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PubMed2006

A reevaluation of the cultural eutrophication of Lake Okeechobee using multiproxy sediment records.

Lake Okeechobee, the hydrological lynchpin of the Everglades ecosystem, is the subject of an ambitious, multiagency restoration effort aimed at reducing phosphorus inputs and resulting algal blooms and impaired water clarity. This restoration is predicated on returning the lake to something closer to its predisturbance condition, but that goal has been challenged on the premise that the lake has always been eutrophic. The resolution of this debate and the appropriateness of the nutrient reduction goals thus depend on obtaining a reliable sediment record of past limnological conditions--the aim of this study. Because of the potential for severe sediment mixing from tropical storms, this investigation used multiple dating tools to examine the integrity of the sediment record and then analyzed proxies for nutrient enrichment, phytoplankton composition, and paleoproductivity. Sediment profiles for atmospheric pollutants, fertilizer contaminants, and radiocesium from three widely spaced cores showed good preservation of stratigraphic detail and coherence with the 210Pb chronologies. These results demonstrated that sediment stratigraphy is largely intact and retains a reliable record of limnological change. Geochemical proxies provide strong evidence of increased nutrient loading beginning ca. 1950. Concentrations of sediment P double, and N:P and C:N ratios drop, while those for N isotopes (delta15N) increase. At the same time, tracers of phosphate fertilizers (uranium, vanadium, and arsenic) rise. These changes are synchronous among cores and constitute a robust, internally consistent record of increasing water-column P. Biotic responses are manifested in higher concentrations and in changing composition of fossil algal pigments, including (1) large increases in the concentrations of chemically robust carotenoids, (2) corresponding decreases in the ratios of pigments from diatoms to chlorophyte and cyanobacterial algae, and (3) increases in UVR-photo-protective compounds indicating greater prevalence of surface algal blooms. This study provides strong evidence that Lake Okeechobee has experienced accelerated eutrophication linked with post-1950s land use changes in its watershed, a conclusion consistent with the nutrient reduction goals of the Lake Okeechobee Protection Program. The results contradict recent claims that the lake's trophic state has not changed over time, as well as the assertion that sediments of large shallow lakes cannot support a reliable chronology of past events.

Carbon↗
PubMed2004

Extraction and coordination studies of the unexplored bifunctional ligand carbamoyl methyl sulfoxide (CMSO) with uranium(VI) and cerium(III) nitrates. Synthesis and structures of [UO2(NO3)2(PhSOCH2CON(i)Bu2)] and [Ce(NO3)3(PhSOCH2CONBu2)2].

The bifunctional carbamoyl methyl sulfoxide ligands, PhCH(2)SOCH(2)CONHPh (L1), PhCH(2)SOCH(2)CONHCH(2)Ph (L2), PhSOCH(2)CON(i)Pr(2)(L3), PhSOCH(2)CONBu(2)(L4), PhSOCH(2)CON(i)Bu(2)(L5) and PhSOCH(2)CON(C(8)H(17))(2)(L6) have been synthesized and characterized by spectroscopic methods. The selected coordination chemistry of L1, L3, and L5with [UO(2)(NO(3))(2)] and [Ce(NO(3))(3)] has been evaluated. The structures of the compounds [UO(2)(NO(3))(2)(PhSOCH(2)CON(i)Bu(2))](10) and [Ce(NO(3))(3)(PhSOCH(2)CONBu(2))(2)](12) have been determined by single crystal X-ray diffraction methods. Preliminary extraction studies of ligand L6 with U(VI), Pu(IV) and Am(III) in tracer level showed an appreciable extraction for U(VI) and Pu(IV) in up to 10 M HNO(3) but not for Am(III). Thermal studies on compounds 8 and 10 in air revealed that the ligands can be destroyed completely on incineration. The electron spray mass spectra of compounds 8 and 10 in acetone show that extensive ligand distribution reactions occur in solution to give a mixture of products with ligand to metal ratios of 1: 1 and 2 :1. However, 10 retains its solid state structure in CH(2)Cl(2).

Journal Article↗
PubMed2004

Use of the emergency room in Elliot Lake, a rural community of Northern Ontario, Canada.

