We used picosecond pulsed radiolysis to generate electrons in liquid water or diethylene glycol (DEG) to observe the dynamics of electron capture by DNA/RNA bases. In a liquid, it is necessary to distinguish at least three different states of the electron: a quasi-free electron (eql–), which has some kinetic energy in the liquid, a presolvated electron, which has lost its kinetic energy but is not fully solvated, and a fully solvated electron. Damage to DNA from the dissociative attachment of electrons has been well studied in the gas and solid phases. However, understanding this process in the aqueous environment of DNA remains a challenge. We used picosecond pulsed radiolysis to generate electrons in liquid water or DEG to observe the dynamics of electron capture by DNA/RNA bases (Figure 3). We demonstrate that, unlike the solvated electron (eDEG-) and the presolvated electron, the quasi-free electron effectively attaches to ribothymidine, forming just after energy deposition an excited state anionic radical that undergoes dissociation of the N1-C1' glycosidic bond [Ma2018b, Ma2019a, Ma2019b, Kaczmarek2020, Denisov2022, Adjei2023]. Due to this dissociation, this process, induced by a quasi-free electron in water, effectively constitutes an oxidation of the molecule, leading to the same strand break caused by oxidation induced by the oxidizing radical •OH. Therefore, for the first time, we succeeded in directly observing the dissociative attachment reaction of a free electron in solution on a biomolecule [Ma2021].

Transient absorption profiles of pure diethylene glycol solutions or those containing ribothymidine under ambient conditions. Spectra (a, c) and kinetics (b, d) for pure DEG and ribothymidine solutions at 0.3 M (rT), respectively.