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 beta(11) (G6P) = 5.89 +/- 0.40, log beta(12)(G6P)= 9.45 +/- 0.08, log beta(11)(F6P)= 5.72 +/- 0.21, and log beta(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 beta(11) (G6P) = 6.35 +/- 0.28, and log beta(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 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 mus. 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 Angstrom), compared to the UO22+ (H2O)(5) ion (2.40 +/- 0.02 Angstrom), due to a monodentate coordination via the oxygen atoms of the phosphate group.