Technical description of the radiological safety system for X-ray absorption spectroscopy experiments on radioactive samples at the Rossendorf Beamline

The Rossendorf Beamline at the European Synchrotron Radiation Facility is equipped with a unique radiochemistry experimental station. This dedicated station has been designed to perform environmentally relevant experiments on radionuclides, in particular actinides, using synchrotron based X-ray absorption fine structure spectroscopy. The technical concepts and the layout of this experimental station, where radioactive solids and liquids with activities of up to 185 MBq can be studied, are presented. The radiological safety of experimenters, equipment, and of the environment are ensured by the specially developed radiochemistry safety system. The multibarrier concept, the ventilation and air monitoring systems, the radiological protection system, and special software components for recording and visualisation of the safety status are described in detail.

Ozone-climate interactions and effects on solar ultraviolet radiation

This report assesses the effects of stratospheric ozone depletion and anticipated ozone recovery on the intensity of ultraviolet (UV) radiation at the Earth's surface. Interactions between changes in ozone and changes in climate, as well as their effects on UV radiation, are also considered. These evaluations focus mainly on new knowledge gained from research conducted during the last four years. Furthermore, drivers of changes in UV radiation other than ozone are discussed and their relative importance is assessed. The most important of these factors, namely clouds, aerosols and surface reflectivity, are related to changes in climate, and some of their effects on short- and long-term variations of UV radiation have already been identified from measurements. Finally, projected future developments in stratospheric ozone, climate, and other factors affecting UV radiation have been used to estimate changes in solar UV radiation from the present to the end of the 21^st century. New instruments and methods have been assessed with respect to their ability to provide useful and accurate information for monitoring solar UV radiation at the Earth's surface and for determining relevant exposures of humans. Evidence since the last assessment reconfirms that systematic and accurate long-term measurements of UV radiation and stratospheric ozone are essential for assessing the effectiveness of the Montreal Protocol and its Amendments and adjustments. Finally, we have assessed aspects of UV radiation related to biological effects and human health, as well as implications for UV radiation from possible solar radiation management (geoengineering) methods to mitigate climate change.

Environmental effects of ozone depletion, UV radiation and interactions with climate change: UNEP Environmental Effects Assessment Panel, update 2017

The Environmental Effects Assessment Panel (EEAP) is one of three Panels of experts that inform the Parties to the Montreal Protocol. The EEAP focuses on the effects of UV radiation on human health, terrestrial and aquatic ecosystems, air quality, and materials, as well as on the interactive effects of UV radiation and global climate change. When considering the effects of climate change, it has become clear that processes resulting in changes in stratospheric ozone are more complex than previously held. Because of the Montreal Protocol, there are now indications of the beginnings of a recovery of stratospheric ozone, although the time required to reach levels like those before the 1960s is still uncertain, particularly as the effects of stratospheric ozone on climate change and vice versa, are not yet fully understood. Some regions will likely receive enhanced levels of UV radiation, while other areas will likely experience a reduction in UV radiation as ozone- and climate-driven changes affect the amounts of UV radiation reaching the Earth's surface. Like the other Panels, the EEAP produces detailed Quadrennial Reports every four years; the most recent was published as a series of seven papers in 2015 (Photochem. Photobiol. Sci., 2015, 14, 1-184). In the years in between, the EEAP produces less detailed and shorter Update Reports of recent and relevant scientific findings. The most recent of these was for 2016 (Photochem. Photobiol. Sci., 2017, 16, 107-145). The present 2017 Update Report assesses some of the highlights and new insights about the interactive nature of the direct and indirect effects of UV radiation, atmospheric processes, and climate change. A full 2018 Quadrennial Assessment, will be made available in 2018/2019.

Ozone depletion and climate change: impacts on UV radiation

Percentage changes in the UV Index (UVI) for 2090 relative to 2015 due to changes in ozone (left) and aerosols (right) only. Large decreases are projected over Antarctica due to stratospheric ozone recovery. Increases are projected for parts of Asia due to decreases in aerosols, partly reversing the possible large reductions in UVI after the 1950s.

Np(V) reduction by humic acid: contribution of reduced sulfur functionalities to the redox behavior of humic acid

The role of sulfur-containing functional groups in humic acids for the Np(V) reduction in aqueous solution has been studied with the objective to specify individual processes contributing to the overall redox activity of humic substances. For this, humic acid model substances type M1-S containing different amounts of sulfur (1.9, 3.9, 6.9 wt.%) were applied. The sulfur functionalities in these humic acids are dominated by reduced-sulfur species, such as thiols, dialkylsulfides and/or disulfides. The Np(V) reduction behavior of these humic acids has been studied in comparison to that of the sulfur-free humic acid type M1 at pH 5.0, 7.0 and 9.0 under anaerobic conditions by means of batch experiments. For Np redox speciation in solution, solvent extraction and ultrafiltration were applied. In addition, redox potentials of the sample solutions were monitored. At pH 5.0, both rate and extent of Np(V) to Np(IV) reduction were found to increase with increasing sulfur content of the humic acids. At pH 7.0 and 9.0, sulfur functional groups had only a slight influence on the reduction behavior of humic acid toward Np(V). Thus, in addition to quinoid moieties and non-quinoid phenolic OH groups, generally acknowledged as main redox-active sites in humic substances, sulfur functional groups have been identified as further redox-active moieties of humic substances being active especially in the slightly acidic pH range as shown for Np(V). Due to the low sulfur content of up to 2 wt.% in natural humic substances, their contribution to the total reducing capacity is smaller than that of the other redox-active functional groups.

