Search

Pink euclase of gem quality and centimeter size, presenting an unusual pink-orange coloration and a pink to orange pleochroism, was discovered near Livramento de Nossa Senhora, in Bahia State, Brazil. The origin of the pink coloration has been investigated using several spectroscopic techniques: UV-Vis-NIR spectroscopy, electron paramagnetic resonance (EPR), luminescence, and X-ray absorption near edge structure (XANES). The coloration is mainly due to the presence of Mn3+ substituted to octahedral Al3+ that causes an intense split band at about 18 500 and 21 000 cm−1. The crystal field splitting Dq, crystal field stabilization energy (CFSE), and Racah parameter B for Mn3+ are 2055.5 cm−1, 147 kJ/mol, and 886 cm−1, respectively. The Mn3+ molar extinction coefficient varies as a function of polarization, between 23 and 55 L.mol−1·cm−1. An additional absorption band, near 24 000 cm−1, together with the rising background toward the UV, tentatively assigned to the O → Fe3+ OMCT, contributes to the pink-orange hue. The in-situ UV-Vis-NIR spectra on heating up to 500 °C show a color change toward an intense, stable pink color. CIE colorimetric parameters demonstrate that the color of the investigated euclase remains in the pink domain before and after heat treatment. In the absence of Mn2+, shown by EPR and luminescence, the presence of Mn3+ evidences oxidative formation conditions due to contamination of the hydrothermal fluids by the surrounding host rock.

International audience; Magnetite and maghemite multi-core nanoflowers (NFs) synthesized using the modified polyol-mediated routes are to date among the most effective nano-heaters in magnetic hyperthermia (MHT). Recently, magnetite NFs have also shown high photothermal (PT) performances in the most desired second near infra-red (NIR-II) biological window making them attractive in the field of nanoparticle-activated thermal therapies. However, what makes 2 magnetic NFs efficient heating agents in both modalities still remain an open question. In this work, we investigate the role of many parameters of the polyol synthesis on the final NFs size, shape, chemical composition, number of cores and crystallinity. These nanofeatures are later correlated to the magnetic, optical and electronic properties of the NFs as well as their collective macroscopic thermal properties in MHT and PT to find relationships between their structure, properties and function. We evidence the critical role of iron(III) and heating ramps on the elaboration of well-defined NFs with high number of multi-cores. While MHT efficiency is found to be proportional to the average number of magnetic cores within the assemblies, the optical responses of the NFs and their collective photothermal properties depend directly on the mean volume of the NFs (as supported by optical cross sections numerical simulations) and strongly on the structural disorder in the NFs, rather than the stoichiometry. The concentration of defects in the nanostructures, evaluated by photoluminescence and Urbach energy (EU), evidences a switch in the optical behavior for a limit value of EU = 0.4 eV where a discontinuous transition from high to poor PT efficiency is also observed.

International audience; The structure and vibrational properties of water molecules confined in unidirectional hydrophilic nanopores of AlPO4-54·xH2O were investigated from room temperature down to 10 K by single-crystal synchrotron X-ray diffraction, neutron pair-distribution function analysis, incoherent inelastic neutron scattering, far- and mid-infrared spectroscopy, ab initio molecular dynamics, and grand canonical Monte Carlo simulations. The ensemble of results indicates that water confined in AlPO4-54·xH2O nanopores does not crystallize down to 10 K and points at the existence of two different types of water networks, whose local arrangement and dynamical behavior become more and more distinguished when lowering the temperature below 150 K. Upon cooling, water close to the zeolite pore wall shows a highly ordered local arrangement induced by the pore wall, with a more defined site occupancy and lower density with respect to bulk water. Conversely, water in the pore core shows a denser, more disordered, and orientationally distorted arrangement and a glassy like behavior down to the lowest investigated temperature.

While HgTe nanocrystals (NCs) in the mid-infrared region have reached a high level of maturity, their far-infrared counterparts remain far less studied, raising the need for an in-depth investigation of the material before efficient device integration can be considered. Here, we explore the effect of temperature and pressure on the structural, spectroscopic, and transport properties of HgTe NCs displaying an intraband absorption at 10 THz. The temperature leads to a very weak modulation of the spectrum as opposed to what was observed for strongly confined HgTe NCs. HgTe NC films present ambipolar conduction with a clear prevalence of electron conduction as confirmed by transistor and thermoelectric measurements. Under the application of pressure, the material undergoes phase transitions from the zinc blende to cinnabar phase and later to the rock salt phase which we reveal using joint X-ray diffraction and infrared spectroscopy measurements. We discuss how the pressure existence domain of each phase is affected by the particle size.

The role of carbon in the formation of alpha boron at high pressure and high temperature (HPHT) has been investigated by combining HPHT experiments and density functional theory (DFT) calculations. Starting from beta rhombohedral or amorphous boron and amorphous carbon at 5 GPa, the alpha boron phase has been repeatedly observed between 1473 K and 2273 K, at temperatures that are much higher than those reported in the phase diagram of boron. The DFT investigation of the effect of carbon insertion into the alpha rhombohedral boron atomic structure on the formation enthalpy, volume and optical properties shows that only the (B11C) substituted icosahedron defect accounts for the slight volume contraction observed in {\alpha} boron. It is also compatible with the observed red colour of {\alpha} boron crystals, and consistently has a very low formation energy. Our calculations also provide a calibration tool to evaluate the carbon concentration in the samples. Finally, the synthesis temperature is found to be an easy means to tune the carbon concentration on demand.

International audience; A key challenge in the design of magnetic molecular switches is to obtain bistability at room temperature. Here, we show that application of moderate pressure makes it possible to convert a paramagnetic FeIII2CoII2 square complex into a molecular switch exhibiting a full dia‐ to paramagnetic transition: FeIICoIII ⇔ FeIIICoII. Moreover, the complex follows a rare behavior: the higher the pressure, the broader the magnetic hysteresis. Thus, the application of an adequate pressure allows inducing a magnetic bistability at room temperature with predictable hysteresis width. The structural studies at different pressures suggest that the pressure‐enhanced bistability is due to the strengthening of intermolecular interactions upon pressure increase. An original microscopic Ising‐like model including pressure effects is developed to simulate this unprecedented behavior. Overall, this study shows that FeCo complexes could be very sensitive piezo switches with potential use as sensors.

