Uranyl Oxalate Research Articles

Aqueous coordination chemistry and photochemistry of uranyl(vi) oxalate revisited: a density functional theory study

Using density functional theory (DFT) calculations, we revisited a classical problem of uranyl(VI) oxalate photochemical decomposition. Photoreactivities of uranyl(VI) oxalate complexes are found to correlate largely with ligand-structural arrangements. Importantly, the intramolecular photochemical reaction is inhibited when oxalate is bound to uranium exclusively in chelate binding mode. Previously proposed mechanisms involving a UO(2)(C(2)O(4))(2)(2-) (1:2) complex as the main photoreactive species are thus unlikely to apply, because the two oxalic acids are bound to uranium in a chelating binding mode. Our DFT results suggest that the relevant photoreactive species are UO(2)(C(2)O(4))(3)(4-) (1:3) and (UO(2))(2)(C(2)O(4))(5)(6-) (2:5) complexes binding uranium in an unidentate fashion. These species go through decarboxylation upon excitation to the triplet state, which ensues the release of CO(2) and reduction of U(vi) to U(v). The calculations also suggest an alternative intermolecular pathway at low pH via an electron transfer between the excited state *UO(2)(2+) and hydrogen oxalate (HC(2)O(4)(-)) which eventually leads to the production of CO and OH(-) with no net reduction of U(VI). The calculated results are consistent with previous experimental findings that CO is only detected at low pH while U(IV) is detected only at high pH.

Uranyl–organic assemblies with the macrocyclic ligand 1,4,8,11-tetraazacyclotetradecane-1,4,8,11-tetraacetate (TETA)

Three uranyl ion complexes obtained from the reaction of uranyl nitrate hexahydrate and 1,4,8,11-tetraazacyclotetradecane-1,4,8,11-tetraacetic acid (H4TETA) were characterized by their crystal structure. The centrosymmetric macrocycle, in the [3434] conformation with either carbon or nitrogen atoms as corners, is zwitterionic, with four carboxylate groups and two or four protonated nitrogen atoms. The complexes [(UO2)2(H2TETA)(C2O4)(H2O)2] (1) and [UO2(H4TETA)(H2O)]·NO3·Cl (2) were synthesized under hydrothermal conditions and 1 includes additional oxalate ligands generated in situ. Both compounds are two-dimensional polymers in which the four-fold monodentate macrocyclic ligand unites either four uranyl oxalate dinuclear species (1) or isolated uranyl ions (2). Complex 3, [UO2(H2TETA)(H2O)]·6H2O, was obtained at room temperature and, although it displays the same stoichiometry as 2, it differs from it by being a three-dimensional framework. Both 2 and 3 present channels containing either counter-ions or water molecules. As often observed, the water content of the low-temperature species, 3, is higher than that of the high-temperature one, 2.

Uranyl Ion Complexation by Cucurbiturils in the Presence of Perrhenic, Phosphoric, or Polycarboxylic Acids. Novel Mixed-Ligand Uranyl−Organic Frameworks

Six novel complexes formed under hydrothermal conditions by reaction of uranium trioxide or uranyl nitrate with cucurbit[6]uril (CB6), or cucurbit[7]uril (CB7) in one case, in the presence of additional ligands, either tetrahedral oxoanions or polycarboxylic acids, have been structurally characterized. In [(UO2)2(CB6)(ReO4)4(H2O)3]·2HReO4·5H2O (1), three perrhenate ions are bound to uranyl ions and one is encapsulated in the CB6 cavity, while perrhenate acts as a counterion only in the CB7 complex [UO2(CB7)(NO3)(H2O)2](ReO4)·5H2O (2). 1 is a molecular complex and 2 a one-dimensional polymer. Complex 3, [UO2(H2PO4)2(H2O)]2·CB6·H3PO4·6H2O, obtained in the presence of orthophosphoric acid, comprises one-dimensional uranyl dihydrogen phosphate chains, and the CB6 molecules are uncoordinated, as in [(UO2)4(C2O4)3(NO3)2(H2O)6]·CB6·6H2O (4), which displays an unprecedented tetranuclear uranyl oxalate moiety hydrogen bonded to the CB6 molecules. With pyrazinetetracarboxylic acid (H4PZTC), a one-dimensional polyme...

