, the chemical composition and the crystalline structure of the cobalt carbide film were investigated. Vibrating Sample Magnetometer (VSM) measurements revealed magnetic hysteresis loops with a coercivity reaching 500 Oe and a maximal saturation magnetization of 0.9 T with a grain size less than 15 nm. Magnetic properties are shown to be tuneable by adjusting the deposition parameters that significantly affect the microstructure and the composition of the deposited films.

International audience; Single-walled carbon nanotubes (SWCNT) synthesized using the HiPco (R) process and purified thereafter were submitted to two covalent functionalization processes: i) a mild oxidation in a concentrated HNO3 solution using microwave irradiation and ii) a radical functionalization to graft methoxyphenyl groups. The samples were analyzed by Raman spectroscopy and spectroscopic ellipsometry in the energy window 0.07-4.96 eV. The complex dielectric function was analytically calculated in order to extract the real (epsilon(r)) and imaginary (epsilon(i)) parts of this function vs. the incident energy of the light. The ellipsometric data in the infrared part of the spectrum revealed that process i) mainly affected the amorphous carbon deposited on the surface of SWCNTs while process ii) strongly changed the electronic nature of the film due to a charge transfer between methoxyphenyl groups and SWCNTs. These results demonstrate the richness of information that spectroscopic ellipsometry is able to bring about on an entire carbon nanotube ensemble compared to Raman spectroscopy, while not suffering from limitation on their electronic structure and/or aggregate state/presence of surfactants.

In this chapter, the Bayesian Positive Source Separation (BPSS) is presented. First, we motivate the use of the proposed Bayesian approach by analyzing the rotational ambiguities of the NMF from a geometrical point of view. The proposed BPSS is particularly well adapted to difficult problems suffering from rotational ambiguities and with spectral sources having complex shapes. It consists in assigning Gamma distribution as an a priori model on pure component spectra and mixing coefficient. Three examples of successful applications of BPSS are given.

In the current work, we show that it is possible to favor the selective growth of single-walled carbon nanotubes (SWCNTs) with a narrow diameter distribution on supported catalyst particles with a broad size distribution. Carbon nanotubes were grown at 600 °C on silicon substrates. The structure of carbon deposits was controlled by managing the carbon feedstock for adjusting the rate of carbon nanostructures formation on the surface of catalyst particles. Either carbon nanofibers (CNFs) carpets or isolated SWCNTs were obtained. With the fine tune of carbon feedstock, small isolated SWCNTs with a narrow diameter distribution were obtained by limiting the catalytic activity of the largest catalyst particles. HRTEM observations of nanotube embryos have suggested a possible mechanism of multi-walled carbon nanotubes (MWCNTs) formation that can explain why the growth of MWCNTs with parallel walls seems to be more difficult than SWCNTs or CNFs at low temperature.

Double wall carbon nanotubes (DWCNTs) have proven to have a very good structural stability when exposed to high static pressures. We report here on the study of DWCNTs after application of shock wave (dynamic) compression up to 36 GPa in a recovery assembly. TEM images of so-treated samples reveal a threshold between 19 and 26 GPa of shock wave compression above which significant structural damage is induced whereas only minor damage can be detected below. The threshold detected with TEM coincides well with the collapse pressure of DWCNTs previously reported [You et al., High Press. Res. 31, 186 (2011); Aguiar et al., Phys. Chem. C 115, 5378 (2011)]. Raman data demonstrate a gradual accumulation of structural defects via an increase in D-band to G-band intensity ratio (ID/IG-ratio) from ∼0.2 to ∼0.8 in going from the source CNT material to the nanotubes after compression to 36 GPa. Despite severe damage; the DWCNTs exposed to 36 GPa of shock wave compression survived which is evidenced by Raman spectra. The DWCNTs demonstrate a higher susceptibility to structural damage under dynamic than static pressure.

International audience; Polarization analysis in Raman spectroscopy provides a powerful tool in chemical physics to identify the symmetry of the vibration modes of molecules, macromolecules and crystals, according to their crystallographic structure and local spatial orientation. In this paper we propose two new approaches in polarized Raman spectroscopy for data with rotational and spatial diversity, respectively. We show that the joint use of parallel and crossed polarization data yields more accurate source separation results and improves the uniqueness properties of the solution in blind nonnegative source separation algorithms. The proposed approaches are validated on two real polarized Raman data sets.

