Quenching and generation of singlet oxygen by hydroethidine and related chromophores

Abstract

We have found that the oxidative probe hydroethidine (HE) is an efficient 1O 2 quencher with k q = 1.1 × 10 9 M −1 s −1 in CH 3CN. The structurally related MitoSOX Red had k q = 2.1 × 10 9 M −1 s −1 in D 2O–CH 3CN containing DNA. Ethidium cation, the main oxidation product, and three model compounds, 5-ethyl-5,6-dihydro-3,8-dinitro-6-phenyl-6-phenanthridinol, 3-amino-2-naphthenol, and 2-aminophenol, were lesser 1O 2 quenchers. Another product, 2-OH-ethidium cation, quenched 1O 2 with k q = 5.5 × 10 8 M −1 s −1 in a D 2O–CH 3CN mixture. Interestingly, both ethidium and 2-OH-ethidium cations are weak 1O 2 photosensitizers with quantum yields of 1O 2 production in CH 3CN of 0.06 and 0.03, respectively. Thus, 1O 2 can be involved in photochemical experiments with MitoSOX Red and HE.