Depletion of phosphatidylcholine affects endoplasmic reticulum morphology and protein traffic at the Golgi complex

The mutant Chinese hamster ovary cell line MT58 contains a thermosensitive mutation in CTP:phosphocholine cytidylyltransferase, the regulatory enzyme in the CDP-choline pathway. As a result, MT58 cells have a 50% decrease in their phosphatidylcholine (PC) level within 24 h when cultured at the nonpermissive temperature (40 degrees C). This is due to a relative rapid breakdown of PC that is not compensated for by the inhibition of de novo PC synthesis. Despite this drastic decrease in cellular PC content, cells are viable and can proliferate by addition of lysophosphatidylcholine. By [(3)H]oleate labeling, we found that the FA moiety of the degraded PC is recovered in triacylglycerol. In accordance with this finding, an accumulation of lipid droplets is seen in MT58 cells. Analysis of PC-depleted MT58 cells by electron and fluorescence microscopy revealed a partial dilation of the rough endoplasmic reticulum, resulting in spherical structures on both sites of the nucleus, whereas the morphology of the plasma membrane, mitochondria, and Golgi complex was unaffected. In contrast to these morphological observations, protein transport from the ER remains intact. Surprisingly, protein transport at the level of the Golgi complex is impaired. Our data suggest that the transport processes at the Golgi complex are regulated by distal changes in lipid metabolism.

Metal complexes stability constant determination by hyphenation of capillary electrophoresis with inductively coupled plasma mass spectrometry: The case of 1:1 metal-to-ligand stoichiometry

Nuclear energy development has raised new issues like radionuclides biogeochemistry. The modelling of their biochemical properties involves the accurate determination of thermodynamical data, like stability constants. This can be achieved by using hyphenated capillary electrophoresis (CE)–ICPMS and the method was applied successfully on 1:1 lanthanum–oxalate and uranyl–oxalate complexes. Several significant steps are discussed: choice of analytical conditions, electrophoretic mobility calculation, mathematical treatment of experimental data by using linear regressions, ligand concentration and ionic strength corrections. The following values were obtained with a good precision for lanthanum–oxalate and uranyl–oxalate complexes: log( K°(LaOxa +)) = 6.10 ± 0.10 and log( K°(UO 2Oxa)) = 6.40 ± 0.30, respectively, at infinite dilution. These values are consistent with the literature data, showing CE–ICPMS potential for metal complexes stability constants determination.

Structural variability in uranyl–lanthanide heterometallic complexes with DOTA and oxalato ligands

Four novel 4f–5f heterometallic complexes could be obtained from the reaction of uranyl and lanthanide nitrates with DOTA (H4L) under hydrothermal conditions. In all cases, as in the previous examples reported, additional oxalato ligands are formed in situ. Variations in the stoichiometry of the final products and the presence of hydroxo ions in some cases appear to result in a large structural variability. In the two isomorphous complexes [(UO2)2Ln2(L)2(C2O4)] with Ln = Sm (1) or Eu (2), the lanthanide ion is located in the N4O4 site and is also bound to a carboxylate oxygen atom from a neighbouring unit, to give zigzag chains which are further linked to one another by [(UO2)2(C2O4)]2+ dications, resulting in the formation of a 3D framework. In [(UO2)4Gd2(L)2(C2O4)3(H2O)6]·2H2O (3), 2D bilayer subunits of the “double floor” type with uranyl oxalate pillars are assembled into a 3D framework by other, disordered uranyl ions. [(UO2)2Gd(L)(C2O4)(OH)]·H2O (4) is a 2D assembly in which cationic {[(UO2)2(C2O4)(OH)]+}n chains are linked to one another by the [Gd(L)]−groups. The most notable feature of this compound is the environment of the 4f ion, which is eight-coordinate and twisted square antiprismatic (TSA′), instead of nine-coordinate monocapped square antiprismatic (SA), as generally observed in DOTA complexes of gadolinium(III) and similarly-sized ions.

