A simple fluorescent sensor for highly sensitive detection of UO22+

Extensive application of nuclear energy has caused widespread environmental uranium contamination. New detection approaches without complicated sample pretreatment and precision instruments are in demand for on-site and in-time determination of uranyl ions in environmental monitoring, especially in an emergency situation. In this work, a simple and effective fluorescent sensor (Z)-N'-hydroxy-4-(1,2,2-triphenylvinyl)benzimidamide (TPE-A) with aggregation-induced emission (AIE) character was established and studied. It could realize to detect UO₂²⁺ via quenching the fluorescence of its aggregation-induced emission, with good selectivity and sensitivity. Such strategy shows a wide linear range from 5.0 × 10^?8 mol/L to 4.5 × 10^?7 mol/L (R² = 0.9988) with exceptional sensitivity reaching 4.7 × 10^?9 mol/L, which is far below the limit for uranium in drinking water (30 μg/L, ca. 1.1 × 10^?7 mol/L) stipulated by the WHO. A response time less than four minutes make it rapid for uranyl ion measurement. It was applied for detection of uranyl ion in spiked river water samples with recoveries in the range of 98.7%-104.0%, comparable to those obtained by ICP-MS. With the advantages of portable apparatus, rapid detection process and high sensitivity, TPE-A can serve as a promising fluorescent sensor for the detection of UO₂²⁺ in environmental water samples.     

Photophysics and photochemistry of uranyl ions in aqueous solutions: Refining of quantitative characteristics

The photochemistry and photophysics of aqueous solutions of uranyl nitrate have been investigated by nanosecond laser photolysis with excitation at 266 and 355 nm and by time-resolved fluorescence spectroscopy. The quantum yield has been determined for (UO₂²⁺)* formation under excitation with λ = 266 and 355 nm light (φ = 0.35). The quantum yield of uranyl luminescence under the same conditions is 1 × 10^–2 and 1.2 × 10^–3, respectively, while the quantum yield of luminescence in the solid state is unity, irrespective of the excitation wavelength. The decay of (UO₂²⁺)* in the presence of ethanol is biexponential. The rate constants of this process at pH 3.4 are k₁ = (2.7 ± 0.2) × 10⁷ L mol^–1 s^–1 and k₂ = (5.4 ± 0.2) × 10⁶ L mol^–1 s^–1. This biexponential behavior is explained by the existence of different complex uranyl ion species in the solution. The addition of colloidal TiO₂ to the solution exerts no effect on the quantum yield of (UO₂²⁺)* formation or on the rate of the reaction between (UO₂²⁺)* and ethanol. The results of this study have been compared with data available from the literature.     

Polarographic Behaviour and Determination of Stability Constants of Uranyl-Ascorbate Complex

The complex species of UO₂(HA)(H₂A)⁺ and UO₂(HA)₂ were identified in the ascorbic acid solution of uranyl ion at pH<2.1 and pH>2.1, respectively. Polarographic wave was proved to be the simultaneous reduction of UO₂⁺² and UO₂(HA)(H₂A)⁺ at pH <2.1. However, at pH>2.1, the wave is due to the reduction of U0₂(HA)₂ The stability constants of the two complex species were found to be 5.1×10⁺ and 1.0×10⁵, respectively. The hydrolysis constant of uranyl ion in the solution of ascorbic acid was determined.     

Trace Determination of Uranyl Ion Using a Blue Led as Excitation Source in Phase-Resolved Luminescence Spectroscopy

Abstract

A phase-resolved luminescence system based on the use of a light emitting diode (LED) is applied to the trace determination of uranyl ion (UO₂ ²⁺). The system performance is evaluated, phase resolved spectra of UO₂ ²⁺ are shown as well as its lifetime determination using multifrequency phase resolved measurements. Analytical figures of merit are also presented for this system. A limit of detection (LOD) of 10 μg/L is obtained at the blue LED excitation wavelength of 460 nm and its results compare well with a conventional system. Also, a linear dynamic range of ca. 5 orders of magnitude is observed. In situ quenching correction of the analytical signal was evaluated and was applied to a real sample for uranyl determination.     

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.     

