Coordination chemistry of 2,2'-biphenylenedithiophosphinate and diphenyldithiophosphinate with U, Np, and Pu.

New members of the dithiophosphinic acid family of potential actinide extractants were prepared: heterocyclic 2,2'-biphenylenedithiophosphinic acids of stoichiometry HS2P(R2C12H6) (R = H or (t)Bu). The time- and atom-efficient syntheses afforded multigram quantities of pure HS2P(R2C12H6) in reasonable yields (∼60%). These compounds differed from other diaryldithiophosphinic acid extractants in that the two aryl groups were connected to one another at the ortho positions to form a 5-membered dibenzophosphole ring.

Structural and spectroscopic characterization of plutonyl(VI) nitrate under acidic conditions.

The plutonyl(VI) dinitrate complex [PuO(2)(NO(3))(2)(H(2)O)(2)]·H(2)O (1) has been structurally characterized by single-crystal X-ray diffraction and spectroscopically characterized by solid-state vis-NIR and Raman spectroscopies. Aqueous solution spectroscopic studies indicate only weak plutonyl(VI) nitrate complexation, with the mononitrate complex dominating and negligible dinitrate formation, even in concentrated nitric acid.

Plutonium(V/VI) Reduction by the Metal-Reducing Bacteria Geobacter metallireducens GS-15 and Shewanella oneidensis MR-1.

We examined the ability of the metal-reducing bacteria Geobacter metallireducens GS-15 and Shewanella oneidensis MR-1 to reduce Pu(VI) and Pu(V). Cell suspensions of both bacteria reduced oxidized Pu [a mixture of Pu(VI) and Pu(V)] to Pu(IV). The rate of plutonium reduction was similar to the rate of U(VI) reduction obtained under similar conditions for each bacteria.

Low-valent molecular plutonium halide complexes.

Treatment of plutonium metal with 1.5 equiv of bromine in tetrahydrofuran (thf) led to isolation of PuBr3(thf)4 (1), which is a new versatile synthon for exploration of non-aqueous Pu(III) chemistry. Adventitious water in the system resulted in structural characterization of the eight-coordinate complex [PuBr2(H2O)6][Br] (2).

Experimental and theoretical comparison of actinide and lanthanide bonding in M[N(EPR(2))(2)](3) complexes (M = U, Pu, La, Ce; E = S, Se, Te; R = Ph, iPr, H).

Treatment of M[N(SiMe3)2]3 (M = U, Pu (An); La, Ce (Ln)) with NH(EPPh2)2 and NH(EPiPr2)2 (E = S, Se), afforded the neutral complexes M[N(EPR2)2]3 (R = Ph, iPr). Tellurium donor complexes were synthesized by treatment of MI3(sol)4 (M = U, Pu; sol = py and M = La, Ce; sol = thf) with Na(tmeda)[N(TePiPr2)2]. The complexes have been structurally and spectroscopically characterized with concomitant computational modeling through density functional theory (DFT) calculations.

Structural characterization of Pu[N(SiMe(3))(2)](3), a synthetically useful nonaqueous plutonium(III) precursor.

A rare, and synthetically versatile, nonaqueous plutonium complex, Pu[N(SiMe3)2]3 (1), has been structurally characterized by single-crystal X-ray diffraction for the first time and reveals significantly shorter agostic interactions compared to the cerium(III) analogue, indicating possible covalency differences.

Plutonium(IV) reduction by the metal-reducing bacteria Geobacter metallireducens GS15 and Shewanella oneidensis MR1.

The bacterial reduction of actinides has been suggested as a possible remedial strategy for actinide-contaminated environments, and the bacterial reduction of Pu(VI/V) has the potential to produce highly insoluble Pu(IV) solid phases. However, the behavior of plutonium with regard to bacterial reduction is more complex than for other actinides because it is possible for Pu(IV) to be further reduced to Pu(III), which is relatively more soluble than Pu(IV). This work investigates the ability of the metal-reducing bacteria Geobacter metallireducens GS15 and Shewanella oneidensis MR1 to enzymatically reduce freshly precipitated amorphous Pu(IV) (OH)(4) [Pu(IV)(OH)(4(am))] and soluble Pu(IV)(EDTA).

Biological reduction of Np(V) and Np(V) citrate by metal-reducing bacteria.

Oxidized actinide species are often more mobile than reduced forms. Bioremediation strategies have been developed to exploit this chemistry and stabilize actinides in subsurface environments. We investigated the ability of metal-reducing bacteria Geobacter metallireducens and Shewanella oneidensis to enzymatically reduce Np(V) and Np(V) citrate, as well as the toxicity of Np(V) to these organisms.

