Photo-oxidation of duplex DNA with the stable trioxatriangulenium ion

We show that 5′-Gs in 5′-GG-3′ duplex DNA dinucleotide steps are preferentially oxidized by the trioxatriangulenium ion (TOTA ) upon photo-activation, an oxidation pattern characteristic of guanine radical cation formation. Some photo-oxidation of the 3′G in 5′GG3′ steps and of isolated guanines is also observed but reactions carried out in D2O reveal only a minor increase in oxidation damage at these sites, indicating that electron transfer is the primary mechanism of guanine oxidation.