Involvement of ·OH radicals in the mechanism of excitation of the uranyl ion in the chemiluminescent oxidation of U(IV) by atmospheric oxygen in aqueous solutions of perchloric acid

The chemiluminescence (CL) kinetics in U(IV) oxidation by atmospheric oxygen in aqueous HClO₄ has been investigated. The CL quantum yield (η_CL, E/(mol U(IV))) in this reaction is 1.4 × 10^?8. The elementary event generating the CL emitter, which is the electronically excited uranyl ion *(UO ₂ ²⁺ ), is electron transfer from the uranyl ion UO ₂ ⁺ to the oxidizer (^·OH radical). The Ag⁺ ion quenches CL, and the Cu²⁺ ion enhances CL.     

Kinetics of Complexation of Uranium with 2-(5-Bromo-2-Pyridylazo)-5-(Diethylamino) Phenol (Br-PADAP) in a 1:1 Water-Ethanol Medium

2-(5-Bromo-2-pyridylazo)-5-(diethylamino) phenol (Br-PADAP) forms a 1:1 complex with the uranyl ion in the presence of sulphosalicylic acid, which acts as stabilizer for this complex in the triethanol amine/perchloric acid buffer system. A change in the stoichiometry of the complex was seen at pH<5. Kinetic measurements were carried out using stopped-flow spectrophotometer in the presence of an excess concentration of U(VI) in the pH range 6.5 to 8. The dependence of the pseudo-first-order rate constant, k(obs), on the concentrations of U(VI), ligand and hydrogen ion showed that Br-PADAP reacts with UO₂(OH)⁺ to form an intermediate species (equilibrium constant = 1.28×10⁴mol.dm⁻³) that then rearranges (rate constant = 5.6×10⁻²s⁻¹) to form the product species. UO₂(OH)⁺ is present in equilibrium with the unreactive species UO₂(OH)₂, as well as with the unreactive sulfosalicylic acid complex.     

Trace analysis of uranyl ion (UO2) in aqueous solution by fluorescence turn-on detection via aggregation induced emission enhancement effect

A sensitive fluorescence turn-on method for trace amounts of uranyl ion (UO₂²⁺) in solution has been developed in this study, based on aggregation induced emission enhancement (AIEE) characteristics of 4-pethoxycarboxyl salicylaldehyde azine (PCSA) induced by complex interaction between UO₂²⁺ and PCSA. Under optimized conditions, a fluorescence enhancement at 540 nm could be observed, which was linearly related to the concentration of UO₂²⁺ in the range of 1–25 ppb (part per billion). Analytical data showed that a detection limit of 0.2 ppb was achieved with the relative standard deviation (R.S.D.) 1.3% (n = 5). The proposed method was successfully utilized in quantifying UO₂²⁺ in fuel processing wastewaters.     

Formation of excited uranyl in oxidation of tetravalent uranium with oxygen in HClO<Subscript>4</Subscript> aqueous solutions: IV. Enhancement of the chemiluminescent reaction in the presence of Fe<Superscript>2+</Superscript>

Experimental data that support the hypothesis on the determining role of ^•OH radicals in the emergence of luminescence during the oxidation of U(IV) with atmospheric oxygen in aqueous HClO₄ solutions have been obtained using the H₂O₂-FeSO₄ system as a source of OH radicals. It has been found that brighter chemiluminescence (CL) is observed in the presence of 10⁻⁵ mol/l Fe²⁺ in a 5 × 10⁻⁴ mol/l U(IV) solution in 0.1 mol/l HClO₄ compared with the FeSO₄-free solution. The CL yield in the presence of Fe²⁺ (η_CL = 3.9 × 10⁻⁸) is 2.8 times that in the solution without iron (η_CL = 1.4 × 10⁻⁸). These results can be regarded as a further piece of evidence for the idea that the elementary event of the formation of a CL emitter—electronically excited uranyl ion *(UO₂²⁺)—in radical chain U(IV) oxidation reactions is electron transfer from the uranoyl ion (UO₂⁺) to the oxidant, the ^•OH radical. Thus, one of the main prerequisites for light emission during U(IV) oxidation reactions is a high generation efficiency of ^•OH radicals and their easy access to the uranoyl UO₂⁺ ion.     