A new uranyl benzoate species characterized by different spectroscopic techniques

For the first time in the aqueous phase the existence of a U(VI)-benzoate complex with a 1:2 stoichiometry could be proven. Using UV-Vis spectroscopy and especially cryo time-resolved laser-induced fluorescence spectroscopy (TRLFS) it was possible to characterize this complex in detail.

Room temperature TRLFS measurements revealed a static as well as a dynamic ligand-initiated quench process in the U(VI)-benzoic acid system. At these conditions no luminescence emission resulting from complex formation was found. Consequently cryo TRLFS was applied to increase the maximum detectable benzoate:U(VI) ratio. By this for the first time a luminescence spectrum of the 1:2 U(VI)-benzoate complex could be determined. This species is characterized by emission bands at 467, 485, 505, 526, and 550 nm which are blue-shifted compared to the ones of the UO2 2+ ion. The luminescence lifetime of the 1:2 complex amounts to 9.21±0.01 μs at −18 ºC compared to 150.4±0.5 μs for UO2 2+.

The stability constant of the newly found species log β 120 has been calculated to be 4.48±0.24. The stability constant of the 1:1 complex was validated to amount to 2.64±0.19. UV-Vis spectroscopy combined with factor analysis yielded the molar absorption spectrum of the 1:2 U(VI)-benzoate species which is characterized by absorption bands at 406, 418, 432.5, 447, and 461 nm and a molar absorption coefficient of 22 L mol−1 cm−1.

The influence of temperature and small organic ligands on the sorption of Eu(III) on Opalinus Clay

The influence of temperature up to 50 ºC and small organic ligands (citrate, tartrate) on the sorption of Eu(III) on the natural clay rock Opalinus Clay (OPA) under aerobic (p CO2 = 10−3.5 atm) synthetic OPA pore water conditions (pH 7.6, I = 0.4 mol L−1) was investigated. Batch sorption experiments and time-resolved laser-induced fluorescence spectroscopy (TRLFS) were used to study these influencing factors on the Eu(III) sorption.

Sorption isotherms and distribution coefficients R d (15 ºC: log R d = 4.50 ± 0.05...50 ºC: log R d = 5.54 ± 0.06) at 2 × 10−9 mol L−1 Eu(III) as a function of the solid-to-liquid ratio (up to 3 g L−1) and temperature were determined. A significant temperature dependency of the Eu(III) sorption was observed. With rising temperature the Eu(III) sorption increases. The surface reaction is endothermic (Δ H sorb ∼ 50 kJ mol−1). Using TRLFS, a surface species with a luminescence emission lifetime of 201 ± 9 μs was identified.

In the presence of tartrate or citrate the Eu(III) sorption decreases with increasing ligand concentration due to a complex formation of Eu(III) in solution, with citrate having a more pronounced influence on the sorption than tartrate. With the batch sorption experiments it can be shown that at a citrate concentration larger than 10−5 mol L−1 and at a tartrate concentration larger than 10−4 mol L−1 an increasing Eu(III) desorption occurs. This result is supported by TRLFS measurements, which show the correlation between the complexation of Eu(III) by citrate or tartrate in solution and the Eu(III) desorption process. Possible Eu(III) citrate or Eu(III) tartrate surface species on OPA could not be detected using TRLFS.

Interaction of uranium(VI) towards glutathione – an example to study different functional groups in one molecule

Glutathione, the most abundant thiol compound of the cell, has a great binding potential towards heavy metal ions. Hence it might influence the distribution of actinides on a cellular level. The unknown strength of the interaction of uranium(VI) with glutathione at physiologically relevant pH is subject of this paper and was studied with UV-vis spectroscopy and time-resolved laser-induced fluorescence spectroscopy (TRLFS). The complex stability constant of UO2H2GS+, logβ 0 121, was calculated to be 39.09 ± 0.15 and 39.04 ± 0.02 in case of UV-vis spectroscopy and TRLFS respectively. Therefore the average formation constant for UO2 2+ + H2GS− = UO2H2GS+ can be assigned to be log K 0 11 = 19.83 ± 0.15. Furthermore it was demonstrated that derivatization of the ligand associated with an enhancement of the ligand's spectroscopic properties can be used for the determination of complex stability constants and to assess the coordination chemistry in more detail. Using UV-vis spectroscopy, the stability constant of the complex between UO2 2+ and glutathione pyruvate S-conjugate, a well absorbing ligand in contrast to glutathione, was calculated to be >39.24 ± 0.08. Furthermore the interaction of UO2 2+ with glutathione derivatized with the fluorescent label monobromobimane was examined with femtosecond laser fluorescence spectroscopy. Thereby the stability constant of the 1:1 complex was determined to be >39.35 ± 0.02. Although the thiol group of glutathione was blocked a strong coordination was found. Thus a significant involvement of the thiol group in the coordination of U(VI) can be excluded.

