The very specific binding of the HgII ion unexpectedly and significantly stabilizes naturally occurring thymine-thymine base mispairing in DNA duplexes. Following this finding, we prepared DNA duplexes containing metal-mediated base pairs at the desired sites, as well as novel double helical architectures consisting only of thymine-HgII-thymine pairs.

N−N J-coupling across a metal center (2 J NN) was clearly detected in a biological macromolecule (DNA duplex) for the first time. By using 2 J NN, the base pairing mode of mercury-mediated T−T pairs (T−HgII−T) was definitely determined. This pairing mode was found to be a novel metal ion-binding mode for DNA and RNA molecules, in which imino proton−metal exchange processes are included. Accordingly, 2 J NN is highly important for the determination of the chemical structures of metal-mediated base pairs.