Changes in cellular Ca2+ and Na+ regulation during the progression towards heart failure in the guinea pig.

KEY POINTS: During compensated hypertrophy in vivo fractional shortening (FS) remains constant until heart failure (HF) develops, when FS decreases from 70% to 39%. Compensated hypertrophy is accompanied by an increase in INa,late and a decrease in Na+ ,K+ -ATPase current. These changes persist as HF develops. SR Ca2+ content increases during compensated hypertrophy then decreases in HF. In healthy cells, increases in SR Ca2+ content and Ca2+ transients can be achieved by the same amount of inhibition of the Na+ ,K+ -ATPase as measured in the diseased cells. SERCA function remains constant during compensated hypertrophy then decreases in HF, when there is also an increase in spark frequency and spark-mediated Ca2+ leak. We suggest an increase in INa,late and a decrease in Na+ ,K+ -ATPase current and function alters the balance of Ca2+ flux mediated by the Na+ /Ca2+ exchange that limits early contractile impairment. ABSTRACT: We followed changes in cardiac myocyte Ca2+ and Na+ regulation from the formation of compensated hypertrophy (CH) until signs of heart failure (HF) are apparent using a trans-aortic pressure overload (TAC) model. In this model, in vivo fractional shortening (FS) remained constant despite HW:BW ratio increasing by 39% (CH) until HF developed 150 days post-TAC when FS decreased from 70% to 39%. Using live and fixed fluorescence imaging and electrophysiological techniques, we found an increase in INa,late from -0.34 to -0.59 A F-1 and a decrease in Na+ ,K+ -ATPase current from 1.09 A F-1 to 0.54 A F-1 during CH. These changes persisted as HF developed (INa,late increased to -0.82 A F-1 and Na+ ,K+ -ATPase current decreased to 0.51 A F-1 ). Sarcoplasmic reticulum (SR) Ca2+ content increased during CH then decreased in HF (from 32 to 15 µm l-1 ) potentially supporting the maintenance of FS in the whole heart and Ca2+ transients in single myocytes during the former stage. We showed using glycoside blockade in healthy myocytes that increases in SR Ca2+ content and Ca2+ transients can be driven by the same amount of inhibition of the Na+ ,K+ -ATPase as measured in the diseased cells. SERCA function remains constant in CH but decreases (τ for SERCA-mediated Ca2+ removal changed from 6.3 to 3.0 s-1 ) in HF. In HF there was an increase in spark frequency and spark-mediated Ca2+ leak. We suggest an increase in INa,late and a decrease in Na+ ,K+ -ATPase current and function alters the balance of Ca2+ flux mediated by the Na+ /Ca2+ exchange that limits early contractile impairment.

Microbial mobilization of plutonium and other actinides from contaminated soil.

We examined the dissolution of Pu, U, and Am in contaminated soil from the Nevada Test Site (NTS) due to indigenous microbial activity. Scanning transmission x-ray microscopy (STXM) analysis of the soil showed that Pu was present in its polymeric form and associated with Fe- and Mn- oxides and aluminosilicates. Uranium analysis by x-ray diffraction (µ-XRD) revealed discrete U-containing mineral phases, viz., schoepite, sharpite, and liebigite; synchrotron x-ray fluorescence (µ-XRF) mapping showed its association with Fe- and Ca-phases; and µ-x-ray absorption near edge structure (µ-XANES) confirmed U(IV) and U(VI) oxidation states. Addition of citric acid or glucose to the soil and incubated under aerobic or anaerobic conditions enhanced indigenous microbial activity and the dissolution of Pu. Detectable amount of Am and no U was observed in solution. In the citric acid-amended sample, Pu concentration increased with time and decreased to below detection levels when the citric acid was completely consumed. In contrast, with glucose amendment, Pu remained in solution. Pu speciation studies suggest that it exists in mixed oxidation states (III/IV) in a polymeric form as colloids. Although Pu(IV) is the most prevalent and generally considered to be more stable chemical form in the environment, our findings suggest that under the appropriate conditions, microbial activity could affect its solubility and long-term stability in contaminated environments.

