Showing papers on "Uranyl published in 2000"
TL;DR: In this paper, the adsorption of the uranyl ion (UO22+) in contact with amorphous silica (SiO2), γ-alumina (Al2O3), and montmorillonite surfaces was investigated using X-ray absorption fine structure (XAFS) spectroscopy to observe the local structure around the uranium atom.
420 citations
TL;DR: Accumulation of 'tethered' metal phosphate within the LPS is suggested to prevent fouling of the cell surface by the accumulated precipitate and localization of phosphatase exocellularly is consistent with its possible functions in homeostatis and metal resistance.
Abstract: A Citrobacter sp. accumulated uranyl ion (UO2(2+)) via precipitation with phosphate ligand liberated by phosphatase activity. The onset and rate of uranyl phosphate deposition were promoted by NH4(+), forming NH(4)UO(2)PO(4), which has a lower solubility product than NaUO(2)PO(4). This acceleration decoupled the rate-limiting chemical crystallization process from the biochemical phosphate ligand generation. This provided a novel approach to monitor the cell-surface-associated changes using atomic-force microscopy in conjunction with transmission electron microscopy and electron-probe X-ray microanalysis, to visualize deposition of uranyl phosphate at the cell surface. Analysis of extracted surface materials by (31)P NMR spectroscopy showed phosphorus resonances at chemical shifts of 0.3 and 2.0 p.p.m., consistent with monophosphate groups of the lipid A backbone of the lipopolysaccharide (LPS). Addition of fUO2(2+) to the extract gave a yellow precipitate which contained uranyl phosphate, while addition of Cd(2+) gave a chemical shift of both resonances to a single new resonance at 3 p.p.m. Acid-phosphatase-mediated crystal growth exocellularly was suggested by the presence of acid phosphatase, localized by immunogold labelling, on the outer membrane and on material exuded from the cells. Metal deposition is proposed to occur via an initial nucleation with phosphate groups localized within the LPS, shown by other workers to be produced exocellularly in association with phosphatase. The crystals are further consolidated with additional, enzymically generated phosphate in close juxtaposition, giving high loads of LPS-bound uranyl phosphate without loss of activity and distinguishing this from simple biosorption, or periplasmic or cellular metal accumulation mechanisms. Accumulation of 'tethered' metal phosphate within the LPS is suggested to prevent fouling of the cell surface by the accumulated precipitate and localization of phosphatase exocellularly is consistent with its possible functions in homeostatis and metal resistance.
221 citations
TL;DR: In this article, the binding of uranium(VI) by Suwannee River humic and fulvic acids was studied at pH values of 4.0 and 5.0 in 0.10 M NaClO4 using an ion exchange technique.
Abstract: The binding of uranium(VI) by Suwannee River humic and fulvic acids was studied at pH values of 4.0 and 5.0 in 0.10 M NaClO4 using an ion-exchange technique. Few data sets currently exist for metal binding to different molecular weight fractions from the same source. The complexation of U(VI) by citric acid was also studied under the same experimental conditions in order to “calibrate” the experimental and modeling approaches. For the citric acid system, the experimental results were analyzed using Schubert’s ion-exchange method, which indicated the formation of only a 1 :1 uranylcitrate complex. Close agreement was found for the values of log β1,1 (6.69 60.03 at I 5 0.10) determined from nonlinear regression of data collected at pH values of 4.0 and 5.0. This value represents a more direct measurement of the binding constant for the 1 :1 uranyl-citrate complex than do other existing literature values derived from experimental data requiring the simultaneous consideration of 1:1 and 2 :2 species. Both humic and fulvic acids were demonstrated to strongly bind U(VI), with humic acid forming slightly stronger complexes and exhibiting greater pH dependence. Analyses of the data for the humic and fulvic acid systems using the Schubert’s equation previously applied to the citrate system result in an apparent nonintegral number of ligands binding the uranyl ion. Schubert’s method is only appropriate for interpreting mononuclear complexes with integral moles of binding ligands. Thus, a more elaborate binding model was required and the data were interpreted assuming either : (1) a mixture of 1 :1 and 1 :2 uranyl-ligand complexes or (2) a limited number of high affinity sites forming a 1:1 complex. While both of these modeling approaches are shown to provide excellent fits to the data, the second is deemed more appropriate given the large size of humic and fulvic acid molecules as well as previous results obtained with other metal cations, such as Cu(II).
200 citations
TL;DR: In this paper, the authors measured the stoichiometry and thermo- dynamic stabilities of the uranyl-surface complexes of Bacillus subtilis using batch experiments in 0.1 M NaClO4 as a function of pH, time and solid:solute ratio at 25 °C.
