Coumarin-Based Turn-On Fluorescence Probe for Specific Detection of Glutathione over Cysteine and Homocysteine

Abstract

We have prepared a turn-on fluorescent probe for biothiols based on bromoketo coumarin (<b>KC-Br</b>). The emission intensity of the coumarin chromophore is modulated by both the heavy atom effect and internal charge transfer (ICT) process. The probe <b>KC-Br</b> is intrinsically nonfluorescent; however, after being reacted with thiols, the bromide moiety is substituted by the −SH group, which elicits a significant fluorescence increase. We surmised the free −NH₂ group would further react with carbonyl in the Cys/Hcy-substituted intermediate product yielding to Schiff base compound <b>KC-Cys</b>/<b>KC-Hcy</b>, but not in compound <b>KC-GSH</b>. The ICT effect has a stronger influence in compound <b>KC-GSH</b> than that in compound <b>KC-Cys</b>/<b>KC-Hcy</b>, resulting in compound <b>KC-GSH</b> having a stronger fluorescence. Thus, the probe has a good selectivity for GSH over other various biologically relevant species and even two other similar biothiols (Cys/Hcy) and could image glutathione (GSH) in living cells. We expect the design concept presented in this work would be widely used for the design of fluorescent probes for distinguishing among biothiols