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In the framework of a protein–ligand-fishing strategy to identify proteins that bind to trans-resveratrol, a natural phenolic compound with pharmacological benefits, we have developed magnetic nanoparticles covalently linked to trans-resveratrol through three different derivatives and examined their aggregation behavior in aqueous solution. The monodispersed magnetic core (18 nm diameter) with its mesoporous silica shell (93 nm diameter) exhibited a notable superparamagnetic behavior useful for magnetic bioseparation. The hydrodynamic diameter, deduced from dynamic light scattering analysis, of the nanoparticle increased from 100 to 800 nm when the aqueous buffer changed from pH 10.0–3.0. A size polydispersion occurred from pH 7.0–3.0. In parallel, the value of the extinction cross section increased according to a negative power law of the UV wavelength. This was mainly due to light scattering by mesoporous silica, whereas the absorbance cross section remained very low in the 230–400 nm domain. The three types of resveratrol-grafted magnetic nanoparticles exhibited similar scattering properties, but their absorbance spectrum was consistent with the presence of trans-resveratrol. Their functionalization increased their negative zeta potential when pH increased from 3.0 to 10.0. The mesoporous nanoparticles were monodispersed in alkaline conditions, where their anionic surface strongly repulsed each other but aggregated progressively under van der Waals forces and hydrogen bonding when negative zeta potential decreased. The characterized results of nanoparticle behavior in aqueous solution provide critical insight for further study of nanoparticles with proteins in biological environment.

International audience; The compounds Li3Ba2Ln3(MoO4)8 (Ln = Er, Tm) have been obtained by the high-temperature flux technique using the slow cooling method. Crystals grown spontaneously were used to characterize the materials and investigate their properties using X-ray diffraction (XRD), Raman spectroscopy, and magnetic measurements. Single crystal structures were solved and refined in the monoclinic space group C2/c. Lattice dimensions are a = 5.1935, b = 12.6364, c = 19.1022 Å,  = 91.399 ° for Er-based triple molybdate (pink crystals) and a = 5.1846, b = 12.5766, c = 19.1557 Å,  = 91.525 ° for Tm-molybdate (green crystals). The Ln cations, mainly at general position 8f, are coordinated by eight oxygen atoms and adopt a distorted antiprismatic geometry. The distribution of atoms over the three cationic sites is discussed comparatively to literature reports. Unpolarized Raman characterization supports both the disordered cation distribution, and the distortion of the MoO4 units. From the magnetic susceptibility measurements, it is found that the two triple molybdates follow a Curie-Weiss law in the 10-300 K domain, with a negative paramagnetic temperature θCW. The antiferromagnetic character is highlighted by the field-dependent magnetization curves.

In the search of smarter routes to control the conditions of N-heterocyclic carbene (NHCs) formation, a two-component air-stable NHC photogenerating system is reported. It relies on the irradiation at 365 nm of a mixture of 2-isopropylthioxanthone (ITX) with 1,3-bis(mesityl)imidazoli(ni)um tetraphenylborate. The photoinduced liberation of NHC is evidenced by reaction with a mesitoyl radical to form an NHC-radical adduct detectable by electron spin resonance spectroscopy. The NHC yield can be determined by 1 H NMR spectroscopy through the formation of a soluble and stable NHC-carbodiimide adduct. To deprotonate the azolium salt and liberate the NHC, a mechanism is proposed in which the role of base is played by ITX radical anion formed in situ by a primary photoinduced electron-transfer reaction between electronically excited ITX (oxidant) and BPh4 - (reductant). An NHC yield as high as 70 % is achieved upon starting with a stoichiometric ratio of ITX and azolium salt. Three different photoNHC-mediated polymerizations are described: synthesis of polyurethane and polyester by organocatalyzed step-growth polymerization and ring-opening copolymerization, respectively, and generation of polynorbornene by ring-opening metathesis polymerization using an NHC-coordinated Ru catalyst formed in situ.

International audience; Crystals of the Yb-containing double tungstate and double molybdate LiYbX2O8 (X = W, Mo) have been spontaneously grown by a high-temperature flux technique. Their structure has been determined from single-crystal X-ray diffraction at room temperature. LiYbW2O8 crystallizes in the monoclinic P2/n space group (No. 13), with unit cell parameters a = 4.9910(2), b = 5.7964(2), c = 9.8886(4) Å, β = 93.353(1) °. LiYbMo2O8 displays the tetragonal symmetry and is described in the noncentrosymmetric I4̅ space group (No. 82) with a = b = 5.1149(1), c = 11.0919(4) Å. Structural features such as coordination numbers around the atoms and ordered/disordered arrangement of the Yb3+ and Li+ cations explain the differences between these compounds whose vibrational and magnetic properties have also been studied.

