Photoexcitation of 2-aminopurine riboside (2APr, 2-amino-9-β-D-ribofuranosylpurine) and 2-aminopurine (2AP) in oxygenated aqueous buffer solutions (pH 7.0) with 308 nm XeCl excimer laser pulses (fwhm = 12 ns, ca. 70 mJ/pulse/cm 2) results in the consecutive two-photon ionization of the aromatic 2APr (or 2AP) residues. In neutral solutions, the 2APr (or 2AP) radical cations rapidly deprotonate (<100 ns). The 2APr(-H) · (or 2AP(-H) · neutral radicals thus formed reversibly oxidize 2-deoxyguanosine 5′-monophosphate (dGMP) on μs time scales, resulting in the formation of dGMP(-H) · neutral radicals. Transient absorption measurements show that a remarkable solvent isotope effect is observed on the kinetics of oxidation of dGMP by 2APr(-H) · (or 2AP(-H) ·) radicals in H 2O and D 2O solutions. In H 2O, the rate constants of dGMP(-H) · formation, as well as the rate constants of the reverse reaction of the 2APr (or 2AP) oxidation by dGMP(-H) · is larger than in D 2O by a factor of 1.5-2. This kinetic isotope effect indicates that the electron-transfer reaction from dGMP to 2APr(-H) · (or to 2AP(-H) ·), and the reverse electron transfer from 2APr (or 2AP) to dGMP(-H) ·, is coupled to a deprotonation of the primary electron-transfer radical cation products, dGMP ·+ and 2APr ·+ (or 2AP ·+). Therefore, these reactions, involving redox equilibria between different nucleobases, can be considered in terms of proton-coupled electron-transfer reactions.
|Original language||English (US)|
|Number of pages||3|
|Journal||Journal of Physical Chemistry B|
|Publication status||Published - Jan 13 2000|
ASJC Scopus subject areas
- Physical and Theoretical Chemistry