A mitochondria-targeted ratiometric fluorescent sensor based on naphthalimide derivative-functionalized silica-based nanodots for imaging formaldehyde in living cells and zebrafish

A mitochondria-targeted ratiometric fluorescent sensor (Mito-Si-NA) for formaldehyde (FA) has been constructed by functionalizing silica-based nanodots (silica-based ND). As the fluorescence reference and carrier, the silica-based ND conjugate with small molecule probe for FA via covalent. Further modifying with mitochondria targeting moiety enables the sensor to specifically target mitochondria. In the presence of FA, the emission of silica-based ND remain constant to act as an internal reference (445 nm) while the response signal of small molecule probe was gradually enhanced (545 nm). This sensor exhibits excellent selectivity towards FA with great changes of fluorescence intensity ratio values (I545/I445). The FA ratiometric fluorescence imaging in mitochondria was achieved successfully. In addition, the sensor was also successfully used for imaging FA in zebrafish. The good performance of Mito-Si-NA for FA bioimaging confirms that Mito-Si-NA is an appealing imaging tool to monitor FA in mitochondria and shows great potential to study the functions of FA on mitochondria.

Naphthalimide-based Functional Glycopolymeric Nanoparticles as Fluorescent Probes for Selective Imaging of Tumor Cells

A series of functional glycopolymer nanoparticles with 1,8-naphthalimide motif was designed, synthesized and applied for tumor cell imaging. With the pH-sensitive and aggregation-induced emission (AIE) effect of the 1,8-naphthalimide fluorescent probe, the presence of glucose-based glycopolymers enhanced its water-solubility and biocompatibility. Owing to the dual tumor-targeting effects of the dense glucose part and the boronic ester modification, the obtained glycopolymers showed high affinity to tumor cells, with a much faster staining rate than normal cells, indicating a great potential for diagnosis and treatments of cancers.

Visualization of an Endogenous Mitochondrial Azoreductase Activity under Normoxic Conditions Using a Naphthalimide Azo-Based Fluorogenic Probe

In this paper, we demonstrate the existence of an endogenous mitochondrial azoreductase (AzoR) activity that can induce the cleavage of N═N double bonds of azobenzene compounds under normoxic conditions. To this end, 100% OFF-ON azo-based fluorogenic probes derived from 4-amino-1,8-naphthalimide fluorophores were synthesized and evaluated. The in vitro study conducted with other endogenous reducing agents of the cell, including reductases, demonstrated both the efficacy and the selectivity of the probe for AzoR. Confocal experiments with the probe revealed an AzoR activity in the mitochondria of living cells under normal oxygenation conditions, and we were able to demonstrate that this endogenous AzoR activity appears to be expressed at different levels across different cell lines. This discovery provides crucial information for our understanding of the biochemical processes occurring within the mitochondria. It thus contributes to a better understanding of its function, which is implicated in numerous pathologies.

New 1,8-naphthalimide-based colorimetric fluorescent probe for specific detection of hydrazine and its multi-functional applications

Detection of hydrazine is particularly important given its toxicity and extensive application in various industries. In the present paper, a colorimetric fluorescent probe NI-CIN based on 1,8-naphthalimide derivative was rationally designed and simply synthesized for specific detection of hydrazine based on the intramolecular charge transfer (ICT) mechanism. Upon the addition of hydrazine, a significant fluorescence enhancement at 556 nm could be observed within 4 min with a distinct color change from colorless to bright yellow, readily observed by naked eye. Except for HRMS and 1H NMR, density functional theory (DFT) calculations were also performed to support the sensing mechanism. In addition, eco-friendly paper test strips were easily prepared by NI-CIN for selective and real-time detection of hydrazine under aqueous and vapor phases. Furthermore, NI-CIN shows many potential applications for detecting hydrazine in real water and soil samples along with bio-imaging in HepG-2 cells and zebrafish.

Synthesis, Characterization, Cytotoxicity, Cellular Imaging, Molecular Docking, and ADMET Studies of Piperazine-Linked 1,8-Naphthalimide-Arylsulfonyl Derivatives

To reduce the mortality and morbidity associated with cancer, new cancer theranostics are in high demand and are an emerging area of research. To achieve this goal, we report the synthesis and characterization of piperazine-linked 1,8-naphthalimide-arylsulfonyl derivatives (SA1-SA7). These compounds were synthesized in good yields following a two-step protocol and characterized using multiple analytical techniques. In vitro cytotoxicity and fluorescent cellular imaging of the compounds were assessed against non-cancerous fibroblast (3T3) and breast cancer (4T1) cell lines. Although the former study indicated the safe nature of the compounds (viability = 82-95% at 1 μg/mL), imaging studies revealed that the designed probes had good membrane permeability and could disperse in the whole cell cytoplasm. In silico studies, including molecular docking, molecular dynamics (MD) simulation, and ADME/Tox results, indicated that the compounds had the ability to target CAIX-expressing cancers. These findings suggest that piperazine-linked 1,8-naphthalimide-arylsulfonyl derivatives are potential candidates for cancer theranostics and a valuable backbone for future research.

Rhodamine hydrazide-linked naphthalimide derivative: Selective naked eye detection of Cu2+, S2- and understanding the therapeutic potential of the copper complex as an anti-cervical cancer agent

A naphthalimide-labeled rhodamine hydrazone derivative HL has been synthesized, characterized and examined in metal ion recognition. It shows selective colorimetric detection of Cu2+ over a number of other metal ions with a detection limit of 1.66 × 10-7 M in CH3CN/HEPES buffer (v/v = 2:1, pH = 6.8). The spirolactam ring of rhodamine and the imino-phenol motif of naphthalimide in HL are involved in complexation of Cu2+ as shown by single crystal X-ray. Single crystal of the copper-complex is prepared by utilizing NaSCN and it is characterized as CuL(SCN). The emergence of new absorption at 550 nm in UV-vis and the pink color of the solution reveal the selective interaction toward Cu2+. HL is characterized as a fluorescence resonance energy transfer (FRET) system that remains 'turned OFF' while spirolactam ring exists. In the presence of Cu2+, FRET is 'turned ON' via the opening of spirolactam ring to give emission at 580 nm which is less intense due to the quenching effect of Cu2+ ion. The complexation is reversible and the ensemble of Cu2+.HL selectively recognizes S2- over a series of different anions involving a color change from pink to colorless via the formation of spirolactam ring. The copper complex CuL(SCN) is further employed to understand its efficacy as a therapeutic agent. The complex is cytotoxic to high-risk HPV positive cervical cancer cell lines like SiHa and HeLa and is efficient in the generation and accumulation of reactive oxygen species (ROS). The complex also initiates nuclear blebbing and shows DNA degradation as understood by DNA laddering assay.

Nucleolus imaging based on naphthalimide derivatives

Nucleolus was an important cellular organelle. The abnormal morphology and number of the nucleolus have been considered as diagnostic biomarkers for some human diseases. However, the imaging agent based on nucleolus was limited. In this manuscript, a series of nucleolar fluorescent probes based on naphthalimide derivatives (NI-1 ∼ NI-5) had been designed and synthesized. NI-1 ∼ NI-5 could penetrate cell membranes and nuclear membranes, achieve clear nucleolar staining in living cells. These results suggested that the presence of amino groups on the side chains of naphthalimide backbone could enhance the targeting to the cell nucleolus. In addition, the molecular docking results showed that NI-1 ∼ NI-5 formed hydrogen bonds and hydrophobic interactions with RNA, and exhibited enhanced fluorescence upon binding with RNA. These results will provide favorable support for the diagnosis and treatment of nucleolus-related diseases in the future.

