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Purpose: The actinides are chemical poisons and radiological hazards. One challenge to better appraise their toxicity and develop countermeasures in case of exposure of living organisms is to better assess pathways of contamination. Because of the high chemical affinity of those actinide elements for phosphate groups and the ubiquity of such chemical functions in biochemistry, nucleotides and in particular adenosine triphosphate nucleotide (ATP) may be considered critical target building blocks for actinides. Materials and methods: Combinations of spectroscopic techniques (Fourier transformed Infra Red [FTIR], Electrospray Ionization Mass Spectrometry [ESI-MS], and Extended X-ray Absorption Fine Structure [EXAFS]) with quantum chemical calculations have been implemented in order to assess the actinides coordination arrangement with ATP. Results: We describe and compare herein the interaction of ATP with thorium and americium; thorium(IV) as a representative of actinide(IV) like plutonium(IV) and americium(III) as a representative of all heavier actinides. In the case of thorium, an insoluble complex is readily formed. In the case of americium, a behavior identical to that described previously for lutetium has been observed with insoluble and soluble complexes. Conclusions: The comparative study of ATP complexation with Th(IV) and Am(III) shows their ability to form insoluble complexes for which a structural model has been proposed by analogy with previously described Lu(III) complexes. [ABSTRACT FROM AUTHOR]

Supramolecular assembly of peptides and proteins into amyloid fibrils is of multifold interest, going from materials science to physiopathology. The binding of metal ions to amyloidogenic peptides is associated with several amyloid diseases, and amyloids with incorporated metal ions are of interest in nanotechnology. Understanding the mechanisms of amyloid formation and the role of metal ions can improve strategies toward the prevention of this process and enable potential applications in nanotechnology. Here, studies on ZnII binding to the amyloidogenic peptide Aβ11-28 are reported. ZnII modulates the Aβ11-28 aggregation, in terms of kinetics and fibril structures. Structural studies suggest that Aβ11-28 binds ZnII by amino acid residues Glu11 and His14 and that ZnII is rapidly exchanged between peptides. Structural and aggregation data indicate that ZnII binding induces the formation of the dimeric ZnII1(Aβ11-28)2 species, which is the building block of fibrillar aggregates and explains why ZnII binding accelerates Aβ11-28 aggregation. Moreover, transient ZnII binding, even briefly, was enough to promote fibril formation, but the final structure resembled that of apo-Aβ11-28 amyloids. Also, seeding experiments, i.e., the addition of fibrillar ZnII1(Aβ11-28)2 to the apo-Aβ11-28 peptide, induced aggregation but not propagation of the ZnII1(Aβ11-28)2-type fibrils. This can be explained by the dynamic ZnII binding between soluble and aggregated Aβ11-28. As a consequence, dynamic ZnII binding has a strong impact on the aggregation behavior of the Aβ11-28 peptide and might be a relevant and so far little regarded parameter in other systems of metal ions and amyloidogenic peptides. [ABSTRACT FROM AUTHOR]

Our previous studies on the met- and met-azido-Hc forms from Octopus vulgaris (mollusc) and Carcinus aestuarii (arthropod) at pH 7.5 and on some related binuclear models without X-ray diffraction have considered and resolved some fundamental aspects of their binuclear type-3 copper site (i.e. correct values of the Cu-Cu distances; apical distortion, when present, at the copper site; presence and type of bridging groups). In this contribution the multiple- scattering (MS) calculations performed in order to refine the EXAFS modulation of the absorption spectra are presented. It is only with a composite and advanced approach that some severe problems, mainly deriving from the presence of two absorbing atoms and from the fact that the metal-metal contribution in the absorption spectra overlaps with the Cu-His signals, have been overcome. Results are also presented which indicate the role of the MS calculations in the XANES edge region, and which show how it is possible to extract quantitative information from this zone of the spectrum in order to refine the structure of the site also in the case of a binuclear centre. [ABSTRACT FROM AUTHOR]