INTRODUCTION: There is ample documentation that use of hospital emergency facilities for reasons other than urgencies/emergencies results in clogged services in many urban centers. However, little has been published about similar misuse of emergency rooms/departments in rural and remote areas, where the situation is usually compounded by a scarcity of healthcare professionals. In Canada there is a shortage of physicians in rural and remote areas as a consequence of misdistribution (most physicians staying in southern urban centers after residence), and there is a chronic misuse of facilities meant for urgencies/emergencies to cope with primary healthcare needs. We address the problem in Elliot Lake, a rural Northern Ontario community of 12,000 people. The economy of Elliot Lake was based on uranium mining until the mid-1990s, when it drastically changed to become a center for affordable retirement and recreational tourism. As a consequence, at the present time the proportion of seniors in Elliot Lake doubles the Canadian average. Our objectives are to elucidate the demographics of emergency room (ER) clients and the effect of the elderly population; the nature of ER use; the perceived level of urgency of clients versus health professionals; and possible alternatives offered to non-urgent/emergency visits. This is the first study of the kind in Northern Ontario, a region the size of France. METHODS: The study, conducted in July 2001, used a prospective survey, completed by patients and attending clinicians at the time of a patient's presentation to the ER of St Joseph's General Hospital. This hospital is staffed by family physicians, a nurse practitioner, and registered nurses (RNs). The catchment area population (town plus surrounding areas) of the hospital is approximately 18,000 people. ER clients were interviewed verbally, and the attending health professionals responded to written questionnaires. Demographics were recorded (age, sex, employment and marital status), as was each client's reason for making an ER visit. Clients were asked if they had a family physician and if they had contacted him/her before visiting the ER, and if they would use another agency to address their health problem. Each client's, nurse's, and physician/nurse practitioner's perceived urgency level was recorded on a scale from 1 (non-urgent) to 5 (extremely urgent/life threatening). The attending physician/nurse practitioner and attending nurse were also asked to recommend appropriate alternatives, in their judgment, to each ER visit. RESULTS: Of a total of 1472 ER cases, 1096 (74.5%) verbal interviews with clients were conducted, as well as 1298 (88.2%) and 1013 (68.8%) questionnaires were completed respectively by attending nurses and physicians/nurse practitioner. The age of the clients was roughly proportional to their cohorts in the catchment area. Males and females were equally represented in the sample. Only 28.8% of the clients contacted their family physicians before visiting the ER, although 80.9% of them had a family physician. The reasons for visiting the ER are mostly typical of a primary care practice in Canada, and ER clients considered 19.4% of their visits non-urgent/non-emergency. In contrast, 45.2% of the physicians/nurse practitioner and 63.7% of the nurses considered the visits non-urgent/non-emergency. To reduce ER misuse, two-thirds of the recommendations by staff were to recruit more family physicians and nurse practitioners, and another one-fifth of the recommendations suggested the creation of a walk-in clinic. Other alternatives, such as the use of a variety of agencies available in town, were minimally recommended by healthcare professionals. CONCLUSION: The core of the problem identified by this research is that more physicians, nurse practitioners, and other health care professionals are needed in Elliot Lake to provide continuity of care. A new medical school is being created for the region, but the first family physicians from this initiative will only be available in 2012. In the meantime, healthcare professionals may need to take more preventive and educational measures to reduce ER misuse, and the use of other town's agencies, Telehealth, case-management of recurrent clients, and collaboration with local pharmacists need to be maximized. Further research is urgently needed into the effects on health outcomes in rural communities that may result from health services having to function beyond their capacity. Rural health clinicians, communities, researchers, and policy makers must work together to design, implement, and evaluate, both immediate and longer term solutions to the problems identified in this study.

Journal Article↗
PubMed1985

Theoretical models for determining 222Rn and 220Rn progeny levels in Canadian underground U mines--a comparison with experimental data.

