Singlet Oxygen Reacts with 2′,7′‐Dichlorodihydrofluorescein and Contributes to the Formation of 2′,7′‐Dichlorofluorescein

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Abstract
There are controversial reports in the literature concerning the reactivity of singlet oxygen (1O2) with the redox probe 2′,7′‐dichlorodihydrofluorescein (DCFH). By carefully preparing solutions in which 1O2 is quantitatively generated in the presence of DCFH, we were able to show that the formation rate of the fluorescent molecule derived from DCFH oxidation, which is 2′,7′‐dichlorofluorescein (DCF), increases in D2O and decreases in sodium azide, proving the direct role of 1O2 in this process. We have also prepared solutions in which either 1O2 or dication (MB•2+) and semi‐reduced (MB•) radicals of the sensitizer and subsequently super‐oxide radical (O2•−) are generated. The absence of any effect of SOD and catalase ruled out the DCFH oxidation by O2•−, indicating that both 1O2 and MB•2+ react with DCFH. Although the formation of DCF was 1 order of magnitude larger in the presence of MB•2+ than in the presence of 1O2, considering the rate of spontaneous decays of these species in aqueous solution, we were able to conclude that the reactivity of 1O2 with DCFH is actually larger than that of MB•2+. We conclude that DCFH can continue to be used as a probe to monitor general redox misbalance induced in biologic systems by oxidizing radicals and 1O2.

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