Photochemical upconversion and triplet annihilation limit from a boron dipyrromethene emitter.

Non-coherent sensitized red-to-green upconversion has been achieved utilizing platinum(II) tetraphenyltetrabenzoporphyrin (PtTPTBP) as the triplet sensitizer and a nearly quantitatively fluorescent meso-(2,6-dichloropyridyl)-substituted boron dipyrromethene (Cl2PyBODIPY) chromophore (Φ = 0.99 in toluene) as the energy acceptor/annihilator in deoxygenated toluene. Dynamic Stern-Volmer analysis revealed that PtTPTBP phosphorescence as quenched by Cl2PyBODIPY occurs with a KSV of 108,000 M(-1), yielding a triplet-triplet energy transfer rate constant of 2.3 × 10(9) M(-1) s(-1). Using a non-coherent red light-emitting diode excitation source centered at 626 nm, the incident power dependence responsible for generating singlet BODIPY fluorescence in the green was shown to traverse quadratic to linear regimes, the latter being achieved near 60 mW cm(-2). These data were consistent with a photochemical upconversion mechanism being responsible for generating singlet fluorescence from the Cl2PyBODIPY chromophores through sensitized triplet-triplet annihilation (TTA). Integrated delayed fluorescence transients were utilized to reveal the TTA efficiency for the Cl2PyBODIPY chromophore and saturated near 46%, representing the lower limit for the TTA process. Kinetic modelling of the delayed fluorescence transient produced from 1.5 mJ laser pulses (λex = 615 nm) revealed a maximum limiting TTA efficiency of 64% for this upconverting composition, implying that this is indeed an extremely relevant acceptor/annihilator composition for photochemical upconversion.

Hormetic effect of ionic liquid 1-ethyl-3-methylimidazolium acetate on bacteria.

The biological effect of ionic liquids (ILs) is one of the highly debated topics as they are being contemplated for various industrial applications. 1-ethyl-3-methylimidazolium acetate ([EMIM][Ac]) showed remarkable hormesis on anaerobic Clostridium sp. and aerobic Pseudomonas putida. Bacterial growth was stimulated at up to 2.5 g L(-1) and inhibited at >2.5 g L(-1) of [EMIM][Ac]. The growth of Clostridium sp. and P. putida were higher by 0.4 and 4-fold respectively, in the presence of 0.5 g L(-1) [EMIM][Ac]. Assessment of the effect of [EMIM][Ac] under different growth conditions showed that the hormesis of [EMIM][Ac] was mediated via regulation of medium pH. Hormetic effect of [EMIM][Ac] was evident only in medium with poor buffering capacity and in the presence of a fermentable substrate as the carbon source. The hormetic effect of [EMIM][Ac] on bacterial growth is most likely associated with the buffering capacity of acetate anion. These observations have implications in ILs toxicity studies and ecological risk assessment.

Toxicity of ionic liquids to Clostridium sp. and effects on uranium biosorption.

As green solvents ionic liquids (ILs) show high potential in nuclear industry for extraction and purification of actinides. However, to date relatively little information has been gained on ILs application in microbial processes, for example biosorption of radionuclides. We investigated the effects of three ILs, 1-butyl-3-methylimidazolium hexafluorophosphate (BMIMPF6), N-ethylpyridinium trifluoroacetate (EtPyCF3COO) and N-ethylpyridinium tetrafluoroborate (EtPyBF4) on the growth and biosorption of uranium by Clostridium sp. The ILs affected the growth of the bacterium as evidenced by decreases in optical density, total gas production, and organic acids production from glucose metabolism. The IC50-48h of three ILs decreased in the order of BMIMPF6 (8.26mM)>EtPyBF4 (7.04mM)>EtPyCF3COO (4.05mM). Uranium biosorption by the bacterial cells decreased by 75% in the presence of 1% (v/v) BMIMPF6 and by about 90% with 1% (v/v) EtPyBF4 or EtPyCF3COO, in comparison to the control without ILs. The diminished biosorption may be attributed to the membrane damages induced by EtPyBF4 and EtPyCF3COO, which can be visualized by Transmission Electron Microscope (TEM) analysis. Energy-dispersive X-ray spectroscopy (EDS) analysis revealed the accumulation of uranium inside peripheral membrane of the cells exposed to uranium alone or with BMIMPF6, while little or no accumulation was observed in the presence of EtPyBF4 and EtPyCF3COO. These results imply that potential toxicity of ILs towards microorganisms is a particularly important issue in limiting its biotechnological applications.