Use has been made of several theoretical models to predict radiation levels in underground U mines. The models used are the Evans model, the Thomas-Epps mine model, the isolated mine model, the mine tunnel with no air flow and the mine tunnel with air flow (Beckman and Holub). Calculations based on the above models have been extended to include 220Rn gas and its progeny, a common occurrence in some Canadian U mines. Theoretical predictions include 222Rn and 220Rn progenies working levels and concentrations, as well as some ratios of great practical interest. The main differences between the models are pointed out and comparison is made with experimental data gathered during the last 3 yr in several Canadian underground U mines. In general terms, the mine models reported in the literature and presented here are neither satisfactory nor clearly distinguishable for practical application on the basis of the experimental data so far collected. The reason for such lack of agreement lies mainly in the unrealistic assumptions on which the models are based. Compounded is the gross oversimplification of quite complex dynamic situations encountered in actual practice. Deficiencies inherent to the models are noted and suggestions to improve the applicability of mine models to practical situations are indicated.

Air Pollutants↗
PubMed2005

Growth of Geobacter sulfurreducens under nutrient-limiting conditions in continuous culture.

A system for growing Geobacter sulfurreducens under anaerobic conditions in chemostats was developed in order to study the physiology of this organism under conditions that might more closely approximate those found in the subsurface than batch cultures. Geobacter sulfurreducens could be cultured under acetate-limiting conditions with fumarate or Fe(III)-citrate as the electron acceptor at growth rates between 0.04 and 0.09 h(-1). The molar growth yield was threefold higher with fumarate as the electron acceptor than with Fe(III), despite the lower mid-point potential of the fumarate/succinate redox couple. When growth was limited by availability of fumarate, high steady-state concentrations were detected, suggesting that fumarate is unlikely to be an important electron acceptor in sedimentary environments. The half-saturation constant, Ks, for acetate in Fe(III)-grown cultures (10 microM) suggested that the growth of Geobacter species is likely to be acetate limited in most subsurface sediments, but that when millimolar quantities of acetate are added to the subsurface in order to promote the growth of Geobacter for bioremediation applications, this should be enough to overcome any acetate limitations. When the availability of electron acceptors, rather than acetate, limited growth, G. sulfurreducens was less efficient in incorporating acetate into biomass but had higher respiration rates, a desirable physiological characteristic when adding acetate to stimulate the activity of Geobacter species during in situ uranium bioremediation. These results demonstrate that the ability to study the growth of G. sulfurreducens under steady-state conditions can provide insights into its physiological characteristics that have relevance for its activity in a diversity of sedimentary environments.

Acetates↗
PubMed2005

Structural variation in organically templated uranium sulfate fluorides.

The ability of templated uranium sulfate fluorides to adopt diverse inorganic architectures is demonstrated in six novel materials. The inorganic structures present in [N2C6H16][UO2F2(SO4)](USFO-2), [N2C6H16][UO2F(SO4)]2(USFO-3), [N2C3H12][UO2F(SO4)]2.H2O (USFO-4), [N2C5H14][UO2F(H2O)(SO4]2(USFO-5), [N2C6H18]2[UO2F(SO4)]4.H2O (USFO-6) and [N2C3H12][UO2F(SO4)]2.H2O (USFO-7) range from infinite chains to five different layer topologies. The chain, and two of the five layers, have unprecedented structure types. These compounds illustrate the structural diversity within this new family of materials, arising from the varied coordination of the U6+ centres. Each material was synthesised under hydrothermal conditions, through reaction of uranyl acetate, sulfuric acid, HF(aq), water, and the respective organic template.

Journal Article↗
PubMed1992

Arctic terrestrial ecosystem contamination.

Limited data have been collected on the presence of contaminants in the Arctic terrestrial ecosystem, with the exception of radioactive fallout from atmospheric weapons testing. Although southern and temperate biological systems have largely cleansed themselves of radioactive fallout deposited during the 1950s and 1960s, Arctic environments have not. Lichens accumulate radioactivity more than many other plants because of their large surface area and long life span; the presence and persistence of radioisotopes in the Arctic is of concern because of the lichen----reindeer----human ecosystem. Effective biological half-life of cesium 137 is reckoned to be substantially less than its physical half-life. The database on organochlorines in Canadian Arctic terrestrial mammals and birds is very limited, but indications are that the air/plant/animal contaminant pathway is the major route of these compounds into the terrestrial food chain. For terrestrial herbivores, the most abundant organochlorine is usually hexachlorobenzene followed by hexachlorocyclohexane isomers. PCB accumulation favours the hexachlorobiphenyl, pentachlorobiphenyl and heptachlorobiphenyl homologous series. The concentrations of the various classes of organochlorine compounds are substantially lower in terrestrial herbivore tissues than in marine mammal tissues. PCBs and DDT are the most abundant residues in peregrine falcons (a terrestrial carnivore) reaching average levels of 9.2 and 10.4 micrograms.g-1, respectively, more than 10 times higher than other organochlorines and higher than in marine mammals, including the polar bear. Contaminants from local sources include metals from mining activities, hydrocarbons and waste drilling fluids from oil and gas exploration and production, wastes from DEW line sites, naturally occurring radionuclides associated with uranium mineralization, and smoke containing SO2 and H2SO4 aerosol from the Smoking Hills at Cape Bathurst, N.W.T.

