Radioactive technetium-99 (99Tc) is present in nuclear and medical wastes. Its immobilization by magnetite (FeIIFeIII 2O4) has been studied in the last decades, showing that magnetite reduces pertechnetate (TcVIIO4 -) to TcIV, which is either incorporated into the magnetite structure or forms TcIV-TcIV-dimers attached to the magnetite surface. The distribution between both phases and the incorporation mechanism remain, however, unclear. Therefore, we investigated the molecular environment of Tc after contacting TcVII with synthesized nanoparticulate magnetite as a function of pH (2-13) and time (up to 7 weeks). X-ray absorption spectroscopy was combined with density functional theory (DFT) simulations to decipher the mechanism of TcIV incorporation. We observed that the sorption of TcIV-TcIV-dimers initially occurs at pH 5 and pH 7, while TcIV incorporation in magnetite prevails at longer times and at pH 10. We suggest that TcIV-TcIV-dimer sorption on magnetite is due to (surficial) maghemitization of the magnetite nanoparticles, whereas TcIV incorporation is due to the electron transfer from sorbed Fe2+ through magnetite and subsequent release of FeII in solution (redox conveyor belt model), "burying" TcIV into the magnetite structure. DFT calculations indicate that TcIV incorporates in magnetite by an exchange of two FeII atoms for one TcIV, keeping the charge balanced by creating a vacancy.

Abstract Uranium contamination is a major global concern, as its chemical and radiological effects threaten ecosystems and human health, particularly in mining-impacted regions. Pentavalent uranium is a key but often overlooked intermediate in U biogeochemistry, challenging the conventional view of a direct U(VI) to U(IV) transition and precipitation in natural waters. Here we demonstrate the formation and stability of U(V) under environmentally relevant mine-water conditions using advanced spectroscopic and microscopic analyses. Our data reveal concurrent U(VI) reduction to U(IV), as biogenic uraninite nanoparticles, and to U(V) as FeU(V)O₄ nanoparticles and U(V)-carbonate complexes. U(V) persists for at least 130 days under anoxic conditions and four weeks after exposure to oxygen. Microbial community analysis reveals enrichment of fermentative and sulphate-reducing taxa, consistent with redox conditions favouring U reduction. By demonstrating the stability of immobilised U(V) alongside U(IV), this work advances the understanding of uranium biogeochemistry and offers new insights for sustainable remediation strategies.

Recent synthesis and characterization of tetravalent U and Np complexes [AnIVX((S)-PEBA)3] and [AnIVX(iPr2BA)3] (X = F, Cl) bearing the (S,S)-N,N'-bis(1-phenylethyl)benzamidinate ((S)-PEBA) and the N,N'-bis(isopropyl)benzamidinate (iPr2BA) ligands, respectively, have revealed a characteristic inversion of paramagnetic 1H NMR shifts for both [UF(L)3] representatives compared to the [UCl(L)3] compounds. The same effect is not observed for [NpF(L)3] and [NpCl(L)3], with currently no satisfactory explanation for these observations. Using straightforward CASSCF-SOC-NEVPT2 calculations and point-group-optimized geometries, in combination with the Kuprov model approach [G. T. P. Charnock and I. Kuprov, Phys. Chem. Chem. Phys., 2014, 16] for the calculation of pseudo-contact shifts (PCS), the experimentally derived 1H paramagnetic shifts could be reproduced qualitatively and in most cases also quantitatively. The good agreement for most signals allowed for a first evaluation of the contribution of Fermi-contact shifts (FCS) for more strongly deviating data points, which could be supported by unrestricted DFT spin densities and spin populations. To finally gain a deeper understanding as to where the differing magnetic anisotropy for the [UF(L)3] compounds stems from, the magnetic sublevels of the ground atomic multiplet |J,mJ〉 were investigated for all complexes. These revealed that only for the [UF(L)3] compounds a high |mJ〉 (pseudo) doublet showing sufficient isolation is stabilized in the ground state, whose high axiality in the end enables the realization of a prolate χ tensor responsible for the inverse PCS field.