Electrochemical and spectroscopic studies of arsenopyrite samples were carried out under calcareous soil weathering conditions. Electrochemical study consisted of cyclic voltammetry using carbon paste electrodes with embedded FeAsS particles (CPE-FeAsS) in order to evaluate the oxidation process and the effect of the oxidation products on global reactivity. Leaching procedure consisted of mineral alteration by humid and aeration stages under calcareous conditions. Leached samples were characterized by cyclic voltammetry, SEM-EDS, Raman spectroscopy and XPS. Chemical analysis of leachates provided understanding of the extent of the mineral weathering process. The results indicated the formation of non-stoichiometric layers with variable composition (NL, e.g., Fe1-xAs1-yS) at all stages and the formation of α,β,δ-FeOOH compounds. Arsenic species were retained in this phases. A cyclic dissolution process of arsenopyrite was identified that seems to be influenced by NL composition. On the experimental basis, a dissolution process of arsenopyrite under calcareous soil weathering conditions is proposed.

We report on a systematic study of the influence of laser irradiation on the Raman spectra of HiPco-produced single-wall , CNTS. Specifically, we have examined the Raman response of bundled CNTs to: i) laser power density; ii) exposure time and iii) photon energy (1.96 and 2.33 eV). Our results show that irreversible destruction of CNTs in the bundles can occur at even low laser power density (0.15 kW/cm2). The tubes with smaller diameters are influenced first and the rate of CNT destruction increases with photon energy. Finally, we determined that when investigating destruction of CNT bundies, the use of a low laser power density is required because changes in the structure of the bundles can lead to sample temperature changes for otherwise identical measurement parameters.

International audience; Single-walled carbon nanotubes (SWNTs) were functionalized in a three-step procedure: a radical reaction leading to the introduction of p-methoxyphenyl groups, deprotection of the methoxy functions to generate free alcohol groups, and esterification to install a double bond for further polymerization. Visual dispersion tests in several solvents and thermal gravimetric analysis were used in conjunction with Raman spectroscopy to follow the three functionalization steps. Results indicated that the chemical procedure led to a functionalization yield as low as one grafted function per 110 carbon atoms and that the SWNTs were not homogeneously functionalized. Confocal Raman spectroscopy and optical microscopy observations, based on image analysis, were combined to objectively describe the state of aggregation of semiconducting SWNTs through calculation of an optical parameter. This parameter was found to be strongly correlated to some features of the Raman phonon modes, revealing the interplay between functionalization and aggregation effects. It is concluded that, to compare raw and functionalized SWNTs using confocal Raman spectroscopy, samples should be examined at similar states of aggregation.

International audience; The efficiencies of two methods of functionalizing single wall carbon nanotubes (SWCNTs) are compared, either through a radical addition of 4-methoxyphenylhydrazine hydrochloride by a classical thermally activated procedure, or via a microwave-assisted method. X-ray photoelectron spectroscopy and thermal gravimetric analysis clearly indicate the efficiency of both methods. Raman and absorption spectroscopy further confirm the functionalization and reveal the covalent nature of the bonds created at the carbon nanotube surface. For the microwave-assisted reaction, 5–15min is enough to functionalize the SWCNTs. Longer microwave exposure times reduce the functionalization yield and lead to a removal of groups which were bonded in a previous stage. An optimal choice of microwave irradiation time allows reducing the reaction time from days to minutes.

Reduced glutathione (GSH) is involved in biochemical and physiological processes in cells. Flocculation is an important mechanism in microorganisms. The present study concerned the potential relationship between GSH metabolism and flocculation. Two yeast strains, a flocculent (Kluyveromyces lactis 5c) and a nonflocculent (Kluyveromyces lactis 5a) strain, were used. The level of intracellular GSH measured during the growth period was significantly higher in the nonflocculent than in the flocculent strain; in contrast, the flocculent strain exhibited brighter staining of vacuoles than the nonflocculent strain when observed using epifluorescence microscopy. Compounds acting either on flocculation (EDTA, galactose) or on GSH metabolism (buthionine sulfoximine, and N-acetylcysteine) were tested on the flocculent strain during the growth period. Both EDTA and galactose fully inhibited flocculation and induced GSH overproduction of 58% and 153%, respectively. Buthionine sulfoximine decreased GSH level by 76% but had no effect on flocculation; N-acetylcysteine increased the GSH level and flocculation by 106% and 41%, respectively. Combination of EDTA and N-acetylcysteine produced similar effects than with each of them. Combination of galactose and N-acetylcysteine increased the GSH level but decreased flocculation. These results demonstrated that GSH homeostasis is linked to the flocculation mechanism. A hypothesis related to stress is given.

