Nucleophilic Ring-Opening of N-Benzoylaziridine Combined with Spirolactamization of Rhodol Enables Ratiometric Fluorescence Imaging of Hydropersulfides in Arabidopsis thaliana.

Hydropersulfides (RSSH) are an important class of reactive sulfur species (RSS) involved in a variety of physiological processes in biological systems. However, selective detection of RSSH is challenging since the persulfide group (-SSH) exhibits reactivity akin to biologically abundant biothiols. To address this issue, we designed CRBA as a ratiometric fluorescent probe for RSSH by integrating the nucleophilic ring-opening of an N-benzoylaziridine and spirolactamization of a rhodol. The ratiometric sensing of RSSH is realized by modulating Förster resonance energy transfer (FRET) in the coumarin-rhodol dyad. Nucleophilic attack of the N-benzoylaziridine moiety in CRBA by RSSH affords the corresponding secondary amide ring-opened product, which subsequently undergoes a spontaneous intramolecular spirolactamization to disrupt the π-conjugation structure of the rhodol. The tandem reaction decreases the intramolecular FRET efficiency within the probe and causes a clear dual-emission signal change. Probe CRBA possesses outstanding selectivity toward RSSH over biothiols and H2S, and is capable of tracking RSSH levels in Arabidopsis thaliana roots. Moreover, we observed the upregulation of RSSH levels in heavy metal (HM)-induced stress of A. thaliana with probe CRBA, and revealed the correlation between S-persulfidation and H2S levels in living plants.