Real-time imaging of intracellular cysteine level fluctuations during Cu2+ or H2O2 induced redox imbalance using a turn-on fluorescence sensor.

Redox balance is a necessary guarantee to maintain the normal physiological activities of organisms. Cysteine (Cys), a critical biological thiol, has the effect of maintaining redox balance in the body. The concentration of intracellular Cys is abnormal under redox imbalance, thereby resulting in multiple diseases. Additionally, studies have revealed that Cu2+ can stimulate the body to produce excess reactive oxygen species (ROS, similar to H2O2), and the generated ROS will consume reducing substances (such as Cys) in the body, leading to redox imbalance. Thus, finding a simple and effective method to monitor Cys under redox imbalance is pressing. Here, a turn on probe (DDNO) was proposed by connecting SBD-Cl to a red dye (HDM). The probe can specifically recognize Cys with rapid response (180 s) and low detection limit (0.61 µM) through substitution-rearrangement reaction between sulfhydryl and chlorine atom. Bioimaging experiments indicated that the probe has good biocompatibility and cell membrane permeability, which can be applied to monitor the fluctuation of Cys levels in live cells and zebrafish under the redox imbalance induced by Cu2+ or H2O2.

A fluorescent probe for monitoring Cys fluctuations in the oxidative stress environment simulated by Cu2+ or H2O2.

Redox balance is the core of holding the good physiological state of the body. Cysteine (Cys) is one of the important biomolecules, which plays an indispensable role in maintaining the body's redox homeostasis. The redox of organisms is mainly the result of the dynamic balance between reactive oxygen species (ROS) and biological reducing agents (such as Cys). Fluorescent probes have the advantages of simple operation, good specificity and high sensitivity, and have become a common tool for bio-sensing in complex systems. In this article, we designed a probe NF-O-SBD that can specifically detect Cys. The chlorine atom of NF-O-SBD was easily substituted by sulfhydryl as a reaction site. After the formation of sulfur substitution products, intramolecular rearrangement occurred and fluorescent signal was emitted in the yellow channel at 550 nm. It can be seen from the spectroscopy experiment that the content of Hcy in organisms (15 µM) basically did not cause significant fluorescence changes, Therefore, based on the practical application in biology, we further used NF-O-SBD to visualize endogenous and exogenous Cys in HepG-2 cells and zebrafish. Simultaneously, we used Cu2+ or H2O2 induction to simulate the oxidative stress environment of cells and zebrafish, under which the concentration variation of Cys was monitored.

Optimizing the framework of indolium hemicyanine to detect sulfur dioxide targeting mitochondria.

Endogenous sulfur dioxide (SO2) is mainly produced by the enzymatic reaction of sulfur-containing amino acids in mitochondria, which has unique biological activity in inflammatory reaction, regulating blood pressure and maintaining the homeostasis of biological sulfur. It is more and more common to detect monitor SO2 levels by fluorescence probe. In recent years, the indolium hemicyanine skeleton based on the D-π-A structure has been widely used in the development of fluorescent sensors for the detection of SO2. However, subtle changes in the chemical structure of indolium may cause significant differences in SO2 sensing behavior. In this article, we designed and synthesized two probes with different lipophilicities to further study the relationship between the structure and optical properties of hemicyanine dyes. On the basis of previous studies, the structure of indolium hemicyanine skeleton was optimized by introducing -OH group, so that MC-1 and MC-2 had the best response to SO32- in pure PBS system. In addition, the lipophilicity of MC-2 was better than that of MC-1, which enabled it to respond quickly to SO32- and better target mitochondria for SO2 detection. Most importantly, the low detection limits of MC-1 and MC-2 conducive to the detection of endogenous SO2. This work provided an idea for developing SO2 fluorescent sensors with excellent water solubility and low detection limit.

Construction of a pillararene-based supramolecular polymer network and its application in efficient removal of dyes from water.

