Confining Thiolysis of Dinitrophenyl Ether to a Luminescent Metal-Organic Framework with a Large Stokes Shift for Highly Efficient Detection of Hydrogen Sulfide in Rat Brain

Hydrogen sulfide (H2S) is a gaseous signaling molecule that regulates various physiological and pathological processes in the central nervous system. It is vital to develop an effective method to detect H2S in vivo to elucidate its critical role. However, current fluorescent probes for accurate quantification of H2S still face big challenges due to complicated fabrication, small Stokes shift, unsatisfactory selectivity, and especially delayed response time. Herein, based on simple postsynthetic modification, we present an innovative strategy by confining H2S-triggered thiolysis of dinitrophenyl (DNP) ether within a luminescent metal-organic framework (MOF) to address those issues. Due to the cleavage of the DNP moiety by H2S, the nanoprobe gives rise to a remarkable fluorescence turn-on signal with a large Stokes shift of 190 nm and also provides high selectivity to H2S against various interferents including competing biothiols. In particular, by virtue of the unique structural property of the MOF, it exhibits an ultrafast sensing ability for H2S (only 5 s). Moreover, the fluorescence enhancement efficiency displays a good linear correlation with H2S concentration in the range of 0-160 μM with a detection limit of 0.29 μM. Importantly, these superior sensing performances enable the nanoprobe to measure the basal value and monitor the change of H2S level in the rat brain.

Wavelength specific aggregation induced emission in aqueous media permits selective detection of Ag+ and Hg2+ ions

A new 1,8-naphthalimide derivative (probe 1) adopts V-shaped structure, emits fluorescence and displays the Mie effect and aggregation-induced emission (AIE). Selective interactions of thiophilic Ag+ and Hg2+ ions (10 µM) with 1 (10 µM) resulted in AIEs at 499 and 521 nm, respectively. Both Ag+ and Hg2+ induce the formation of 1:2 complexes with 1, leading to the formation of AIE active aggregates with an average size of 423 and 198 nm, respectively. The formation of crystalline needles with Ag+ and spherical aggregates with Hg2+ results in wavelength specific AIE that permits the naked-eye and fluorometric detection of Ag+ and Hg2+ ions. Probe 1 shows excellent selectivity toward Ag+ and Hg2+ among various metal ions, therefore, 1 is suitable for the selective and quantitative detection of Ag+ and Hg2+ ions. Job plots are used for the determination of the stoichiometry of the complexes formed. It is evident from the fluorescence images of probe 1 in Rhizoctonia oryzae mycelia cells that they can be employed as potential candidates for in-vitro bioimaging.

Cellular Uptake of Cell-Penetrating Peptides Activated by Amphiphilic p-Sulfonatocalix[4]arenes

We report the synthesis of a series of amphiphilic p-sulfonatocalix[4]arenes with varying alkyl chain lengths (CX4-Cn) and their application as efficient counterion activators for membrane transport of cell-penetrating peptides (CPPs). The enhanced membrane activity is confirmed with the carboxyfluorescein (CF) assay in vesicles and by the direct cytosolic delivery of CPPs into CHO-K1, HCT 116, and KTC-1 cells enabling excellent cellular uptake of the CPPs into two cancer cell lines. Intracellular delivery was confirmed by fluorescence microscopy after CPP entry into live cells mediated by CX4-Cn, which was also quantified after cell lysis by fluorescence spectroscopy. The results present the first systematic exploration of structure-activity relationships for calixarene-based counterion activators and show that CX4-Cn are exceptionally effective in cellular delivery of CPPs. The dodecyl derivative, CX4-C12, serves as best activator. A first mechanistic insight is provided by efficient CPP uptake at 4 °C and in the presence of the endocytosis inhibitor dynasore, which indicates a direct translocation of the CPP-counterion complexes into the cytosol and highlights the potential benefits of CX4-Cn for efficient and direct translocation of CPPs and CPP-conjugated cargo molecules into the cytosol of live cells.

Activity-Based Fluorescent Probes for Hydrogen Sulfide and Related Reactive Sulfur Species

Hydrogen sulfide (H2S) is not only a well-established toxic gas but also an important small molecule bioregulator in all kingdoms of life. In contemporary biology, H2S is often classified as a "gasotransmitter," meaning that it is an endogenously produced membrane permeable gas that carries out essential cellular processes. Fluorescent probes for H2S and related reactive sulfur species (RSS) detection provide an important cornerstone for investigating the multifaceted roles of these important small molecules in complex biological systems. A now common approach to develop such tools is to develop "activity-based probes" that couple a specific H2S-mediated chemical reaction to a fluorescent output. This Review covers the different types of such probes and also highlights the chemical mechanisms by which each probe type is activated by specific RSS. Common examples include reduction of oxidized nitrogen motifs, disulfide exchange, electrophilic reactions, metal precipitation, and metal coordination. In addition, we also outline complementary activity-based probes for imaging reductant-labile and sulfane sulfur species, including persulfides and polysulfides. For probes highlighted in this Review, we focus on small molecule systems with demonstrated compatibility in cellular systems or related applications. Building from breadth of reported activity-based strategies and application, we also highlight key unmet challenges and future opportunities for advancing activity-based probes for H2S and related RSS.