International audience; Osteoarthritis (OA) is the most common cause of joint chronic pain and involves the entire joints. Subchondral osteoarthritic osteoblasts present a mineralization defect and, to date, only a few molecules (Vitamin D3 and Bone Morphogenetic Protein2) could improve the mineralization potential of this cell type. In this context, we have tested for the first time the effect of nacre extract on the mineralization capacity of osteoblasts from OA patients. Nacre extract is known to contain osteogenic molecules which have demonstrated their activities notably on the MC3T3 pre-osteoblastic cell line. For this goal, molecules were extracted from nacre (ESM, Ethanol Soluble Matrix) and tested on osteoblasts of the subchondral bone from OA patients undergoing total knee replacement and on MC3T3 cells for comparison. We chose to investigate the mineralization with Alizarin Red staining and with the study of extracellular matrix (ECM) structure and composition. In a complementary way the structure of the ECM secreted during the mineralization phase was investigated using second harmonic generation (SHG). Nacre extract was able to induce the early presence (after 7 days) of precipitated calcium in cells. Raman spectroscopy and electron microscopy showed the presence of nanograins of an early crystalline form of calcium phosphate in OA osteoblasts ECM and hydroxyapatite in MC3T3 ECM. SHG collagen fibers signal was present in both cell types but lower for OA osteoblasts. In conclusion, nacre extract was able to rapidly restore the mineralization capacity of osteoarthritis osteoblasts, therefore confirming the potential of nacre as a source of osteogenic compounds. (C) 2015 Elsevier Inc. All rights reserved.

International audience; Mining activities release arsenopyrite into calcareous soils where it undergoes weathering generating toxic compounds. The research evaluates the environmental impacts of these processes under semi-alkaline carbonated conditions. Electrochemical (cyclic voltammetry, chronoamperometry, EIS), spectroscopic (Raman, XPS), and microscopic (SEM, AFM, TEM) techniques are combined along with chemical analyses of leachates collected from simulated arsenopyrite weathering to comprehensively examine the interfacial mechanisms. Early oxidation stages enhance mineral reactivity through the formation of surface sulfur phases (e.g., S (n) (2-)/S-0) with semiconductor properties, leading to oscillatory mineral reactivity. Subsequent steps entail the generation of intermediate siderite (FeCO3)-like, followed by the formation of low-compact mass sub-micro ferric oxyhydroxides (alpha, gamma-FeOOH) with adsorbed arsenic (mainly As(III), and lower amounts of As(V)). In addition, weathering reactions can be influenced by accessible arsenic resulting in the formation of a symplesite (Fe-3(AsO4)(3))-like compound which is dependent on the amount of accessible arsenic in the system. It is proposed that arsenic release occurs via diffusion across secondary alpha, gamma-FeOOH structures during arsenopyrite weathering. We suggest weathering mechanisms of arsenopyrite in calcareous soil and environmental implications based on experimental data.

The results of a study on the evolution of HiPco single-walled carbon nanotubes during the oxidizing action of H2SO4 and HNO3 are presented. The process conditions used have been chosen so as to avoid any significant damage to the nanotube structure. The type and level of functionalization, the location of the grafted functions on the surface of the nanotube and the changes in morphological characteristics of the samples were examined by using a wide and complementary range of analytical techniques. We propose an explanation for the differences in the oxidizing action of sulfuric and nitric acids. The combined results allow us to suggest possible reaction mechanisms that occur on the surface of the nanotube., Comment: {\'E}quipe 104 : Nanomat{\'e}riaux

In calcareous sites, hard rock mining activities release pyrite (FeS2), pyrrhotite (Fe1−x S) and other sulfides to soils. The sulfides then undergo weathering processes, generating acid rock drainage and secondary compounds. Despite the potentially important environmental impacts, very few studies have considered the mechanisms of pyrite and pyrrhotite weathering and the transformation of secondary compounds under neutral-alkaline carbonated conditions. In this study, we used an experimental approach combining electrochemical, microscopic and spectroscopic techniques to examine the interfacial processes involved in pyrite and pyrrhotite weathering under simulated calcareous soil conditions. The results showed an initial oxidation step with the formation of variable amounts of surface sulfur compounds (e.g., polysulfides, S 2− , and elementary sulfur, S0) and acid generation, leading to significant modification of the oxidative behavior of the minerals. The surface changes that occurred as a result of mineral weathering provoked transient enhancement of pyrite reactivity and progressive passivation in the pyrrhotite system. Iron sulfides weathering was found to involve the formation of an intermediate siderite (FeCO3)-like compound, preceding the predominant formation of K-jarosite (K·Fe3(SO4)2(OH)6) and/or ferric oxyhydroxide (α, γ-FeOOH) compounds, depending on the surface acid condition reached in the systems. Mechanisms of pyrite and pyrrhotite weathering in calcareous soils are suggested on the basis of surface characterization and chemical analysis of the leachates generated, and the environmental implications are discussed.