Abstract: Uranyl adsorption onto the Gram-positive soil bacterium Bacillus subtilis was measured using batch experiments in 0.1 M NaClO4 as a function of pH, time, and solid:solute ratio at 25 °C. The experimental data were interpreted using a surface complexation approach. The experimental measurements constrain the stoichiometry and thermo- dynamic stabilities of the important uranyl-surface complexes. The U adsorption data require two separate adsorption reactions, with the uranyl ion forming surface complexes with the neutral phosphate functional groups and the deprotonated carboxyl functional groups of the bacterial cell wall: R−POH0 + UO22+ ⇔ R−POH−UO22+ (log K = 11.8 ± 0.2) and R−COO- + UO22+ ⇔ R−COO−UO2+ (log K = 5.4 ± 0.2). These new stability constants, in conjunction with other experimental and predicted stability constants, may be incorporated in surface complexation models to determine the mobility and fate of U in bacteria-bearing water−rock systems.
161 citations
TL;DR: Amberlite XAD-2 was functionalized with Tiron (disodium salt) by coupling it through an NN spacer as mentioned in this paper, and the resulting chelating resin was used to preconcentrate CuII, Cd, Co, Ni, Pb, Zn, Fe and U.
Abstract: Amberlite XAD-2 was functionalized with Tiron (disodium salt
of 1,2-dihydroxybenzene-3,5-disulfonic acid) by coupling it through an
–NN– spacer. The resulting chelating resin,
characterized by elemental analyses, thermogravimetric analysis and
infrared (IR) spectra, was used to preconcentrate CuII,
CdII, CoII, NiII, PbII,
ZnII, MnII, FeIII and
UO2II. They were determined by flame atomic
absorption spectrometry, except for uranium, for which fluorimetry was
used. The pH ranges for quantitative sorption were 4.0–6.0,
4.5–6.0, 5.0–7.0, 5.0–6.0, 4.0–5.5, 5.0–6.0,
6.5–7.5, 5.0–6.0 and 4.5–5.5, for Cu, Cd, Co, Ni, Pb, Zn,
Mn, Fe and U, respectively. All these metal ions can be desorbed (recovery
91–99%) with 4 mol l−1 HNO3 or HCl,
except for uranyl ion, for which only 4 mol l−1
HNO3 is suitable. The sorption capacity of the resin was 14.0,
9.5, 6.5, 12.6, 12.6, 11.1, 10.0, 5.6 and 7.7 mg of metal ion per gram of
resin, respectively, for the nine metals. The loading half time
(t1/2) was less than 5 min for all the metal ions. The
effects of NaF, NaCl, NaNO3, Na2SO4, and
Na3PO4 on the sorption of these metal ions (0.2 μg
ml−1) are reported. CaII and MgII
are tolerated with each of them (0.2 μg ml−1) up to a
concentration level of 2–30 and 2–10 mmol l−1,
respectively. The enrichment factors for CuII, CdII,
CoII, NiII, PbII, ZnII,
MnII, FeIII and UO2II were 200,
50, 55, 150, 25, 180, 65, 80 and 150 (concentration level 2–25 μg
l−1), respectively. The limits of detection for these
metal ions are 2.0, 1.3, 5.0, 4.0, 24.0, 0.5, 2.5, 5.0 and 1.0 μg
l−1, respectively. Simultaneous enrichment and
determination of all the metal ions is possible. The flame AAS method was
applied to determine these metal ions (except uranyl ion) in river water
samples (RSD ⩽8%) after their enrichment with the present matrix.
Uranium in well water samples and cobalt contents of pharmaceutical vitamin
tablets were also determined fluorimetrically (RSD <5%) and by flame AAS
(RSD ≡3%), respectively, after enrichment on the present resin.
147 citations
TL;DR: A series of B3LYP/pseudopotential calculations has been undertaken on oxide species related to the uranyl dication by the addition of one, two, or three electrons as discussed by the authors.
Abstract: Reactions of laser-ablated uranium atoms, cations, and electrons with O2 during condensation with excess neon produce UO, UO2, UO3, UO2+, and UO2- as characterized by infrared spectra with oxygen isotopic substitution and B3LYP/pseudopotential calculations. Differences in low-lying states for UO2 give rise to substantial shifts and ground state reversal between argon and neon matrices. A series of B3LYP/pseudopotential calculations has been undertaken on oxide species related to the uranyl dication by the addition of one, two, or three electrons. Several electronic states have been characterized for each species. These simple, low-cost calculations predict vibrational frequencies which match those observed in neon matrices extremely well (typically 3−5% too high). The ground state of neutral UO2 appears to have 3Φu symmetry, while 2Φu ground states are implied for UO2+ and UO2-.
125 citations
TL;DR: In this paper, the reduction of uranyl to the relatively insoluble tetravalent form (U(IV)) by Shewanella alga (BrY), a dissimilatory metal-reducing bacteria, was studied in the presence of environmentally relevant iron hydrous oxides.