International audience; A study of five diamonds containing mineral and fluid inclusions, selected among forty-nine specimens from the Cullinan Mine, South Africa, was carried out to better document the origin and formation of N-absent B-poor (type IIb) diamonds. The combination of several in-situ non-destructive techniques was used to identify the mineralogy and the chemical composition of primary and secondary inclusions. These include breyite, larnite, graphite, Fe-Ni-Cu native metallic alloys, sulfides of the pyrrhotite group, Ni-rich oxide and potential hydrous ferric sulfates. A common and abundant hydrous fluid containing H2O + CH4 was also identified. From the various observations, we suggest that these type IIb diamonds grew in an aqueous oxidized fluid reacting with a reduced mantle characterized by low oxygen fugacity. Remnant pressures recorded in primary breyite by Raman shifts and XRD measurements enabled the calculation of minimal entrapment pressures of inclusions using elastic geothermobarometry. Applying pressure corrections caused by elastic relaxation, minimum trapping pressures from 4.9 GPa to 5.6 GPa were calculated, suggesting lithospheric depths consistent with the occurrence of numerous graphite inclusions. The association of breyite and larnite, which is often considered as an indicator of sublithospheric origin, also occurs at pressures of 6 GPa or lower in a H2O-rich and carbonate/Ca-rich environment. The B-poor and N-absent features of type IIb diamonds do not require the classic subduction-related model of their formation. Whereas high-pressure minerals would host boron in cold subducting slabs, slabs are also important carriers of nitrogen into the deep mantle, with this latter element mostly absent in these diamonds. In our alternative model, the mantle is proposed as an alternative source of boron, whereby metallic alloys or N speciation between fluid and melt would still prevent the incorporation of nitrogen, leading to the expression of the blue, boron-related and N-absent features of type IIb diamonds. The observed mineralogical assemblage neither proves sublithospheric origin nor does it exclude lithospheric depths of formation for these diamonds. Hence, we propose that type IIb diamonds form in a mantle continuum, from sublithospheric to lithospheric depths.

International audience; Carbon disulphide (CS2) is, together with its closest analogue CO2, one of the simplest molecular systems made of double covalent bonds. Under high pressure, the molecular structure is expected to break up to form extended crystalline or polymeric solids. Here we show that by compression at 300 K to ∼10 GPa (100 kbar) using large-volume high pressure techniques, a sudden reaction leads to a mixture of pure sulphur and a well-defined compound with stoichiometry close to C2S which can be recovered to ambient pressure. We present neutron and x-ray diffraction as well as Raman data which show that this material consists of sulphur bonded to sp2 graphite layers of nanometric dimensions. The compound is a semiconductor with a gap of 45 meV, as revealed by temperature dependent resistivity measurements, and annealing at temperatures above 200 °C allows to reduce its sulphur content up to C10S. Its structural and electronic properties are fundamentally different to “Bridgman black” reported from previous high pressure experiments on CS2.

Polarization-resolved Raman spectroscopy is used to access the Fermi liquid properties of Sr${}_{2}$RuO${}_{4}$ in an orbital-resolved way. A clear orbital dependence is observed in the energy and temperature dependence of the quasiparticle scattering rate and mass, with the ${d}_{x\phantom{\rule{0}{0ex}}y}$-derived quasiparticles being significantly more correlated than the ${d}_{y\phantom{\rule{0}{0ex}}z}$/${d}_{x\phantom{\rule{0}{0ex}}z}$-derived ones. The observed dichotomy is consistent with the picture of Sr${}_{2}$RuO${}_{4}$ as a Hund's metal with significant orbital differentiation among quasiparticles.

Long-term uranium mobility in tailings is an environmental management issue. The present study focuses on two U-enriched layers, surficial and buried 14.5 m, of the tailings pile of Cominak, Niger. The acidic and oxidizing conditions of the tailings pile combined with evapotranspiration cycles related to the Sahelian climate control U speciation. Uraninite, brannerite, and moluranite as well as uranophane are relict U phases. EXAFS spectroscopy, HR-XRD, and SEM/WDS highlight the major role of uranyl sulfate groups in uranium speciation. Uranyl phosphate neoformation in the buried layer (paleolayer) acts as an efficient trap for uranium.

By means of single-crystal X-ray diffraction, we give direct crystallographic evidence of a centrosymmetry breaking below TS = 200 K, concomitant with the onset of a commensurate structural modulation in the quadruple perovskite YMn3Mn4O12. This result, which explains the anomalously large thermal coefficient of the Y3+ ion in previously reported structural models, is attributed to the small size of the Y3+ ion, which causes its underbonding within the dodecahedral coordination polyhedron. The present data are consistent with a commensurate superstructure described by an I-centered pseudo-orthorhombic cell with polar Ia symmetry and a ? aF?2 = 10.4352(7) Å, b ? 2bF = 14.6049(9) Å, c ? cF?2 = 10.6961(7) Å, and ? = 90.110(3)°, where aF ? cF ? 7.45 Å, bF ? 7.34 Å, and ? ? 91° are the unit cell parameters of the I2/m structure observed at room temperature. Consistent with the above polar structure, at lower temperature, T* = 70 K, we observe in polycrystalline samples an anomaly of the direct current (DC) and alternating current (AC) magnetization, concomitant with the appearance of a net electric polarization, as indicated by pyrocurrent and dielectric constant measurements. These results, complemented by electrical transport measurements, suggest a magnetic ferroelectricity driven by short-range magnetic order in YMn3Mn4O12.

Along the years, ruthenium oxides have been deeply investigated for their magnetic or catalytic properties. The exploration of new synthesis processes, and especially low-temperature ones, is of primary importance to obtain new materials with interesting properties. Here, we highlight the tunability of a low-temperature (200 °C) hydrothermal synthesis route of alkaline-earth ruthenates. Changing only simple physicochemical parameters such as pH, it is possible to obtain a large diversity of metastable compounds. Among them, four compounds, namely, BaRu2O6, Ba2Ru3O10, Ba5Ru4O15, and Sr2Ru3O9(OH) are reported here for the first time. The influence of the reaction parameters (temperature, counter ions, reactant ratio, and pH) is studied. According to these observations, the importance of the reaction pH is highlighted and a reaction scenario is proposed. Finally, the crystal structures of Ba2Ru3O10, Ba5Ru4O15, and Sr2Ru3O9(OH) are reported. These findings further highlight the richness of low-temperature chemistry in the discovery of new metastable phases to be further explored by scientists

