A p and N NMR study of the extraction of uranyl nitrate by Di-2-ethylhexyl phosphoric acid

Low temperature ³¹P and ¹⁵N NMR spectroscopy was used to investigate the species forming in the organic layer following the extraction of uranium from nitric acid solutions with di-2-ethylhexyl phosphoric acid. It was found that uranium is extracted from neutral solutions as the 1:2 complex UO₂A₂ regardless of what anion is present. For dilute nitric acid solutions, the uranium is extracted both as associated and mixed nitrato species. As the nitric acid concentration of the aqueous layer increases, the mixed nitrato complex, UO2(NO₃)A·HA, becomes predominant.     

A 31P and 15N NMR study of the synergistic extraction of uranyl nitrate by tributylphosphate and Di-2-ethylhexyl phosphoric acid

Low temperature ³¹P and ¹⁵N NMR spectroscopy was used to investigate the species forming in the organic layer following the extraction of uranium from nitric acid solutions with the synergistic mixture, TBP-DEHPA. It was found that the complex formed during extraction was a mixed nitrato complex UO₂(NO₃)A·TBP. Although the existence of the complex UO₂A₂·χTBP may be demonstrated in model systems, the complex does not form under actual extraction conditions.     

Synthesis and characterization of uranyl(VI) and thorium(IV) complexes with phosphine oxides. The crystal structure of UO2(NO3)2(NO2-C6H4Ph2PO)2

Uranyl(VI) and thorium(IV) complexes of the type UO₂(NO₃)₂(L¹)₂, UO₂(NO₃)₂(L²)₂, UO₂(CH₃COO)₂L¹, UO₂(CH₃COO)₂L², Th(NO₃)₄(L¹)₂ and Th(NO₃)₄(L²)₂ (L¹ = (2-nitro)phenyl-bis-phenyl phosphine oxide, L² = triferrocenylphosphine oxide) are reported, together with their physico-chemical properties.The crystal structure of UO₂(NO₃)₂(L¹)₂ is also reported. The crystals are monoclinic, space group P2₁/n with a = 17.78(1), b = 13.88(1), c = 17.37(1) Å, β = 114.8(1)° for Z = 4. The uranium atom is 8-coordinated, the uranyl(VI) group being equatorially surrounded by an irregular hexagon of six oxygen atoms from two trans neutral ligands and two nitrato groups.     

Solvent-extraction complex of uranium(VI) with cis,syn, cis-dicyclohexano-18-crown-6

The extraction of U(VI)with dicyclohexano-18-crown-6 (mixed isomers or isomer A) from HCl medium is effective and selective, and can be used for separating and analysing uranium and thorium. However, little is known of the properties of the extraction complex of uranium with crown-ether in organic phase. In this paper we report the preparation, characteristic and structure of the crystalline extraction complex IaUO₂Cl₂HClH₂O, Iabeing isomer A of dicyclohexano-18-crown-6.After extracting uranium(VI) from aqueous hydrochloric acid solution with Ia in 1,2-dichloroethane, the crystalline product of the extraction complex was prepared from the organic phase by diluting with a non-polar solvent at 25 °C. The content of uranium, crown-ether and HCl was determined. The IR spectrum of the crystals shows that the strong hydronium-crown ether/oxygen hydrogen bond absorption is found in the region 2300–2400 cm⁻¹. The chemical shift in the range 9–12 ppm was observed. The ¹H NMR signal of hydronium protons appears at 9.890 ppm. The results of assay correspond to the formula Ia₂·(H₃O⁺)₂·UO₂Cl₄²⁻.Crystal structure of the extraction complex has been determined by X-ray crystallography. Crystals are monoclinic, space group C_2/c (No. 15) a=32.464, b=10.203, c=21.616 Å, β=119.73° and Z=4. In the complex each of the two H₃O⁺ cations is anchored in the crown-ether cavity by three stronger hydrogen bonds (distances approximately 2.65 Å), whereas uranium forms UO₂Cl₄²⁻ with Cl⁻ as counterion about 8 Å away from the H₃O⁺.     

