PHOTOINDUCED ELECTRON-TRANSFER AND STRAND CLEAVAGE IN PYRENYL-DNA COMPLEXES AND ADDUCTS

The fluorescence of pyrenyl residues in complexes with the nucleic aci d bases G, C and T, but not A, is strongly quenched by photoinduced el ectron transfer mechanisms. Site-specifically modified 11-mer oligonuc leotide duplexes containing a single modified guanosyl base G bearing a covalently attached pyrenyl residue were prepared in order to probe for photochemical damage associated with these photoinduced electron transfer reactions. When the pyrenyl residue positioned at G is photo excited with 355 nm light, direct strand cleavage is observed at that site with low quantum yield. Frank strand breaks are also observed up to five base pairs away from G, suggesting that intrastrand migration of a reactive intermediate from base to base is occurring. (C) 1998 J ohn Wiley & Sons, Ltd.