International audience; Although N-heterocyclic carbenes (NHCs) have brought profound changes in catalytic organic synthesis, their generation generally requires an inert atmosphere and harsh conditions. To overcome these limitations, an air-stable NHC photogenerator has been developed involving two mild components: 1,3-bis(mesityl)imidazolium tetraphenylborate (IMesH+BPh4−) and electronically excited isopropylthioxanthone (ITX). In this study, the photochemical mechanism is investigated via the accurate identification of the transient species and photoproducts. Electron transfer reaction between the excited triplet state of ITX and BPh4− is demonstrated as being the primary photochemical step. Nanosecond laser spectroscopy shows an efficient quenching and the formation of the expected ITX radical anion. The oxidized borane species is not observed, suggesting that this short-lived species could dissociate very rapidly to give the phenyl radical – successfully identified using electron paramagnetic resonance – and triphenylborane. As regards the final photoproducts, 1H and 13C NMR spectroscopies support the formation of the targeted NHC, 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene (IMes), suggesting the occurrence of a subsequent proton transfer reaction between ITX radical anion and imidazolium cation (IMesH+). Gas chromatography-mass spectrometry reveals three other products: biphenyl, isopropylthioxanthene and ITX. Their formation can be reconciled with a 2-step mechanism of photoinduced electron/proton transfer reactions. 11B NMR spectroscopy demonstrates that the main organoboron photoproduct is diphenylborinic acid formed by oxidation of BPh3. Due to its Lewis acidity, Ph2BOH can react with IMes to yield an NHC–boron adduct.

International audience; Langatate La3Ga5.5Ta0.5O14 is piezoelectric crystal from langasite family, commonly grown by Czochralski method from Ir crucible. Langatate crystals of different colors (colorless, orange, green) have been studied by optical spectroscopy in UV-Visible (200 – 800 nm) and IR (7000 – 1000 cm-1) ranges. Furthermore, the effects of irradiation by ultraviolet laser source (λ=266 nm) and post-growth annealing in N2+O2 atmosphere have been investigated. The yellow-orange is mainly due to an absorption centered in the ultraviolet that extends into the blue of the visible spectrum (250-500 nm). The IR optical absorption spectra of Langatate crystals exhibit an absorption band at 5370 cm-1. It seems linked to a point defect responsible for color. The intensity of the absorption band at 3430 cm-1 increases after annealing in oxygen containing atmosphere. We have discussed phenomenon that can occur simultaneously in langatate crystals and produce very similar colors which are related to structural defects. First, metal ions impurities (as Iron, Titanium…), whose presence is previously confirmed by femtosecond laser ablation coupled with ICP-MS spectroscopy, can contribute to langatate color. Second, ultraviolet absorption leads us to think about charge transfer phenomenon such as O2- → Fe3+ and/or Fe3+-Fe3+ pair transitions. Third, the irradiation by ultraviolet (λ=266 nm) laser source locally color the langatate sample by the creation of color centers. Origins of color centers, particularly those related to oxygen vacancies, ( , 2e′)x, are discussed. And, finally, point defects changes the band gap of langatate, leading to extend the absorption to visible light regions.

We report on the magnetic properties of the B20 polycrystalline MnGe compound synthesized under high-temperature and high-pressure conditions. From isothermal ac susceptibility experiments, we found the presence of several different magnetic-field–induced phases presenting similarities with those in the isostructural compounds MnSi and FeGe but with much broader existence range in the domain. From anomalies found in the ac magnetic susceptibility, we found not only the presence of an A phase similar to the one observed in MnSi but also a second phase we call B, whose magnetic signature is very similar to that of the A phase. Our discovery indicates that MnGe is a promising compound in order to further explore the existence conditions of the phases containing skyrmions.

Before using any piezoelectric crystal to realize acoustic devices (sensors, transducers, actuators or ultra-stable resonators) and beyond its mechanical properties, the crystal material itself has to be characterized. Whether the very interesting properties of the LGT crystal make it the best candidate to substitute quartz crystal for frequency output devices, we must take into account the crystal quality. Indeed, applications require homogeneous crystals with reproducible physical properties.