Animals↗
PubMed1990

Degradation of metal-labeled collagen implants: ultrastructural and X-ray microanalysis.

Three different metal salts, silver nitrate, uranyl acetate and lead citrate, are mixed with a collagen gel to produce 3 metal/collagen sponges. These sponges were implanted subcutaneously in the rat and samples harvested after 5 days of implantation. TEM observation shows that sponges are degraded and digested by macrophages, polymorphonuclear cells (PMN) and fibroblasts. We have observed that the location of the precipitates differs according to the metal added to the collagen. Lead precipitates stay longer on the collagen mesh while silver precipitates, after 5 days, are soon digested and are found in phagosomes of macrophages. Uranium precipitates are digested with the collagen and uranium/collagen associated pictures are seen in phagolysosomes. Metal precipitates accumulated in phagolysosomes of macrophagic cells are recognized by X-ray microanalysis. The degradation process of implanted collagen is discussed.

Animals↗
PubMed2003

Gaseous and particulate emissions from a DC arc melter.

Tests treating soils contaminated with metal compounds and radionuclide surrogates were conducted in a DC arc melter. The soil melted, and glassy or ceramic waste forms with a separate metal phase were produced. Tests were run in the melter plenum with either air or N2 purge gases. In addition to nitrogen, the primary emissions of gases were CO2, CO, oxygen, methane, and oxides of nitrogen (NO(x)). Although the gas flow through the melter was low, the particulate concentrations ranged from 32 to 145 g/m3. Cerium, a nonradioactive surrogate for plutonium and uranium, was not enriched in the particulate matter (PM). The PM was enriched in cesium and highly enriched in lead.

Air Pollutants↗
PubMed1999

Syntheses and Crystal Structures of a Linear-Chain Uranyl Phenylphosphinate UO(2)(O(2)PHC(6)H(5))(2) and Layered Uranyl Methylphosphonate UO(2)(O(3)PCH(3)).

Two extended uranyl organophosphorus compounds have been synthesized and structurally characterized. Linear-chain uranyl bis(phenylphosphinate), UO(2)(O(2)PHC(6)H(5))(2), was synthesized at 60 degrees C, and its structure was solved by single-crystal methods. UO(2)(O(2)PHC(6)H(5))(2) crystallizes in the triclinic space group P&onemacr; with unit cell parameters a = 5.648(1) Å, b = 8.115(2) Å, c = 9.171(2) Å, alpha = 64.97(3) degrees, beta = 80.59(3) degrees, gamma = 83.34(3) degrees, and Z = 1. The geometry of the uranium atom is tetragonal bipyramidal, and the neighboring uranyl ions are bridged by pairs of phenylphosphinate anions. The phenyl groups form two rows pointing in opposite directions of each chain, and neighboring chains arrange in a staircase fashion. Layered uranyl methylphosphonate, UO(2)(O(3)PCH(3)) (UPMe), was synthesized hydrothermally at 200 degrees C, and its structure was solved by powder pattern X-ray methods and refined by the Rietveld method. UPMe crystallizes in space group P&onemacr; with unit cell parameters a = 6.4027(3) Å, b = 6.6912(3) Å, c = 7.0983(3) Å, alpha = 90.473(2) degrees, beta = 99.684(2) degrees, gamma = 97.333(2) degrees, and Z = 2. The uranyl ions, connected by the phosphonate anions, form parallel inorganic layers, and the methyl groups point perpendicularly between the layers.

Journal Article↗
PubMed1965

Steroid lysis of protoplasts and effects of stabilizers and steroid antagonists.

