Dynamic Behavior of Secondary Electrons in Liquid Water at the Earliest Stage upon Irradiation: Implications for DNA Damage Localization Mechanism.

To clarify the formation of radiation damage in DNA, the dynamic behavior of low-energy secondary electrons produced by ionizing radiation in water was studied by using a dynamic Monte Carlo code that considers the Coulombic force between electrons and their parent cations. The calculated time evolution of the mean energy, total track length, and mean traveling distance of the electrons indicated that the prehydration of the electrons occurs competitively with thermalization on a time scale of hundreds of femtoseconds. The decelerating electrons are gradually attracted to their parent cations by Coulombic force within hundreds of femtoseconds, and finally about 12.6% electrons are distributed within 2 nm of the cations. The collision fraction for ionization and electronic excitation within 1 nm of the cation was estimated to be about 40%. If these electrons are decelerated in a living cell, they may cause highly localized lesions around a cation in a DNA molecule through additional dissociative electron transfer (DET) as well as ionization and electronic excitation (EXC), possibly resulting in cell death or mutation.