Abstract: The reduction of uranyl (U(VI)) to the relatively insoluble tetravalent form (U(IV)) by Shewanella alga (BrY), a dissimilatory metal-reducing bacteria, was studied in the presence of environmentally relevant iron hydrous oxides. Because this process is dependent on U(VI) being used as the terminal electron acceptor (TEA) during anaerobic respiration, it is important to understand how other potential TEAs might affect this process. When cell suspensions of BrY were added to uranyl acetate (400 μM), uranyl was removed from solution within 10 h. Similarly, uranyl in the presence on goethite (11.1 μmol of U/m2 of solid) underwent dramatic reduction (>90%) with active BrY cells. In contrast, when ferrihydrite was available (0.67 μmol of U/m2 of solid) only 48% of the initial U(VI) was removed after 10 h. When varying ratios of goethite and ferrihydrite were incorporated into cell suspensions, the extent of uranyl reduction was inversely related to the fraction of ferrihydrite present. Increasing uranyl concent...
106 citations
TL;DR: 1H NMR spectroscopic studies indicate that THF adds reversibly as a ligand to 3 to expand the trigonal bipyramidal geometry, and the effects on the axial U=O bonding as a function of increased electron density donated from the equatorial region show progressive axial bond weakening as the number of amido donors is increased.
Abstract: The synthesis and structural characterization of a rare example of a uranyl complex possessing three equatorial ligands, [M(THF)2][UO2(N(SiMe3)2)3] (3a, M = Na; 3b, M = K), are described. The sodium salt 3a is prepared by protonolysis of [Na(THF)2]2[UO2(N(SiMe3)2)4], whereas the potassium salt 3b is obtained via a metathesis reaction of uranyl chloride UO2Cl2(THF)2 (4) with 3 equiv of K[N(SiMe3)2]. A single-crystal X-ray diffraction study of 3a revealed a trigonal-bipyramidal geometry about uranium, formed by two axial oxo and three equatorial amido ligands, with average UO and U−N bond distances of 1.796(5) and 2.310(4) A, respectively. One of the oxo ligands is also coordinated to the sodium counterion. 1H NMR spectroscopic studies indicate that THF adds reversibly as a ligand to 3 to expand the trigonal bipyramidal geometry. The degree to which the coordination sphere in 3 is electronically satisfied with only three amido donors is suggested by (1) the reversible THF coordination, (2) a modest elongati...
102 citations
TL;DR: In this article, the existence of four triuranyl complexes was confirmed in the presence of high uranium concentrations and in strongly acidic solutions (pH ≤ 194), and one additional weakband was observed at 883±1 cm−1 with a reduced hydration number.
Abstract: Raman spectra have been used to identify and characterize aqueous hydroxouranyl(VI) complexes from 00038 to 0647M at pH from 024 to 1496 adjusted witheither HCF3SO3 and/or (CH3)4NOH under ambient conditions In acidic media(024 ≤ pH ≤ 563), the existence of four species UO2+
2,(UO2)2(OH)3+,(UO2)2(OH)2+
2, and (UO2)3(OH)+
5 was confirmed At high uranium concentrations(ΣU ≥ 01M) and in strongly acidic solutions (pH ≤ 194), one additional weakband was observed at 883±1 cm−1 This band was assumed torepresent thespecies UO2+
2 with a reduced hydration numberIn neutral and basic solutions(563 ≤ pH ≤ 1496), five complexes were postulated: (UO2)3(OH)−
7,(UO2)3(OH)2−
8,(UO2)3(OH)4−
10,(UO2)3(OH)5−
11, andUO2(OH)2−
4, based on theassigned symmetrical stretching frequencies of the UO2 group in each complex(UO2)3(OH)−
7 is the dominant species over mostof the pH range (453–1278)The stability ranges of the other trinuclear species are:(UO2)3(OH)2−
8 (1097 ≤pH ≤ 1383), (UO2)3(OH)4−
10 (1097 ≤ pH ≤ 1385) and (UO2)3(OH)5−
11(1253 ≤pH ≤ 1410), which were identified for the first time Finally, the monomericuranate anion OU2(OH)2−
4 dominates in highly basic solution (1248 ≤ pH ≤1496) The linear correlation between the symmetrical vibrational frequency v
1of the linear O = U = O entity and the average number
$$\overline n$$
of hydroxide ligandscoordinated to each uranium atom in a given species has been reaffirmed andexpanded:
$$v_1 ({\text{cm}}^{{\text{ - 1}}} ) = - 22X\overline n + 870$$
The v
1 correlation was also used to predict the vibration frequencies of theundetected monomers UO2(OH)+, UO2(OH)o
2,UO2(OH)−
3 at 848±2, 826±2, and804±2 cm±1, respectively Characteristic band areas for eachuranyl hydrolyzedspecies were determined by Raman spectra decomposition and their hydrolysisquotients log Q, were calculated Structures of the four triuranylspecies are proposed
98 citations
TL;DR: Comparison of the present iminato (UNPR3) calculations with previous extended Hückel work on d block imido (MNR) systems reveals that in all cases there is little or no preference for linearity over bending at the nitrogen when R is (a) only sigma-bound to the nitrogen and (b) sterically unhindered.