By means of in situ synchrotron X-ray diffraction and Raman spectroscopy under hydrostatic pressure, we investigate the structural stability of the quadruple perovskite LaMn7O12. At 34 GPa, the data unveil a first-order structural phase transition from monoclinic I2/m to cubic Im-3 symmetry characterized by a pronounced contraction of the unit cell and by a significant modifications in the Raman phonon modes. The phase transition is also marked by the suppression of Jahn-Teller distortion which is present in the ambient monoclinic phase. In addition, above 20 GPa pressure, a sudden and simultaneous broadening is observed in several Raman modes which suggests the onset of a sizable electron-phonon interaction and incipient charge mobility. Considering that LaMn7O12 is paramagnetic insulator at ambient, and Jahn-Teller distortion is frozen in the high-pressure Im-3 phase, we argue that this phase could be a potential candidate to host a purely electronic insulator-metal transition with no participation of the lattice, 6 pages, 4 figures

International audience; The [Fe II (C6F5Tp)2] spin-crossover complex is an atypical molecular switch, which can be converted upon annealing between two archetypal spin-crossover behaviours: from an extremely gradual spin-crossover to a broad hysteretic spin-transition (of ca. 65 K). The hysteresis shows an uncommon "rounded shape" that is reproducible upon cycling temperature. In depth structural studies reveal a first crystal phase transition, which occurs upon melting and recrystallizing at high temperature. This first irreversible transition is associated with a radical change in the crystal packing. More importantly, the "rounded and broad" hysteretic transition is shown to occurs in a noncooperative SCO system and is associated with the occurrence of a symmetry-breaking phase transition that appears when roughly ca. 50% of the SCO complexes are switched.

The [Fe

International audience; The glass formation, crystallization behavior and structure were investigated in the ZnO-Al2O3-SiO2 system. The boundaries of the glass forming region are defined, indicating the absence of glasses along the ZnO-SiO2 binary and the role of Al to improve glass formation. The crystallization behavior has been clarified for representative glass compositions showing first crystallization of willemite near the ZnO-SiO2 binary and a metastable zinc aluminosilicate solid solution for higher Al2O3/SiO2 content. Gahnite appears as a second phase and is mainly present near the center of the tectosilicate join. Glass structure was studied using 27 Al NMR spectroscopy, neutron and X-ray diffraction and molecular dynamics simulation. Both Al and Zn are shown to be distributed between four-fold and five-fold sites. The proportion of [4] Al is more important near the ZnAl2O4-SiO2 join. A remarkable similar behavior is revealed for the glass forming ability and structural properties between MgO and ZnO aluminosilicate systems.; La formation du verre, le comportement en cristallisation et la structure ont été étudiés dans le système ZnO-Al2O3-SiO2. Les limites de la région de formation du verre sont définies, indiquant l’absence de verres le long du binaire ZnO-SiO2 et le rôle d’Al pour améliorer la formation du verre. Le comportement en cristallisation a été clarifié pour des compositions de verre représentatives montrant la première cristallisation de willemite près du binaire ZnO-SiO2 et une solution solide d’aluminosilicate de zinc métastable pour une teneur plus élevée en Al2O3/SiO2. La gahnite apparaît comme une deuxième phase et est principalement présente près du centre du joint tectosilicate. La structure du verre a été étudiée en utilisant la spectroscopie 27Al RMN, la diffraction des neutrons et des rayons X et la simulation par dynamique moléculaire. Il est démontré que Al et Zn sont répartis entre des sites de coordinence quatre et cinq La proportion de [4]Al est plus importante près du joint ZnAl2O4-SiO2. Un comportement similaire est révélé pour la capacité de formation du verre et les propriétés structurelles entre les systèmes d'aluminosilicate de MgO et de ZnO.

International audience; Pyrite formation at low temperature during early diagenesis in (sub-)surface sediments is an essential step of Fe and S biogeochemical cycles and the presence of this ubiquitous mineral of surface environments is often used as an indicator of paleo-redox conditions. Pathways of pyrite formation are usually discussed in environmental settings by involving a variety of nanosized Fe-S mineralogical precursors as a function of the local geochemical conditions. However, the influence of trace element impurities such as Ni and As in the solution at the time of pyrite formation has been poorly studied, whereas specific chemical signatures of trace elements are commonly observed in sedimentary pyrites. A better understanding of the impact of Ni and As incorporation at trace levels on pyrite formation is essential to help refining the use of these elements as paleo-redox indicators and to evaluate the role of pyrite as a sink regulating the biogeochemical cycle of potentially toxic trace elements. In this study, we have performed syntheses of pyrite at low temperature by the polysulfide pathway using aqueous Fe(III) and H2S in the presence of trace amounts of Ni(II) (0.001 mol%Fe) and As(III) (0.001 mol%Fe). Analysis of the solids collected at different time steps over the course of the experiments using X-Ray absorption spectroscopy at both the Fe and S K-edges shows that pyrite starts to precipitate within 5 days in presence of Ni(II) and within 32 days in presence of As(III), while the control experiment showed an intermediate precipitation rate of 14 days. Shell-by-shell analysis of Fe K-edge EXAFS data shows that the initial mineralogical precursors are the same whatever the experimental conditions and correspond to poorly-crystalline FeS (3.0±0.1 Fe-S@2.25 Å; 1.7±0.2 Fe-Fe@2.67 Å). In addition, XANES qualitative analysis suggests the incorporation of small amounts of Fe(III) within these FeS precursors. Synchrotron-based XRD and WAXS-PDF analysis of the starting solids show that in addition to S(0), the FeS precursors correspond to a continuum of FeS particles that ranges from tetragonal nanocrystalline FeS (a = 3.70(2) Å, c = 5.24(7) Å, MCDab = 41±4 Å MCDc = 21±2 Å) to cluster-type FeS (MCDabc < 8.4±4.3 Å). We propose that Ni(II) and As(III) have a different type of interaction with these FeS precursors, resulting respectively in an increase and a decrease in the rate of pyrite nucleation. While Ni(II) would incorporate within the structure of the FeS precursors, As would interact with (poly)sulfides in solution to form thio-As, possibly binding or precipitating onto FeS surfaces and thus slowing FeS transformation to FeS2. Given that both Ni and As were introduced at trace levels in our experiments, these results suggest that the occurrence of trace amounts of impurities could have a strong influence on pyrite precipitation kinetics in natural settings such as pore-scale microenvironments. In addition to emphasizing the importance of trace elements such as Ni or As on the persistence of mobile colloidal FeS species in anoxic conditions, the results of the present study also point to the importance of considering the actual nature of the impurities when using pyrite composition for ancient environments and past climates reconstruction.

