Optical control of DNA base radio sensitivity.

We describe manipulation of the radio sensitivity of the nucleotide base driven by the spin blockade mechanism of diffusive free radicals against ionizing radiation. We theoretically propose a mechanism which uses the simultaneous application of circularly polarized light and an external magnetic field to control the polarization of the free radicals and create S=1 electron-hole spin excitations (excitons) on a nucleotide base. We deploy an ab initio molecular dynamics model to calculate the characteristic parameters of the light needed for optical transitions. As a specific example, we present the numerical results calculated for a guanine in the presence of an OH free radical. To increase the radio resistivity of this system, an energy gap for the optical pumping and induction of excitons on guanine is predicted. The effect of spin injection on the formation of a free energy barrier in diffusion-controlled chemical reaction pathways leads to the control of radiation-induced base damage. The proposed method allows us to manipulate and partially suppress the damage induced by ionizing radiation.