Singlet Oxygen and Its Reactivity

The production of 02 has been reported to occur by energy transfer from the singlet- and triplet-excited states of the sensitizer, but that from the triplet excited state is highly preferred because singlet-triplet interaction is of very low probability. The lifetime of 02 is highly dependent on the solvent medium and the presence of scavengers or oxidizable acceptors it was determined to be about 3.1 x 1(T6 s in water (Rodgers and Snowden, 1982) and 50 to 100 x 106 s in lipid (Henderson and 

Dougherty, 1992). A half-life in tissue was estimated to be less than 5 x 10-7 s (Patterson et al., 1990). Singlet oxygen might diffuse about 0.01 to 0.02 pm in a cellular environment (Moan et al., 1979). 

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This reaction indicates a distinct stereospecificity due to the structure of singlet oxygen and its reactivity. It was found, for example, that the quantitative distribution of oxidation products from 1-methyl-2-iso-propylethylene and l,l-dimethyl-2-isopropylethylene differs when molecular or singlet oxygen is used [249]. 

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