Physicochemical Modeling of the Role of Free Radicals in Photodynamic Therapy. III. Interactions of Stable Free Radicals with Excited Photosensitizers Studied by Kinetic ESR Spectroscopy

Temoporfin (Foscan®, 5,10,15,20‐Tetra(m‐hydroxyphenyl)chlorin)—A Second‐generation Photosensitizer†,‡

“…To enable research into kinetic phenomena of the radical Type I mechanism, ESR experiments observing m THPC with and without stable free radicals ( e.g. di‐ tert ‐butyl nitroxide) have been undertaken (48). A suite of photophysical measurements were performed on the o ‐, m ‐ and p ‐tetra(hydroxyphenyl)porphyrins in 1988 by Bonnett et al.…”

“…To enable research into kinetic phenomena of the radical Type I mechanism, ESR experiments observing mTHPC with and without stable free radicals (e.g. di-tert-butyl nitroxide) have been undertaken (48). A suite of photophysical measurements were performed on the o-, m-and p-tetra(hydroxyphenyl)porphyrins in 1988 by Bonnett et al including fluorescence, flash photolysis and pulse radiolysis studies in order to characterize the singlet and triplet excited states of these macrocycles (49).…”

Photodynamic antimicrobial activity of avian eggshell pigments

“…A photosensitizer can transfer energy from its triplet state by two processes: directly to molecular oxygen with the generation of singlet oxygen ( 1 O 2 ) (type II reaction); or by interaction with a solvent or substrate via electron or proton transfer, with the generation of radicals (type I reaction). Although 1 O 2 is believed to be the major mediator of photochemical cell damage for many types of photosensitizers, oxygen species such as the superoxide anion and the hydroxyl radical (OH) can also induce deleterious effects that include lipid peroxidation and membrane damage [10].…”

Ionic Liquid-Based Chlorins and Type III Mechanism of Photodynamic Therapy (PDT)

“…188 Experimental results and further kinetic approaches have made it clear that this MTO mechanism basically differs from the Type I mechanism and thus called the Type III mechanism ( Figure 16). [189][190][191][192][193] Although all three pathways occur in the photosensitization process, it is suggested that Type II predominates over the others, in which 1 O 2 shows relatively high reactive property and causes irreversible destruction of tumor cells. 194 Antioxidants are primarily reducing agents prone to scavenge reactive species in one way or another.…”