Room-temperature-persistent magnetic interaction between coordination complexes and nanoparticles in maghemite-based nanohybrids.

Maghemite nanoparticles functionalised with Co(II) coordination complexes at their surface show a significant increase of their magnetic anisotropy, leading to a doubling of the blocking temperature and a sixfold increase of the coercive field. Magnetometric studies suggest an enhancement that is not related to surface disordering, and point to a molecular effect involving magnetic exchange interactions mediated by the oxygen atoms at the interface as its source. Field- and temperature-dependent X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) studies show that the magnetic anisotropy enhancement is not limited to surface atoms and involves the core of the nanoparticle. These studies also point to a mechanism driven by anisotropic exchange and confirm the strength of the magnetic exchange interactions. The coupling between the complex and the nanoparticle persists at room temperature. Simulations based on the XMCD data give an effective exchange field value through the oxido coordination bridge between the Co(II) complex and the nanoparticle that is comparable to the exchange field between iron ions in bulk maghemite. Further evidence of the effectiveness of the oxido coordination bridge in mediating the magnetic interaction at the interface is given with the Ni(II) analog to the Co(II) surface-functionalised nanoparticles. A substrate-induced magnetic response is observed for the Ni(II) complexes, up to room temperature.

Uranium contamination of bivalve Mytilus galloprovincialis, speciation and localization.

Uranium is a natural radioelement (also a model for heavier actinides), but may be released through anthropogenic activities. In order to assess its environmental impact in a given ecosystem, such as the marine system, it is essential to understand its distribution and speciation, and also to quantify its bioaccumulation. Our objective was to improve our understanding of the transfer and accumulation of uranium in marine biota with mussels taken here as sentinel species because of their sedentary nature and ability to filter seawater. We report here on the investigation of uranium accumulation, speciation, and localization in Mytilus galloprovincialis using a combination of several analytical (Inductively Coupled Plasma Mass Spectrometry, ICP-MS), spectroscopic (X ray Absorption Spectroscopy, XAS, Time Resolved Laser Induced Fluorescence Spectroscopy, TRLIFS), and imaging (Transmission Electron Microscopy, TEM, µ-XAS, Secondary Ion Mass Spectrometry, SIMS) techniques. Two cohorts of mussels from the Toulon Naval Base and the Villefranche-sur-Mer location were studied. The measurement of uranium Concentration Factor (CF) values show a clear trend in the organs of M. galloprovincialis: hepatopancreas â‰« gill > body ≥ mantle > foot. Although CF values for the entire mussel are comparable for TNB and VFM, hepatopancreas values show a significant increase in those from Toulon versus Villefranche-sur-Mer. Two organs of interest were selected for further spectroscopic investigations: the byssus and the hepatopancreas. In both cases, U(VI) (uranyl) is accumulated in a diffuse pattern, most probably linked to protein complexing functions, with the absence of a condensed phase. While such speciation studies on marine organisms can be challenging, they are an essential step for deciphering the impact of metallic radionuclides on the marine biota in the case of accidental release. Following our assumptions on uranyl speciation in both byssus and hepatopancreas, further steps will include the inventory and identification of the proteins or metabolites involved.

Solvent-Induced Aggregation of Self-Assembled Copper-Cysteine Nanoparticles Reacted with Glutathione: Enhancing Linear and Nonlinear Optical Properties.

