Showing papers on "Uranyl published in 1978"

The response of cell walls of Bacillus subtilis to metals and to electron-microscopic stains

Abstract: Purified cell walls of Bacillus subtilis were subjected to solutions of 40 independent metals and the metal uptake, the electron-scattering power of thin sections, and the type of staining response evaluated. This was repeated for six typical electron-microscopic stains (uranyl acetate, uranyl magnesium acetate, osmium tetroxide, Os-meth, osmium-dimethylethylenediamine, and ruthenium red) and one new staining reagent (a potassium platinum chloride - dimethylsulfoxide complex) whose specificity is for amine functions. The reaction of select metals can be specific in terms of both uptake and staining response. Of the metals studied most transition elements had a high affinity for the wall fabric and some (i.e., Sc III, most lanthanides, UIV, ZrIV,HfIV, Fe III, Pd II, Ru III, and In III) may be suitable as contrasting agents for electron microscopy. Furthermore, when the thickness of metal-reacted walls was compared to freeze-each and ultracryotomy data, statistical-dimensional differences were commonly seen, which indicates that wall ultrastructure can be profoundly affected by the type of metal and (or) staining reagent.

Relativistic Xα–scattered‐wave calculations for the uranyl ion

Abstract: Relativistic Xα–scattered‐wave molecular orbital calculations have been carried out on the uranyl ion UO22+. The calculated orbital eigenvalues are in good agreement with the results of a recent x‐ray photoelectron spectroscopy study of uranyl compounds. An interpretation of the optical spectrum of the uranyl ion in terms of a Hund’s case (c) (ω, ω) coupling scheme is given.

Crystal and molecular structure of dichlorodioxobis(triphenylphosphine oxide)uranium(VI)

Abstract: The crystal structure of [UO2Cl2(PPh3O2)] has been determined from three-dimensional X-ray diffraction data. Crystals are triclinic, space group P, with a= 10.0101(6), b= 10.2589(9), c= 9.2347(8)A, α= 110.093(6), β= 92.129(6), and γ= 78.384(6)°, and Z= 1. The structure has been solved by the heavy-atom method from counter data, and refined by least squares to a final R of 0.054. The co-ordination polyhedron around uranium is a distorted octahedron, with a linear uranyl group (U–O 1.764 A) perpendicular to a plane in which the two chloride and two oxide ions trans to each other occupy the corners of a rectangle (U–O 2.300; U–Cl 2.645 A).

Crystal and molecular structure of trimeric bis(1,1,1,5,5,5-hexafluoropentane-2,4-dionato)dioxouranium(VI)

Abstract: The deep red crystals of the title compound (UO/sub 2/(hfa)/sub 2/)/sub 3/ are monoclinic, space group P2/sub 1//c, with a = 16.526 (11) A, b = 15.470 (11) A, c = 22.277 (15) A,..beta.. = 103.00(1)/sup 0/, Z = 4, V = 5549 A/sup 3/, and d/sub calcd/ = 2.457 g/cm/sup 3/. X-ray diffraction data were collected for 3239 independent reflections to 2theta = 36/sup 0/ on an automatic x-ray diffractometer with Mo K..cap alpha.. radiation, and the structure was refined to R = 0.095. The three uranium atoms in the asymmetric unit form an equilateral triangle with edges 4.2 A in length and are bridged by half the uranyl oxygen atoms; the other uranyl oxygen atoms are terminal. The six hfa molecules in the asymmetric unit are bidentate and complete pentagonal-bipyramidal coordination about U(1), U(2), and U(3). The crystal is thus an assembly of (UO/sub 2/(hfa)/sub 2/)/sub 3/ trimeric molecules. The CF/sub 3/ groups are disordered. This compound is unique in uranyl structural chemistry, being the first example of a uranyl trimer. 3 figures, 5 tables.

