Intermolecular Interactions and Photogeneration of Free Radicals in Metal-free Tetrasulphophthalocyanine—tryptophan Systems

Complex formation between free-base tetrasulphophthalocyanine (TSPC) and tryptophan (Trp) in solutions of high dielectric constant was studied using absorption/emission spectroscopy. ESR experiments demonstrated dye/substrate electron or hydrogen atom transfer reactions during illumination, competing with superoxide radical generation. To discriminate between the well-known Trp photodynamic (1O2 mediated) oxidation and other reactions, Fe(III)-EDTA was added to initiate the Haber-Weiss reaction. The TSPC/Trp complex showed an enhanced ability to reduce Fe(III)-EDTA. Spin-trapping experiments and the SOD and catalase-independent formation of 2-deoxyribose/thiobarbituric acid products imply involvement of a photoinduced Haber-Weiss reaction with generation of Trp-peroxyl and Trp-alkoxy radicals as intermediates, followed by formation of Trp carbon-centred radical(s).