Copper-thiolate self-assembly nanostructures are a unique class of nanomaterials because of their interesting properties such as hierarchical structures, luminescence, and large nonlinear optical efficiency. Herein, we synthesized biomolecule cysteine (Cys) and glutathione (GSH) capped sub-100 nm self-assembly nanoparticles (Cu-Cys-GSH NPs) with red fluorescence. The as-synthesized NPs show high emission enhancement in the presence of ethanol, caused by the aggregation-induced emission. We correlated the structure and optical properties of Cu-Cys-GSH NPs by measuring the mass, morphology, and surface charge as well as their two-photon excited fluorescence cross-section (σ2PEPL), two-photon absorption cross-section (σTPA) and first hyperpolarizability (ß) of Cu-Cys-GSH NPs in water and water-ethanol using near-infrared wavelength. We found a high ß value as (77 ± 10) × 10-28 esu (in water) compared to the reference medium water. The estimated values of σ2PEPL and σTPA are found to be (13 ± 2) GM and (1.4 ± 0.2) × 104 GM, respectively. We hope our investigations of linear and nonlinear optical properties of copper-thiolate self-assemblies in water and its solvent-induced aggregates will open up new possibilities in designing self-assembled systems for many applications including sensing, drug delivery, and catalysis.

Uranium Speciation in a Chalky Soil.

In this article, the speciation and behavior of anthropogenic metallic uranium deposited on natural soil are approached by combining EXAFS (extended X-ray absorption fine structure) and TRLFS (time-resolved laser-induced fluorescence spectroscopy). First, uranium (uranyl) speciation was determined along the vertical profile of the soil and bedrock by linear combination fitting of the EXAFS spectra. It shows that uranium migration is strongly limited by the sorption reaction onto soil and rock constituents, mainly mineral carbonates and organic matter. Second, uranium sorption isotherms were established for calcite, chalk, and chalky soil materials along with EXAFS and TRLFS analysis. The presence of at least two adsorption complexes of uranyl onto carbonate materials (calcite) could be inferred from TRLFS. The first uranyl tricarbonate complex has a liebigite-type structure and is dominant for low loads on the carbonate surface (<10 mgU/kg(rock)). The second uranyl complex is incorporated into the calcite for intermediate (∼10 to 100 mgU/kg(rock)) to high (high: >100 mgU/kg(rock)) loads. Finally, the presence of a uranium-humic substance complex in subsurface soil materials was underlined in the EXAFS analysis by the occurrence of both monodentate and bidentate carboxylate (or/and carbonate) functions and confirmed by sorption isotherms in the presence of humic acid. This observation is of particular interest since humic substances may be mobilized from soil, potentially enhancing uranium migration under colloidal form.

Metal-to-metal electron transfer in a cyanido-bridged {Fe2Co2} square complex followed by X-ray diffraction and absorption techniques.

The switching properties of a cyanido-bridged Fe/Co square molecule were investigated by single-crystal X-ray diffraction and X-ray absorption spectroscopy at both Fe and Co K-edges. Combining these two techniques, a complete picture of the thermal-, light- and X-ray-induced metal-to-metal electron transfer is obtained, illustrating the concerted role played by the Fe and Co sites.

Accumulation and Speciation of Cobalt in Paracentrotus lividus.

Since the first human release of radionuclides on Earth at the end of the Second World War, impact assessments have been implemented. Radionuclides are now ubiquitous, and the impact of local accidental release on human activities, although of low probability, is of tremendous social and economic consequences. Although radionuclide inventories (at various scales) are essential as input data for impact assessment, crucial information on physicochemical speciation is lacking. Among the metallic radionuclides of interest, cobalt-60 is one of the most important activation products generated in the nuclear industry. In this work, a marine model ecosystem has been defined because seawater and more generally marine ecosystems are final receptacles of metal pollution. A multistep approach from quantitative uptake to understanding of the accumulation mechanism has been implemented with the sea urchin Paracentrotus lividus. In a well-controlled aquarium, the day-by-day uptake of cobalt and its quantification in different compartments of the sea urchin were monitored with various conditions of exposure by combining ICP-OES analysis and γ spectrometry. Cobalt is mainly distributed following the rating intestinal tract ≫ gonads > shell spines. Cobalt speciation in seawater and inside the gonads and the intestinal tract was determined using extended X-ray absorption fine structure (EXAFS). The cobalt inside the gonads and the intestinal tract is mainly complexed by the toposome, the main protein in the sea urchin P. lividus. Complexation with purified toposome was characterized and a complexation site combining EXAFS and AIMD (ab initio molecular dynamics) was proposed implying monodentate carboxylates.