International audience; The use of solvothermal conditions has succesfully led to the preparation of heterometallic 1D coordination polymers from a co-bidentate-tridentate phenolato-oxamato ligand. The reaction of the N-(2-hydoxyphenyl)oxamic acid (ohpma) with acetate salts of transition metal ions at 80°C has yielded the heterobimetallic [Cu(ohpma)M(OAc)(DMF)2] (M = Co (1); Mn (2)) and the heterotrimetallic [Cu(ohpma)Co0.57Mn0.43(OAc)(DMF)2] (3) chain compounds. Single-crystal and powder diffraction studies show that the polymers are isostructural. Magnetic studies suggest the existence of an inter-chain two-dimensional antiferromagnetic interaction taking place in compounds 1-3.

By means of magnetic, specific heat, and pyroelectric measurements, we report on magnetic ferroelectricity in the quadruple perovskite $\mathrm{Na}{\mathrm{Mn}}_{7}{\mathrm{O}}_{12}$, characterized by a canted antiferromagnetic (AFM) CE structure. Surprisingly, ferroelectricity is concomitant to a dramatic broadening of the magnetic hysteresis loop, well below the AFM ordering temperature. This unconventional behavior shows that the formation of ferroelectric domains is induced by the symmetric exchange interaction in the local scale, e.g., at magnetic domain boundaries or defects. The value of electric polarization, $P=0.027\phantom{\rule{4pt}{0ex}}\ensuremath{\mu}\mathrm{C}\phantom{\rule{0.16em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}2}$, measured in polycrystalline samples is comparatively large as compared to other magnetic multiferroics, suggesting that the above scenario is promising indeed for the rational design of practical multiferroic materials.

International audience; Applying elastic deformation can tune a material’s physical properties locally and reversibly. Spatially modulated lattice deformation can create a bandgap gradient, favoring photogenerated charge separation and collection in optoelectronic devices. These advantages are hindered by the maximum elastic strain that a material can withstand before breaking. Nanomaterials derived by exfoliating transition metal dichalcogenides (TMDs) are an ideal playground for elastic deformation, as they can sustain large elastic strains, up to a few percent. However, exfoliable TMDs with highly strain-tunable properties have proven challenging for researchers to identify. We investigated 1T-ZrS2 and 1T-ZrSe2, exfoliable semiconductors with large bandgaps. Under compressive deformation, both TMDs dramatically change their physical properties. 1T-ZrSe2 undergoes a reversible transformation into an exotic three-dimensional lattice, with a semiconductor-to-metal transition. In ZrS2, the irreversible transformation between two different layered structures is accompanied by a sudden 14% bandgap reduction. These results establish that Zr-based TMDs are an optimal strain-tunable platform for spatially textured bandgaps, with a strong potential for novel optoelectronic devices and light harvesting.

Ferruginous duricrusts record a part of the Earth’s geodynamical and climatic history in tropical area, because they can be formed over a wide geologic period. However, the events and processes related to their formation, transformation and distribution are still obscure. This is mainly due to the complexity arising from their finely divided and polycrystalline nature together with the coexistence of various generations of supergene minerals, such as iron and aluminum oxides, oxyhydroxides or hydroxides (e.g. goethite, hematite and gibbsite) and kaolinite, even at microscopic scale. Classical mineralogical investigations are often realized using powders samples, which hinders subsequent analyses on the same sample, such as SEM or (U-Th)/He dating. Thus, the aim of this study was to propose a new way to investigate the mineralogy of supergene ferruginous samples on micrometric grains that will be analyzed by (U-Th)/He dating method. Prior to this analysis, we first compare the X-ray diffraction data of grains and small amounts of powders looking to reveal the mineralogical composition of populations of secondary minerals of a ferruginous duricrust by taking into account the heterogeneity of the material. Samples were collected from a ferruginous duricrust with pisolitic structure developed over epiclastic conglomerates and sandstones deposited by alluvial fan and fluvial streams from the Upper Cretaceous at the western Minas Gerais state (Brazil). The geomorphology of the study area is delineated by remnants of paleosurface (up to 1,000 m a.s.l.), which comprises an important record of long-term Brazilian continental history.Macroscopic facies recognized on duricrusts sections were described, which allowed the identification of various populations of secondary minerals. After this detailed description, grains (size < 0.5 mm) were collected and powder samples of each population were prepared by crushing. Overall, the results point out that the grain and powder samples could be used to identify mineralogical composition at fine resolution of secondary minerals from ferruginous duricrusts. In addition, XRD results are similar for both types of sample preparation, however the < 0.5 mm grain samples are more advantageous because they are not destructive and thus allow to get a finer description of the mineralogy of different populations and can subsequently be used for e.g. (U-Th)/He dating, providing critical information for interpreting and discussing the ages of iron oxides.Grant: 19/10708-7; 17/22292-4; 17/20788-2, São Paulo Research Foundation (FAPESP)ReferencesAllard, T., Gautheron, C., Riffel, S.B., Balan, E., Soares, B.F., Pinna-Jamme, R., Derycke, A., Morin G., Bueno, G.T., Nascimento, N., 2018. Combined dating of goethites and kaolinites from ferruginous duricrusts. Deciphering the Late Neogene erosion history of Central Amazonia. Chemical Geology 479, 136-150.Monteiro, H.S., Vasconcelos, P.M.P., Farley, K.A., Spier, C.A., Mello, C.L., 2014. (U-Th)/He geochronology of goethite and the origin and evolution of cangas. Geochim. Cosmochim. Acta 131, 267–289.Vasconcelos, P.M., Heim, J.A., Farley, K.A., Monteiro, H.S., Waltenberg, K., 2013. 40Ar/39Ar and (U–Th)/He - 4He/3He geochronology of landscape evolution and channel irondeposit genesis at LynnPeak, Western, Australia. Geochim. Cosmochim. Acta 117, 283-312.

We measure the dispersion of the Cu-O bond-stretching phonon mode in the high-temperature superconducting parent compound ${\mathrm{Ca}}_{2}{\mathrm{CuO}}_{2}{\mathrm{Cl}}_{2}$. Our density functional theory calculations predict a cosine-shaped bending of the dispersion along both the $(\ensuremath{\xi}00$) and $(\ensuremath{\xi}\ensuremath{\xi}0$) directions, while comparison with previous results on ${\mathrm{Ca}}_{1.84}{\mathrm{CuO}}_{2}{\mathrm{Cl}}_{2}$ show it only along $(\ensuremath{\xi}00$), suggesting an anisotropic effect which is not reproduced in calculation. Comparison with isostructural ${\text{La}}_{2\ensuremath{-}x}{\text{Sr}}_{x}{\text{CuO}}_{4}$ and literature suggests that these calculations reproduce well the dispersion in the overdoped regime.

