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One‐electron Oxidation of a Pyrenyl Photosensitizer Covalently Attached to DNA and Competition Between its Further Oxidation and DNA Hole Injection
Author(s) -
Yun Byeong Hwa,
Dedon Peter C.,
Geacintov Nicholas E.,
Shafirovich Vladimir
Publication year - 2010
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.2010.00719.x
Subject(s) - chemistry , guanine , adduct , dna , oligonucleotide , pyrene , nucleoside , stereochemistry , photochemistry , photosensitizer , deoxyguanosine , nucleotide , organic chemistry , biochemistry , gene
The photosensitized hole injection and guanine base damage phenomena have been investigated in the DNA sequence, 5′‐d(CAT G 1 Py C G 2 TCCTAC) with a site‐specifically positioned pyrene‐like (Py) benzo[ a ]pyrene 7,8‐diol 9,10‐epoxide‐derived N 2 ‐guanine adduct (G 1 Py ). Generation of the Py radical cation and subsequent hole injection into the DNA strand by a 355 nm nanosecond laser pulses (∼4 mJ cm −2 ) results in the transformation of G 1 Py to the imidazolone derivative Iz 1 Py and a novel G 1 Py * photoproduct that has a mass larger by 16 Da (M+16) than the mass (M) of G 1 Py . In addition, hole transfer and the irreversible oxidation of G 2 , followed by the formation of Iz 2 was observed (Yun et al. [2007], J. Am. Chem. Soc., 129, 9321). Oxygen‐18 and deuterium isotope labeling methods, in combination with an extensive analysis of the MS/MS fragmentation patterns of the individual dG Py * nucleoside adduct and other data show that dG Py * has an unusual structure with a ruptured cyclohexenyl ring with a carbonyl group at the rupture site and intact guanine and pyrenyl residues. The formation of this product competes with hole injection and thus diminishes the efficiency of oxidation of guanines within the oligonucleotide strand by at least 15% in comparison with that in the dG Py nucleoside adduct.