Electron transfer reactions between nucleic acid residues in DNA and strong oxidants are often the critical initial steps that initiate oxidative, irreversible DNA damage. Employing laser flash photolysis transient absorption spectroscopic techniques, we investigated the characteristics of electron transfer reactions in aqueous solutions between the 2'- deoxynucleoside 5'-monophosphates, dGMP, dAMP, dCMP and dTMP and a representative one-electron oxidant. The latter was a radical cation of a pyrene derivative with enhanced water-solubility, 7,8,9,10- tetrahydroxytetrahydrobenzo[a]pyrene (BPT). The BPT radical cation BPT+, was generated by intense nanosecond laser pulse (308 or 355 nm, 50-70 mJ pulse- 1 cm-2) by a non-linear consecutive two-photon absorption process. No electron transfer reactions were observed with dAMP, dTMP and dCMP, consistent with their unfavorable redox potentials. However, BPT+ efficiently oxidized dGMP with a rate constant k(b) = 1.7 ± 0.1) x 109 M- 1 s-1, which is smaller than the diffusion-controlled value by a factor of only ~ 3. The dGMP(-H) neutral radicals formed on time scales of a few microseconds, were identified by their characteristic transient absorption spectrum (λ(max) ~ 310 mn). The rate constant of electron transfer from dGMP to BPT+ was smaller in D2O by a factor of ~ 1.5 than in H2O. This kinetic isotope effect indicates that the electron transfer reaction from dGMP to BPT+ is accompanied by the deprotonation of dGMP+, and therefore appears to be a proton-coupled electron transfer reaction.
ASJC Scopus subject areas
- Physics and Astronomy(all)
- Physical and Theoretical Chemistry