Ba-rich and Si-rich phlogopites occur in the talc-bearing rocks of the La Creuse sulfide ore deposit in Beaujolais, France. They form a group of compositions completely separated from the common Al-rich phlogopites that occur in the surrounding talc-free metasiltites and metarhyolites, with higher Ba and Mg and lower Al contents. The Ba-rich phlogopites have a relatively narrow compositional range (0.24 to 0.80 Ba per formula unit, for 44 valencies) with high and constant Si (5.8 atoms per formula unit, apfu) and Mg + Fe (5.6 apfu), probably buffered by the presence of talc. Compared to low-Al phlogopites from talc-free rocks, the excess charge introduced by the BaK–1 substitution is compensated by interlayer vacancies. Such a high level of interlayer vacancy (0.56 pfu), related to the talc-producing metasomatic conditions, is essential for the stability of this special group of Ba-rich and Si-rich phlogopites.Single crystal X-ray diffraction analyses were performed. Ba-rich and Si-rich phlogopite is monoclinic, space group C2/m, (R = 5.31%) with a = 5.3185(5), b = 9.2136(9), c = 10.1349(11) Å and β = 100.131(11)°. The occupancies of Mg/Fe and K/Ba were refined exploring different vacancies. The solutions giving the best R factor (4.77%) and goodness-of-fit (1.06) are obtained with 15% < vacancy < 40% at the interlayer site.

In euxinic sediments, the reaction between iron and sulfides results in the formation of Fe(II)-sulfides, which are known to play a key role in trace metal sequestration. The present study investigates the sequestration of nickel during Fe(II)-sulfide formation mediated by the (thio)sulfate-reducing bacterium Desulfovibrio capillatus in the presence of soluble Fe(III)-citrate and thiosulfate as the terminal electron acceptor. XRD, HRTEM and Fe K-edge EXAFS data indicate that biogenic mackinawite (FeS) was the sole mineral formed in our experiments. These data also show that the kinetics of mackinawite crystal growth was significantly accelerated when nickel was present in the starting solution. In addition, the lack of detection of other Fe(II)-sulfides indicates inhibition of the mackinawite (FeS) to greigite (Fe3S4) and/or pyrite (FeS2) transformation that is likely related to (i) the efficiency of Desulfovibrio capillatus in reducing S(0) to H2S and (ii) the absence of O2 during the experiments. Finally, chemical analyses show that 98% of the nickel is associated with biogenic mackinawite and no release of nickel from mackinawite was observed after up to 10 months of incubation under anoxic conditions. This finding is consistent with Ni K-edge EXAFS data which show that Ni(II) substitutes for Fe(II) in the structure of biogenic mackinawite. This study shows that (thio)sulfate-reducing bacteria can efficiently promote the formation of mackinawite in euxinic sedimentary environments and that these Fe(II)-sulfides can act as efficient and long-term trapping minerals for nickel in such settings. Considering the capacity of mackinawite at incorporating other trace metals such as Mn, Co, Cu and Zn, this iron sulfide could also serve as a host for these elements as well. This study suggests that mackinawite likely plays a more important role in the biogeochemical cycles of Fe, S, and associated trace metals than considered up to now.

International audience; The binary assembly DDA-{Mo 132 }/OA-γ-Fe 2 O 3 (DDA = didodecyldimethylammonium, {Mo 132 } = [Mo 132 O 372 (CH 3 COO) 30 (H 2 O) 72 ] 42− , OA = oleic acid) constitutes one of the two examples in the literature of binary superlattices made of a mixing of nanocrystals and oxo-clusters. In a precedent work, we reported in details the preparation of such magnetic binary systems and studied the effect of the nature of the polyoxometalates (POMs) on the magnetic properties. In the present paper, we study the stability of this model binary assembly under heating at various temperatures. Indeed, especially if magnetic and/or transport properties are targeted, an annealing can be essential to change the phase of the nanocrystals in a more magnetic one and/or to desorb the organic capping of the nano-objects that can constitute an obstacle to the electronic communication between the nano-objects. We gave evidence that the maghemite organization in the binary assembly is maintained until 370 • C under vacuum thanks to the presence of the POMs. This latter evolve in the phase MoO 3 , but still permits to avoid the aggregation of the nanocrystals as well as preserve their periodical arrangement. On the contrary, an assembly made of pure γ-Fe 2 O 3 nanocrystals displays a clear aggregation of the nano-objects from 370 • C, as attested by transmission and scanning electronic microscopies and confirmed by magnetic measurements. The stability of the magnetic nanocrystals in such POMs/nanocrystals assemblies opens the way to (i) the elaboration of new binary assemblies from POMs and numerous kinds of nanocrystals with a good control on the magnetic properties and to (ii) the investigation of new physical properties as exchange coupling, or magneto-transport in such systems.

International audience; The chemical and isotopic compositions of biogenic apatite are important geochemical markers, which can suffer modifications during fossilisation. Compared with modern ones, fossil apatites generally exhibit variations in carbonate content, enrichment in fluorine, incorporation of trace elements and an increase in crystallinity parameters. Detailed understanding of these transformations induced by fossilisation should help assess the preservation of geochemical records in apatites. In this contribution, we investigate the transformation of modern bone altered under controlled conditions. Modern bone samples were soaked in aqueous solutions of neutral to alkaline pH (9–10) for one and three weeks at various temperatures (20 and 70 °C) and experiments were duplicated in fluorine-free and in 10−2 M NaF solutions. Bone transformation was monitored through the modifications of chemical (F, Ca, P) and isotopic (δ13C, δ18Oc, δ18Op) composition as well as using vibrational (ATR-FTIR, Raman) and solid-state (1H, 13C, 19F) NMR spectroscopies. The observed modifications sustain a transformation mechanism through partial dissolution of biogenic apatite and precipitation of secondary apatite. This transformation occurs irrespective of the presence or absence of fluorine and leads to the formation of carbonate-bearing fluorapatite or carbonate-bearing hydroxylapatite, respectively. The fraction of secondary apatite seems to be limited to ~60%, suggesting that its formation has a protecting role against further dissolution of the primary apatite. The observation of clumped (CO32−, F−) defects in the structural B-site of some samples as well as perturbation of the isotopic compositions attest to carbonate incorporation in the secondary apatite. Although the incorporation of fluoride ions can serve as a probe revealing dissolution-recrystallization of bone, the present study also underlines the difficulty to systematically relate mineralogical transformations to an open-system behaviour in bioapatite.

