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# SUPRAMOLECULAR CATIONIC TETRARUTHENATED PORPHYRIN AND LIGHT INDUCE DECOMPOSITION OF 2’-DEOXYGUANOSINE PREDOMINANTLY BY SINGLET MOLECULAR OXYGEN ### Jean-Luc Ravanat, Paolo Di Mascio*, Sandrine Spinelli, Marisa H.G. Medeiros*, Koiti Araki*, Henrique E.Toma and Jean Cadet Département de Recherche Fondamentale sur la Matière Condensée, Service de Chimie Inorganique et Biologique, Laboratoire des Lésions des Acides Nucléiques, CEA Grenoble, 17 rue des Martyrs, 38054 Grenoble cedex 9 France. e-mail : jravanat@cea.fr *Departamento de Bioquímica, Instituto de Química, Universidade de São Paulo, CP 26077, CEP 05599-970, SP, Brasil. e-mail: pdmascio@quim.iq.usp.br Summary The ability for tetraruthenated porphyrin derivatives to induce photosensitization reactions has been determined using 2'-deoxyguanosine as a DNA model compound. The main photooxidation products of the nucleoside were identified and classified according to their mechanism of formation. These involve a radical pathway (type I) and/or a singlet oxygen mediated mechanism (type II). Quantification of the different oxidation products provides a means to evaluate the relative contribution of type I and type II pathways associated with the oxidative photosensitization of 2'-deoxyguanosine by tetraruthenated porphyrin derivatives. Results indicate that singlet oxygen plays a major role in the mechanism of photooxidation mediated by these porphyrin derivatives. For each sensitizer, the ratio between type II and type I photoproducts have been calculated and compared to that of other known dyes such as methylene blue and riboflavin