We report and discuss here the unambiguous uranium valence state determination on the complex compound [Ni(H2O)4]3[U(OH,H2O)(UO2)8O12(OH)3] by using high-energy-resolution fluorescence detection-X-ray absorption near-edge structure spectroscopy (HERFD-XANES). The spectra at both U L3- and M4-edges confirm that all five nonequivalent U atoms are solely in the hexavalent form in this compound, as previously suggested by bond-valence-sum analysis and X-ray diffraction pattern refinement. Moreover, the presence of the preedge feature, due to the 2p3/2-5f quadrupole transition, has been observed in the U L3-edge HERFD-XANES spectrum, in agreement with theoretical and experimental observations of other uranium-based compounds. Recently, this feature has been proposed as a possible tool to determine the uranium oxidation state in a manner similar to that of 3d and 4d metals. Nevertheless, this feature is also very sensitive to the uranium local environment, as revealed by our theoretical calculations, and consequently could not be used to attribute without ambiguity the uranium valence state. In contrast, U M4-edge HERFD-XANES appears to be the most straightforward and reliable way to assess the uranium valence state in very complex materials such as [Ni(H2O)4]3[U(OH,H2O)(UO2)8O12(OH)3] or a mixture of compounds. [ABSTRACT FROM AUTHOR]

The industrial fluorination of UO2 to UF4 is based on a complex process involving the manipulation of a large amount of HF, a very toxic and corrosive gas. We present here a safer way to accomplish this reaction utilizing ionic liquid [Bmim][PF6] as a unique reaction medium and fluoride source. [ABSTRACT FROM AUTHOR]

In molecular solids derived from Prussian blue, intermetallic charge transfer is fostered through a cyano bridge two metal ions. In this study, isostructural trivalent lanthanide and tetravalent actinide Prussian blue analogs’ valence orbitals are probed by soft X-ray absorption measurements. [ABSTRACT FROM AUTHOR]

To understand the fission products behaviour during a Nuclear Severe Accident (NSA), simulated high burnup UO 2 fuels produced by sintering at high temperature (SIMFUEL) were submitted to thermal treatments in conditions representative of the beginning of a Pressurized Water Reactor (PWR) severe accident. The samples made of UO 2 doped with eleven fission products (FP) surrogates were thus thermally treated from 400 ​°C up to 1000 ​°C at different oxygen potentials (up to −290 ​kJ ​mol (O2) −1 at 1000 ​°C). The samples were characterized before and after the heat treatments by Secondary Electron Microscopy coupled with Energy Dispersive X-ray Spectroscopy (SEM-EDX) and X-ray Absorption Spectroscopy (XAS) at the MARS beamline, SOLEIL Synchrotron and at the FAME-UHD beamline, ESRF. Initially the SIMFUEL is constituted of a UO 2 matrix, a metallic phase composed of Mo, Pd, Ru, Rh and Tc, and an oxide phase with perovskite structure depicted as (Ba, Sr)(Zr, U, RE)O 3 where RE stands for Rare Earths. Around 1000 ​°C, it was found that Mo, initially contained in the metallic inclusions, oxidizes into MoO 2. In the same conditions, a part of the oxidized Mo interacts with the perovskite phase containing Ba to form BaMoO 4. These results will be useful to validate the theoretical models used in calculation codes and to assess thermodynamic databases, which are one of the main sources of errors when calculating a NSA sequence involving molten fuel. The study on UO 2 -based SIMFUEL allowed describing the formation of BaMoO 4 during thermal treatments representative the early stage of a severe nuclear accident sequence. Schematic mechanism for the evolution of the metallic and oxide precipitates at ΔG O2 ​= ​−290 ​kJ ​mol (O2) −1 at 1000 °C. [Display omitted] • Evolution of the perovskite phase studied by XANES coupled with SEM-EDX analyses. • Reaction between Mo and Ba at the periphery of the oxide precipitates. • Formation of BaMoO 4 around 1000 ​°C at −290 ​kJ ​mol−1. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Investigating uranium migration mechanisms related to the weathering of waste rocks is essential for developing strategies that can address the potential environmental issues caused by uranium mining. This work is based on environmental samples containing 2 L ferrihydrite, lepidocrocite and goethite collected in the technosols from granitic waste rock piles, mine drainage conduits and mine waters. The results show the important role of iron oxyhydroxide in U immobilization and re-concentration. EXAFS spectroscopy combined with mineralogical and geochemical studies (Scanning electronic microscopy, Wavelength-dispersive X-ray spectroscopy microprobe, inductively coupled plasma - optical emission spectrometry/mass spectrometry and X-ray diffraction) allowed for the identification of uranyl ternary surface complexes at the ferrihydrite surface that were either composed of phosphate groups or organic matter. Moreover, goethite and lepidocrocite were also identified as a secondary trap for U immobilization. U(VI) is known to be mobile in oxidizing conditions. This study highlights the control of the uranyl mobility by various iron oxyhydroxides in supergene conditions. Image 1 • Iron oxyhydroxide paragenese controls the U-mobility in the post-mining environment. • U sorption on the ferrihydrite. • U ternary surface complexes with phosphates or organic matter on the ferrihydrite. • Goethite and lepidocrocite are identified as secondary uranyl traps. [ABSTRACT FROM AUTHOR]

