UC Davis

The uranyl cage clusters (UO2)22(O2)15(PHO3)20(H2O)1026- (U22) and (UO2)28(O2)20(PHO3)24(H2O)1232- (U28) can be probed in aqueous solutions by using a combination of 1H Diffusion-Ordered Spectroscopy (DOSY) and 1H-31P Heteronuclear-Single Quantum Coherence (HSQC) spectroscopy. This class of clusters is ideal for 1H NMR analysis in D2O because of the covalent character of the H-P bond in the phosphonic bridges. 1H DOSY indicates that the clusters are stable in solution and provides hydrodynamic radii of 9.8 ± 0.4 Å for the U22 and 12.3 ± 0.5 Å for the U28 clusters. Furthermore, 1H-31P HSQC delivers unequivocal signal assignment for both nuclei, which enables solution dynamics to be monitored by variable-temperature experiments, and reveals the presence of phosphonic-bridge conformers. The results provide some of the first dynamic information about steady conformational changes in these enormous actinide macroions.