Bioreduction and precipitation of uranium in ionic liquid aqueous solution by Clostridium sp.

The ionic liquids, 1-butyl-3-methylimidazolium hexafluorophosphate [BMIM][PF6], N-ethylpyridiniumtrifluoroacetate [EtPy][CF3COO] and N-ethylpyridiniumtetrafluoroborate [EtPy][BF4], affected the reduction and precipitation of uranium by Clostridium sp. to a varying degree. Characterization of uranium association with the ionic liquids showed that uranium formed a monodentate complex with the anion BF4(-) and PF6(-) of [EtPy][BF4] and [BMIM][PF6], respectively; and a bidentate complex with carboxylate of [EtPy][CF3COO]. Bioreduction of U(VI) was influenced by the type of complex formed: monodentate complexes were readily reduced whereas the bidentate complex of U(VI) with [CF3COO] was recalcitrant. [EtPy][BF4] affected the rate and extent of precipitation of the reduced uranium; at higher concentration the reduced U(IV) remained in the solution phase. The results suggest that by tuning the properties of ionic liquids they may be valuable candidates for uranium biotreatment.

Outcome in 55 dogs with pulmonic stenosis that did not undergo balloon valvuloplasty or surgery.

OBJECTIVE: To determine the outcome, independent predictors of cardiac death, and the Doppler-derived pressure gradient cut-off for predicting cardiac death in dogs with pulmonic stenosis, with or without tricuspid regurgitation, that do not undergo balloon valvuloplasty or valve surgery. METHODS: Review of medical records of two UK referral centres between July 1997 and October 2008 for all cases of pulmonic stenosis that had no balloon valvuloplasty or valve surgery. Inclusion criteria included a diagnosis of pulmonic stenosis; spectral Doppler pulmonic velocity greater than 1·6 m/s; characteristic valve leaflet morphological abnormalities. Exclusion criteria included concurrent significant cardiac defects, including tricuspid dysplasia. Dogs with tricuspid regurgitation were included. Dogs were classified according to Doppler-derived pressure gradients into mild, moderate or severe pulmonic stenosis categories. RESULTS: Presence of tricuspid regurgitation and severe stenosis were independent predictors of cardiac death. A pulmonic pressure gradient of more than 60 mmHg was associated with 86% sensitivity, and 71% specificity of predicting cardiac death. CLINICAL SIGNIFICANCE: There is an increased probability of cardiac death in those cases which have a pulmonary pressure gradient greater than 60 mmHg and tricuspid regurgitation, though the effect of severity of tricuspid regurgitation on outcome was not measurable because of small sample sizes. These animals might benefit from intervention.

Alkyl-methylimidazolium ionic liquids affect the growth and fermentative metabolism of Clostridium sp.

In this study, the effect of ionic liquids, 1-ethyl-3-methylimidazolium acetate [EMIM][Ac], 1-ethyl-3-methylimidazolium diethylphosphate [EMIM][DEP], and 1-methyl-3-methylimidazolium dimethylphosphate [MMIM][DMP] on the growth and glucose fermentation of Clostridium sp. was investigated. Among the three ionic liquids tested, [MMIM][DMP] was found to be least toxic. Growth of Clostridium sp. was not inhibited up to 2.5, 4 and 4 g L(-1) of [EMIM][Ac], [EMIM][DEP] and [MMIM][DMP], respectively. [EMIM][Ac] at <2.5 g L(-1), showed hormetic effect and stimulated the growth and fermentation by modulating medium pH. Total organic acid production increased in the presence of 2.5 and 2 g L(-1) of [EMIM][Ac] and [MMIM][DMP]. Ionic liquids had no significant influence on alcohol production at <2.5 g L(-1). Total gas production was affected by ILs at ≥ 2.5 g L(-1) and varied with type of methylimidazolium IL. Overall, the results show that the growth and fermentative metabolism of Clostridium sp. is not impacted by ILs at concentrations below 2.5 g L(-1).

