A dual emission fluorescent probe enables simultaneous detection of glutathione and cysteine/homocysteine

Abstract

Many studies have shown that glutathione (GSH) and cysteine (Cys) / homocysteine (Hcy) levels are interrelated in biological systems. To unravel the complicated biomedical mechanisms by which GSH and Cys/Hcy are involved in various disease states, probes that display distinct signals in response to GSH and Cys/Hcy are highly desirable. In this work, we report a rhodol thioester (1) that responds to GSH and Cys/Hcy with distinct fluorescence emissions in neutral media. Probe 1 reacts with Cys/Hcy to form the corresponding deconjugated spirolactam via a tandem native chemical ligation (NCL) reaction. This intramolecular spirocyclization leads to the “quinone – phenol” transduction of rhodol dyes, and an excited-state intramolecular proton transfer (ESIPT) process between the phenolic hydroxyl proton and the aromatic nitrogen in the benzothiazole unit occurs upon photoexcitation, thus affording 2-(2’-hydroxyphenyl) benzothiazole (HBT) emission (454 nm). In the case of the tripeptide GSH, only transthioesterification takes place removing the intramolecular photo-induced electron transfer (PET) process caused by the electron deficient 4-nitrobenzene moiety giving rise to a large fluorescence enhancement at the rhodol emission band (587 nm). The simultaneous detection of GSH and Cys/Hcy is attributed to the significantly different rates of intramolecular S,N-acyl shift of their corresponding thioester adducts derived from 1. The utility of probe 1 has been demonstrated in various biological systems including serum and cells.

Design strategies of fluorescent probes for selective detection among biothiols

“…33). 76 They introduced a benzothiazole unit adjacent to the phenolic oxygen in the xanthene dye, thus facilitating the manipulation of ESIPT process within the molecule. In addition, the nitrothiophenol group served both as the leaving group and as a fluorescence quencher by the PET process.…”

Selective fluorescence swing from cysteine to glutathione by switchover from solid to in situ probe in 100% water and bio-imaging studies for living species

“…Considering its basic physiological resemblance with higher animals including humans, it is the most suitable living species for bio-imaging [44]. Conventionally different cell lines are used to detect individual/total biothiols [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][31][32][33]. Here for the first time [51], we used multi-cellular organism C. elegans for sensing individual biothiols.…”

“…Moreover, interference due to high level of intercellular GSH often limits the precise detection of Cys and Hcy in biological systems [8][9][10][11]. Consequently, among a large number of biothiol sensors reported so far [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26], only a few are capable of discriminating Cys, Hcy and GSH from one another and with exceptions [27][28][29], most of them remain associated with serious limitations, including the use of biotoxic organic/water mixed medium, poor biocompatibility and delayed response. Hence, there still remains a http://dx.doi.org/10.1016/j.snb.2014.…”

“Quinone–phenol” transduction activated excited-state intramolecular proton transfer: A new strategy toward ratiometric fluorescent probe for sulfite in living cells

“…Herein, as a proof-of-concept we report such a "quinoneephenol" transduction-activated ESIPT sensing scheme for sulfite. To the best of our knowledge, such a method was rarely used for switching the fluorescence of ESIPT chromophores [51,52].…”