The environmental impact of uranium released during nuclear power production and related mining activity is an issue of great concern. Innovative environmental-friendly water remediation strategies, like those based on U biomineralization through phosphatase activity, are desirable. Here, we report the great U biomineralization potential of Stenotrophomonas sp. Br8 CECT 9810 over a wide range of physicochemical and biological conditions. Br8 cells exhibited high phosphatase activity which mediated the release of orthophosphate in the presence of glycerol-2-phosphate around pH 6.3. Mobile uranyl ions were bioprecipitated as needle-like fibrils at the cell surface and in the extracellular space, as observed by Scanning Transmission Electron Microscopy (STEM). Extended X-Ray Absorption Fine Structure (EXAFS) and X-Ray Diffraction (XRD) analyses showed the local structure of biogenic U precipitates to be similar to that of meta-autunite. In addition to the active U phosphate biomineralization process, the cells interact with this radionuclide through passive biosorption, removing up to 373 mg of U per g of bacterial dry biomass. The high U biomineralization capacity of the studied strain was also observed under different conditions of pH, temperature, etc. Results presented in this work will help to design efficient U bioremediation strategies for real polluted waters. Image 1 • Bacterial strain Stenotrophomonas sp. Br8 mediates soluble U(VI) immobilization. • Uranium immobilization process is stable under changing environmental conditions. • Main Br8-uranium interaction mechanisms are linked to phosphatase enzymes. • U phosphate phases presented a local coordination similar to that of autunite groups. [ABSTRACT FROM AUTHOR]

The cell parameter evolution along the cubic U(Al 1− x Ge x) 3 solid solution shows a significant deviation from Vegard's law. The origin of such deviation has been investigated by X-ray powder and electron diffractions, EXAFS and HERFD XANES at the U L 3 and Ge K edges and specific heat measurements. The results of such investigations show that, from the structural point of view, U(Al 1− x Ge x) 3 does not present any local or long range ordering and the deviation from Vegard's law is caused by valence instability of U with an actual decrease of the U–Ge bond length with increasing Al-content and cell parameter. Image 1 • Crystallography of U(Al 1-x Ge x) 3 solid solution examined by XRD, TEM, EXAFS and HERFD. • Deviation from Vegard law explained by unusual variation of the U–Ge distance. • Increasing 5f electron delocalization with Al-content confirmed. [ABSTRACT FROM AUTHOR]

