Fluorogenic Ubiquinone Analogue for Monitoring Chemical and Biological Redox Processes

We report herein the synthesis and characterization of a fluorogenic analogue of ubiquinone designed to reversibly report on redox reactions in biological systems. The analogue, H2B-Q, consists of the redox-active quinone segment found in ubiquinone, 2,3-dimethoxy-1,4-benzoquinone, coupled to a boron-dipyrromethene (BODIPY) fluorophore segment that both imparts lipophilicity in lieu of the isoprenyl tail of ubiquinone, and reports on redox changes at the quinone/quinol segment. Redox sensing is mediated by a photoinduced electron transfer intramolecular switch. In its reduced dihydroquinone form, H2B-QH2 is highly emissive in nonpolar media (quantum yields 55–66%), while once oxidized, the resulting quinone H2B-Q emission is suppressed. Cyclic voltammetry of H2B-Q shows two reversible, 1-electron reduction peaks at −1.05 V and −1.37 V (vs ferrocene) on par with those of ubiquinone. Chemical reduction of H2B-Q by NaBH4 resulted in >200 fold emission enhancement. H2B-QH2 is shown to react with peroxyl radic...