6444
Properties of Benzopyrene-DNA Complexes Investigated by Fluorescence and Triplet Flash Photolysis Techniques Nicholas E. Geacintov,* Thaddeus Prusik, and John M. Khosrofian Contribution from the Chemistry Department and Radiation and Solid State Laboratory, New York University, New York, New York 10003. Received January 7 , I976
Abstract: Properties of benzo(a)pyrene (BaP) and benzo(e)pyrene (BeP) in physical complexes with native calf thymus DNA dissolved in aqueous solutions at 24 f 1 "C were studied by means of fluorescence quantum yield, single photon counting fluorescence decay, and triplet flash photolysis techniques. There are three types of binding sites for these polycyclic aromatic hydrocarbons bound to DNA. Between 40 and 60% of the aromatic molecules are located at a type of site where the excited singlet states decay nonradiatively and the other sites are characterized by different fluorescence decay times; for BaP the fluorescence lifetimes are 3.2 and 10 ns, while for BeP the lifetimes are 10 and 33 ns. Addition of silver ions, which in the range of silver ion/nucleotide ratios used (