Biosorption of U(VI) by the green algae Chlorella vulgaris in dependence of pH value and cell activity

Biosorption of uranium(VI) by the green alga Chlorella vulgaris was studied at varying uranium concentrations from 5 μM to 1mM, and in the environmentally relevant pH range of 4.4 to 7.0. Living cells bind in a 0.1mM uranium solution at pH 4.4 within 5 min 14.3 ± 5.5 mg U/g dry biomass and dead cells 28.3 ± 0.6 mg U/g dry biomass which corresponds to 45% and 90% of total uranium in solution, respectively. During 96 h of incubation with uranium initially living cells died off and with 26.6 ± 2.1 mg U/g dry biomass bound similar amounts of uranium compared to dead cells, binding 27.0 ± 0.7 mg U/g dry biomass. In both cases, these amounts correspond to around 85% of the initially applied uranium. Interestingly, at a lower and more environmentally relevant uranium concentration of 5 μM, living cells firstly bind with 1.3 ± 0.2 mg U/g dry biomass to 1.4 ± 0.1 mg U/g dry biomass almost all uranium within the first 5 min of incubation. But then algal cells again mobilize up to 80% of the bound uranium during ongoing incubation in the time from 48 h to 96 h. The release of metabolism related substances is suggested to cause this mobilization of uranium. As potential leachates for algal-bound uranium oxalate, citrate and ATP were tested and found to be able to mobilize more than 50% of the algal-bound uranium within 24h. Differences in complexation of uranium by active and inactive algae cells were investigated with a combination of time-resolved laser-induced fluorescence spectroscopy (TRLFS), extended X-ray absorption fine structure (EXAFS) spectroscopy and attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy. Obtained results demonstrated an involvement of carboxylic and organic/inorganic phosphate groups in the uranium complexation with varying contributions dependent on cell status, uranium concentration and pH.

Excited-state proton transfer of 3-hydroxybenzoic acid and 4-hydroxybenzoic acid

The excited-state proton transfer of 3-hydroxybenzoic acid and 4-hydroxybenzoic acid was studied by time-resolved laser-induced fluorescence spectroscopy with ultra-short laser pulses. The excited-state reactions were identified in aqueous media as a function of the pH value. Apart from the well-known inversion of the ordinary dissociation properties of these compounds, new species were found which exist only in the excited-state resulting from a temporal and reversible annihilation of the aromatic bond system. These species and their reaction mechanisms were detected by their absorption and fluorescence spectra.

EXAFS study on the neptunium(V) complexation by various humic acids under neutral pH conditions

The structure of Np(V) humic acid (HA) complexes at pH 7 was studied by extended X-ray absorption fine structure analysis (EXAFS). For the first time, the influence of phenolic OH groups on the complexation of HA and Np(V) in the neutral pH range was investigated using modified HAs with blocked phenolic OH groups and Bio-Rex70, a cation exchange resin having only carboxyl groups as proton exchanging sites.

The formation of Np(V) humate complexes was verified by near-infrared (NIR) spectroscopy. Axial Np-O bond distances of 1.84–1.85 Å were determined for the studied Np(V) humate complexes and the Np(V)-Bio-Rex70 sorbate. In the equatorial plane Np(V) is surrounded by about 3 oxygen atoms with bond lengths of 2.48–2.49 Å. The comparison of the structural parameters of the Np(V) humates with those of Np(V)-Bio-Rex70 points to the fact that the interaction between HA and Np(V) in the neutral pH range is dominated by carboxylate groups. However, up to now a contribution of phenolic OH groups to the interaction process cannot be excluded completely. The comparison of the obtained structural data for the Np(V) humates to those of Np(V) carboxylates and Np(V) aquo ions reported in the literature indicates that humic acid carboxylate groups predominantly act as monodentate ligands. A differentiation between equatorial coordinated carboxylate groups and water molecules using EXAFS spectroscopy is impossible.

Uranium(VI) complexes with sugar phosphates in aqueous solution

The complex formation in the aqueous systems of uranium(VI) with glucose 6-phosphate (G6P) and fructose 6-phosphate (F6P) were studied using potentiometric titration, TRLFS, and EXAFS. Two complexes with a uranyl-to-ligand ratio of 1:1 and 1:2 for both sugars were observed. Complex stability constants were determined by potentiometric titration for both complexes to be log β11(G6P)=5.89±0.40, log β12(G6P)=9.45±0.08, log β11(F6P)=5.72±0.21, and log β12(F6P)=9.54±0.09. Stability constants could be determined with TRLFS under the specific experimental conditions only for the 1:1 complexes: log β11(G6P)=6.35±0.28, and log β11(F6P)=5.66±0.17.

The TRLFS measurements results show the UO2G6P complex to exhibit no fluorescence properties. For this system, only a decrease of the fluorescence intensity with increasing ligand concentration was observed. For the UO2F6P system, a red shift of the fluorescence emission bands of about 8 to 9 nm compared to the free uranyl ion was observed. The fluorescence emission wavelengths of the UO2F6P complex were determined to be 483, 496, 518, 542, and 567 nm, and the lifetime of this complex is 0.13±0.05 μs.

