Xi Dai

A simple and effective coumarin-based fluorescent probe for cysteine

Acrylic acid 3-acetyl-2-oxo-2 H-chromen-7-yl ester (ACA) was rationally designed and synthesized as a simple and effective fluorescent probe for sensing cysteine with high selectivity and naked-eye detection. The probe can detect cysteine by fluorescence spectrometry with a detection limit of 0.657 μM and can be used with calf serum and in live cell imaging. The conjugate addition/cyclization sequence mechanism of the reaction between ACA and cysteine was confirmed by ESI-MS and fluorescence spectra.

An effective colorimetric and ratiometric fluorescent probe for bisulfite in aqueous solution.

We have developed the first two-photon colorimetric and ratiometric fluorescent probe, BICO, for the detection of bisulfite (HSO3(-)) in aqueous solution. The probe contains coumarin and benzimidazole moieties and can detect HSO3(-) based on the Michael addition reaction with a limit of detection 5.3 × 10(-8) M in phosphate-buffered saline solution. The probe was used to detect bisulfite in tap water, sugar and dry white wine. Moreover, test strips were made and used easily. We successfully applied the probe to image living cells, using one-photon fluorescence imaging. BICO overcomes the limitations in sensitivity of previously reported probes and the solvation effect of bisulfite, which demonstrates its excellent value in practical application.

A colorimetric, ratiometric and water-soluble fluorescent probe for simultaneously sensing glutathione and cysteine/homocysteine.

A chlorinated coumarin-aldehyde was developed as a colorimetric and ratiometric fluorescent probe for distinguishing glutathione (GSH), cystenine (Cys) and homocysteine (Hcy). The GSH-induced substitution-cyclization and Cys/Hcy-induced substitution-rearrangement cascades lead to the corresponding thiol-coumarin-iminium cation and amino-coumarin-aldehyde with distinct photophysical properties. The probe can be used to simultaneously detect GSH and Cys/Hcy by visual determination based on distinct different colors - red and pale-yellow in PBS buffer solution by two reaction sites. From the linear relationship of fluorescence intensity and biothiols concentrations, it was determined that the limits of detection for GSH, Hcy and Cys are 0.08, 0.09 and 0.18 μM, respectively. Furthermore, the probe was successfully used in living cell imaging with low cell toxicity.

An effective colorimetric and ratiometric fluorescent probe based FRET with a large Stokes shift for bisulfite

Bisulfite plays crucial roles in diverse physiological processes. Therefore, the efficient detection of bisulfite is very important. In this study, we report a colorimetric and ratiometric fluorescent probe (CPT) with a large Stokes shift (162 nm) for bisulfite (HSO3−) based FRET mechanism. The probe can quantitatively detect HSO3− with low detection limit (45 nM) and high specificity over other common anions and biothiols. A nucleophilic addition reaction was proposed for the sensing mechanism, which was confirmed by HRMS spectra. The test strips of the probe were made and used easily. Moreover, probe CPT was used to ratiometric fluorescent imaging of exogenous and endogenous HSO3− in living cells.

A coumarin-indole based colorimetric and "turn on" fluorescent probe for cyanide.

A novel coumarin-indole based chemodosimeter with a simple structure was designed and prepared via a condensation reaction in high yield. The probe exhibited very high selectivity towards cyanide on both fluorescence and UV-vis spectra, which allowed it to quantitatively detect and imaging cyanide ions in organic-aqueous solution by either fluorescence enhancement or colorimetric changes. Confirmed by (1)H NMR and HRMS spectra, the detection mechanism was proved to be related with the Michael addition reaction induced by cyanide ions, which blocked the intramolecular charge transfer (ICT) of the probe. Moreover, the probe was able to be utilized efficiently in a wide pH range (7.5-10) with negligible interference from other anions and a low detection limit of 0.51μM. Application in 5 kinds of natural water source and accurate detection of cyanide in tap water solvent system also indicated the high practical significance of the probe.

A ratiometric lysosomal pH probe based on the imidazo[1,5-a]pyridine–rhodamine FRET and ICT system

A new pH-activatable ratiometric fluorescent probe (RhMP) has been developed, in which an imidazo[1,5-a]pyridine fluorophore as a fluorescence resonance energy transfer (FRET) donor linked to a rhodamine B fluorophore as a FRET acceptor. The simultaneous fluorescence intensity enhancement of imidazo[1,5-a]pyridine and rhodamine B moieties along with the decrease of pH value should result from the integration of ICT and FRET processes. Its the first time a ratiometric fluorescent probe based on FRET system using imidazo[1,5-a]pyridine derivative as a fluorophore donor has been reported. At pKa = 4.96, the fluorescence intensity ratio (I476.5/I577.5) of the probe displayed excellent pH-dependent performance and responded linearly to minor pH changes in the range of 4.0–5.8. The probe exhibited excellent selectivity among different metal cations and brilliant reversibility. In addition, RhMP has low cytotoxicity and has been successfully applied in HeLa cells. The fluorescence microscopic images demonstrated this probe could image weak acid pH changes of the lysosome in live cells.

An effective fluorescent probe to detect glutathione from other sulfhydryl compounds in aqueous solution and its living cell imaging

We designed and synthesized a two-photon fluorescent probe, 2-(1,5-diphenyl-4,5-dihydro-1H-pyrazol-3-yl)naphthalen-1-yl acrylate (PPN) with improved properties based on the naphthalene–pyrazoline fluorophore. The probe exhibits high sensitivity to glutathione (GSH) in PBS–CTAB buffer solution with a low detection limit of 1.5 × 10−8 M and a response time less than 10 min. According to the HRMS and fluorescence spectra analysis, the detection mechanism was confirmed to be a Michael addition reaction induced by the sulfhydryl of GSH. In addition, probe PPN has very good selectivity and is able to discriminate GSH from cysteine (Cys), homocysteine (Hcy) and other sulfhydryl compounds with bright two-photon-excited fluorescence. Moreover, we have successfully applied PPN to calf serum samples and living cell imaging with good effect.

Discovery of a novel fluorescent HSP90 inhibitor and its anti-lung cancer effect

A series of novel fluorescent pyrazoline coumarin derivatives were synthesized. From them, we screened a compound possessing strong growth inhibitory effects on lung cancer cells. By taking advantage of fluorescence combined with LC-MS/MS and chemoinformatics technique, we successfully identified HSP90 as the target of the compound.

Discovery of novel HSP90 inhibitors that induced apoptosis and impaired autophagic flux in A549 lung cancer cells

Heat shock protein 90 (HSP90) inhibition has aroused increasing enthusiasm in antitumor strategies in recent years. According to our previous studies, we synthesized a series of coumarin pyrazoline compounds HCP1-HCP6 that might be HSP90 inhibitors. Interactions between HCP1-HCP6 and HSP90 were examined and antitumor activities of them were investigated in A549 lung cancer cells. Results showed that all the six derivatives could interact with HSP90, in which HCP1 exhibited the best binding ability and inhibited the activity of HSP90. Meanwhile, HCP1-HCP6 reduced the cell viability of A549 cells and HCP1 possessed the lowest IC50 value. Above all HCP1 exerted better HSP90 inhibitory and anticancer effects than our initially identified HSP90 inhibitor DPB. As to the underlying mechanism, HCP1-HCP6 not only induced apoptosis as DPB but also blocked autophagic flux in A549 cells. Therefore, we discovered a novel HSP90 inhibitor HCP1 that had better biological activity and provided us a useful tool to explore the underlying mechanism of lung cancer therapy.