Magnetic Hysteresis in a Monolayer of Oriented 6 nm CsNiCr Prussian Blue Analogue Nanocrystals.

Prussian blue analogue nanocrystals of the CsINiII[CrIII(CN)6] cubic network with 6 nm size were assembled as a single monolayer on highly organized pyrolytic graphite (HOPG). X-ray magnetic circular dichroism (XMCD) studies, at the Ni and Cr L2,3 edges, reveal the presence of an easy plane of magnetization evidenced by an opening of the magnetic hysteresis loop (coercive field of ≈200 Oe) when the magnetic field, B, is at 60° relative to the normal to the substrate. The angular dependence of the X-ray natural linear dichroism (XNLD) reveals both an orientation of the nanocrystals on the substrate and an anisotropy of the electronic cloud of the NiII and CrIII coordination sphere species belonging to the nanocrystals' surface. Ligand field multiplet (LFM) calculations that reproduce the experimental data are consistent with an elongated tetragonal distortion of surface NiII coordination sphere responsible for the magnetic behavior of monolayer.

Four orders-of-magnitude enhancement in the two-photon excited photoluminescence of homoleptic gold thiolate nanoclusters following zinc ion-induced aggregation.

Herein we report unprecedented determination of the molar mass of zinc mediated assemblies of homoleptic gold nanoclusters, based on charge detection mass spectrometry measurements. The accurate determination of the molar mass of zinc coordinated assemblies of gold clusters has further allowed unambiguous determination of the two-photon excited photoluminescence cross section of the same. Furthermore, in line with one-photon excited photoluminescence measurements, four orders-of-magnitude enhancement in two-photon excited photoluminescence of gold nanoclusters has been observed following complexation with zinc ions. The study reported herein is envisioned to not only deepen the fundamental understanding of the multiphoton excitation properties of atomic clusters but also widen their application potential as luminescence markers.

Functionalized Au15 nanoclusters as luminescent probes for protein carbonylation detection.

Atomically precise, ligand-protected gold nanoclusters (AuNCs) attract considerable attention as contrast agents in the biosensing field. However, the control of their optical properties and functionalization of surface ligands remain challenging. Here we report a strategy to tailor AuNCs for the precise detection of protein carbonylation-a causal biomarker of ageing. We produce Au15SG13 (SG for glutathione) with atomic precision and functionalize it with a thiolated aminooxy moiety to impart protein carbonyl-binding properties. Mass spectrometry and molecular modelling reveal the key structural features of Au15SG12-Aminooxy and its reactivity towards carbonyls. Finally, we demonstrate that Au15SG12-Aminooxy detects protein carbonylation in gel-based 1D electrophoresis by one- and two-photon excited fluorescence. Importantly, to our knowledge, this is the first application of an AuNC that detects a post-translational modification as a nonlinear optical probe. The significance of post-translational modifications in life sciences may open avenues for the use of Au15SG13 and other nanoclusters as contrast agents with tailored surface functionalization and optical properties.

6 months of radioxenon detection in western Europe with the SPALAX-New generation system - Part 2: Atmospheric transport modelling.

Atmospheric transport modeling has been used to interpret the unprecedented number of multi-isotope detections of radioxenons observed during the six months of the qualification process by the Comprehensive Nuclear-Test-Ban Treaty Organization of the new SPALAX-NG system (Système de Prélèvement Automatique en Ligne avec l'Analyse du Xénon - Nouvelle Génération). Highest 133Xe activity concentrations were found to be systematically associated with the concomitant measurement of several other radioxenons at the prevailing wind direction of north/northeast pointing to the Institute for Radio Elements (IRE), a medical isotope production facility located in Fleurus (Belgium). The lowest 133Xe activity concentrations were not associated with a prevailing wind direction or other radioxenons, indicating the contribution of distant sources (global background). The IRE's average source terms for 133mXe and to a lesser extent for 133Xe (slightly overestimated by a factor of 1.7) showed good agreement with the literature values, while corrections by a factor of ~23 and ~53 were proposed for 131mXe and 135Xe since the initial values were underestimated. However, detections of 131mXe alone and some low-activity concentrations of 133Xe associated with only one of the other radioxenons could not be linked to the IRE releases. Analysis of these cases suggests the contribution of local source releases that have been difficult to identify to date. In addition to the global background, releases from such local sources, if not identified, could affect the analysis of the isotopic ratios measured following a nuclear test. The characterization of these local contributions is now possible owing to the capacity of the SPALAX-NG and other new generation measurements systems.

