Effect of anion coordination upon radiationless transitions of the uranyl ion

At 80 K, where the deactivation processes in uranyl luminescence in solutions are temperature independent, the radiationless transition rate depends upon the presence of H₂O in the first coordination sphere of the uranyl ion, UO₂²⁺. It is found that such radiationless transitions are due to a photophysical intramolecular process.     

Osteopontin: A Uranium Phosphorylated Binding‐Site Characterization

Herein, we describe the structural investigation of one possible uranyl binding site inside a nonstructured protein. This approach couples spectroscopy, thermodynamics, and theoretical calculations (DFT) and studies the interaction of uranyl ions with a phosphopeptide, thus mimicking a possible osteopontin (OPN) hydroxyapatite growth‐inhibition site. Although thermodynamical aspects were investigated by using time‐resolved laser fluorescence spectroscopy (TRLFS) and isothermal titration calorimetry (ITC), structural characterization was performed by extended X‐ray absorption fine structure (EXAFS) at the U L_III‐edge combined with attenuated total reflection Fourier transform infrared (ATR‐FTIR) spectroscopy. From the vibrational and fluorescence spectra, several structural models of a UO₂²⁺/peptide complex were developed and subsequently refined by using theoretical calculations to fit the experimental EXAFS obtained. The structural effect of the pH value was also considered under acidic to moderately acidic conditions (pH 1.5–5.5). Most importantly, the uranyl/peptide coordination environment was similar to that of the native protein.     

Raman,resonance Raman and infrared spectra of potassium uranyl croconate

The Raman, resonance Raman and IR spectra of potassium uranyl croconate, UO₂(H₂O)K₂(C₅O₅)₂ were obtained and interpreted. Several croconate modes are split indicating a substantial decrease in the oxocarbon symmetry, as is to be expected from a recent crystallographic investigation, revealing the coordination of the oxocarbon to be two non-equivalent UO²⁺₂ moieties in a monodentate fashion. In terms of vibrational frequency shifts it can be concluded that the UO²⁺₂ moiety behaves as an isolated oscillator.The resonance Raman results suggest that the strong band centered around 450 nm in the UV—vis spectrum should be assigned to a charge transfer transition from the oxocarbon to the uranyl ion. In fact, as resonance is approached, both uranyl and croconate modes are enhanced. It can also be inferred that the chromophore is rather delocalized into the oxocarbon ring, rather than localized in the carbonyl groups as previously observed for other croconate complexes.     

Cooperative Capture of Uranyl Ions by a Carbonyl‐Bearing Hierarchical‐Porous Cu–Organic Framework

To efficiently capture the toxic uranyl ions (UO₂²⁺), a new hierarchical micro‐macroporous metal–organic framework was prepared under template‐free conditions, featuring interconnected multi‐nanocages bearing carbonyl groups derived from a semi‐rigid ligand. The material exhibits an unusually high UO₂²⁺ sorption capacity of 562 mg g^?1, which occurs in an intriguing two‐steps process, on the macropore‐based crystal surface and in the inner nanocages. Notably, the latter is attributed to the cooperative interplay of the shrinkage of the host porous framework induced by uranyl accommodation and the free carbonyl coordination sites, as shown by both single‐crystal X‐ray diffraction and a red‐shift of the infrared [O=U^VI=O]²⁺ antisymmetric vibration band.     

On the coordination symmetry of the hydrated uranyl ion

The literature indicates a four-fold or six-fold coordination symmetry for UO²⁺₂ in aqueous solution. However, the uranyl ion in crystalline UO₂(ClO₄)₂·7H₂O has been found by X-ray diffraction to be coordinated by five water molecules. From the MCD of aqueous UO₂(ClO₄)₂·nH₂O we have found evidence for five-fold coordination. A tentative assignment for the excited states in the visible spectrum is also proposed.     

