Excess electron transfer from an internally conjugated aromatic amine to 5-bromo-2'-deoxyuridine in DNA

DNA duplexes containing an N,N,N',N'-tetramethyl-1,5-diaminonaphthalene analogue and 5-bromo-2'-deoxyuridine (BrdU) provide a readily accessible system for investigating excess electron transfer in DNA. Photoexcitation of the aromatic amine (lambda > 335 nm) induces reductive electron transfer as observed by strand cleavage adjacent to the BrdU residue. The weak exponential distance dependence (0.3 A-1) of electron transfer determined for this system of mixed dA-T and dG-dC base pairs suggests that thermally activated electron hopping is competitive with proton transfer within the dG.dC radical anion. The UV-dependent transfer of excess electrons and subsequent strand cleavage proceeds equivalently under anaerobic and aerobic conditions and is not sensitive to e-(aq) or hydroxyl radical trapping agents.