A Benzooxazole‐Based Probe for the Sensitive Detection of Hydrogen Sulfide: Kinetic and Transition‐State Studies and In Vitro Application in HepG2 Cells

Abstract

AbstractA benzooxazole based probe, 2‐[4‐(2, 4‐dinitrophenoxy)‐phenyl]‐benzooxazole has been synthesized and thoroughly characterized by mass, 1H‐NMR and FT‐IR spectroscopy. The probe exhibits sensitive and selective response towards H2S in DMSO:PBS buffer (6:4, v/v, pH 7.4) over the other reactive sulfur species especially the biological thiols like cysteine, homocysteine and glutathione. Due to thiolysis of dinitrophenyl ether, this probe displays turn‐on fluorescence response where the sensing mechanism follows inhibited photoinduced electron transfer (d‐PET) process. This thiolysis reaction proceeds through aromatic nucleophilic substitution (SNAr) type mechanism. Moreover, the transition state study shows that this process is exoergic with favorable energy barrier of 5.0 kcal/mol. The kinetic studies of the probe with HS– at various pH assist to evaluate the acid dissociation constant value (Ka1 =1.09 × 10−8 M−1) of H2S that illustrate a reasonable agreement with the literature value, Ka (9.5 x 10−8 M−1). Finally, this probe is cell permeable, non‐cytotoxic and suitable for intracellular cytoplasmic HS– sensing in live cells with a very low detection limit (51.8 nM).