A Chalcone-based Fluorescence Probe for H2S Detecting Utilizing ESIPT Coupled ICT Mechanism

The accurate and effective identification of hydrogen sulfide holds great significance for environmental monitoring. Azide-binding fluorescent probes are powerful tools for hydrogen sulfide detection. We combined the 2'-Hydroxychalcone scaffold with azide moiety to construct probe Chal-N3, the electron-withdrawing azide moiety was utilized to block the ESIPT process of 2'-Hydroxychalcone and quenches the fluorescence. The fluorescent probe was triggered with the addition of hydrogen sulfide, accompanied by great fluorescence intensity enhancement with a large Stokes shift. With excellent fluorescence properties including high sensitivity, specificity selectivity, and wider pH range tolerance, the probe was successfully applied to natural water samples.

Carboxylesterase-activated near-infrared fluorescence probe for highly sensitive imaging of liver tumors

Carboxylesterases (CESs) are critical for metabolizing ester-containing biomolecules and are specifically important in liver metabolic disorders. The modulation of CESs is also an important issue in pharmacology and clinical applications. Herein, we present a near-infrared (NIR) CES fluorescent probe (NCES) based on the protection-deprotection of the hydroxyl group for monitoring CES levels in living systems. The NCES probe has good selectivity and sensitivity for CESs with a limit of detection (LOD) of 5.24 mU mL-1, which allows for tracing the fluctuation of cellular CES after treatment with anticancer drugs and under inflammation and apoptosis states. Furthermore, NCES can be successfully applied for guiding liver cancer surgery with high-contrast in vivo imaging and detecting clinical serum samples from liver cancer patients. This work showed that the NCES probe has great potential in drug development, imaging applications for medical diagnosis, and early-stage detection for clinical liver diseases.

A near infrared fluorescence probe with dual-site for hydrogen sulfide and sulfur dioxide detection

Both hydrogen sulfide (H2S) and sulfur dioxide (SO2) are regarded as double-edged swords. They are toxic gases at high concentration, and at low concentration they are beneficial to the human. Therefore, it is of great significance to develop single chemosensor which enable to detect them with different fluorescence signal changes. In this work, a novel dual-site fluorescence probe (AMN-SSPy) with near infrared emission (675 nm) was designed, which realized quantitative detection for H2S and SO2 by fluorescence enhancement and fluorescence quenching, respectively. AMN-SSPy showed advantages such as excellent selectivity to H2S and SO2, strong anti-interference ability, high sensitivity for H2S (LOD 1.03 µM for H2S and 77.08 µM for SO2) and low toxicity. In addition, AMN-SSPy possessed the capacity to successfully image the endogenous and exogenous H2S, and it was also used to demonstrate that Ca2+ could induce accumulation of H2S in cell and zebrafish. Finally, the rapid detection of SO2 by AMN-SSPy in real samples was also established.

A Universal, Continuous Assay for SAM-dependent Methyltransferases

Enzyme-catalyzed late-stage functionalization (LSF), such as methylation of drug molecules and lead structures, enables direct access to more potent active pharmaceutical ingredients (API). S-adenosyl-l-methionine-dependent methyltransferases (MTs) can play a key role in the development of new APIs, as they catalyze the chemo- and regioselective methylation of O-, N-, S- and C-atoms, being superior to traditional chemical routes. To identify suitable MTs, we developed a continuous fluorescence-based, high-throughput assay for SAM-dependent methyltransferases, which facilitates screening using E. coli cell lysates. This assay involves two enzymatic steps for the conversion of S-adenosyl-l-homocysteine into H2 S to result in a selective fluorescence readout via reduction of an azidocoumarin sulfide probe. Investigation of two O-MTs and an N-MT confirmed that this assay is suitable for the determination of methyltransferase activity in E. coli cell lysates.

