Ultrafast nonadiabatic dynamics of λ-DNA upon low energy proton irradiation

Abstract

Direct ionizing damage and indirect secondary electron damage play important parts in the cell death under ion beam radiation. Depending on the real-time time-dependent density functional theory, we study the physical and chemical properties of the normal (α-) and mutant DNA (λ-DNA) in the process of low energy proton irradiation. The mutation of base pair causes the change in local chemical environment of DNA molecule and further changes the charge density of trajectory, proton–DNA interaction energy, force and track for moving proton, energy deposition, and the secondary electron evolution. The layered discrete charge in the intruding direction results in a spatial insensitivity of the electrons on the base pair to the energetic ion. The abnormal energy deposition for λ-DNA is ascribed to the mutation of the charge density and the nucleus–nucleus interaction potential. A more stable bond is formed between the mutant base pairs for λ-DNA, and there exists a flow of secondary electrons on the phosphate backbone under the ion beam radiation, resulting in a subsequent indirect chemical damage. These results provide an understanding for the central role of the physical states in radiation-induced cell death and a theoretical reference to improve the success rate of ion beam radiotherapy.