Abstract: The electronic and geometric structures of the title species have been studied computationally using quasi-relativistic gradient-corrected density functional theory. The valence molecular orbital ordering of UO22+ is found to be πg < πu < σg ≪ σu (highest occupied orbital), in agreement with previous experimental conclusions. The significant energy gap between the σg and σu orbitals is traced to the “pushing from below” mechanism: a filled−filled interaction between the semi-core uranium 6p atomic orbitals and the σu valence level. The U−N bonding in UON+ and UN2 is significantly more covalent than the U−O bonding in UON+ and UO22+. UO(NPH3)3+ and U(NPH3)24+ are similar to UO22+, UON+, and UN2 in having two valence molecular orbitals of metal−ligand σ character and two of π character, although they have additional orbitals not present in the triatomic systems, and the U−N σ levels are more stable than the U−N π orbitals. The inversion of U−N σ/π orbital ordering is traced to significant N−P (and P−H) σ c...
97 citations
TL;DR: In this article, a carbon electrode composed of vapor-grown fibers in a continuous flow-through cell was used to remove adsorbed uranium from the carbon fiber by passing a 0.1 M KNO 3 solution through the cell and applying a positive potential on the electrode.
TL;DR: 5-LIO(Me-3,2-HOPO) and 5-LICAM(S) are identified as the most effective low-toxicity agents and chelate circulating U(VI) efficiently at ligand:uranium molar ratios ≥ 20, remove useful amounts of newly deposited U (VI) from kidney and bone at molar ratio ≥ 100, and reduce kidney U( VI) levels significantly when given orally at m polar ratios ≥ 100.
Abstract: Uranium(VI) (UO2(2+), uranyl) is nephrotoxic. Depending on isotopic composition and dosage, U(VI) is also chemically toxic and carcinogenic in bone. Several ligands containing two, three, or four bidentate catecholate or hydroxypyridinonate metal binding groups, developed for in vivo chelation of other actinides, were found, on evaluation in mice, to be effective for in vivo chelation of U(VI). The most promising ligands contained two bidentate groups per chelator molecule (tetradentate) attached to linear 4- or 5-carbon backbones (4-LI, butylene; 5-LI, pentylene; 5-LIO, diethyl ether). New ligands were then prepared to optimize ligand affinity for U(VI) in vivo and low acute toxicity. Five bidentate binding groups--sulfocatechol [CAM(S)], carboxycatechol [CAM(C)], methylterephthalamide (MeTAM), 1,2-hydroxypyridinone (1,2-HOPO), or 3,2-hydroxypyridinone (Me-3,2-HOPO)--were each attached to two linear backbones (4-LI and 5-LI or 5-LIO). Those ten tetradentate ligands and octadentate 3,4,3-LI(1,2-HOPO), an effective actinide chelator, were evaluated in mice for in vivo chelation of 233U(VI) (injection at 3 min, 1 h, or 24 h or oral administration at 3 min after intravenous injection of 233UO2Cl2) and for acute toxicity (100 micromol kg(-1) injected daily for 10 d). The combined efficacy and toxicity screening identified 5-LIO(Me-3,2-HOPO) and 5-LICAM(S) as the most effective low-toxicity agents. They chelate circulating U(VI) efficiently at ligand:uranium molar ratios > or = 20, remove useful amounts of newly deposited U(VI) from kidney and bone at molar ratios > or = 100, and reduce kidney U(VI) levels significantly when given orally at molar ratios > or = 100. 5-LIO(Me-3,2-HOPO) has greater affinity for kidney U(VI) while 5-LICAM(S) has greater affinity for bone U(VI), and a 1:1 mixture (total molar ratio = 91) reduced kidney and bone U(VI) to 15 and 58% of control, respectively--more than an equimolar amount of either ligand alone.
TL;DR: In this article, the authors used vertex sharing with UrO 4 square bipyramids [Ur=(UO 2 ) 2+ uranyl ion], forming a framework of polyhedra of higher bond-valence.
TL;DR: A substructural molecular fragment (SMF) method has been developed to model the relationships between the structure of organic molecules and their thermodynamic parameters of complexation or extraction.
