A sensitive fluorescent probe based on coumarin for detection of cysteine in living cells

A dicyanoisophorone-based long-wavelength fluorescent probe for detection of cysteine in vitro and in vivo

In this research, an "off-on" long-wavelength fluorescent probe (DCMN-Cl) based on (E)-2-(3-(2-(6-hydroxynaphthalen-2-yl)vinyl)-5,5-dimethylcyclohex-2-en-1-ylidene) malononitrile (DCMN) is designed and synthesized for cysteine (Cys) detection. DCMN-Cl exhibits a large Stokes shift (211 nm) and shows rapid response and high specificity to Cys. The fluorescence initensity at 635 nm reveals a good linear relationship with Cys concentration in the 0 to 50 μM range, and the detection limit is as low as 159 nM. The probe is also used for fluorescence imaging of Cys in cells and mice. Moreover, the probe provided visual evidence of Cu2+ and curcumin-induced intracellular Cys fluctuations.

A dual-response NIR fluorescent probe for separately and continuously recognizing H2S and Cys with different fluorescence signals and its applications

Given the significant interactions between hydrogen sulfide (H2S) and cysteine (Cys) in organisms, a dual-site multi-purpose fluorescent probe (Cy-NP) for H2S and Cys was synthesized. Cy-NP is composed of two fluorophores: naphthalimide that emits in the visible region of 500-600 nm, and cyanine dye that emits in the NIR region of 700-800 nm. Cy-NP showed admirable sensitivity and selectivity for identifying H2S and Cys by fluorescent signals with limits of detection as low as 0.15 μM and 1.4 μM, respectively. Furthermore, other biological thiols (especially GSH and Hcy) showed no positive response to Cy-NP compared with H2S and Cys. The chemical mechanism of Cy-NP with H2S and Cys in DMF/PBS (1/1, v/v, pH = 7.4) solution was verified by HRMS and DFT calculations. Further, Cy-NP was successfully applied to monitor H2S released in raw meat and adapted to detect H2S and Cys in MCF-7 cells independently and continuously.

Novel Boronate Probe Based on 3-Benzothiazol-2-yl-7-hydroxy-chromen-2-one for the Detection of Peroxynitrite and Hypochlorite

Derivatives of coumarin, containing oxidant-sensitive boronate group, were recently developed for fluorescent detection of inflammatory oxidants. Here, we report the synthesis and the characterization of 3-(2-benzothiazolyl)-7-coumarin boronic acid pinacol ester (BC-BE) as a fluorescent probe for the detection of peroxynitrite (ONOO-), with high stability and a fast response time. The BC-BE probe hydrolyzes in phosphate buffer to 3-(2-benzothiazolyl)-7-coumarin boronic acid (BC-BA) which is stable in the solution even after a prolonged incubation time (24 h). BC-BA is slowly oxidized by H2O2 to form the phenolic product, 3-benzothiazol-2-yl-7-hydroxy-chromen-2-one (BC-OH). On the other hand, the BC-BA probe reacts rapidly with ONOO-. The ability of the BC-BA probe to detect ONOO- was measured using both authentic ONOO- and the system co-generating steady-state fluxes of O2•- and •NO. BC-BA is oxidized by ONOO- to BC-OH. However, in this reaction 3-benzothiazol-2-yl-chromen-2-one (BC-H) is formed in the minor pathway, as a peroxynitrite-specific product. BC-OH is also formed in the reaction of BC-BA with HOCl, and subsequent reaction of BC-OH with HOCl leads to the formation of a chlorinated phenolic product, which could be used as a specific product for HOCl. We conclude that BC-BA shows potential as an improved fluorescent probe for the detection of peroxynitrite and hypochlorite in biological settings. Complementation of the fluorescence measurements by HPLC-based identification of oxidant-specific products will help to identify the oxidants detected.

A Phenothiazine-HPQ Based Fluorescent Probe with a Large Stokes Shift for Sensing Biothiols in Living Systems

Due to the redox properties closely related to numerous physiological and pathological processes, biothiols, including cysteine (Cys), homocysteine (Hcy) and glutathione (GSH), have received considerable attention in biological science. On account of the important physiological roles of these biothiols, it is of profound significance to develop sensitive and selective detection of biothiols to understand their biological profiles. In this work, we reported an efficient fluorescent probe, PHPQ-SH, for detecting biothiols in vitro and vivo, based on the phenothiazine-HPQ skeleton, with DNBS (2,4-dinitrobenzenesulfonate) as the response unit. Probe PHPQ-SH exhibited brilliant sensing performances toward thiols, including a large Stokes shift (138 nm), excellent sensitivity (for GSH, LOD = 18.3 nM), remarkable fluorescence enhancement (163-fold), low cytotoxicity, rapid response (8 min), and extraordinary selectivity. Finally, the probe PHPQ-SH illustrated herein was capable of responding and visualizing biothiols in MCF-7 cells and zebrafish.

Recognition of Thiols in Living Cells and Zebrafish Using an Imidazo[1,5-α]pyridine-Derivative Indicator

A new cyan fluorescent probe, MIPY-DNBS, using an imidazo[1,5-α]pyridine derivative as the fluorophore and 2,4-dinitrobenzensufonate as the recognition site for the selective detection of thiols (Cys, GSH, and Hcy), was designed and synthesized. Probe MIPY-DNBS exhibited a 172 nm Stokes shift, a fast response time (400 s), low cytotoxicity, low detection limits (12.7 nM for Cys), and excellent selectively in the detection of thiols. In addition, MIPY-DNBS was successfully applied to imaging thiols in living MCF-7 cells and zebrafish.