6 months of radioxenon detection in western Europe with the SPALAX-New generation system - Part1: Metrological capabilities.

The SPALAX-NG is a new-generation system that is designed to detect radioactive xenon at trace levels in the atmosphere following a nuclear explosion or civilian source release. This new system formed part of a validation program led by the Provisional Technical Secretary of the Comprehensive Nuclear-Test-Ban Treaty (CTBT) Organization. In this study, the first SPALAX-NG unit was tested for six months between October 2018 and April 2019 at the CEA/DIF premises near Paris, France. This test period provided an outstanding opportunity to illustrate the high level of detectability and reliability of the system. The data availability obtained over this period was approximately 99%, which was well above the CTBT Data Availability criteria of 95%. The data reliability was demonstrated by a comparison with a collocated SPALAX-1 unit (former version of SPALAX) and by re-measuring several samples at the CTBT-certified French laboratory FRL08. The high sensitivity to the detection of the four relevant radioxenon isotopes was fully demonstrated and enabled the recording of a major dataset for western Europe. A large set of isotopic ratios was measured, which enabled the discrimination criteria between civilian sources and nuclear test signatures to be refined.

Uranium Uptake in Paracentrotus lividus Sea Urchin, Accumulation and Speciation.

Uranium speciation and bioaccumulation were investigated in the sea urchin Paracentrotus lividus. Through accumulation experiments in a well-controlled aquarium followed by ICP-OES analysis, the quantification of uranium in the different compartments of the sea urchin was performed. Uranium is mainly distributed in the test (skeletal components), as it is the major constituent of the sea urchin, but in terms of quantity of uranium per gram of compartment, the following rating: intestinal tract > gonads ≫ test, was obtained. Combining both extended X-ray Absorption Spectroscopy and time-resolved laser-induced fluorescence spectroscopic analysis, it was possible to identify two different forms of uranium in the sea urchin, one in the test, as a carbonato-calcium complex, and the second one in the gonads and intestinal tract, as a protein complex. Toposome is a major calcium-binding transferrin-like protein contained within the sea urchin. EXAFS data fitting of both contaminated organs in vivo and the uranium-toposome complex from protein purified out of the gonads revealed that it is suspected to complex uranium in gonads and intestinal tract. This hypothesis is also supported by the results from two imaging techniques, i.e., Transmission Electron Microscopy and Scanning Transmission X-ray Microscopy. This thorough investigation of uranium uptake in sea urchin is one of the few attempts to assess the speciation in a living marine organism in vivo.

Atomic Scale Evidence of the Switching Mechanism in a Photomagnetic CoFe Dinuclear Prussian Blue Analogue.

Molecular complexes based on Prussian Blue analogues have recently attracted considerable interest for their unique bistable properties combined to ultimately reduced dimensions. Here, we investigate the first dinuclear FeCo complex exhibiting both thermal and photomagnetic bistability in the solid state. Through an experimental and theoretical approach combining local techniques-X-ray absorption spectroscopy (XAS), X-ray magnetic circular dichroism (XMCD), and ligand field multiplet calculations-we were able to evidence the changes occurring at the atomic scale in the electronic and magnetic properties. The spectroscopic studies were able to fully support at the atomic level the following conclusions: (i) the 300 K phase and the light-induced excited state at 4 K are both built from FeLSIII-CoHSII paramagnetic pairs with no apparent reorganization of the local structure, (ii) the 100 K phase is composed of FeLSII-CoLSIII diamagnetic pairs, and (iii) the light-induced excited state is fully relaxed at an average temperature of ≈50 K. In the paramagnetic phase at 2 K, XAS and XMCD reveal that both Fe and Co ions exhibit a rather large orbital magnetic moment (0.65 µB and 0.46 µB, respectively, under an external magnetic induction of 6.5 T), but it was not possible to detect a magnetic interaction between spin centers above 2 K.