Selective and Sensitive Determination of Uranyl Ions in Complex Matrices by Ion Imprinted Polymers‐Based Electrochemical Sensor

We report on the design of a UO₂²⁺‐selective electrode based on the use of UO₂²⁺ imprinted polymer nanoparticles (IP‐NPs), and its application for the differential pulse adsorptive cathodic stripping voltammetry determination of uranyl ions. A carbon paste electrode was modified with the IP‐NPs, and differential pulse adsorptive cathodic stripping voltammetry was applied as the detection technique after open‐circuit sorption of UO₂²⁺ ions. The modified electrode responses to UO₂²⁺ was linear in the 0.1 µg L^?1 to 10 µg L^?1 and in the 0.01 mg L^?1 to 10 mg L^?1. The method detection limit of the sensor was 0.03 µg L^?1.     

Hydrothermal synthesis,crystal structure and properties of a two‐dimensional uranyl coordination polymer based on a flexible zwitterionic ligand

The interaction between the uranyl cation, (UO₂)²⁺, and organic species is of interest due to the potential applications of the resulting compounds with regard to nuclear waste disposal and nuclear fuel reprocessing. The hydrothermal reaction of various uranyl compounds with flexible zwitterionic 1,1′‐[1,4‐phenylenebis(methylene)]bis(pyridin‐1‐ium‐4‐carboxylate) dihydrochloride (Bpmb·2HCl) in deionized water containing drops of H₂SO₄ resulted in the formation of a novel two‐dimensional uranyl coordination polymer, namely poly[tetraoxido{μ₂‐1,1′‐[1,4‐phenylenebis(methylene)]bis(pyridin‐1‐ium‐4‐carboxylate)}di‐μ₃‐sulfato‐diuranium(VI)], [(UO₂)₂(SO₄)₂(C₂₀H₁₆N₂O₄)]_n, (1). Single‐crystal X‐ray diffraction reveals that this coordination polymer exhibits a layered arrangement and the (UO₂)²⁺ centre is coordinated by five equatorial O atoms. The structure was further characterized by FT–IR spectroscopy, powder X‐ray diffraction (PXRD) and thermogravimetric analysis (TGA). The polymer shows high thermal stability up to 696 K. Furthermore, the photoluminescence properties of (1) has also been studied, showing it to exhibit a typical uranyl fluorescence.     

Complexation between uranyl(VI) and CMPO in a hydroxyl-functionalized ionic liquid: An extraction,spectrophotography, and calorimetry study

The extraction complexes of uranyl(VI) in HNO₃ to a hydroxyl-functionalized ionic liquid (IL) phase, HOEtmimNTf₂ bearing CMPO, were investigated. Three possibly successive extraction complexes, UO₂L²⁺ (L = CMPO), UO₂L₂²⁺ and UO₂L₃²⁺, were detected based on variable U/L ratios. Uranyl(VI) prefers to be extracted as complex UO₂L₃²⁺, combining with the ions from HOEtmimNTf₂ to construct a solid material through self-assembly. The thermodynamics of complexes, UO₂L_j²⁺ (j = 1-3), were studied by spectrophotometry and microcalorimetry. All the formation reactions are principally driven by entropy, although a small part of the driving force of complexes UO₂L₂²⁺ and UO₂L₃²⁺ comes from enthalpy. Based on the thermodynamic properties for complex UO₂L₃²⁺, we provide a possible coordination mode in HOEtmimNTf₂: the first CMPO molecule coordinates with UO₂²⁺ in a bidentate fashion while the others do in a monodentate fashion. The results offer a thermodynamic insight into the formation behaviors of the uranyl(VI)/CMPO complexes involving the special IL HOEtmimNTf₂, which is of significance to advance the novel IL extraction strategy.     