Infrared spectroscopic studies of aqueous solutions of dioxouranium(VI) and its hydrolysed products and of in situ electro-generated dioxouranium(V)

Aqueous solutions of dioxouranium(VI) (pH range 0 to 4) give rise to bands at 954 and 938 cm⁻¹ attributable to the v₃(MO₂) stretching modes of the UO₂²⁺ and (UO₂)₂(OH)_2²⁺ cations, respectively. A shoulder at 916 cm⁻¹ is assigned to the v₃(MO₂) mode of hydrolysed dioxouranium(VI) species of higher nuclearity. Infrared spectro-electrochemical studies using a thin-layer reflection-absorption cell have facilitated the study of the reduction of aqueous solutions of dioxouranium(VI) to yield dioxouranium(V) which may be further reduced to uranium(IV). The electrogeneration of dioxouranium(V) is monitored by following the increase in intensity of a band at 914 cm⁻¹ which is present in the spectra at potentials between −0.2 and −0.8 V. The dioxouranium(V) species is predominantly in the form UO₂⁺, which may be in solution or incorporated into an insoluble phase of uranium oxides which deposit onto the working electrode. The U^VO bond length is estimated to be 1.76 Å, 0.03 Å longer than the U^VIO bond in aqueous solution. The maximum concentration of UO₂⁺able to be achieved is highly dependent on the pH and is optimum at pH 3.4. Changes in the pH of the solution under study can be monitored by infrared spectroscopy during the course of the reduction by determining the relative concentrations of hydrolysed dioxouranium(VI) species.     

Insights into the interactions of cyanobacteria with uranium

Due to various activities associated with nuclear industry, uranium is migrated to aquatic environments like groundwater, ponds or oceans. Uranium forms stable carbonate complexes in the oxic waters of pH 7–10 which results in a high degree of uranium mobility. Microorganisms employ various mechanisms which significantly influence the mobility and the speciation of uranium in aquatic environments. Uranyl bioremediation studies, this far, have generally focussed on low pH conditions and related to adsorption of positively charged UO₂ ²⁺ onto negatively charged microbial surfaces. Sequestration of anionic uranium species, i.e. [UO₂(CO₃) ₂ ^2? ] and [UO₂(CO₃) ₃ ^4? ] onto microbial surfaces has received only scant attention. Marine cyanobacteria are effective metal adsorbents and represent an important sink for metals in aquatic environment. This article addresses the cyanobacterial interactions with toxic metals in general while stressing on uranium. It focusses on the possible mechanisms employed by cyanobacteria to sequester uranium from aqueous solutions above circumneutral pH where negatively charged uranyl carbonate complexes dominate aqueous uranium speciation. The mechanisms demonstrated by cyanobacteria are important components of biogeochemical cycle of uranium and are useful for the development of appropriate strategies, either to recover or remediate uranium from the aquatic environments.     

Uranyl mixed-ligand complex formation in artificial seawater

Abstract

The stability constants of the mixed uranyl-hydroxo-peroxo-carbonato species have been calculated. By incorporating those and including stability constants and corresponding equilibria into the developed model of seawater species distribution enables the dependence of uranyl species on pH to be evaluated. The calculations show that at seawater conditions (pH = 8), 88.3% of total uranyl-ion is in the form UO₂(CO₃)^4-, 11% is in the form UO₂(CO₃)₂(OH)^3-, and 0.5% in the UO₂(CO₃)(OH)₂^2- mixed-ligand complex form, while in the photic layer, 81.2% of uranyl-ion is in the tricarbonate complex, 10.1% in the form UO₂(CO₃)₂(OH₂)^3-, 7% as UO₂(CO₃)₂(OH)^3-, 0.5% as UO₂(CO₃)(OH)₂^4- and 0.5% as UO₂(O₂)₂^2- species.     

