New phthalimide-methionine dyad-based fluorescence probes for reactive oxygen species: Singlet oxygen, hydrogen peroxide, and hypochlorite

Abstract

Different reactive oxygen species were detected by the molecular probes 1-3 that were composed of the phthalimide fluorophore as reporter and a methionine-derived thioether side-chain as receptor part. The sulfoxides that were formed as the primary oxidation products show strong fluorescence in the blue-green (430-540 nm) spectral region. Self-sensitized oxidation by singlet oxygen is in general inefficient indicating rapid electron-transfer quenching of the excited probe molecules. With hydrogen peroxide as thermal oxidant conversion to the sulfoxides is slow but can be accelerated by addition of titanium(IV) catalysts, whereas hypochlorite as oxidant behaves much more reactive even under uncatalyzed conditions. Singlet oxygen that is generated by energy transfer from the photosensitizer Rose Bengal was detected by sensor 1a with rate constants of >107M–1 s–1, a typical rate constant for the oxidation of thioethers to sulfoxides.