The rise of atmospheric oxygen as a result of photosynthesis in cyanobacteria and chloroplasts has transformed most environmental iron into the ferric state. In contrast, cells within organisms maintain a reducing internal milieu and utilize predominantly ferrous iron. Ferric reductases are enzymes that transfer electrons to ferric ions, either extracellularly or within endocytic vesicles, enabling cellular ferrous iron uptake through Divalent Metal Transporter 1. In mammals, duodenal cytochrome b is a ferric reductase of the intestinal epithelium, but how insects reduce and absorb dietary iron remains unknown. Here we provide indirect evidence of extracellular ferric reductase activity in a small subset of Drosophila melanogaster intestinal epithelial cells, positioned at the neck of the midgut's anterior region. Dietary-supplemented bathophenanthroline sulphate (BPS) captures locally generated ferrous iron and precipitates into pink granules, whose chemical identity was probed combining in situ X-ray absorption near edge structure and electron paramagnetic resonance spectroscopies. An increased presence of manganese ions upon BPS feeding was also found. Control animals were fed with ferric ammonium citrate, which is accumulated into ferritin iron in distinct intestinal subregions suggesting iron trafficking between different cells inside the animal. Spectroscopic signals from the biological samples were compared to purified Drosophila and horse spleen ferritin and to chemically synthesized BPS-iron and BPS-manganese complexes. The results corroborated the presence of BPS-iron in a newly identified ferric iron reductase region of the intestine, which we propose constitutes the major site of iron absorption in this organism., Competing Interests: Declarations. Conflict of interest: The authors have no relevant financial or non-financial interests to disclose., (© 2024. The Author(s).)

Uranium-plutonium mixed oxides, containing few mol % of Am, are currently studied as fuel for Sodium Fast Reactors. The study of the O/M ratio of these fuels is of main interest, as its variation can induce issues for reactor safety. For this purpose, four U 1- y - z Pu y Am z O 2± x samples (0.235 ≤ y ≤ 0.39 and 0.005 ≤ z ≤ 0.02) were studied using electron probe microanalysis (EPMA), X-ray powder diffraction (XRD), and X-ray absorption spectroscopy (XAS) experiments. EPMA analyses revealed a homogeneous matrix phase with few U- and Pu-rich agglomerates. A matrix phase of fluorite structure (face-centered cubic), as well as a small contribution of a UO 2 phase of the same structure, was evidenced for all of the samples by XRD. The O/M ratios of the (U,Pu)O 2± x matrix were calculated based on the obtained lattice parameters. XANES experiments highlighted the simultaneous presence of U 5+ and Pu 3+ /Am 3+ for all of the samples, indicating a charge compensation mechanism even for stoichiometric samples. Based on the EPMA and XRD results, it was evidenced that this coexistence of U 4+ , U 5+ , Pu 3+ , Pu 4+ , and Am 3+ was not originating from the U- and Pu-rich agglomerates. It was found to be rather a peculiarity of the U 1- y - z Pu y Am z O 2± x matrix phase, discussed with the help of thermodynamic calculations performed on the U-Pu-Am-O system.

In the context of the separation of uranium and plutonium from spent fuel allowed by N,N -dialkylamides, three regioisomers of N,N -di(2-ethylhexyl) butyramide (DEHBA or ββ) and the diastereopure isomers of N -(2-ethylhexyl)- N -(oct-3-yl)butyramide (EHOBA or αβ) were synthesized to assess their extraction performance and to study the mechanisms at the origin of the differences observed between the stereo- and regioisomers. The N,N -dialkylamides showed differences in extraction, with a greater effect of regio- than stereoisomerism. A mechanistic study at both the molecular and supramolecular scales was initially applied to explain these effects. X-ray absorption and UV-vis spectroscopy showed that uranium is extracted by a UO 2 (NO 3 ) 2 L 2 complex, which is not very sensitive to steric hindrance, while plutonium is extracted by two complexes, Pu(NO 3 ) 4 L 2 and Pu(NO 3 ) 6 (HL) 2 , which are differently affected by stereo- and regioisomerism. Investigations at the supramolecular scale also showed that Pu(NO 3 ) 4 L 2 complexes are disadvantaged by the bulkiness of the extractants, while Pu(NO 3 ) 6 (HL) 2 is favored by the preformation of larger supramolecular aggregates.

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 ≫ 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., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: DEN AUWER Christophe reports financial support was provided by French Alternative Energies and Atomic Energy Commission. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Inc. All rights reserved.)

