Over thirty-five uranyl peroxide nanocapsule topologies have been produced to date. These feature UO2(O2)3 and UO2(O2)2(OH)2 polyhedral units, and encapsulated alkali cations and other species, that play a role in templating the square, pentagonal and hexagonal rings that compose nanospheres. Two of the most commonly obtained topologies are U24 featuring 24 UO2(OH)2(O2)2 polyhedra arranged in squares and hexagons; and U28 featuring 28 UO2(O2)3 polyhedra arranged in pentagons and hexagons. We have taken advantage of the excellent NMR nuclei, 6,7Li, 23Na, 133Cs; as well as 1H to characterize the encapsulated and charge-balancing alkali cations, water and hydroxyl species, and the OH- ligand of the UO2(OH)2(O2)2 polyhedron. Additionally, 23Na-1H and 6,7Li-1H 2-dimensional correlation experiments defined the chemical nature of the encapsulated alkalis and the encapsulated hydrous species. Finally, geometry optimization via computational studies revealed excellent agreement with both arrangement of the encapsulated species, and identity of the hydrous species. Further, the optimal orientation of the U-OH ligands and the encapsulated hydrous species (driven by H-bonding) are revealed, as they have not yet been observed from X-ray data. While solid-state NMR and computational studies have provided unprecedented information on the static crystalline state of uranyl peroxide nanocapsules, multinuclear NMR of dissolved capsules reveal that the alkalis are not rigidly encapsulated; rather they undergo exchange with alkalis in solution, outside the capsule. Exchange studies via 23Na NMR of Na+ in both U24 and U28 were carried out, revealing much faster exchange for U24. Arguments can be made that the process of exchange involves a concerted motion of all the encapsulated species; and the absence of larger alkalis (i.e. Cs) in the U24 system is the reason for its more rapid exchange, relative to U28.Reference: �Dynamics of Uranyl Peroxide Nanocapsules� May Nyman and Todd Alam, JACS 2012, doi.org/10.1021/ja308673f

Uranyl peroxide nanocapsules: The encapsulated species

246th National Meeting (2013)

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