Uranium(VI) complexes with sugar phosphates in aqueous solution

Abstract

Summary 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.