The development of luminescent mechanochromic materials depends mainly on the possibility to rationally design them with the desired properties. Molecular copper iodide clusters constitute an unprecedented family of compounds exhibiting great changes of their luminescence properties upon mechanical stress. From previous studies, the mechanochromic properties of cubane [Cu4I4L4] (L = organic ligand) clusters have been attributed to modifications of cuprophilic interactions induced by mechanical solicitation. In this study, we ascertain our hypothesis by choosing to study the luminescence mechanochromism of a [Cu4I4(PPh3)4] cluster which presents two crystalline polymorphs exhibiting strikingly different Cu–Cu bond lengths. As forecasted, only one of these two polymorphs exhibits mechanochromic properties. Structural and optical characterization methods are reported along with structural characterization under controlled pressure allowing a precise analysis of the structural changes occurring under mechanical stress. In addition to confirming our mechanism based on enhancement of cuprophilic interactions under pressure, this study demonstrates the possibility of prediction of mechanochromic properties in the family of copper iodide compounds that constitutes a step further toward the rational design of stimuli-responsive materials.

International audience; The nature of defects in ZnO smoke was studied at different stages of the materials' history by combining photoluminescence (PL) and electron paramagnetic resonance (EPR) spectroscopies. In contrast to studies previously reported on ZnO nanopowders, high vacuum conditions (P < 10-5 mbar) have been applied during sample's storage, handling and spectroscopic investigations. Two pairs of violet-PL/EPR signals (2.88 eV / g = 1.956 and 2.80 eV / g = 1.960) were observed in the as-synthesized ZnO powder and attributed to surface (dominant) and bulk zinc interstitials (Zni +). Upon annealing in O2-poor conditions, green-PL emission (2.41 eV) and EPR at g = 2.002 develop along with EPR signals specific of superoxide radicals (O2-). In absence of any external O2 supply, the oxygen necessary for the creation of notable amount of O2-is provided by the lattice of ZnO smoke, so that the green emission, and its EPR counterpart, are unambiguously assigned to singly charged oxygen vacancies (Vo +). Annealing in high PO2 results in a broad yellow-PL emission (~2.07 eV) without an EPR counterpart, and was assigned to peroxide-like surface species (O2 2-). Overall, this study shows that the visible emissions in ZnO smoke nanopowders can range from violet, over green to yellow as a function of sample's 2 history and that the corresponding PL/EPR fingerprints can serve as guidelines for the recognition of defects in other ZnO types.

Innovative synthesis routes revolutionized nanomaterial combination and design possibilities resulting in a new generation of fine-tuned nanoparticles featuring exquisite shape and constitution control. However, there is still room for improvement when it comes to the development of multi-functional nanoparticle agents merging a plurality of therapeutic functions to tackle tumors simultaneously by synergic mechanisms. Herein, we report the design of an optimized nanohybrid for cancer tri-therapy featuring a maghemite (γ-Fe2O3) nanoflower-like multicore nanoparticle conceived for efficient magnetic hyperthermia (MHT) and a spiky copper sulfide shell (IONF@CuS) with a high near-infrared (NIR) absorption coefficient suitable for photothermal (PTT) and photodynamic therapy (PDT). Methods: Spiky-like IONF@CuS nanohybrids were obtained through a straightforward and scalable water-based template sacrificial synthesis, which allows the shell shape control by tuning polyvinylpyrrolidone (PVP) concentration. A comprehensive characterization of nanohybrid size, shape and structural properties was carried out by combining complementary TEM, SEM, HR-TEM, EELS, XRD and NTA. The all-in-one therapeutic multi-functionality was assessed on cancer cells and on tumor-bearing nude mice. Results: Tests carried out on IONF@CuS nanohybrid aqueous dispersion demonstrated their impressive efficiency to convert light (conversion coefficient = 42 ± 6 %) and magnetic stimulation (SAR ~ 350 W g-1) into heat as well as to induce concurrent reactive oxygen species (ROS) formation upon laser irradiation. Such capabilities were further confirmed in cellular environment by in vitro tests and at the organism level by in vivo tests in a murine tumor model. Notably, complete tumor regression was obtained for the PTT mode at low Cu concentration. Overall, these results allowed determining windows of applicability for each therapy individually or in combination. Conclusions: Altogether, the obtained data evidence the successful synthesis of a unique tri-therapeutic nanoparticle featuring highly relevant assets for clinical translation such as reduced nanoparticle administered dose, reduced laser power exposure, reduced magnetic field frequency, and the possibility of serial heating cycles and therapy monitoring by photoacoustic (PA) and magnetic resonance imaging (MRI). Furthermore, the integration of the dual heating capability (MHT + PTT) with the PDT insult offers a unique asset to tackle tumors by multiple cytotoxic strategies in order to improve the therapeutic outcome in a broader spectrum of clinical conditions.

This study presents a description of the structure of amorphous slags, with particular attention to the Ca local environment and the medium range arrangement of Ca-sites. Using Ca K-edge X -ray absorption spectroscopy (XANES and EXAFS) and pair distribution function (PDF) as well as numerical modeling combining Molecular Dynamics and Reverse Monte-Carlo, we demonstrate that Ca occurs in a complex environment with a distribution between 6- and 7-coordinated sites. Ca atoms are not distributed randomly within the glass structure: the Ca sites are linked by edges and form a complex percolating sub-network of network-modifying cations. The aluminosilicate network in slags is highly depolymerized with, on average, Q2.06 arrangements for Si, indicating the predominance of chain-like structural units and Q2.67 arrangements for Al in more polymerized units cross-linking the Ca-domains. The Ca percolating sub-network forms clusters that may enhance the early dissolution rate of slags in water.

By means of high-pressure synthesis in the 4–6 GPa range, we report on the successful growth of high-quality 1T-V1+xS2 single crystals with controlled concentration, x = 0.09–0.17, of self-intercalated V atoms in the van der Waals gap. A systematic X-ray diffraction and energy-dispersive X-ray spectroscopy study unveils a linear decrease of x with the synthesis pressure, dx/dP = −0.042 GPa–1, suggesting that the stoichiometric (x = 0) phase is stable above 8 GPa. Transmission electron microscopy and electrical resistivity measurements show that, for all x values studied, the system is metallic up to 400 K, with no charge-density-wave order, contrary to the x = 0 composition. This finding clarifies the controversial electronic phase diagram of the 1T-V1+xS2 system and unveils a connection between the charge-density-wave phase observed at x = 0 and the itinerant antiferromagnetic phase stable for x > 0.25.