A fluorous-tag-assisted fluorescent probe for simple and selective detection of hydrogen sulfide: application for turbid dyeing solutions

Accurate hydrogen sulfide (H2S) detection has attracted much attention because its toxicity may affect aquatic environments and human health. However, recognizing H2S levels by conventional fluorescent probes in turbid wastewater has been challenging because the opaque environment interferes with their photophysical properties. To overcome this limitation, a fluorous-tagging strategy can be used for the development of fluorescent sensors to detect H2S in turbid solutions. The use of fluorescent probe assisted with fluorous-tag allowed for easy isolation of the probe using polytetrafluoroethylene (PTFE) material, while disturbing species were eliminated through a simple aqueous wash. This approach enabled the fluorescent probe to effectively quantify H2S, even in opaque solutions containing organic dyes that could interfere with fluorescence emission.

Fluorescent deactivation behaviors based on ESIPT and TICT of novel double target fluorescent probe and its sensing mechanism for Al3+/Mg2+: A TD-DFT study

Based on density functional theory (DFT) and time-dependent DFT (TD-DFT) methods with integral equation formula polarized continuum model (IEFPCM), the fluorescent behavior and recognizing mechanism of probe N'-((1-hydroxynaphthalen-2-yl)methylene)isoquinoline-3-carbohydrazide (NHMI) for Al³⁺/Mg²⁺ ion were investigated in more detail. Excited state intramolecular proton transfer (ESIPT) process in probe NHMI occurs in the stepwise pattern. The proton H₅ of enol structure (E1) firstly moves from O₄ to N₆ to form single proton-transfer (SPT2) structure, and then the proton H₂ of SPT2 transfers from N₁ to N₃ to form the stable double proton-transfer (DPT) structure. Subsequently, the transformation from DPT to its isomer (DPT1) induces the twisted intramolecular charge transfer (TICT) process. Two non-emissive TICT states (TICT1 and TICT2) were obtained, and TICT2 state quenches the fluorescence observed in the experiment. With the addition of aluminum (Al³⁺) or magnesium (Mg²⁺) ion, TICT process is prohibited by the coordination interaction between NHMI and Al³⁺/Mg²⁺, and the strong fluorescent signal is turned on. For probe NHMI, the twisted C-N single bond of acylhydrazone part leads to the TICT state. This sensing mechanism may inspire researchers to develop new probes from a different direction.

Characterization of Glutathione Dithiophosphates as Long-Acting H2S Donors

Considering the important cytoprotective and signaling roles but relatively narrow therapeutic index of hydrogen sulfide (H₂S), advanced H₂S donors are required to achieve a therapeutic effect. In this study, we proposed glutathione dithiophosphates as new combination donors of H₂S and glutathione. The kinetics of H₂S formation in dithiophosphate solutions suggested a continuous H₂S release by the donors, which was higher for the dithiophosphate of reduced glutathione than oxidized glutathione. The compounds, unlike NaHS, inhibited the proliferation of C2C12 myoblasts at submillimolar concentrations due to an efficient increase in intracellular H₂S. The H₂S donors more profoundly affected reactive oxygen species and reduced glutathione levels in C2C12 myocytes, in which these parameters were elevated compared to myoblasts. Oxidized glutathione dithiophosphate as well as control donors exerted antioxidant action toward myocytes, whereas the effect of reduced glutathione dithiophosphate at (sub-)micromolar concentrations was rather modulating. This dithiophosphate showed an enhanced negative inotropic effect mediated by H₂S upon contraction of the atrial myocardium, furthermore, its activity was prolonged and reluctant for washing. These findings identify glutathione dithiophosphates as redox-modulating H₂S donors with long-acting profile, which are of interest for further pharmacological investigation.

Computational Insights into Sensing Mechanism for Al3+ in a New Acylhydrazone Fluorescent Probe Based on Excited-State Intramolecular Proton Transfer (ESIPT) and Twisted Intramolecular Charge Transfer (TICT)

The work explored the fluorescent properties of probe N'-(2, 4-dihydroxy-benzylidene)pyridine-3-carbohydrazide (HL) and its sensing mechanism for the Al³⁺ ion in detail. HL has two competing deactivation processes: ESIPT and TICT. Upon light-excitation, only one proton can transfer, and the SPT1 structure is generated. The SPT1 form is highly emissive, which is inconsistent with the colorless emission observed in the experiment. Then a nonemissive TICT state was obtained by rotating the C-N single bond. The energy barrier of the TICT process is lower than that of the ESIPT process, which indicates that probe HL will decay to the TICT state and quench the fluorescence. When Al³⁺ is recognized by probe HL, strong coordinate bonds are formed between HL and Al³⁺, and then the TICT state is prohibited, and the fluorescence of HL is turned on. Al³⁺ as a coordinated ion can effectively remove the TICT state but cannot influence the photoinduced electron transfer (PET) process of HL.