Parametric Investigation of Laser-Induced Fluorescence of Solid-State Uranyl Compounds

The combination of remote/standoff sensing and laser-induced fluorescence (LIF) spectroscopy shows potential for detection of uranyl (UO2(2+)) compounds. Uranyl compounds exhibit characteristic emission in the 450-600 nm (22,200 to 16,700 cm(-1)) spectral region when excited by wavelengths in the ultraviolet or in the short-wavelength portion of the visible spectrum. We report a parametric study of the effects of excitation wavelength [including 532 nm (18,797 cm(-1)), 355 nm (28,169 cm(-1)), and 266 nm (37,594 cm(-1))] and excitation laser power on solid-state uranium compounds. The uranium compounds investigated include uranyl nitrate, uranyl sulfate, uranyl oxalate, uranium dioxide, triuranium octaoxide, uranyl acetate, uranyl formate, zinc uranyl acetate, and uranyl phosphate. We observed the characteristic uranyl fluorescence spectrum from the uranium compounds except for uranium oxide compounds (which do not contain the uranyl moiety) and for uranyl formate, which has a low fluorescence quantum yield. Relative uranyl fluorescence intensity is greatest for 355 nm excitation, and the order of decreasing fluorescence intensity with excitation wavelength (relative intensity/laser output) is 355 nm > 266 nm > 532 nm. For 532 nm excitation, the emission spectrum is produced by two-photon excitation. Uranyl fluorescence intensity increases linearly with increasing laser power, but the rate of fluorescence intensity increase is different for different emission bands.

Supramolecular Structure of the Casein Micelle

The supramolecular structure of colloidal casein micelles in milk was investigated by using a sample preparation protocol based on adsorption of proteins onto a poly-l-lysine and parlodion-coated copper grid, staining of proteins and calcium phosphate by uranyl oxalate, instantaneous freezing, and drying under a high vacuum. High-resolution transmission electron microscopy stereo-images were obtained showing the interior structure of casein micelles. On the basis of our interpretation of these images, an interlocked lattice model was developed in which both casein-calcium phosphate aggregates and casein polymer chains act together to maintain casein micelle integrity. The caseins form linear and branched chains (2 to 5 proteins long) interlocked by the casein-stabilized calcium phosphate nanoclusters. This model suggests that stabilization of calcium phosphate nanoclusters by phosphoserine domains of αs1-, αs2-, or β-casein, or their combination, would orient their hydrophobic domains outward, allowing interaction and binding to other casein molecules. Other interactions between the caseins, such as calcium bridging, could also occur and further stabilize the supramolecule. The combination of having an interlocked lattice structure and multiple interactions results in an open, sponge-like colloidal supramolecule that is resistant to spatial changes and disintegration. Hydrophobic interactions between caseins surrounding a calcium phosphate nanocluster would prevent complete dissociation of casein micelles when the calcium phosphate nanoclusters are solubilized. Likewise, calcium bridging and other electrostatic interactions between caseins would prevent dissociation of the casein micelles into casein-calcium phosphate nanocluster aggregates when milk is cooled or urea is added to milk, and hydrophobic interactions are reduced. The appearance of both polymer chains and small aggregate particles during milk synthesis would also be expected based on this interlocked lattice model of casein micelles, and its supramolecule structure thus exhibits the principles of self-aggregation, interdependence, and diversity observed in nature.

In situ ligand synthesis with the [formula omitted] cation under hydrothermal conditions

A novel uranium (VI) coordination polymer, (UO 2) 2(C 2O 4)(C 5H 6NO 3) 2 ( 1), has been prepared under the hydrothermal reaction of uranium nitrate hexahydrate and l-pyroglutamic acid. Compound 1 (monoclinic, C2/ c, a=22.541(6) Å, b=5.7428(15) Å, c=15.815(4) Å, β=119.112(4)°, Z=4, R 1=0.0237, w R 2=0.0367) consists of uranium pentagonal bipyramids linked via l-pyroglutamate and oxalate anions to form an overall two-dimensional (2D) structure. With the absence of oxalic acid within the starting materials, the oxalate anions are hypothesized to form in situ whereby decarboxylation of l-pyroglutamic acid occurs followed by coupling of CO 2 to form the oxalate linkages as observed in the crystal structure. Addition of copper (II) to this system appears to promote oxalate formation in that synthetic moolooite (Cu(C 2O 4)· nH 2O; 0⩽ n⩽1) and a known uranyl oxalate [(UO 2) 2(C 2O 4)(OH) 2(H 2O) 2·H 2O], co-crystallize in significant quantity. Compound 1 exhibits the characteristic uranyl emission spectrum upon either direct uranyl excitation or ligand excitation, the latter of which shows an increase in relative intensity. This subsequent increase in the intensity indicates an energy transfer from the ligand to the uranyl cations thus illustrating an example of the antenna effect in the solid state.

