Ion Type Dependence of DNA Electronic Excitation in Water under Proton, α-particle, and Carbon Ion Irradiation: A First-Principles Simulation Study

Understanding how the electronic excitation response of DNA changes with different irradiating ions is central to advancing ion beam cancer therapy and other related therapies, such as boron neutron capture therapy. Unlike photon-based radiation, high-energy ions show a highly localized energy deposition profile and can more precisely target tumor cells without damaging surrounding healthy cells. While protons have been the predominant ion of choice in ion beam cancer therapy, heavier ions, particularly carbon ions, have drawn significant attention over the past decade. However, the molecular-level details of the electronic excitation under higher-Z ion irradiation remain unknown. Here we use real-time time-dependent density functional theory (RT-TDDFT) to simulate the non-equilibrium energy transfer excitation process in solvated DNA under proton, α-particle, and carbon ion irradiation^[1-2]. Our results show that the energy transfer rate does indeed increase for the heavier ions, albeit differently from the behavior predicted by linear response theory. The simulations also reveal that increased hole formation on DNA, together with the formation of large numbers of highly energetic holes, both contribute significantly to the increase.

[1] C. Shepard, D. C. Yost, Y. Kanai, Physical Review Letters 2023, 130, 118401.

[2] C. Shepard, R. Zhou, D. C. Yost, Y. Yao, Y. Kanai, The Journal of Chemical Physics 2021, 155, 100901.