Marine mussel byssus is recognized for its capacity to accumulate trace metals from seawater including metallic radionuclides. This study deals with uranium and neptunium, two actinides involved in the electronuclear cycle. We propose to elucidate the underlying molecular mechanisms at the origin of uranium and neptunium uptake by the byssus threads of mussel using model systems of increasing molecular complexity: PEG–DOPA (4‐arm polyethylene glycol–dihydroxyphenylalanine), purified mfp‐1 (mussel foot protein‐1), and native byssus. Ex vivo sorption isotherms display a linear adsorption behavior at environmentally relevant concentrations, reflected in high uranium concentration factors that emphasize the byssus as an efficient passive accumulator. Extended X‐ray absorption fine structure analysis showed that uranium (uranyl(VI)) coordinates through oxygen donors ligands, consistent with chelation by catechols in mfp‐1 and byssus. X‐ray absorption near edge structure (XANES) confirmed that uranyl(VI) remained unreduced in all systems. For neptunium (neptunyl(V)), UV–Vis–NIR spectra and XANES both revealed partial reduction of neptunyl(V) to Np(IV) in the presence of mfp‐1 , while PEG–DOPA induced no such reduction, suggesting the presence of redox‐active moieties in the mfp‐1 . These findings advance our understanding of uranium and neptunium accumulation in mussel byssus, highlighting the central role of mfps and their catechol‐rich domains in selective and redox‐active actinide binding.

Cesium radioactive isotopes (134Cs and 137Cs) are key fission products released during nuclear accidents such as Fukushima and through routine operations of nuclear power plants. This study presents a combined experimental and computational investigation of the speciation of the cesium cation in natural seawater, with the aim of elucidating its local hydration structure under environmentally relevant conditions. X-ray Absorption Fine Structure (XAFS) measurements at the Cs LIII edge were performed on cesium solutions prepared in distilled water, natural seawater and NaCl saturated seawater. Complementary molecular dynamics (MD) simulations were carried out using four model systems of increasing ionic complexity to characterize Cs+ solvation. In both distilled water and natural seawater, a coordination environment consisting of eight oxygen atoms at a Cs-O distance of approximately 3.11-3.12 Å is consistent with the known chaotropic character of Cs+ and its loosely ordered first hydration shell. Molecular dynamics simulations confirm these findings and demonstrate that Cl- anions remain outside the first coordination sphere of Cs+ under natural seawater conditions. In NaCl saturated seawater, EXAFS data are similar and the possible entry of one or two Cl- into the Cs+ coordination sphere cannot be clearly inferred (but not excluded either). These results establish that cesium speciation in natural seawater is dominated by water coordination and is not significantly perturbed by the ionic matrix of seawater, providing a structural foundation for modeling cesium bioavailability and environmental fate in marine ecosystems.

Tau protein is a microtubule-associated protein central to the pathogenesis of Alzheimer's disease (AD) and other tauopathies. While metal ion homeostasis is disrupted in AD, the presence of copper and zinc in neurofibrillary tangles suggests a pathological role for metal-tau interactions. In this study, the metal binding properties of Tau441 were probed using a wide range of spectroscopic tools. Specifically, electron paramagnetic resonance, circular dichroism, nuclear magnetic resonance (NMR) and X-ray absorption spectroscopy (XAS) results point to a single high-affinity Cu2+ binding site within the microtubule-binding domain (MTBD), coordinated by the bis-His motif in R3 (His329/His330), possibly His299 and an oxygen-based ligand. This complex can be reduced resulting in a trigonal Cu+-Tau441 complex involving Cys322, His299 and a third ligand (likely Cys291 or His329/330), as characterized by XAS and NMR. NMR and XAS results indicate the presence of three Zn2+ binding sites: one high-affinity site in the MTBD involving His299, His330, Cys322 and Asp295, and two lower-affinity sites in the N-terminal region, coordinated predominantly by carboxylate and His residues. Moreover, the impact of Cu2+ and Zn2+ ions on the amyloid aggregation of full length Tau441 was evaluated using thioflavin T fluorescence, electrophoresis and transmission electron microscopy. Both metal ions significantly accelerate aggregation, promoting the formation of amyloid fibrils with distinct morphologies. Our study provides valuable structural insights into the copper and zinc binding sites in Tau441 that provide a rational basis to understand the impact of metal ions on amyloid fibril aggregation and morphology. The current study expands the bioinorganic facet of AD and other tauopathies, and it underscores the importance of metal-tau interactions as potential therapeutic targets in these neurodegenerative diseases.