An AB-type monomer based on a pillar[5]arene host and an imidazolium salt guest was successfully synthesized through a facile way. This monomer can self-assemble into linear supramolecular polymers in chloroform. After the addition of silver ions, the imidazolium salt group coordinated with silver ions to crosslink the linear supramolecular polymers at their ends, resulting in the formation of supramolecular polymer networks. Meanwhile, after further adding iodide ions, the supramolecular polymer network changed back to the linear supramolecular polymer. As a result, the topological structure of the system can be reversibly tuned. Furthermore, this supramolecular polymer network can be applied to remove organic dyes in water, suggesting its great potential in the treatment of waste water.

A sequentially activated bioluminescent probe for observation of cellular H2O2 production induced by cysteine.

We report herein a caged luciferin probe Cy-Hy as a sequentially activated probe to selectively and sensitively sense L-Cys and H2O2. The probe displayed fluorescence and bioluminescence responses toward the two analytes. Utilizing the present probe, cellular excess L-Cys-induced H2O2 up-regulation was observed for the first time in living MDA-MB-231 cells.

Sulphide activity-dependent multicolor emission dye and its applications in in vivo imaging.

Reactive sulfur species (RSS) play pivotal roles in various pathological and physiological processes. There exists an intricate relevance in generation and metabolism among these substances. Although they are nucleophilic, there are still some differences in their reactivity. There are many methods to detect them by using reactive fluorescent probes, but the systematic study of their reactivity is still lacking. In our study, we designed a multiple reaction site fluorescent probe based on benzene conjugated benzopyrylium and NBD. The study revealed that besides both biothiols and hydrogen sulfide, sulfur dioxide (SO2) can cleave the ether bond. There are two reaction forms for GSH with low reactivity: cutting the ether bond and adding the conjugated double bond of benzopyrylium. Nevertheless, Cys/Hcy with higher activity can further rearrange with NBD after cutting the ether bond. In addition, SO2 can not only cleave the ether bond, but also continue to add the conjugated double bond of benzopyrylium. The above processes lead to multicolor emission of the probe, thus realizing the characteristic analysis of different sulfides. Thus the probe can be used for the detection of sulfide in mitochondria, and further for the imaging of sulfide in cells and zebrafish. This effective analysis method will provide a broad application prospect for practical applications.

A reversible coumarin-based sensor for intracellular monitoring cysteine level changes during Cu2+-induced redox imbalance.

Biological thiols are crucial small molecule amino acids widely existing in cells, which play indispensable roles in maintaining redox homeostasis of living systems. Owing to their abnormal levels have close relation with many diseases, thus, developing more convenient, rapid and practical in-vivo detection tools is imminent. Herein, a reversible coumarin-based probe (HNA) was successfully constructed through a simple two-step synthesis. HNA can detect Cys/Hcy with high response speed and desirable selectivity based on Michael addition recognition mechanism. Free HNA has an orange emission at 580 nm, but after addition of Cys/Hcy, the conjugated structure of probe HNA was destroyed by the attack of sulfhydryl, resulting in a new green emission at 507 nm. Further, HNA has been applied to monitor Cys/Hcy in HeLa cells and zebrafish. Notably, HNA has also been successfully applied for real-time tracing Cys levels changes in living cells and zebrafish during the imbalance in redox status caused by copper (II). This provides a new strategy for studying the process of oxidative stress in cells.

A near-infrared fluorescent probe targeting mitochondria for sulfite detection and its application in food and biology.

Sulfur dioxide (SO2) is the main air pollutant in the environment, causing great harm to human health. Abnormal SO2 levels are usually associated with some respiratory diseases, cardiovascular diseases, and neurological disorders (even brain cancer). Therefore, monitoring SO2 levels is helpful to better understand its special physiological and pathological role. Although many fluorescent probes for SO2 have been reported, many of them were not ideal for in vivo imaging due to the short emission wavelength. In this work, a near-infrared fluorescent probe NIR-BN with emission wavelength of 680 nm was constructed by conjugating the benzopyrylium moiety and 6-hydroxy-2-naphthaldehyde. NIR-BN had high selectivity and rapidity for SO2 detection. In addition, the detection limit of NIR-BN was relatively low, which can be used for the determination of sulfite in different sugar samples with high accuracy. Of course, due to the excellent spectral and structural properties of NIR-BN, we have applied NIR-BN to the detection of SO2 in biological systems.