Legacy radioactive waste can be defined as the radioactive waste produced during the infancy of the civil nuclear industry's development in the mid-20th Century, a time when, unfortunately, waste storage and treatment were not well planned. The marine environment is one of the environmental compartments worth studying in this regard because of legacy waste in specific locations of the seabed. Comprising nearly 70% of the earth's service, the oceans are the largest and indeed the final destination for contaminated fresh waters. For this reason, long-term studies of the accumulation biochemical mechanisms of metallic radionuclides in the marine ecosystem are required. In this context the brown algal compartment may be ecologically relevant because of forming large and dense algal beds in coastal areas and potential important biomass for contamination. This report presents the first step in the investigation of uranium (U, an element used in the nuclear cycle) bioaccumulation in the brown alga Ascophyllum nodosum using a multi-scale spectroscopic and imaging approach. Contamination of A. nodosum specimens in closed aquaria at 13 °C was performed with a defined quantity of U(VI) (10 -5 M). The living algal uptake was quantified by ICP-MS and a localization study in the various algal compartments was carried out by combining electronic microscopy imaging (SEM), X-ray Absorption spectroscopy (XAS) and micro X-ray Florescence (μ-XRF). Data indicate that the brown alga is able to concentrate U(VI) by an active bioaccumulation mechanism, reaching an equilibrium state after 200 h of daily contamination. A comparison between living organisms and dry biomass confirms a stress-response process in the former, with an average bioaccumulation factor (BAF) of 10 ± 2 for living specimens (90% lower compared to dry biomass, 142 ± 5). Also, these results open new perspectives for a potential use of A. nodosum dry biomass as uranium biosorbent. The different partial BAFs (bioaccumulation factors) range from 3 (for thallus) to 49 (for receptacles) leading to a compartmentalization of uranium within the seaweed. This reveals a higher accumulation capacity in the receptacles, the algal reproductive parts. SEM images highlight the different tissue distributions among the compartments with a superficial absorption in the thallus and lateral branches and several hotspots in the oospheres of the female individuals. A preliminary speciation XAS analysis identified a distinct U speciation in the gametes-containing receptacles as a pseudo-autunite phosphate phase. Similarly, XAS measurements on the lateral branches (XANES) were not conclusive with regards to the occurrence of an alginate-U complex in these tissues. Nonetheless, the hypothesis that alginate may play a role in the speciation of U in the algal thallus tissues is still under consideration., (© 2024. The Author(s).)

Transferrin (Tf) is a glycoprotein that transports iron from the serum to the various organs. Several studies have highlighted that Tf can interact with metals other than Fe(III), including actinides that are chemical and radiological toxics. We propose here to report on the behavior of Th(IV) and Pu(IV) in comparison with Fe(III) upon Tf complexation. We considered UV-Vis and IR data of the M 2 Tf complex (M=Fe, Th, Pu) and combined experimental EXAFS data with MD models. EXAFS data of the first M-O coordination sphere are consistent with the MD model considering 1 synergistic carbonate. Further EXAFS data analysis strongly suggests that contamination by Th/Pu colloids seems to occur upon Tf complexation, but it seems limited. SAXS data have also been recorded for all complexes and also after the addition of Deferoxamine-B (DFOB) in the medium. The Rg values are very close for apoTf, ThTf and PuTf, but slightly larger than for holoTf. Data suggest that the structure of the protein is more ellipsoidal than spherical, with a flattened oblate form. From this data, the following order of conformation size might be considered:holoTf2 Tf (M=Th, Pu)2 Tf-DFOB (M=Fe, Th, Pu)., (© 2023 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

The impact of the contamination of living organisms by actinide elements has been a constant subject of attention since the 1950s. But to date still little is understood. Ferritin is the major storage and regulation protein of iron in many organisms, it consists of a protein ring and a ferrihydric core at the center. This work sheds light on the interactions of early actinides (Th, Pu) at oxidation state +IV with ferritin and its ability to store those elements at physiological pH compared to Fe. The ferritin-thorium load curve suggests that Th IV saturates the protein (2840 Th atoms per ferritin) in a similar way that Fe does on the protein ring. Complementary spectroscopic techniques (spectrophotometry, infrared spectroscopy, and X-ray absorption spectroscopy) were combined with molecular dynamics to provide a structural model of the interaction of Th IV and Pu IV with ferritin. Comparison of spectroscopic data together with MD calculations suggests that Th IV and Pu IV are complexed mainly on the protein ring and not on the ferrihydric core. Indeed from XAS data, there is no evidence of Fe neighbors in the Th and Pu environments. On the other hand, carboxylates from amino acids of the protein ring and a possible additional carbonate anion are shaping the cation coordination spheres. This thorough description from a molecular view point of Th IV and Pu IV interaction with ferritin, an essential iron storage protein, is a cornerstone in comprehensive nuclear toxicology., (© 2020 Wiley-VCH GmbH.)