An entry route into non-aqueous plutonyl coordination chemistry.

The Pu(VI) molecular complex, [PuO(2)Cl(2)(thf)(2)]2, is prepared by addition of a HCl/Et(2)O solution to a suspension of PuO(2)CO(3) in thf, yielding the first example of a precursor suitable for investigation of the non-aqueous chemistry of the plutonyl dioxo cation under inert atmospheric conditions.

Redox behavior of cyclo[6]pyrrole in the formation of a uranyl complex.

A uranyl complex, the first metal complex to be formed from the cyclo[n]pyrrole series of expanded porphyrins, is formed when cyclo[6]pyrrole is treated with the uranyl cation under aerobic conditions. Spectroscopic, spectroelectrochemical, and electron spin resonance data of this species are consistent with the ligand in the complex being oxidized to an antiaromatic form.

Purification and characterization of rhodobactin: a mixed ligand siderophore from Rhodococcus rhodochrous strain OFS.

The siderophore produced by Rhodococcus rhodochrous strain OFS, rhodobactin, was isolated from iron-deficient cultures and purified by a combination of XAD-7 absorptive/partition resin column and semi-preparative HPLC. The siderophore structure was characterized using 1D and 2D (1)H, (13)C and (15)N NMR techniques (DQFCOSY, TOCSY, NOESY, HSQC and LR-HSQC) and was confirmed using ESI-MS and MS/MS experiments. The structural characterization revealed that the siderophore, rhodobactin, is a mixed ligand hexadentate siderophore with two catecholate and one hydroxamate moieties for iron chelation.

Complexation of Pu(IV) with the natural siderophore desferrioxamine B and the redox properties of Pu(IV)(siderophore) complexes.

The bioavailability and mobility of Pu species can be profoundly affected by siderophores and other oxygen-rich organic ligands. Pu(IV)(siderophore) complexes are generally soluble and may constitute with other soluble organo-Pu(IV) complexes the main fraction of soluble Pu(IV) in the environment. In order to understand the impact of siderophores on the behavior of Pu species, it is important to characterize the formation and redox behavior of Pu(siderophore) complexes.

U(IV) chalcogenolates synthesized via oxidation of uranium metal by dichalcogenides.

Treatment of uranium metal with dichalcogenides in the presence of a catalytic amount of iodine in pyridine affords molecular U(IV) chalcogenolates that do not require stabilizing ancillary ligands. Oxidation of U(0) by PhEEPh yields monomeric seven-coordinate U(EPh)4(py)3 (E = S(1), Se(2)). The dimeric eight-coordinate complexes [U(EPh)2(mu2-EPh)2(CH3CN)2]2 (E = S(3), Se(4)) are obtained by crystallization from solutions of 1 and 2 dissolved in acetonitrile.

Iron(III) coordination properties of a pyoverdin siderophore produced by Pseudomonas putida ATCC 33015.

The iron complexation of a fluorescent green pyoverdin siderophore produced by the environmental bacterium Pseudomonas putida was characterized by solution thermodynamic methods. Pyoverdin binds iron through three bidentate chelate groups, a catecholate, a hydroxamate, and an alpha-hydroxycarboxylic acid. The deprotonation constants of the free pyoverdin and Fe(III)-pyoverdin complex were determined through a series of potentiometric and spectrophotometric experiments.

Enhanced exopolymer production and chromium stabilization in Pseudomonas putida unsaturated biofilms.

Chromium-contaminated soils threaten surface and groundwater quality at many industrial sites. In vadose zones, indigenous bacteria can reduce Cr(VI) to Cr(III), but the subsequent fate of Cr(III) and the roles of bacterial biofilms are relatively unknown. To investigate, we cultured Pseudomonas putida, a model organism for vadose zone bioremediation, as unsaturated biofilms on membranes overlaying iron-deficient solid media either containing molecular dichromate from potassium dichromate (Cr-only treatment) or with deposits of solid, dichromate-coated hematite (Fe+Cr treatment) to simulate vadose zone conditions.

Pu(VI) hydrolysis: further evidence for a dimeric plutonyl hydroxide and contrasts with U(VI) chemistry.

A significant fraction of plutonium that is soluble in environmental waters and other aqueous solutions can be present as complexes of plutonyl, PuO2(2+). Few thermodynamic data are available for this ion, representing a problematic gap in plutonium chemistry and in the forecasting of radionuclide behavior under contamination and nuclear repository conditions. To address this need and more accurately determine the stoichiometry and stability of the basic hydrolytic products, we completed complimentary potentiometric and spectrophotometric studies of plutonium(VI) hydrolysis over the concentration range of 10(-2) to 10(-5) M Pu(VI).