Contamination of natural habitats, including the food chains, by chemotoxic and/or radiotoxic f-elements is a substantial threat to human life. Dairy products are an integral part of the daily diet of various human cultures and contain high amounts of proteins with phosphorylated amino acid residues, especially serine. These proteins are responsible for the ability to bind Ca2+ but they can also bind poisonous f-elements. The present paper aims to characterize the metal-binding properties at the molecular level by studying the interactions of O-phospho-L-serine with selected ions in solution as well as in solid precipitates by the combined application of liquid-state and solid-state nuclear magnetic resonance (NMR) spectroscopy, complemented by time-resolved laser-induced fluorescence spectroscopy (TRLFS). In solution, trivalent ions of lanthanum, europium, and lutetium, as well as the lighter, NMR-active surrogate yttrium, are primarily coordinated via bidentate phosphate complexation. In the obtained solids, the ligand's carboxylate group is involved in coordination. Depending on solution conditions, three complex species are formed, one of which prevails as a soluble 1:1 complex species, and two of which form solid phases of 3:2 and 1:1 SerP:metal ratios.

Abstract Two series of actinide tetrachloride complexes with the monodentate carboxylic amide ligands phthalimidine (H-phthal) and 2-pyridone (HPyO) of the general formula [AnIVCl4(L)2] (An = U, Np, Pu) were synthesized and characterized in the solid state and in solution. SC-XRD analysis revealed an octahedral coordination environment with trans orientation of either H-phthal or HPyO in all cases, with and without THF molecules hydrogen-bonded to the NH group of the ligands. In the case of [NpCl4(H-phthal)2], the absence of THF leads to a significant distortion of the coordination geometry around the metal, including the shortest Np–Cl bonds observed so far (2.4394(8) Å). A quantum chemical bonding analysis (QTAIM) showed that the main bonding interaction is found between the actinide and chloride ligands, with the amides rather loosely bound. Despite their unusually low coordination number, the complexes were found to be stable, even in coordinating solvents. This allowed for an in-depth analysis of their 1H and 13C NMR spectroscopy. Due to their pseudoD4h symmetry in the first coordination sphere, these complexes are excellent model systems to analyze their electronic structure and magnetic properties. We applied SQUID magnetometry to extract magnetic properties (μeff) and crystal field parameters ( Bqk, Wybourne) in combination with quantum chemical calculations, which allows for the comprehensive description of the electronic ground state from an experimental and theoretical point of view.

Hydrogen isotope exchange at aminoacetate carbons is facilitated in lanthanide aminopolycarboxylate complexes in NaOD D2O solution. Ionic radius-dependent yields revealed that Lu3+ is the choice. NMR and Raman spectroscopy evidence yields insights into selectivity, while theoretical calculations help in understanding the mechanism.

Although uranyl(VI)-malate systems have been repeatedly studied, there are still open questions regarding their structures, stoichiometry, and thermodynamic key parameters. We therefore examined the interactions between the uranyl(VI) ion, U(VI), and malic acid, H2Mal, using a multi-technique approach performing nuclear magnetic resonance spectroscopy (NMR), time-resolved laser-induced fluorescence spectroscopy (TRLFS), isothermal titration calorimetry (ITC), and ultraviolet-visible spectroscopy (UV-vis), complemented by density functional theory (DFT) calculations. In acidic solution (pH 1.5-5.5), by covering metal excess through ligand excess, two dinuclear complexes of 2 : 1 and 2 : 2 U(VI) : malate stoichiometry form predominantly. This species distribution is mainly influenced by the metal-to-ligand ratio given in solution. DFT and NMR confirmed that the 2 : 1 U(VI) malate complex involves a bridging hydroxo ligand (µ2-OH). In both the 2 : 1 and 2 : 2 complexes, malate features a (κ3O,O',O″) coordination motif with two carboxylate groups and the alkoxylato group including bridging between two U(VI). In the 2 : 2 complex, changing the ligands' relative orientation yields two geometric isomers. Thermodynamic quantities (ΔG, ΔH, and ΔS) and formation constants (log β) of both complexes were determined by calorimetric titrations and TRLFS. The formation of the 2 : 1 and 2 : 2 species is endothermic and entropy-driven, with log β of 17.1 ± 0.1 and 37.7 ± 0.1, respectively. Notably, even for U(VI) concentrations as low as 10 µM, dinuclear species are predominant, while mononuclear species exist only in very acidic and/or very dilute solutions. This study provides new data which complement and expand the understanding of both structures and thermodynamics of these complexes.

