Interaction between photoexcited aqua-uranyl (VI) and perchlorate

In sufficient concentrations, perchlorate is found to produce a decrease in the decay and an exaltation of the luminescence of aqueous acidic solutions of uranyl. This is shown to be due to the excited-state interaction between excited uranyl and perchlorate, giving a complex in which the oxidative activity of the UO²⁺₂ moiety towards water is diminished.     

Photoluminescence of Uranium(VI): Quenching Mechanism and Role of Uranium(V)

The photoluminescence of uranium(VI) is observed typically in the wavelength range 400–650 nm with the lifetime of several hundreds μs and is known to be quenched in the presence of various halide ions (case A) or alcohols (case B). Here, we show by density functional theory (DFT) calculations that the quenching involves an intermediate triplet excited state that exhibits uranium(V) character. The DFT results are consistent with previous experimental findings suggesting the presence of photoexcited uranium(V) radical pair during the quenching process. In the ground state of uranyl(VI) halides, the ligand contributions to the highest occupied molecular orbitals increase with the atomic number (Z) of halide ion allowing larger ligand‐to‐metal charge transfer (LMCT) between uranium and the halide ion. Consequently, a larger quenching effect is expected as Z increases. The quenching mechanism is essentially the same in cases A and B, and is driven by an electron transfer from the quencher to the UO₂²⁺ entity. The relative energetic stabilities of the triplet excited state define the “fate” of uranium, so that in case A uranium(V) is oxidized back to uranium(VI), while in case B uranium remains as pentavalent.     

HNO3溶液中Np(V)与U(VI)配位行为的研究I

Purex流程中,同时定量测定浓度约为10-4～10-5mol.L-1且共存于HNO3溶液中的Np(IV)、Np(V)和Np(VI)各种价态,是乏燃料后处理中的重要课题.传统的萃取-色谱法、离子交换法、载带法以及共沉淀法虽然对其价态测定有一定效果,但操作冗长,稍有不慎,易出差错.因此,多年来光度法很受重视.然而,U(VI)的存在对利用光度法测定Np(IV、V、VI)价态有很大影响,常常会使Np(V)的测定结果偏低.研究发现了在3 mol.L-1HNO3溶液中[U(VI)]/[Np(V)]>104时,Np(V)与U(VI)之间形成的1∶1型配合物是其测定结果偏低的主要原因,基于此求得了配位平衡常数.     

Determination of the Uranium(VI) and ‐(IV) Species in Uranium Ores

The determination of the two species of uranium(VI and IV) present in 6 uranium ores was studied in relation to the chemical and mineralogical composition, humidity, and pH of the samples taken over from the mine. X‐ray diffraction studies, performed on the uranium ores in powder form allowed to establish their mineralogical composition. Thechemical analysis pointed out the presence, besides the two uranium species, of some microelements able to influence the U^VI/U^IV ratio in minerals and to leach out U^VI as uranyl ions from the corresponding minerals.     

Polarography of Uranium (VI)-Arsonoacetate Complex

The complexation of uranium (VI) with arsonacetic acid has been studied polarographically. A two-step polarographic wave was obtained at lower pH value. The dissociation reaction of the complex was deduced from the kinetic current of the prewave. The asymmetry to half-wave of polarograms was interpreted on the basis of polynuclear complex. The limits of reversibility, chelation, polymerization and precipitation of the complex, which are functions of pH and ligand concentration, were shown.     

Extraction of Uranium(VI) by N-Octanoylpiperidine in Toluene

The extraction of uranium(VI) from nitric acid by N-octanoylpiperidine (OPPD) in toluene has been investigated at varying concentrations of nitric acid, extractant, salting-out agent LiNO₃ and at different temperatures. The mechanism of extraction is discussed in the light of the results obtained. The extracted species have also been investigated using FT-IR spectrometry. The related thermodynamic functions were calculated.     

The Extraction of Uranium(VI) with n-Octyldecylsulfoxides (ODSO)-Toluene

The liquid-liquid extraction of uranium(VI) from aqueous nitric acid with n-octyldecylsulfoxide (ODSO) in toluene has been studied over a wide range of conditions. The extracted species appears to be UO₂(NO₃)₂·2ODSO. The extraction increased with increasing nitric acid concentration up to 2.0 mol/l and then decreased. Extraction also increased with increasing extractant concentration. The influence of temperature, salting-out agent concentration and complex anion concentration on the extraction equilibrium were also investigated, and the enthalpy of the extraction reaction was calculated.     