Abstract: A substructural molecular fragment (SMF) method has been developed to model the relationships between the structure of organic molecules and their thermodynamic parameters of complexation or extraction. The method is based on the splitting of a molecule into fragments, and on calculations of their contributions to a given property. It uses two types of fragments: atom/bond sequences and “augmented atoms” (atoms with their nearest neighbors). The SMF approach is tested on physical properties of C2−C9 alkanes (boiling point, molar volume, molar refraction, heat of vaporization, surface tension, melting point, critical temperature, and critical pressures) and on octanol/water partition coefficients. Then, it is applied to the assessment of (i) complexation stability constants of alkali cations with crown ethers and phosphoryl-containing podands, and of β-cyclodextrins with mono- and 1,4-disubstituted benzenes, and (ii) solvent extraction constants for the complexes of uranyl cation by phosphoryl-containing ...
TL;DR: Vibrational spectroscopic measurements of 2-4 imply that, in contrast to the case of uranyl complexes prepared in aqueous environments, coordination of relatively strongly donating alkoxide ligands allows for enhancement of electron density on the uranyl groups such that the uranol U=O bonds are weakened.
Abstract: Uranium(VI) alkoxide complexes are prepared via metathesis reactions of [UO2Cl2(THF)2]2 with potassium alkoxides in nonaqueous media. The dark red compound U[OCH2C(CH3)3]6, 1, results from redistributive exchange of oxo and neopentoxide ligands between more than one uranium species. Single-crystal X-ray diffraction analysis of 1 reveals a monomer in which the uranium is coordinated in a pseudooctahedral fashion by six neopentoxide ligands. Imposition of steric congestion at the metal center prevents oxo-alkoxide ligand exchange in the reactions using more sterically demanding alkoxides. Simple metathesis between uranyl chloride and alkoxide ligands occurs in the synthesis of golden yellow-orange UO2(OCHPh2)2(THF)2, 2, and yellow UO2[OCH(tBu)Ph]2(THF)2, 3. Single-crystal X-ray diffraction analysis of 2 reveals a monomer in which the uranium is coordinated in a pseudooctahedral fashion by two apical oxo ligands, two diphenylmethoxide ligands occupying trans positions, and two tetrahydrofuran ligands. Coordination of diisopropylmethoxide allows for synthesis of a more complex binary alkoxide system. Single-crystal X-ray diffraction analysis of watermelon red [UO2(OCH(iPr)2)2]4, 4, reveals a tetramer in which each uranium is coordinated in a pseudooctahedral fashion by two apical oxo ligands, one terminal alkoxide, two bridging alkoxide ligands, and one bridging oxo ligand from a neighboring uranyl group. These compounds are characterized by elemental analysis, 1H NMR, infrared spectroscopy, and, for 1, 2, and 4, single-crystal X-ray diffraction analysis. Luminescence spectroscopy is employed to evaluate the extent of aggregation of compounds 2-4 in various solvents. Vibrational spectroscopic measurements of 2-4 imply that, in contrast to the case of uranyl complexes prepared in aqueous environments, coordination of relatively strongly donating alkoxide ligands allows for enhancement of electron density on the uranyl groups such that the uranyl U=O bonds are weakened. Crystal data are as follows. 1: monoclinic space group C2/m, a = 10.6192(8) A, b = 18.36(1) A, c = 10.6151(8) A, beta = 109.637(1) degrees, V = 1949.1(3) A3, Z = 2, dcalc = 1.297 g cm-3. Refinement of 2065 reflections gave R1 = 0.045. 2: monoclinic space group P2(1)/c, a = 6.1796(4) A, b = 15.669(1) A, c = 16.169(1) A, beta = 95.380(1) degrees, V = 1558.7(2) A3, Z = 2, dcalc = 1.664 g cm-3. Refinement of 3048 reflections gave R1 = 0.036. 4: tetragonal space group I4, a = 17.8570(6) A, b = 17.8570(6) A, c = 11.4489(6) A, V = 3650.7(3) A3, Z = 2, dcalc = 1.821 g cm-3. Refinement of 1981 reflections gave R1 = 0.020.
TL;DR: In this paper, the IR-ATR and Raman spectroscopies are used to identify the complexed species of uranyl with hydroxide in aqueous solutions as a function of pH in the range 1.55-4.20.
TL;DR: The structure of dioxouranium(VI) as a function of pH at different (CH3)(4)N-OH concentrations has been investigated with the aid of U L-III-edge EXAFS.
Abstract: The structure of dioxouranium(VI) as a function of pH at different (CH3)(4)N-OH concentrations has been investigated with the aid of U L-III-edge EXAFS. Polynuclear hydroxo species were identified by an U-U interaction at 3.80(8) Angstrom at pH = 4.1. The precipitate formed at pH = 7 has a schoepite like structure. In solution at high pH [0.5 M (CH3)(4)N-OH], the EXAFS data are consistent with the formation of a monomeric four coordinated uranium(VI) hydroxide complex UO2(OH)(4)(2-) of octahedral geometry. The first shell contains two O atoms with a U=O distance of 1.83(o) Angstrom, and four O atoms were identified at a U-O distance of 2.26(5) Angstrom. In strong alkaline solutions [>1 M (CH3)(4)N)-OH],O-17-NMR spectra indicate the presence of two species, presumably UO2(OH)(4)(2-) and UO2(OH)(5)(3-), the latter in low concentration, which are in rapid equilibrium with one another at 268 K in aqueous solution.
