Physico-chemical modeling of the role of free radicals in photodynamic therapy. III. Interactions of stable free radicals with excited photosensitizers studied by kinetic ESR spectroscopy.
The loss of paramagnetism of the stable free radical 4,4'-di-tert.-butyl- diphenyl-1-nitroxy during illumination of the photosensitizer meso-tetrahydroxyphenyl chlorine by light above 620 nm in the absence of oxygen has been followed by kinetic ESR spectroscopy. Addition of the spin trap alpha-(4-pyridyl-1-oxide)- N-tert.-butyl-nitrone reduces the initial rate of the disappearance of the free radical enabling to separate triplet-doublet interactions from processes between radicals stemming from the triplet sensitizer and the stable free radical. Kinetic treatment of the mechanism suggested yielded the rate constant of the triplet-doublet interaction proceeding via electron transfer being about 6% of the rate constant of the overall interaction including both energy transfer and electron transfer.
Kriska
T
T
Central Research Institute for Chemistry of the Hungarian Academy of Sciences, Budapest.
Korecz
L
L
Nemes
I
I
Gál
D
D
D001713:Biphenyl Compounds / Q000737:chemistry; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D004578:Electron Spin Resonance Spectroscopy; D005609:Free Radicals; D007700:Kinetics; D008956:Models, Chemical; D010778:Photochemotherapy; D017319:Photosensitizing Agents / Q000737:chemistry*
C096005:4,4'-di-(tert-butyl)diphenyl-1-nitroxy; D001713:Biphenyl Compounds; D005609:Free Radicals; D017319:Photosensitizing Agents