Photodegradation of DNA induced by modified forms of titanium dioxide

The UV-induced photodegradation of supercoiled DNA in aqueous solution is accelerated in the presence of a suspension of TiO2 nanoparticles. While nearly all samples of TiO2 are active in this respect, they differ markedly according to (i) the crystal structure of the TiO2; (ii) the presence of an external oxide coating on the TiO2; (iii) the presence within the TiO2 of dopant transition metal ions. Thus anatase is more active than rutile; coated TiO2 is less active than uncoated TiO2; the presence of all transition metal ions except Cr(III) acts to enhance the activity of the TiO2 . Only Cr(III) acts to protect the DNA from enhanced degradation, while Mo(VI) ions render the TiO2 highly aggressive. The relative behaviour of these modified forms of TiO2 towards DNA on UV excitation closely parallels that previously found in that towards a number of synthetic polymers. The mechanisms for the varying actions of the pigments are discussed.