Incorporation of 14CO2, 14C-phenylalanine and 14C-cinnamate into soluble and insoluble cinnamic derivatives in Mentha arvensis

With the successful development of methods for the isolation and purification of ethanol-insoluble cinnamic acid esters in mint it became possible to initiate kinetic, isotopic studies on purified, ‘insoluble’ derivatives of caffeic acid, ferulic acid and p-coumaric acid. Pulse-feeding experiments were conducted with ¹⁴CO₂, phenylalanine-U-¹⁴C and cinnamic acid-3-¹⁴C. The ferulic acid derivative exhibited a significant turnover as compared to the other insoluble derivatives which were relatively stable. Time-course tracer studies were performed to compare the turnover of soluble caffeic acid derivatives with ‘insoluble’ forms of caffeic acid. Caffeic acid associated with a macromolecular fraction consistently showed a higher specific activity than either soluble caffeic acid or the caffeic acid associated with a second insoluble derivative.     

Uranium complexes of cyclic O,O-bidentate ligands with the P-N-P backbone

The formation of uranium complexes of novel ligands belonging to phosphorylated 2-oxo-1,2-azaphospholane series, namely 2-ethoxy-1-diethoxyphosphoryl-2-oxo-1,2λ⁵-azaphospholane (1a) and both individual R^∗,R^∗- and R^∗,S^∗-diastereomers of the related 2-oxo-2-phenyl-1,2λ⁵-azaphospholanes 1b,c with different surrounding at the exocyclic phosphorus atom, has been studied. The structures of the complexes of ML composition obtained in the reaction with uranyl nitrate in 1:1 ratio were found to depend on the difference in donor properties of the oxygen atom of endo- and exocyclic phosphoryl groups. The ligand 1a possessing the greater difference, serves as O-monodentate one with metal-oxygen bonding via the endocyclic PO function while both isomers of 1b,c coordinate to uranyl cation in a O,O-bidentate fashion. In solutions the ML complexes reacted with air oxygen to afford (μ₂-peroxo)-bridged uranium complexes [{UO₂(L)NO₃}₂(μ₂-O₂)] which structures were confirmed by X-ray crystallography data.     

Synthesis and crystal structure of bis(tetramethylammonium) aquotetra-fluorodioxouranate(VI) dihydrate, [(CI3)4 N]2[UO2 F4(H2 O)]·2H2O

The title compound has been synthesized and subjected to crystal structure analysis. M_r = 548.50, m.p. 108.1 °C (decom.), orthorhombic, Im2m,a = 7.006(2), b = 8.938(2), c = 13.619(2) Å V = 852.8(3) ų, Z = 2, D_x = 2.136, D_m, (flotation in CCl₄/CH₂I₂) = 2.128 g cm^?3, λ(Mo-Kα) = 0.71069 Å, μ = 90.79 cm^?1, F(000) = 519.89, T = 295 K, final R_F = 0.036 and R_G = 0.044 for 566 observed reflections. The discrete [UO₂F₄(H₂0)]^2? anion has site symmetry m2m, its virtually linear uranyl moiety being surrounded by fluoro and aquo ligands occupying the vertices of a pentagon in the equatorial plane. Watet molecules serve to link the complex anions by hydrogen bonds into layers, between which the organic cations are accommodated.     

14CO2 dark fixation in the halophytic species mesembryanthemum crystallinum

The time course of ¹⁴CO₂ dark fixation was studied in leaves of the facultatively halophytic plant species Mesembryanthemum crystallinum cultivated with and without 400 mM NaCl in the nutrient medium. It is generally known from the literature that plants grown under saline conditions incorporate ¹⁴C predominately into amino acids. By contrast in leaves of M. crystallinum grown on NaCl and exposed to ¹⁴CO₂ in the dark, relatively more radioactivity is incorporated in the organic acids (especially malate) than in amino acids. The data obtained are discussed in relation to the NaCl induced Crassulacean acid metabolism in M. crystallinum reported earlier.     