Analytical application of arsenazo III to the spectrophotometric determination of palladium: Preliminary investigation of the complex formation in the arsenazo III-Pd (II)--H2O system

The reaction of arsenazo III with palladium(II) was investigated. Complex species of types M₂L and ML are formed at pH 2–4; the complex M₂L shows a very sharp maximum at 630 nm while the ML species shows maximum absorption at 620 nm. The molar absorptivities of the complexes are 4.2(±0.1) · 10⁴ and 1.6(±0.2) · 10⁴ respectively. The complex ML conforms to Beer's law at 620 nm in the range 10–250 μg Pd(II)/50 ml. The sensitivity of the reaction of Pd(II) with arsenazo III is about the same as that of a new reagent, palladiazo, but the latter is more selective for Pd(II). Serious interferences might be caused by UO₂²⁺, U⁴⁺, Th⁴⁺, Cu²⁺, Ni²⁺, Co²⁺, Y³⁺ and the rare-earth elements.     

Photobiological effects of metal ions. Photosensitizing action of uranyl acetate on Escherichia coli K-12

Abstract— The Uranyl acetate sensitized killing of Escherichia coli K-12 by a light source approximating sunlight in both intensity and wavelength distribution is demonstrated to occur at a concentration of 5.0 × 10O^-4M uranyl acetate (pH 7.0). The photosensitized killing was evident after 150 min and almost complete within 320 min. Auxotrophic mutants were isolated from cultures incubated in both light and dark for 160 min at this concentration of uranyl acetate. Binding of UO₂²⁺ to E. coli is shown to occur with 82% of the UO₂²⁺ ions in a 5 × 10^-4M solution (pH 7.0) being bound to the cell wall. In the dark as well as at other pH values the extent of binding was much less. Most of the binding occurred in a time less than 30 min. The observation of rapid binding but delayed photosensitization is attributed to the necessity for penetration of uranyl ions into the cells' interior to effect photosensitization.     

Liquid—liquid extraction and determination of uranium(IV) with 2,6-diacetylpyridine bis(benzoylhydrazone)

2,6-Diacetylpyridine bis(benzoylhydrazone) (H₂DPBH) is proposed as a ligand for the extraction of uranium(VI). Complete extraction from aqueous solutions into dichloromethane is achieved with a ligand/metal mole ratio of < for 10^?5?10^?4 M uranyl ion. Potentiometric measurements indicate that the extracted species is UO₂ (DPBH). Uranium can be determined in the extract by spectrophotometric measurements at 420 nm and by differentail pulse polarography (E_p = ?0.67 V) with tetraethylammonium bromide as supporting electrolyte. For both methods, the detection limit is about 2 × 10^?6 M in the extract.     

Separation through liquid–liquid extraction and spectrophotometric determination of U(VI) with the ortho-aminophenol reagent

The extractive properties of the ortho-aminophenol reagent upon U(VI) were investigated in two solvents: 4-chlor-acetophenone and acetylacetone, in a water-organic solvent system. The method here proposed is based on the complexation reaction of the uranyl ion, UO₂ ²⁺, with ortho-aminophenol dissolved in 4-chlor-acetophenone, at room temperature, over a pH interval = 4–6, followed by spectro-photometry of the organic phase, involving measuring of absorbancy at 569.6 nm. The Beer law is valid over the 1–12 μg U(VI)/mL concentration interval, with molar absorbtivity ε_max = 4.3 × 10⁵ mol⁻¹ cm² and Sandell sensitivity = 0.0526 μg cm⁻². The structure, stability and solubility of the formed complex was studied by UV–VIS and IR spectrometry, diffractometry and scanning electron microscopy. The mixed complex formed between the uranyl ion and the ortho-aminophenol dissolved in 4-chlor-acetophenone, [UO₂.(L)₂.(S)₄], is characterized by the following parameters: metal/ligand combination ratio: M/L = 1/2, stability constant β = 2.06 × 10⁶, distribution coefficient D = 66.56 (V_org = V_aq), percentage extraction E% = 98.52, and recovery factor, R%, ranging between 99.48 and 99.85%.     

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.     