Uranium L III-edge EXAFS measurements at pH 3.5, 4.0, and 5.5 yielded a shortened U–Oeq bond distance (2.30±0.02 to 2.37±0.02 Å), compared to the UO2 2+(H2O)5 ion (2.40±0.02 Å), due to a monodentate coordination via the oxygen atoms of the phosphate group.

Uranyl(VI) carbonate complex formation: Validation of the Ca2UO2(CO3)3(aq.) species

We recently discovered a neutral dicalcium uranyl tricarbonate complex, Ca2UO2(CO3)3(aq.), in uranium mining related waters [1]. We are now reporting a further validation of the stoichiometry and the formation constant of this complex using two analytical approaches with time-resolved laser-induced fluorescence spectroscopy (TRLFS) species detection: i) titration of a non-fluorescent uranyl tricarbonate complex solution with calcium ions, and quantitative determination of the produced fluorescent calcium complex via TRLFS; and ii) variation of the calcium concentration in the complex by competitive calcium complexation with EDTA4-.

Slope analysis of the log (fluorescence intensity)versuslog[Ca2+] with both methods have shown that two calcium ions are bound to form the complex Ca2UO2(CO3)3(aq.). The formation constants determined from the two independent methods are: i) logβ°213=30.45±0.35 and ii) logβ°213=30.77±0.25.

A bathochrome shift of 0.35 nm between the UO2(CO3)34-complex and the Ca2UO2(CO3)3(aq.) complex is observed in the laser-induced photoacoustic spectrum (LIPAS), giving additional evidence for the formation of the calcium uranyl carbonate complex.

EXAFS spectra at the LIIand LIII-edges of uranium in uranyl carbonate solutions with and without calcium do not differ significantly. A somewhat better fit to the EXAFS of the Ca2UO2(CO3)3(aq.) complex is obtained by including the U-Ca shell. From the similarities between the EXAFS of the Ca2UO2(CO3)3(aq.) species in solution and the natural mineral liebigite, we conclude that the calcium atoms are likely to be in the same positions both in the solution complex and in the solid.

This complex influences considerably the speciation of uranium in the pH region from 6 to 10 in calcium-rich uranium-mining-related waters.

Uranium(VI) sorption onto phyllite and selected minerals in the presence of humic acid

We studied the influence of humic acid (HA) on the uranium(VI) sorption onto the rock material phyllite and onto its main mineral constituents quartz, muscovite, chlorite, and albite at an ionic strength of 0.1 M in the pH range of 3.5 to 9.5 under aerobic conditions. The uranium(VI) concentration was 1 × 10-6M and the HA concentration was 5 and 60 mg/L, respectively. The solid/solution ratio was 12.5 g/L. Furthermore, we studied the uranium and HA sorption on ferrihydrite (3 × 10-4M Fe) and compared the results to the sorption behavior of phyllite. The study showed that the uranium sorption onto phyllite and onto its mineral constituents is influenced by the pH-dependent sorption behavior of the HA. Due to high HA sorption onto the solids in the acidic pH range the uranium uptake is enhanced compared to the uranium uptake in the absence of HA. A high concentration of dissolved HA in the near-neutral pH range reduces the uranium sorption due to formation of aqueous uranyl humate complexes. Furthermore, we could show that the high uranium and HA sorption on phyllite is primarily caused by minor amounts of the secondary mineral ferrihydrite that is formed due to weathering of phyllite. Thus, the ferrihydrite predominates the contributions of the main minerals quartz, muscovite, chlorite, and albite, that are naturally present in the rock material phyllite.

Investigation of humic acid complexation behavior with uranyl ions using modified synthetic and natural humic acids

We investigated the influence of phenolic OH groups on the complexation behavior of humic acid (HA) with UO22+ions at pH 4. Starting from synthetic HA type M1, natural HA Aldrich, and natural HA Kranichsee, we synthesized modified HAs with blocked phenolic OH groups by derivatization with diazomethane. The partial blocking of phenolic OH groups was confirmed by a radiometric method which quantitatively determined the functional groups and by FTIR spectroscopy. The complexation behavior of the chemically modified and unmodified HAs with UO22+ions was investigated by time-resolved laser-induced fluorescence spectroscopy. The experimental data were evaluated with the metal ion charge neutralization model. We determined comparable complexation constants for all HAs. Two modified HAs (type M1 and Aldrich) had significantly lower loading capacities for UO22+ions (10.5 ± 0.9% and 9.7 ± 1.6%, respectively) than the corresponding unmodified HAs 18.0 ± 2.0% and 17.5 ± 1.6%, respectively). This indicates that the blocking of the phenolic OH groups changes the complexation behavior of HAs.

EXAFS investigation of uranium(VI) complexes formed at Bacillus cereus and Bacillus sphaericus surfaces

Uranium(VI) complex formation at vegetative cells and spores of Bacillus cereus and Bacillus sphaericus was studied using uranium L II-edge and L III-edge extended X-ray absorption fine structure (EXAFS) spectroscopy. A comparison of the measured equatorial U-O distances and other EXAFS structural parameters of uranyl species formed at the Bacillus strains with those of the uranyl structure family indicates that the uranium is predominantly bound as uranyl complexes with phosphoryl residues.