Toxicity of imidazolium- and pyridinium-based ionic liquids and the co-metabolic degradation of N-ethylpyridinium tetrafluoroborate.

We examined the effects of the ionic liquids (ILs), 1-butyl-3-methylimidazolium hexafluorophosphate [BMIM][PF6], N-ethylpyridinium tetrafluoroborate [EtPy][BF4], and N-ethylpyridinium trifluoroacetate [EtPy][CF3COO] on Pseudomonas fluorescens, a ubiquitous soil bacterium. In the presence of 0.5- and 1% of [BMIM][PF6] or [EtPy][CF3COO] the growth of bacteria was inhibited, whereas exposing them to 1% [EtPy][BF4] increased the lag period wherein bacteria adapt to growth conditions before continuing to grow. However, at higher concentrations (5% and 10%), no growth was observed. The inhibitory effects were evident by a decrease in the optical density of the culture, a decline in the consumption of the carbon source, citric acid, and a change in the size of the bacterium. At concentrations below 1%, [EtPy][BF4] was metabolized by P. fluorescens in the presence of citric acid. Oxidation of the side alkyl-chain of [EtPy][BF4] caused the accumulation of N-hydroxylethylpyridinium and pyridinium as major degradation products.

Immobilization of Cr(VI) and its reduction to Cr(III) phosphate by granular biofilms comprising a mixture of microbes.

We assessed the potential of mixed microbial consortia, in the form of granular biofilms, to reduce chromate and remove it from synthetic minimal medium. In batch experiments, acetate-fed granular biofilms incubated aerobically reduced 0.2 mM Cr(VI) from a minimal medium at 0.15 mM day(-1) g(-1), with reduction of 0.17 mM day(-1) g(-1) under anaerobic conditions. There was negligible removal of Cr(VI) (i) without granular biofilms, (ii) with lyophilized granular biofilms, and (iii) with granules in the absence of an electron donor. Analyses by X-ray absorption near edge spectroscopy (XANES) of the granular biofilms revealed the conversion of soluble Cr(VI) to Cr(III). Extended X-ray absorption fine-structure (EXAFS) analysis of the Cr-laden granular biofilms demonstrated similarity to Cr(III) phosphate, indicating that Cr(III) was immobilized with phosphate on the biomass subsequent to microbial reduction. The sustained reduction of Cr(VI) by granular biofilms was confirmed in fed-batch experiments. Our study demonstrates the promise of granular-biofilm-based systems in treating Cr(VI)-containing effluents and wastewater.

Colloidal cutin-like substances cross-linked to siderophore decomposition products mobilizing plutonium from contaminated soils.

Relatively recently, inorganic colloids have been invoked to reconcile the apparent contradictions between expectations based on classical dissolved-phase Pu transport and field observations of "enhanced" Pu mobility (Kersting et al. Nature 1999, 397, 56-59). A new paradigm for Pu transport is mobilization and transport via biologically produced ligands. This study for the first time reports a new finding of Pu being transported, at sub-pM concentrations, by a cutin-like natural substance containing siderophore-like moieties and virtually all mobile Pu. Most likely, Pu is complexed by chelating groups derived from siderophores that are covalently bound to a backbone of cutin-derived soil degradation products, thus revealing the history of initial exposure to Pu. Features such as amphiphilicity and small size make this macromolecule an ideal collector for actinides and other metals and a vector for their dispersal. Cross-linking to the hydrophobic domains (e.g., by polysaccharides) gives this macromolecule high mobility and a means of enhancing Pu transport. This finding provides a new mechanism for Pu transport through environmental systems that would not have been predicted by Pu transport models.