Interaction of uranium(VI) with lipopolysaccharide

Bacteria have a great influence on the migration behaviour of heavy metals in the environment. Lipopolysaccharides form the main part of the outer membrane of Gram-negative bacteria. We investigated the interaction of the uranyl cation (UO2(2+)) with lipopolysaccharide (LPS) from Pseudomonas aeruginosa by using potentiometric titration and time-resolved laser-induced fluorescence spectroscopy (TRLFS) over a wide pH and concentration range. Generally, LPS consists of a high density of different functionalities for metal binding such as carboxyl, phosphoryl, amino and hydroxyl groups. The dissociation constants and corresponding site densities of these functional groups were determined using potentiometric titration. The combination of both methods, potentiometry and TRLFS, show that at an excess of LPS uranyl phosphoryl coordination dominates, whereas at a slight deficit on LPS compared to uranyl, carboxyl groups also become important for uranyl coordination. The stability constants of one uranyl carboxyl complex and three different uranyl phosphoryl complexes and the luminescence properties of the phosphoryl complexes are reported.     

Bacterial formation of extracellular U(VI) nanowires

Shewanella oneidensis MR-1 rapidly accumulates long, extracellular, U(VI) nanowires composed of polycrystalline chains of discrete meta-schoepite (UO(3)·2H(2)O) nanocrystallites. The production of uranium(VI) nanowires could provide a novel strategy for remediation of uranium contamination in sediments and aquifers, as well as the recovery of uranium in manufacturing processes.     

Separation of Uranium(VI) by Extraction with Dibutylditiophosphoric Acid

The extraction of uranium(VI) from aqueous solutions with dibutylditiophosphoric acid in organic solvents was studied. The influence of different factors as pH of the aqueous phase, extractant concentration and nature of solvent was investigated in order to find the optimum conditions for separation of metal from aqueous nitrate solutions. The effect of neutral donor extractants was also searched and the efficiency of the extraction was calculated.     

Complexation of Uranium(VI) by Gluconate in Alkaline Solutions

Gluconate (C₆H₁₁O₇) is a polyhydroxycarboxylic acid that can be assumed as a representative model compound for a wide variety of additives in cement formulations. It can play an important role in the cementitious environments characteristic of radioactive waste disposal sites, as actinides (such as U(VI)) may form stable complexes with gluconate. As a consequence, the presence of the organic ligand can lead to an enhancement of actinide mobility. The results presented in this work show that gluconate increases significantly the uranium solubility at pH_c = 12; the study of U(VI) speciation in alkaline solutions is complex, mainly due to formation of sparingly soluble uranates of varying compositions (e.g. sodium and potassium uranates). UV–Vis measurements in the alkaline pH range have been used to determine the stability constant for the formation of a 1:1 U(VI):gluconate complex. The results obtained with spectroscopic techniques allow explaining the results from solubility experiments, from both over- and under-saturation conditions.     

Effect of Diluents on the Extraction of Uranium(VI) Using N-Octanoylpiperidine

The extraction performance of uranium(VI) from nitric acid with N-octanoylpiperidine (OPPD) in series of diluents has been investigated. The dependence of extraction distribution on the concentrations of aqueous nitric acid and OPPD and also the temperature has been studied. The experimental results showed that the decreasing order of extraction ability of OPPD is as follows: benzene, dimethyl benzene (DMB), toluene, 1,2-dichloroethene, n-octane, carbon tetrachloride, cyclohexane, chloroform. It cannot be interpreted only on the basis of polarity of the diluents. The interaction between extractant or extracted species and diluent is discussed.     