Uranyl(VI) complexes with alpha-substituted carboxylic acids in aqueous solution

The complex formation in the binary uranium(VI)-glycolate, -α-hydoxyisobutyrate, -α-aminoisobutyrate systems in 1.0 M NaClO4 medium was studied by means of UV-vis, TRLFS, and EXAFS. An increase in absorption and a red shift of the spectra, 5 nm compared to the free UO2 2+, indicate a complex formation between UO2 2+ and α-substituted carboxylic acids already at pH 2. 1:1 complexes dominate the uranyl speciation in the glycolate, α-hydoxyisobutyrate, and α-aminoisobutyrate system at pH 2 and 3, respectively. At higher ligand concentrations a 1:2 complex between UO2 2+ and α-aminoisobutyric acid was observed. There is a very strong quenching of the U(VI) fluorescence in theuranyl–α-hydroxycarboxylate systems that can be quantitatively described by the Stern–Volmer equation. As a result of the strong quenching it is not possible to detect fluorescence spectra for these complexes using TRLFS. The UO2 2+(aq) concentration calculated from the Stern–Volmer equation was used to determine equilibrium constants which are in good agreement with those obtained by potentiometry and NMR spectroscopy. No quenching was observed in the α-aminoisobutyrate system and their fluorescence spectra could be deconvoluted into components for the different species present. The following stability constants result from our TRLFS experiments: a) for the glycolate system log β UO₂(HOCH₂COO)⁺=2.52±0.20, b) for the α-hydroxyisobutyrate system log β UO₂[HOC(CH₃)₂COO]⁺=3.40±0.21, and c) for the α-aminoisobutyrate system logβUO₂[NH₃C(CH₃)₂COO]²⁺=1.30±0.10 and log β UO₂[NH₃C(CH₃)₂COO]₂²⁺=2.07±0.25. An increase of the fluorescence intensity connected with a red shift of the fluorescence emission spectra was observed in the system uranyl–α-aminoisobutyric acid. Fluorescence lifetimes and spectra were obtained for UO2 2+, UO2[NH3C(CH3)2COO]2+, and UO2[NH3C(CH3)2COO]2 2+. Uranium L III-edge EXAFS measurements yielded an U-Oeq distance of 2.40 to 2.43 Å in the pH range from 2 to 4 in the α-hydroxyisobutyrate system showing a dominant bidentate coordination via the oxygens of the carboxylic group. Slightly shorter U-Oeq distances of 2.40 to 2.38 Å and no evidence for U-C distances around 2.90 Å in the glycolate system in this pH range may indicate a monodentate coordinated ligand via one oxygen from the carboxylic group. The decrease in the U-Oeq distance of the equatorial oxygens in both systems to 2.36-2.37 Å at pH values ≥5 is a strong indication for the formation of a chelate complex due to the deprotonation of the α-OH-group of the ligand. In the glycolate system in the pH range 5.5 to 11, the EXAFS spectrum showed evidence of U-U interaction at 3.81 Å indicating the formation of dimeric species.

Complex formation between uranium(VI) and α-D-glucose 1-phosphate

The complex formation of uranium(VI) with α-D-glucose 1-phosphate (C6H11O6PO3 2-, G1P) was determined by time-resolved laser-induced fluorescence spectroscopy (TRLFS) at pH 4 and potentiometric titration in the pH range from 3 to 10. Both measurements show the formation of a 1:1 complex at lower pH values. The formation constant of UO2(C6H11O6PO3) was calculated from TRLFS measurements to be log β 11=5.72±0.12, and from potentiometric titration log β 11=5.40±0.25, respectively.It was found by potentiometric titration that at higher pH values the complexation changes to a 1:2 complex. The stability constant for this complex was calculated to be log β 12 = 8.96±0.18.

Study of uranyl(VI) malonate complexation by time resolved laser-induced fluorescence spectroscopy (TRLFS)

The uranyl(VI) malonate complex formation was studied by time-resolved laser-induced fluorescence spectroscopy (TRLFS) at pH 4 and an ionic strength of 0.1 M NaClO4. The uranium concentration was 5 × 10−6M at ligand concentrations from 1 × 10−5to 1 ×−2M.

The measured fluorescence lifetimes of the 1:1 and 1:2 uranyl(VI) malonate complexes are 1.24 ± 0.02 µs and 6.48 ± 0.02 µs, respectively. The fluorescence lifetime of the uranyl(VI) ion is 1.57 ± 0.06 µs in 0.1 M perchloric media. The main fluorescence bands of the malonate complexes show a bathochromic shift compared to the uranyl(VI) ion and are centered at 494 nm, 515 nm and 540 nm for the 1:1 complexes and at 496 nm, 517 nm and 542 nm for the 1:2 complex. The spectra of the individual uranyl(VI) malonate complexes were calculated using a multi exponential fluorescence decay function for each intensity value at each wavelength, covering the entire wavelength range. Stability constants were determined for the complexes UO2C3H2O4°(aq)and UO2(C3H2O4)22−from results of spectra deconvolution using a least square fit algorithm (logβ1° = 4.48 ± 0.06, logβ2° = 7.42 ± 0.06 or logK2° = 2.94 ± 0.04). The results are compared with literature values obtained by potentiometric measurements.