Six synthetic antimicrobial steroids were examined for indications of their mechanism of action. Dequadin acetate, cetyl pyridinium chloride (CPC), and sodium deoxycholate were studied for comparison. Aerated cells of Sarcina lutea were washed, suspended in 1.06 M sucrose, and converted to protoplasts with 20 mug/ml of lysozyme. Lysis was measured optically at 650 mmu as a decrease in optical density. Screening tests with 50 mug/ml of each compound showed five steroids and CPC to be lytic. Protoplasts were strongly protected from lysis by pretreatment with 0.001 to 0.004 M spermine tetrahydrochloride. Other polyamines, such as spermidine phosphate, were less protective, and putrescine was ineffective. Uranyl nitrate (5 x 10(-4) M) rapidly agglutinated protoplasts and protected them from rupture by the lytic agents. Similar studies with 0.001 to 0.004 M Mg(++) showed varying degrees of protection, which, in most cases, was only temporary. Steroidal lysis did not appear to be related to chelation, since ethylenediaminetetraacetate did not cause lysis alone and antagonized some lytic compounds. Lecithin, Tween 80, Tween 20, and Span 20 at 0.05% exhibited certain effects on protoplast stability. Span 20 strongly prevented lysis by steroids. Tween 20 alone quickly caused protoplast rupture. Lecithin and Tween 80, which also caused lysis alone, interfered with lytic steroids and CPC. The test compounds were both inhibitory and lethal to cells of Sarcina lutea. The results suggest that direct action on cell membranes may be chiefly responsible for the antimicrobial properties of the steroids.

Bacteriolysis↗
PubMed1997

Alkoxide and Aryloxide Derivatives of a (Triamidoamine)uranium Complex.

The (triamidoamine)uranium chloride complex [{U(NN(3))(&mgr;-Cl)}(2)] [NN(3) = N(CH(2)CH(2)NSiMe(3))(3)] reacts with alkali metal alkoxides and aryloxides to give a range of complexes [U(NN(3))(OR)] (R = Bu(t), t-C(4)F(9), Ph, 2,6-Bu(t)(2)-4-MeC(6)H(2)). Crystallographic investigations (including the molecular structure of the perfluoro-tert-butoxido derivative [U(NN(3))(O-t-C(4)F(9))]), molecular weight determinations, and NMR spectroscopic data are consistent with these molecules being monomeric with a 3-fold symmetric arrangement of the triamidoamine fragment. The three turquoise ate complexes [U(NN(3))(OR)(OR')Li(THF)(n)()] (R, R' = Bu(t) or Ph), are prepared by reaction of the corresponding uranium alkoxides with lithium phenoxide or tert-butoxide. The complex with R = Ph, R' = Bu(t), n = 1 is shown by X-ray crystallography to have a capped trigonal bipyramidal structure. A lithium atom is incorporated into the ligand sphere by coordination to an amido nitrogen and a tert-butoxido oxygen. The mixed alkoxide ate complex [U(NN(3))(OBu(t))(OPh)Li(THF)] gives only [U(NN(3))(OBu(t))] on heating in vacuo. The one-electron oxidation of these ate complexes to the three neutral pentavalent compounds [U(NN(3))(OR)(OR')] (R, R' = Bu(t) or Ph) has been characterized by cyclic voltammetric studies and performed on the chemical scale by reaction with [FeCp(2)][PF(6)].

Journal Article↗
PubMed2006

Fluoride abstraction and reversible photochemical reduction of cationic uranyl(VI) phosphine oxide complexes.

The syntheses, structural and spectroscopic characterization, fluoride abstraction reactions, and photochemical reactivity of cationic uranyl(VI) phosphine oxide complexes are described. [UO2(OPPh3)4][X]2 (1a, X = OTf; 1b, X = BF4) and [UO2(dppmo)2(OPPh3)][X]2 (2a, X = OTf; 2b, X = BF(4)) are prepared from the corresponding uranyl(VI) chloride precursor and 2 equiv each of AgX and phosphine oxide. The BF4- compounds 1b and 2b are prone to fluoride abstraction reactions in methanol, leading to dinuclear fluoride-bridged uranyl(VI) complexes. Fluoride abstraction of 2b in methanol generates two structural isomers of the fluoride-bridged uranyl(VI) dimer [(UO2(dppmo)2)2(mu-F)][BF4]3 (4), both of which have been structurally characterized. In the major isomer 4C, the four dppmo ligands are all chelating, while in the minor isomer 4B, two of the dppmo ligands bridge adjacent uranyl(VI) centers. Photolysis of 2b in methanol proceeds through 4 to form the uranium(IV) fluoride complex [UO2F2(dppmo)3][BF4]2 (5), involving another fluoride abstraction step. X-ray crystallography shows 5 to be a rare example of a structurally characterized uranium(IV) complex possessing terminal U-F bonds. Complex 5 reverts to 4 in solution upon exposure to air.