Synthesis of organic-solvent-soluble cellulose and preparation of fluorescent polyurethanes for the detection and removal of Hg+ ions

Modifying cellulose to obtain materials with favorable processing properties and functions is highly significant, especially, for the detection and removal of heavy metal ions. In this study, fluorescent cellulose-based polyurethane (PU) films containing naphthalimide fluorophore were synthesized and could use for the convenient detection and removal of Hg+ ions. Firstly, the microcrystalline cellulose was treated with SOCl2 to convert some -OH groups into -Cl. Simultaneously, a naphthalimide derivative (NAN) with -NH- groups was synthesized. Subsequently, a fluorescent cellulose-based probe (Cel-NAN) was prepared by utilizing the substitution reaction between -Cl on cellulose and -NH- on NAN. Finally, two cellulose-based fluorescent PU films (Cel-NAN-PU1 and Cel-NAN-PU2) were successfully synthesized by reacting the unreacted -OH groups on Cel-NAN with PEG-1000 and HDI/IPDI. These as-prepared PU films could serve as portable fluorescence test papers to Hg+ ions in aqueous solutions. Upon contact with Hg+ ions, the fluorescence was quenched, acting as a "turn-off" probe. Simultaneously, these films could serve as adsorbents for the removal of Hg+ ions from aqueous systems. Cel-NAN-PU1 film exhibited a removal efficiency over 80 % and an adsorption capacity of 8.4 mg·cm-2 for Hg+. These cellulose-based fluorescent PU films possess promising potential in the field of mercury pollution control.

Fabrication of 1,8-naphthalimide modified cellulose derivative composite fluorescent hydrogel probes and their application in the detection of Cr(VI)

The design and development of a rapid and quantitative method for the detection of heavy metal ions is of great importance for environmental protection. We have prepared a 1,8-Naphthalimide modified cellulose composite fluorescent hydrogel (CENAEA/PAA) with a stereo double network structure. Characterized by excellent hydrogel functional structure and fluorescence detection performance, it can efficiently and selectively identify and detect Cr(VI) with linear quenching in the range of 0-400 μmol/L and detection limit of 0.58 μmol/L for Cr(VI). The results show that the CENAEA/PAA can effectively adsorb Cr(VI) with a maximum adsorption capacity of 189.04 mg/g. Finally, the morphological characteristics, chemical structure, fluorescence properties and adsorption behavior of CENAEA/PAA were analyzed and fitted well with the pseudo-second-order model and Freundlich model. Thus, the present work provides a green and sustainable approach for the synthesis of a functional material that can be used for the detection and adsorption of heavy metal ions.

A series of fluorescent dyes based on 4-phenylacetylene-1,8-naphthalimide: Synthesis, theoretical calculations, photophysical properties and application in two-color imaging and dynamic behavior monitoring of lipid droplets and lysosomes

A series of fluorescent dyes (NapPAs) based on 4-phenylacetylene-1,8-naphthalimide were synthesized and characterized, whose conjugated structures were extended by the introduction of phenylethynyl. Furthermore, changes in the photophysical properties of the dyes when substituents with varying electron richness were introduced at the p-position of phenylacetylene were studied. The theoretical calculation of the dye molecules was carried out by B3LYP functional and 6-31G(d,p) basis set, and the effects of different substituents at the p-position of phenylacetylene on the electronic structure and photophysical properties of the dyes were studied by theoretical calculation results. Theoretical calculations provided a reliable means of predicting the properties of dyes, which could help in the design of more efficient and novel dyes. To verify the practicability of the dyes, two dyes with excellent photophysical properties (large Stokes shift, high polarity-viscosity sensitivity, good biocompatibility) were selected as fluorescent probes for visualization of LDs and two-color imaging of LDs and lysosomes. Cell imaging showed that NapPA-LDs and NapPA-LDs-Lyso serve as excellent imaging tools to monitor the dynamic changes, movements, and behaviors of LDs and lysosomes in real time. Notably, NapPA-LDs-Lyso held promise as a potential tool to study the interaction between LDs and lysosomes.

Naphthalimide-Based AIEgens for Sensing Protein Disulfide Isomerase through Thiol-Disulfide Redox Exchange

Aggregation-induced emission (AIE)-based fluorescent organic nanoparticles (FONPs) with distinctive characteristics are emerging as superior sensors due to their facile fabrication, high signal-to-noise ratio, and good biocompatibility. The present article delineates the detection and analysis of the redox behavior of the protein disulfide isomerase (PDI) enzyme by exploitation of the AIE of novel naphthalimide (NI) derivatives having thiol (-SH) and disulfide (-S-S-) moieties. Self-aggregated spherical-shaped organic nanoparticles were prepared by synthesized NI-based amphiphiles (NISH, NISS, NINSS, and TNINSH) through J-type aggregation in DMSO-water (fw = 99 vol %). Naphthyl residue containing NI-derived amphiphiles (NINSS and TNINSH) exhibited AIE (blue and yellow) at 470 and 550 nm, respectively, in DMSO-water (fw = 99 vol %). NINSS and TNINSH FONPs were suitably utilized in sensing PDI through their redox nature of thiol-disulfide exchange. Fluorescence quenching of NINSS FONPs was observed due to reduction of disulfide to thiol by PDI, whereas emission intensity was progressively red-shifted and enhanced ("Dual-AIE") for TNINSH (containing ER-targeting N-tosylethylenediamine), owing to oxidation of thiol to disulfide by PDI. NINSS and TNINSH FONPs were found to be highly efficient in sensing PDI through the AIE-based "fluorescence off/on" mechanism having limits of detection of ∼12.6-17.7 and ∼11.7-16.5 ng/mL, respectively. In vitro cell imaging for NIH3T3 (noncancer) and B16F10 (melanoma) cells with NINSS and TNINSH FONPs displayed excellent diagnosis of eukaryotic cells upon interaction with indigenous PDI. Notably, detection of cancer cells was more sensitive over the noncancerous cells by these FONPs due to overexpression of PDI within cancer cells.

An efficient chitosan-naphthalimide fluorescent probe for simultaneous detection and adsorption of Hg2+ and its application in seafood, water and soil environments

As a virulent heavy metal ion, Hg2+ will lead to a serious threat to ecosystem and human health. In this work, we reported a chitosan-naphthalimide fluorescent probe CS-NA-ITC for specific recognition and efficient adsorption of Hg2+. CS-NA-ITC showed no fluorescence in solution state, while the fluorescence intensity increased obviously at the presence of Hg2+, accompanied by the fluorescence color becomes from colorless to bright yellow. It displayed favorable properties like low detection limit (73 nM), extensive pH detection range (5-10) and excellent anti-interference ability. The binding pattern of CS-NA-ITC to Hg2+ was verified by Job's plot, XPS analysis and FT-IR test. In addition, CS-NA-ITC was utilized to recognition of Hg2+ in actual water and soil samples and seafood products. Furthermore, the CS-NA-ITC hydrogel could be employed as an efficient Hg2+ adsorbent with good reusability, which adsorption ability was enhanced compared to chitosan hydrogel.