Bioreduction of uranium(VI) complexed with citric acid by Clostridia affects its structure and solubility.

Uranium contamination of the environment from mining and milling operations, nuclear-waste disposal, and ammunition use is a widespread global problem. Natural attenuation processes such as bacterial reductive precipitation and immobilization of soluble uranium is gaining much attention. However, the presence of naturally occurring organic ligands can affect the precipitation of uranium. Here, we report that the anaerobic spore-forming bacteria Clostridia, ubiquitous in soils, sediments, and wastes, capable of reduction of Fe(III) to Fe(II), Mn(IV) to Mn(II), U(VI) to U(IV), Pu(IV) to Pu(III), and Tc(VI) to Tc(IV); reduced U(VI) associated with citric acid in a dinuclear 2:2 U(VI): citric acid complex to a biligand mononuclear 1:2 U(IV):citric acid complex,which remained in solution, in contrast to reduction and precipitation of uranium. Our findings show that U(VI) complexed with citric acid is readily accessible as an electron acceptor despite the inability of the bacterium to metabolize the complexed organic ligand. Furthermore, it suggests that the presence of organic ligands at uranium-contaminated sites can affect the mobility of the actinide under both oxic and anoxic conditions by forming such soluble complexes.

Analysis of novel soluble chromate and uranyl reductases and generation of an improved enzyme by directed evolution.

Most polluted sites contain mixed waste. This is especially true of the U.S. Department of Energy (DOE) waste sites which hold a complex mixture of heavy metals, radionuclides, and organic solvents. In such environments enzymes that can remediate multiple pollutants are advantageous. We report here evolution of an enzyme, ChrR6 (formerly referred to as Y6), which shows a markedly enhanced capacity for remediating two of the most serious and prevalent DOE contaminants, chromate and uranyl. ChrR6 is a soluble enzyme and reduces chromate and uranyl intracellularly. Thus, the reduced product is at least partially sequestered and nucleated, minimizing the chances of reoxidation. Only one amino acid change, (Tyr)128(Asn), was responsible for the observed improvement. We show here that ChrR6 makes Pseudomonas putida and Escherichia coli more efficient agents for bioremediation if the cellular permeability barrier to the metals is decreased.

Coordination modes in the formation of the ternary Am(III), Cm(III), and Eu(III) complexes with EDTA and NTA: TRLFS, 13C NMR, EXAFS, and thermodynamics of the complexation.

The formation and the structure of the ternary complexes of trivalent Am, Cm, and Eu with mixtures of EDTA+NTA (ethylenediamine tetraacetate and nitrilotriacetate) have been studied by time-resolved laser fluorescence spectroscopy, 13C NMR, extended X-ray absorption fine structure, and two-phase metal ion equilibrium distribution at 6.60 m (NaClO4) and a hydrogen ion concentration value (pcH) between 3.60 and 11.50. In the ternary complexes, EDTA binds via four carboxylates and two nitrogens, while the binding of the NTA varies with the hydrogen ion concentration, pcH, and the concentration ratios of the metal ion and the ligand. When the concentration ratios of the metal to ligand is low (1:1:1-1:1:2), two ternary complexes, M(EDTA)(NTAH)(3-) and M(EDTA)(NTA)(4-), are formed at pcH ca. 9.00 in which NTA binds via three carboxylates, via two carboxylates and one nitrogen, or via two carboxylates and a H2O. At higher ratios (1:1:20 and 1:10:10) and pcH's of ca. 9.00 and 11.50, one ternary complex, M(EDTA)(NTA)(4-), is formed in which NTA binds via three carboxylates and not via nitrogen. The two-phase equilibrium distribution studies at tracer concentrations of Am, Cm, and Eu have also confirmed the formation of the ternary complex M(EDTA)(NTA)(4-) at temperatures between 0 and 60 degrees C. The stability constants (log beta111) for these metal ions increase with increasing temperature. The endothermic enthalpy and positive entropy indicated a significant effect of cation dehydration in the formation of the ternary complexes at high ionic strength.

Enantioselective surface chemistry of R-2-bromobutane on Cu(643)R&S and Cu(531)R&S.