Uranium(III)/(IV) nitrile adducts including UI4(N[triple bond]CPh)4, a synthetically useful uranium(IV) complex.

The synthesis of complexes used to elucidate an understanding of fundamental An(III) and An(IV) coordination chemistry requires the development of suitable organic-soluble precursors. The reaction of oxide-free uranium metal turnings with 1.3 equivalents of elemental iodine in acetonitrile provided the U(III)/U(IV) complex salt, [U(N[triple bond]CMe)9][UI6][I] (1), in which the U(III) cation is surrounded by nine acetonitrile molecules in a tricapped trigonal prismatic arrangement, a [UI6]2- counterion, and a noncoordinating iodide.

Homoleptic uranium(III) imidodiphosphinochalcogenides including the first structurally characterised molecular trivalent actinide-Se bond.

Preparation of U[N(EPPh2)2]3 (E = S or Se) by treating U[N(SiMe3)2]3 with three equivalents of NH(EPPh2)2 is described together with presentation of a hitherto unreported molecular crystal structure containing An(III)-Se bonds (An = actinide).

Actinide and metal toxicity to prospective bioremediation bacteria.

Bacteria may be beneficial for alleviating actinide contaminant migration through processes such as bioaccumulation or metal reduction. However, sites with radioactive contamination often contain multiple additional contaminants, including metals and organic chelators. Bacteria-based bioremediation requires that the microorganism functions in the presence of the target contaminant, as well as other contaminants.

Local and nanoscale structure and speciation in the PuO2+x-y(OH)2y.zH2O system.

Pu L(3) X-ray absorption fine structure spectra from 24 samples of PuO(2+x) (and two related Pu-substituted oxides), prepared by a variety of methods, demonstrate that (1) although the Pu sublattice remains the ordered part of the Pu distribution, the nearest-neighbor O atoms even at x = 0 are found in a multisite distribution with Pu-O distances consistent with the stable incorporation of OH(-) (and possibly H(2)O and H(+)) into the PuO(2) lattice; (2) the excess O from oxidation is found at Pu-O distances <1.9 A, consistent with the multiply bound "oxo"-type ligands found in molecular complexes of Pu(V) and Pu(VI); (3) the Pu associated with these oxo groups is most likely Pu(V), so that the excess O probably occurs as PuO(2)(+) moieties that are aperiodically distributed through the lattice; and (4) the collective interactions between these defect sites most likely cause them to cluster so as give nanoscale heterogeneity in the form of domains that may have unusual reactivity, observed as sequential oxidation by H(2)O at ambient conditions. The most accurate description of PuO(2) is therefore actually PuO(2+x-y)(OH)(2)(y).

EDTA and mixed-ligand complexes of tetravalent and trivalent plutonium.

EDTA forms stable complexes with plutonium that are integral to nuclear material processing, radionuclide decontamination, and the potentially enhanced transport of environmental contamination. To characterize the aqueous Pu(4+/3+)EDTA species formed under the wide range of conditions of these processes, potentiometry, spectrophotometry, and cyclic voltammetry were used to measure solution equilibria. The results reveal new EDTA and mixed-ligand complexes and provide more accurate stability constants for previously identified species.

Higher order speciation effects on plutonium L(3) X-ray absorption near edge spectra.

Pu L(3) X-ray near edge absorption spectra for Pu(0-VII) are reported for more than 60 chalcogenides, chlorides, hydrates, hydroxides, nitrates, carbonates, oxy-hydroxides, and other compounds both as solids and in solution, and substituted in zirconolite, perovskite, and borosilicate glass. This large database extends the known correlations between the energy and shape of these spectra from the usual association of the XANES with valence and site symmetry to higher order chemical effects. Because of the large number of compounds of these different types, a number of novel and unexpected behaviors are observed, such as effects resulting from the medium and disorder that can be as large as those from valence.

Preparation and structures of homoleptic Pu(III) and U(III) acetonitrile salts.

Nine-coordinate homoleptic acetonitrile solvate complexes of Pu(III) and U(III) ions have been prepared through oxidation of Pu metal suspended in acetonitrile with metal-hexafluorophosphate salts and dissolution of UI3(THF)4 in acetonitrile, respectively.

Speciation and unusual reactivity in PuO2+x.

Pu L(3) XAFS measurements show that the excess oxygen in single phase PuO(2+)(x)() occurs as oxo groups with Pu-O distances of 1.83-1.91 A.