Neutron diffraction study of uranyl oxalate [UO2(C2O4)(D2O)] · 2D2O

A powdered sample of uranyl oxalate [UO2(C2O4)(D2O)] · 2D2O (compound I) is studied using neutron diffraction. The crystals are monoclinic, space group P21/c, with a = 5.608(1) A, b = 17.016(3) A, c = 9.410(2) A, β = 98.9369(2)°, Z = 4, R f = 0.042, R I = 0.054, x 2 = 1.5. The main structural units of the crystals are [UO2(C2O4)(D2O)] chains. These chains, which belong to the AK02M1 (A = UO 2 2+ ) crystal-chemical group of the uranyl complexes, lie parallel to [101]. The water molecules in the crystals of I are hydrogen-bonded into zigzag chains running along [100]. Since each third oxygen atom of the chain formed of water molecules is coordinated to the uranium atom, the uranyl oxalate chains are linked into {[UO2(C2O4)(D2O)] · 2D2O} layers that lie normal to [010]. The layers are linked into the framework through interlayer hydrogen bonds (D2O)O-D···O (oxalate).

A series of sheet-structured alkali metal uranyl oxalate hydrates: structures and IR spectra

Abstract The novel compounds K[(UO2)2(C2O4)2OH] · 2 H2O (KUrOx), Rb[(UO2)2(C2O4)2OH] · 2 H2O (RbUrOx), and Cs[(UO2)2(C2O4)2OH] · H2O (CsUrOx) have been synthesized by mild hydrothermal methods. Single crystal diffraction data collected at 125 K using MoK α radiation and a CCD-based area detector were used to solve and refine the crystal structures by full-matrix least-squares techniques to agreement indices (KUrOx, RbUrOx, CsUrOx) wR 2 = 0.045, 0.062, 0.042 for all data, and R1 = 0.023, 0.030, 0.022 calculated for 1834, 1863, 1821 unique reflections respectively. The compounds KUrOx, RbUrOx, and CsUrOx are all monoclinic, space group P21/m, Z = 2. The unit cell of KUrOx has the dimensions a = 5.6427(4), b = 13.7123(9), c = 9.2669(6) Å, β = 98.7490(10)°, V = 708.68(8) Å3. The unit cell of RbUrOx has the dimensions a = 5.6225(4), b = 13.8339(9), c = 9.3308(6) Å, β = 98.1590(10)°, V = 718.41(8) Å3. The unit cell of CsUrOx has the dimensions a = 5.4688(3), b = 13.5710(8), c = 9.5408(5) Å, β = 97.5830(10)°, V = 701.90(7) Å3. The structures consist of chains of uranyl pentagonal bipyramids connected by oxalate groups and hydroxyl groups, and are isotypic with the compound NH4[(UO2)2(C2O4)2OH] · 2 H2O studied by Artem’eva et al. (2003); all four of these compounds are structurally composed of sheets made by polymerizing the chains of UO2C2O4(H2O) · 2 H2O (Jayadevan and Chackraburtty, 1972; Mikhailov et al., (1999), this being achieved by removing a H atom from an H2O group in the coordination sphere of the uranyl ion to form a hydroxyl vertex that is shared by two uranyl ions. Compensating positive charges are provided by the inclusion of large monovalent cations in channels that run through the sheets; these channels also contain hydrogen-bound H2O groups. The positions of the cations and H2O groups change in relation to the uranyl oxalate sheets and to each other through the series. The infrared spectra of these materials collected at room temperature are also presented and compared with previous work.

