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A tyrosinase-activatable fluorescent probe with endoplasmic reticulum targetability was developed for the first time. It can ratiometrically fluoresce and hence be used to monitor refluxed tyrosinase into the endoplasmic reticulum. [ABSTRACT FROM AUTHOR]

As a high reactive oxygen species (ROS) and a reactive nitrogen species (RNS), peroxynitrite anion (ONOO−) is widely present in organisms and plays influential roles in physiological and pathological processes. It is of great significance to develop effective fluorescent probes for imaging peroxynitrite variation in living systems. Herein we present a novel fluorescent probe TQC0 for monitoring ONOO− based on the iminocoumarin platform, and this probe was synthesized by the knoevenagel condensation between a dihydropyridine‐salicylaldehyde derivative and 2‐benzothiazole‐acetonitrile, and subsequently masked with the boronate moiety. The obtained probe TQC0 exhibited a high signal‐to‐noise ratio (206‐fold) and a quick 'turn‐on' response (about 10 min) with great selectivity and sensitivity. Furthermore, the probe TQC0 was successfully applied for imaging ONOO− in living cells with low cytotoxicity. [ABSTRACT FROM AUTHOR]

Herein, we developed a rhodium(III)‐catalyzed synthesis of indenones from 2‐aryl‐3‐nitrosoindoles and alkynes in a redox‐neutral manner. The reaction did not require harsh conditions or any external oxidants. Mechanistic experiments and DFT calculation revealed that the reaction involved directed C−H activation, dearomative spirocyclization, N−O/C−C bond cleavage and ketimine hydrolysis cascade processes. [ABSTRACT FROM AUTHOR]

A direct strategy for the preparation of fused thienoindoles from substituted indoles and elemental sulfur has been reported. The present approach produces a range of structurally valuable fused thienoindoles in 51–78% yield under transition‐metal‐free conditions, which may have potential applications in pharmaceutical industry and organic functional materials. In this work, the double C−S bonds formation is achieved via base promoted direct sulfuration of C−H bonds with elemental sulfur. [ABSTRACT FROM AUTHOR]

Herein, we develop a Rh(III)-catalyzed intermolecular regioselective dearomative spirocyclization of 2-aryl-3-nitrosoindoles with alkynes, featuring the redox-neutral and atom-economic construction of spiroindoline-3-one oximes bearing a C2 spirocyclic quaternary carbon center under mild conditions. Both aryl alkyl alkynes and 1,3-diynes generally proceeded smoothly in the reaction with moderate to good regioselectivities. DFT calculations provided in-depth insights into the reaction mechanism and disclosed the origins of the regioselectivities. [ABSTRACT FROM AUTHOR]

A regioselective synthesis of 2‐amino‐para‐iminonaphthoquinones and 4‐amino‐1,2‐naphthoquinones was described via the substrate‐dependent divergent multi‐functionalization of β‐tetralone with primary and secondary amines under metal‐free conditions. This developed strategy features extremely green and mild conditions (O2 as oxidant, ethanol as solvent under ambient temperature), broad substrate scope, and various pharmaceutical derivatizations. [ABSTRACT FROM AUTHOR]

Fatty liver diseases are a spectrum of liver disorders consisting of the benign fatty liver, which could eventually lead to cirrhosis or even hepatocellular cancer (HCC) without timely treatment. Therefore, early diagnosis is crucial for fatty liver diseases. Liver biopsy is regarded as the gold standard in the diagnosis of fatty liver diseases. However, it is not recommended for routine use due to its invasiveness and complicated operation. Thus, it is urgent to diagnose fatty liver diseases with non-invasive and precise methods. In this regard, fluorescence imaging technology has attracted intensive attention and become a robust non-invasive method for fatty liver visualization, and a series of fluorescent probes are being intensively designed to track the biomarkers in fatty liver. In this brief review, the small molecular fluorescent probes employed in fatty liver are summarized, mainly focusing on the last four years. Moreover, current opportunities and challenges in the development of fluorescent probes for fatty liver will be highlighted. [ABSTRACT FROM AUTHOR]