Sensitive Detection of Various Forms of Hydrogen Sulfide via Highly Selective Naphthalimide-Based Fluorescent Probe

Hydrogen sulfide (H2S) is an important gasotransmitter, but only a few methods are available for real-time detection. Fluorescent probes are attractive tools for biological applications because of their high sensitivity, convenience, rapid implementation, noninvasive monitoring capability, and simplicity in fluorescent imaging of living cells and tissues. Herein, we report on a pro-fluorescent probe, NAP-Py-N3 based on naphthalimide derivative, which was found to show high selectivity toward H2S over various other analytes, including biothiols, making it feasible to detect H2S. After reaction with H2S, this probe showed rapid and significant turn-on green fluorescent enhancement at 553 nm (about 54-fold, k2 = 9.62 M-1s-1), high sensitivity (LOD: 15.5 nM), significant Stokes shift (118 nm), and it was found that the fluorescence quantum yield of fluorescence product can reach 0.36. Moreover, the probe has also been successfully applied to detect the gaseous H2S and to confirm the presence of H2S released from modern organic donors, which in recent years have been commonly used to investigate the role of H2S in biological systems. All the results indicate that this probe is excellent and highly valuable.

Application of Natural Bioresources to Sustainable Agriculture: A C-Glycoside Insecticide Based on N-Acetyl-glucosamine for Regulating Insect Molting of Ostrinia furnacalis

In order to increase the application of natural bioresources in drug discovery and development, a study on N-acetyl-glucosamine (GlcNAc) derivatives of chitin as green pesticides was necessary. In this study, we designed and synthesized a series of novel C-glycoside naphthalimides using GlcNAc as a starting material. Compound 10l showed high inhibitory activity against OfHex1 (IC₅₀ = 1.77 μM), with a nearly 30-fold increase in activity over our previously reported C-glycoside CAUZL-A (IC₅₀ = 47.47 μM). By observing the morphology of the Ostrinia furnacalis, we found that the synthesized compounds significantly inhibited the molting process. In addition, we further explored the morphological changes of the inhibitor-treated O. furnacalis cuticle using scanning electron microscopy. This is the first study to validate the insecticidal mechanism of OfHex1 inhibitors at the microscale level. Several compounds also exhibited excellent larvicidal activity against Plutella xylostella. Moreover, the toxicity measurements and predictions indicated that the C-glycoside naphthalimides have little effect on the natural enemy Trichogramma ostriniae and rats. Together, our results highlight an approach for the design of green pesticides, taking advantage of natural bioresources to control pests in agriculture.

An effective fluorescent probe for detection of phosgene based on naphthalimide dyes in liquid and gaseous phases

A fluorescent probe was developed for the detection of phosgene based on 1,8-naphthalimide, of which o-diaminobenzene was used as the recognition moiety. The probe does not fluoresce due to nonradiative decay. The probe reacts rapidly with phosgene via an intramolecular cyclization reaction, which induces large fluorescence due to increased rigidity in the resulting molecule and a low detection limit (0.23 nM). This probe has excellent selectivity for phosgene against competing interference analytes and, in the form of probe-loaded test paper, is an extremely sensitive method for phosgene sensing in the gas phase below 1 ppm concentrations.

A water-soluble naphthalimide fluorescent probe for Cr2O72- and Fe3+ based on inner filter effect

A probe 3 (2-ethoxy-N-(2-(2-(2-hydroxyethoxy)ethyl)-1,3-dioxo-2,3-dihydro-1H-benzo[de] isoquinolin-6-yl)benzamide) that could selectively respond to Cr₂O₇^2- and Fe³⁺ was reported in this paper. The selectivity, pH titration, concentration titration, detection limit, time dependence, quenching constant and recognition mechanism of probe 3 for Cr₂O₇^2- and Fe³⁺ were studied in CH₃CN/HEPES buffer solution. The results showed that Cr₂O₇^2- and Fe³⁺ could rapidly quench the fluorescence of probe 3 through the inner filter effect (IFE). The quenching kept constant after 30 s, and the quenching constants were 7.99 × 10³ L^.mol^-1 and 4.13 × 10³ L^.mol^-1, respectively. The detection limits of probe 3 for Cr₂O₇^2- and Fe³⁺ were 1.15 μmol^.L^-1 and 1.95 μmol^.L^-1, respectively, which were lower than the maximum allowable concentrations in drinking water stipulated by EPA. The determination results of Cr₂O₇^2- and Fe³⁺ in water samples indicated that probe 3 could be used as a potential detection tool in practical applications.

A naphthalimide-tyrosine-based dicationic amphiphile for intracellular 'turn-on' simultaneous detection of ATP and CTP

We have developed a new naphthalimide-based amphiphile (YN-1) for the simultaneous detection of ATP and CTP. In YN-1, the cationic tyrosine-linked polyamine (+2 charge, hydrophilic unit) is appended at the -peri position of naphthalimide (hydrophobic unit). YN-1 and its Boc-protected compound 4 were characterized using state-of-the-art spectroscopic and optical techniques such as NMR, IR, UV-vis and fluorescence. The fluorescence data revealed that YN-1 showed a 'turn-on' (λ_em = 440 nm) fluorescence response for nanomolar detection of nucleoside triphosphates such as ATP and CTP in 20% HEPES buffer-DMSO solution. YN-1 also showed a concentration-based discrimination between ATP and CTP. YN-1 has been successfully applied for bioimaging of nucleoside triphosphates in MCF-7 live cancer cells with good compatibility. Therefore, the important findings from the present work will provide insight for future development of fluorescent probes to detect various kinds of essential nucleoside triphosphates.

Hydrogen-bond activated ESIPT in naphthalimide-based fluorescent probe for sensing volatile amines

Amines levels present important indicative value in food safety and human health. Although they are involved in some normal physiological responses of the organism, their overproduction or intake may cause pathological responses. Herein, we report a recyclable visual packaging bag for volatile amines detections based on the naphthylamide derivative N-S and its positive PL characteristics. Specifically, handmade test strips based on compound N-S have been applied to fish freshness labeling, and the cyclic fumigation experiment shows its restorable PL effect and efficiency. The possible PL transfer mechanism of naphthylamide derivative N-S is uncovered by the density functional theory (DFT) calculation and titration mass spectrometer and ¹H NMR. This work expands a conjugation in a molecule by hydrogen-bond activated ESIPT (H-ESIPT) and provides a portable detection method for volatile amines detection.

Naphthalimide-Based Fluorescent Probe for Profiling of Aldehydes during Oxidation of Unsaturated Lipids

A lipophilic naphthalimide hydrazine fluorescent probe was successfully developed in this study for profiling aldehyde oxidation products. Dodecyl amine was applied to afford lipophilicity of the fluorescent probe for lipids. Investigation of fluorescence properties of the probe and condensation products with typical aldehydes including MDA and hexanal revealed significant enhancement of fluorescence intensity after condensation due to the inhibition of photo-induced electron transfer. MDA and hexanal could be differentiated by the probe through emission of different fluorescence colors (blue, MDA; green, hexanal). Eight major oxidation components including seven aldehydes were detected by the fluorescent probe coupled with high-performance liquid chromatography-mass spectrometry during aerobic oxidation of typical unsaturated lipids. Formation of these aldehyde oxidation products was rationalized through the radical oxidation mechanism. Detection of representative aldehyde products demonstrated the generality in the application of this fluorescent probe for profiling of aldehydes after lipid oxidation.

