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Abstract  

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.

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Abstract  

The new bridged diacetato–diamido–diamine–uranyl complex {2[(UO2)(H2N)(H3N)(OOCCH3)]} was prepared and characterized by elemental analysis, IR measurement as well as TG and DTA analysis. The kinetic parameters; activation energy (E a), pre-exponential factor (A) and the order of decomposition (n) were calculated from TG curves using Coats–Redfern and Flynn–Wall–Ozawa methods. The mechanism of decomposition has been established from TG and DTA data. The data obtained agree quite well with the expected structure and show that the complex finally decomposes to form UO3. A general mechanism describing the formation of bridged complex {2[(UO2)(H2N)(H3N)(OOCCH3)]} is proposed.

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Abstract  

8-Hydroxyquinoline (8-HOQ) is known as an important chelating agent for several metal ions. This compound is practically insoluble in water. For this reason, in this study its water soluble sulfate salt has been used for complexing uranyl ions and the stability constants of the complex have been determined. The Irving-Rosotti method computing the Calvin-Bjerrum pH-titration data, was applied. Finally, the stability constants of the complex formed between (8-HOQN-H)2SO4 and uranyl ions were found to be lgK1=8.25 and lgK2=4.15, the overall stability constant being {ie55-1}.

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Abstract  

Uranyl–sulphate complexes are the predominant U(VI) species present in acid solutions resulting either from underground uranium ore leaching or from the remediation of leaching sites. Thus, the study of U(VI) speciation in these solutions is of practical significance. The spectra of UO2(NO3)2 + Na2SO4 solutions of different Φ S = [SO4 2−]/[U(VI)] ratio at pH = 2 were recorded for this purpose. As the presence of uranyl-nitrate complexes should be expected under these experimental conditions, the spectra of UO2(NO3)2 + NaNO3 solutions with different Φ N = [NO3 ]/[U(VI)] ratio at pH = 2 were also measured. The effects of Φ S and Φ N ratios value were most pronounced in wavelength interval 380–500 nm. Therefore, these parts of experimental overall spectra were used for deconvolution into the spectra of individual species by the method proposed. It enabled to calculate stability constants of anticipated species at zero ionic strength. The Specific Ion Interaction Theory (SIT) was used for this purpose. Stability constants of UO2SO4, UO2(SO4)2 2−, UO2NO3 + and UO2(NO3)2 coincided well with published data, but those for UO2(SO4)3 4− and UO2(NO3)3 were significantly lower.

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Abstract  

A rapid method for fluorimetric estimation of uranium in silicate rocks is described. The fluorescence of uranyl complex is induced by laser beam in the ultraviolet region provided by nitrogen laser tube. The emission spectrum is quite intense and relatively persistent. For direct estimation of uranium in geological silicate materials without prior extraction, the interference of certain cations and anions that might be present in silicate rocks on uranium determination was studied. The limit of detection is 0.5 ppb.

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Abstract  

A simple and rapid, laser fluorimetric method for the determination of uranium concentration in raffinate stream of Purex process during reprocessing of spent nuclear fuel has been developed. It works on the principle of detection of fluorescence of uranyl complex formed by using fluorescence enhancing reagent like sodium pyrophosphate. The uranium concentration was determined in the range of 0–40 ppb and detection limit of 0.2 ppb. The optimum time discrimination is obtained when the uranyl ion is complexed with sodium pyrophosphate. Need of preconcentration step or separation of uranium from interfering elements is not an essential step.

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Abstract  

The effects of polyphenols on plasmid DNA strand breaks by depleted uranium were studied using four catechins: (+)-catechin, (−)-epicatechin, (−)-epigallocatechin (EGC), and (−)-epigallocatechin gallate (EGCG); seven tannins: Chinese gallotannin, persimmon tannin (PST), mimosa tannin (MMT), myrobalan tannin, quebracho tannin, gambir tannin, and chestnut tannin; and gallic acid. The plasmid DNA strand breaks by uranyl ion (UO2 2+) with hydrogen peroxide (H2O2) were strongly enhanced by EGC, EGCG, MMT, and PST (condenced tannins). The obtained results showed that the DNA strand breaks are caused by UO2 2+ through the direct interaction between the uranyl complex and the negatively charged DNA phosphate backbone. The additional DNA strand breaks by the addition of polyphenols occurred through an indirect process by the reduction of UO2 2+ to UO2 + and hydroxyl radical formation through a Fenton-type reaction with H2O2.

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Abstract  

The uranium content of airborne particulates collected on cellulose filters was investigated. As a case study, filter samples from the large area of Thessaloniki, Greece, were used. For the uranium determination instrumental neutron activation analysis was used. To obtain equal counting conditions for all samples after irradiation, independent from the initial matrix, uranium was leached from the filter by using a 0.1M NH4HCO3 solution, forming a stable uranyl complex [UO2(CO3)3]. This complex was absorbed in a batch process on a small amount of chelating ion exchanger Srafion NMRR, which was directly irradiated in the reactor of the NCSR Demokritos. The study showed that over the investigated time period in 1997 the mean concentration was found to be 0.047 ng U/m3. In relation to the collected amount of airborne particulates having a mean concentration of 0.52 ng/gU. It can be assumed as a natural uranium level in the environment.

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Abstract  

The study of the chemical behavior of uranium in biological medium is still of great interest. By the use of capillary electrophoresis (CE) and time-resolved laser-induced fluorescence (TRLIF), it is possible to characterize the different complexes of uranium. Hence, CE, using the isoelectric focusing mode (CIEF), allows for the separation of the different complexes as a function of their isoelectric points (pI) and TRLIF as a speciation method leads to the identification at very low level of different uranyl complexes by temporal resolution and spectral deconvolution. Results obtained on various inorganic chemical systems (phosphate, bicarbonate) together with biological systems (citrate, transferrin) will be presented and discussed. The complexation between uranium and human transferrin has been pointed out through CIEF.

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31P-NMR study of the organophosphorous complexes of uranium(VI)

II. The system uranyl nitrate-tri- N -butylphosphate-tri- N -octylphosphine oxide

Journal of Radioanalytical and Nuclear Chemistry
Authors: A. Vasilescu-Saidel, C. Turcanu, and R. Grosescu

Abstract  

The formation of the mixed complex UO2(TOPO)(TBP)(NO3)2 is reported by31P-NMR spectroscopy for the first time. The extraction of the uranyl nitrate by a TBP and TOPO mixture was simulated in a NMR vial and monitored in situ. The equilibrium constant values of the processes in which the mixed complex is involved, i.e.:K R, for the redistribution of TBP and TOPO ligands between their uranyl complexes,K M, for the formation from consititutive molecules,K s, for the substitution of the uranyl coordinated TBP by TOPO are determined. The redistribution constant,K r at 25°C (4.43±0.5) and the changes of the thermodynamic variables H (0.59±0.14 kcal/mol). S (5.04±0.51 cal/mol·degree) have values close to the statistical values, suggesting a random nature of this process. TheK S value (4.5·103) reveals the much greater affinity for uranium(VI) of TOPO relative to TBP.

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