SUPRAMOLECULAR CATIONIC TETRARUTHENATED PORPHYRIN AND LIGHT-INDUCED DECOMPOSITION OF 2'-DEOXYGUANOSINE PREDOMINANTLY VIA A SINGLET OXYGEN-MEDIATED MECHANISM

The tetraruthenated porphyrin, mu-[meso-5,10,15,20-tetra(pyridyl)pyrid yl porphyrin]tetrakis[bis-(bipyridine)chloride ruthenium(II)] (TRP) is a supramolecular cationic species. The aim of the present investigati on was to evaluate the photodynamic properties of TRP and Zn-TRP to da mage DNA with emphasis on the mechanistic aspects. The ability for tet raruthenated porphyrin derivatives to induce photosensitization reacti ons has been determined using 2'-deoxyguanosine as a DNA model compoun d. The main photooxidation products of the targeted nucleoside were id entified and classified according to their mechanisms of formation, in volving either a radical pathway (type I) or a singlet oxygen-mediated mechanism (type II). Quantification of the different oxidation produc ts provides a means to evaluate the relative contribution of type I an d type II pathways associated with the oxidative photosensitization of 2'-deoxyguanosine by tetraruthenated porphyrin derivatives. Results i ndicate that O-1(2) plays a major role in the mechanism of photoxidati on mediated by these porphyrin derivatives. In addition an increase of the photosensitizing effect in the presence of zinc is observed. For each sensitizer, the ratio between type II and type I photoproducts ha s been calculated and compared to that of other known dyes such as met hylene blue and riboflavin.