A four-component synthesis of 2-phenyl-9H-pyrimido[4,5-b]indoles was developed using indole-3-carboxaldehydes, aromatic aldehyde and ammonium iodide as the raw materials under transition-metal-free conditions. The pyrimidine ring was formed in one pot through [4 + 2] annulation reaction. Four C–N bonds were formed in one pot promoted by iodine and iodide additives. This work is highlighted by using two ammonium iodides as the sole nitrogen source. [ABSTRACT FROM AUTHOR]

Covalent organic frameworks (COFs) were fabricated with a hierarchical flower-like hollow structure, possessing a large specific surface area, high porosity, and excellent environmental stability. In situ growth of noble silver nanoparticles (AgNPs) onto COFs was conducted yielding COF–Ag nanozymes. The structural advantages of COFs can ensure the uniform dispersion and effective size control of AgNPs. More interestingly, the oxidase-like catalytic activity of the obtained COF–Ag nanozymes could be enhanced in the presence of Hg2+ ions, which could specifically interact with AgNPs to form Ag–Hg alloys. A COF–Ag catalysis-based colorimetric platform was thereby constructed for highly selective and sensitive analysis of Hg2+ ions, showing a linear concentration range from 0.050 to 10.0 μM, with a limit of detection of about 3.7 nM. Besides, the developed colorimetric strategy was successfully applied for detecting Hg2+ ions in human blood with favorable detection recoveries, indicating its potential for applications in the biomedical analysis, environmental monitoring, and food safety fields. [ABSTRACT FROM AUTHOR]

The coupling of benzyl mercaptans to disulfide compounds is an important reaction in the production of pharmaceuticals, life medicine and other valuable fine chemicals. However, the coupling of benzyl mercaptans to disulfide compounds under aerobic and mild conditions remains a great challenge. Herein, we use cyclotriphosphazene as the basic skeleton to connect pyrimidine rings through ether bonds to form porous organic polymers (OBCPs). Research shows that OBCP samples not only exhibit fast carrier mobility, but also build up more negative reduction potential as well as low oxidation potential. In the photocatalytic reaction of benzyl mercaptans, OBCP sample generates the coupling of benzyl mercaptan to disulfide compounds rather than thiol oxidation products. Meanwhile, OBCPs also showed excellent photocatalytic reduction of CO2 to produce CH4. This work highlights that the dipole modulation of monomer molecules is important for designing polymers for excellent photocatalytic reactions. [ABSTRACT FROM AUTHOR]

A visible and sensitive assay for the quantitative detection of β-glucosidase (β-glu) activity based on Au@CeO2 core-shell nanoparticles (Au@CeO2 NPs) is described. As a hydrolytic enzyme, β-glu can promote the hydrolysis of β-arbutin to hydroquinone (HQ), which can trigger the decomposition of the CeO2 shell. With the single-particle enumeration (SPE) strategy coupled with dark field optical microscopy (DFM), an obvious color alteration of single Au@CeO2 NPs during the etching process can be observed in real-time. By statistically calculating the number of the etched nanoparticles, the β-glu activity level can be quantified accurately. This assay displays a broad linear range from 0.5 to 50 mU⋅mL−1 and low detection limit of 0.12 mU⋅mL−1. In addition, this method was successfully used to determine β-glu in real samples and acquires satisfactory recoveries in the range of 97.1-102.0%. This study provides a visualization analysis method for β-glu, which may be helpful for monitoring other targets in the future. [ABSTRACT FROM AUTHOR]

The stoichiometric coupling of readily available methylarenes and diverse acid chlorides into α-aryl ketones, a valued structural motif present in pharmacologically relevant molecules, has been developed. The utility of this protocol is demonstrated by the late-stage acylation of biologically active molecules in a stoichiometric manner. Mechanistic investigation reveals that the photocatalytically generated bromine radical acts as a hydrogen atom abstraction reagent and delivers a nucleophilic benzyl radical, which is intercepted by nickel-catalyzed cross coupling to accomplish benzylic acylation. [ABSTRACT FROM AUTHOR]

