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Mechanisms of Singlet‐Oxygen and Superoxide‐Ion Generation by Porphyrins and Bacteriochlorins and their Implications in Photodynamic Therapy
Author(s) -
Silva Elsa F. F.,
Serpa Carlos,
Dąbrowski Janusz M.,
Monteiro Carlos J. P.,
Formosinho Sebastião J.,
Stochel Grazyna,
Urbanska Krystyna,
Simões Sérgio,
Pereira Mariette M.,
Arnaut Luis G.
Publication year - 2010
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201000111
Subject(s) - singlet oxygen , superoxide , photodynamic therapy , ion , photochemistry , oxygen , chemistry , porphyrin , biochemistry , organic chemistry , enzyme
New halogenated and sulfonated bacteriochlorins and their analogous porphyrins are employed as photosensitizers of singlet oxygen and the superoxide ion. The mechanisms of energy and electron transfer are clarified and the rates are measured. The intermediacy of a charge‐transfer (CT) complex is proved for bacteriochlorins, but excluded for porphyrins. The energies of the intermediates and the rates of their interconversions are measured, and are used to obtain the efficiencies of all the processes. The mechanism of formation of the hydroxyl radical in the presence of bacteriochlorins is proposed to involve a photocatalytic step. The usefulness of these photosensitizers in the photodynamic therapy (PDT) of cancer is assessed, and the following recommendations are given for the design of more effective PDT protocols employing such photosensitizers: 1) light doses should be given over a more extended period of time when the photosensitizers form CT complexes with molecular oxygen, and 2) Fe 2+ may improve the efficiency of such photosensitizers if co‐located in the same cell organelle assisting with an in vivo Fenton reaction.