Photochemical pathways of 8-oxo-2′-deoxyguanosine under photodegradation

The common product of an oxidatively damaged DNA, 8-oxo-2′-deoxyguanosine (8-oxo-dG), is known for photorepairing cyclobutane pyrimidine dimers. This study is to uncover the dynamics of 8-oxo-dG under photodegradation, which are poorly understood. The photodegradation of aqueous 8-oxo-dG was investigated by transient absorption spectroscopy. Two major stages of the photodegradation showing different excited-state dynamics, the energy shift, and the pH change were observed. The two stages were distinguished by the main events that are the electron ejection in the early stage and the photochemical dynamics in the late stage. Two mechanisms were proposed for the photochemical dynamics under the photodegradation. One of the mechanisms (8-oxo-dG· + ·Haq → 8-oxo-dG) represents the pathway increasing the photophysical properties (photostability and the reactivity toward radicals) in the system, and the other describes the pathway degrading the system (8-oxo-dG· + ·OHaq → 5-OH-8-oxo-dG* → Sp or Gh/Ia). The results might imply that the photodegradation of the oxidatively damaged nucleoside would provide electrons, required for CPD photorepair, and advantageous photophysical properties simultaneously.