Equilibrium and structural studies of silicon(IV) and aluminium(III) in aqueous solution. 12. A potentiometric and 29Si-NMR study of silicon tropolonates

Complexation in the H⁺-Si(OH)₄-tropolone (HL) system was studied in 0.6 M (Na)Cl medium at 25° C. Speciation and formation constants were determined from potentiometric (glass electrode) and ²⁹Si-NMR data. Experimental data cover the ranges 1.5 ? - log[H⁺] ? 8.4, 0.002 ? B ? 0.012 M, and 0 ? C ? 0.060 M (B and C stand for the total concentration of Si and tropolone, respectively). In acid solutions (-log[H⁺] ? 3) a hexacoordinated cationic complex, SiL₃⁺, is formed with log K(Si(OH)₄ + 3HL + H⁺ XXX SiL₃⁺ + 4H₂O) = 7.08 ± 0.03. Furthermore, the formation of a disilicic acid was established from ²⁹Si-NMR data. The dimerization constant of Si(OH)₄ was found to be 10 exp (1.2 ± 0.1). In model calculations the solubility of quartz and amorphous SiO₂ in the presence of tropolone is demonstrated. Data were analyzed using the least-squares computer program LETAGROPVRID.     

Dioxouranium complexes as ligand. Synthesis and characterization of sandwich-type polyoxometalates [X2W18(UO2)2{(H2O)3M}2O68] (X = As and P) (M = Co, Cu, Mn, Ni and Zn)

The title complexes are synthesized by the reaction of an unusual ligand of [K₂P₂W₁₈(UO₂)₂O₆₈]¹²⁻ (1) and [KAs₂W₁₈(UO₂)₂O₆₈]¹³⁻ (2) with divalent metal ions of Co^II, Cu^II, Mn^II, Ni^II and Zn^II in 1:2 mole ratio and are characterized by elemental analysis, IR, ³¹P NMR, UV-Vis spectroscopy, TGA, and single crystal structure analysis. Crystals of [P₂W₁₈(UO₂)₂{(H₂O)₃Co}₂O₆₈]¹⁰⁻ (1a) and [As₂W₁₈(UO₂)₂{(H₂O)₃Cu}₂O₆₈]¹⁰⁻ (2b) are orthorhombic space group Cmca. Both 1a and 2b have structures in which two [M(H₂O)₃] (M = Co^II, Cu^II) and two UO₂ groups are sandwiched between two symmetry equivalent (XW₉) (X = P, As) units in a virtual C_i symmetry. In solution, 1a and [P₂W₁₈(UO₂)₂{(H₂O)₃Zn}₂O₆₈]¹⁰⁻ (1d) give two-line P NMR spectra that are consistent with a C_s symmetry structures so, are not consistent with the solid-state structures. The sodium salts of them give one-line P NMR spectra and are consistent with the C_i symmetry of solid-state structures. The uranium atoms have pentagonal-bipyramidal coordination, achieved by three equatorial bonds to the one XW₉ and two bonds to the other. The M atoms have octahedral or square pyramidal coordination, but only one bond to the one XW₉ and one bond to the other.     

Multinuclear magnetic resonance studies of the hydrolyzed and aquated species of the antitumor complexes cis-Pt(cyclobutylamine)2X2 and cis-Pt(NH3)(cyclobutylamine)X2 and antitumor testing of mixed-amine Pt(II) compounds