Journal Article↗
PubMed1996

Structure Determination of a Complex Tubular Uranyl Phenylphosphonate, (UO(2))(3)(HO(3)PC(6)H(5))(2)(O(3)PC(6)H(5))(2).H(2)O, from Conventional X-ray Powder Diffraction Data.

The three-dimensional structure of a complex tubular uranyl phosphonate, (UO(2))(3)(HO(3)PC(6)H(5))(2)(O(3)PC(6)H(5))(2).H(2)O, was determined ab initio from laboratory X-ray powder diffraction data and refined by the Rietveld method. The crystals belong to the space group P2(1)2(1)2(1), with a = 17.1966(2) Å, b = 7.2125(2) Å, c = 27.8282(4) Å, and Z = 4. The structure consists of three independent uranium atoms, among which two are seven-coordinated and the third is eight-coordinated. These metal atoms are connected by four different phosphonate groups to form a one-dimensional channel structure along the b axis. The phenyl groups are arranged on the outer periphery of the channels, and their stacking forces keep the channels intact in the lattice. The determination of this structure which contains 50 non-hydrogen atoms in the asymmetric unit, from conventional X-ray powder data, represents significant progress in the application of powder techniques to structure solution of complex inorganic compounds, including organometallic compounds.

Journal Article↗
PubMed2002

Oligomerization and hydroamination of terminal alkynes promoted by the cationic organoactinide compound [(Et2N)3U][BPh4].

The three ancillary amido moieties in the cationic complex [(Et2N)3U][BPh4] are highly reactive and are easily replaced when the complex is treated with primary amines. The reaction of [(Et2N)3U][BPh4] with excess tBuNH2 allows the formation of the cationic complex [(tBuNH2)3(tBuNH)3U][BPh4]. X-ray diffraction studies on the complex indicate that three amido and three amine ligands are arranged around the cationic metal center in a slightly distorted octahedral mer geometry. The cationic complex reacts with primary alkynes in the presence of external primary amines to primarily afford the unexpected cis dimer and, in some cases, the hydroamination products are obtained concomitantly. The formation of the cis dimer is the result of an envelope isomerization through a metal-cyclopropyl cationic complex. In the reaction of the bulkier alkyne tBuC identical to CH with the cationic uranium complex in the presence of various primary amines, the cis dimer, one trimer, and one tetramer are obtained regioselectively, as confirmed by deuterium labeling experiments. The trimer and the tetramer correspond to consecutive insertions of an alkyne molecule into the vinylic CH bond trans to the bulky tert-butyl group. The reaction of (TMS) C identical to CH with the uranium catalyst in the presence of EtNH2 followed a different course and produced the gem dimer along with the hydroamination imine as the major product. However, when other bulkier amines were used (iPrNH2 or tBuNH2) both hydroamination isomeric imines Z and E were obtained. During the catalytic reaction, the E (kinetic) isomer is transformed into the most stable Z (thermodynamic) isomer. The unique reactivity of the alkyne (TMS) C identical to CH with the secondary amine Et2NH is remarkable because it afforded the trans dimer and the corresponding hydroamination enamine. The latter probably results from the insertion of the alkyne into a secondary metal-amide bond, followed by protonolysis.

Journal Article↗
PubMed1989

A comparison of excretion and retention between the current ICRP lung model and a proposed new model.