An alternative to culture methods for the control of drinking water disinfection would use fluorescent dyes that could evidence the nucleic acid damages provoked by sodium hypochlorite treatment. The two dyes selected in this study, SYBR Green II RNA gel stain and TOTO-1 iodide, efficiently stain nucleic acids (DNA and RNA) and quite poorly the other biomolecules considered (Bovine serum albumin, palmitic acid and dextrane). After treatment of nucleic acid solutions with increasing amounts of sodium hypochlorite, a decrease of fluorescence intensity is observed for both DNA and RNA stained with either SYBR-II or TOTO-1. However, the two fluorochromes do not lead to the same results, which shows that the two dyes are not bound to nucleic acids in the same way. Contrary to TOTO-1, SYBR-II reveals to be sufficiently sensitive to indicate both DNA or RNA damages as soon as the latter are in contact with hypochlorite even at concentrations of HClO lower than 10 micromol/L. Moreover, SYBR-II offers the opportunity to make quantitative titration of chlorine treated DNA and therefore seems to be the appropriate candidate to control the efficiency of the hypochlorite disinfection process of drinking water samples.

The effects of wood phenolic compounds on the photopolymerization of an acrylate resin were evaluated under model conditions, in the presence of different photoinitiating systems, based on a bisacylphosphineoxide derivative, an amine, and isopropylthioxanthone. The steady-state photolysis of these systems and their excited-state processes were also characterized. The kinetic scheme, derived from these experiments, promoted discussion of the performances attained in photopolymerization experiments. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1154–1164, 2004

The rate constants kred of the thermal electron-transfer reaction between several aminoalkyl radicals and two ground-state aromatic ketones, benzophenone (BP) and thioxanthone (TX), were measured by nanosecond transient photoconductivity in acetonitrile. The kred values were strongly at variance from those expected from the free energy change ΔGred of the reaction within the framework of the Marcus' theory of electron transfer. Moreover, addition of small amounts of water in acetonitrile strongly enhanced kred and the ion quantum yield. These results were rationalized by invoking a 1 : 1 complex formation between amino-alkyl radicals and water, and semi-empirical AM1 calculations were used to sustain this explanation.

Fluorescence quenching by photoinduced electron transfer (PET) of polyaromatic acceptors by aliphatic amines was studied in acetonitrile. Sorting the quenching rate constants kQ according to the different amines led to monotonic curves of log kQvs. ΔGet (the Gibbs energy change), which could be fitted in some cases by Marcus' law. However, detailed examination of the fitting parameters led to the conclusion that this approach misinterpreted the data. By contrast, sorting the data according to the acceptors showed that kQ rose rapidly as the exergonicity increased, and reached a plateau located under the limiting diffusion rate constant. This was ascribed to weak and variable electronic coupling between the various accepting orbitals and the donating n orbital of the homogeneous set of aliphatic amines. Moreover, when the plateau values log(kmaxet) were plotted against the excited reduction potential of the acceptors, a good correlation was revealed. This underlined the crucial role of the accepting orbital topology towards a homogeneous set of donors.

International audience

International audience; Shearforce regulated scanning electrochemical microscopy (SECM) has been associated with Raman microspectrometry in order to perform combined electrochemical and spectrochemical analysis on reactive interfaces. The interest of the method was evaluated by analyzing local corrosion phenomena in damaged Zn(Mg, Al) self healing coatings,deposited on steel Despite the high aspect ratio of the analyzed sample displaying here more than a 50 pm depth profile, the optimized setup allowed (1) precise electrode positioning, with the help of shearforce detection, (2) electrochemical measurement at a constant clistance from the sample surface, and (3) local chemical analysis of the solid surface by confocal Raman microspectroscopy performed at a constant focal distance from the sample. All in all, this new setup allows one to approach the detailed reactivity involved in defective metal samples.