Uranyl selenite and uranyl tellurite

Abstract: UOzSeO 3, monoclinic, P2~/m, a = 5.408 (2), b = 9.278 (1), c = 4.2545 ( 1 ) / ~ , f l = 93.45 (10) °, V = 213.1 /k 3, Z = 2, D x = 6-19 g cm -3. UO2TeO3, orthorhombic, Pbcm, a = 5.363 (3), b = 10.161 (4), c = 7.862 (3)/k, Z = 4, D x = 6.91, D m = 6.91 (4) g cm -3. The structure of uranyl selenite was solved from neutron powder data; that of uranyl tenurite was redetermined from Mo Ka single-crystal data. Both structures are identical in a topological sense, but the coordination polyhedra of the heavy atoms are dissimilar. Introduction. Polycrystalline UO2SeO 3 was obtained during an investigation of uranyl selenates and selenites (Brandenburg & Cordfunke, 1978). Its structure was determined to obtain a better understanding of the thermochemical measurements of both this compound and uranyl tellurite. A sample was prepared by heating a mixture of amorphous UO 3 with a slight excess of SeO 2 in a sealed and evacuated tube overnight at 360 °C. After grinding in a dry box the product was again given the same treatment. Excess SeO 2 was removed by sublimation into the cooled empty part of the sample capsule. Analysis gave U 60.22% (59.96% calculated), Se 19.6% (19-89% calculated). The sample was of moderate crystallinity. X-ray powder pattern lines (Cu Ka, Guinier camera) were indexed with the computer program of Visser (1969). Errors in the cell constants quoted above represent the spread between various samples. In addition to the film data, step-scanned Cu Ka X-ray diffractometer data were obtained. Neutron powder data were collected at the Petten H F R with slits ~q = ~3 = 10' in the range 0 < (sin 0)/2 < 0 . 3 6 / t -1. The sample was contained in a thin-walled vanadium can, ~ = 10 mm. Neutrons with 2 = 2.571 ,~ were used. Space group P21 or P2~/m was indicated by the systematic absences 0k0 with k = 2n + 1. All X-ray lines with k = 2n were found to be systematically stronger than those with k = 2n + 1. From this it follows that the U atoms must be at or close to the screw axis. A 35-term Patterson function was computed from the X-ray diffractometer data, separated into single reflections as far as possible. From this the Se atom was found to be at 0.66, 0.25, 0.37 relative to the U atom. No further use was made of the X-ray data. The rest of the structure determination and refinement was based on the neutron data. Least-squares refinement with Rietveld's (1969) profile fitting program was attempted in P2~ starting from a model based on seven-coordination of the U atom by O atoms. As this was unsuccessful the selenite O atoms were introduced in a refinement in which constraints maintained the known selenite dimensions. It then became clear that the space group is P2~/m with U at a centre of symmetry and hence Se in the mirror plane. The U atom is surrounded by eight O atoms at the corners of a hexagonal bipyramid. Final unconstrained refinement led to the coordinates of Table 1. The final R as defined by Rietveld (1969) is 0.099. Table 2 presents the main bond distances and angles. In Fig. 1 the observed and calculated pattern is shown. It is seen that the 002 peak at 20 = 74.3 ° is poorly represented by the calculation. This is mainly due to an anomalous peak width in the observed pattern. In Fig. 2 the structure is depicted in projection along a. In Table 3 the coordinates of UOETeO 3 as determined by Meunier & Galy (1973) are given (after transformation by 0 , -1 ,0 ,0 ; 1,0,0,0; 0,0,1,1⁄4). As also shown in Table 3, the atoms are found to be almost at the positions required by space group Pbcm. From the Table 1. Coordinates and thermal parameters for

Spectroscopic studies on the binding of uranium by brown coal

Abstract: Brown coal removes uranium from sea water where it is present mainly as [UO2(CO3)3]4−. The adsorption and binding of uranium is studied by infrared spectroscopy. The spectra of the coal-uranium adducts still exhibit the asymmetric stretching vibration of the uranyl ion, but no CO32− frequencies, suggesting that uranium is retained as UO22+. The coal humic acids are shown to be responsible for the decomposition of the carbonato complex. The subsequent uptake of uranium is not a pure cation exchange process since the shift of the asymmetric uranyl stretching frequency from 950 cm−1 (hydrated UO22+) to 890 cm−1 points to complexation of UO22+ by carboxylate groups which act as bidentate ligands.