Fe‐catalyzed three‐component strategy have been developed for the synthesis of 2,3′‐biquinolines from readily available 2‐methyl quinolines, anthranils and N, N‐dimethylacetamide (DMA), This annulation procedure undergoes C(sp3)−H activation, amination, nucleophilic addition, dehydration and oxydehydrogenation steps. DMA acts not only as a solvent but also as a one carbon donor in the reaction. [ABSTRACT FROM AUTHOR]

Nitrogen-enriched carbon dots (NCDs) with green fluorescence were prepared with an average diameter of 4.8 nm by a room temperature self-polymerization method using catechol and ethylenediamine as precursors. It was found that the green fluorescence of NCDs can be quenched directly by uric acid (UA). A facile and fast fluorescent enzyme-free sensor has been developed for the detection of UA in the linear concentration range of 0–30 μM, with a limit of detection of 0.22 μM. High sensitivity, stability and selectivity can also be achieved for the detection of UA. In addition, the mechanism of fluorescence quenching of NCDs induced by UA was the dynamic quenching type according to the linearity of the Stern–Volmer equation and the change of the lifetime of NCDs after adding UA. Furthermore, UA in saliva samples was successfully detected using this established fluorimetric method, showing the feasible detection of UA in complicated body fluid samples. This NCD-based fluorimetric non-invasive method can be used for the highly selective determination of UA in the clinical laboratory. [ABSTRACT FROM AUTHOR]

The generation of high-calorific-value hydrocarbon fuels is still limited by poor photoinduced carrier transport in organic polymers. Herein, 2D polymers with different porous structures were synthesized by adopting a good-solvent/poor-solvent control strategy, and the photocatalytic CO2 reduction behavior was further compared. It was verified that the ultrafine porous structure in the 2D polymer (D1M4-PC) is responsible for the selective formation of CH4. The CH4 yield of the D1M4-PC sample reached 6733 μmol g−1, and the CH4 selectivity was near 100%. Experiments and theoretical calculations show that the ultrafine porous structure can provide an extremely short carrier transport distance and has accessible active sites, which enables the photoinduced carrier migration to the trapped CO2 molecules rapidly, enabling high selectivity photocatalytic CO2 conversion. This work offers a promising strategy for designing polymers for the conversion of CO2 into high-calorific-value hydrocarbon fuels with high selectivity and activity. [ABSTRACT FROM AUTHOR]

A synthetic method of o‐sulfanylanilines from cyclohexanones, amines, and thiophenols under transition‐metal‐free conditions is disclosed. This is the first report on the direct thioamination of cyclohexanones via N‐iodosuccinimide (NIS) promoted oxidative dehydroaromatization. Non‐aromatic cyclohexanones were smoothly dehydrogenated, and acted as an aryl source using oxygen as a green oxidant. The capacity of the resultant o‐sulfanylanilines for synthesis of N‐arylphenothiazines has been further demonstrated. [ABSTRACT FROM AUTHOR]

A metal‐ and solvent‐free strategy for the preparation of maleimide‐fused carbazoles has been developed. This protocol started from 2‐(indol‐3‐yl)cyclohexanones and maleimides, providing various maleimide‐fused carbazoles in 45–90% yields. The present approach was catalyzed by trimethylsulfoxonium iodide and involved a cascade of oxidation, [4+2] annulation, and dehydrogenative aromatization. Moreover, these maleimide‐fused carbazole products could be further transformed into other polycyclic aromatic hydrocarbons. [ABSTRACT FROM AUTHOR]