Exploring the influence of intermolecular hydrogen bonding on the fluorescence properties of HQCT and HQPH fluorescent chemosensors

Recently, two trace water detection probes, 8-hydroxyquinoline-2-carboxaldehyde thiosemicarbazone(HQCT) and 8-hydroxyquinoline-2-carboxaldehyde (pyridine-2-carbonyl)-hydrazine(HQPH) have been successfully designed in the experiment. The original intramolecular proton transfer can be prevented by the water molecules, leading to fluorescence quenching. In order to investigate the fluorescence quenching mechanism, the effect of water molecules on the excited state proton transfer process will be studied in detail. In this contribution, the six models have been optimized and the related analysis have been carried out. When water molecules are involved in the proton transfer process, the energy barrier decreases significantly and the conversion of the enol structure to the keto structure is accelerated. Moreover, the intermolecular hydrogen bonding, not participating in the proton transfer process, can facilitate the proton transfer process by affecting the distribution of the electrostatic potential within the molecule, which in turn lowers the energy barrier for proton transfer.

A biocompatible ratiometric fluorescent nanoprobe for intracellular hydrogen sulfide accurate detection based on rare earth nanoparticle

Hydrogen sulfide (H₂S) is an important signal molecule involved in intracellular activities. To understand the role of H₂S in cellular physiological and pathological process, the development of sensitive and selective methods, especially biocompatible assays, for efficient monitoring the level of H₂S is necessary. Herein, we modified novel rare earth element europium (EU) based fluorescent nanospheres with azide (-N₃) based sensor to construct an ingenious ratiometric fluorescent nanoprobe EU-N3. This nanoprobe showed excellent water solubility and high biocompatibility for intracellular H₂S accurate detection. Nanoprobe EU-N3 had two obvious emission peaks, the green fluorescence peak at 540 nm increased according to the increasing of H₂S concentration and the red fluorescence peak at 616 nm was stable as ratiometric reference. The fluorescence intensity ratio (I₅₄₀/I₆₁₆) displayed good linear response (R = 0.99136) in H₂S range of 0.5 ∼ 30 μM. The analytes response assay demonstrated that the nanoprobe EU-N3 possessed a better specificity for H₂S, compared with other 9 anions and 3 cations. The cell viability assay indicated the nanoprobe EU-N3 had an excellent biocompatibility. The cell imaging showed that the proposed nanoprobe could be applied for detecting the intracellular H₂S changes accurately in live cells. Such nanoprobe provided a safe and accurate strategy for intracellular H₂S detection, which is helpful for the real-time H₂S visualization in the live cell activities.

Amplified Spontaneous Emission from Zwitterionic Excited-State Intramolecular Proton Transfer

The unique four-level photocycle characteristics of excited-state intramolecular proton transfer (ESIPT) materials enable population inversion and large spectral separation between absorption and emission through their respective enol and keto forms. This leads to minimal or no self-absorption losses, a favorable feature in acting as an optical gain medium. While conventional ESIPT materials with an enol-keto tautomerism process are widely known, zwitterionic ESIPT materials, particularly those with high photoluminescence, are scarce. Facilitated by the synthesis and characterization of a new family of 2-hydroxyphenyl benzothiazole (HBT) with fluorene substituents, HBT-Fl1 and HBT-Fl2, we herein report the first efficient zwitterionic ESIPT lasing material (HBT-Fl2). The zwitterionic ESIPT HBT-Fl2 not only shows a remarkably low solid-state amplified spontaneous emission (ASE) threshold of 5.3 μJ/cm² with an ASE peak at 609 nm but also exhibits high ASE photostability. Coupled with its substantially large Stokes shift (≈236 nm ≈10,390 cm^-1) and an extremely small overlap of excited-state absorption with ASE emission, comprehensive density functional theory (DFT) and time-dependent DFT studies reveal the zwitterionic characteristics of HBT-Fl2. In opposition to conventional ESIPT with π-delocalized tautomerism as observed in analogue HBT-Fl1 and parent HBT, HBT-Fl2 instead shows charge redistribution in the proton transfer through the fluorene conjugation. This structural motif provides a design tactic in the innovation of new zwitterionic ESIPT materials for efficient light amplification in red and longer-wavelength emission.