Metal-catalyzed Organic Photoreactions. The Photooxidation of Olefins in the Presence of Uranyl Acetate

Abstract: The photooxidation of olefins in pyridine in the presence of uranyl acetate afforded β-hiydroxy hydroperoxides. It was confirmed by spectroscopic studies and isotope-incorporation experiments that (1) the stereochemistry of the hydroxyl and hydroperoxyl groups in the β-hiydroxy hydroperoxides was trans, (2) the hydroxyl group was added to the less substituted carbon of the double bond, and (3) the oxygen atom in the hydroxyl group originated mainly from the water molecule, while the oxygen atoms in the hydroperoxyl group originated mainly from molecular oxygen. From these results, we proposed a reaction scheme of: (i) the formation of the hydroxyl radical from water by uranyl acetate-catalyzed photolysis, (ii) the addition of the hydroxyl radical to the double bond, (iii) the combination of the resulted radical with molecular oxygen, and (iv) the hydrogen abstraction of the peroxyl radical to give the product. The scheme was further supported by the photoreaction of 2-methyl-2-butene with bromotrichlorome...

Uranium recovery from wet process phosphoric acid

Abstract: Improvement in the process for recovering uranium from wet-process phosphoric acid solution derived from the acidulation of uraniferous phosphate ores by the use of two ion exchange liquid-liquid solvent extraction circuits in which in the first circuit (a) the uranium is reduced to the uranous form; (b) the uranous uranium is recovered by liquid-liquid solvent extraction using a mixture of mono- and di-(alkyl-phenyl) esters of orthophosphoric acid as the ion exchange agent; and (c) the uranium oxidatively stripped from the agent with phosphoric acid containing an oxidizing agent to convert uranous to uranyl ions, and in the second circuit (d) recovering the uranyl uranium from the strip solution by liquid-liquid solvent extraction using di(2-ethylhexyl)phosphoric acid in the presence of trioctylphosphine oxide as a synergist; (e) scrubbing the uranium loaded agent with water; (f) stripping the loaded agent with ammonium carbonate, and (g) calcining the formed ammonium uranyl carbonate to uranium oxide, the improvement comprising: (1) removing the organics from the raffinate of step (b) before recycling the raffinate to the wet-process plant, and returning the recovered organics to the circuit to substantially maintain the required balance between the mono and disubstituted esters; (2) using hydogren peroxide as the oxidizing agent in step (c); (3) using an alkali metal carbonate as the stripping agent in step (f) following by acidification of the strip solution with sulfuric acid; (4) using some of the acidified strip solution as the scrubbing agent in step (e) to remove phosphorus and other impurities; and (5) regenerating the alkali metal loaded agent from step (f) before recycling it to the second circuit.

Preparation and crystal structure of a nickel (II)-Uranyl(VI) binuclear chelate

Abstract: The structure of the heterobinuclear complex of Ni2+ and [U022]2+ with the tetraanionic ligand derived from the condensation of 1,2-diaminoethane with o-acetoacetylphenol has been determined from diffractometer data and refined to R = 7.2%. The crystals are monoclinic, P21 /a, with α = 20.65(2), b = 8.58(1), c = 14.68(2) A and β = 97.78(5); Z = 4. The ligand employed has two different coordination sets of atoms, N2O2 and O2O2, two oxygen atoms being common to both donor sets. In the complex the nickel ion, which is four coordinate but not square planar, is retained in the inner N2O2 chamber, whilst the uranyl ion is incorporated in the outer O2O2 chamber. A molecule of solvent is retained to preserve the preferred seven coordination of uranium.

Methods for removing uranyl acetate precipitate from ultrathin sections

Abstract: Precipitate resulting from en bloc staining with uranyl acetate was removed by treating sections with 15% oxalic acid in 50% methanol for 30 minutes at 40 C. Precipitate resulting from poststaining sections with hot uranyl acetate was removed by rinsing sections in 0.25-0.50% aqueous oxalic acid for 10-15 seconds at room temperature. Rinsing sections for longer than 30 seconds removed uranyl precipitate and also destained the sections. These procedures did not damage the embedding medium or cellular detail.

Uranyl luminescence quenching. An experiment in photochemistry and kinetics

Abstract: This article shows that the quenching of uranyl luminescence by alcohols provides a convenient experiment in this area.

Nicotinic Acid Complexes with Uranyl Salts

Abstract: The potentially bidentate ligand, nicotinic acid, forms 2 : 1 complexes with uranyl chloride, sulphate, nitrate and acetate which have been characterized by i.r. spectral measurements down to 200 cm−1 in the solid state. These studies indicate conclusively that nicotinic acid coordinates onlyvia its pyridine ring nitrogen in all cases. The uranyl chloride arid sulphate complexes are monomeric hexacoordinated structures, while the nitrate and acetate complexes are octacoordinate around uranium.