Investigation on the fluorescence quenching of 2,3-diazabicyclo[2.2.2]oct-2-ene (DBO) by certain estrogens and catechols

The fluorescence quenching of singlet excited 2,3-diazabicyclo[2.2.2]oct-2-ene (DBO), a fluorescent probe for antioxidants, by various estrogens and certain catechols has been investigated. The time resolved and steady state fluorescence quenching experiments were conducted in acetonitrile and dichloromethane. The bimolecular quenching rate constant (kq) values are in the range of 107–109 M−1 s−1 for estrogens and 109–1010 M−1 s−1 for catechols. In the case of estrogens, a direct hydrogen atom abstraction is proposed, while exciplex induced quenching becomes competitive for catechols with electron donating (ED) substituents. The quenching mechanism was analysed on the basis of exciplex formation, deuterium isotopic effects and cyclicvoltammetric studies. Further, the invitro-antioxidant activity of estrogens and catechols were evaluated with rat liver catalase by gel electrophoresis. The data suggest the involvement of hydrogen atom transfer in the fluorescence quenching of DBO by estrogens and catechols.