TL;DR: Under most conditions with dendrimers present, the d endrimers, rather than the liposomes, are visible in the TEM images, demonstrating that the UO22+ is complexed to the dendedrimers and not to the Liposomes.
Abstract: Transmission electron micrographs (TEM) of UO22+-negatively stained starburst dendrimers (SBDs), members of the family of dendritic macromolecules, have been analyzed in the absence and in the presence of dimyristoyl-phosphatidylcoline (DMPC) liposomes and mixed DMPC/DMPA-Na (the sodium salt of DMP-colate) liposomes at different relative percentages of DMPC and DMPA-Na. Under most conditions with dendrimers present, the dendrimers, rather than the liposomes, are visible in the TEM images, demonstrating that the UO22+ is complexed to the dendrimers and not to the liposomes. Only at high composition of DMPA-Na in the liposomes (>40%) and under the condition of high protonation of the dendrimer surface are the liposomes imaged by TEM. Mixed liposomes show a rodlike shape. To confirm the TEM results, an EPR study was performed by adding to the SBD solution various amounts of Cu2+ and UO22+. Uranyl ions compete favorably with copper ions for the complexation with the nitrogen ligand sites at both the external ...
TL;DR: In this paper, the transformations of uranyl nitrate, uranyl citrate, or uranyl EDTA to the brine or bacterial growth medium resulted in the precipitation of uranium. But the results showed that the uranyl carbonate was not biosorbed by the growing culture nor by washed resting cells suspended in 20% NaCl brine (3.4 M).
Abstract: We investigated the transformations of uranyl nitrate, uranyl citrate, uranyl ethylenediaminetetraacetate (U-EDTA), and uranyl carbonate by a denitrifying halophilic bacterium, Halomonassp. (WIPP1A), isolated from the Waste Isolation Pilot Plant (WIPP) repository. The addition of uranyl nitrate, uranyl citrate, or uranyl EDTA to the brine or bacterial growth medium resulted in the precipitation of uranium. Extended X-ray absorption fine structure (EXAFS) analysis of the precipitates formed in the brine and in the growth medium were identified as uranyl hydroxide [UO 2( OH) 2 ] and uranyl hydroxophosphato species [K(UO 2 ) 5 (PO 4 ) 3( OH) 2 .nH 2 O], respectively. Dissolution of the uranium precipitate was concomitant with the growth of the bacteria under anaerobic conditions. The UV-vis spectra of the culture medium during growth showed that a uranyl dicarbonate complex [UO 2 (CO 3 ) 2 ] 2- was formed due to CO 2 production from the metabolism of the carbon source succinate. The bacterium completely metabolized the citrate released from the uranyl citrate complex but not the EDTA released from the U-EDTA complex. Adding uranyl carbonate to the growth medium caused no changes in the uranium speciation due to bacterial growth. Uranyl carbonate was not biosorbed by the growing culture nor by washed resting cells suspended in 20% NaCl brine (3.4 M) because the complex was either neutral or anionic. Our results demonstrate that bacterial activity can enhance the dissolution of uranium phosphate by forming uranyl carbonate species.
TL;DR: In this article, the hydration numbers of the actinyls (U, Np, and Pu) have been studied using the ab initio Hartree-Fock method including the effective core potentials.
Abstract: Hydration numbers of the pentavalent and hexavalent actinyls (U, Np, and Pu) have been studied using the ab initio Hartree‐ Fock method including the effective core potentials. The calculations were carried out inclusive of the primary and the secondary hydration spheres and the dissociation energy was used to discuss the most stable structure. The results suggest that the hydration number na 5 is the most stable for the actinyls we have studied. The result for neptunyl(V) was in conflict with the previous Hartree‐Fock calculation, which only included the primary hydration sphere. It was concluded that the secondary hydration sphere is quite important in studying the hydration numbers of the actinyls. The atomic bond lengths of hydrated uranyl(VI) and neptunyl(V) obtained by the MP2 level calculation gave good agreement with experimental results. q 2000 Elsevier Science B.V. All rights reserved.
TL;DR: In this article, the structures, energies, and charges of uranyl cation complexes with water molecules, nitrate ion, and carbonate ions were determined using Hartree-Fock, second-order Moeller-Plesset (MP2) perturbation theory, and density functional theory (DFT) ab initio quantum chemical methods.
