Type I and Type II photosensitization of DNA etheno adducts.

Photophysical and photochemical studies were carried out to examine the photoreactivity of etheno adducts, 1,N-ethenoadenine (εdA) and 1,N-ethenoguanine (εdG), in the presence of two well-known photosensitizers acting by Type I and/or Type II mechanisms such as 4-carboxybenzophenone (CBP) and rose Bengal (RB), respectively. Steady-state photolysis experiments combined with HPLC and mass spectroscopy measurements lead to photoproducts that correspond to the repaired nucleosides. To determine the mechanism of this photooxidation processes, phosphorescence spectroscopy, direct detection of singlet oxygen luminescence and laser flash photolysis were carried out. This work establishes that εdG and εdA are sensitive to both types of processes (Type I and II).