Incorporation of lanthanide (Ln) and actinide (An) ions into the human body poses significant chemotoxic and radiotoxic risks, necessitating effective decorporation strategies. This study investigates the displacement of biologically relevant ligands from trivalent ions of europium, Eu(III), and curium, Cm(III), in artificial biofluids by various complexing agents, i.e., ethylenediaminetetraacetic acid (EDTA), ethylene glycol-bis(β-aminoethyl ether)-N,N,N′,N′-tetraacetic acid (EGTA), diethylenetriaminepentaacetic acid (DTPA), and spermine-based hydroxypyridonate chelator 3,4,3-LI(1,2-HOPO) (HOPO). Utilizing a modified unified bioaccessibility method (UBM) to simulate gastrointestinal conditions, we conducted concentration-dependent displacement experiments at both room and body temperatures. Time-resolved laser-induced fluorescence spectroscopy (TRLFS) supported by 2H nuclear magnetic resonance (NMR) spectroscopy and thermodynamic modelling revealed the complexation efficacy of the agents under physiological conditions. Results demonstrate that high affinity, governed by complex stability constants and ligand pKa values, is critical to overcome cation and anion competition and leads to effective decorporation. Additionally, there is evidence that cyclic ligands are inferior to linear ligands for this application. HOPO and DTPA exhibited superior displacement efficacy, particularly in the complete gastrointestinal tract simulation. This study highlights the utility of in vitro workflows for evaluating decorporation agents and emphasizes the need for ligands with optimal binding characteristics for enhanced chelation therapies.

Complexes of tetravalent actinides (An: Th, U, Np, and Pu) with the bidentate (N,S)-donor ligand pyridine-2-thiolate (2-PyS, PyS-) were synthesized in 1:4 or 1:5 ratios. This includes the first structurally characterized Np complex with (N,S)-donor ligands, filling a notable gap in the An coordination chemistry. An improved synthetic approach with PyS-SiMe3 enabled efficient formation of the 1:4 complexes in THF as a coordinating solvent. The compounds were comprehensively characterized in solution and in the solid phase, supported by quantum chemical calculations. Experimental and theoretical results show matching trends in the binding behavior of AnIV. The covalent bond contributions in An-N and An-S bonding increase along the series of An from Th to Pu. The bonds to the soft sulfur donors consistently have the highest covalent contributions with a remarkably high percentage for Pu-S (IQA analysis: >34%) over the harder N donors or An-O bonds of coordinating THF. High-resolution X-ray absorption and infrared spectroscopy indicate similar electronic and structural properties across AnIV complexes, while SQUID magnetometry uncovered significant differences in magnetic behavior at low temperatures depending on the complex compositions. This work advances the understanding of An-ligand bonding, emphasizing covalency and electronic structures, and expands fundamental insights into An chemistry.

Diatoms are essential bio-indicators for assessing the impact of heavy metals and hazardous materials on aquatic ecosystems. This study seeks to advance our understanding of the interaction between uranium (U) and the freshwater diatom species Achnanthidium saprophilum, employing macroscopic, microscopic, and spectroscopic approaches. Bio-association experiments with hexavalent U (U(VI)) were conducted during various diatom growth phases and revealed time- and concentration-dependent U retention by the diatoms. U bio-association was observed by scanning electron microscopy and energy-dispersive X-ray spectroscopy (EDX), indicating co-localization of U with phosphorus (P). Time-resolved laser-induced fluorescence spectroscopy on U(VI)-associated diatoms suggested the formation of two adsorbed U(VI) species, whose proportions depend on the diatom growth phase. Fourier-transform infrared spectroscopy confirmed the interaction of U(VI) dominated by carboxyl groups on diatoms, while the contribution of silanol groups from the diatom frustule appeared insignificant. U bio-association experiments revealed also U incorporation into diatom cells, confirmed by transmission electron microscopy coupled with EDX. Co-localization of U with P within the vacuole was evident, suggesting co-precipitation of various metals, including U, in form of phosphates. The results of this study highlight not only the adsorption but also the internalization of U by diatoms, which influences the fate of U in aquatic ecosystems and affects its mobility and bioavailability. These findings are highly relevant for the further development of radioecological models.

