The +4 Oxidation State of Protactinium in Aqueous Solution

Prediction of Redox Potentials for Ac, Th, and Pa in Aqueous Solution

Density functional theory in conjunction with small core pseudopotentials and the associated basis sets was used to calculate potentials for multiple redox couples, covering a range of oxidation states for Ac (0 to III), Th (0 to IV), and Pa (0 to V) in aqueous solution. Solvation effects were incorporated using a supermolecule-continuum approach, with 30 water molecules representing two solvation shells, and the COSMO and SMD implicit solvation models. The calculated geometries for Ac(III), Th(IV), and Pa(V) were in reasonable agreement with the available experimental data. Using the COSMO model with the B3LYP functional, the calculated redox potentials were within ±0.2 V from experiment for most redox couples. Several pathways were explored for the Pa(V/IV) redox couple for different forms of Pa(V) and Pa(IV). Most Pa(V/IV) redox couples have very similar potentials, ranging from 0 to -0.4 V up to a pH of 1.4. At pH = 1.4, the potentials shift to values that are more negative than -0.7 V, reflecting the growing unfavorable nature of the redox process at higher pH levels. The calculated values for An(III/II) potentials were consistent with prior estimates and the available experimental data. The predicted redox potentials for An(II/I) were highly negative, as expected. For An(I/0) potentials, Th and Pa exhibited positive values, contrasting with the negative values calculated for Ac. The An+m/An(0) potentials agreed better with the experimental data when using the COSMO solvation model as compared to the SMD model.

The speciation of protactinium since its discovery: a nightmare or a path of resilience

This review concerns the speciation of protactinium in aqueous solution under its both oxidation states +IV and +V. Emphasis is placed on experimental data obtained at trace level but also in macroscopic amount leading to the determination of thermodynamic and structural data. Thus, the complexation of Pa(V) with mineral acids and organic acids, mainly polyaminocarboxylic acids (iminodiacetic acid [IDA], nitrilotriacetic acid [NTA], ethylenediaminetetraacetic acid [EDTA] and diethylenetriaminepentaacetic acid [DTPA]) are highlighted and compared. The review also includes the actual knowledge about the Pa(IV) aqueous chemistry pinpointing its spectroscopic features.

What do we know about actinides-proteins interactions?

Since the early 40s when the first research related to the development of the atomic bomb began for the Manhattan Project, actinides (An) and their association with the use of nuclear energy for civil applications, such as in the generation of electricity, have been a constant source of interest and fear. In 1962, the first Society of Toxicology (SOT), led by H. Hodge, was established at the University of Rochester (USA). It was commissioned as part of the Manhattan Project to assess the impact of nuclear weapons production on workers’ health. As a result of this initiative, the retention and excretion rates of radioactive heavy metals, their physiological impact in the event of acute exposure and their main biological targets were assessed. In this context, the scientific community began to focus on the role of proteins in the transportation and in vivo accumulation of An. The first studies focused on the identification of these proteins. Thereafter, the continuous development of physico-chemical characterization techniques has made it possible to go further and specify the modes of interaction with proteins from both a thermodynamic and structural point of view, as well as from the point of view of their biological activity. This article reviews the work performed in this area since the Manhattan Project. It is divided into three parts: first, the identification of the most affine proteins; second, the study of the affinity and structure of protein-An complexes; and third, the impact of actinide ligation on protein conformation and function.

First structural characterization of Pa(iv) in aqueous solution and quantum chemical investigations of the tetravalent actinides up to Bk(IV): the evidence of a curium break

More than a century after its discovery the structure of the Pa(4+) ion in acidic aqueous solution has been investigated for the first time experimentally and by quantum chemistry. The combined results of EXAFS data and quantum chemically optimized structures suggest that the Pa(4+) aqua ion has an average of nine water molecules in its first hydration sphere at a mean Pa-O distance of 2.43 Å. The data available for the early tetravalent actinide (An) elements from Th(4+) to Bk(4+) show that the An-O bonds have a pronounced electrostatic character, with bond distances following the same monotonic decreasing trend as the An(4+) ionic radii, with a decrease of the hydration number from nine to eight for the heaviest ions Cm(4+) and Bk(4+). Being the first open-shell tetravalent actinide, Pa(4+) features a coordination chemistry very similar to its successors. The electronic configuration of all open-shell systems corresponds to occupation of the valence 5f orbitals, without contribution from the 6d orbitals. Our results thus demonstrate that Pa(iv) resembles its early actinide neighbors.

Effect of pH and temperature on the sorption of Np and Pa to mixed anaerobic bacteria

While considering the geological disposal of radioactive wastes, the behaviour of the radionuclide Np and its daughter element Pa was investigated in the presence of a mixture of anaerobic bacteria (MAB). Originally, MAB were used for the treatment of pulp and paper wastewater. The interaction between radionuclides and bacteria was evaluated by determining distribution coefficients (Kd) over 10 days and at 5 degrees C and 35 degrees C. Kd for Np at 35 degrees C after 5 days had a low value around 10(-2) After 10 days, however, Kd was > 100-fold higher. On the other hand, Kd at 5 degrees C was low (10(-2)) throughout, without any significant increase over time. The interaction between Pa and MAB was found to be stronger than that for Np, with Kd for Pa about 100 times higher. The Kd was controlled by some basic factors, the activity of MAB, the complexing capacity of MAB, and the chemical conditions in the solution such as pH and Eh.