The enantioselective surface chemistry of chiral R-2-bromobutane was studied on the naturally chiral Cu(643)R&S and Cu(531)R&S surfaces by comparing relative product yields during temperature-programmed reaction spectroscopy. Molecularly adsorbed R-2-bromobutane can desorb molecularly or debrominate to form R-2-butyl groups on the surfaces. The R-2-butyl groups react further by beta-hydride elimination to form 1- or 2-butene or by hydrogenation to form butane. Temperature-programmed reaction spectroscopy was used to quantify the relative yields of the various reaction products. At low coverages of R-2-bromobutane on Cu(643)R&S and Cu(531)R&S, the surface chemistry is not enantioselective. At monolayer coverage, however, the product yields indicate that the R-2-bromobutane decomposition reaction rates are sensitive to the handedness of the two chiral surfaces. The impact of surface structure on enantioselectivity was examined by studying the chemistry of R-2-bromobutane on both Cu(643)R&S and Cu(531)R&S. The selectivity of R-2-bromobutane desorption versus debromination is enantiospecific and differs significantly from Cu(643) to Cu(531). The selectivity of the R-2-butyl reaction by beta-hydride elimination versus hydrogenation is only weakly enantiospecific and is similar on both the Cu(643) and Cu(531) surfaces. These results represent the first quantitative observations of enantioselectivity in reactions with well-known mechanisms probed using a simple adsorbate on naturally chiral metal surfaces.

Decontamination of uranium-contaminated steel surfaces by hydroxycarboxylic acid with uranium recovery.

We developed a simple, safe method to remove uranium from contaminated metallic surfaces so that the materials can be recycled or disposed of as low-level radioactive or nonradioactive waste. Surface analysis of rusted uranium-contaminated plain carbon-steel coupons by X-ray photoelectron spectroscopy and Rutherford backscattering spectroscopy showed that uranium was predominantly associated with ferrihydrite, lepidocrocite, and magnetite, or occluded in the matrix of the corrosion product as uranyl hydroxide and schoepite (UO3 x 2H2O). Citric acid formulations, consisting of oxalic acid-hydrogen peroxidecitric acid (OPC) or citric acid-hydrogen peroxidecitric acid (CPC), were used to remove uranium from the coupons. The efficiency of uranium removal varied from 68% to 94% depending on the extent of corrosion, the association of uranium with the iron oxide matrix, and the accessibility of the occluded contaminant. Decontaminated coupons clearly showed evidence of the extensive removal of rust and uranium. The waste solutions containing uranium and iron from decontamination by OPC and CPC were treated first by subjecting them to biodegradation followed by photodegradation. Biodegradation of a CPC solution by Pseudomonas fluorescens resulted in the degradation of the citric acid with concomitant precipitation of Fe (>96%), whereas U that remained in solution was recovered (>99%) by photodegradation as schoepite. In contrast, in an OPC solution citric acid was biodegraded but not oxalic acid, and both Fe and U remained in solution. Photodegradation of this OPC solution resulted in the precipitation of iron as ferrihydrite and uranium as uranyl hydroxide.

A survey of sleep problems in autism, Asperger's disorder and typically developing children.

BACKGROUND: Sleep problems are common in typically developing (TD) children and in children with autism, however, less is known about the sleep of children with Asperger's disorder (AD). The aim of this study was to compare sleep patterns of children with autism and AD to a TD group of children. METHODS: Sixty-six parents of TD children, 53 parents of children with autism, and 52 parents of children with AD completed a survey on their child's sleep patterns, the nature and severity of any sleep problems and success of any treatment attempted. RESULTS: The results showed high prevalence of sleep problems with significantly more problems reported in the autism and AD groups (TD = 50%, autism = 73%, AD = 73%), with no significant differences between groups on severity or type of sleep problem. Children with AD were significantly more likely to be sluggish and disoriented after waking and had a higher Behavioral Evaluation of Disorders of Sleep (BEDS) total score compared to the other two groups. The autism and AD groups reported significantly better treatment success for medication compared to the TD group. The autism group reported significantly better success for behavioural treatment compared to the AD group. CONCLUSIONS: In conclusion, children with AD may have more symptoms of sleep disturbance, and different types of sleep problems than children with autism. As this is the first study to compare autism and AD and to survey treatment outcomes, further research is needed to validate these findings.