Rare earth elements (REEs) are considered to be critical resources and play a key role in the development of advanced technologies. However, REE-bearing minerals often contain naturally occurring radioactive materials (NORMs), such as uranium and radium, which can pose radiological risks in mining operations if improperly treated. This study investigates the mobility and speciation of uranium and radium during weathering using a benchtop column model and three types of uranium sources: from the mine, from natural ore at secular equilibrium, and synthetically purified from decay products. Results indicate that radium exhibits a relatively high gradient of concentration in the leachate while uranium does not. Imaging techniques such as SEM-EDX revealed the colocalization of uranium within and on the surface of organic matter particles. Extended X-ray Absorption Fine Structure analysis suggests that uranyl species may be bound to the carboxylate complexes of the soil organic matter. These findings provide critical insights into the behavior of NORMs in REE mining environments, helping us to assess potential environmental risks.

Since the end of nuclear weapon testing, anthropogenic metallic radionuclides have originated from nuclear accidents such as Chernobyl and Fukushima and controlled releases from the nuclear industry. 60Co is an activation product found in the effluents of nuclear power plants, mobile nuclear reactors, and fuel reprocessing facilities. In this paper, we are addressing the question of (radio)cobalt speciation upon bioaccumulation in the sentinel organism Mytilus galloprovincialis after in vivo contamination in a pseudo-natural system. For this study, inductively coupled plasma mass spectrometry and gamma spectroscopy were used to quantify the cobalt distribution in the various organs: hepatopancreas, gills, visceral mass, mantle, foot, and byssus, as well as in subcellular compartments. Two X-ray spectroscopic techniques were used to decipher cobalt speciation and localization, bulk X-ray absorption spectroscopy (XAS with EXAFS and XANES regimes), and micro X-ray fluorescence imaging (μ-XRF). Lastly, secondary ion mass spectrometry images provided information on cobalt distribution at a subcellular scale. The accumulation of cobalt exhibits significant differences depending on the origin of the individuals, with higher concentration factor values for mussels from the Toulon Naval Base (considered as polluted) compared to Villefranche sur Mer, France (considered as unpolluted). However, concentration in organs always follows the same order: byssus ≫ hepatopancreas ≫ other organs. In terms of spatial distribution, cobalt has been visualized in the hepatopancreas, revealing the presence of preferred zones within some digestive cells and this could be linked to detoxification mechanisms. Finally, the determination of speciation data using XAS suggested the presence of a Co(II)-metallothionein complex in the hepatopancreas and a potential Co(II)-mfp-1 complex in the byssus. While they can be challenging, accumulation and speciation studies in radioecology are essential steps for a comprehensive approach to the impact of trace metallic radionuclides on the marine biota.

Studies of metallic radionuclides in oceans represent an important field of research. Because of their direct impact on marine ecosystems, they are especially important for assessing environmental health and safety. The high chemical - and radio - toxicity of heavy actinide elements makes them a particular threat to organisms, regardless of isotopy. Among these, americium is well known for its strong biosorption potential and combined chemo - radiotoxic effects. This study investigates the bioaccumulation of 241Am and of 153Eu (stable) and 152Eu as its chemical surrogate, in the brown macroalga Ascophyllum nodosum. Environmental analogies between 152Eu and 241Am are discussed, validating Europium as a reliable homolog in this system. Biokinetic accumulation models across trace and ultra-trace concentration levels are reported showing consistent behavior within the data, with a mono-exponential saturation pattern best fitting. Alginate was identified as a primary chelating agent, with speciation studies revealing potential alginate - Europium complexes in algal tissues. These findings highlight the essential role of algal polysaccharides in the uptake of metallic radionuclides and provide an entry into the ecological risk assessment associated with marine ecosystem contamination.

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After the first atomic bomb test in Alamogordo in July 1945, followed by the Hiroshima and Nagasaki bombs in August 1945, radioecology became recognized as a branch of ecology in response to the radioactive fallout associated with the subsequent proliferation of atmospheric nuclear weapons testing which continued throughout the Cold War. In parallel, environmental radiochemistry emerged in the 70s to understand the chemical behavior of possible nuclear contaminants of the environment. In this discussion we stress the need to crosslink radioecology and chemical speciation, where radiochemistry and radioecology should meet to go beyond the present state of the art. Accordingly, we are seeking a methodology that calls for several angles of investigation: speciation (chemistry), toxicology (physiology and biology), accumulation data (environmental studies), distribution (geochemistry).

