Size and structure of hexanuclear plutonium oxo-hydroxo clusters in aqueous solution from synchrotron analysis

Abstract

The size and shape of a water-soluble hexanuclear plutonium cluster were probed by combining synchrotron small-angle X-ray scattering (SAXS) and extended X-ray absorption fine structure (EXAFS). A specific setup coupling both techniques and dedicated to radioactive samples on the MARS beamline endstation at Synchrotron SOLEIL is described. The plutonium hexanuclear cores are well stabilized by the 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid ligands and this allows a good evaluation of the setup to probe the very small plutonium core. The results show that, in spite of the constrained conditions required to avoid any risk of sample dispersion, the flux and the sample environment are optimized to obtain a very good signal-to-noise ratio, allowing the detection of small plutonium aggregates in an aqueous phase. The structure of the well defined hexanuclear cluster has been confirmed by EXAFS measurements in solution and correlated with SAXS data processing and modelling. An iterative comparison of classical fit models (Guinier or sphere form factor) with the experimental results allowed a better interpretation of the SAXS signal that will be relevant for future work under environmentally relevant conditions.

Synthesis and multi-scale properties of PuO2 nanoparticles: recent advances and open questions

“…It is worth noting that combined SAXS/XAS synchrotron techniques recently allowed probing the size, shape and local structure of a watersoluble plutonium hexanuclear cluster. 146 The stabilization of these very small and low concentration aggregates with the DOTA ligand (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) allowed their characterization with a good signal-to-noise ratio, thus demonstrating the technical capacity of the mutual approach. Scattering techniques are obviously strongly considered in modern actinide science [147][148][149] but remain poorly applied for trans-uranium oxide nanoparticles and we expect a stronger interest for the technique in the near future.…”

Synchrotron Radiation Techniques and their Application to Actinide Materials

“…Besides the scientific importance, actinide speciation studies are key to understanding extraction mechanisms and separation processes in fuel reprocessing (Dressler et al, 2022;Moeyaert et al, 2021;Pruessmann et al, 2022), the corrosion and the reduction-oxidation behavior of nuclear waste forms in storage facilities (Glasauer et al, 2022;Husar et al, 2022), the mechanisms by which actinides can contaminate the biosphere (Cot-Auriol et al, 2021;Estevenon et al, 2021;Pidchenko et al, 2020;Vitova et al, 2020), their mobility in contaminated sites and how best they can be removed from the environment (Dumas et al, 2022;Jegou et al, 2022;Le Pape et al, 2020). The clean up of the Rocky Flats Nuclear Weapons Plant, near Denver, is exemplary of the practical importance of these studies (Clark et al, 2006).…”

Macrocyclic Ligand Coordinating Amide-Arm Hydrolysis Reaction Activation in Aqueous Solutions: Tetravalent Uranium Does It Better

“…The kinetics analysis was performed in two stages: 126 spectra were acquired over about 20 h with a 10 min interval between each spectrum acquisition in the first stage. The sample was left sealed after that, and its 1 H NMR spectrum was acquired after 3,5,8,15,19,24,29,36,50,68, and 85 days in the second stage. All spectra acquisition was carried out with the same settings and pulse setup.…”

“…Even though much remains to be discovered merely by following the footsteps of those who have meticulously studied how various lanthanide cations interact with such cyclen derivatives, it is not easy to elaborate further on the subject regarding the actinides mentioned above. Four significant obstacles stand in the way of this effort: (1) actinide cation radioactivity, which requires specially equipped laboratories; (2) heavy actinide scarce availability; (3) the lack of simplified model theories for data interpretation that can compensate for the actinides’ intricate electronic configuration, similar to that enabled by Bleaney’s theory for the lanthanide ligand field effects; and (4) the sluggish complex formation kinetics of cyclen-based chelates with aqueous cations. , The ligand–cation interaction often results in ligand-supported multinuclear “out-of-cage” products rather than the characteristic “in-cage” complex for higher-valency cations. ,− The fourth obstacle mentioned gets even harder to get by for one who is trying to study the interaction of the natural, easy-to-work-with, and aqueous stable U VI cation, whose most common aqueous form is the hydrolyzed uranyl form, [UO 2 ] 2+ aq . That D ∞h cation favors mostly equatorial bonding schemes with respect to the central U VI cation and its axial coordination sphere is completely saturated by the two O 2– bonded ligands.…”