Photoinduced electron transfer and enhanced triplet yields in benzo[a]pyrene derivative-nucleic acid complexes and covalent adducts

• Published in: Journal of the American Chemical Society 1994-01, Vol.116 (1), p.63-72
• Main Authors: Shafirovich, Vladimir Ya, Levin, Peter P, Kuzmin, Vladimir A, Thorgeirsson, Thorgeir E, Kliger, David S, Geacintov, Nicholas E
• Format: Article
• Language: English
• Subjects: 400201 - Chemical & Physicochemical Properties; 560300 - Chemicals Metabolism & Toxicology; ADDUCTS; AMINES; Animal cells; AROMATICS; AZAARENES; BENZOPYRENE; Biological and medical sciences; CARCINOGENS; Cell cultures. Hybridization. Fusion; CHEMICAL REACTIONS; COMPLEXES; CONDENSED AROMATICS; DNA ADDUCTS; ELECTROMAGNETIC RADIATION; ELECTRON TRANSFER; ENERGY LEVELS; EPOXIDES; EXCITED STATES; FLUORESCENCE; Fundamental and applied biological sciences. Psychology; GUANINE; HETEROCYCLIC COMPOUNDS; HYDROCARBONS; HYDROXY COMPOUNDS; INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; ION PAIRS; LASER RADIATION; LUMINESCENCE; Molecular and cellular biology; MULTIPLETS; MUTAGENS; ORGANIC COMPOUNDS; ORGANIC NITROGEN COMPOUNDS; ORGANIC OXYGEN COMPOUNDS; PHOTOCHEMICAL REACTIONS; PURINES; QUENCHING; RADIATION, THERMAL, AND OTHER ENVIRON. POLLUTANT EFFECTS ON LIVING ORGS. AND BIOL. MAT; RADIATIONS; RADICALS; TRIPLETS
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja00080a008

The carcinogenic and mutagenic benzo[a]pyrenediol epoxide derivative 7r,8t-dihydroxy-9t,10t-epoxy-7,8,9,-10-tetrahydrobenzo[a] pyrene (BPDE) binds via its C-10 position predominantly to the exocyclic amino group of guanine residues in native DNA. In such DNA adducts, the fluorescence of the pyrenyl moieties is strongly quenched by physicochemical interaction with the DNA bases. Using nanosecond time scale transient absorption techniques, products of the fluorescence quenching have been examined in two model systems in aqueous and polar organic solvents. The first is a monomeric, covalently linked (+)-trans-BPDE-N[sup 2]-2[prime]-deoxyguanosine adduct (BPDE-dG), the most abundant adduct when (+)-BPDE binds to native DNA; the second consists of mixtures of 7,8,9,10-tetrahydroxytetrahydrobenzo[a]pyrene (BPT) with dG, which was used to study the role of noncovalent interactions in solvents of different hydrophobicities. At moderate laser pulse energies ([le] 25 mJ/cm[sup 2]/pulse, 347 nm), the primary products of the fluorescence quenching reaction are pyrenyl residue triplet excited states, with greatly enhanced yields (by factors of 3-10 or more relative to the yields expected from simple intersystem crossing). The primary quenching reaction involves photoinduced electron transfer from dG to pyrenyl residues, followed by efficient recombination to form triplet excited states. 72 refs., 9 figs., 1 tab.