EXAFS structural analysis of aqueous uranium(VI) complexes with lignin degradation products

Uranium LIII-edge extended X-ray absorption fine structure (EXAFS) analysis was carried out on aqueous uranium(VI) complexes with monomeric intermediates of the natural wood-degradation process such as protocatechuic acid (3,4-dihydroxybenzoic acid), catechol (2-hydroxyphenol), pyrogallol (1,2,3-trihydroxybenzol), and vanillic acid (4-hydroxy-3-methoxybenzoic acid). The structural parameters of the 1:1 complexes with protocatechuic acid and vanillic acid in weakly acidic solution indicate that the carboxylic group coordinates the uranyl cation in a bidentate mode in the equatorial plane. Based on the identical structural parameters observed for protocatechuic acid, catechol and pyrogallol in alkaline media, we conclude that the coordination with uranium occurs via the neighboring OH groups of the phenols under formation of a five-membered ring.

Complex formation of U(VI) with Bacillus-isolates from a uranium mining waste pile

Accumulation studies with vegetative cells and spores of three Bacillus isolates (JG-A 30, JG-A 12, JG-A 22, classified as Bacillus cereus, Bacillus sphaericus, Bacillus megaterium) from a uranium mining waste pile (Johanngeorgenstadt, Saxony) and their corresponding reference strains have shown that Bacilli accumulate high amounts of U(VI) in the concentration range examined (11-214 mg/L). Information on the binding strength and the reversibility were obtained from extraction studies with different extractants. With 0.01 M EDTA solution the uranium bound to the biomass was released almost quantitatively. The characterization of the bacterial-UO22+-complexes by time-resolved laser fluorescence spectroscopy (TRLFS) showed the formation of inner-sphere complexes with phosphate groups of the biomass. The results lead to the conclusion that the cell wall components with phosphate residues e.g., polysaccharides, teichoic and teichuroic acids or phospholipide layers of the membranes are responsible for the uranium binding. The spectroscopic studies of the U(VI)-complexes with isolated bacterial cell walls and isolated surface-layer proteins of the strain Bacillus sphaericus NCTC 9602 after cell fractionation have shown that the complexation of U(VI) with intact cells (vegetative cells or spores) is different from the coordination with isolated cell wall components, especially with the S-layer proteins. For all Bacillus strains studied in this work, a significant contribution of the S-layer proteins to the binding of uranyl to living cells can be excluded.

NIR spectroscopic study of the complexation of neptunium(V) with humic acids: influence of phenolic OH groups on the complex formation

The influence of phenolic OH groups on the Np(V) complexation by humic acids was studied at pH 7 and pH 8 under nitrogen atmosphere applying chemically modified humic acids with blocked phenolic OH groups in comparison to their corresponding unmodified humic acids. The studies were performed by near-infrared (NIR) absorption spectroscopy using the metal ion charge neutralization model for evaluation of the experimental data. For all humic acids under investigation comparable complexation constants were determined. However, the studied modified humic acids Aldrich and M42 show significantly lower loading capacities for NpO2+ions (e.g., pH 7: 7.2%±1.1% and 5.3%±1.0%, respectively) than the corresponding unmodified humic acids (e.g., pH 7: 10.0%±1.5 and 11.2%±1.1, respectively). This result points to a lower amount of maximal available humic acid ligand sites after blocking of phenolic OH groups. From that, it can be concluded that humic acid phenolic OH groups contribute to the interaction between humic acid and Np(V) under the studied conditions. The comparison of the loading capacities obtained for unmodified and modified Aldrich humic acid at pH 7 and pH 8 shows that the impact of phenolic OH groups on the Np(V) complexation by humic acids is increased with increasing pH value.

Neptunium(IV) complexation by humic substances studied by X-ray absorption fine structure spectroscopy

We studied the coordination environment of neptunium(IV) in complexes with various natural and synthetic humic and fulvic acids at pH 1 by X-ray absorption fine structure (XAFS) spectroscopy. The results were compared to those obtained for the interaction of neptunium(IV) with Bio-Rex70, a cation exchange resin having solely carboxylic groups as metal binding functional groups. In both neptunium humate complexes and neptunium Bio-Rex70 sorbates, Np4+is surrounded by about 10 oxygen atoms at an average distance of 2.36±0.02 Å. This verifies that the carboxylic groups are the main complexing sites of the humic substances responsible for binding neptunium(IV) in the acidic pH range. The data suggest a predominant monodentate coordination of the carboxylate groups to neptunium(IV) ions.

A novel time-resolved laser fluorescence spectroscopy system for research on complexation of uranium(IV)

To date only a small number of studies have investigated the chemical speciation of complexes and the fluorescence properties of metal ions whose emitted fluorescence lifetime is in the range of only few nanoseconds. This is due to a lack of advanced methods which allow the conduction of these measurements. In the current study we set up a new time-resolved laser fluorescence spectroscopy system with which the fluorescence properties of metal ions with very short fluorescence lifetimes such as uranium(IV) and its compounds can be investigated. By studying the fluorescence properties of uranium(IV) in perchloric acid, we showed uranium(IV) to have a detection limit of 5 x 10(-7)M and a fluorescence decay time of 2.74+/-0.36 ns. We further investigated the fluorescence properties of uranium(IV) during the reaction with fluoride and applied our novel laser system to study the complexation of uranium(IV) with fluoride. Our data revealed the formation of a 1:1 complex of uranium(IV) and fluoride. The corresponding complex formation constant of uranium(IV) fluoride UF(3+) was found to be log beta(0)=9.43+/-1.94. Our results demonstrate that our novel time-resolved laser fluorescence spectroscopy system can successfully conduct speciation measurements of metal ions and their compounds with very short-lived fluorescence lifetimes. Using this laser system, it is possible to analytically investigate such elements and compounds in environmentally relevant concentration ranges.

