Singlet Oxygen: Current Mechanistic Aspects of Photo-Oxidation
Two principal biological photo-oxidation processes are well-recognised, termed “Type I” and “Type II.” The former is characterised by primary interaction of substrate with the sensitizer excited state to give radicals whose subsequent reaction with oxygen leads to products. The “Type II” classification is restricted to oxidation processes involving the intermediacy of the lowest electronically excited state of molecular oxygen, O2(1Δg). The principal mode of formation of the latter, both in vivo and in vitro, is via electronic energy transfer from a sensitizer triplet state to ground state molecular oxygen. In this paper it is shown that the oxygen quenching of triplet states also can lead to radicals which are produced via a process which competes with singlet oxygen formation. In addition, current results concerning the mechanism of reaction of the latter species with organic/biological substrates will be discussed.
KeywordsSinglet Oxygen Pulse Radiolysis Azide Radical Aromatic Ketone Oxygen Lead
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