Unveiling the effects of atomic electronegativity on the ESIPT mechanism and luminescence property of new coumarin benzothiazole Fluorophore: A TD-DFT exploration

The excited-state intramolecular proton transfer (ESIPT) mechanism, photophysical properties of 8-(benzo[D] thiazole-2-yl)-7-hydroxy-2H-benzopyran-2-one (L-HKS) and the effect of O/Se atomic substitution on L-HKS have been studied in detail based on density functional theory (DFT) and time-dependent DFT (TD-DFT) methods. The S atom in the thiazole ring of L-HKS has been replaced by O/Se atom (denoted to L-HKO/L-HKSe) to analyze the effects of atomic electronegativity on the intramolecular H-bond, absorption/emission spectrum and ESIPT process. Through the analysis of series of calculated results, it can be found that the intramolecular H-bonds at normal form and tautomer form are enhanced and weakened in the S₁ state, respectively, which is favorable to ESIPT process. The potential energy curves revealed that the ESIPT process is much easier to occur gradually from L-HKO to L-HKS and L-HKSe, as the electron-withdrawing ability of atom (from O to S and Se) is weakened. The atomic substitution also has an effect on the photophysical properties. From L-HKO to L-HKS, the emission peak at tautomer form red-shifts 70 nm. The energy gaps of the three compounds follow the decreased order of L-HKO (4.866 eV) > L-HKS (4.753 eV) > L-HKSe (4.371 eV) with the weakened electron-withdrawing ability of atom (from O to S and Se), which leads to the gradual red-shift of the absorption spectra from L-HKO to L-HKS and L-HKSe.

Dual-wavelength electrochemiluminescence ratiometry for hydrogen sulfide detection based on Cd2+-doped g-C3N4 nanosheets

Herein, a novel and facile dual-wavelength ratiometric electrochemiluminescence-resonance energy transfer (ECL-RET) sensor for hydrogen sulfide (H₂S) detection was constructed based on the interaction between S^2- and Cd²⁺-doped g-C₃N₄ nanosheets (NSs). Cd²⁺-doped g-C₃N₄ NSs exhibited a strong ECL emission at 435 nm. In the presence of H₂S, CdS was formed in situ on g-C₃N₄ NSs by the adsorption of S^2- and Cd²⁺, generating another ECL emission at 515 nm. Furthermore, the overlapping of the absorption spectrum of the formed CdS and the ECL emission spectrum of g-C₃N₄ NSs led to a feasible RET, thus quenching the ECL intensity from g-C₃N₄ at 435 nm. Through an ECL decrease at 435 nm and an increase at 515 nm, a dual-wavelength ratiometric ECL-RET system for H₂S was designed. The sensor exhibited a lower detection limit of 0.02 μM with a wide linear range of 0.05-100.0 μM. In addition, the applicability of the method was validated by plasma sample analysis with a linear range of 80.0-106.0%. We believe that such a proposal would provide new insight into advanced dual-wavelength ECL ratiometric assays.

Investigating the Influence of Electronic Effects of Functional Groups on the Fluorescence Mechanism of Probes in Water Samples

This study investigates the fluorescence quenching mechanism of formaldehyde detection probe Naph1 and its contrast probe Naph3 in water samples and discussed the effect of the electron-donating group and electron-withdrawing group on fluorescence characteristics based on density functional theory (DFT) and time-dependent density functional theory (TD-DFT). We optimized the structures of the four probes Naph1, Naph1-S, Naph3, and Naph3-S (Scheme 1) and calculated the absorption and emission spectra, which were in good agreement with the experiment. Frontier molecular orbitals (FMOs) were used to analyze the charge arrangement in the excited state. To investigate the intramolecular proton transfer (ESIPT) phenomenon, a potential energy curve was constructed. The amount of fragment charge transfer was analyzed by the IFCT method, and then it was determined whether there was an intramolecular charge transfer (ICT) process. It was found that there was an ICT process in Naph3. The electronic effect of the functional groups did not determine the ICT characteristics and the fluorescence characteristics of the substance. Furthermore, the spin-orbit coupling  (SOC) constant based on the intersystem crossing (ISC) was supplemented, which showed that the fluorescence quenching of Naph1 and Naph3 was caused by the ISC and the corresponding quenching of Naph3-S was caused by charge transfer (CT) in the excited state.

A cancer cell-specific benzoxadiazole-based fluorescent probe for hydrogen sulfide detection in mitochondria

The present work describes the design and biological applications of a novel colorimetric and fluorescence turn-on probe for hydrosulfide detection. The probe was designed to introduce hemicyanine as the fluorescent skeleton and 7-nitro-1,2,3-benzoxadiazole as the recognition site. The optical properties and responses of the probe towards HS^-, anions and some biothiols indicate an impressively high selectivity of the probe towards HS^- such that it can be effectively used as an indicator for monitoring the level of HS^- in living cells. In biological experiments using the probe, the H₂S levels are found to be higher in cancer cells than in normal cells. In addition, the probe is shown to specifically and rapidly detect endogenous H₂S, which is produced primarily in the mitochondria of cancer cells, as demonstrated by a co-localization experiment using specific trackers for the detection of cellular organelles in pharmacological inhibition or stimulation studies, without any significant cytotoxic effects. Thus, the results of the chemical and biological experiments described herein demonstrate the potential of this novel probe to specifically, safely, and rapidly detect H₂S to distinguish cancer cells from normal cells by targeting it specifically in mitochondria.