International audience; In this paper, we consider hyperspectral unmixing problems where the observed images are blurred during the acquisition process, \emph{e.g.} in microscopy and spectroscopy. We derive a joint observation and mixing model and show how it affects endmember identifiability within the geometrical unmixing framework. An analysis of the model reveals that nonnegative blurring results in a contraction of both the minimum-volume enclosing and maximum-volume enclosed simplex. We demonstrate this contraction property in the case of a spectrally-invariant point-spread function. The benefit of prior deconvolution on the accuracy of the restored sources and abundances is illustrated using simulated and real Raman spectroscopic data.

International audience; Atomic layer deposition (ALD) of nickel and nickel carbide is reported starting from nickel acetylacetonate and a primary alcohol. The sequential reactions of both reactants with the adsorbed species are shown to be self-limited. Use of propanol or ethanol as reducing agents yields the formation of the technologically relevant carbon-Ni3C thin films, whereas the carbon content with use of methanol is less than 5 atom %. These metallic nickel thin films are electrically conductive and feature a soft ferromagnetic behavior. The thermally stable cubic lattice of nickel was grown at 300 degrees C with methanol as a reducing agent while the metastable hexagonal structure was obtained at lower temperatures. The morphology and the structure of the films were investigated with use of scanning electron microscopy and X-ray diffraction. The films are nanocrystalline featuring an average crystallite size of similar to 10 nm. Hydrogen-free ALD of nickel is particularly appealing for the deposition of (i) conformal coatings on hydrogen-sensitive substrates such as highly reducible oxides and metals with high capacity to form hydrides and (ii) 3D nanomaterials with high aspect ratio.

International audience; This research treats a particularly challenging undertaking in carbon nanoscience: controlling the diameter distribution of single walled carbon nanotubes (SWCNTs) grown using CVD. To do so requires the fabrication of well-separated and monodispersed catalytic metal nanoparticles which can be uniformly distributed on a substrate. We propose a new strategy involving the preparation of a monolayer of chemisorbed nickel acetylacetonate which is shown by infrared spectroscopy and coupled thermogravimetric-mass spectrometry analyses to be anchored to the surface silanol groups of the substrate. After decomposition of this precursor, the nickel remains bonded with these surface silanol groups which upon further heating results in good dispersion of the nanoparticles over the silica surface. Using this catalyst, SWCNTs with a very discrete chiral preference and a narrow diameter distribution were synthesized at moderate temperature. This work thus opens new perspectives for the fabrication of uniform-diameter carbon nanotubes. (C) 2013 Elsevier Ltd. All rights reserved.

This comment draws attention to the fact that a biased set of electron donor/acceptor couples can lead to an unorthodox vision of fluorescence quenching mechanism. It is shown that the results reported by Inada et al. can be adequately explained by resorting to adiabaticity and stereo-electronic effects.

The photopolymerization of acrylate resins on wood surfaces suffers from retardation and inhibition effects due to the phenolic derivatives present at the interface. This article details the study of the effect of a set of phenolic compounds on the initiation step. The global effect was recorded by differential scanning calorimetry and photocalorimetry. A comparison between a direct photocleavable initiator such as 2,2-dimethyloxy-2-phenylacetophenone (DMPA) and a two-component system like benzophenone/N-methyldiethanolamine (BP/MDEA) suggests that the retardation effect observed in the latter case is due to the interaction between phenols and the triplet state of BP. Subsequently, nanosecond transient absorption (NTA) spectroscopy was used to measure in acetonitrile the quenching rate constants k Q . A hydrogen abstraction occurred, and the ketyl radical quantum yield was also determined by NTA experiments. In comparison with the photoreduction mechanisms proposed in the literature, the high k Q values obtained were tentatively correlated to the half-wave oxidation potentials of phenols in order to discuss the involvement of an electron transfer within the reaction. Some EPR experiments were done to confirm in situ the photoreduction process at the wood surface and the creation of phenoxyl radicals. The interaction of phenols with some initiating radicals was also studied.

The dark secondary reactions following the photoreduction of benzophenone by triethylamine constitute an example of tricky reactions involving radicals throughout proton, hydrogen atom and electron transfer. In this work, nanosecond transient absorption spectroscopy is used to detect the influence of hydrogen bonding ability of the solvent on these reactions by means of adding water or methanol to acetonitrile solutions. The effect of increasing polarity is studied with the addition of LiClO 4 and it is found at this occasion that dark processes are also sensitive to Lewis acid-base properties of the solvent. The secondary reactions in the reference medium, i.e., neat acetonitrile, are conveniently monitored by photoconductivity technique, which reveals to be a useful complement to absorption spectroscopy and underlines the crucial role of residual water on the reactions.