Endogenous Generation of Singlet Oxygen and Ozone in Human and Animal Tissues: Mechanisms, Biological Significance, and Influence of Dietary Components

Figure 6

Proposed formation of ¹O₂ from catechol derivative 15 via hydroperoxide 17 formed by superoxide anion addition and ¹O₂ formation via oxidation of semiquinone radical 16 to quinone 18 in the presence of Cu²⁺ ions [30]. Catechol derivative 15 may undergo oxidation to the semiquinone radical 16 without metal catalysis [31].