Uranium(VI) Complexes of Glutathione Disulfide Forming in Aqueous Solution

The interactions between glutathione disulfide, GSSG, the redox partner and dimer of the intracellular detoxification agent glutathione, GSH, and hexavalent uranium, U­(VI), were extensively studied by solution NMR (in D2O), complemented by time-resolved laser-induced fluorescence and IR spectroscopies. As expected for the hard Lewis acid U­(VI), coordination facilitates by the ligands’ O-donor carboxyl groups. However, owing to the adjacent cationic α-amino group, the glutamyl-COO reveal monodentate binding, while the COO of the glycyl residues show bidentate coordination. The log K value for the reaction UO2 2+ + H3GSSG– → UO2(H3GSSG)+ (pH 3, 0.1 M NaClO4) was determined for the first time, being 4.81 ± 0.08; extrapolation to infinite dilution gave log K ⊖ = 5.24 ± 0.08. U­(VI) and GSSG form precipitates in the whole pD range studied (2–8), showing least solubility for 4 < pD < 6.5. Thus, particularly GSSG, hereby representing also other peptides and small proteins, affects the mobility of U­(VI), strongly depending on the speciation of either component.