Weak Ferromagnetic Interaction at the Surface of the Ferrimagnetic Rb2Co4[Fe(CN)6]3.3·11H2O Photoexcited State.

CoFe Prussian blue analogues (PBAs) are well-known for their magnetic bistability tuned by external stimuli. The photoswitching properties are due to the electron transfer from CoLSIII-NC-FeLSII to CoHSII-NC-FeLSIII linkage, accompanied by the spin change of the Co ions (HS stands for high spin and LS for low spin). In this work, we investigated 100 nm particles of the Rb2Co4[Fe(CN)6]3.3·11H2O PBA (named RbCoFe). The photoexcited state of the PBA was reached by red laser excitation (λ = 635 nm) and observed by X-ray absorption spectroscopy and X-ray magnetic circular dichroism (XMCD) that are element-specific probes. The XMCD measurements at the Co and Fe L2,3 edges, probing the magnetic 3d orbitals, have provided a direct evidence of the antiferromagnetic interaction between the CoHSII and the FeLSIII ions belonging to the core of the particles, thus confirming the previously published, though indirect XMCD measurements at K edges. Because of the surface sensitivity of XMCD at the L2,3 edges, the magnetic properties of the particle surface were also revealed. Surface CoHSII-FeLSIII pairs exhibit a weak ferromagnetic interaction. Thus, the magnetic structure of the photomagnetic RbCoFe 100 nm particles can be described as a ferrimagnetic core surrounded by a ferromagnetic shell. This finding brings new insights into the understanding of the complex magnetic properties of photoexcited RbCoFe and shows that the surface can have different magnetic behavior than the core. This should impact the nature of magnetic coupling in nanoparticles of CoFe PBA, where surface effect will dominate.

Bulky Counterions: Enhancing the Two-Photon Excited Fluorescence of Gold Nanoclusters.

Increasing fluorescence quantum yields of ligand-protected gold nanoclusters has attracted wide research interest. The strategy consisting in using bulky counterions has been found to dramatically enhance the fluorescence. In this Communication, we push forward this concept to the nonlinear optical regime. We show that by an appropriate choice of bulky counterions and of solvent, a 30-fold increase in two-photon excited fluorescence (TPEF) signal at ≈600 nm for gold nanoclusters can be obtained. This would correspond to a TPEF cross-section in the range of 0.1 to 1 GM.

Development toward a double focusing isotopic separator for noble gas isotope enrichment.

A double focusing sector field mass filter used in Nier-Johnson geometry has been built in order to perform Kr isotope enrichment for 81 Kr and 85 Kr isotopes. The principle consists in implanting Kr+ ions accelerated at 7 keV in Al foils after separation using the magnetic sector. A specific ion source has been designed capable of generating high Kr+ ion beams (>0.5 µA) to transfer into the collecting Al foils in 3 to 5 h significant fractions of large Kr samples (1015 to 1016 atoms) initially introduced in the instrument. Implanted Kr isotopes can be further selectively released from the Al foil by surface ablation using an infrared laser beam. Implantation yields and enrichment factors are measured using a conventional mass spectrometer. Copyright © 2016 John Wiley & Sons, Ltd.

How Do Radionuclides Accumulate in Marine Organisms? A Case Study of Europium with Aplysina cavernicola.

