Chemistry of Sequence-Dependent Remote Guanine Oxidation: Photoreaction of Duplex DNA Containing Cyanobenzophenone-Substituted Uridine

There has been much debate on the efficiency of charge transport (CT) mediated by DNA pi -stack, especially with regard to the distance and sequence dependencies. Earlier studies of DNA-mediated CT employed oligodeoxynucleotides (ODNs) that were tethered to electron acceptors such as Rh(III) intercalator, anthraquinone derivative, stilbene, acridine, and ethidium intercalator by flexible linkers, with guanine (G) base as an intrisic electron donor. Recently, improved ODNs that provide more accurate donor-acceptor distance within DNA duplex have been reported. We have recently developed ODNs that contain a strong electron-accepting base stack in B-form duplex by incorporating cyanobenzophenone substituted 2'-deoxyuridine (d super(CNBP)U). We have examined the photoreactions of a series of oligomer duplexes containing both d super(CNBP)U and GG hole trap, which were separated by various intervening base sequences. We herein report that G radical cation (G super(.+)) was site-selectively generated at the G of the core of d(AG)/d(C super(CNBP)U) sequence, and the hole migrated over 24 angstroms to the remote GG site via a successive hole-hopping between guanine bases.