Artificial Light-Harvesting System with White-Light Emission in a Bicontinuous Ionic Medium

Artificial light-harvesting systems (ALHSs), which are closely related to Förster resonance energy transfer (FRET), are among the most attractive scientific topics during the past few decades. Specifically, binary ALHSs that are composed of a fluid donor and acceptor have a simplified composition and high number density of the donor units. However, largely due to the difficulty in obtaining a fluid donor, investigation of these systems is still quite limited, especially for the ionic systems. Herein, we report a new type of binary ALHS using an ionic naphthalimide (NPI) derivative as a donor, which shows greatly improved photoluminescence for its bicontinuous liquid structure. When blending with an acceptor such as rhodamine 6G or trans-4-[4-(dimethylamino)styryl]-methylpyridinium iodide, efficient FRET was confirmed by both experimental results and molecular dynamics simulations, with an energy transfer efficiency up to ∼90%. Tunable color, including white-light emission, was achieved by tuning the acceptor/donor ratio, opening the door for a variety of applications such as light-emitting diodes and photoluminescent inks.

A novel hydrogen peroxide fluorescent probe for bioimaging detection and enables multiple redox cycles

In this subject, a novel hydrogen peroxide (H₂O₂) fluorescent probe (MNG) was designed and developed using naphthalimide derivatives and selenomorpholine. In PBS buffer (10 mM, pH = 7.4, 1 %DMSO), the selenomorpholine on the probe is capable of qualitatively and quantitatively detecting (H₂O₂) at a small amount under a detection limit of 61 nM. The probe follows a mechanism that Se (Ⅱ) in selenomorpholine is transformed to Se (Ⅳ), thus changing the spectra of the probe MNG. It is noteworthy that MNG can continuously make a cyclic response to H₂O₂ and glutathione (GSH), so it can potentially achieve redox process imaging in vivo. Moreover, this subject verified the redox process of the probe's continuous redox response in the Gaussian 09 programme through simulation calculation and mass spectrometry. The probe exhibits high biocompatibility. Moreover, it can detect H₂O₂ in MCF-7 cells and Argentine Bloodfin.

Naphthalimide-Fused Dipyrrins: Tunable Halochromic Switches and Photothermal NIR-II Dyes

A family of tunable halochromic switches is developed using a naphthalimide-fused dipyrrin as the core π-conjugated motif. Electronic properties of these dipyrrins are tuned by substitution of their alpha and meso positions with aryl groups of variable donor-acceptor strength. The first protonation results in a conformational change that enhances electronic coupling between the dipyrrin chromophore and the meso substituent, leading to halochromic effects that occasionally exceed 200 nm and switch the absorption between the near-infrared (NIR)-I and NIR-II ranges. A NIR-II photothermal effect, switchable by acid-base chemistry is demonstrated for selected dipyrrins. Further protonation is possible for derivatives bearing additional amino groups, leading to up to four halochromic switching step. The most electron-rich dipyrrins are also susceptible to chemical oxidation, yielding NIR-absorbing radical cations and closed-shell dications.

Photocatalytic performance of heterojunction S-Tyr-NDI-Tyr/TiO2 formed by self-assembled naphthalimide derivatives and titanium dioxide

In this paper, a type of heterojunction photocatalyst S-Tyr-NDI-Tyr/TiO₂ was prepared by self-assembly of tyrosine-substituted naphthamide (NDA) and bonding with titanium dioxide. The self-assembly process and driving force of monomer M-Tyr-NDI-Tyr were simulated by theoretical calculation. Taking atenolol as the target pollutant, the photocatalytic performance of the heterojunction photocatalyst under visible light was studied, and the degradation products were analyzed by mass spectrometry. The environmental toxicity of photocatalytic process was evaluated by luminescent bacteria. The principle of high photocatalytic activity of S-Tyr-NDI-Tyr/TiO₂ heterojunction photocatalyst was proposed by analyzing the fluorescence spectrum, photocurrent density and resistance, electron paramagnetic resonance spectrum, free radical capture experiment and energy band position of S-Tyr-NDI-Tyr/TiO₂ heterojunction photocatalyst. In addition, the photocatalytic degradation of different pollutants by S-Tyr-NDI-Tyr/TiO₂ heterojunction photocatalyst was also studied. This work will provide a useful example for the further development of new and efficient organic supramolecular/inorganic semiconductor composite photocatalysts.

Exploring the Aggregation and Light-Harvesting Aptitude of Naphthalimide-Based Amphiphile and Non-amphiphile AIEgen

Herein, we report a comparative study of two naphthalimide-tethered amphiphile and non-amphiphile with their aggregation-induced emission properties. A synthetic modulation of a hydrophobic tail on the framework repressed the ACQ-phoric fluorophore to an AIEgen. L₁ and L₂ remain in the dispersed form in DMF and exhibits aggregation and intense emission signal in aqueous media. Microscopy detailing of the aggregating process has been analyzed. Not only the AIEgens are emissive in water but also they are emissive in the solid state. The natural light-harvesting process is mimicked by the aggregated state, establishing an energy transfer process between L₁ and commercial dye. Disaggregation of the AIEgen has also been utilized in the detection of nitroaromatics. Analytical utility of the AIE-gen is being demonstrated concerning the detection of explosives in aqueous media.

Photostable fluorescent probes based on multifunctional group substituted naphthalimide dyes for imaging of lipid droplets in live cells

We designed and synthesized multifunctional group substituted naphthalimide (MFGNI) dyes by introducing glycine ethyl ester and azetidine on 1,8-naphthalimide. With different azetidine substituents, the emission of the MFGNI dyes was shifted from blue to green. These MFGNI dyes exhibited high photoluminescence quantum yields (61% to 85%) and large Stokes shifts (67 nm). The amides and hydroxyl groups improved the photostability of the MFGNI dyes. Due to the small molecular weight and lipophilic properties, these MFGNI dyes specifically stained lipid droplets in living cells.

