Rationalization of the Solvation Effects on the AtO⁺ Ground-State Change

²¹¹At radionuclide is of considerable interest as a radiotherapeutic agent for targeted alpha therapy in nuclear medicine, but major obstacles remain because the basic chemistry of astatine (At) is not well understood. The AtO⁺ cationic form might be currently used for ²¹¹At-labeling protocols in aqueous solution and has proved to readily react with inorganic/organic ligands. But AtO⁺ reactivity must be hindered at first glance by spin restriction quantum rules: the ground state of the free cation has a dominant triplet character. Investigating AtO⁺ clustered with an increasing number of water molecules and using various flavors of relativistic quantum methods, we found that AtO⁺ adopts in solution a Kramers restricted closed-shell configuration resembling a scalar-relativistic singlet. The ground-state change was traced back to strong interactions, namely, attractive electrostatic interactions and charge transfer, with water molecules of the first solvation shell that lift up the degeneracy of the frontier π* molecular orbitals (MOs). This peculiarity brings an alternative explanation to the highly variable reproducibility reported for some astatine reactions: depending on the production protocols (with distillation in gas-phase or “wet chemistry” extraction), ²¹¹At may or may not readily react

QTAIM Analysis in the Context of Quasirelativistic Quantum Calculations

Computational chemistry currently lacks ad hoc tools for probing the nature of chemical bonds in heavy and superheavy-atom systems where the consideration of spin–orbit coupling (SOC) effects is mandatory. We report an implementation of the Quantum Theory of Atoms-In-Molecules in the framework of two-component relativistic calculations. Used in conjunction with the topological analysis of the Electron Localization Function, we show for astatine (At) species that SOC significantly lowers At electronegativity and boosts its propensity to make charge-shift bonds. Relativistic spin-dependent effects are furthermore able to change some bonds from mainly covalent to charge-shift type. The implication of the disclosed features regarding the rationalization of the labeling protocols used in nuclear medicine for ²¹¹At radioisotope nicely illustrates the potential of the introduced methodology for investigating the chemistry of (super)­heavy elements

Evidence for the Heaviest Expected Halide Species in Aqueous Solution, At^–, by Electromobility Measurements

At^– (astatide) is commonly expected to be the heaviest halide in the halogen group. However, there is no proof for the existence of this −1 charged species. Furthermore, investigations with astatine are restricted by its specific radioactive properties, which entail working at ultratrace concentrations (typically less than 10^–10 M). In this work, an especially built electromigration device is applied to obtain information about the charge/size ratio characterizing an ion in aqueous solution. An anionic At species is observed in reducing conditions. Moreover, we propose the first absolute mobility value for the astatine species in acidic reducing condition: (−8.26 ± 0.59) × 10^–4 cm²·V^–1·s^–1. This value appears close to that of I^– ((−8.30 ± 0.33) × 10^–4 cm²·V^–1·s^–1), which is obtained by the same method. The similar absolute mobilities obtained for both ions are coherent with theoretical calculations indicating similar diffusion behaviors for At^– and I^–. This good agreement confirms the existence of the At^– species

Number of DSB per Gray per Mbp as a function of the energy of <i>α</i>-particles.

(+): different values of the SPointProb parameter in our work, (○): simulations using other codes found in the literature [67–70], (□): experiments found in the literature [71–73].</p

Measured mass activities of radionuclides present in sediments in five mineral springs in Auvergne (Massif central).

Measured mass activities of radionuclides present in sediments in five mineral springs in Auvergne (Massif central).</p

Deposited energy distributions for ²²⁶Ra (orange) and ²²²Rn (blue) in the benthic mixture for diatoms.

Solid lines: total deposited energy, Dotted lines: ion ionisation, Dashed lines: electron ionisation.</p

Total specific energy probability distribution (Gy⁻¹) for nucleosomes (90% porosity).

Total specific energy probability distribution (Gy−1) for nucleosomes (90% porosity).</p

Dose rates to diatom in the benthic mixture.

Blue bar: 222Rn contribution, Orange bar: 226Ra contribution.</p

Summary of GATE simulation characteristics.

Mineral springs in Massif Central, France can be characterized by higher levels of natural radioactivity in comparison to the background. The biota in these waters is constantly under radiation exposure mainly from the α-emitters of the natural decay chains, with 226Ra in sediments ranging from 21 Bq/g to 43 Bq/g and 222Rn activity concentrations in water up to 4600 Bq/L. This study couples for the first time micro- and nanodosimetric approaches to radioecology by combining GATE and Geant4-DNA to assess the dose rates and DNA damages to microorganisms living in these naturally radioactive ecosystems. It focuses on unicellular eukaryotic microalgae (diatoms) which display an exceptional abundance of teratological forms in the most radioactive mineral springs in Auvergne. Using spherical geometries for the microorganisms and based on γ-spectrometric analyses, we evaluate the impact of the external exposure to 1000 Bq/L 222Rn dissolved in the water and 30 Bq/g 226Ra in the sediments. Our results show that the external dose rates for diatoms are significant (9.7 μGy/h) and comparable to the threshold (10 μGy/h) for the protection of the ecosystems suggested by the literature. In a first attempt of simulating the radiation induced DNA damage on this species, the rate of DNA Double Strand Breaks per day is estimated to 1.11E-04. Our study confirms the significant mutational pressure from natural radioactivity to which microbial biodiversity has been exposed since Earth origin in hydrothermal springs.</div

Kinetic and deposited energy of <i>α</i>-particles at the nucleus for different environments (when considering frustule, values are provided in the parentheses).

Kinetic and deposited energy of α-particles at the nucleus for different environments (when considering frustule, values are provided in the parentheses).</p