Effects of metal binding to mismatched base pairs on DNA-mediated charge transfer

Photoinduced hole transfer reaction in DNA duplex bearing cytosine–cytosine (CC) or thymine–thymine (TT) mismatched base pairs as metal-ion binding sites was studied using polyacrylamide gel electrophoresis. Site-specific binding of silver (I) ion to a CC mismatched base pair as well as non-specific binding to multiple sites of nucleobases in the DNA suppressed hole migration through the sequence. In the case of mercury (II) binding to duplex DNA containing single TT mismatch at N3 of the pyrimidine rings, little effect on the efficiency of hole transfer was observed, which is in accordance with a recent theoretical prediction. On the other hand, addition of Hg(II) to duplex containing tandem TT base pairs remarkably reduced hole transfer efficiency, although the calculation has suggested such binding could form high degree of electronic coupling between the hole carrier bases.