Effect of the photocatalytic activity of TiO2 on plasmid DNA

We investigated the photodynamic DNA strand-breaking activity of TiO2. A so lution of super-coiled pBR 322 DNA was irradiated with 5 J/cm(2) of UVA in the presence of TiO2 and the products were analyzed by using gel electropho resis. The ratio of open-circular DNA to super-coiled circular DNA was calc ulated from the resulting peak areas as a DNA strand-breaking index (SBI). The SBI of anatase-structure TiO2 (band gap = 3.23 eV) was greater than tha t of rutile structure (band gap = 3.06 eV), and the level of SBI correlated with the photocatalytic activity for degradation of 2-propanol. The inhibi tory effects of active oxygen scavengers, including DMSO, glutathione and h istidine, on the DNA strand-breaking activity were examined. All of the sca vengers except ascorbic acid showed inhibitory effects, as did several poly hydric alcohols including mannitol, a well-known hydroxyl radical scavenger . These results suggest that the photodynamic DNA strand-breaking activity of TiO2 is due to active oxygen species, especially hydroxyl radicals. Poly hydric alcohols showed an inverse correlation between the inhibitory effect on DNA strand-breaking activity and the octanol/water partition coefficien t (log P). (C) 2000 Elsevier Science B.V. All rights reserved.