Theoretical study on the sensing mechanism of chalcone-based fluorescence probe for detecting hydrogen sulfide and biothiols

The single fluorescence phenomenon of Comp2 experimentally is explained by the Boltzmann distribution. Pr1 has three distorted dihedral angles under photo-excitation.

Small-molecule Bifunctional Fluorescent Probes for the Differential Detection of Multiple Guests

During the last few years, the preparation of bifunctional fluorescent probes, which exhibit differential response towards multiple analytes, has attracted considerable attention since they are cost-effective and highly desirable for real-time applications. This review focuses on the recent advances in the design principles, recognition mechanisms, and applications of multifunctional fluorescent probes for the differential detection of multiple guests.

Copper ion modified graphitic C3N4 nanosheets enhanced luminol-H2O2 chemiluminescence system: Toward highly selective and sensitive bioassay of H2S in human plasma

A high-efficient chemiluminescence (CL) platform for highly selective and sensitive H₂S detection was constructed on the basis of the quenching effect of S^2- on the copper ion modified graphitic carbon nitride nanosheets (Cu²⁺-g-C₃N₄ NSs) enhanced luminol-H₂O₂ system. Cu²⁺-g-C₃N₄ NSs with horseradish peroxidase-like catalytic activity were prepared and provide a great improvement for luminol-H₂O₂ system. The presence of S^2- induced the formation of CuS precipitate on g-C₃N₄ NSs surface. The precipitate can block the catalytic Cu²⁺ sites on the g-C₃N₄ NSs surface, resulting in a great CL decrease of CL system. Based on such a mechanism, a simple, highly selective and sensitive CL biosensor for H₂S detection was designed. Under the optimized conditions, luminol-H₂O₂-Cu²⁺-g-C₃N₄ NSs system gave a decrease of CL intensity with the Na₂S concentration increasing. The CL biosensor is in a linear range of 10.0 pM-50.0 nM and the detection limit for detecting Na₂S is as low as 2.0 pM. Moreover, the method here has enjoyed a successful application for determining H₂S in human plasma samples and the recovery is between 95.7% and 110.0%.

A new phenylsulfonamide-based Golgi-targeting fluorescent probe for H2S and its bioimaging applications in living cells and zebrafish

We have synthesized a simple Golgi-targeting H₂S fluorescent probe which can detect endogenous and exogenous H₂S in cells and zebrafish. In addition, this probe provides a new chemical tool for the detailed study of generation pathways of H₂S under Golgi stress response.

Novel blue-green emitting NLOphoric triphenylamine-imidazole based donor-π-acceptor compound: Solvatochromism, DFT, TD-DFT and non-linear optical studies

Novel Donor (D)-π-Acceptor (A) NLOphoric triphenylamine-imidazole based dye 9 was designed, synthesized, and confirmed by Mass, ¹³C NMR, and ¹H NMR analysis. Photophysical properties of 9 were studied in solvents of different polarities and compared with analogues compounds 7 and 8. Phenonthroline acceptor based dye 9 shows highly bathochromic shifted absorption and emission compared to dyes 7 and 8. Positive solvatochromism was noticed in 7, 8, and 9 which was supported by the linear (i.e. Lippert-Mataga and Mac-Rae polarity functions) and multi-linear (i.e. Kamlet-Taft and Catalan parameters) analysis. Moreover, solvent polarizability (d_SP) and solvent dipolarity (C_SdP) are the major factors responsible for red shift in absorption as well as in emission spectra. Charge transfer descriptors as well as the polarity graphs are in good relation with Generalized Mulliken-Hush (GMH) parameters. NLO properties of 7, 8, and 9 were studied by using solvatochromic and computational methods. The static first hyperpolarizability (β₀) and relevant microscopic parameters (μ,α₀,α,β,γ) were determined using DFT with B3LYP, BHHLYP, and CAM-B3LYP functionals. Third-order NLO properties of nitrogen containing phenanthroline based compound 9 were observed to be several times higher than those of the compounds 7 and 8, justify the design approach.