Naphthalimide-Based Azo-Functionalized Supramolecular Vesicle in Hypoxia-Responsive Drug Delivery

Supramolecular materials that respond to external triggers are being extensively utilized in developing spatiotemporal control in biomedical applications ranging from drug delivery to diagnostics. The present article describes the development of self-assembled vesicles in 1:9 (v/v), tetrahydrofuran (THF)-water by naphthalimide-based azo moiety containing amphiphile (NI-Azo) where azo moiety would act as the stimuli-responsive junction. The self-assembly of NI-Azo took place through H-type of aggregation. Microscopic and spectroscopic analyses confirmed the formation of supramolecular vesicles with a dimension of 200-250 nm. Azo (-N═N-) moiety is known to get reduced to amine derivatives in the presence of the azoreductase enzyme, which is overexpressed in the hypoxic microenvironment. The absorbance intensity of this characteristic azo (-N═N-) moiety of NI-Azo (1:9 (v/v), THF-water) at 458 nm got diminished in the presence of both extracellular and intracellular bacterial azoreductase extracted from Escherichia coli bacteria. The same observation was noted in the presence of sodium dithionite (mimic of azoreductase), indicating that azoreductase/sodium dithionite induced azo bond cleavage of NI-Azo, which was confirmed by matrix-assisted laser desorption ionization time-of-flight spectrometric data of the corresponding aromatic amine fragments. The anticancer drug, curcumin, was encapsulated inside NI-Azo vesicles that successfully killed B16F10 cells (cancer cells) in CoCl₂-induced hypoxic environment owing to the azoreductase-responsive release of drug. The cancer cell killing efficiency by curcumin-loaded NI-Azo vesicles in the hypoxic condition was 2.15-fold higher than that of the normoxic environment and 2.4-fold higher compared to that of native curcumin in the hypoxic condition. Notably, cancer cell killing efficiency of curcumin-loaded NI-Azo vesicles was 4.5- and 1.9-fold higher than that of noncancerous NIH3T3 cells in normoxic and hypoxic environments, respectively. Cell killing was found to be primarily through the early apoptotic pathway.

A novel lysosome-located fluorescent probe for highly selective determination of hydrogen polysulfides based on a naphthalimide derivative

Hydrogen polysulfides (H₂S_n, n > 1) belongs to sulfane sulfur in the reactive sulfur species (RSS) family and plays a significant regulatory role in organisms. Highly selective and lysosome-located probes for detecting hydrogen polysulfides are rare. Thus, it is important to develop a technique to detect the changes of H₂S_n level in lysosomes. In this work, a lysosome-targeting fluorescent probe for H₂S_n was designed and developed based on a naphthalimide derivative. 4-Hydroxynaphthalimide was selected as the fluorescent group and 2-chloro-5-nitrobenzoate group was used as a specific recognition unit for H₂S_n. A morpholine unit was chosen as a lysosome-located group. In the absence of H₂S_n, the fluorescent probe exhibited almost no fluorescence. In the presence of H₂S_n, the fluorescent probe showed strong fluorescence owing to H₂S_n-mediated aromatic substitution-cyclization reactions. The fluorescence emission intensity at 548 nm of the probe showed a good linear relationship toward H₂S_n in the range of 2.0 × 10^-7 - 9.0 × 10^-5 mol·L^-1, and the detection limit was found to be 1.5 × 10^-7 mol·L^-1. The probe possessed a wide work range of pH, including the pH of physiological environment, and high selectivity for H₂S_n. There are almost no cytotoxicity and the ability of detecting endogenous and exogenous H₂S_n in lysosomes. These results indicate that the fluorescent probe can provide a good tool for intracellular and extracellular detection of H₂S_n.

A fluorescent pH probe for evaluating the freshness of chicken breast meat

A fluorescent probe, Nap-MOR, based on the naphthalimide fluorophore, was designed and developed for pH measurement in aqueous solutions. Nap-MOR had a close linear relationship between fluorescence intensity and pH, in the range 4.5-8, which covers the full range of pH found in normal fresh, defective and spoiled meat. pH measurement with Nap-MOR was free from interference by a wide range of ions and biochemicals found in meat and the results were not significantly different in comparison with a pH meter. Therefore, Nap-MOR is a robust and convenient way to evaluate the freshness of chicken breast meat by measuring its pH.

A turn-on fluorescent probe via substitution-rearrangement for highly sensitive and discriminative detection of cysteine and its imaging in living cells

Biothiols play an important role in many physiological and pathological processes, especially in the occurrence of oxidative stress caused by abnormal cysteine (Cys) concentration. Therefore, it is particularly critical to develop a method that can specifically identify Cys to avoid interference from other biological analytes. However, most Cys-specific fluorescent probes are difficult to distinguish between homocysteine (Hcy) and glutathione (GSH). In this work, to avoid the interference of Hcy and GSH, we developed a fluorescent probe triarylimidazole-naphthalimide-piperazine-sulfonyl benzoxadiazole (TNP-SBD-Cl) based on fluorescence resonance energy transfer (FRET) on platform of naphthalimide-sulfonyl benzoxadiazole (SBD), the main SBD 4-chlorine groups have mild reactivity to undergo substitution and rearrangement to distinguish Hcy and GSH. The TNP-SBD-Cl response to Cys would turn on FRET and generate a new yellow fluorescence with a large Stokes shift (157 nm), and with excellent selectivity and low detection limit (0.87 μM). Moreover, TNP-SBD-Cl can be used to monitor Cys in living HeLa cells with low cytotoxicity, suggesting that it has markedly diagnostic significance in physiological and pathological processes.

Development of an esterase fluorescent probe based on naphthalimide-benzothiazole conjugation and its applications for qualitative detection of esterase in orlistat-treated biosamples

Esterase is a large hydrolysis family, and widely distributed in many kinds of cells. It is responsible for multiple physiological and pathological functions including metabolism, gene expression. While abnormality of esterase is associated with many pathological activities in obesity, Wolman's disease, and cancer. Thereby, it is essential to design an effective tool for esterase in situ detection in biological systems. Herein, a novel fluorescent probe Y-1 for monitoring esterase in living cells was rationally designed. Probe Y-1 was synthesized by the conjugation between an acetylation of 4-hydroxy naphthalimide and benzothiazole group. Benzothiazole moiety is a typical Excited-state intramolecular proton transfer (ESIPT) controller. Acetate group was selected as the responsive site and ESIPT initiator. As the acetate group could block the ESIPT effect, the probe emits no fluorescence under the excitation of 455 nm. When binding with esterase, Y-1 shows distinct fluorescence with the peak at 560 nm with short time when ESIPT is on. Y-1 displays high sensitivity (LOD is 0.216 × 10^-3 U/mL), fast response (within 5 min), high selectivity and photostability towards esterase. Furthermore, the %RSD (relative standard deviation) of within-day and day-to-day precision was no more than 13.0% and the accuracy ranged from -6.5 to -12.3%. Kinetics performance of Y-1 indicates that esterase has high affinity and hydrolysis to Y-1. For biological applications, our probe is a time-dependent visualizing esterase in living HepG2 and CoLo205 cells within 15 min. After the treatment of orlistat (1 and 5 μM) for inhibiting the activity of esterase, the bright fluorescence has also been detected using our probe. Furthermore, it has been successful in monitoring the esterase in zebrafish, the data were consistent with cellular phenomena. Therefore, all these findings indicate that the robust probe Y-1 is a useful qualitative tool for detecting esterase in biological systems.

