Spontaneous Chelation‐Driven Reduction of the Neptunyl Cation in Aqueous Solution

Carter, Korey P.; Smith, Kurt F.; Tratnjek, Toni; Shield, Katherine M.; Moreau, Liane M.; Rees, Julian A.; Booth, C. H.; Abergel, Rebecca J.

doi:10.1002/chem.201905695

Cited by 11 publications

(11 citation statements)

References 40 publications

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“…Such features are indicative of the axial U−O pairs (hereby denoted U−O ax ) of an "yl" complex 42 and are consistent with the presence of the high energy shoulder in the XANES spectra for each of the U IV -343-chelator complexes (Figure 2). When fits 22 The EXAFS spectrum of U VI -343-HOPO has been collected previously 10 but was recollected here to allow for comparison with U IV -343-HOPO, as well as U VI complexes with the other 343-chelators. The FT of the EXAFS spectra for U VI with all four 343-chelators revealed the characteristic two peaks that are well-known for actinyl moieties (Figure S2, Supporting Information).…”

Section: ■ Introductionmentioning

confidence: 99%

Controlling the Reduction of Chelated Uranyl to Stable Tetravalent Uranium Coordination Complexes in Aqueous Solution

et al. 2020

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The solution-state interactions between octadentate hydroxypyridinone (HOPO) and catecholamide (CAM) chelating ligands and uranium were investigated and characterized by UV− visible spectrophotometry and X-ray absorption spectroscopy (XAS), as well as electrochemically via spectroelectrochemistry (SEC) and cyclic voltammetry (CV) measurements. Depending on the selected chelator, we demonstrate the controlled ability to bind and stabilize U IV , generating with 3,4,3-LI(1,2-HOPO), a tetravalent uranium complex that is practically inert toward oxidation or hydrolysis in acidic, aqueous solution. At physiological pH values, we are also able to bind and stabilize U IV to a lesser extent, as evidenced by the mix of U IV and U VI complexes observed via XAS. CV and SEC measurements confirmed that the U IV complex formed with 3,4,3-LI(1,2-HOPO) is redox inert in acidic media, and U VI ions can be reduced, likely proceeding via a two-electron reduction process.

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Section: ■ Introductionmentioning

confidence: 99%

Controlling the Reduction of Chelated Uranyl to Stable Tetravalent Uranium Coordination Complexes in Aqueous Solution

et al. 2020

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“…For EXAFS analysis, FEFF8.5L [46] was used with a manual shift of +20 eV applied to the EXCHANGE card within the Np(V) standard FEFF input file (produced by substituting the U in a liebigite (Ca 2 UO 2 (CO 3 ) 3 ) structure [47] for Np). Large E 0 values have been previously observed within multiple Np EXAFS studies [12,[48][49][50][51][52][53][54] and are likely a result of FEFF not accurately calculating potentials for transuranic elements, particularly in systems containing actinyl moieties.…”

Section: X-ray Absorption Spectroscopymentioning

confidence: 86%

Neptunium and Uranium Interactions with Environmentally and Industrially Relevant Iron Minerals

et al. 2022

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Neptunium (237Np) is an important radionuclide in the nuclear fuel cycle in areas such as effluent treatment and the geodisposal of radioactive waste. Due to neptunium’s redox sensitivity and its tendency to adsorb strongly to mineral phases, such as iron oxides/sulfides, the environmental mobility of Np can be altered significantly by a wide variety of chemical processes. Here, Np interactions with key iron minerals, ferrihydrite (Fe5O8H·4H2O), goethite (α-FeOOH), and mackinawite (FeS), are investigated using X-ray Absorption Spectroscopy (XAS) in order to explore the mobility of neptunyl(V) (Np(V)O2+) moiety in environmental (radioactive waste disposal) and industrial (effluent treatment plant) scenarios. Analysis of the Np LIII-edge X-ray Absorption Near-Edge Structure (XANES) and Extended X-ray Absorption Fine Structure (EXAFS) showed that upon exposure to goethite and ferrihydrite, Np(V) adsorbed to the surface, likely as an inner-sphere complex. Interestingly, analysis showed that only the first two shells (Oax and Oeq) of the EXAFS could be modelled with a high degree of confidence, and there was no clear indication of Fe or carbonate in the fits. When Np(V)O2+ was added to a mackinawite-containing system, Np(V) was reduced to Np(IV) and formed a nanocrystalline Np(IV)O2 solid. An analogous experiment was also performed with U(VI)O22+, and a similar reduction was observed, with U(VI) being reduced to nanocrystalline uraninite (U(IV)O2). These results highlight that Np(V) may undergo a variety of speciation changes in environmental and engineered systems whilst also highlighting the need for multi-technique approaches to speciation determination for actinyl (for example, Np(V)O2+) species.

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“…In this way, new actinyl complexes can be obtained by gas-phase two-electron actinyl reduction, otherwise not obtainable due to synthetic limitations [ 70 ]. The reduction in the NpO 2 2+ /Np 4+ redox pair (from +6 to +4), upon chelation with L27 or with the bis-catecholamide analogue 3,4,3-LI(CAM) 2 (1,2-HOPO) 2 ( L28 ), was observed to be nearly instantaneous by X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) [ 71 ]. This finding is important in terms of potential implementation of reprocessing of high-level nuclear waste (with considerable amount of long term radiotoxic 237 Np), because the electron transfer kinetics of Np-oxo bond cleavage is known to be extremely slow both from the synthetical and environmental point of view.…”

Section: Poly-hydroxypyridinonesmentioning

confidence: 99%

Hydroxypyridinone-Based Metal Chelators towards Ecotoxicity: Remediation and Biological Mechanisms

et al. 2022

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Hydroxypyridinones (HPs) are recognized as excellent chemical tools for engineering a diversity of metal chelating agents, with high affinity for hard metal ions, exhibiting a broad range of activities and applications, namely in medical, biological and environmental contexts. They are easily made and functionalizable towards the tuning of their pharmacokinetic properties or the improving of their metal complex thermodynamic stabilities. In this review, an analysis of the recently published works on hydroxypyridinone-based ligands, that have been mostly addressed for environmental applications, namely for remediation of hard metal ion ecotoxicity in living beings and other biological matrices is carried out. In particular, herein the most recent developments in the design of new chelating systems, from bidentate mono-HP to polydentate multi-HP derivatives, with a structural diversity of soluble or solid-supported backbones are outlined. Along with the ligand design, an analysis of the relationship between their structures and activities is presented and discussed, namely associated with the metal affinity and the thermodynamic stability of the corresponding metal complexes.

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Spontaneous Chelation‐Driven Reduction of the Neptunyl Cation in Aqueous Solution

Cited by 11 publications

References 40 publications

Controlling the Reduction of Chelated Uranyl to Stable Tetravalent Uranium Coordination Complexes in Aqueous Solution

Controlling the Reduction of Chelated Uranyl to Stable Tetravalent Uranium Coordination Complexes in Aqueous Solution

Neptunium and Uranium Interactions with Environmentally and Industrially Relevant Iron Minerals

Hydroxypyridinone-Based Metal Chelators towards Ecotoxicity: Remediation and Biological Mechanisms

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