4 research outputs found
Addressing Ruthenium Speciation in Triâ<i>n</i>âbutyl-phosphate Solvent Extraction Process by Fourier Transform Infrared, Extended Xâray Absorption Fine Structure, and Single Crystal Xâray 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 RuâTBP 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 CaMÎ increases the uranyl-binding affinity by about 2 orders
of magnitude to logâŻKpH7 = 9.55
± 0.11 (KdpH7 = 280 ± 60 pM).
Structural analysis by FTIR, XAS, and molecular dynamics simulations
suggests an optimized coordination of the CaMÎ-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 CaMÎ
binding loop. In addition, CaMÎ 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>âDialkyl Amides from Crystallography, Xâray Absorption Spectra, and Theoretical Calculations
The structures of plutoniumÂ(IV) and
uraniumÂ(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 uraniumÂ(VI) and plutoniumÂ(IV) from highly concentrated
nitric acid solution. EXAFS analysis combined with XRD shows that
the coordination structure of UÂ(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, PuÂ(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 PuÂ(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 DebyeâWaller 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