Nowadays, test strips are widely applied, but their use is mostly limited to the qualitative or half-quantitative analysis of targets. The main reason for their limited use is the "Coffee Ring Effect" (CRE) of probe materials, which leads to a heterogeneous probe distribution and poor testing reproducibility and sensitivity. In the present work, a fluorescent test strip was fabricated with a suppressed CRE of silver nanocluster (AgNC) probes coated by gelatin (Gel) under vacuum-aided fast lyophilization. Uniform and stable deposition of AgNC probes was achieved onto the test strips with a high loading capacity. The AgNCs displayed specific responses to Hg2+ ions, allowing sensitive and quantitative analysis in the linear concentration ranges from 0.20 to 50000 nM with a limit of detection of 0.10 nM. Given the advantages of rapid and facile preparation, CRE suppression, high biocompatibility, and cost-effectiveness, such a fabrication protocol may pave the way for the design of various test strips-based devices for point-of-care analytical applications in the fields of environmental monitoring, food quality analysis, and clinical diagnostics. [ABSTRACT FROM AUTHOR]

Zeolitic Imidazolate Frameworks (ZIFs) derived nitrogen‐doped porous carbon (NPC) materials have been proposed as promising metal‐free electrocatalysts for oxygen reduction reactions (ORR). Herein, we report a strategy to control the morphology of ZIF‐8 and ZIF material‐derived NPC materials by the amount of L‐cysteine. The prepared NPC electrocatalysts exhibit different morphologies and ORR properties. The best of these catalysts exhibited a nanosheet‐like morphology with an onset potential of 0.95 V and a half‐wave potential of 0.87 V in alkaline media, which are comparable to those of commercial Pt/C (20 wt%) catalysts. In addition, this catalyst exhibited high stability and methanol resistance. This work not only reveals the effect of L‐cysteine amount on the growth process of ZIF, but also provides a strategy for designing various excellent catalysts in the fuel cell field. [ABSTRACT FROM AUTHOR]

Hypochlorous acid (HOCl) was crucial for maintaining the homeostasis in cells and plays vital roles in many physiological and pathological processes. In this work, a highly selective fluorescent probe for hypochlorous acid in living cells was constructed and prepared based on a naphthalene derivative. A naphthalene derivative was utilized as the fluorescent group, and N,N-dimethylthiocarbamate was applied as the selective recognition site for HOCl. Before adding HOCl, the fluorescent probe exhibited weak fluorescence. Upon adding HOCl, the fluorescent probe displayed remarkable fluorescence enhancement. The fluorescence intensity at 502 nm showed a linear response to the concentration of HOCl from 3.0 × 10−7 to 1.0 × 10−5 mol·L−1. The detection limit was estimated to be 1.5 × 10−7 mol·L−1 for HOCl. The fluorescent probe showed fast response and outstanding selectivity toward HOCl. It owned good biocompatibility and had also been successfully applied in the confocal imaging of exogenous and endogenous HOCl in living cells. [ABSTRACT FROM AUTHOR]

A high-throughput and selective fluorimetric platform has been constructed for the analysis of ammonia in blood by using a polymer-stabilized metal–organic framework (MOF) of porous NH2-MIL-125, which was coated onto a wettable microwells array constructed on an indium tin oxide (ITO) substrate. It was found that the nitrogen plasma treatment for the ITO substrate could create a super-hydrophilic interface that combined with the hydrophobic pattern yielded a wettable microwells array, enabling the condensation-based enrichment of targets from the sample droplets. Moreover, the NH2-MIL-125 MOF encapsulated using polymers could be firmly coated onto the microwells to act as fluorescent probes for sensing NH3 with enhanced responses. In addition, the use of the polymer polyvinyl pyrrolidone could protect and stabilize the crystals of NH2-MIL-125 probe in aqueous media, revealing the improved hydrophilicity and significantly depressed signal background. The as-developed fluorimetric platform, containing a MOF-coated microwells array, can enable the detection of ammonia in blood, with concentrations ranging linearly from 0.10 to 300 μM. More importantly, this plasma treatment-based fabrication route may hold promise for designing different wettable microwells arrays for the high-throughput detection of multiple targets in the fields of biomedical analysis and environmental monitoring. [ABSTRACT FROM AUTHOR]