As rare earth elements gain strategic importance, knowledge of their environmental pathways becomes increasingly needed. In particular, mechanistic insight into plant uptake of rare earth elements informs both risk assessment and mitigation strategies in case of environmental contaminations and modern green applications such as biomining. In this study, we addressed the mobility, speciation and deposition of Eu(III), serving as surrogate for trivalent lanthanides, within the Poaceae Sand oat (Avena strigosa) from both microscopic and macroscopic perspectives. Using hydroponic bioassociation and extraction experiments, we tracked the metal's pathway within the plant. A combination of (micro)spectroscopic and chromatographic techniques, mass spectrometry, autoradiography and iterative factor analysis enabled us to develop a comprehensive understanding of Eu(III) speciation and its influence on translocation of lanthanides within plants. The results show that Eu(III) is absorbed by epidermal cells and root tips, but predominantly the apoplast, in which Eu(III) is subjected to cell wall binding and phosphate precipitation. Internalized Eu(III) is bound to organophosphate ligands in the cell interior. Xylem loading occurs within less than one hour and translocation to the shoots is achieved by complexes with oxalate, citrate and malate. The use of radioactive 152Eu(III) as tracer revealed that the majority of the metal remains in the roots, while a minor portion is deposited uniformly in the non-vascular tissue of both young and mature leaf lamina. These findings advance our mechanistic comprehension of rare earth element transport, the chemical binding environments encountered in plants and lay the foundation for environmental risk assessments and phytomanagement for metal-enriched areas.

Understanding the behavior of contaminants in soils and their transport in water is crucial. This study focuses on the mobility of uranium (U) in a buried contaminated sediment layer, deposited in a wetland 70 years ago by the first U mining activities in France. U mobilization is kinetically limited in the contaminated layer with a small fraction of labile U as deduced from laboratory desorption-based studies and in situ studies performed by DET (Diffusive Equilibration in Thin films)/DGT (Diffusive Gradients in Thin films) passive sampler data monitored over time. The smart-Kd approach, combined with a comprehensive system characterization, identified this labile fraction as U(VI) primarily adsorbed on 2:1 clay minerals, which is in line with X-ray Absorption Spectroscopy (XAS) data. The inert fraction was found to correspond to U minerals and adsorbed U(IV) and U(VI) species exhibiting desorption hysteresis. Combining laboratory and field studies, this multiscale approach allows to connect molecular processes to operational Kd(labile) parameters.

The ZrO2-CeO2 system is fundamental to various technological applications, yet unresolved questions persist regarding cation miscibility and the occurrence of metastable phases in the Zr1-xCexO2 phase diagram. This work addresses these gaps through a comprehensive investigation of Zr1-xCexO2 compositions with varying cerium concentrations and incorporating Eu3+ as a luminescent probe. Synchrotron powder X-ray diffraction analysis unveiled a miscibility gap between 20 and 50 mol % cerium. Beyond this gap, the formation of solid solutions and multiple crystalline phases was observed, including tetragonal prime (t') and tetragonal double prime (t″) structures, depending on cerium content. Raman investigations revealed a unique distortion band in all compositions containing the t' phase. Our high energy resolution fluorescence detected X-ray absorption near edge structure spectroscopy (HERFD-XANES) analysis implies that this feature results from oxygen ion displacement in the t' structure. Luminescence spectroscopy of the europium environment revealed distinct excitation and emission spectra across the various crystal phases, enabling unambiguous identification of all metastable phases. These findings highlight the complex polymorphism of the ZrO2-CeO2 system. The ability to precisely control phase composition offers significant potential for optimizing properties for diverse applications, including oxygen sensors, three-way catalysts, and solid oxide fuel cells for clean, sustainable energy generation.

This study represents a first comprehensive investigation on how the decorporation agents CaNa3-DTPA (DTPA) and 3,4,3-LI(1,2-HOPO) (LIHOPO) affect EuIII interactions with human and rat kidney cells in vitro. Cell biological investigations were complemented with physicochemical measurements to correlate cytotoxic impairments with intracellular metal uptake and EuIII speciation. Upon exposure to sole DTPA or LIHOPO, cell viability and morphology are affected in a time- and concentration-dependent manner. For both decorporation agents, detailed EC50 values for renal cells in vitro are reported. Simultaneous application of EuIII + DTPA in the medium leads to formation of the soluble and largely cell impermeable EuDTPA2- complex. At ligand excess, this significantly reduces intracellular EuIII uptake. However, EuDTPA2- was spectroscopically detected also inside cells indicating that small fractions of this complex are able to pass the plasma membrane. When EuIII + LIHOPO is applied to the medium, the soluble EuLIHOPO- complex is formed. In contrast to DTPA, this drastically enhances intracellular EuIII uptake even at ligand deficit demonstrating that EuLIHOPO- is highly cell permeable. Concomitantly, this complex was spectroscopically detected inside cells confirming its plasma membrane passage and intracellular stability. Nevertheless, due to stable EuIII binding, the cell viability is not influenced by the increased intracellular EuIII content. In fact, the applied ligand concentration is much more critical in this regard, emphasizing the need for cytotoxic investigations. Our results improve the knowledge of the cellular interactions of lanthanides ± decorporation agents and demonstrate the combination of in vitro cell culture and spectroscopy being a sophisticated toolbox for this.