Separation processes based on room temperature ionic liquids (RTIL) and electrochemical refining are promising strategies for the recovery of lanthanides from primary ores and electronic waste. However, they require the speciation of dissolved elements to be known with accuracy. In the present study, Eu coordination and Eu III /Eu II electrochemical behavior as a function of water content in 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIm][NTf 2 ]) was investigated using UV-visible spectrophotometry, time-resolved laser fluorescence spectroscopy, electrochemistry, and X-ray absorption spectroscopy. In situ measurements were performed in spectroelectrochemical cells. Under anhydrous conditions, Eu III and Eu II were complexed by NTf 2 , forming Eu-O and Eu-(N,O) bonds with the anion sulfoxide function and N atoms, respectively. This complexation resulted in a greater stability of Eu II , and in quasi-reversible oxidation-reduction with an E 0 ' potential of 0.18 V versus the ferrocenium/ferrocene (Fc + /Fc) couple. Upon increasing water content, progressive incorporation of water in the Eu III coordination sphere occurred. This led to reversible oxidation-reduction reactions, but also to a decrease in stability of the +II oxidation state (E 0 '=-0.45 V vs. Fc + /Fc in RTIL containing 1300 mm water)., (© 2020 Wiley-VCH GmbH.)

Although the preparation of CeSiO4 has been already reported, the formation of pure cerium silicate from aqueous precursors appears as a challenge. An innovative way of synthesis has been identified in this study, allowing the formation of CeSiO4 after hydrothermal treatment starting from Ce(iii) silicate precursors. Among the experimental parameters examined, significant effects were found according to the nature of the precursor and of the reactive media considered, the pH of the reactive media and the temperature of the hydrothermal process. This study allows the determination of optimized conditions for the hydrothermal synthesis of pure CeSiO4 (A-Ce2Si2O7 or Ce4.67(SiO4)3O as starting precursors, nitric medium, pH = 7, 7 days at 150 °C). The in situ low oxidation rate of Ce(iii) into Ce(iv) was a key parameter to consider in order to avoid the presence of CeO2 in the final mixtures.

The magnetic properties of Ln III and An III complexes formed with dipicolinate ligands have been studied by NMR spectroscopy. To know precisely the geometries of these complexes, a crystallographic study by single-crystal X-ray diffraction (XRD) and extended X-ray absorption fine structure (EXAFS) in solution was performed. Several methods to separate the paramagnetic shifts observed in the NMR spectra were applied to these complexes. Methods using a number of nuclei of the dipicolinate ligands revealed an abrupt change in the geometries of the complexes and a metal-ligand interaction in the middle of the lanthanide series. A study of the variation of the paramagnetic shifts with temperature demonstrated that higher-order terms of the dipolar and contact contributions are required, especially for the lightest Ln III and almost all the studied An III . Bleaney's parameters z > a and C a D relating to the contact and dipolar terms, respectively, were deduced from experimental data and compared with the results of ab initio calculations. Quite a good agreement was found for the temperature dependencies of z > a and C a D . However, the C a D values obtained from cation magnetic anisotropy calculations showed some discrepancies with the values derived from Bleaney's equation defined for Ln III . Other parameters, such as the crystal field parameter and the hyperfine constants F i obtained from the experimental data of the [An(ethyl-dpa) 3 ] 3- complexes (ethyl-dpa=4-ethyl-2,6-dipicolinic acid), are at odds with the assumptions underlying Bleaney's theory., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)