Uranyl oxalate hydrates: structures and IR spectra

Abstract The novel compound (UO2)2C2O4(OH)2(H2O)2 (UrOx2A) and the previously studied compound UO2C2O4(H2O)3 (UrOx3) have been synthesized by mild hydrothermal methods. Single crystal diffraction data collected at 125 K using MoK α radiation and a CCD-based area detector were used to solve and refine the crystal structures by full-matrix least-squares techniques to agreement indices (UrOx2A, UrOx3) wR 2 = 0.037, 0.049 for all data, and R1 = 0.015, 0.024 calculated for 1285, 2194 unique reflections respectively. The compound UrOx2A is triclinic, space group P-1, Z = 1, a = 5.5353(4), b = 6.0866(4), c = 7.7686(6) Å, α = 85.6410(10)°, β = 89.7740(10)°, γ = 82.5090(10)°, V = 258.74(3) Å3. The compound UrOx3 is monoclinic, space group P21/c, Z = 4, a = 5.5921(4), b = 16.9931(13), c = 9.3594(7) Å, β = 99.5330(10)°, V = 877.11(11) Å3. The structures consist of chains of uranyl pentagonal bipyramids connected by oxalate groups and, in UrOx2A, hydroxyl groups; UrOx2A is also notable for its high (2 : 1) ratio of uranyl to oxalate groups, higher than any observed in other published structures of uranyl oxalates. The structure determined for UrOx3, previously studied by Jayadevan and Chackraburtty (1972); Mikhailov et al. (1999) is in agreement with the previous results; however, the increased precision of the present low-temperature structure refinement allows for the assignment of H atom positions based on the difference Fourier map of electron density. The infrared spectra of these two materials collected at room temperature are also presented and compared with previous work on uranyl oxalate systems.

Hydrothermal synthesis and crystal structures of new uranyl oxalate hydroxides: α- and β-[(UO 2) 2(C 2O 4)(OH) 2(H 2O) 2] and [(UO 2) 2(C 2O 4)(OH) 2(H 2O) 2]·H 2O

Two modifications of the new uranyl oxalate hydroxide dihydrate [UO 2) 2(C 2O 4)(OH) 2(H 2O) 2] ( 1 and 2) and one form of the new uranyl oxalate hydroxide trihydrate [(UO 2) 2(C 2O 4)(OH) 2(H 2O) 2]·H 2O ( 3) were synthesized by hydrothermal methods and their structures determined from single-crystal X-ray diffraction data. The crystal structures were refined by full-matrix least-squares methods to agreement indices R(w R)=0.0372(0.0842) and 0.0267(0.0671) calculated for 1096 and 1167 unique observed reflections ( I>2 σ( I)), for α ( 1) and β ( 2) forms, respectively and to R(w R)=0.0301(0.0737) calculated for 2471 unique observed reflections ( I>2 σ( I)), for 3. The α-form of the dihydrate is triclinic, space group P 1 ¯ , Z = 1 , a = 6.097 ( 2 ) , b = 5.548 ( 2 ) , c = 7.806 ( 3 ) Å , α = 89.353 ( 5 ) , β = 94.387 ( 5 ) , γ = 97.646 ( 5 ) ° , V = 260.88 ( 15 ) Å 3 , β-form is monoclinic, space group C 2 / c , Z = 4 , a = 12.180 ( 3 ) , b = 8.223 ( 2 ) , c = 10.777 ( 3 ) Å , β = 95.817 ( 4 ) , V = 1073.8 ( 5 ) Å 3 . The trihydrate is monoclinic, space group P 2 1 / c , Z = 4 , a = 5.5095 ( 12 ) , b = 15.195 ( 3 ) , c = 13.398 ( 3 ) Å , β = 93.927 ( 3 ) , V = 1119.0 ( 4 ) Å 3 . In the three structures, the coordination of uranium atom is a pentagonal bipyramid composed of dioxo UO 2 2+ cation perpendicular to five equatorial oxygen atoms belonging to one bidentate oxalate ion, one water molecule and two hydroxyl ions in trans configuration in 2 and in cis configuration in 1 and 3. The UO 7 polyhedra are linked through hydroxyl oxygen atoms to form different structural building units, dimers [U 2O 10] obtained by edge-sharing in 1, chains [UO 6] ∞ and tetramers [U 4O 26] built by corner-sharing in 2 and 3, respectively. These units are further connected by oxalate entities that act as bis-bidentate to form one-dimensional chains in 1 and bi-dimensional network in 2 and 3. These chains or layers are connected in frameworks by hydrogen-bond arrays.

