Substitution of the thymidine moiety in DNA by C5-substituted halogenated thymidine analogues causes significant augmentation of radiation damage in living cells. However, the molecular pathway involved in such radiosensitization process has not been clearly elucidated to date in solution at room temperature. So far, low-energy electrons (LEEs; 0–20 eV) under vacuum condition and solvated electrons (esol–) in solution are shown to produce the σ-type C5-centered pyrimidine base radical through dissociative electron attachment involving carbon–halogen bond breakage. Formation of this σ-type radical and its subsequent reactions are proposed to cause cellular radiosensitization. Here, we report time-resolved measurements at room temperature, showing that a radiation-produced quasi-free electron (eqf–) in solution promptly breaks the C5-halogen bond in halopyrimidines forming the σ-type C5 radical via an excited transient anion radical. These results demonstrate the importance of ultrafast reactions of eqf–, which are extremely important in chemistry, physics, and biology, including tumor radiochemotherapy.
The reactivity of presolvated electrons with CO2 and N2O was studied in the gas pressure range from 1 to 52 bar. To measure this reactivity, the home-made spectroscopic cell with liquid circulation was developed working up to 70bar of gas pressure. The efficiency of presolvated electron scavenging was determined from the decrease of solvated electrons yield after the 5ps electron pulse. In addition, the reaction rate between these molecules and solvated electrons was directly determined at gas pressures below the critical point, which is in agreement with those presented in the literature measured at gas pressures below <1atm.
by Jun Ma, Anil Kumar, Yusa Muroya, Shinichi Yamashita, Tsuneaki Sakurai, Sergey A. Denisov, Michael D. Sevilla, Amitava Adhikary, Shu Seki and Mehran Mostafavi
Damage to DNA via dissociative electron attachment has been well-studied in both the gas and condensed phases; however, understanding this process in bulk solution at a fundamental level is still a challenge. Here, we use a picosecond pulse of a high energy electron beam to generate electrons in liquid diethylene glycol and observe the electron attachment dynamics to ribothymidine at different stages of electron relaxation. Our transient spectroscopic results reveal that the quasi-free electron with energy near the conduction band effectively attaches to ribothymidine leading to a new absorbing species that is characterized in the UV-visible region. This species exhibits a nearly concentration-independent decay with a time constant of ~350 ps. From time-resolved studies under different conditions, combined with data analysis and theoretical calculations, we assign this intermediate to an excited anion radical that undergoes N1-C1′ glycosidic bond dissociation rather than relaxation to its ground state.