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  • Author: Takuo Ozaki x
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Summary

We investigated the interactions of the Fe(III)-, Eu(III)-, and Hf(IV)-desferrioxamine B (DFO) complexes with the Gram-negative aerobic bacterium Pseudomonas fluorescens. Potentiometric titration of 1:1 Fe(III)-, Eu(III)-, and Hf(IV)-DFO complexes showed that Hf(IV) formed a strong complex with DFO whose stability was comparable to that of the Fe(III)-DFO complex, while Eu(III) formed a weaker one. DFO in a growth medium was not degraded by P. fluorescens. Contact of P. fluorescens cells with the Fe(III)-, Eu(III)-, and Hf(IV)-DFO complexes at pH 4-9 revealed that there was negligible adsorption of Hf(IV) and Fe(III), whereas Eu(III) was dissociated from DFO and was readily adsorbed by the cells. These results suggest that Fe(III) and Hf(IV) form stable complexes with DFO and are not adsorbed by P. fluorescens cells. Europium(III) forms a weaker complex with DFO than Fe(III) and Hf(IV) do and its DFO complex is readily dissociated in the presence of the cells.

We studied the effect of ionic strength on the interactions of Europium(III) and Curium(III) with a Gram-negative bacterium Paracoccus denitrificans . Bacterial cells grown in 0.5-, 3.5-, and 5.0% NaCl were used in adsorption experiments and laser experiments that were performed at the same ionic strengths as those in the original growth media. The distribution ratio (logK d) for Eu(III) and Cm(III) was determined at pHs 3−5. To elucidate the coordination environment of Eu(III) adsorbed on P. denitrificans, we estimated the number of water molecules in the inner sphere and strength of the ligand field by time-resolved laser-induced fluorescence spectroscopy (TRLFS) at pHs 4−6. The logK d of Eu(III) and Cm(III) increased with an increase of pH at all ionic strengths because there was less competition for ligands in cells with H+ at higher pHs, wherein less H+ was present in solution: cation adsorption generally occurs through an exchange with H+ on the functional groups of coordination sites. No significant differences were observed in the logK d of Eu(III) and Cm(III) at each pH in 0.5-, 3.5-, and 5.0% NaCl solutions, though competition for ligands with Na+ would be expected to increase at higher NaCl concentrations. The logK d of Eu(III) was almost equivalent to that of Cm(III) under all the experimental conditions. TRLFS showed that the coordination environments of Eu(III) did not differ from each other at 0.5-, 3.5-, and 5.0% NaCl at pHs 4−6. TRLFS also showed that the characteristic of the coordination environment of Eu(III) on P. denitrificans was similar to that on a halophile, Nesterenkonia halobia, while it significantly differed from that on a non-halophile, Pseudomonas putida . These findings indicate that the number of coordination sites for Eu(III) on P. denitrificans, whose cell surface may have similar structures to that of halophiles, increased with increasing ionic strength, though their structure remained unchanged.

Summary

An optical cell system for spectroscopic speciation of f-elements in hydrothermal solutions was developed and applied to study the luminescence properties of lanthanide[Ln](III) ions by time-resolved laser-induced fluorescence spectroscopy. The apparatus to maintain the hydrothermal conditions consists of a HPLC pump, an optical cell with three sapphire windows, an electric furnace, a back pressure regulator, etc. Temperature and pressure of sample solutions can be controlled independently in the range of ambient conditions to 723 K and 40 MPa, respectively. Emission spectra and lifetimes of Ln(III) in HClO4 solutions were measured as a function of temperature and pressure. The pressure effect on the emission spectra and lifetimes was not observed in the range of 0.1 to 40 MPa at a constant temperature. From the temperature dependence of the luminescence properties at 40 MPa, it was found that Ln(III) exist as a hydrated ion up to ca. 500 K and that the variation of the luminescence properties at higher temperature is mainly due to the hydrolysis of Ln(III). Thermodynamic parameters and isotope effects for the quenching of excited Ln(III) in H2O and D2O solutions were also estimated from the temperature dependence of the luminescence lifetimes.

Summary

The simultaneous permeation of Sc, Y, Ce, Pm, Eu, Gd, Yb and Lu through a 2-ethylhexyl phosphonic acid-2-ethylhexyl ester (EHEHPA)-decalin membrane supported on a microporous polytetrafluoroethylene sheet was studied using a multitracer. The permeation rates of the elements from feed solutions of various acidity into receiving solutions of 2mol dm-3 HCl were determined. The feed solution at pH 1.5 gave the highest percentage of permeation for Ce, Pm, Eu, Gd and Yb, amounting to about 90 after -25h permeation. The percentage of permeation of Y and Lu was the highest at pH 1, amounting to about 90 after -25h permeation. The permeation of Sc from all the feed solutions was less than 4 due to its adsorption on the vessel. The permeation from the feed solution at pH 1.5 into the receiving solutions of 1, 2, 3, 4 and 5mol dm-3 HCl showed that the maximum percentage of transport for Y and Yb was obtained in 2mol dm-3 HCl receiving solution and that for Lu in 2-4mol dm-3 HCl receiving solutions. The other elements gave a percentage of transport more than 90 in 1-5mol dm-3 HCl receiving solutions, showing no obvious HCl concentration effect. The permeability coefficients of these elements were determined. Solvent extraction of the elements by EHEHPA-decalin was also carried out for comparison.