A coumarin-based fluorescence sensor for rapid discrimination of cysteine/homocysteine and glutathione under dual excitation wavelengths.

Biological thiols (Cys, Hcy and GSH) are crucial biomolecules in living cells and play indispensable roles in maintaining the redox homeostasis of organisms. But due to their similar molecular structure, the development of effective tools for distinguishing two or three of them remains a great difficulty. Herein, we constructed a sensitive sensor (CB) by connecting the bifunctional fluorescent reagent with coumarin derivatives for simultaneous recognition of these three thiols through different pathways. Free CB had no fluorescence; however, with gradual addition of thiols, the chlorine unit was replaced by sulfhydryl. Furthermore, the intramolecular rearrangement occurred between the amino and sulfhydryl groups of Cys/Hcy and yellow fluorescence was observed at 570 nm. However, GSH with a large structure could not undergo intramolecular rearrangement, and green fluorescence was excited at 505 nm. In this way, Cys/Hcy and GSH can be detected distinctively. Under dual excitation wavelengths, CB exhibited high selectivity and fast response to the three thiols. Furthermore, CB was successfully applied to imaging endogenous and exogenous thiols in living cells and zebrafish, providing us with a reliable tool for thiols recognition.

A Pyrene-Based Fluorescent Probe for Specific Detection of Cysteine and its Application in Living Cell.

Cysteine (Cys) is an essential amino acid in organism, which is transformed from methionine in vivo and participates in protein synthesis and cell redox process. Therefore, the detection of Cys is of great significance. In this work, a novel fluorescent probe, (E)-3-(2-chloroquinolin-3-yl)-1-(pyren-3-yl) prop-2-en-1-one (PAQ) was designed and synthesized to specifically detect Cys. The response mechanism of the reaction between PAQ and Cys was due to the addition reaction of Cys to α,ß-unsaturated ketone of PAQ. Interestingly, the addition of Cys induced significant fluorescence intensity enhancement at 462 nm. PAQ exhibited favorable sensing properties towards Cys such as the low limit of detection (0.27 µM) and fast response speed (2 min). In addition, PAQ displayed high selectivity and anti-interference ability toward Cys among various analytes. Notably, PAQ has been successfully used to image exogenous and endogenous Cys in HeLa cells.

High-Specific Fluorescence Probe for SO32- Detection and Bioimaging.

It is well known that sulfite (SO32-) plays an indispensable role in various physiological processes. Abnormal levels of SO32- can trigger a wide variety of diseases involving respiratory, nervous and cardiovascular systems. Hence, it is necessary to find an efficient approach for detection of SO32-. In this study, a pyrene derivative, (E)-4-(3-oxo-3-(pyren-1-yl)prop-1-en-1-yl)phenyl acrylate (PPA), was designed and synthesized for monitoring SO32-. The probe possessed simple synthetic steps, excellent anti-interference ability and specific response to SO32- in the presence of other substances. The reaction between PPA and SO32- was ascribed to Michael addition and the detection mechanism was confirmed by HRMS spectra analysis and FTIR analysis. Additionally, PPA responded linearly to detect SO32- within the rang of 0-100 µM. The limit of detection was calculated as low as 0.17 µM in accordance with the recommendation of IUPAC (CDL =3sb/m). Notably, PPA was further applied in biological imaging in HepG2 cells, which provided a possibility to monitor SO32- in vivo.

Rapid Reaction, Slow Dissociation Aggregation, and Synergetic Multicolor Emission for Imaging the Restriction and Regulation of Biosynthesis of Cys and GSH.