Synthesis and characterization of poly(tetraphenylimidazole)s and their application in the detection of fluoride ions

Here, we describe the synthesis and characterization of a silyl protected tetraphenylimidazole monomer and its homo and co-polymer. The requisite monomer was accessed by Suzuki–Miyaura cross-coupling of 2-(1-(4-bromophenyl)-4,5-diphenyl-1H-imidazol-2-yl)phenol and 4-vinylphenylboronic acid followed by protection of the phenolic group by tert-butyl(chloro)diphenylsilane. The desired polymers were readily synthesized by using free radical polymerization. Both the polymers and monomer were characterized using different analytical techniques including multinuclear NMR, GPC (for polymers), and single crystal X-ray crystallography (for the monomer). By utilizing the greater fluorophilicity of the silyl atom, the polymers were studied as probes for the detection of fluoride ions. The selectivity and sensitivity of the synthesized polymers were investigated in detail.

We describe the synthesis and characterization of a silyl protected tetraphenylimidazole monomer and its polymers. The polymers were studied as probes for the detection of fluoride ions. Both the probes showed high selectivity and sensitivity over other ions tested.

FRET-based fluorescent ratiometric probes for the rapid detection of endogenous hydrogen sulphide in living cells

FRET strategy was adopted for designing ratiometric fluorescent H₂S sensors using Coumarin-derived merocyanine fluorophore.

Sensing of zinc ions and sulfide using a highly practical and water-soluble fluorescent sensor: applications in test kits and zebrafish

A practical fluorescent sensor was synthesized for recognition of Zn²⁺ and S²⁻ and applied in various applications such as in live zebrafish.

Electronically-tuned triarylmethine scaffolds for fast and continuous monitoring of H2S levels in biological samples

A sensor for the detection and quantification of H2S in biological samples should ideally meet a set of criteria such as fast detection, high sensitivity in the desired concentration range, high selectivity, non-interference from biomolecules like proteins, ease of synthesis, long-term stability and water solubility. Although a number of H2S probes are known, none of them possess all the above attributes that are relevant for practical applications. As part of a program to develop reliable chemical probes for continuous monitoring of this gasotransmitter in the blood plasma of sepsis-prone individuals in post-operative wards, we have looked at the possibility of improving the reactivity and selectivity profile of triarylmethine dyes towards different nucleophiles. After achieving high sensitivity through electronic control, the interference from sulfite, thiosulfate and metabisulfite was addressed by introducing a metal salt-mediated desulfuration step that results in dye regeneration selectively from its H2S adduct. Typically, if the analyte contains only H2S, the loss of absorbance in the first step gets completely reinstated after the second step; absorbance changes in both steps vary linearly with sulfide concentration and either of these two steps can be used for the quantification of H2S with the help of standard plots. In the presence of interfering ions, the first step will show decolourization due to the presence of all of them whereas only the H2S-adduct will undergo desulfuration in the second step which can be used for quantification. The decolourization step is instantaneous while the desulfuration requires only about 50 s, making the entire protocol complete in less than a minute. The methodology optimized here also meets the requirements mentioned above for real-life applications.

Chelation of specific metal ions imparts coplanarity and fluorescence in two imidazo[1,2-a]pyridine derivatives: Potential chemosensors for detection of metal ions in aqueous and biosamples

Synthesis and chelation induced fluorescence emission from two imidazo[1,2-a]pyridine derivatives are described. The nonfluorescent molecule 1 containing N and O donor atoms, achieves coplanarity upon interactions with trivalent cations Al³⁺, Fe³⁺ and Cr³⁺, that favors fluorescence emission. Molecule 2 containing two N donor atoms attains coplanarity upon interaction with the only Zn²⁺ and becomes fluorescent. Both molecules 1 and 2 form a 1:1 complex with interacting metal ions. Other trivalent metal ions (including Bi³⁺ and In³⁺) and common divalent metal ions (including Hg²⁺ and Cd²⁺) fail to form any complex with 1 or 2, and they do not interfere in the detection of Zn²⁺, Al³⁺, Fe³⁺ or Cr³⁺ ions. Noninterference of other metal ions renders 1 and 2 suitable for the detection of fungal cells contaminated with Zn²⁺, Al³⁺, Fe³⁺ or Cr³⁺ ions.