ADSORPTION OF UO2 2+ BY POLYETHYLENE HOLLOW FIBER MEMBRANE WITH AMIDOXIME GROUP

The polyethylene (PE) membrane was prepared by the radiation-induced grafting of acrylonitrile (AN) onto PE hollow fiber and by the subsequent amidoximation of cyano groups in poly-AN graft chains. The adsorption characteristics of the chelating hollow fiber membrane was examined as the solution of UO₂ ²⁺ permeated across the chelating hollow fiber membrane. The inner and outer diameter increased with an increasing grafting yield, whereas, the pure water flux and pore diameter decreased with an increasing grafting yield. The adsorption of UO₂ ²⁺ by the chelating hollow fiber membranes increased with an increasing amidoxime group. The adsorbed amount of UO₂ ²⁺ in the uranyl acetate solution was higher than that in the uranyl nitrate solution. The adsorbed amount of UO₂ ²⁺ is higher than that of Cu²⁺ when the solution of UO₂ ²⁺ and Cu²⁺ permeated across the chelating membrane, respectively. The adsorption characteristics of UO₂ ²⁺ by the amidoxime group-chelating fiber membrane in the presence of Na¹⁺ and Ca²⁺ showed a high selectivity for UO₂ ²⁺ even though there was a high concen-tration of Na¹⁺ and Ca²⁺ in the inlet solution.     

Identification of uranyl binding proteins from human kidney-2 cell extracts by immobilized uranyl affinity chromatography and mass spectrometry

To improve our knowledge on protein targets of uranyl ion (UO₂²⁺), we set up a proteomic strategy based on immobilized metal-affinity chromatography (IMAC). The successful enrichment of UO₂²⁺-interacting proteins from human kidney-2 (HK-2) soluble cell extracts was obtained using an ion-exchange chromatography followed by a dedicated IMAC process previously described and designed for the uranyl ion. By mass spectrometry analysis we identified 64 proteins displaying varied functions. The use of a computational screening algorithm along with the particular ligand-based properties of the UO₂²⁺ ion allowed the analysis and categorization of the protein collection. This profitable approach demonstrated that most of these proteins fulfill criteria which could rationalize their binding to the UO₂²⁺-loaded phase. The obtained results enable us to focus on some targets for more in-depth studies and open new insights on its toxicity mechanisms at molecular level.     

Uranyl oxamate hydrates: hydrothermal synthesis,crystal structure,photophysical properties,and selective crystallization

Presented here are two isostructural uranyl coordination polymers [UO₂(EDO)(H₂O)]·H₂O (1) and [UO₂(BDO)(H₂O)]·2H₂O (2) (EDO^2-=ethylene-1,2-dioxamate; BDO^2-=butylene-1,2-dioxamate) with identical stepwise zigzag chain structure and distinct interchain hydrogen bonding interaction, prepared from hydrothermal reaction of DEEDO or DEBDO (DEEDO=diethyl ethylene-1,2-dioxamate; DEBDO=diethyl butylene-1,2-dioxamate) with uranyl ions. The monomeric uranyl-based fluorescence emissions of compounds 1 and 2 are red-shifted by about 6 and 5 nm respectively, compared to that of uranyl nitrate hexahydrate. Compound 1 has stronger emission than compound 2, but both their emissions exhibit triple-exponential decay. The photophysics of uranyl oxalate trihydrate was also investigated for comparison. The selective crystallization of compound 1 in alkaline solution was applied to the sequestration of uranyl ions, showing a kinetic preference.     

Electrochemical uranyl biosensor with DNA oligonucleotides as receptor layer

The feasibility of using gold electrodes modified with short-chain ssDNA oligonucleotides for determination of uranyl cation is examined. Interaction between UO₂²⁺ and proposed recognition layer was studied by means of voltammetric and quartz crystal microbalance measurements. It was postulated that ssDNA recognition layer functions via strong binding of UO₂²⁺ to phosphate DNA backbone. The methylene blue was used as a redox marker for analytical signal generation. Biosensor response was based on the difference in electrochemical signal before and after subjecting it to sample containing uranyl ion. The lower detection limit of 30 nmol L⁻¹ for UO₂²⁺ was observed for a sample incubation time of 60 min. Proposed ssDNA-modified electrodes demonstrated good selectivity towards UO₂²⁺ against common metal cations, with only Pb²⁺ and Ca²⁺ showing considerable interfering effect.     