The crystal structure of Ca2CuO2Cl2, dicalcium oxidocuprate(II) dichloride, was redetermined on the basis of single-crystal X-ray diffraction data using a laboratory Mo anode. Previous structure determinations based on single-crystal X-ray data [Grande & Müller-Buschbaum (1977). Z. Anorg. Allg. Chem. 429, 88–90], powder X-ray diffraction data [Yamada et al. (2005). Phys. Rev. B, 72, 224503–1–5] or neutron diffraction data [Argyriou et al. (1995). Phys. Rev. B, 51, 8434–8437] were confirmed. The present study allowed the refinement of anisotropic displacement parameters for all crystallographic sites, accompanied with higher accuracy and precision for bond lengths and angles. The layered title compound comprises of [CuO4] square-planar and [CaO4Cl4] square-antiprismatic coordination polyhedra, and is the undoped parent compound of a high-temperature superconducting cuprate.

International audience

International audience; Hexagonal Si allotropes are expected to enhance light absorption in the visible range as compared to common cubic Si with diamond structure. Therefore, synthesis of these materials is crucial for the development of Si-based optoelectronics. In this work, we combine in situ high-pressure high-temperature synthesis and vacuum heating to obtain hexagonal Si. High pressure is one of the most promising routes to stabilize these allotropes. It allows one to obtain large-volume nanostructured ingots by a sequence of direct solid–solid transformations, ensuring high-purity samples for detailed characterization. Thanks to our synthesis approach, we provide the first evidence of a polycrystalline bulk sample of hexagonal Si. Exhaustive structural analysis, combining fine-powder X-ray and electron diffraction, afforded resolution of the crystal structure. We demonstrate that hexagonal Si obtained by high-pressure synthesis correspond to Si-4H polytype (ABCB stacking) in contrast with Si-2H (AB stacking) proposed previously. This result agrees with prior calculations that predicted a higher stability of the 4H form over 2H form. Further physical characterization, combining experimental data and ab initio calculations, have shown a good agreement with the established structure. Strong photoluminescence emission was observed in the visible region for which we foresee optimistic perspectives for the use of this material in Si-based photovoltaics.

International audience; Under-doped La-214 cuprates show a charge-and spin-modulation known as " stripes " [1]. These stripe modulations are (quasi)-static close to 1/8 hole doping where superconductivity is suppressed. The pseudo-gap phase of other cuprate compounds recently also revealed charge modulation, but interpreted rather as a charge density wave (CDW) [2, 3, 4], that possibly competes with superconductivity. In this context, to better understand the interplay between the stripe phase and the superconductivity, we use angle-resolved photoemission spectroscopy to study the electronic band structure and gap in La-214 cuprates near 1/8 doping (La 2−x−y Nd y Sr x CuO 4 (x = 0.12; y = 0.0 & 0.4)) and compare with the previous results in the same system [5] and La 1.86 Ba 0.14 CuO 4 [6]. Our data shows a loss of spectral intensity towards the end of the Fermi arcs, that is possibly due to a strong renormalisation, as already pointed out elsewhere * matteo.dastuto@neel.cnrs.fr-Institut Néel CNRS-25, av des Martyrs-38042 Grenoble cedex 9; tel: (+33)(0)4 76 88 12 84 [5], with a noisy but still measurable gap. On the nodal direction no gap is observed within our statistics, but a sizeable decrease in intensity with temperature. Moreover, we do not see any shadow band, but our Fermi surface can be well modelled with a single electron band calculation in the tight binding approximation, even very close to the 1/8 doping La 2−x−y Nd y Sr x CuO 4 with and without Nd substitution.

Recent results have demonstrated an exceptionally high permittivity in the range 200–330 K in crystalline titanium oxide Rb2Ti2O5. In this article, the possibility of a structural transition giving rise to ferroelectricity is carefully inspected. In particular, X-ray diffraction, high-resolution transmission electron microscopy and Raman spectroscopy are performed. The crystal structure is shown to remain invariant and centrosymmetric at all temperatures between 90 K and 450 K. The stability of the C2/m structure is confirmed by density functional theory calculations. These important findings allow the existence of a conventional ferroelectric phase transition to be ruled out as a possible mechanism for the colossal permittivity and polarization observed in this material.

We report on the successful high-pressure synthesis of single-phase powders of the quadruple perovskite $({\mathrm{YMn}}_{3}){\mathrm{Mn}}_{4}{\mathrm{O}}_{12}$, where the chemical pressure exerted by the small ${\mathrm{Y}}^{3+}$ ion is expected to enhance the exchange interaction between ${\mathrm{Mn}}^{3+}$ ions. According to this expectation, powder neutron diffraction, specific heat, and magnetization measurements give evidence of a C-type antiferromagnetic ordering of the ${\mathrm{Mn}}^{3+}$ ions in the octahedrally coordinated $B$ sites at ${T}_{N,B}=108\phantom{\rule{0.28em}{0ex}}\mathrm{K}$, 30 K higher than in the isostructural and isovalent compound, $({\mathrm{LaMn}}_{3}){\mathrm{Mn}}_{4}{\mathrm{O}}_{12}$. Surprisingly, we found no evidence of long-range magnetic order of the square-coordinated ${A}^{\ensuremath{'}}$ sites, although an indication of latent magnetic order is given by a broad peak of the DC magnetization between 70 and 40 K and by a sharp peak in the AC susceptibility at ${T}^{*}=70\phantom{\rule{0.28em}{0ex}}\mathrm{K}$. A further unexpected feature of $({\mathrm{YMn}}_{3}){\mathrm{Mn}}_{4}{\mathrm{O}}_{12}$, not found in previously reported $(A{\mathrm{Mn}}_{3}){\mathrm{Mn}}_{4}{\mathrm{O}}_{12}$ compounds, is a second-order structural phase transition at ${T}_{s}=200\phantom{\rule{0.28em}{0ex}}\mathrm{K}$, attributed to a partial redistribution of charge involving both the $B$ and ${A}^{\ensuremath{'}}$-site ${\mathrm{Mn}}^{3+}$ ions. The present results suggest the existence of competing magnetic orderings, which may be linked to the occurrence of magnetic ferroelectricity in the $(A{\mathrm{Mn}}_{3}){\mathrm{Mn}}_{4}{\mathrm{O}}_{12}$ system.