Crystal structure of new uranyl oxalates (NH4)2[UO2(C2O4)2· H2O]·2H2O and (NH4)2-x(N2H5)x[(UO2)2(C2O4)3]·3H2O (x=0 and x=1). Comparison with other uranyl oxalates

SummaryTwo new ammonium uranyl oxalates (NH4)2-[UO2(C2O4)2H2O]·2H2O (1) and (NH4)2[(UO2)2(C2O4)3]· 3H2O (2) and one mixed ammonium hydrazinium uranyl oxalate (NH4)(N2H5)[(UO2)2(C2O4)3]·3H2O (3) have been prepared. The crystal structures of the three compounds have been determined by single-crystal X-ray diffraction. The crystal structures were solved by the Patterson method and Fourier difference techniques, and refined by a least square method on the basis of F2for all unique reflections. Crystallographic data: 1, hexagonal, space group P6122,a=8.143(2) Å,c=36.179(18) Å,Z=6,R1= 0.0268 for 105 parameters with 1223 reflections withI≥ 2σ(I); 2, monoclinic, space groupP21/n,a=8.705(3) Å,b= 19.454(6) Å,c=5.5105(18) Å, β=101.741(5)°,Z=2,R1= 0.0314 for 139 parameters with 2059 reflections withI≥ 2σ(I); 3, monoclinic, space groupP21/n,a=8.958(3) Å,b=19.601(7) Å,c= 11.007(4) Å, β=112.928(5)°,Z=4,R1=0.0363 for 131 parameters with 3346 reflections withI≥ 2σ(I). The crystal structure of 1 contains [UO2(C2O4)2· H2O]2−anions, NH4+cations and water molecules. In the anion, the linear uranyl group is coordinated by two bidentate oxalate anions and one water molecule giving a pentagonal bipyramidal environment for the uranium atom. The structures of 2 and 3 consist of two-dimensional networks built from uranyl and oxalate ions forming hexagonal rings. The oxalate ions are tetradentate, each bridging two uranyl ions which are coordinated by three oxalate groups to give distorted hexagonal bipyramidal environments for the uranium atoms. In 3, the ammonium and hydrazinium ions are ordered in successive layers. The various possible coordinations for the uranyl cation and the great versatility of the oxalate anion are magnificently illustrated in the monovalent ion-uranyl double oxalates series and other structures are expected by the diversification of the synthesis methods and experimental conditions.

Crystal Structure of Uranyl Carboxylates

AbstractUranyl-organic complexation in geologic fluids can have a profound impact upon uranium solubility and transport. Studies of uranyl organometallic crystal structures provide a basis for understanding complexation of the uranyl ion in solution.The crystal structures of several novel uranyl oxalates, synthesized under mild hydrothermal conditions, have been determined. These structures demonstrate new features little seen or not previously known in this chemical system, in particular polymerization into infinite sheets and direct linkage of uranyl polyhedra. Further work on the chemistry of this and other systems of hexavalent uranium and low molecular weight carboxylic acids, especially formic acid, is likely to turn up new insights.Although a hierarchical scheme exists for classifying inorganic uranyl compounds [1], no similar work has been done for organic compounds. Such a hierarchy would have practical benefits, in particular making structural information more accessible and understandable to workers studying related problems such as the environmental transport of hexavalent uranium as dissolved organic complexes. We offer a simple scheme that classifies uranyl oxalate structures by analyzing the long-range structural features and the coordination environments of uranyl ions, which leads to a structural symbol that can be used to easily identify uranyl oxalates with common structural features. This system is equally applicable to other carboxylate complexes with the uranyl ion, and could be extended to apply to any organic complex of the uranyl ion.