A HBT-based bifunctional fluorescent probe for the ratiometric detection of fluoride and sulphite in real samples

Based on a core of 2-(benzo[d]thiazol-2-yl)phenol (HBT), a bifunctional ratiometric fluorescent probe, HBT-FS, was constructed for the discriminative detection of fluoride (F^-) and sulphite (SO₃^2-) with high sensitivity and selectivity. HBT-FS itself displayed a green fluorescence with λ_Em^max = 498 nm. The treatment of HBT-FS with F^- resulted in a red fluorescence (λ_Em^max = 634 nm) with a large Stokes shift and a 291-fold enhancement in the ratio of the fluorescence intensity (I_{634 nm}/I_{498 nm}). Upon the addition of SO₃^2-, HBT-FS exhibited a blue fluorescence (λ_Em^max = 371 nm) and the ratiometric fluorescence enhancement was remarkable (9445 folds for I_{371 nm}/I_{498 nm}). HBT-FS was successfully used to qualitatively and quantitatively determine F^- and SO₃^2- in a ratiometric manner in real samples.

Development of dansyl based copper(ii) complex to detect hydrogen sulfide in hypoxia

Hydrogen sulfide (H2S) has been reported as a gaseous signaling molecule in cells. H2S modulation is dependent on the partial pressure of oxygen in cells, which means hypoxia can induce H2S production under various pathophysiological conditions. Hypoxia is a common condition in solid tumors and can lead to malignant tumors that may become aggressive and result in worse prognosis. We designed and synthesized probe Cu-CD for H2S detection under hypoxia conditions. It is selective and sensitive toward various biological thiols, reactive nitrogen species (RNS), and reactive oxygen species (ROS). The fluorescence intensity of Cu-CD in the cytoplasms of HeLa and EMT6 cells was enhanced in proportion to the concentration of exogenous/endogenous H2S. Moreover, Cu-CD can be able to detect endogenous H2S production accompanied by expression of HIF-1α. Therefore, Cu-CD can be a key tool to explore how H2S contributes to neovascularization and growth of solid tumor tissues in pathophysiological or hypoxic conditions.

A simple highly specific fluorescent probe for simultaneous discrimination of cysteine/homocysteine and glutathione/hydrogen sulfide in living cells and zebrafish using two separated fluorescence channels under single wavelength excitation

Biothiols such as cysteine (Cys), homocysteine (Hcy), glutathione (GSH) and hydrogen sulfide (H₂S) are widely found in mammalian cells. They are closely related to the production and metabolic pathways and play very important roles in physiological and pathological activities. Therefore, the quantitative detection of these biothiols is of great significance. Although many fluorescent probes have been successfully used to track biothiols in biological samples, the fluorescence method for simultaneously detecting these biothiols using separated fluorescence emission channels under single wavelength excitation is still immature. In this work, we prepared the conjugate of seminaphthorhodafluor (SNARF) dye and 7-nitro-1,2,3-benzoxadiazole (NBD) using as a simple long-wavelength fluorescent probe SNARF-NBD for specific detection of biothiols. Cys/Hcy and GSH/H₂S were identified by two separated fluorescence emission channels under single wavelength excitation, which showed good selectivity and sensitivity. In addition, SNARF-NBD has low cytotoxicity and shows good imaging ability in living cells and zebrafish.

A ratiometric fluorescent probe for detection of endogenous and exogenous hydrogen sulfide in living cells

A ratiometric visualized fluorescent probe of H₂S of intramolecular charge transfer (ICT) and excited intramolecular proton transfer (ESIPT) mechanisms due to solvation effects has been designed and synthesized. This chemosensor shows the distinct signal changes with dual-emission in blue and green fluorescence spectral channel (from 495 nm to 525 nm) upon the addition of H₂S in a single wavelength excitation. This chemosensor exhibits the low detection limit (91 nM) and high sensitivity and selectivity. Based on this, this chemosensor was successfully used not only to monitor H₂S exogenously but also used to detect and image the endogenously generated H₂S in HeLa cells with excellent performance.

The design of hydrogen sulfide fluorescence probe based on dual nucleophilic reaction and its application for bioimaging

Hydrogen sulfide (H₂S) can undergo dual nucleophilic reaction, which is a wise and effective way to distinguish biothiols and H₂S. A novel H₂S fluorescence probe, 4-{2-[4-(2-disulfide pyridyl-benzoyloxy)-phenyl]-vinyl}-1-methyl-pyridinium[e]iodide (DSPBP), with two nucleophilic reaction sites has been developed. The spectra results showed that DSPBP could detect H₂S in ratiometric and colorimetric signals and has excellent selectivity and sensitivity. The fluorescence ratiometric signals (F₅₂₀/F₄₅₀) displayed a prominent increase from 0.74 to 7.08, the fluorescence color turned to yellow form blue simultaneously. The linear range was 2-14 μM and its detection limit was 25.7 nM. Moreover, the biocompatibility of DSPBP was fine and its toxicity was very low. It has been successfully used for imaging H₂S in cells.