Mixed complexes of alkaline earth uranyl carbonates: a laser-induced time-resolved fluorescence spectroscopic study

The interaction of the alkaline earth ions Mg(2+), Sr(2+) and Ba(2+) with the uranyl tricarbonato complex has been studied by time-resolved laser-induced fluorescence spectroscopy. In contrast to the non-luminescent uranyl tricarbonato complex at ambient temperature the formed products show luminescence properties. These have been used to determine the stoichiometry and complex stabilities of the formed compounds. As the alkaline earth elements are located in an outer shell of the complex the influence of the type of the alkaline earth element on the stability constant is not very drastic. The stability constants range from log beta113 degrees = 26.07+/-0.13 to log beta113 degrees = 26.93+/-0.25 for the first reaction step and from log beta213 degrees = 29.73+/-0.47 to log beta213 degrees = 30.79+/-0.29 for the overall complex formation with two alkaline earth ions.

Sorption of U(VI) onto an artificial humic substance-kaolinite-associate

An artificial humic substance-kaolinite-associate (HSKA) was synthesized as a model substance for natural clays containing organic matter in clay formations, soils, and sediments. The U(VI) sorption onto this model substance was studied in batch experiments as a function of pH and compared to the U(VI) sorption onto kaolinite in absence and presence of separately added humic acid (HA). The HSKA has a TOC content of 4.9 mg g(-1). It was found that the humic matter associated with kaolinite exhibits an immobilizing as well as an mobilizing effect on U(VI). Between pH 3 and 5, humic matter causes an increase of the U(VI) sorption onto kaolinite, whereas at pH above 5 the release of humic matter from the associate into the solution and the formation of dissolved uranyl humate complexes reduces the U(VI) sorption. The U(VI) sorption onto the synthetic HSKA differs from that of U(VI) in the system U(VI)/HA/kaolinite with comparable amounts of separately added HA. Separately added HA causes a stronger mobilizing effect on U(VI) than humic matter present in HSKA. This can be attributed to structural and functional dissimilarities of the humic substances.

Uranium(VI) complexes with phospholipid model compounds--a laser spectroscopic study

We present the complex formation of the uranyl ion (UO(2)(2+)) in the aqueous system with phosphocholine, O-phosphoethanolamine and O-phosphoserine. These phosphonates (R-O-PO(3)(2-)) represent the hydrophilic head groups of phospholipids. The complexation was investigated by time-resolved laser-induced fluorescence spectroscopy (TRLFS) at pH=2-6. An increase of the fluorescence intensity, connected with a strong red-shift of about 8 nm compared to the free uranyl ion, indicates a complex formation between UO(2)(2+) and the phosphonates already at pH=2. Even at pH=6 these complexes prevail over the uranyl hydroxide and carbonate species, which are generated naturally at this pH. At pH=4 and higher a 1:2 complex between uranyl and O-phosphoserine was found. Complexes with a metal-to-ligand ratio of 1:1 were observed for all other ligands. Fluorescence lifetimes, emission maxima and complex stability constants at T=22+/-1 degrees C are reported. The TRLFS spectra of uranyl complexes with two phosphatidic acids (1,2-dimyristoyl-sn-glycero-3-phosphate and 1,2-dipalmitoyl-sn-glycero-3-phosphate), which represent the apolaric site of phospholipids, show in each case two different species.

Comparative EXAFS investigation of uranium(VI) and -(IV) aquo chloro complexes in solution using a newly developed spectroelectrochemical cell

The coordination of the U(IV) and U(VI) ions as a function of the chloride concentration in aqueous solution has been studied by U L(III)-edge extended X-ray absorption fine structure (EXAFS) spectroscopy. The oxidation state of uranium was changed in situ using a gastight spectroelectrochemical cell, specifically designed for the safe use with radioactive solutions. For U(VI) we observed the complexes UO2(H2O)5(2+), UO2(H2O)4Cl+, UO2(H2O)3Cl2(0), and UO2(H2O)2Cl3- with [Cl-] increasing from 0 to 9 M, and for U(IV) we observed the complexes U(H2O)9(4+), U(H2O)8Cl3+, U(H2O)(6-7)Cl2(2+), and U(H2O)5Cl3+. The distances in the U(VI) coordination sphere are U-Oax = 1.76+/-0.02 A, Oeq = 2.41 +/- 0.02 A, and U-Cl = 2.71 +/- 0.02 A; the distances in the U(IV) coordination sphere are U-O = 2.41 +/- 0.02 A and U-Cl = 2.71 +/- 0.02 A.