Hydroxy Naphthol Blue as a Spectrophotometric and Fluorometric Reagent for the Uranyl Ion

Abstract

The utility of hydroxy naphthol blue (HNB) as a spectrophotometric and fluorometric reagent for the uranyl ion has been investigated. In phthalate buffer (at a pH of 4.0), UO₂ ²⁺ forms a brown complex of low absorptivity with the red form of HNB. By following the decrease in HNB absorbance at 530 nm (which has ε = 4.1 × 10³) uranyl ion can be determined to levels as low as 1.1 × 10^?6 M (0.30 μg/ml). HNB also emits at 460 nm when excited at 365 nm at these pH values, while the UO₂ ²⁺ complex exhibits greatly reduced emission. Examination of the quenching of HNB emission by UO₂ ²⁺ allows the determination of uranyl ion to levels as low as 3.2 × 10^?6 M (0.86 μg/ml). A 1:1 type complex was formed between UO₂ ²⁺ and HNB, and a formation constant of 9.77 × 10³ (log K₁ = 3.99) was measured for the complex.     

Study of solvent extraction of <Superscript>114m</Superscript>In(III) using quinaldic acid into isoamyl alcohol

A complementary study of hydroxyl radical formation in the depleted uranium (DU)-hydrogen peroxide (H₂O₂) system and the effect of biosubstances on the system were examined using the spin-trapping method. Hydroxyl radical was formed in the uranyl ion (UO₂ ²⁺), 5,5-dimethyl-1-pyrroline-N-oxide (DMPO), and hydrogen peroxide (H₂O₂) mixture solution. The pseudo first order rate constants of DMPO-OH formation were estimated to be 0.033 s⁻¹ for UO₂ ²⁺-H₂O₂-DMPO solution and 0.153 s⁻¹ for UO₂₊-H₂O₂-DMPO solution. The obtained results indicated that the hydroxyl radical formation in the UO₂ ²⁺-H₂O₂ solution could be described as a stepwise reaction process including the reduction of UO₂ ²⁺ to UO₂ ²⁺ by H₂O₂ and the Fenton-type reaction of UO₂ ⁺ with H₂O₂. Biosubstances, such as proteins, amino acids and saccharides, decreased the DMPO-OH formation, which was caused by the direct hydroxyl radical scavenging and the suppression of hydroxyl radical formation by coupling with uranyl ion.     

Preparation and characterization of uranyl complexes with phosphonate ligands

The preparation, spectroscopic characterization and thermal stability of neutral complexes of uranyl ion, UO₂ ²⁺, with phosphonate ligands, such as diphenylphosphonic acid (DPhP), diphenyl phosphate (DPhPO) and phenylphosphonic acid (PhP) are described. The complexes were prepared by a reaction of hydrated uranyl nitrate with appropriate ligands in methanolic solution. The ligands studied and their uranyl complexes were characterized using thermogravimetric and elemental analyses, ESI-MS, IR and UV–Vis absorption and luminescence spectroscopy as well as luminescence lifetime measurements. Compositions of the products obtained dependent on the ligands used: DPhP and DPhPO form UO₂L₂ type of complexes, whereas PhP forms UO₂L complex. Based on TG and DTG curves a thermal stability of the complexes was determined. The complexes UO₂PhP·2H₂O and UO₂(DPhPO)₂ undergo one-step decomposition, while UO₂PhP · 2H₂O is decomposed in a two-step process. The thermal stability of anhydrous uranyl complexes increases in the series: DPhPO < PhP < DPhP. Obtained IR spectra indicate bonding of P–OH groups with uranyl ion. The main fluorescence emission bands and the lifetimes of these complexes were determined. The complex of DPhP shows a green uranyl luminescence, while the uranyl emission of the UO₂PhP and UO₂(DPhPO)₂ complexes is considerably weaker.     

Uranyl-catalyzed chemiluminescent reaction of U4+ oxidation by dioxygen in aqueous HClO4 solution

