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Examples of DNA Radical Reactions

An example of this process is the two-photon ionization of 2-aminopurine (2AP) - a nucleic acid base analog that can site-specifically inserted into any DNA sequence [27-31]. We have shown that photoexcitation of 2AP, which has a broad absorption maximum at 305 nm, by 308-nm intensive nanosecond XeCl excimer laser pulses, induced efficient and selective photoionization of 2AP residues. Absorption of the first photon results in the formation of the 2AP singlet excited state ( 2AP) and absorption of the second photon causes photoionization according to  [Pg.86]

Other examples of generating free radicals utilized in our laboratory are the consecutive two-photon ionization of the aromatic pyrene residue in the benzo[a] pyrene derivative 7,8,9,10-tetrahydroxytetrahydrobenzo[a]pyrene (B[a]PT) or the covalent adducts derived from the reactions of racemic anti-r7,t8-dihydroxy-t9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (B[a]PDE) with the N2-exocyclic amino groups of guanine or adenine bases in DNA [43-47]. The selective excitation of the pyrenyl residue of B[a]PT by intense 355-nm nanosecond laser pulses yields free radical products by a two-photon mechanism  [Pg.87]

A similar mechanism applies to covalently bound B[a]PDE-DNA adducts and it has been shown that the 355-nm laser photoexcitation of the pyrenyl residues can be used to inject holes into double-stranded DNA at the site of modified guanine residues [47]. [Pg.87]

The 2AP and B[o]PT absorption bands are positioned above 300 nm, and are thus beyond the threshold of the absorption spectrum of DNA. Thus, the canonical DNA bases are not photoionized by either 308- or 355-nm nanosecond laser pulses used in these experiments. [Pg.87]

The photoinduced dissociation of persulfate anions [23] using light above 300 nm in wavelength is yet another method for generating reactive radical intermediates that can oxidize DNA [14, 32-35]  [Pg.87]


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