Naphthalimide appended isoquinoline fluorescent probe for specific detection of Al3+ ions and its application in living cell imaging

Herein, a novel Schiff base fluorescent probe NIQ based on naphthalimide and iso-quinoline units has been readily prepared for the selective detection of Al³⁺ ions. The obviously visible color changes and prominent fluorescence enhancement were observed upon the addition of Al³⁺ to NIQ, which could be attributed to the complexation of NIQ with Al³⁺ and thus leading to the inhibition of photo-induced electron transfer (PET) and the chelation-enhanced fluorescence (CHEF) progress. The limit of detection (LOD) was 52 nM that was far below the standard recommended by the WHO. Binding ratio (1:1) of NIQ with Al³⁺ ions was supported by Job's plot. The binding constant of NIQ for Al³⁺ were calculated to be 3.27 × 10⁵ M^-1 on the basis of benesi-Hildebrand plot. The plausible binding mechanism for NIQ towards Al³⁺ ions was evidenced by the density functional theory (DFT) and ¹H NMR titration experiment. Furthermore, this "turn-on" probe NIQ has been successfully applied as a biomarker for imaging the Al³⁺ ions in living cells.

Synthesis of Phthaladyn-29 and Naphthalimide-10, GTP Site Directed Dynamin GTPase Inhibitors

Herein we describe the detailed synthesis of the dynamin inhibitors Phthaladyn-29 and Napthaladyn-10, and their chemical scaffold matched partner inactive compounds. Combined with the assay data provided, this allows the interrogation of dynamin in vitro and potentially in vivo.

A simple and rapid fluorescent approach for Pb2+ determination and application in water samples and living cells

A novel selective fluorescent chemosensor, thiosemicarbazide-appended naphthalimide derivative (TND), has been designed and synthesized, which exhibited good selectivity and sensibility for Pb²⁺ in CH₃CN:H₂O (1:1) solution. The probe TND showed obvious color changes under UV light of 365 nm and displayed turn-on fluorescence response with Pb²⁺ added. The binding mode of TND with Pb²⁺ was found to be 1:1 based on the Job's plot analysis. The detection limit of Pb²⁺ was 4.7 nM, which is far below the allowable concentration determined by WHO in drinking water. Moreover, the fortified recoveries of Pb²⁺ were from 100.54% to 113.68% in water samples. TND is also applied for fluorescence imaging of Pb²⁺ in lysosomes of human stromal cell line (HSC). This study indicated that TND would be a potential sensor detecting Pb²⁺ in real sample.

A new fluorescent probe for neutral to alkaline pH and imaging application in live cells

A new pH-sensitive fluorescent probe NAP-MDA was designed and synthesized. NAP-MDA consists of 1,8-naphthalimide as fluorophore, morpholine and N,N-dimethylethylenediamine as pH-responsive groups. Due to the photoinduced electron transfer (PET) mechanism, the fluorescence of 1, 8-naphthalimide was thoroughly quenched under alkaline condition (pH > 10.0), however, NAP-MDA displayed increasing fluorescence as the rise of acidity. Notably, NAP-MDA possessed an excellent linear dependence with neutral to alkaline pH (7.2-9.4), with a pKa of 8.38. NAP-MDA had good photostability and reversibility. Meanwhile, the probe was selective to pH without interference from common reactive species, temperature and viscosity. Fluorescent testing strips were fabricated with NAP-MDA and were successfully utilized to visualize the different pH with a handhold UV lamp. Confocal fluorescence imaging in live cells demonstrated that NAP-MDA mainly fluoresced in lysosomes, and could be applied for quantification of the pH within live cells.

A novel 1,8-naphthalimide-based Cu2+ ion fluorescent probe and its bioimaging application

A new 1,8-naphthalimide-based Schiff base compound, named as (Z)-2-butyl-6-(((2-hydroxyphenyl)imino)methyl)-1H-benzo[de]isoquinoline-1,3(2H)-dione (BHBD), has been simply synthesized with high yields. BHBD can be employed as a "turn-on" fluorescent probe for Cu²⁺ ion with high sensitivity, high selectivity and relatively low detection limit (0.48 × 10^-6 M). The fluorescence emission of BHBD is very weak in H₂O/THF (v/v: 7/3) mixture, which is significantly enhanced after addition of Cu²⁺ ion. The proposed mechanism is verified by ¹H NMR, Job's plot and TOF-MS experiments. Anti-interference experiment, cytotoxicity assay and pH influence results indicated that BHBD meets the requirements of bioimaging. Therefore, BHBD has been successfully applied in detecting Cu²⁺ ion in HeLa cells.

A dual-channel Hill-type small-molecule pH probe

By combining a Hill-type pH probe and a pH-insensitive naphthalimide fluorophore, we synthesized a FRET-based ratiometric pH probe (PHHF), exhibiting a reduced pH transition width, representing a unique approach for development of sensitive probes for detection of biorelevant pH changes.

High-contrast colourimetric probes for fluoride and trace water based on tautomerization of naphthalimide and application in fingerprint imaging

Three probes for fluoride ion and trace water based on naphthalimide were designed and synthesized. A new sensing mechanism based on naphthalimide tautomerization induced by fluoride ion and water was explored in the aprotic organic solvent. In the fluoride ion sensing process, the probes exhibited a remarkable absorption peak centred at 560 nm in the visible range of 400-700 nm. When trace water presented, the newly formed absorption peak centred at 560 nm gradually disappeared. The sensitive colour variation of the probe also was used in fingerprint imaging. Accordingly, the significant changes in chemical shift of dept135 and ¹HNMR spectrum confirmed the structural transformation of the probes with high contrast. Furthermore, this work also presented an optimization strategy for the sensitivity of the probe based on regulatory tautomerization.

The development of an endoplasmic reticulum-targeting fluorescent probe for the imaging of 1,4-dithiothreitol (DTT) in living cells

1,4-Dithiothreitol (DTT) is a robust reducing agent that contributes significantly to the folding process of proteins and maintaining endoplasmic reticulum (ER) homeostasis. Abnormally high levels of DTT can lead to severe endoplasmic reticulum stress (ERS), which induces cell death. In addition, DTT can also hinder cell growth and enhance reactive oxygen species (ROS) production in the ER. Herein, an effective turn-on ER-targeting fluorescent probe, ER-DTT, was designed to image DTT for the first time. The probe ER-DTT was based upon naphthalimide as a fluorophore, p-toluenesulfonamide as an exceptional unit for ER-targeting, and sulfoxide as a response site for imaging DTT based on an intramolecular charge transfer (ICT) mechanism. Optical-response experiments showed that the probe ER-DTT had good selectivity and sensitivity for DTT. Furthermore, confocal microscopy indicated that ER-DTT was suitable for selectively targeting ER in living cells and could be implemented to recognize cellular DTT.

Construct a lysosome-targeting and highly selective fluorescent probe for imaging of hydrogen sulfide in living cells and inflamed tissues

Since the fluctuation of cellular hydrogen sulfide (H₂S) is a very important third endogenously generated gaseous signaling molecule and plays a key role in the development of numerous human disorders, the real-time fluorescence detection of H₂S in living systems has attracted plenty of interest during past decade. Although a lot of H₂S fluorescent probes have been reported, the relationship between the physiology and pathology of H₂S in organelles remains unclear, especially for inflammatory tissue. In this work, by adopting a weakly basic morpholine group as the lysosome-targeting site, a naphthalimide derivative as the signal reporter group and a 4-dinitrobenzene-ether (DNB) as fluorescence signal quencher and H₂S-selective recognition moiety, we reported a new lysosome-targeting TP fluorescent probe LyNP-H₂S for H₂S detection and imaging in living cells and inflamed tissues. The probe LyNP-H₂S exhibits very low fluorescence signal in the absence of H₂S, and displays a significant 262-fold fluorescence intensity enhancement in the presence of H₂S at 540 nm. Moreover, LyNP-H₂S has the capability of quantitative detection of H₂S at concentrations ranging from 0 to 12.0 μM (limit of detection = 9.8 nM), rapid response, as well as high sensitivity and selectivity toward H₂S. Impressively, the results of living cell and inflamed tissues imaging test demonstrate that LyNP-H₂S has the potentiality of being an ideal probe for real-time H₂S detection in biosystems.