A new nonadentate ligand, DEGTA (diethylene glycol-bis(3-aminopropyl ether)-N,N,N',N'-tetraacetic acid), from the polyaminopolycarboxylate family, was synthesized in a two-step reaction. The ligand's pH-dependent behavior (structure and pKa values) was determined by nuclear magnetic resonance (NMR) spectroscopy. The complexation ability of the ligand toward trivalent lanthanides and actinides was studied by time-resolved laser-induced fluorescence spectroscopy (TRLFS) using Eu(III) and Cm(III) as representatives. For Eu(III), two species occurring at different pH values were observed and corroborated by concentration- and pD-dependent NMR-titration series, viz. [EuH2(DEGTA)]+ and [Eu(DEGTA)]-. The latter is shown to be nine-coordinate, forming isostructural complexes with Cm(III) and Sm(III) as inferred from TRLFS and 2D NMR experiments, respectively. Since DEGTA can be seen as a consecutive derivative of EDTA and EGTA with an elongated backbone, the structures of their Eu(III) complexes were calculated using density functional theory (DFT) and the same aminoacetate binding motif proven by Fourier-transform infrared (FT-IR) spectroscopy. Upon comparison of structure-property relationships (denticity and chain length vs coordination geometry and complex stability) one can draw conclusions on DEGTA's complexation behavior in particular, and some generalizable trends in complexation properties within the complexone series are discussed. Looking further ahead, this knowledge will help in further developing decontamination, decommissioning, and decorporation strategies.

Isostructural trivalent lanthanide and actinide amidinates bearing the N,N'-bis(isopropyl)benzamidinate (iPr2BA) ligand [LnIII/AnIII(iPr2BA)3] (Ln = La, Nd, Sm, Eu, Yb, Lu; An = U, Np) have been synthesized and characterized in both solid and solution states. All compounds were examined in the solid state utilizing single crystal X-ray diffraction (SC-XRD), revealing a notable deviation in the actinide series with shortened bond lengths compared to the trend in the lanthanide series, suggesting a nonionic contribution to the actinide-ligand bonding. Quantum-chemical bonding analysis further elucidated the nature of these interactions, highlighting increased covalency within the actinide series, as evidenced by higher delocalization indices and greater 5f orbital occupation, except for Th(III) and Pa(III), which demonstrated substantial 6d orbital occupancies. An in-depth paramagnetic NMR study in solution also sheds light on the covalent character of actinide-ligand bonding, with the separation of pseudocontact (PCS) and contact shift (FCS) contributions employing the Bleaney and Reilley method. This analysis unveiled significant contact contributions in the actinide complexes, indicating enhanced covalency in actinide-ligand bonding. To corroborate these observations, an accurate PCS calculation method based on the Kuprov equation, incorporating both the distribution of electronic spin density and magnetic susceptibility obtained from CASSCF calculations, was applied and compared with experimental values.

High-level radioactive waste needs to be safely stored for a long time in a deep geological repository by using a multi-barrier system. In this system, suitable barrier materials are selected that ideally show long-term stability to prevent early radionuclide release into the biosphere. In this study, different container matals (copper and cast iron) and pore water compositions (Opalinus Clay pore water and saline cap rock solution) were combined with Bavarian bentonite in static batch experiments to investigate microbial-influenced corrosion. The increasing concentration of iron and copper in the solution as well as detected corrosion products on the metal surface are indicative of anaerobic corrosion of the respective metals during an incubation of 400 days at 37 °C. However, although the intrinsic microbial bentonite community was stimulated with either lactate or H2, an acceleration of cast iron- and copper corrosion did not occur. Furthermore, neither corrosive bacteria nor conventional bacterial corrosion products, such as metal sulfides, were detected in any of the analyzed samples. The analyses of geochemical parameters (e.g. ferrous iron-, iron-, copper- and potassium concentrations as well as redox potentials) showed significant changes in some cast iron- and copper-containing setups, but these changes did not correlate with the microbial community structure in the respective microcosms, as confirmed by statistical analyses. Hence, the analyzed Bavarian bentonite (type B25) showed no significant contribution to cast iron and copper corrosion under the applied conditions after 400 days of incubation. From this perspective, bentonite B25 could be a suitable candidate as a geotechnical barrier in future repositories.