Mechanisms for Dye‐mediated Photodynamic Action: Singlet Oxygen Production, Deoxyguanosine Oxidation and Phage Inactivating Efficiencies

The production of singlet oxygen ( 1 O 2 ) upon irradiation of several dyes in aqueous solution at pH 9.0, was quantitatively analyzed on the basis of the appearance of stable nitroxide radicals using the amine 2,2,6,6‐tetramethyl‐4‐piperidone as 1 O 2 acceptor. The dyes were checked for purity, their concentrations uniformized in terms of absorbance values and a correction factor was introduced which took into account the amount of photons absorbed. The rates of 1 O 2 production (in arbitrary units per min) were: 71 with rose Bengal, 70 with methylene blue, 61 with eosin Y, 18 with thiopyronine, 10 with proflavine and 9 with acridine yellow. Production of 1 O 2 was not observed with 9‐aminoacridine, acridine orange, quinacrine and ethidium bromide. Irradiated lumichrome initiated, with the same amine, another type of reaction. The rates of two other photoreactions were also determined under similar experimental conditions by following (i) the deoxyguanosine decomposition in which case the reaction was found to be less sensitive but largely parallel to the 1 O 2 production and (ii) the bacteriophage ØX174 inactivation in which case the dyes showed differences in their relative efficiencies. The proteinic capsid of the phage appeared as an effective impermeability barrier towards externally generated 1 O 2 . Moreover, some of the dyes studied intercalated into the phage DNA, a process known to favor radicalar reactions.