A highly sensitive, fast responsive and reversible naphthalimide-based fluorescent probe for hypochlorous acid and ascorbic acid in aqueous solution and living cells

It is very important to exploit real-time, ultrasensitive and specific visualization detection methods for hypochlorous acid/hypochlorite (HOCl/ClO^-) in biological systems as they are the guardians of the human immune system against pathogens invasion. In our work, we designed a novel reversible naphthalimide-based fluorescent probe NAP-OH to recognize HClO/ClO^- with a unique selective colorimetric and fluorescent response, a short response time (<8 s) and a high sensitivity (10.3 nM). In addition, NAP-OH exhibits a novel on-off-on fluorescence response to ClO^-/ascorbic acid (AA) with good cycle stability. The fluorescence signal is quenched because HClO/ClO^- oxidizes the subunit of NAP-OH to the segment 2,2,6,6-tetramethyl-1-oxo-piperidinium in NAP-O, which can be reduced by AA with the recovery of fluorescence. Finally, the confocal fluorescence imaging has been performed, which proves that NAP-OH can satisfactorily monitor intracellular endogenous and exogenous HClO/AA redox cycles.

An endoplasmic reticulum targetable turn-on fluorescence probe for imaging application of carbon monoxide in living cells

Carbon monoxide (CO) is a significant mediator in regulating endoplasmic reticulum (ER) stress, and its level may play a potential role in the treatment of vascular diseases combined with ER stress. In-situ visualization of CO in the ER helps to elucidate its physiological and pathological mechanistic behavior. Herein, a novel CO fluorescent probe (Na-CM-ER) with ER-targeting characteristics was structured. Na-CM-ER with naphthalimide as a fluorescent group, under the trigger of CO, an ICT (Intramolecular Charge Transfer) mechanism was constructed by converting a nitro group to an amino group and showed dazzling green fluorescence. Na-CM-ER exhibited satisfactory response speed, selectivity, photo-stability and sensitivity to CO in vitro. Furthermore, biological imaging experiments demonstrated that Na-CM-ER could monitor the changes of exogenous/endogenous CO in living cells and possess an ER-targeting property. To sum up, we hope that Na-CM-ER can be as a serviceable molecular tool for imaging CO in cellular ER.

A Two-Photon Probe Based on Naphthalimide-Styrene Fluorophore for the In Vivo Tracking of Cellular Senescence

Cellular senescence is a state of stable cell cycle arrest that can negatively affect the regenerative capacities of tissues and can contribute to inflammation and the progression of various aging-related diseases. Advances in the in vivo detection of cellular senescence are still crucial to monitor the action of senolytic drugs and to assess the early onset or accumulation of senescent cells. Here, we describe a naphthalimide-styrene-based probe (HeckGal) for the detection of cellular senescence both in vitro and in vivo. HeckGal is hydrolyzed by the increased lysosomal β-galactosidase activity of senescent cells, resulting in fluorescence emission. The probe was validated in vitro using normal human fibroblasts and various cancer cell lines undergoing senescence induced by different stress stimuli. Remarkably, HeckGal was also validated in vivo in an orthotopic breast cancer mouse model treated with senescence-inducing chemotherapy and in a renal fibrosis mouse model. In all cases, HeckGal allowed the unambiguous detection of senescence in vitro as well as in tissues and tumors in vivo. This work is expected to provide a potential technology for senescence detection in aged or damaged tissues.

Naphthalimide-based a highly selective two-photon fluorescent probe for imaging of hydrogen sulfide in living cells and inflamed tissue of mouse model

Hydrogen sulfide (H₂S) is a very important third endogenously generated gaseous signaling molecule and plays a key role in physiological and pathological regulation processes of living biosystems. Although a lot of H₂S fluorescent probes have been reported, the relationship between the physiology and pathology of H₂S in inflamed tissues remains unclear. Herein, by adopting a donor-π-acceptor (D-π-A)-structured naphthalimide derivative as the two-photon (TP) fluorophore and a 4-dinitrobenzene-ether (DNB) with a strong intramolecular charge transfer (ICT) effect as the recognition moiety, we reported a novel TP bioimaging probe NP-H₂S for H₂S with improved sensitivity. The NP-H₂S exhibits very low background fluorescence in the absence of H₂S, and a significant 258-fold fluorescence intensity enhancement was observed in the presence of H₂S, resulting in a high sensitivity and selectivity to H₂S in aqueous solutions with a detection limit of 18.8 nM observed. The probe also shows a wide linear response concentration range (0-10.0 μM) to H₂S with high selectivity. All these features are favorable for direct monitoring of H₂S in complex biological samples. It was then applied for direct TP imaging of H₂S in tissues of inflammation model with satisfactory sensitivity, indicating it has the latent capability in further biological applications for investigation of the interaction H₂S with inflammation.

Visualizing and Isolating Iron-Reducing Microorganisms at the Single-Cell Level

Iron-reducing microorganisms (FeRM) play key roles in many natural and engineering processes. Visualizing and isolating FeRM from multispecies samples are essential to understand the in situ location and geochemical role of FeRM. Here, we visualized FeRM by a "turn-on" Fe2+-specific fluorescent chemodosimeter (FSFC) with high sensitivity, selectivity, and stability. This FSFC could selectively identify and locate active FeRM from either pure culture, coculture of different bacteria, or sediment-containing samples. Fluorescent intensity of the FSFC could be used as an indicator of Fe2+ concentration in bacterial cultures. By combining the use of the FSFC with that of a single-cell sorter, we obtained three FSFC-labeled cells from an enriched consortium, and all of them were subsequently shown to be capable of iron reduction; two unlabeled cells were shown to have no iron-reducing capability, further confirming the feasibility of the FSFC.IMPORTANCE Visualization and isolation of FeRM from samples containing multiple species are commonly needed by researchers from different disciplines, such as environmental microbiology, environmental sciences, and geochemistry. However, no available method has been reported. In this study, we provide a method to visualize FeRM and evaluate their activity even at the single-cell level. When this approach is combined with use of a single-cell sorter, FeRM can also be isolated from samples containing multiple species. This method can be used as a powerful tool to uncover the in situ or ex situ role of FeRM and their interactions with ambient microbes or chemicals.

Novel turn-on fluorescence sensor for detection and imaging of endogenous H2S induced by sodium nitroprusside

Currently, fluorescence analysis method has a good application in the detection and imaging of biomarkers and has become an important analytical method. Although there are many fluorescent probes for detecting hydrogen sulfide(H₂S), they are mostly based on fluorophores which already existed, such as 1,8-naphthalimide, coumarin, rhodamine and their derivatives. Here, a new type of fluorescent molecule (BOTD) was synthesized and applied to the detection of H₂S. The probe BOTD could quickly and sensitively detect H₂S and turn on fluorescence. Moreover, the probe BOTD was successfully applied to the detection of exogenous and endogenous H₂S in living cells, and may be expected to become a research tool for studying H₂S-induced drugs.

