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Biothiols, including homocysteine (Hcy), cysteine (Cys) and reduced glutathione (GSH), play various roles in physiological and pathological processes. Because these biothiols possess similar in structures, it is difficult to discriminate Hcy, Cys and GSH from one another. In this work, a novel fluorescent probe, 4-BrCP , based on coumarin as a fluorophore to discriminate GSH from Hcy and Cys was rationally designed and synthesized in three steps with good total yield. The benzothiazol ring played the role of a fluorescent emission wavelength adjuster, while the ester part served as a fluorescent quencher and reactive sites with Hcy, Cys and GSH. The results of responsive experiment indicated that the probe could discriminate GSH from Hcy and Cys distinctly and exhibited a relatively high fluorescence quantum yield (0.84) and low detection limit (9.8 nM). In addition, the probe 4-BrCP also showed good stability and low toxicity. The reaction mechanism of 4-BrCP with GSH was speculated on according to the LC-MS data. Most importantly, because of the length of the skeletons of Hcy, Cys and GSH, different dynamic fluorescent phenomena were observed. Furthermore, imaging experiments suggested that the probe could be used to monitor GSH in living cells and organisms. [Display omitted] • A novel fluorescent probe based on coumarin was rationally designed and synthesized. • The probe could selectively discriminate GSH from Hcy, Cys, or Hcy/Cys/GSH coexisting condition. • The probe showed a good quantum yield (0.84) and low detection limit (9.8 nM). • The probe could trace endogenous GSH in living cells and organisms. [ABSTRACT FROM AUTHOR]

This study aimed to develop a novel and practical fluorescent method for GSH detection in complex biological samples. To this end, a series of coumarin-based fluorescent probes was designed and synthesized using various aliphatic halogens as the sensing group. By using a new evaluation method of GSH/Cys/Hcy coexisting conditions, the probe with chloropropionate (CBF3) showed a high selectivity, excellent sensitivity, good stability for GSH detection. The reaction mechanism is proposed as nucleophilic substitution/cyclization and intramolecular charge transfer (ICT), which was confirmed by LC-MS and NMR analysis, as well as density functional theory calculations. In addition, CBF3 was demonstrated to be competent not only for the quantitative detection of GSH in real serum samples, but also for sensing GSH changes in different oxidative stress models in living cells and nematodes. This study showed a practical strategy for constructing GSH-specific fluorescent probes, and provided a sensitive tool for real-time sensing of GSH in real biological samples. The findings would greatly facilitate further investigations on GSH-associated clinical diagnosis and biomedical studies. Image 1 • A novel SN 2 -triggered and ICT-based fluorescent probe was developed for sensing GSH. • The reaction mechanism was confirmed by experimental and theoretical investigations. • The probe selectively responded to GSH in the GSH/Cys/Hcy coexisting conditions. • The probe exhibited a low detection limit of 9.2 nM. • The probe could monitor GSH in real serum sample, and in living cells and nematodes. [ABSTRACT FROM AUTHOR]

A novel two-photon pH probe, 3-benzimidazole-7-hydroxycoumarin (BHC), was designed and synthesized based on the structures of hydroxycoumarin and benzimidazole. BHC showed good linearity in the pH ranges of 3.30–5.40 (pKa = 4.20) and 6.50–8.30 (pKa = 7.20) at a maximum emission wavelength of 480 nm. BHC in acidic and alkaline media could be distinguished by an obvious spectral shift of the maximum absorption wavelength from 390 nm to 420 nm. In addition, BHC was well localized to mitochondria and successfully applied to one-photon and two-photon imaging of pH changes in the mitochondria of HeLa cells. The findings presented herein suggest that BHC can serve as an excellent fluorescent probe for selectively sensing mitochondrial pH changes with remarkable photostability and low cytotoxicity. Unlabelled Image • A new fluorescent probe for one- and two-photon sensing of pH was developed. • The probe responded sensitively and selectively to pH changes within 3.0–6.0 (pKa = 4.20) and 6.0–9.0 (pKa = 7.20). • The probe was successfully applied for monitoring and imaging of mitochondrial pH in living cells. [ABSTRACT FROM AUTHOR]