Biosynthesis is a necessary process to maintain life. In recent years, research has fully shown that three kinds of biothiols (Cys, Hcy, GSH) mainly play the role in oxidative stress and maintaining cell homeostasis in cells, and that abnormal concentrations will lead to the occurrence of cardiovascular diseases, cancers, etc. Various fluorescent probes have shown unprecedented advantages in detecting their concentrations and studying their biological functions. As a matter of fact, these three kinds of biothiols are generated in the process of biosynthesis in vivo. It is of great significance to understand their biosynthetic pathways and elucidate their synthetic relationships. In this work, to α,ß-unsaturated ketones conjugated ethylenediamine coumarin and pyrandione was introduced boron fluoride and, through its strong electron deficiency effect, afforded a molecule having near-infrared emission and regulated the rigidity of molecules. At the same time, the conjugated double bond is used to respond to molecular rigidity. The rapid response of the probe to biothiols and the slow dissociation aggregation of the probe itself through the response environment could monitor the absence of biothiols in cells. In addition, based on the difference in sensitivity of response of Cys and GSH to the probe, this work studied the interaction between biosynthetic pathways of Cys and GSH in cells through enzyme inhibition for the first time. The relationship of restriction and regulation of biosynthesis in vivo was revealed.

Thiol "Click" Chromene Ring Opening and Subsequent Cascade Nucleophilic Cyclization NIR Fluorescence Imaging Reveal High Levels of Thiol in Drug-Resistant Cells.

As the structural unit of natural products, chromene derivatives show a wide range of biological activity and pharmacological activity due to their unique photophysical and chemical properties. Ten years ago, our research group discovered the "thiol-chromene" click reaction, which achieved the selective detection of thiols through the change of the optical spectrum. Afterward, we attempted to develop various chromene-based fluorescent probes for imaging including near-infrared (NIR) probe, ratiometric probe, and multifunctional probe. However, how to integrate the fluorophore and reaction sites into the chromene-based skeleton remains challenging. In this work, we connected the chromene motif with the NIR fluorophore methylene blue utilizing a carbamate spacer to provide a new fluorescent probe (CM-NIR), which is triggered by thiols to open the pyran ring followed by attacking the carbamate by phenolate to releases the methylene blue. This novel cascade mechanism avoids the formation of para-quinone methides, which proved to be toxic to normal cells. CM-NIR also showed the specific imaging of thiols in living cells and mice. More importantly, the thiols level in drug-resistant cancer cells was found to be significantly higher than that in the corresponding cancer cell, which indicated that the thiols level may have an important role in cancer cells developing drug resistance.

A New Strategy: Distinguishable Multi-substance Detection, Multiple Pathway Tracing Based on a New Site Constructed by the Reaction Process and Its Tumor Targeting.

In recent years, it has become a trend to employ organic molecular fluorescent probes with multireaction sites for the distinguishable detection and biological imaging of similar substances. However, the introduction of multireaction sites brought great challenges to organic synthesis, and at the same time, often destroyed the conjugated structure of the molecules, leading to an unsatisfactory fluorescence emission wavelength not conducive to practical application. As the eternal theme of life, metabolism goes on all the time. Metabolism is a series of ordered chemical reactions that occurs in the organism to maintain life. Chemical reactions in metabolism can be summarized as metabolic pathways. Simultaneous monitoring of different metabolic pathways of the same substance poses a lofty challenge to the probe. Here, we developed a new strategy: to construct new sites through the preliminary reactions between probes and some targets, which can be used to further distinguish among targets or detect their metabolites, so as to realize the simultaneous visualization tracer of multiple metabolic pathways. By intravenous injection, it revealed that the probe containing benzopyrylium ion can target tumors efficiently, and thiols are highly expressed in tumors compared to other tissues (heart, lung, kidney, liver, etc.). The consumption of thiols by the probe could not prevent tumor growth, suggesting that the tumor cure was not correlated with thiol concentration. The construction of new sites in the reaction process is a novel idea in the pursuit of multiple reaction sites, which will provide more effective tools for solving practical problems.

A practical pH-compatible fluorescent sensor for hydrazine in soil, water and living cells.

The excellent water solubility of hydrazine (N2H4) allows it to easily invade the human body through the skin and respiratory tract, thereby damaging human organs and the central nervous system. To realize the monitoring of N2H4 effectively, first, coumarin was used to construct an inner alicyclic ring as the reaction site, extending the conjugation and strengthening the rigidity of the probe Co-Hy to improve its luminescence performance and enhance its ability to resist acids and alkalis. Second, we introduced a carboxyl group at the ortho position of the inner alicyclic ring to improve the water solubility of Co-Hy, and its strong electron pulling effect increased the activity of the reaction site. Spectroscopy experiments showed that Co-Hy featured excellent water solubility, high pH resistance (pH 4-11), excellent selectivity, fast analysis speed (within 5 minutes), and a low detection limit toward N2H4 (69 nM, 2.2 ppb). In addition, test-strip, spray, and cell-imaging experiments confirmed the outstanding application potential of Co-Hy for convenient N2H4 analysis in a variety of environments.