Bacillus cereus Toxin Repertoire: Diversity of (Iso)cereulide(s)

The emetic Bacillus cereus toxin cereulide (1) poses a significant safety risk in the food industry, causing emesis and nausea after consumption of contaminated foods. Analogously to cereulide, the structures of various isocereulides, namely, isocereulides A–G, have been recently reported and could also be identified in B. cereus-contaminated food samples. The HPLC fractionation of B. cereus extracts allows us to isolate additional isocereulides. By applying MSⁿ sequencing, post-hydrolytic dipeptide, amino acid and α-hydroxy acid analyses using UPLC-ESI-TOF-MS to purify the analytes, seven new isocereulides H–N (2–8) could be elucidated in their chemical structures. The structure elucidation was supported by one-dimensional and two-dimensional NMR spectra of the isocereulides H (2), K (5), L and N (6 + 8) and M (7). The toxicity of 2–8 was investigated in a HEp-2 cell assay to determine their respective 50% effective concentration (EC₅₀). Thus, 2–8 exhibited EC₅₀ values ranging from a 0.4- to 1.4-fold value compared to cereulide (1). Missing structure-activity correlations indicate the necessity to determine the toxic potential of all naturally present isocereulides as single compounds to be able to perform a thorough toxicity evaluation of B. cereus-contaminated foods in the future.     

Complex Formation Between Uranium(VI) Ion and some α-Aminoacids

The formation constants for the complexation of the VO₂²⁺ by a number of C-substituted glycines have been determined by potentiometric titratio     

Extraction Mechanism of Uranium(VI) with Di(1-Methylheptyl)Phosphoric Acid

The extraction of U(VI) from nitric acid solutions with di-(1-methylheptyl) phosphoric acid has been investigated. The dependence on nitric acid concentration, DMHPA concentration and temperature has been considered and the infra-red spectra of extracted species and extractant were recorded. The mechanism of extraction is discussed in the light of the results obtained.     

Back-Extraction of Uranium(VI) from Organophosphoric Acid with Hydrazine Carbonate

The back-extraction of uranium(VI) from di(2-ethylhexyl)phosphoric acid (HDEHP) and diisodecylphosphoric acid (DIDPA) was studied by using hydrazine carbonate as back-extractant. U(VI) was back-extracted from n-dodecane solutions of 0.5M HDEHP - 0.2M TBP and 0.5M DIDPA - 0.1M TBP by hydrazine carbonate. The distribution ratios were decreased with an increase of hydrazine carbonate concentration. The back-extraction equilibria were expressed by slope analysis in consideration of neutralization between the extractant (DIDPA, HDEHP) and hydrazine carbonate, which occurred quantitatively during the back-extraction.     

Uranium(VI) extraction with benzyloctadecyldimethylammonium chloride (BODMAC) from chloride and sulfate solutions

Summary The solvent extraction of uranium(VI) from concentrated chloride solutions by quaternary salt benzyloctadimethylammonium chloride (BODMAC, R₄NCl) in three diluents was studied. The composition of the extracted species was R₄N^. UO₂Cl₃and (R₄N)₂^. UO₂Cl₄in the three diluents investigated. The dependence of the distribution ratios on the concentration of hydrochloric acid, extractant, salting-out agents and temperature was investigated. The extraction efficiency of BODMAC strongly depends on the nature of the diluent. The presence of Mg(SO₄)₂basically alters the sequence of diluent extraction efficiency.     

Two‐Electron Reductive Carbonylation of Terminal Uranium(V) and Uranium(VI) Nitrides to Cyanate by Carbon Monoxide

Two‐electron reductive carbonylation of the uranium(VI) nitride [U(Tren^TIPS)(N)] ( 2 , Tren^TIPS=N(CH₂CH₂NSiiPr₃)₃) with CO gave the uranium(IV) cyanate [U(Tren^TIPS)(NCO)] ( 3 ). KC₈ reduction of 3 resulted in cyanate dissociation to give [U(Tren^TIPS)] ( 4 ) and KNCO, or cyanate retention in [U(Tren^TIPS)(NCO)][K(B15C5)₂] ( 5 , B15C5=benzo‐15‐crown‐5 ether) with B15C5. Complexes 5 and 4 and KNCO were also prepared from CO and the uranium(V) nitride [{U(Tren^TIPS)(N)K}₂] ( 6 ), with or without B15C5, respectively. Complex 5 can be prepared directly from CO and [U(Tren^TIPS)(N)][K(B15C5)₂] ( 7 ). Notably, 7 reacts with CO much faster than 2 . This unprecedented f‐block reactivity was modeled theoretically, revealing nucleophilic attack of the π* orbital of CO by the nitride with activation energy barriers of 24.7 and 11.3 kcal mol^?1 for uranium(VI) and uranium(V), respectively. A remarkably simple two‐step, two‐electron cycle for the conversion of azide to nitride to cyanate using 4 , NaN₃ and CO is presented.