Determination of silver(I)-binding sites in canonical B-DNA by NMR spectroscopy.

The interaction of metal ions with nucleic acids was studied by determining the initial binding sites of Ag ions at unmodified B-DNA by NMR spectroscopy. In particular, NMR spectra were recorded of the Dickerson-Drew dodecamer sequence in the presence of different ratios of Ag ions to DNA. The data indicate that the coordination of the first three Ag ions per duplex preferentially takes place inside the B-DNA helix rather than at other possible binding sites such as the negatively charged phosphate backbone and/or the endocyclic N7 position of purine residues. Larger DNA aggregates are formed in the presence of excess Ag ions, as indicated by the formation of a precipitate and by significant changes in the circular dichroism spectra. As shown by a titration with chloride ions, the Ag ions are only loosely bound to the nucleic acids and can be released by precipitation of AgCl.