Alzheimer's disease (AD) is the most common form of dementia worldwide. AD brains are characterized by the accumulation of amyloid-β peptides (Aβ) that bind Cu2+ and have been associated with several neurotoxic mechanisms. Although the use of copper chelators to prevent the formation of Cu2+-Aβ complexes has been proposed as a therapeutic strategy, recent studies show that copper is an important neuromodulator that is essential for a neuroprotective mechanism mediated by Cu2+ binding to the cellular prion protein (PrPC). Therefore, in addition to metal selectivity and blood-brain barrier (BBB) permeability, an emerging challenge for copper chelators is to prevent the formation of neurotoxic Cu2+-Aβ species without perturbing the neuroprotective Cu2+-PrPC interaction. Previously, we reported the design of a tetrapeptide (TP) that withdraws Cu2+ from Aβ(1-16) and impacts the Cu2+-induced aggregation of Aβ(1-40). In this study, we improved the drug-like properties of TP in a BBB model, evaluated the metal selectivity of the optimized peptide (TP*), and tested its effect on Cu2+ coordination to PrPC and proteins involved in copper trafficking, such as copper transporter 1 and albumin. Our results show that changing the stereochemistry of the first residue prevents TP degradation in the BBB model and coadministration of TP with a peptide that increases BBB permeability allows its passage through the BBB model. TP* is highly selective toward Cu2+ in the presence of Zn2+ ions, transfers Cu2+ to copper-trafficking proteins, and forms a ternary TP*-Cu2+-PrP species that does not perturb the physiological conformation of PrP and displays only a minor impact in the neuroprotective Cu2+-dependent interaction of PrPC with the N-methyl-d-aspartate receptor. Overall, these results show that TP* displays desirable features for a copper chelator with therapeutic potential against AD. Moreover, this is the first study that explores the effect of a Cu2+ chelator with therapeutic potential for AD on Cu2+ coordination to PrPC (an emerging key player in AD pathology), integrating recent knowledge about metalloproteins involved in AD with the design of copper chelators against AD.

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.

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.

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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.

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 M2Tf 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:holoTf<M2Tf (M=Th, Pu)<apoTf<M2Tf-DFOB (M=Fe, Th, Pu). Metalloprotein: With a toolbox of X-ray spectroscopy and molecular dynamics, this work sheds light on the binding interaction of plutonium and thorium (early actinides at oxidation state +IV) with iron transport transferrin protein and its tertiary structure.image

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.

Uranium is a naturally occurring radionuclide. Its redistribution, primarily due to human activities, can have adverse effects on human and non-human biota, which poses environmental concerns. The molecular mechanisms of uranium tolerance and the cellular response induced by uranium exposure in bacteria are not yet fully understood. Here, we carried out a comparative analysis of four actinobacterial strains isolated from metal and radionuclide-rich soils that display contrasted uranium tolerance phenotypes. Comparative proteogenomics showed that uranyl exposure affects 39–47% of the total proteins, with an impact on phosphate and iron metabolisms and membrane proteins. This approach highlighted a protein of unknown function, named UipA, that is specific to the uranium-tolerant strains and that had the highest positive fold-change upon uranium exposure. UipA is a single-pass transmembrane protein and its large C-terminal soluble domain displayed a specific, nanomolar binding affinity for UO22+ and Fe3+. ATR-FTIR and XAS-spectroscopy showed that mono and bidentate carboxylate groups of the protein coordinated both metals. The crystal structure of UipA, solved in its apo state and bound to uranium, revealed a tandem of PepSY domains in a swapped dimer, with a negatively charged face where uranium is bound through a set of conserved residues. This work reveals the importance of UipA and its PepSY domains in metal binding and radionuclide tolerance.

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.

The physicochemical properties of the monovalent actinyl cations, PuO2+ and NpO2+, in water have been studied by means of classical molecular dynamic simulations. A specific set of cation-water intermolecular potentials based on ab initio potential energy surfaces has been built on the basis of the hydrated ion concept. The TIP4P water model was adopted. Given the paramagnetic character of these actinyls, the cation-water interaction energies were computed from highly correlated wave functions using the NEVPT2 method. It is shown that the multideterminantal character of the wave function has a relevant effect on the main distances of the hydrated molecular cations. Several structural, dynamical, and energetic properties of the aqueous solutions have been obtained and analyzed. Structural RDF analysis gives An-Oyl distances of 1.82 and 1.84 Å and An-O(water) distances of 2.51 and 2.53 Å for PuO2+ and NpO2+ in water, respectively. Experimental EXAFS spectra from dilute aqueous solutions of PuO2+ and NpO2+ are revisited and analyzed, assuming tetra- and pentahydration of the actinyl cations. Simulated EXAFS spectra have been computed from the snapshots of the MD simulations. Good agreement with the experimental information available is found. The global analysis leads us to conclude that both PuO2+ and NpO2+ cations in water are stable pentahydrated aqua ions.