Addressing Ruthenium Speciation in Tri‑<i>n</i>‑butyl-phosphate Solvent Extraction Process by Fourier Transform Infrared, Extended X‑ray Absorption Fine Structure, and Single Crystal X‑ray Diffraction

In industrial nuclear fuel reprocessing, small amounts of ruthenium are extracted by tri-<i>n</i>-butyl-phosphate (TBP) at the same time as uranium and plutonium. This behavior increases solvent radiolysis and requires secondary extraction cycles to minimize the residual ruthenium content in uranium and plutonium products. However, the solvent ruthenium extraction mechanism remains largely unexplored. This study addresses the speciation of ruthenium in solvent extraction conditions by complementary infrared and X-ray absorption spectroscopy. First, spectroscopic result interpretation is supported by a single crystal X-ray diffraction study on reference compounds to unambiguously demonstrate that the ruthenium extraction mechanism is driven by a weak outer-sphere Ru–TBP interaction. Second, the ruthenium coordination sphere is quantitatively characterized. Ruthenium speciation in the organic phase depends on the initial aqueous phase, and both monomeric ruthenium nitrosyl trinitrate complexes and a hydrolyzed dimeric ruthenium nitrosyl complex are shown. Average coordination numbers for nitrate, hydroxide, and aquo ligands are accurately determined in both phases, by applying a constrained EXAFS fit approach

Optimized Coordination of Uranyl in Engineered Calmodulin Site 1 Provides a Subnanomolar Affinity for Uranyl and a Strong Uranyl versus Calcium Selectivity

As an alpha emitter and chemical toxicant, uranium toxicity in living organisms is driven by its molecular interactions. It is therefore essential to identify main determinants of uranium affinity for proteins. Others and we showed that introducing a phosphoryl group in the coordination sphere of uranyl confers a strong affinity of proteins for uranyl. In this work, using calmodulin site 1 as a template, we modulate the structural organization of a metal-binding loop comprising carboxylate and/or carbonyl ligands and reach affinities for uranyl comparable to that provided by introducing a strong phosphoryl ligand. Shortening the metal binding loop of calmodulin site 1 from 12 to 10 amino acids in CaMΔ increases the uranyl-binding affinity by about 2 orders of magnitude to log KpH7 = 9.55 ± 0.11 (KdpH7 = 280 ± 60 pM). Structural analysis by FTIR, XAS, and molecular dynamics simulations suggests an optimized coordination of the CaMΔ-uranyl complex involving bidentate and monodentate carboxylate groups in the uranyl equatorial plane. The main role of this coordination sphere in reaching subnanomolar dissociation constants for uranyl is supported by similar uranyl affinities obtained in a cyclic peptide reproducing CaMΔ binding loop. In addition, CaMΔ presents a uranyl/calcium selectivity of 107 that is even higher in the cyclic peptide

Role of Silver Nanoparticles in Enhanced Xenon Adsorption Using Silver-Loaded Zeolites

Molecular simulation is used to unravel the adsorption mechanisms of xenon on Ag-doped ZSM-5 zeolite. We show that silver nanoparticles, which form at the external surface of zeolite crystallites, are responsible for enhanced xenon physisorption at very low pressure. We also propose a simple model of adsorption on such composite materials made up of silver-exchanged zeolites and silver nanoparticles adsorbed at the zeolite surface. This model, which allows predicting the adsorption of other gases without any additional parameters, provides a tool to characterize the amount of reduced silver as well as the silver particle size distribution (in good agreement with transmission electron microscopy images). The presence of a majority of silver nanoparticles is further characterized by means of X-ray diffraction and X-ray Absorption Spectroscopy at the silver K edge

Structures of Plutonium(IV) and Uranium(VI) with <i>N</i>,<i>N</i>‑Dialkyl Amides from Crystallography, X‑ray Absorption Spectra, and Theoretical Calculations

The structures of plutonium­(IV) and uranium­(VI) ions with a series of <i>N</i>,<i>N</i>-dialkyl amides ligands with linear and branched alkyl chains were elucidated from single-crystal X-ray diffraction (XRD), extended X-ray absorption fine structure (EXAFS), and theoretical calculations. In the field of nuclear fuel reprocessing, <i>N</i>,<i>N</i>-dialkyl amides are alternative organic ligands to achieve the separation of uranium­(VI) and plutonium­(IV) from highly concentrated nitric acid solution. EXAFS analysis combined with XRD shows that the coordination structure of U­(VI) is identical in the solution and in the solid state and is independent of the alkyl chain: two amide ligands and four bidentate nitrate ions coordinate the uranyl ion. With linear alkyl chain amides, Pu­(IV) also adopt identical structures in the solid state and in solution with two amides and four bidentate nitrate ions. With branched alkyl chain amides, the coordination structure of Pu­(IV) was more difficult to establish unambiguously from EXAFS. Density functional theory (DFT) calculations were consequently performed on a series of structures with different coordination modes. Structural parameters and Debye–Waller factors derived from the DFT calculations were used to compute EXAFS spectra without using fitting parameters. By using this methodology, it was possible to show that the branched alkyl chain amides form partly outer-sphere complexes with protonated ligands hydrogen bonded to nitrate ions