Complex formation of neptunium(V) with 4-hydroxy-3-methoxybenzoic acid studied by time-resolved laser-induced fluorescence spectroscopy with ultra-short laser pulses

The complex formation of neptunium(V) with 4-hydroxy-3-methoxybenzoic acid (vanillic acid) was studied by time-resolved laser-induced fluorescence spectroscopy with ultra-short laser pulses using the fluorescence properties of 4-hydroxy-3-methoxybenzoic acid. A 2:1 complex of neptunium(V) with 4-hydroxy-3-methoxybenzoic acid was found. The stability constant of this complex was determined to be logbeta(210) = 7.33 +/- 0.10 at an ionic strength of 0.1 mol/l (NaClO(4)) and at 21 degrees C. The determination of the stability constant required an investigation of the excited-state proton transfer of 4-hydroxy-3-methoxybenzoic acid over the whole pH range. It was realized that 4-hydroxy-3-methoxybenzoic acid undergoes excited-state reactions only at pH values below 5. At pH values above 5 stability constants can be determined without kinetic calculation of the proton transfer.

Combining entacapone with levodopa/DDCI improves clinical status and quality of life in Parkinson?s Disease (PD) patients experiencing wearing-off, regardless of the dosing frequency: results of a large multicentre open-label study

The efficacy of entacapone and its impact on patient quality of life (QOL) was investigated in an open-label study of 899 patients with idiopathic Parkinson's Disease (PD) experiencing wearing-off fluctuations. Patients were divided into 3 groups (3, 4 or 5 doses daily) based on their current levodopa dosage frequency. Patients received 200 mg entacapone with each levodopa/dopa-decarboxylase inhibitor (DDCI) dose, while continuing their same levodopa/DDCI dosage regimen for 4 weeks. Primary efficacy measure was the Investigators' Clinical Global Impression of Change (CGIC). Patient QoL was assessed using the validated 8-item Parkinson's Disease Questionnaire (PDQ-8). Investigators' CGIC revealed that 76.5% of entacapone treated patients experienced an improvement in global status after 4 weeks. Treatment with entacapone was also associated with improvement in patient QoL, with a mean reduction (improvement) in PDQ-8 score of 1.8 from baseline. This study confirms and extends the results of earlier studies demonstrating that, independent of dosing frequency, completing levodopa/DDCI therapy with entacapone provides clinically relevant improvements in global status and QoL in PD patients experiencing wearing-off on their current levodopa dosing frequency.

Pneumatic dilation for achalasia: late results of a prospective follow up investigation

BACKGROUND

and aims: In this prospective study, we determined the long term clinical course of patients with achalasia who were treated by pneumatic dilation using the Browne-McHardy dilator, and determined whether previously described predictors of outcome remain significant after prolonged follow up.

METHODS

Between 1981 and 1991, 54 consecutive patients were treated by pneumatic dilation and followed up at regular intervals for a median of 13.8 years. Remission was determined with the use of a structured interview and a previously described symptom score. Duration of remission was evaluated by Kaplan-Meier estimates of time to recurrence. Predictors of outcome were determined using the log rank test.

RESULTS

Complete follow up until 2002 was obtained in 98% of all patients. Seven patients had died and were censored. A single pneumatic dilation resulted in a five year remission rate of 40% and a 10 year remission rate of 36%. Repeated dilations only mildly improved the clinical response. Patients who were older than 40 years had a significantly better outcome than younger patients (log rank test, p = 0.0014). However, the most significant predictive factor for a favourable long term outcome was a post-dilation lower oesophageal sphincter pressure of less than 10 mm Hg (log rank test, p = 0.0001).

CONCLUSIONS

Long term results of pneumatic dilation are less favourable than previously thought. Young patients and those not responding to a single pneumatic dilation should be offered alternative therapy. Patients who remain in remission for five years are likely to benefit from the longlasting treatment effect of pneumatic dilation.

Time-resolved laser fluorescence spectroscopy study on the interaction of curium(III) with Desulfovibrio äspöensis DSM 10631T

The influence of microorganisms on migration processes of actinides has to be taken into account for the risk assessment of potential high-level nuclear waste disposal sites. Therefore it is necessary to characterize the actinide-bacteria species formed and to elucidate the reaction mechanisms involved. This work is focused on the sulfate-reducing bacterial (SRB) strain Desulfovibrio äspöensis (D. äspöensis) DSM 10631T which frequently occurs in the deep granitic rock aquifers at the Aspö Hard Rock Laboratory (Aspö HRL), Sweden. We chose Cm(III) due to its high fluorescence spectroscopic sensitivity as a model system for exploring the interactions of trivalent actinides with D. äspöensis in the trace concentration range of 3 x 10(-7) mol/L. A time-resolved laser fluorescence spectroscopy (TRLFS) study has been carried out in the pH range from 3.00 to 7.55 in 0.154 mol/L NaCl. We interpret the pH dependence of the emission spectra with a biosorption forming an inner-sphere surface complex of Cm(III) onto the D. äspöensis cell envelope. This Cm(III)-D. äspöensis-surface complex is characterized by its emission spectrum (peak maximum at 600.1 nm) and its fluorescence lifetime (162 +/- 5 micros). No evidence was found for incorporation of Cm(III) into the bacterial cells under the chosen experimental conditions.