Coumarin-Based Small-Molecule Fluorescent Chemosensors

Coumarins are a very large family of compounds containing the unique 2H-chromen-2-one motif, as it is known according to IUPAC nomenclature. Coumarin derivatives are widely found in nature, especially in plants and are constituents of several essential oils. Up to now, thousands of coumarin derivatives have been isolated from nature or produced by chemists. More recently, the coumarin platform has been widely adopted in the design of small-molecule fluorescent chemosensors because of its excellent biocompatibility, strong and stable fluorescence emission, and good structural flexibility. This scaffold has found wide applications in the development of fluorescent chemosensors in the fields of molecular recognition, molecular imaging, bioorganic chemistry, analytical chemistry, materials chemistry, as well as in the biology and medical science communities. This review focuses on the important progress of coumarin-based small-molecule fluorescent chemosensors during the period of 2012-2018. This comprehensive and critical review may facilitate the development of more powerful fluorescent chemosensors for broad and exciting applications in the future.

A Green-emitting Fluorescent Probe Based on a Benzothiazole Derivative for Imaging Biothiols in Living Cells

A new green-emitting fluorescent probe 1 was developed for biothiol detection. The sensing mechanism was considered to be biothiol-induced cleavage of the 2,4-dinitrobenzene- sulfonate group in probe 1 and resulting inhibition of the probe’s photoinduced electron transfer (PET) process. Probe 1 exhibited favorable properties such as excellent selectivity, highly sensitive (0.12 µM), large Stokes shift (117 nm) and a remarkable turn-on fluorescence signal (148-fold). Furthermore, confocal fluorescence imaging indicated that probe 1 was membrane-permeable and suitable for visualization of biothiols in living A549 cells.

New Variations on the Theme of Gold(III) C∧N∧N Cyclometalated Complexes as Anticancer Agents: Synthesis and Biological Characterization

A series of novel (C^∧N^∧N) cyclometalated Au^III complexes of general formula [Au(bipy^dmb-H)X][PF₆] (bipy^dmb-H = C^∧N^∧N cyclometalated 6-(1,1-dimethylbenzyl)-2,2'-bipyridine) were prepared with a range of anionic ligands X in the fourth coordination position, featuring C (alkynyl)-, N-, O-, or S-donor atoms. The X ligands are varied in nature and include three coumarins, 4-ethynylaniline, saccharine, and thio-β-d-glucose tetraacetate, the tripeptide glutathione (GSH), and a coumarin-substituted amide derived from 4-ethynylaniline. The gold(I) complex [Au(C₂ArNHCOQ)(PPh₃)] (HC₂ArNHCOQ = N-(4-ethynylphenyl)-2-oxo-2 H-chromene-3-carboxamide) was also prepared for comparison. The new compounds were fully characterized by means of analytical techniques, including NMR, absorption, and emission spectroscopy. The crystal structures of three cyclometalated Au^III complexes and of the Au^I derivative were solved by single-crystal X-ray diffraction. The antiproliferative activity of the new Au^III cyclometalated derivatives was evaluated against cancer cells in vitro. According to the obtained results, only complexes 3-PF₆ and 5-PF₆, featuring coumarins as ancillary ligands and endowed with high redox stability in solution, display antiproliferative effects, with 5-PF₆ being the most potent, while all of the others are scarcely active to nonactive in the selected cell lines. In order to study the reactivity of the compounds with biomolecules, the interaction of complexes 3-PF₆ and 5-PF₆ with the protein cytochrome c and the amino acids cysteine and histidine was analyzed by electrospray ionization mass spectrometry (ESI MS), showing adduct formation only with Cys after at least 1 h incubation. Furthermore, the parent hydroxo complex [Au(bipy^dmb-H)(OH)][PF₆] (1OH-PF₆) was investigated in a competitive assay to determine the protein vs oligonucleotide binding preferences by capillary zone electrophoresis (CZE) coupled to ESI-MS. Of note, the compound was found to selectively form adducts with the oligonucleotide over the protein upon ligand exchange with the hydroxido ligand. Adduct formation occurred within the first 10 min of incubation, demonstrating the preference of 1OH-PF₆ for nucleotides in this setup. Overall, the obtained results point toward the possibility to selectively target DNA with gold(III) organometallics.

Fluorescent probes for detecting cysteine

Cysteine plays a crucial role in physiological processes. Therefore, it is necessary to develop a method for detecting cysteine. Fluorimetry has the advantages of convenient detection, short response time, high sensitivity and good selectivity. In this review, fluorescent probes that detect cysteine over the past three years are summarized based on structural features of fluorophores such as coumarin, BODIPY, rhodamine, fluorescein, CDs, QDs, etc and reaction groups including acrylate, aldehyde, halogen, 7-nitrobenzofurazan, etc. Then, effects of different combinations between fluorophores and response groups on probe properties and detection performances are discussed.

Coumarin Derivative Directly Coordinated to Lanthanides Acts as an Excellent Antenna for UV-Vis and Near-IR Emission

A chelating coumarin-derived ligand sensitizes all emitting lanthanide ions in the solid state and gives high absolute quantum yields for ethanol solutions of complexes of Sm, Eu, Tb, and Dy, above 20% for the last two. Crystal structures of these four complexes are [Ln(Cum)₃(H₂O)(X)]·X where X = MeOH or EtOH.

A Fluorescent Coumarin-Based Probe for the Fast Detection of Cysteine with Live Cell Application

A new coumarin-based fluorescent probe, containing an allylic esters group, has been designed and synthesized for sensing cysteine in physiological pH. In this fluorescent probe, the coumarin was applied as the fluorophore and an allylic esters group was combined as both a fluorescence quencher and a recognition unit. The probe can selectively and sensitively detect cysteine (Cys) over homocysteine, glutathione, and other amino acids, and has a rapid response time of 30 min and a low detection limit of 47.7 nM. In addition, the probe could be applied for cell imaging with low cytotoxicity.