Carbazole-conjugated-coumarin by enone realizing ratiometric and colorimetric detection of hypochlorite ions and its application in plants and animals.

Detection of hypochlorite ions (ClO-) in the organisms is of great significance for finding effective treatments for inflammations and diseases. Recently, fluorescent probes have aroused wide public concern as one of the effective tools for detecting molecules and ions. Nevertheless, due to low sensitivity and poor biocompatibility, the effect of fluorescent probes for biological imaging is still not ideal. For this, we developed a novel ratiometric fluorescent probe, 7-(diethylamino)-3-((E)-3-(9-ethyl-9H-carbazol-3-yl)acryloyl)-2H-chromen-2-one (DCC), which could be used for colorimetric detection of ClO-. Study showed that, the detection mechanism of DCC is that probe can be rapidly oxidized to an enoic acid by ClO-, resulting in a series of changes in spectral properties. This mechanism was confirmed experimentally and verified by theoretical calculations. It is worth mentioning that DCC has not only been successfully applied to the detection of exogenous and endogenous OCl- in living cells, but also used for the detection of ClO- in zebrafish, and Arabidopsis.

Independent bi-reversible reactions and regulable FRET efficiency achieving real-time visualization of Cys metabolizing into SO2.

In this work, we synthesized an independent bi-reversible reaction sensor BPC for simultaneously detecting cysteine (Cys) and sulfur dioxide (SO2), showing multi-fluorescence signal modes due to the regulable FRET efficiency, and finally achieving real-time process visualization of Cys metabolizing into SO2 in subcellular organelles and tumors.

Benzenebistriazole-strapped calix[4]pyrrole: a neutral anion receptor with CH and NH donor groups that exhibits high sulfate binding affinity and selectivity in aqueous solutions.

A calix[4]pyrrole strapped by benzenebistriazole has been prepared as an artificial anion binding receptor. This neutral anion receptor shows high sulfate binding affinity and selectivity in an aqueous solution. In solid state, the receptor binds the sulfate anion in a chair-like 3D cavity via multiple N-H and C-H hydrogen bonds.

Palladium-Catalyzed Regioselective Coupling Cyclohexenone into Indoles: Atom-Economic Synthesis of ß-Indolyl Cyclohexenones and Derivatization Applications.

Herein, we report a palladium-catalyzed dehydrogenative cross-coupling of indoles with cyclic enones to give ß-indolyl cyclic enones under mild and neutral reaction conditions. The key to the success is to explore a mild condition, which ensures the indole C-H activation and subsequent syn ß-hydride elimination through rapid enolization isomerization of Pd(II)-enolate while suppressing other undesired side reactions. Synthetic utility has also been demonstrated in the flexible transformation of the coupling products to meta-phenols and benzo[a]carbazoles.

Mitochondria-targeted reversible ratiometric fluorescent probe for monitoring SO2/HCHO in living cells.

Sulfur dioxide (SO2) maintains a certain steady state balance in the body, high concentration SO2 will be harmful to human health. Seeking a suitable detection method to monitor sulfur dioxide in real time becomes an urgent requirement owing to the transient nature of sulfur dioxide in organisms. Here, a novel NIR ratiometric fluorescent probe for detection of SO2 was developed based on a conjugation of coumarin and indol salt with excellent water solubility. The probe Mito-CI displayed highly sensitive (69 nM), fast response time (30 s), large Stokes shift (174 nm) and the NIR fluorescence emission wavelength (655 nm). In the reversibility process of the SO3--probe Mito-CI system induced by HCHO in vitro was also detected. Besides, cell imaging showed that Mito-CI possesses mitochondria-targeted ability. Particularly, Mito-CI was proved to reversibly detect SO2/HCHO in living cells.