As a key reactive oxygen species (ROS), hypochlorous acid (HClO) plays a vital role in living systems. Ratiometric and endoplasmic reticulum-targeting probes for highly sensitive detection of hypochlorous acid are in demand. In this paper, we constructed a novel reticulum-targeting and ratiometric fluorescent probe for determining hypochlorous acid. The probe applied 4-aminonaphthalimide as the fluorescent group, employed the (2-aminoethyl)thiourea group as a specific recognition unit, and used the p-toluenesulfonamide group as the localization group of the endoplasmic reticulum. When HClO is absent, the probe underwent an intramolecular charge transfer (ICT) process and displayed green emission. In the presence of HClO, the ICT process was inhibited, which induced a 49 nm blue-shift of fluorescence emission from 533 nm to 484 nm. The ratiometric fluorescent probe exhibited high sensitivity and selectivity for HClO. Furthermore, the ratiometric fluorescent probe could work in a wide pH range. The fluorescence intensity ratios (I484nm/I533nm) exhibited a linear response to the concentration of HClO from 5.0 × 10−7 to 1.0 × 10−5 mol L−1. The detection limit was evaluated to be 1.0 × 10−7 mol L−1 for HClO. In addition, the probe displayed an excellent endoplasmic reticulum-targeting ability, and has been successfully applied for the confocal imaging of HClO in the endoplasmic reticulum of PC-12 cells with almost no cell toxicity. All of such outstanding properties demonstrated that it could be employed to sense HClO in the endoplasmic reticulum of living cells. [ABSTRACT FROM AUTHOR]

The multifunctional hemin@carbon dot hybrid nanozymes (hemin@CD) with simultaneous peroxidase-like activity and fluorescence signalling property was prepared for the first time. Based on these properties, hemin@CD was applied to develop a dual-channel fluorescent probe for H2O2 and H2O2-based biocatalytic systems. By virtue of the peroxidase-like activity, hemin@CD can catalyze the oxidative coupling of 4-aminoantipyrine with phenol in the presence of H2O2 to form a pink-red quinoneimine dye with a maximum absorbance at 505 nm. Under the excitation wavelength of 480 nm, the green fluorescence of hemin@CD peaks at 540 nm and is quenched by the generated quinoneimine dye due to an inner filter effect, and also by H2O2 because of dynamic quenching. Thus, a colorimetric and fluorimetric dual-channel optical probe for H2O2 is obtained. Due to the glucose/xanthine transformations under formation of H2O2 by the relevant oxidase catalysis, the probe can be applied for detection of glucose and xanthine. The colorimetric detection limits for H2O2, glucose and xanthine are 0.11, 0.15, 0.11 μM, and the and fluorimetric detection limits are 0.15, 0.15, 0.12 μM, respectively. [ABSTRACT FROM AUTHOR]

In the present study, a simple strategy was developed for Ni/Co layered double hydroxides (LDHs) as a substitute for natural peroxidase. The obtained Ni/Co LDHs exhibited ease of preparation, low-cost, and water-solubility; importantly, this material showed high catalytic activity in neutral pH solutions (phosphate buffer, Tris–HCl buffer, and even water). Benefitting from Ni/Co LDHs having a similar pH and temperature with specificity oxidase, such as glucose oxidase, choline oxidase, acetylcholinesterase, etc., a novel one-step method for a biosensor was developed in water. Glucose detection was selected as an application model system to evaluate the performance of this method, which showed a linear detection range from 0.5 μM to 100 μM with a detection limit (DL) of 0.1 μM. We also extended the one-step method to detect acetylcholine (ACh) by taking advantage of the specific catalytic reaction of acetylcholinesterase (AChE) and choline oxidase (ChOx). The linear detection range was from 10 μM to 150 μM with the DL of 1.62 μM. The proposed method had ease of operation, simple steps, and was rapid for glucose and ACh detection in real samples. On the basis of these advantages and virtues, Ni/Co LDHs could become attractive nanozymes in biotechnology and bioassays, and create a great influence on the next generation of enzyme mimetic systems. [ABSTRACT FROM AUTHOR]