Antidepressant action of St. John's Wort, Hypericum perforatum: a test of the circadian hypotheses.

Extracts of the plant St. John's Wort, Hypericum perforatum, are effective for treatment of mild depression. It has been hypothesised that H. perforatum may be acting on the circadian timing system either directly or via a photosensitising action to produce changes in mood. Two experiments were conducted to test these hypotheses. Under constant dark (Experiment 1) or low constant light (Experiment 2) rats were permitted to free-run. Rats were then treated with a 'high' (616mg/kg/day; n = 8 per experiment) or 'low' (308 mg/kg/day; n = 8 per experiment) dose of H. perforatum or a control solution (n = 8 per experiment) in drinking water, and circadian locomotor rhythms examined for alterations of period. A minor shortening of mean period (2.4 min) was observed on cessation of H. perforatum treatment in the low-dose group in Experiment 2, and was considered to be a measurement artifact and of no clinical value. Otherwise, no significant differences in free-running period between treatment groups were observed in either study, indicating that H. perforatum has no direct or photosensitising effect on the mammalian circadian system. These results suggest that the antidepressant action of H. perforatum is not mediated by a circadian mechanism.

Empirical method for prediction of the coordination environment of Eu(III) by time-resolved laser-induced fluorescence spectroscopy.

The number of water molecules in the inner-sphere (N(H2O)) was determined for Eu(III) and the strength of ligand field (R(E/M)) was evaluated for a variety of coordination environments from the luminescence lifetime and the relative intensity at 615 nm and at 592 nm, by time-resolved laser-induced fluorescence spectroscopy. When R(E/M) and deltaN(H2O) for Eu(III) with a known coordination environment were plotted clear regularity was apparent between the location of the R(E/M)-deltaN(H2O) plot and the coordination environment of Eu(III). Here, deltaN(H2O) was calculated by use of the equation, deltaN(H2O)=9-N(H2O). Unknown coordination environments of Eu(III) can, in turn, be characterized, including both the inner- and the outer-sphere, simply by plotting R(E/M) and deltaN(H2O) for Eu(III) on the diagram. This empirical method is effective for prediction of the coordination environment of hydrated and complexed Eu(III) in solutions and that of the adsorbed Eu(III) on ion-exchange resins and by microorganisms.

Association of uranium with iron oxides typically formed on corroding steel surfaces.

Decontamination of metal surfaces contaminated with low levels of radionuclides is a major concern at Department of Energy facilities. The development of an environmentally friendly and cost-effective decontamination process requires an understanding of their association with the corroding surfaces. We investigated the association of uranium with the amorphous and crystalline forms of iron oxides commonly formed on corroding steel surfaces. Uranium was incorporated with the oxide by addition during the formation of ferrihydrite, goethite, green rust II, lepidocrocite, maghemite, and magnetite. X-ray diffraction confirmed the mineralogical form of the oxide. EXAFS analysis at the U L(III) edge showed that uranium was present in hexavalent form as a uranyl oxyhydroxide species with goethite, maghemite, and magnetite and as a bidentate inner-sphere complex with ferrihydrite and lepidocrocite. Iron was present in the ferric form with ferrihydrite, goethite, lepidocrocite, and maghemite; whereas with magnetite and green rust II, both ferrous and ferric forms were present with characteristic ferrous:total iron ratios of 0.65 and 0.73, respectively. In the presence of the uranyl ion, green rust II was converted to magnetite with concomitantreduction of uranium to its tetravalent form. The rate and extent of uranium dissolution in dilute HCl depended on its association with the oxide: uranium present as oxyhydroxide species underwent rapid dissolution followed by a slow dissolution of iron; whereas uranium present as an inner-sphere complex with iron resulted in concomitant dissolution of the uranium and iron.