A systematic approach to endow aromatic molecular architectures with both crystal growth ability from, and solubility in, water., The growth of crystals of aromatic compounds from water much depends on the nature of the water solubilizing functions that they carry. Rationalizing crystallization from water, and structure elucidation, of aromatic molecular and supramolecular systems is of general value across various fields of chemistry. Taking helical aromatic foldamers as a test case, we have validated several short polar side chains as efficient substituents to provide both solubility in, and crystal growth ability from, water. New 8-amino-2-quinolinecarboxylic acids bearing charged or neutral aminomethyl, carboxymethyl, sulfonic acid, or bis(hydroxymethyl)-methoxy side chains in position 4 or 5, were prepared on a multi gram scale. Fmoc protection of the main chain amine and suitable protections of the side chains ensured compatibility with solid phase synthesis. One tetrameric and five octameric oligoamides displaying these side chains were synthesized and shown to be soluble in water. In all cases but one, crystals were obtained using the hanging drop method, thus validating the initial design principle to combine polarity and rigidity. The only case that resisted crystallization appeared to be due to exceedingly high water solubility endowed by eight sulfonic acid functions. The neutral side chain did provide crystal growth ability from water but contributed poorly to solubility.

In a systematic study of the physico-chemical properties of cyclotriphosphates of alkaline earth cations Type MIIMIP3O9.xH2O carried out in our laboratory. (MII = Ca2+, Sr2+, and Ba2+) and (MI = Rb+, K+, Cs+, and NH4+). We are interested in the synthesis of the mixed barium cyclotriphosphate associated with the cesium ion. Chemical preparation and crystal structure are reported for a barium cesium cyclotriphosphate dihydrate BaCsP3O9.2H2O. The phosphoric ring anions are interconnected by BaO8 dodecahedra in the structure of BaCsP3O9.2H2O. The two water oxygens in the present arrangement participate in the coordination spheres of the associated barium and cesium cations. The thermogravimetric analysis shows that the removal of these two water molecules occurs in two stages between 105 and 600°C. The vibrational study by IR absorption spectroscopy of the title compound reveals the presence of P3O9 ring and confirms the existence of nonequivalent positions of water molecules in the structure.

International audience; The low-grade carbonate banded iron formation of the Aguas Claras mine, from the transition of the Caûe to the Gandarela Formation (2.4 Ga, Itabira Group, Brazil), is composed of porous and microsparitic dolomite, quartz, iron oxides and (oxy)hydroxides. Iron oxides occur as bands, veins and as inclusions in the dolomite crystals, whereas iron (oxy)hydroxides only occur as inclusions. Combined mineralogical analyses (X-ray diffraction, Raman spectroscopy, focused-ion-beam thinning and transmission electron microscopy) identified the inclusions in porous dolomite as hematite and minor goethite and/or ferrihydrite, whereas microsparitic dolomite only hosts hematite. Curie balance analysis on whole rock reveals that, at temperatures between ∼680 °C and ∼900 °C, hematite and iron (oxy)hydroxide inclusions react with the surrounding dolomite resulting in the assemblage: magnesioferrite (MgFe 2 O 4), srebrodolskite (Ca 2 Fe 2 O 5), lime (CaO), portlandite (Ca(OH) 2) and periclase (MgO), whereas hematite and pure dolomite do so only at ∼900 °C. This difference is an indirect argument for the presence of iron hydroxide inclusions within the dolomite. The inclusions are either single crystals or form clusters in pores. The fast-Fourier-transform diffraction pattern of one single crystal can be indexed as goethite and ferrihydrite. This finding suggests an incipient solid-state transformation of ferrihydrite to goethite rather than a dissolution-precipitation process. It is suggested that the clustered hematite and the goethite/ferrihydrite precipitated from Fe-and Si-bearing fluid inclusions, which were trapped during early diagenesis at about 2.4 Ga under oxygenated conditions. Microstructural evidence (e.g. dislocations in dolomite from hematite inclusions) point to maximum T < 420 °C. The preservation of goethite/ ferrihydrite clustered inclusions during this low-temperature event may be due to their silica contents increasing their stability.

The first synthesis of BINOL-fused maleimides has been developed. This new chiral scaffold is easily accessible from various BINOL analogues and 2,3-dihalomaleimide derivatives under basic conditions. It can be easily functionalized on the BINOL moiety and is an entry towards promising new classes of chiral organocatalysts and ligands.

Quinoline-based oligoamide foldamers have been identified as a potent class of ligands for G-quadruplex DNA. Their helical structure is thought to target G-quadruplex loops or grooves and not G-tetrads. We report a co-crystal structure of the antiparallel hairpin dimeric DNA G-quadruplex (G4 T4 G4 )2 with tetramer 1-a helically folded oligo-quinolinecarboxamide bearing cationic side chains-that is consistent with this hypothesis. Multivalent foldamer-DNA interactions that modify the packing of (G4 T4 G4 )2 in the solid state are observed.

International audience; Cocatalysis by pivalic acid or copper bromide allows a very fast, clean, and high-yielding palladium-catalyzed coupling of a large array of aryl, thienyl, and pyridyl halides with cyclic nitrones, including DMPO. The study of the reaction conditions, scope, and mechanism is presented. Applied to the chiral nitrone MiPNO, this transformation provides a straightforward access to enantiopure α-methyl α-arylglycine esters.

The reduction of the chiral, racemic nitrone MiPNO provides a secondary hydroxylamine. Its O-acylation with O , O ’-dibenzoyl- l -tartaric acid anhydride gives two diastereomers, that can be easily separated by selective dissolution in orthogonal solvents. The recovery of the enantiopure nitrone is then carried out in a single step. The process allows the straightforward isolation of ( R ) and ( S )-MiPNO in 57% and 38% yield, respectively, from rac -MiPNO.

Synthetic helical aromatic amide foldamers and in particular those based on quinolines have recently attracted much interest due to their capacity to adopt bioinspired folded conformations that are highly stable and predictable. Additionally, the introduction of water-solubilizing side chains has allowed to evidence promising biological activities. It has also created the need for methods that may allow the parallel synthesis and screening of oligomers. Here, we describe the application of solid phase synthesis to speed up oligomer preparation and allow the introduction of various side chains. The synthesis of quinoline-based monomers bearing protected side chains is described along with conditions for activation, coupling, and deprotection on solid phase, followed by resin cleavage, side-chain deprotection, and HPLC purification. Oligomers having up to 8 units were thus synthesized. We found that solid phase synthesis is notably improved upon reducing resin loading and by applying microwave irradiation. We also demonstrate that the introduction of monomers bearing benzylic amines such as 6-aminomethyl-2-pyridinecarboxylic acid within the sequences of oligoquinolines make it possible to achieve couplings using a standard peptide coupling agent and constitute an interesting alternative to the use of acid chloride activation required by quinoline residues. The synthesis of a tetradecameric sequence was thus smoothly carried out. NMR solution structural studies show that these alternate aminomethyl-pyridine residues do not perturb the canonical helix folding of quinoline monomers in protic solvents, contrary to what was previously observed in nonprotic solvents.