Complex Formation of Uranium(VI) with Glucose-1-Phosphate

The uptake of heavy metals into plants is commonly quantified by the soil-plant transfer factor. Up to now little is known about the chemical speciation of actinides in plants. To compare the obtained spectroscopic data of uranium complexes in plants with model compounds, we investigate the complexation of uranium with relevant bioligands of various functionalities. A very important class of ligands are phosphate esters, which serve as phosphate group and energy transmitters as well as energy storage mediums in biological systems.
Therefore, in our study we present the results of uranium complexation with glucose-1-phosphate (G1P) obtained by time-resolved laser-induced fluorescence spectroscopy (TRLFS) and potentiometric titration. The TRLFS-experiments were performed at a fixed uranyl concentration (10^-5 M) as a function of the ligand concentrations (10^-5 to 10^-3 M) in a pH range from 2 to 4.5. The potentiometric titrations were performed at fixed uranyl (10^-4 M) and ligand (10^-3 M) concentrations in a pH range from 3 to 10.
The TRLFS-measurements show a decrease in the fluorescence intensities with increasing ligand concentrations, and no shift of the emission bands. The TRLFS spectra indicate the presence of only one species with fluorescence properties. This species has a lifetime of 1.50 µs and was identified as the free uranyl ion. Therefore we conclude that the complexed uranyl glucose phosphate species shows no fluorescence.
From quantitative evaluation of the TRLFS spectra we conclude, that 1:1 uranyl glucose phosphate species UO₂(G1P) has formed. The complex formation constant was calculated to be log beta=5.60.
The results of the potentiometric titration show the same type of complex with a stability constant of log beta=5.37.