Abstract: The structures, energies, and charges of uranyl cation complexes with water molecules, nitrate ion, and carbonate ions were determined using Hartree-Fock, second-order Moeller-Plesset (MP2) perturbation theory, and density functional theory (DFT) ab initio quantum chemical methods. Reasonable agreement with experimentally determined structures was found. Significant polarization of the ligands as well as charge transfer to the uranyl ion was observed in the complexes. The dissociation energy curves for the complexes were also determined at the MP2 level of theory. Attempts to reproduce these curves with molecular mechanical models with fixed atomic point charges failed, showing that an appropriate force field for these systems must include polarization and charge-transfer effects.
Journal Article•
TL;DR: In this paper, the crystal field parameters of Ni(II) complex were calculated and were found to agree fairly well with the values reported for known square pyramidal complexes, and infrared spectral studies showed a monobasic bidentate behavior with the oxygen and nitrogen donor system.
Abstract: amido)rhodanine (HL) have been prepared and characterized by chemical and thermal analyses, molar conductivity, magnetic susceptibility measurements, and infrared, electronic and EPR spectra. The visible and EPR spectra indicated that the Cu(II) complex has a tetragonal geometry. From EPR spectrum of the Cu(II) complex, various parameters were calculated. The crystal field parameters of Ni(II) complex were calculated and were found to agree fairly well with the values reported for known square pyramidal complexes. The infrared spectral studies showed a monobasic bidentate behaviour with the oxygen and nitrogen donor system. Thermal stabilities of the complexes are also re
TL;DR: The incorporation of Tc 7a into the structure of uranyl phases that are expected to occur as alteration products of spent nuclear fuel will result in underbonding at the U 6a site and will destabilize the structure as discussed by the authors.
TL;DR: The structure of meta-schoepite (UO2)4O(OH)6·5H2O has been determined from a synthetic single crystal as discussed by the authors, which consists of layers of stoichiometry formed from edge-sharing UO7 pentagonal bipyramids interleaved with hydrogen-bonded water molecules.
Abstract: The structure of uranium oxide dihydrate, also known as meta-schoepite (UO2)4O(OH)6·5H2O, has been determined from a synthetic single crystal. The structure, at 150 K, space group Pbcn, lattice constants a = 14.6861 (4), b = 13.9799 (3) and c = 16.7063 (5) A, consists of layers of stoichiometry (UO2)4O(OH)6, formed from edge-sharing UO7 pentagonal bipyramids, interleaved with hydrogen-bonded water molecules. Three of the layer hydroxyl groups are linked through hydrogen bonding to single water molecules and the three remaining OH units form interactions with water molecules that each act as acceptors in two hydrogen bonds. One of the water molecules in the inter-layer region is disordered over two symmetry-related sites and forms hydrogen-bonded interactions only within the layer and with the uranyl O atoms. The relationship of the structure of meta-schoepite to that of schoepite is discussed in detail.
TL;DR: In this paper, the influence of various parameters such as the cone voltage, temperature, and gas flow rate on the results obtained by time-resolved laser-induced fluorescence on the same solutions is presented.
Abstract: Speciation of actinides, lanthanides, and fission products is a major challenge in the framework of nuclear fuel cycle studies. Electrospray-mass spectrometry has been used for uranium speciation. Free uranyl (UO22+), the first hydroxo complex (UO2OH+), and the oligomeric species (UO2)3(OH)5+ have been observed as a function of pH. Different aqueous solvents (sodium perchlorate, perchloric acid/ammonium acetate, and perchloric acid/ammonia) were tested in order to limit the presence of adducts. The influence of various parameters such as the cone voltage, temperature, and gas flow rate is presented. Comparison with results obtained by time-resolved laser-induced fluorescence on the same solutions shows a similar tendency despite a slight shift in pH relative to the OECD database.
TL;DR: In this paper, the UO2+2 ion uptake on P(AAm-MA) hydrogels was investigated using two types of gel systems prepared by a simple irradiation method and a prestructured reaction.
Abstract: Acrylamide–maleic acid (AAm–MA) hydrogels were prepared by gamma-irradiation of their aqueous solutions. UO2+2 ion uptake on P(AAm–MA) hydrogels was investigated using two types of gel systems prepared by a simple irradiation method and a prestructured reaction. It has been observed that gels prestructured with UO2+2 ions adsorbed approximately 15–20% more UO2+2 ions than gels prepared in pure water (the usual method). It was also found that the uranyl ion adsorption capacity of hydrogels increased with an increasing amount of maleic acid in the gel system and an increasing concentration of uranyl ion in the solution. A possible interaction mechanism between the groups in the copolymeric gels and UO2+2 ion has been proposed based on the stoichiometry and the spectroscopic evidence. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 284–289, 2000
TL;DR: The structure and reaction dynamics in the systems UO22+-SO42- and UO 22+ -SO42--OH- were investigated using EXAFS and O-17-NMR spectroscopy as discussed by the authors.