A dual-selective fluorescent probe for discriminating glutathione and homocysteine simultaneously

Homocysteine (Hcy) and glutathione (GSH) play important roles in a variety of physiological and pathological processes. Abnormal levels of Hcy and GSH are related to various diseases. Fluorescent probes for detecting them with sensitive and selective are highly desirable. However, efficient discrimination of Hcy and GSH is still a challenge for their similar molecular structures and chemical properties. Herein, we report a naphthalimide and sulfonyl benzoxadiazole (SBD) based dual-selective fluorescent probe for Hcy and GSH over other amino acids. The probe exhibited weak fluorescence (Φ = 0.075, in DMSO) at 490 nm and fluorescence enhancement upon addition of GSH (1-20 μM) with a detection limit of 0.8 μM. The probe also exhibited ratiometric fluorescence responses for Hcy (fluorescence at 490 nm decreased and fluorescence at 552 nm increased). The fluorescence intensity ratio (I₅₅₂/I₄₉₀) showed a good linear correlation with the Hcy concentrations in range of 3-20 μM and the detection limit was 0.1 μM. Moreover, this probe was successfully utilized for monitoring Hcy and GSH in living cells.

CaMKKβ is involved in AMP-activated protein kinase activation by baicalin in LKB1 deficient cell lines

AMP-activated protein kinase (AMPK) plays an important role in mediating energy metabolism and is controlled mainly by two upstream kinases, LKB1 or Ca²⁺/calmodulin-dependent protein kinase kinase-β (CaMKKβ). Previously, we found that baicalin, one of the major flavonoids in a traditional Chinese herb medicine, Scutellaria baicalensis, protects against the development of hepatic steatosis in rats feeding with a high-fat diet by the activation of AMPK, but, the underlying mechanism for AMPK activation is unknown. Here we show that in two LKB1-deficient cells, HeLa and A549 cells, baicalin activates AMPK by α Thr-172 phosphorylation and subsequent phosphorylation of its downstream target, acetyl CoA carboxylase, at Ser-79, to a similar degree as does in HepG2 cells (that express LKB1). Pharmacologic inhibition of CaMKKβ by its selective inhibitor STO-609 markedly inhibits baicalin-induced AMPK activation in both HeLa and HepG2 cells, indicating that CaMKKβ is the responsible AMPK kinase. We also show that treatment of baicalin causes a larger increase in intracellular Ca²⁺ concentration ([Ca²⁺]_i), although the maximal level of [Ca²⁺]_i is lower in HepG2 cells compared to HeLa cells. Chelation of intracellular free Ca²⁺ by EDTA and EGTA, or depletion of intracellular Ca²⁺ stores by the endoplasmic reticulum Ca²⁺-ATPase inhibitor thapsigargin abrogates baicalin-induced activation of AMPK in HeLa cells. Neither cellular ATP nor the production of reactive oxygen species is altered by baicalin. Finally, in HeLa cells, baicalin treatment no longer decreases intracellular lipid accumulation caused by oleic acid after inhibition of CaMKKβ by STO-609. These results demonstrate that a potential Ca²⁺/CaMKKβ dependent pathway is involved in the activation of AMPK by baicalin and suggest that CaMKKβ likely acts as an upstream kinase of AMPK in response to baicalin.

6-N,N-dimethylamino-2,3-naphthalimide: a new environment-sensitive fluorescent probe in delta- and mu-selective opioid peptides

A new environment-sensitive fluorophore, 6-N,N-(dimethylamino)-2,3-naphthalimide (6DMN) was introduced in the delta-selective opioid peptide agonist H-Dmt-Tic-Glu-NH(2) and in the mu-selective opioid peptide agonist endomorphin-2 (H-Tyr-Pro-Phe-Phe-NH(2)). Environment-sensitive fluorophores are a special class of chromophores that generally exhibit a low quantum yield in aqueous solution but become highly fluorescent in nonpolar solvents or when bound to hydrophobic sites in proteins or membranes. New fluorescent delta-selective irreversible antagonists (H-Dmt-Tic-Glu-NH-(CH(2))(5)-CO-Dap(6DMN)-NH(2) (1) and H-Dmt-Tic-Glu-Dap(6DMN)-NH(2) (2)) were identified as potential fluorescent probes showing good properties for use in studies of distribution and internalization of delta receptors by confocal laser scanning microscopy.

Regulation of the energy sensor AMP-activated protein kinase by antigen receptor and Ca2+ in T lymphocytes

The adenosine monophosphate (AMP)–activated protein kinase (AMPK) has a crucial role in maintaining cellular energy homeostasis. This study shows that human and mouse T lymphocytes express AMPKα1 and that this is rapidly activated in response to triggering of the T cell antigen receptor (TCR). TCR stimulation of AMPK was dependent on the adaptors LAT and SLP76 and could be mimicked by the elevation of intracellular Ca²⁺ with Ca²⁺ ionophores or thapsigargin. AMPK activation was also induced by energy stress and depletion of cellular adenosine triphosphate (ATP). However, TCR and Ca²⁺ stimulation of AMPK required the activity of Ca²⁺–calmodulin-dependent protein kinase kinases (CaMKKs), whereas AMPK activation induced by increased AMP/ATP ratios did not. These experiments reveal two distinct pathways for the regulation of AMPK in T lymphocytes. The role of AMPK is to promote ATP conservation and production. The rapid activation of AMPK in response to Ca²⁺ signaling in T lymphocytes thus reveals that TCR triggering is linked to an evolutionally conserved serine kinase that regulates energy metabolism. Moreover, AMPK does not just react to cellular energy depletion but also anticipates it.

Inhibition of poly (ADP-ribose) polymerase activates ATM which is required for subsequent homologous recombination repair

Poly (ADP-ribose) polymerase (PARP-1), ATM and DNA-dependent protein kinase (DNA-PK) are all involved in responding to DNA damage to activate pathways responsible for cellular survival. Here, we demonstrate that PARP-1-/- cells are sensitive to the ATM inhibitor KU55933 and conversely that AT cells are sensitive to the PARP inhibitor 4-amino-1,8-napthalamide. In addition, PARP-1-/- cells are shown to be sensitive to the DNA-PK inhibitor NU7026 and DNA-PKcs or Ku80 defective cells shown to be sensitive to PARP inhibitors. We believe PARP inhibition results in an increase in unresolved spontaneous DNA single-strand breaks (SSBs), which collapse replication forks and trigger homologous recombination repair (HRR). We show that ATM is activated following inhibition of PARP. Furthermore, PARP inhibitor-induced HRR is abolished in ATM, but not DNA-PK, inhibited cells. ATM and DNA-PK inhibition together give the same sensitivity to PARP inhibitors as ATM alone, indicating that ATM functions in the same pathways as DNA-PK for survival at collapsed forks, likely in non-homologous end joining (NHEJ). Altogether, we suggest that ATM is activated by PARP inhibitor-induced collapsed replication forks and may function upstream of HRR in the repair of certain types of double-strand breaks (DSBs).