Spectrophotometric study of uranyl–oxalate complexation in solution

Uranyl–oxalate complex equilibrium in aqueous solution was studied by UV–Vis spectrophotometry. Due to high spectra correlation, derivative spectrophotometry was also applied during the search for the best chemical model. The absorption spectra of all the complexes were calculated and found in a good agreement with theoretical considerations. Overall protonation constants of oxalate, necessary for accurate calculation of uranyl–oxalate formation constants, were also determined under the same conditions and the following values were obtained log K 1=3.83±0.01; log K 2=4.92±0.01. Stability constants determined for the [(UO 2) p (C 2O 4) q ] 2 p−2 q species were: log β 11=6.31±0.02, log β 12=11.21±0.07, log β 13=13.8±0.04, log β 23=18.5±0.2, log β 25=28.5±0.1 ( I=3.0 M NaClO 4; 25 °C). The equilibrium constants were extrapolated to infinite dilution by applying specific ion interaction theory (SIT) and are the following: log β 11 0=7.41±0.01, log β 12 0=11.80±0.02, log β 13 0=13.96±0.07. Formation of polynuclear [(UO 2) 2(C 2O 4) 3] 2− and [(UO 2) 2(C 2O 4) 5] 6− species was proved and confirmed independently by conductometry and vapor pressure osmometry.

X-ray, Thermal and Infrared Spectroscopic Studies on Potassium, Rubidium and Caesium Uranyl Oxalate Hydrates

M2UO2(C2O4)2⋅nH2O compounds (M=K, Rb and Cs)have been prepared and characterized by chemical and thermal analyses as well as by X-ray diffraction and infrared spectroscopy. X-ray powder data show that the compounds belong to an orthorhombic system. Thermal and infrared studies show that the compounds decompose to M2UO4 through the formation of alkali metal carbonate and UO2 as intermediates. K2UO2(C2O4)2⋅3H2O, and Rb2UO2(C2O4)2⋅2H2O gave K2UO4, Rb2UO4 at 700 and 600°C respectively, while in the case of Cs2UO2(C2O4)2⋅2H2O, the intermediate products of decomposition reacted to yield Cs2U4O13 at 1000°C.

Assessment of the photosynthetically active incident radiation in outdoor photobioreactors using oxalic acid/uranyl sulfate chemical actinometer

A simple actinometric method was evaluated formeasuring the photosynthetically active incidentphoton flux on outdoor photobioreactors. The method isbased on uranyl sulfate catalyzed photodecompositionof oxalic acid in presence of light. The uranyl–oxalate chemical actinometer absorbs radiation ofwavelengths below 535 nm. In the present work, thephotobioreactor wall material did not transmit lightenergy of wavelengths below 350 nm and the effectiveabsorptivity method was used to evaluate the photonflux between 350–535 nm. The standard solar spectrumof the American Society for Testing and Materials(ASTM) was employed for estimating the ratio betweenthe photosynthetically active radiation (400–700 nm)and the solar radiation in the 350–535 nm range. Thisratio (2.21) was taken to be equal to the quotientbetween the photosynthetically active radiation (PAR)and the incident photon flux on the photobioreactor'ssurface (for the solar radiation between 350–535 nm).PAR measurements with 4π spherical and 2πquantum sensors were used to validate the method.

Preparation and characterization of uranyl oxalate powders

Uranyl oxalate powders are prepared by adding 0.5 M oxalic acid solution to the uranyl nitrate (UNH) solutions purified with TBP extraction from dissolution of the Canada originated U 3O 8 commercial concentrate. Uranyl oxalate powders are identified by chemical analysis, TGA/DTG analysis, IR analysis and by single-crystal X-ray diffraction. The effects of the precipitation conditions on the powder properties are determined. A broad particle size distribution is obtained for all precipitation variants. These powders including very fine particles are difficult to filter and are not free flowing. The reactor and mixing type have a considerable effect on the powder properties of the uranyl oxalate powders. It was possible to ameliorate the filtration and the flowability to a certain degree using a conical air agitated reactor. The flowability of these powders is 0.4 g/s with a specific surface area 6.64 m 2/g and an average particle size of 11 μm.

Investigation of the interaction between organic compounds and uranyl ions by raman spectroscopy

Raman spectra of uranyl oxalate, salinate, salicylate, terephthalate and humate have been measured. The O=U=O symmetric stretching frequency of uranyl oxalate, malonate, terephthalate and humate had similar values, suggesting the same number of ligands co-ordinating to central uranium atom, i.e. one carboxyl group is co-ordinated to one uranium atom. The smaller frequency was observed in uranyl salicylate, suggesting the co-ordination of both carboxyl and phenyl groups, under the formation of a 6-membered chelate ring. Ab initio MO calculation supported this idea.