Summary

We investigated the association of europium(III) and curium(III) with the microorganisms Chlorella vulgaris, Bacillus subtilis, Pseudomonas fluorescens, Halomonas sp., Halobacterium salinarum, and Halobacterium halobium . We determined the kinetics and distribution coefficients (K d) for Eu(III) and Cm(III) sorption at pH 3-5 by batch experiments, and evaluated the number of water molecules in the inner-sphere (NH₂O) and the degree of strength of ligand field (R E/M) for Eu(III) by time-resolved laser-induced fluorescence spectroscopy (TRLFS). Exudates from C. vulgaris, Halomonas sp., and H. halobium had an affinity for Eu(III) and Cm(III). The log K d of Eu(III) and Cm(III) showed that their sorption was not fully due to the exchange with three protons on the functional groups on cell surfaces. The halophilic microorganisms (Halomonas sp., Halobacterium salinarum, H. halobium) showed almost no pH dependence in log K d, indicating that an exchange with Na+ on the functional groups was involved in their sorption. The Δ NH₂O(=9-NH₂O) for Eu(III) on C. vulgaris was 1-3, while that for the other microorganisms was over 3, demonstrating that the coordination of Eu(III) with C. vulgaris was predominantly an outer-spherical process. The R E/M for Eu(III) on halophilic microorganisms was 2.5-5, while that for non-halophilic ones was 1-2.5. This finding suggests that the coordination environment of Eu(III) on the halophilic microorganisms is more complicated than that on the other three non-halophilic ones.

Summary

Irrespective of low bioavailability, some plant species accumulate Y and rare earth elements (REEs) to a great extent (accumulator species). The uptake mechanisms of Y and REEs were investigated for autumn fern, one of accumulator species. For comparison, plant species which accumulated poorly REEs (non-accumulator species) were also studied. In the present investigation, two noticeable phenomena were observed. (I) Autumn fern showed no ionic-radius dependence of Y-REE uptake by leaves, while non-accumulator species showed an extremely high uptake for Y compared with REEs. (II) Y-REE uptake by autumn fern was influenced by the addition of chelating reagents to the uptake solution, while no effect was observed for non-accumulator species.

With the aim of preparing carrier-free 28Mg and 47Ca simultaneously, Ti, V and Fe targets were examined by irradiating with high-energy ions of 12C, 14N and 16O accelerated by the RIKEN Ring Cyclotron. Among the targets, V gave the highest cross section for the formation of both 28Mg and 47Ca irrespective of the kind of beams. The cross section for the formation of 28Mg by the reactions of Ti, V and Fe targets with ion beams increased in the order of 12C < 16O<14N. On the other hand, the three beams exhibited almost the same cross sections for the formation of 47Ca by the reaction of a given target. Titanium and V were selected as prospective targets and 14N as a suitable beam for the production of 28Mg and 47Ca. Chemical separation procedures of the radiotracers in carrier- and salt-free states have been established by using cation exchange resins. The recovery yields of 28Mg and 47Ca from Ti target were 70 and 90%, respectively, and the decontamination factor was less than 10-5. The recovery yields of 28Mg and 47Ca from V target were 80% and the decontamination factor was less than 10-7.

We examined the reduction behavior of UO2 2+ in citrate media at pH 2.0−7.0 by column electrodes. At pH 2.0, UO2 2+ was reduced to U(IV) through a one-step reduction process, while it was reduced to U(IV) through a two-step reduction process at pH 3.0−5.0. The reduction potential of UO2 2+ shifted to lower values with an increase in pH from 2.0 to 7.0. At pH 6.0 and 7.0, UO2 2+ was not reduced to U(IV) completely at the electrode potential above -0.8 V vs . silver/silver chloride electrode. Ultraviolet-visible spectroscopy and speciation calculation of UO2 2+ in citrate media indicated that uranium existed as a mixture of UO2 2+, [UO2Cit]- and [(UO2)2Cit2]2- at pH 2−3, and a predominant species at pH 3−5 was [(UO2)2Cit2]2- (H3Cit: citric acid). At pH 5−7, polymeric complexes, probably, [(UO2)3Cit3]3- and [(UO2)6Cit6(OH)10]16- were present. These findings suggest that the reduction of UO2 2+ is more difficult by polymerization of UO2 2+ with citric acid at higher pHs. Absorption spectra of the reduced complexes showed that U(IV) forms soluble complexes with citric acid at pH 2.0−5.0, and presence of U(V) species was not observed during the reduction of UO2 2+.