Uranyl

About: Uranyl is a research topic. Over the lifetime, 7410 publications have been published within this topic receiving 153992 citations. The topic is also known as: Uranyl ion & dioxouranium(2+).

A catalytic beacon sensor for uranium with parts-per-trillion sensitivity and millionfold selectivity

Abstract: Here, we report a catalytic beacon sensor for uranyl (UO22+) based on an in vitro-selected UO22+-specific DNAzyme. The sensor consists of a DNA enzyme strand with a 3′ quencher and a DNA substrate with a ribonucleotide adenosine (rA) in the middle and a fluorophore and a quencher at the 5′ and 3′ ends, respectively. The presence of UO22+ causes catalytic cleavage of the DNA substrate strand at the rA position and release of the fluorophore and thus dramatic increase of fluorescence intensity. The sensor has a detection limit of 11 parts per trillion (45 pM), a dynamic range up to 400 nM, and selectivity of >1-million-fold over other metal ions. The most interfering metal ion, Th(IV), interacts with the fluorescein fluorophore, causing slightly enhanced fluorescence intensity, with an apparent dissociation constant of ≈230 μM. This sensor rivals the most sensitive analytical instruments for uranium detection, and its application in detecting uranium in contaminated soil samples is also demonstrated. This work shows that simple, cost-effective, and portable metal sensors can be obtained with similar sensitivity and selectivity as much more expensive and sophisticated analytical instruments. Such a sensor will play an important role in environmental remediation of radionuclides such as uranium.

Determination of the formation constants of ternary complexes of uranyl and carbonate with alkaline earth metals (Mg2+, Ca2+, Sr2+, and Ba2+) using anion exchange method.

Abstract: The formation constants of ternary complexes (MUO2(CO3)32- and M2UO2(CO3)30) of uranyl and carbonate with alkaline earth metals (M2+ denotes Mg2+, Ca2+, Sr2+, and Ba2+) were determined with an anion exchange method by varying the metal concentrations (01−5 mmol/L) at pH 81 and a constant ionic strength (01 mol/L NaNO3) under equilibrium with atmospheric CO2 The results indicate that the complexes of MUO2(CO3)32- and M2UO2(CO3)3 are simultaneously formed for Ca2+ and Ba2+, while Mg2+ and Sr2+ form only the MUO2(CO3)32- complex under our experimental conditions The cumulative stability constants for the MUO2(CO3)32- complex obtained at I = 0 are as follows: logβ113 = 2611 ± 004, 2718 ± 006, 2686 ± 004, and 2668 ± 004 for Mg2+, Ca2+, Sr2+, and Ba2+, respectively For M2UO2(CO3)30, the value of logβ213 at I = 0 was measured to be 3070 ± 005 and 2975 ± 007 for Ca2+ and Ba2+, respectively Based on the formation constants obtained in this study, speciation calculations indicate that at low Ca2

Highly Sensitive and Selective Colorimetric Sensors for Uranyl (UO22+): Development and Comparison of Labeled and Label-Free DNAzyme-Gold Nanoparticle Systems

Abstract: Colorimetric uranium sensors based on uranyl (UO2(2+)) specific DNAzyme and gold nanoparticles (AuNP) have been developed and demonstrated using both labeled and label-free methods. In the labeled method, a uranyl-specific DNAzyme was attached to AuNP, forming purple aggregates. The presence of uranyl induced disassembly of the DNAzyme functionalized AuNP aggregates, resulting in red individual AuNPs. Once assembled, such a "turn-on" sensor is highly stable, works in a single step at room temperature, and has a detection limit of 50 nM after 30 min of reaction time. The label-free method, on the other hand, utilizes the different adsorption properties of single-stranded and double-stranded DNA on AuNPs, which affects the stability of AuNPs in the presence of NaCl. The presence of uranyl resulted in cleavage of substrate by DNAzyme, releasing a single stranded DNA that can be adsorbed on AuNPs and protect them from aggregation. Taking advantage of this phenomenon, a "turn-off" sensor was developed, which is easy to control through reaction quenching and has 1 nM detection limit after 6 min of reaction at room temperature. Both sensors have excellent selectivity over other metal ions and have detection limits below the maximum contamination level of 130 nM for UO2(2+) in drinking water defined by the U.S. Environmental Protection Agency (EPA). This study represents the first direct systematic comparison of these two types of sensor methods using the same DNAzyme and AuNPs, making it possible to reveal advantages, disadvantages, versatility, limitations, and potential applications of each method. The results obtained not only allow practical sensing application for uranyl but also serve as a guide for choosing different methods for designing colorimetric sensors for other targets.

Reduction of Uranium(VI) by Mixed Iron(II)/Iron(III) Hydroxide (Green Rust): Formation of UO2 Nanoparticles

Abstract: Green rusts, which are mixed ferrous/ferric hydroxides, are found in many suboxic environments and are believed to play a central role in the biogeochemistry of Fe. Analysis by U LIII-edge X-ray absorption near edge spectroscopy of aqueous green rust suspensions spiked with uranyl (UVI) showed that UVI was readily reduced to UIV by green rust. The extended X-ray absorption fine structure (EXAFS) data for uranium reduced by green rust indicate the formation of a UO2 phase. A theoretical model based on the crystal structure of UO2 was generated by using FEFF7 and fitted to the data for the UO2 standard and the uranium in the green rust samples. The model fits indicate that the number of nearest-neighbor uranium atoms decreases from 12 for the UO2 structure to 5.4 for the uranium-green rust sample. With an assumed four near-neighbor uranium atoms per uranium atom on the surface of UO2, the best-fit value for the average number of uranium atoms indicates UO2 particles with an average diameter of 1.7 ± 0.6 nm....

A routine technique for double-staining ultrathin sections using uranyl and lead salts.

Abstract: For more than 2 years, a double-staining of sections of OsO 4-fixed and Epon-embedded tissues with uranyl acetate followed by lead hydroxide has been routine technique in this laboratory. It was found to give substantially higher contrast, thus permitting the use of thinner sections. It facilitated focusing and routinely provided clearer pictures of cell fine structure than could be obtained with either stain alone. However, the formation of a fine precipitate frequently marred the sections, and this difficulty could never be satisfactorily controlled. Apparently, it is caused by the uranyl acetate solution which is not stable at the pH and concentration used. Decreasing the concentration and/or the pH of the solution caused an undesirable loss of staining intensity. Therefore, a number of different uranyl salts were tested as a substitute for uranyl acetate in the procedure, and one of them, uranyl magnesium acetate, has been found to give consistently good results.