Uranium(VI) complexes with sugar phosphates in aqueous solution

Abstract

Uranium / Sugar phosphate / Complex formation / Potentiometric titration / TRLFS / EXAFSSummary. 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 β 11 (G6P) = 5.89 ± 0.40, log β 12 (G6P) = 9.45 ± 0.08, log β 11 (F6P) = 5.72 ± 0.21, and log β 12 (F6P) = 9.54 ± 0.09. Stability constants could be determined with TRLFS under the specific experimental conditions only for the 1 : 1 complexes: log β 11 (G6P) = 6.35 ± 0.28, and log β 11 (F6P) = 5.66 ± 0.17.The TRLFS measurements results show the UO 2 G6P complex to exhibit no fluorescence properties. For this system, only a decrease of the fluorescence intensity with increasing ligand concentration was observed. For the UO 2 F6P 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 UO 2 F6P 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−O eq bond distance (2.30 ± 0.02 to 2.37 ± 0.02 Å), compared to the UO 2 2+ (H 2 O) 5 ion (2.40 ± 0.02 Å), due to a monodentate coordination via the oxygen atoms of the phosphate group.

Uranium biomineralization by a metal resistant Pseudomonas aeruginosa strain isolated from contaminated mine waste

“…The crystalline uranium phosphate formation following uranium accumulation indicates possible complexation of such metal with cellular phosphate groups facilitating metal nucleation and precipitation in a crystalline state [24]. Previous studies on molecular level speciation of uranium complexes within the cells of Stenotrophomonas maltophilia JG-2, M. oxydans SW-3 and Sphingomonas sp., isolated from uranium mill tailings by EXFAS revealed that at higher pH (pH 4.5) cell bound uranium biomineralize as U phosphate compounds [1,25]. The above observations not only indicate the role of bacterial PO 4 2− groups in uranium binding, but also illustrate the effect of pH on crystallinity of the cell bound U deposits.…”

“…In contrast to the amorphous nature of metal free biomass, spectrum for the uranium loaded cells showed distinct reproducible patterns typical for well characterized materials. The XRD pattern of the later biomass showed three distinct peaks at 2Â, 25 (Fig. 3c-e).…”

Complexation of Uranium by Cells and S-Layer Sheets of Bacillus sphaericus JG-A12

“…In previous studies, the combination of EXAFS spectroscopy, TEM, and EDX analysis showed that phosphorus-containing residues of three ecotypes of A. ferrooxidans are involved in the complexation of uranium (40). In addition, the structural parameters of these uranium complexes appear similar to those arising from the complexation of uranium with organic phosphate compounds such as fructose 6-phosphate (28).…”

Uranium Bioremediation: Approaches and Challenges

“…and Sphingomonas sp.) isolated from radioactive subsurface depository have demonstrated the complexation of uranium with cellular organic phosphate (fructose 6 phosphate) present at the cell surface at pH 2 (Koban et al 2004). Various cellular mechanisms employed by cyanobacterial strains for uranium detoxification including surface complexation by ligands harboured within the extracellular polysaccharides (EPS) have been reported (Acharya et al 2009;Acharya and Apte 2013a).…”