Abstract: The structure and reaction dynamics in the systems UO22+-SO42- and UO22+-SO42--OH- were investigated using EXAFS and O-17-NMR spectroscopy. Uranium Lm edge EXAFS indicated a bidentate coordination mode of sulfate to uranyl. In solution, this is characterized by an U-S distance of 3.11 Angstrom. Approximately 5 oxygen atoms were observed in the equatorial plane at 2.39-2.43 Angstrom. The kinetics in the binary uranyl sulfate system can be described by four dominant exchange reactions: (1) UO22++SO(4)(2-)reversible arrow UO2SO4(k(1)), (2) U*O-2(2+)+UO(2)SO(4)reversible arrowU*O2SO4+UO22+(k(2)), (3) UO22++UO2(SO4)(2)(2-)reversible arrow 2UO(2)SO(4)(k(3)), and (4) UO2SO4+SO42-reversible arrowUO2(SO4)(2)(2-)(k(4)). These reactions have rate constants indicating that the exchange is not of the simple Eigen-Wilkins type. Ternary uranyl sulfate hydroxide species were characterized by their O-17 chemical shift and by potentiometry. There are no separate signals for the possible isomers of the ternary species indicating that they are in fast exchange with each other.
TL;DR: In this paper, the adsorption properties of poly(acrylamidoxime) chelating resins for binary metal ion mixtures with Cu(II) and Pb(II), Cr(III), and U(VI) are investigated by the batch technique.
Abstract: The adsorption properties of poly(acrylamidoxime) chelating resin for Cu(II), Cd(II), Hg(II), Zn(II), Pb(II), Cr(III), and U(VI) are investigated by the batch technique. Based on the research results of the binding capacity effect of the pH value on sorption kinetic experiments, it is shown that this resin has higher binding capacity to uranyl ions, fast kinetics, and very good selectivity from binary metal ion mixtures with Cu(II) and Pb(II). The uranyl ion sorption strongly depends on the pH value of the solution. The highest value of 99% is at pH 5, but at pH 1 there is no retention. The adsorbed UO can be eluted by sulfuric acid and sodium carbonate. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1994–1999, 2000
TL;DR: In this article, anion selectivities of polyvinylchloride (PVC) plasticized membranes containing uranyl salophene derivatives were investigated, and the influence of the membrane components (i.e. ionophore structure, dielectric constant and structure of plasticizer, the amount of incorporated ammonium salt) on its phosphate selectivity was investigated.
Abstract: Anion selectivities of poly(vinylchloride) (PVC) plasticized membranes containing uranyl salophene derivatives were presented. The influence of the membrane components (i.e. ionophore structure, dielectric constant and structure of plasticizer, the amount of incorporated ammonium salt) on its phosphate selectivity was investigated. The highest selectivity for H2PO4− over other anions tested was obtained for lipophilic uranyl salophene III (without ortho-substituents) in PVC/o-nitrophenyl octylether (o-NPOE) membrane containing 20 mol% of tetradecylammonium bromide (TDAB). Ion-selective electrodes (ISEs) based on these membranes exhibited linear response in the range 1–4 of pH2PO4− with a slope of 59 mV/decade. The introduction of ortho-methoxy substituents in ionophore structure decreased the phosphate selectivity of potentiometric sensors.
TL;DR: In this article, a catalytic cycle for chlorophenol photooxidation involving uranyl ion and molecular oxygen is proposed, which leads to the conclusion that oxygen favors reaction with uranium and/or the uranium-phenoxyl radical pair, leading to the formation of the superoxide anion and its conjugate acid, HO{sub 2}{sup {sm_bullet}}, which then regenerates UO{sub2}{sup 2+}.
Abstract: The oxidation of chlorophenols by photoexcited uranyl ion was studied in aqueous solution at concentrations where the ground-state interactions were negligible. Nanosecond flash photolysis showed that a clean electron-transfer process from the chlorophenols to the excited uranyl ion is involved. This is suggested to lead to the formation of a U(V)/chlorophenoxyl radical pair complex. The efficiency of this charge-transfer process is unity for the three chlorophenols. However, low product yields suggest that in the absence of oxygen, back electron transfer, both within the radical pair and from separated uranium(V) to phenoxyl radicals, appears to be the major reaction pathway. In the presence of oxygen the quantum yields of disappearance of chlorophenol and of photoproduct formation increased. This leads to the conclusion that oxygen favors reaction with uranium(V) and/or the uranium(V)-phenoxyl radical pair, leading to the formation of the superoxide anion and its conjugate acid, HO{sub 2}{sup {sm_bullet}}, which then regenerate UO{sub 2}{sup 2+}. Based on this, a catalytic cycle for chlorophenol photooxidation involving uranyl ion and molecular oxygen is proposed.