Single-crystalline nanorods of {gamma}-MnOOH (manganite) phase with diameters of 120 nm and lengths of 1100 nm have been prepared using a new cluster growth route under low-temperature hydrothermal conditions starting from [Mn{sub 12}O{sub 12}(CH{sub 3}COO){sub 16}(H{sub 2}O){sub 4}].2CH{sub 3}COOH.4H{sub 2}O or [Mn{sub 12}O{sub 12}(C{sub 2}H{sub 5}COO){sub 16}(H{sub 2}O){sub 3}].4H{sub 2}O without any catalyst or template agents. The so-obtained nanorods were studied by X-ray diffraction (XRD), infrared (IR) spectroscopy, Raman spectroscopy and high resolution transmission electron microscopy (HRTEM). Their thermal conversion opens an access to Mn{sub 3}O{sub 4} (hausmannite) and {beta}-MnO{sub 2} (pyrolusite) nanorods, respectively, under argon or air atmosphere. A coercive field of 12.4 kOe was obtained for the Mn{sub 3}O{sub 4} nanorods.

The first discharge of a nanostructured FeSn2 based negative electrode for Li-ion batteries has been studied by combining operando 119Sn Mossbauer spectroscopy and ex situ magnetic measurements. A modified Swagelok-type cell has been designed to perform in situ Mossbauer measurements, which allowed us to quantitatively follow the first discharge. The electrochemical mechanism consists in a conversion reaction that transforms FeSn2 into Li7Sn2. The Mossbauer spectrum at the end of the first discharge has been analyzed from first principles calculations of the Mossbauer parameters. The observed differences with bulk Li7Sn2 have been explained by the small size of the electrochemically formed particles. The magnetic measurements of the electrode material at the end of the discharge show the existence of rather pure superparamagnetic iron nanoparticles with an average diameter in the range 2–3 nm as evaluated from three different methods. The electrode saturation magnetization increases during the discharge, ...

A series of spinel compounds with composition CuFe{sub 0.5}(Sn{sub (1-x)}Ti{sub x}){sub 1.5}S{sub 4} (0{

International audience; Dopachrome Conversion Factor (DCF) was found in the plasma of the locust Locusta migratoria. It has an apparent molecular mass of 85,000. Its K(m) was 0.2 mM at 22 degrees C and pH 7 with L-dopachrome as substrate. It had a high substrate specificity for L-dopachrome, methyl-L-dopachrome and L-dopachrome methyl ester but no activity on the corresponding D-isomers or on dopaminechrome. DCF was devoid of any phenoloxidase activity. Under action of DCF, L-dopachrome was converted into dihydroxyindole, which showed that a decarboxylation occured in the course of reaction. Locust DCF was inhibited by indole-3-propionic acid but not by indole-3- or indole-2-carboxylic acid. It was also inhibited by L-tryptophan in a competitive manner. Inhibition and substrate specificity suggest that a carboxyl group, either free or as a methyl ester, is necessary but not sufficient for enzyme recognition. When purified prophenoloxidase was activated and then added to dihydroxyindole either prepared by chemical synthesis or obtained by action of purified DCF on dopachrome, black pigments with a maximum absorption at 540 nm were generated. Therefore in the eumelanin pathway of locust plasma, phenoloxidase can catalyze the reaction that converts the product generated by DCF.

International audience; Enzymes are biological catalysts that are interesting for key reactions such as hydrogen evolution, CO2 conversion into hydrocarbons and the fixation of nitrogen. Enzymes are particularly good catalysts for organic reactions because of their high selectivity. However, they exhibit modest stability and require extensive purification, which makes them costly. Here, we report a biomimetic electroactive two-dimensional (2D) catalyst based on single-layer metallic MoS2 nanosheets for the oxidation of alkyl and aryl sulfides. The structure of the MoS2 nanosheets mimics the active site of natural dimethyl sulfoxide (DMSO) reductase found in anaerobic bacteria. We demonstrate that 2D MoS2 nanosheets efficiently oxidize organic sulfides. Notably, we show that dimethyl sulfide can be electro-oxidized to DMSO with activity surpassing that of noble metal catalysts. The production of DMSO using metallic 1T' phase MoS2 reaches 680 L h-1 per gram at 1500 mV vs. NHE-~ 4 times higher than platinum nanoparticles-and is stable for > 24 hours. Our findings provide new directions for electrosynthesis from metallic 2D materials.