The aquated and hydrolyzed species formed from the complexes cis-Pt(cba)₂I₂ and cis-Pt(NH₃)(cba)I₂ (cba = cyclobutylamine) were studied by multinuclear (¹⁹⁵Pt, ¹⁵N and ¹H) magnetic resonance spectroscopy. The iodo ligands were removed with AgNO₃. In acidic medium, the aqueous product consists of the diaqua and the aqua-nitrato cations, although some monohydroxo-bridged dimers are formed after several hours, especially for the mixed-ligand compound. In basic medium, the main species are the dihydroxo compounds. At neutral pD, several species exist in solution, especially with the mixed-amine system, which contained also a small quantity of the symmetric cis-Pt(cba)₂ complexes. Difficulties were encountered because of the insolubility of several oligomeric species, contrary to the cis-Pt(NH₃)₂ system, probably due to the greater lipophilicity of cba compared to NH₃. Monohydroxo-bridged dimers are formed in large quantities and the stereochemistry of the mixed-amine species was determined by ¹⁵N NMR spectroscopy. For the latter system, the cyclic dihydroxo-bridged dimers are the predominant species at neutral pD after a few hours. After an extended period of time, most of the oligomers precipitate, leaving the more soluble monohydroxo-bridged dimers as the major species in solution. The preliminary antitumor testing results on several dichloro mixed-ligand compounds are listed. The results on further testing on the most active compound cis-Pt(NH₃)(cba)Cl₂ are also included.     

Kinetics of luminescence in the 10−6–10−4-s range in Chlorella

The decay of luminescence in the 6–600-μs range following a microsecond flash has been studied in Chlorella. The decay is highly polyphasic; three kinetic components are outlined, in confirmation of the results of K. L. Zankel (1971, Biochim. Biophys. Acta 245, 373–385).Extrapolation of the decay to zero dark time suggests that a unique metastable species C^?₊, resulting from photochemical charge separation in the System II reaction center, is the substrate of the recombination reaction which gives rise to luminescence.The fast (5–10 μs) and medium (50–70 μs) phases of the decay denote different stabilization steps, preceding relaxation of the centers by electron and proton transduction to the photosynthetic chain.NH₂OH specifically inhibits the fast phase and enhances the medium phase. This effect is explained by assuming that the fast phase results from electron transfer from the water splitting system Z to the oxidized primary donor Y.3-(3,4-Dichlorophenyl)-1,1-dimethylurea (DCMU), in the presence of NH₂OH elicits another fast phase. It is believed that DCMU affords a parasitic stabilization of C^?₊ by forming a complex with Q^?.     

13C-NMR study of CO2-fixation during the heterotrophic growth in Chlorobium thiosulfatophilum

The functioning of the biosynthetic pathways of the amino acids alanine, glycine, aspartic acid, glutamic acid and tyrosine, and of nucleosides in the photosynthetic bacterium Chlorobium thiosulfatophilum during heterotrophic growth on ¹³CO₂ and unlabelled acetate was investigated using ¹³C-NMR as the method for determination of the labelling patterns of the separated substances. On the basis of the analysis of the multiplet structure of the spectra of the tightly-coupled systems, the conclusion was drawn that the Calvin cycle does not function in the experimental conditions used. The labelling pattern of the glutamic acid indicated that about 30% of the amino acid molecules were synthesized through the reactions of the reductive carboxylic acid cycle, the remaining 70% being derived from oxaloacetate and exogenous acetate through the reactions of the Krebs cycle. Labelling patterns of the nucleosides were in agreement with their known biosynthetic pathways.     

Stimulatory effect of calcium chelators on Na+-Ca2+ exchange in cardiac sarcolemmal vesicles

The calcium chelators EGTA, EDTA and cyclohexanediamine tetraacetic acid (CDTA) enhance initial rates of Na_i⁺-dependent Ca²⁺ uptake by cardiac sarcolemmal vesicles. The affinity of the exchanger for calcium is increased in the presence of the chelators to an extent dependent on chelator concentration and on the range of free calcium concentrations over which the phenomenon is measured. For free Ca²⁺ in the range of 4 μM or less, the apparent K_m is lowered to approximately 1 μM. The Ca-chelator complex appears to be the species which causes stimulation. The effect is not due to sequestration of contaminating heavy metal ions in the sarcolemmal membrane preparations or the solutions used in experiments. Caution is suggested in the use of EGTA or EDTA as calcium buffers when measuring calcium dependence of phenomena involving calcium binding and transport, because the added chelator may alter the properties of the system.     

