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Type I and Type II Photosensitized Oxidation Reactions: Guidelines and Mechanistic Pathways
Author(s) -
Baptista Maurício S.,
Cadet Jean,
Di Mascio Paolo,
Ghogare Ashwini A.,
Greer Alexander,
Hamblin Michael R.,
Lorente Carolina,
Nunez Silvia Cristina,
Ribeiro Martha Simões,
Thomas Andrés H.,
Vigi Mariana,
Yoshimura Tania Mateus
Publication year - 2017
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/php.12716
Subject(s) - chemistry , radical , singlet oxygen , photochemistry , oxidizing agent , deprotonation , redox , electron transfer , radical ion , oxygen , superoxide , hydroxyl radical , reactive oxygen species , ion , organic chemistry , biochemistry , enzyme
Here, 10 guidelines are presented for a standardized definition of type I and type II photosensitized oxidation reactions. Because of varied notions of reactions mediated by photosensitizers, a checklist of recommendations is provided for their definitions. Type I and type II photoreactions are oxygen‐dependent and involve unstable species such as the initial formation of radical cation or neutral radicals from the substrates and/or singlet oxygen ( 1 O 2 1 ∆ g ) by energy transfer to molecular oxygen. In addition, superoxide anion radical ( O 2 · − ) can be generated by a charge‐transfer reaction involving O 2 or more likely indirectly as the result of O 2 ‐mediated oxidation of the radical anion of type I photosensitizers. In subsequent reactions, O 2 · −may add and/or reduce a few highly oxidizing radicals that arise from the deprotonation of the radical cations of key biological targets. O 2 · −can also undergo dismutation into H 2 O 2 , the precursor of the highly reactive hydroxyl radical (· OH ) that may induce delayed oxidation reactions in cells. In the second part, several examples of type I and type II photosensitized oxidation reactions are provided to illustrate the complexity and the diversity of the degradation pathways of mostly relevant biomolecules upon one‐electron oxidation and singlet oxygen reactions.