Theoretical assessment of the photosensitization mechanisms of porphyrin-ruthenium(II) complexes for the formation of reactive oxygen species

Following a thermodynamics point of view, we analyzed a set of photosensitization mechanisms (energy transfer, electron transfer) given by seven reactions applied to porphyrin-ruthenium(II) complexes (1-6) and their fragments (ruthenium complexes: 7-12; porphyrin: 13) at the B3LYP/6-31G(d,p)/LANL2DZ level of theory in condensed phase (aqueous solution). We found that whereas for the fragments (7-13) an energy-transfer process between their first triplet excited state (T-1) and molecular oxygen (O-3(2)) to yield singlet oxygen (O-1(2)) is favored, the privileged channels for the photosensitizers (1-6) correspond to production of a superoxide anion radical (O-2(center dot-)) by electron transfer between O-3(2) and the photosensitizers (P) either in their P(T-1) excited state or as a radical anion P center dot- . The reaction channels involving P center dot- are more exergonic by 13-17 kcal/mol with respect to the process involving P(T-1). These results suggest that the anionic photosensitizer would likely acquire more importance for the photodamage in the cell. (C) 2014 Elsevier B.V. All rights reserved.