Kinetics and Mechanism of Electron Transfer between Purines and Pyrimidines, Their Dinucleotides and Polynucleotides after Reaction with Hydrated Electrons; A Pulse Radiolysis Study

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Abstract
The radical spectra of mixtures of thymidine 5′-monophosphate (TMP) or uridine 5′-monophosphate (UMP) with adenine 5′-monophosphate (AMP) after hydrated electron attack, measured from 5 to 3000 µs after pulse radiolysis, can only be described in terms of the radical spectra of the nucleotides if an electron transfer is taken into account from the purine radical anion to the pyrimidine, resulting in the formation of a pyrimidine radical anion. From analysis of the spectra of the dinucleoside phosphates ApU, dApT and dCpdA after e−aq attack it follows that the electron-donating species is the purine radical anion (A−·) rather than the protonated purine radical. The electron transfer competes with the fast protonation of the purine radical anion: A−· + py→A + py·− and A−· + H2O⇄AH· respectively. The electron transfer is found to have a diffusion-controlled reaction rate constant of approximately 1·2 × 1010 for TMP and 3·5 × 109 dm3 mol−1 s−1 for UMP.

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