In the ocean, complex interactions between natural and anthropogenic radionuclides, seawater, and diverse marine biota provide a unique window through which to examine ecosystem and trophic transfer mechanisms in cases of accidental dissemination. The nature of interaction between radionuclides, the marine environment, and marine species is therefore essential for better understanding transfer mechanisms from the hydrosphere to the biosphere. Although data pertaining to the rate of global transfer are often available, little is known regarding the mechanism of environmental transport and uptake of heavy radionuclides by marine species. Among marine species, sponges are immobile active filter feeders and have been identified as hyperaccumulators of several heavy metals. We have selected the Mediterranean sponge Aplysina cavernicola as a model species for this study. Actinide elements are not the only source of radioactive release in cases of civilian nuclear events; however, their physicochemical transfer mechanisms to marine species remain largely unknown. We have targeted europium(III) as a representative of the trivalent actinides such as americium or curium. To unravel biological uptake mechanisms of europium in A. cavernicola, we have combined radiometric (γ) measurements with spectroscopic (time-resolved laser-induced fluorescence spectroscopy, TRLIFS, and X-ray absorption near-edge structure, XANES) and imaging (transmission electron microscopy, TEM, and scanning transmission X-ray microscopy, STXM) techniques. We have observed that the colloids of NaEu(CO3)2·nH2O formed in seawater are taken up by A. cavernicola with no evidence that lethal dose has been reached in our working conditions. Spectroscopic results suggest that there is no change of speciation during uptake. Finally, TEM and STXM images recorded at different locations across a sponge cross section, together with differential cell separation, indicate the presence of europium particles (around 200 nm) mainly located in the skeleton and toward the outer surface of the sponge.

Large Orbital Magnetic Moment Measured in the [TpFe(III)(CN)3](-) Precursor of Photomagnetic Molecular Prussian Blue Analogues.

Photomagnetism in three-dimensional Co/Fe Prussian blue analogues is a complex phenomenon, whose detailed mechanism is not yet fully understood. Recently, researchers have been able to prepare molecular fragments of these networks using a building block synthetic approach from mononuclear precursors. The main objective in this strategy is to isolate the smallest units that show an intramolecular electron transfer to have a better understanding of the electronic processes. A prior requirement to the development of this kind of system is to understand to what extent electronic and magnetic properties are inherited from the corresponding precursors. In this work, we investigate the electronic and magnetic properties of the FeTp precursor (N(C4H9)4)[TpFe(III)(CN)3], (Tp being tris-pyrazolyl borate) of a recently reported binuclear cyanido-bridged Fe/Co complex. X-ray absorption spectroscopy and X-ray magnetic circular dichroism measurements at the Fe L2,3 edges (2p → 3d) supported by ligand field multiplet calculations have allowed to determine the spin and orbit magnetic moments. Inaccuracy of the spin sum rule in the case of low-spin Fe(III) ion was demonstrated. An exceptionally large value of the orbital magnetic moment is found (0.9 µB at T = 2 K and B = 6.5 T) that is likely to play an important role in the magnetic and photomagnetic properties of molecular Fe/Co Prussian blue analogues.

Breakthrough in Xenon Capture and Purification Using Adsorbent-Supported Silver Nanoparticles.

Rare gas capture and purification is a major challenge for energy, environment, and health applications. Of utmost importance for the nuclear industry, novel separation processes for Xe are urgently needed for spent nuclear fuel reprocessing and nuclear activity monitoring. The recovered, non-radioactive Xe is also of high economic value for lighting, surgical anesthetic, etc. Here, using adsorption and breakthrough experiments and statistical mechanics molecular simulation, we show the outstanding performance of zeolite-supported silver nanoparticles to capture/separate Xe at low concentrations (0.087-100 ppm). We also establish the efficiency of temperature swing adsorption based on such adsorbents for Xe separation from Kr/Xe mixtures and air streams corresponding to off-gases generated by nuclear reprocessing. This study paves the way for the development of novel, cost-efficient technologies relying on the large selectivity/capacity of adsorbent-supported silver nanoparticles which surpass all materials ever tested.