43Ca NMR studies of Ca2+-Tetrahymena calmodulin complexes

⁴³Ca NMR spectra of Ca²⁺-Tetrahymena calmodulin(Tet. CaM.) complexes have been observed under various conditions. Off-rate of Ca²⁺ from Tet. CaM. is estimated to be approx. 2.7 × 10³ s^?1 under a certain assumption. Relaxation rates of ⁴³Ca NMR of Ca²⁺-Tet. CaM. are remarkably increased(by one order in magnitude) by adding trifluoperazine(TFP), a potent calmodulin antagonist. Relaxation parameters estimated suggest that Ca²⁺ mobility is reduced by the TFP binding. A stoichiometry of TFP is two moles per Tet. CaM. molecule. The relaxation rates of ⁴³Ca NMR signals are increased by adding excessive Mg²⁺ to the Ca²⁺-Tet. CaM. solutions. The addition of Mg²⁺ to the Ca²⁺-Tet. CaM. complex decreases apparent pKa value of the complex as well.     

FT-IR and 1H NMR spectroscopic evidence of sugar ring conformational change in NH4GpG on complexation to form cis-[Pt(NH3)2(GpG)]+

The conformational change of the ribose ring in NH₄GpG and cis-[Pt(NH₃)₂(GpG)]⁺ was confirmed by FT-IR spectroscopic evidence as being C2′-endo, C3′-endo, anti, gg sugar ring pucker in the solid state. These results were compared with ¹H NMR spectral data in aqueous solution. The FT-IR spectrum of NH₄GpG shows marker bands at 802 cm^?1 and 797 cm^?1 which are assigned to the C3′-endo, anti, gg sugar-phosphate vibrations of ribose (?pG) and ribose (Gp?), respectively. The FT-IR spectrum of cis-[Pt(NH₃)₂(GpG)]⁺ (with N7N7 chelation in the GpG sequence) shows a marker band at 800 cm^?1 which is assigned to the C3′-endo, and a new shoulder band at 820 cm^?1 related to a C2′-endo ring pucker. The ribose conformation of (?pG) moiety in NH₄-GpG, C3′-endo, anti, gg changes into C2′-endo, anti, gg when a platinum atom is chelated to N7N7 in the GpG sequence.     

Electrokinetic-enhanced phytoremediation of uranium-contaminated soil using sunflower and Indian mustard

Abstract

Electrokinetic-enhanced phytoremediation is an effective technology to decontaminate heavy metal contaminated soil. In this study, we examined the effects of electrokinetic treatments on plant uptake and bioaccumulation of U from soils with various U sources. Redistribution of uranium in soils as affected by planting and electrokinetic treatments was investigated. The soil was spiked with 100?mg kg^–1 UO₂, UO₃, and UO₂(NO₃)₂. After sunflower and Indian mustard grew for 60 days, 1 voltage of direct-current was applied across the soils for 9 days. The results indicated that U uptake in both plants were significantly enhanced by electrokinetic treatments from soil with UO₃ and UO₂(NO₃)₂. U was more accumulated in roots than in shoots. Electrokinetic treatments were effective on lowering soil pH near the anode region. Overall, uranium (U) removal efficiency reached 3.4–4.3% from soils with UO₃ and uranyl with both plants while that from soil with UO₂ was 0.7–0.8%. Electrokinetic remediation treatment significantly enhanced the U removal efficiency (5–6%) from soils with UO₃ and uranyl but it was 0.8–1.3% from soil with UO₂, indicating significant effects of U species and electrokinetic enhancement on U bioaccumulation. This study implies the potential feasibility of electrokinetic-enhanced phytoremediation of U soils with sunflower and Indian mustard.