The current International Commission on Radiation Protection (ICRP) lung model (Health Phys. 12: 173; 1986) was developed from information available in the early 1960s. Since that time considerable new information on lung morphology, deposition, and retention has become available and, where appropriate, has been incorporated into a new model being discussed by a Task Group of the ICRP. This new model is conceptually much simpler in that it contains only three compartments, as opposed to 11 in the current model. The intent of this simpler model is to make it easier to model experimental retention and excretion data, either from in vitro studies, animal or human experiments, or human experience. However, this conceptually simpler model is somewhat more difficult to use than the current model as the new model parameters vary with time after exposure. That is, parameters are time-varying functions rather than constants, as they are in the current model, and retention is not given by the familiar Bateman equations. Default time-varying parameters for the new model have been developed that give results comparable to the current model for Classes D, W, and Y compounds. In addition, parameters have been developed for U ore dust, based on in vitro and in vivo studies, and for UO2 from human experience in U fuel fabrication facilities. The development of these parameters will be described, and the results with the new model compared with those obtained with the current model.

Aerosols↗
PubMed2003

Self-assembly of a polar open-framework uranyl vanadyl hexaoxoiodate(VII) constructed entirely from distorted octahedral building units in the first uranium hexaoxoiodate: K2[(UO2)2(VO)2(IO6)2O].H2O.

The reaction of UO(3) with V(2)O(5) and KIO(4) under mild hydrothermal conditions produces K(2)[(UO(2))(2)(VO)(2)(IO(6))(2)O].H(2)O (1) in the form of orange acicular crystals. The structure of 1 consists of UO(6), VO(6), and IO(6) distorted octahedra that are assembled into a polar, open-framework structure. The distorted VO(6) and IO(6) octahedra edge-share to form chains that run down the c-axis. Each VO(6) octahedron also shares a vertex with an adjacent vanadium atom to link the chains together into a ribbon. The IO(6) units also partake in corner-sharing with the UO(6) units to create interconnected elliptical tubes. The major channels in 1 are filled with K(+) cations and water molecules. The polarity of this compound is caused by alignment of distorted vanadyl hexaoxoiodate ribbons and UO(6) trapezoidal bipyramids resulting in a large second-harmonic generation response of 300 times that of alpha-quartz. Crystallographic data: 1, orthorhombic, space group Pba2, a = 9.984(2) A, b = 16.763(3) A, c = 4.977(1) A, Z = 4 (T = 193 K).

Journal Article↗
PubMed2005

The role of amine sulfates in hydrothermal uranium chemistry.

A series of novel uranium sulfates containing organic structure directing cations has been synthesized from amine sulfate precursors under hydrothermal conditions. The amine sulfates act as a soluble source of the protonated amines and sulfate ions at low temperature and provide a reaction pathway in which no amine decomposition is observed. The protonated amines act as both space fillers and hydrogen-bond donors in the three-dimensional structure. The factors governing the formation of the observed hydrogen-bonding networks were probed through the use of bond valence sums, which allow the quantification of residual negative charge and determination of the relative nucleophilicity of each oxide ligand. The hydrogen bonding in these new compounds is dependent upon two factors. First, the oxide ligands with the highest nucleophilicities are preferential acceptors with respect to their less nucleophilic counterparts. Second, geometric constraints that result from the formation of multiple hydrogen bonds from a single ammonium center can dictate the donation to oxides with smaller negative charges. Crystal data for [N4C6H12][SO4]2 x 2H2O, a = 7.2651(2) A, b = 7.3012(2) A, c = 8.3877(3) A, alpha = 90.260(1) degrees, beta = 100.323(1) degrees, gamma = 113.0294(15) degrees, triclinic, P-1 (No. 2), Z = 1; for [N4C6H22][UO2(H2O)(SO4)2]2 x 6H2O, a = 6.7318(1) A, b = 9.2975(1) A, c = 13.1457(3) A, alpha = 72.3395(6) degrees, beta = 89.1401(7) degrees, gamma = 70.0267(12) degrees, triclinic, P-1 (No. 2), Z = 1; for [N4C6H22][UO2(SO4)2)2, a = 9.3771(2) A, b = 12.9523(3) A, c = 18.9065(6) A, orthorhombic, Pbca (No. 61), Z = 4; for [N5C8H28]2[(UO2)5(H2O)5(SO4)10] x H2O, a = 7.76380(5) A, b = 14.16890(5) A, c = 56.46930(5) A, orthorhombic, Pbnm (No. 62), Z = 4.

Journal Article↗