NMR studies on the new cluster complexes between 5'-nucleotides and uranyl ions. Structure and dynamic equilibria in alkaline aqueous solution.

Structures of the equimolar uranyl complexes of various 5'-nucleotides, such as AMP, GMP, UMP, and CMP, were extensively studied by high-field proton NMR spectroscopy. The unambiguous assignment of the proton resonances was established by correlating with the C-13 NMR spectrum of the complex from [N-15]AMP, which showed a doublet for the C-1' carbon signal due to the spin coupling with N-15 (N-9). Uranyl-nucleotide complexes were found to be the mixture of several oligomeric species having a common structural unit. The primary coordination sites of the uranyl ion were phosphate and 3'-hydroxyl oxygens, but no interaction was observed for the bases. The major oligomer at a high pH (above 11) was a cage-like octamer, and two isomeric cyclic tetramers predominated at a lower pH (below 10).