Chemiluminescence (CL) accompanying the reaction of U⁴⁺ with O₂ in 0.0004–0.1M HClO₄ was studied. It was found that the electron-excited uranyl ion (UO₂ ²⁺)^* is the CL emitter. The fact that the reaction rate and the CL yield increase as the solution acidity decreases was explained by different reactivities of the U _aq ⁴⁺ aquation and the products of its stepwise hydrolysis, UOH³⁺ and U(OH)₂ ²⁺, toward O₂. Based on the results of analysis of the chain-radical mechanism of the reaction between U⁴⁺ and O₂, it was concluded that transfer of an electron from the UO₂ ⁺ ion to the oxidizing agent (a ·OH radical) is the most plausible elementary step of the reaction of (UO₂ ²⁺)^* formation. It was found that the reaction rate, as well as the CL yield, increase substantially in the presence of uranyl ion. Catalytic action of UO₂ ²⁺ was explained by the formation of a UO₂ ²⁺·UO₂ ⁺ complex, which reduces the rate of the UO₂ ⁺ disproportionation reaction (UO₂ ⁺ is an intermediate of the reaction and is involved in chain propagation), and by regeneration of the active center, UO₂ ⁺, in the reaction of UO₂ ²⁺ with U⁴⁺. Published inIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1522–1528, September, 2000.     

New Reactivity of the Uranyl(VI) Ion

The chemistry of the uranyl ion ([UO₂]²⁺) has evolved remarkably over the past few years, with unexpected reactivity observed that challenge our understanding of this ion, and of actinides in general. This review highlights some recent advances in the field, focussing on the organometallic chemistry of the uranyl moiety, which is not well developed in comparison to lower oxidation states of uranium. The use of uranyl as a catalyst is highlighted and the newly developed supramolecular chemistry is described. The uranyl oxygen atoms have been considered as inert, but recent work has shown that is not necessarily the case and is discussed herein. Finally, reduction to the [UO₂]⁺ ion will be discussed.     

Raman spectra of zeolites exchanged with uranyl(VI) cations—II. Zeolite X

The formation of hydrolysed uranyl(VI) species in UO₂X zeolites prepared by various methods has been investigated by Raman spectroscopy. Ion-exchange in aqueous (pH>3) and non-aqueous (anhydrous methanol and uranyl nitrate melts) media resulted in the formation of hydroxy-bridged complexes such as [(UO₂)₃(OH)₄]²⁺, [(UO₂)₃(OH)₅]⁺, and [(UO₂)₄(OH)₇]⁺. Ion-exchange in more acidic media (initial pH < 3) was accompanied by the formation of a disordered phase incorporating UO₃, following extensive collapse of the zeolite framework structure. Cation speciation in the UO₂X system is compared to that in UO₂Y zeolites.     

Complex formation of peroxouranyl (and uranyl) with polyaminocarboxylate ligands

Complexation of the uranyl ion (UO₂²⁺) and of the peroxouranyl species (UO₄) by some polyaminocarboxylate ligands has been investigated in solution (3M NaClO₄) at 25°C. The logarithms of the cumulative formation constants of the UO₂²⁺ chelates formed are: UO₂edta^2? (15.65), UO₂Hedta^? (18.59), (UO₂)₂edta (20.24); UO₂edda (16.02); UO₂Hnta (12.19); UO₂ida (9.63), UO₂H₂(ida)₂ (23.80). The equilibrium UO₂²⁺ + H₂O₂ ? UO₄ + 2H⁺ has a stability log K = ?3.99. The peroxocomplexes formed are UO₄Hedda^? (14.81, expressed from UO₂²⁺ and H₂O₂) and UO₄Hnta^2? (8.50). Solution structures of the chelates are proposed.     

A uranyl sulfate cluster in Na10[(UO2)(SO4)4](SO4)2·3H2O

Decasodium uranyl hexa­sulfate trihydrate, Na₁₀[(UO₂)(SO₄)₄](SO₄)₂·3H₂O, contains an unusual uranyl sulfate cluster with the composition [(UO₂)(SO₄)₄]^6?. The cluster is composed of a uranyl pentagonal bipyramid and four sulfate tetrahedra. Three sulfate tetrahedra are linked to the uranyl pentagonal bipyramid by the sharing of vertices, and the other shares an equatorial edge of the uranyl pentagonal bipyramid. The uranyl sulfate clusters occur in layers parallel to (010). The structure also contains two isolated symmetrically distinct sulfate tetrahedra, which also occur in layers parallel to (010). The uranyl sulfate clusters and isolated sulfate tetrahedra are linked through bonds to Na⁺ cations, and by hydrogen bonding involving the water molecules.