U(VI) mono-hydroxo humate complexation

The complexation of the uranyl ion with humic acid is investigated. The humic acid ligand concentration is described as the concentration of reactive humic acid molecules based on the number of humic acid molecules, taking protonation of functional groups into account. Excess amounts of U(VI) are used and the concentration of the humic acid complex is determined by the solubility enhancement over the solid phase. pH is varied between 7.5 to 7.9 in 0.1M NaClO₄ under normal atmosphere and room temperature. The solubility of U(VI) in absence of humic acid is determined over amorphous solid phase between pH 4.45 and 8.62. With humic acid, only a limited range of data can be used for the determination of the complexation constant because of flocculation or sorption of the humic acid upon progressive complexation. Analysis of the complex formation dependency with pH shows that the dominant uranyl species in the concerned pH range are UO₂(OH)⁺ and (UO₂)₃(OH)₅ ⁺. The complexation constant is evaluated for the humate interaction with the to UO₂(OH)⁺ ion. The stability constant is found to be logβ = 6.94±0.3 l/mol. The humate complexation constant of the uranyl mono-hydroxo species thus is significantly higher than that of the nonhydrolyzed uranyl ion (6.2 l/mol). Published data on the Cm³⁺, CmOH²⁺ and Cm(OH)₂ ⁺ humate complexation are reevaluated by the present approach. The higher stability of the hydrolysis complex is also found for Cm(III) humate complexation.     

Xylenol Orange,Zirconium(IV) and Fluoride Color Reaction in Mixed Micelles of N-Hexadecylpyridinium Chloride and Brij 35, and Its Analytical Application1

Abstract

The color reaction between Xylenol orange (XO), zirconium (IV) and fluoride ions in the presence of various surfactants alone or in combination was studied at various pH. The XO -zirconium)IV)-fluoride ion ternary complex in mixed micellar media containing a low concentration of N-hexadecylpyridinium chloride (HPC) as a cationic surfactant and large amounts of (poly{oxyethylene)dodecyl ether (Brij 35) as a nonionic surfactant at weakly acidic media was found to be the most stable, and showed a remarkable bathochromic shift and clear contrast against a reagent blank. The maximum absorbance was at 600 nm in the mixed micellar media at pH 3.5, and the apparent molar absorptivities at 600 nm were 7.0 × 10⁴ 1 mol^?1 cm^?1 for zirconium(IV) and 1.4 × 10⁴ 1 mol^?1 cm^?1 for fluoride ion. The calibration curves covered the ranges of 0.5 ～ 20.0 μg/10 ml zirconium! IV) and 0 ～ 20.0 μg/10 ml fluoride ion with the Sandell sensitivities being 0.0013 μg/cm² for zirconium(IV) and 0.0016 μg/cm² for fluoride ion.     

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.     

Complexation of poly(acrylic acid)s with uranyl ion

The complexation of uranyl ion (UO₂²⁺) in aqueous solution with polymers containing carboxylic acid groups was studied potentiometrically. Overall formation constants of the uranyl complexes with poly(methacrylic acid) and crosslinked poly(acrylic acid) were much larger than those with the corresponding low molecular carboxylic acids. Decrease in the viscosity of the polymer solution on adding uranyl ion indicated that poly(acrylic acid) forms intra-polymer chelates with uranyl ion. The crosslinked poly(acrylic acid) adsorbed uranyl ions at higher efficiency than transition metal ions.     

Gamma-induced radiation polymerization of kaolin composite for sorption of lanthanum,europium and uranium ions from low-grade monazite leachate

Gamma radiation polymerization method was used for the modification of kaolin to produce (poly acrylamide-acrylic acid)-Kaolin (PAM-AA-K). Monazite ore is one of the main resources of uranium and lanthanide elements, therefore, this work focused on sorption of uranium, lanthanum and europium ions from low grade monazite leachate. The removal percent for Eu³⁺, La³⁺ and UO₂ ²⁺ are 94.6, 91.6 and 73.4%, respectively. Monolayer capacity of Eu³⁺, La³⁺ and UO₂ ²⁺ were found to be 54.64, 45.87 and 37.59 mg/g, respectively. The sorption mechanism of lanthanum and europium ions on PAM-AA-K composite mainly takes place as Ln(OH)²⁺, and for uranium as uranyl ion, UO₂ ²⁺.     

Photochemical reduction of uranyl ion in nitric acid medium using a XeCl excimer laser

This paper describes the results of photoreduction of uranyl (UO₂ ²⁺) ion to U⁴⁺ in 0.2M HNO₃ and ethanol using a 308 nm XeCl excimer laser. The effects of different concentrations of ethanol and the addition of sulfamic acid on the quantum yield for U⁴⁺ formation are discussed.