A Dual-target Fluorescent Chemosensor for Detecting Indium (III) and Hypochlorite with High Selectivity.

A dual-target fluorescent chemosensor BQC (((E)-N-benzhydryl-2-(quinolin-2-ylmethylene)hydrazine-1-carbothioamide) was synthesized for detecting In3+ and ClO-. BQC displayed green and blue fluorescence responses to In3+ and ClO- with low detection limits (0.83 µM for In3+ and 2.50 µM for ClO-), respectively. Importantly, BQC is the first fluorescent chemosensor capable of detecting In3+ and ClO-. The binding ratio between BQC and In3+ was determined to be a 2:1 through Job plot and ESI-MS analysis. BQC could be successfully utilized as a visible test kit to detect In3+. Meanwhile, BQC showed a selective turn-on response to ClO- even in the presence of anions or reactive oxygen species. The sensing mechanisms of BQC for In3+ and ClO- were demonstrated by 1 H NMR titration, ESI-MS and theoretical calculations.

Smartphone-Based Quantitative Measurement of Cu2+: Fluorescent Turn-on Chemosensor via Radical Cation Formation.

We report a unique radical cation formation-based fluorescent chemosensor (E)-N'-(4-(diphenylamino)benzylidene)thiophene-2-carbohydrazide (DBTC) that quantitatively determines Cu2+ based on the RGB model using a smartphone. DBTC exhibited a weak turquoise fluorescence due to fluorescence suppression by amide isomerization. When Cu2+ was added into DBTC, it showed strong light blue fluorescence with a high quantum yield ([Formula: see text] = 0.470). The detection limit of Cu2+ was determined to be 0.40 µM at the concentration range of 0-7.5 µM. In addition, the detection mechanism of DBTC for Cu2+ was demonstrated to be an oxidative cyclization reaction through 1H NMR titration, ESI-MS analysis, and DFT calculation. Remarkably, DBTC could be applied to the quantitative measurement of Cu2+ using a smartphone and RGB analysis. The detection limit was calculated to be 0.05 µM, which is the lowest detection limit among chemosensors that could detect Cu2+ through smartphone-based fluorescence measurements. Additionally, spike and recovery experiments conducted with different concentrations of Cu2+ showed good recovery values. DBTC exhibited its potential as a chemosensor for determining Cu2+ through the application of a smartphone-based platform capable of real-time monitoring.

A Fluorescent and Colorimetric Chemosensor Detecting Pd2+ Based on Chalcone Structure with Triphenylamine.

A fluorometric and colorimetric chemosensor DiPP ((E)-3-(4-(diphenylamino)phenyl)-1-(pyridin-2-yl)prop-2-en-1-one) based on chalcone structure with a triphenylamine group was synthesized. Sensor DiPP detected Pd2+ with fluorescence turn-off and via colorimetry variation of yellow to purple. The binding ratio of DiPP to Pd2+ turned out to be 1 : 1. Detection limits for Pd2+ by DiPP were analyzed to be 0.67 µM and 0.80 µM through the fluorescent and colorimetric methods. Additionally, the fluorescent and colorimetric test strips were applied for probing Pd2+ and displayed that DiPP could obviously discriminate Pd2+ from other metals. The binding feature of DiPP to Pd2+ was presented by ESI-mass, Job plot, NMR titration, ESI-mass, and DFT calculations.

A colorimetric/ratiometric chemosensor based on an aggregation-induced emission strategy for tracing hypochlorite in vitro and in vivo.

Excessive levels of hypochlorite (ClO-) negatively affect environmental and biological systems. Thus, it is essential to develop sensors that can identify ClO- in various systems such as the environment and living organisms. In this study, we report the development and evaluation of a novel aggregation-induced emission (AIE) strategy-based colorimetric and ratiometric fluorescent chemosensor 2,2'-(((1E,1'E)-[2,2'-bithiophene]- 5,5'-diylbis(methanylylidene))bis(hydrazin-1-yl-2-ylidene))bis(N,N,N-trimethyl-2-oxoethan-1-aminium) chloride (BMH-2∙Cl) for detecting ClO-. BMH-2∙Cl enabled highly selective ClO- detection through a color change from yellow to colorless and a fluorescence color change from turquoise to blue in a perfect aqueous solution. BMH-2∙Cl exhibited low limits of detection (2.4 ×10-6 M for colorimetry and 2.9 ×10-7 M for ratiometric fluorescence) for detecting ClO- with a rapid response within 5 s. The detection mechanism for ClO- and an AIE property change of BMH-2∙Cl were demonstrated by 1H NMR titration, ESI-MS, variation of water fraction (fw) and theoretical calculations. In particular, we confirmed not only the practicality of BMH-2∙Cl by using test strips, but also demonstrated the potential for efficient ClO- detection in biological and environmental systems such as real water samples, living zebrafish and bean sprouts.

Highly Selective Detection of Al3+ by Carboxamide-Based Fluorescent Chemosensor.

We designed a carboxamide-based fluorescent chemosensor HTPQ ((E)-2-(((8-hydroxy-2,3,6,7-tetrahydro-1H,5H-pyrido[3,2,1-ij]quinolin-9-yl)methylene)amino)thiophene-3-carboxamide) for detecting Al3+. HTPQ could probe Al3+ by fluorescence enhancement. Limit of detection for Al3+ toward HTPQ was 1.4 µM. Binding of HTPQ to Al3+ was determined to be a 1:1 ratio with the analysis of Job plot and ESI-mass. In addition, HTPQ was able to detect Al3+ using the test strip by fluorescent variation. The sensing process of Al3+ by HTPQ was presented by UV-vis titration, ESI-MS, Job plot, 1H NMR titration and DFT calculation.

A new sensitive and selective detection of Ga3+ by thiophene-based 'turn-on' fluorescent chemosensor.

We designed a thiophene-based fluorescent chemosensor DHTC ((E)-2-([3,5-dichloro-2-hydroxybenzylidene]amino)thiophene-3-carboxamide) for detecting gallium (Ga3+ ). DHTC could probe Ga3+ using fluorescence enhancement. The limit of detection for Ga3+ by DHTC was 0.39 µM. The binding mode of DHTC to Ga3+ was determined as a 1:1 ratio from analysis by Job's plot and electrospray ionization-mass spectrometry (ESI-MS). In addition, DHTC could selectively detect Ga3+ using test kits. The sensing process of Ga3+ by DHTC was presented using ultraviolet-visible light titration, Job's plot, ESI-MS, 1 H nuclear magnetic resonance titration, and density functional theory calculation.

A chalcone-based fluorescent chemosensor for detecting Mg2+ and Cd2.

SBOD (sodium (E)-2-(3-[5-bromothiophen-2-yl]-3-oxoprop-1-en-1-yl)-4,6-dichlorophenolate) was designed and synthesized as a chalcone-based fluorescent turn-on chemosensor for Mg2+ and Cd2+ . SBOD selectively detected Mg2+ and Cd2+ through the increase in effective fluorescence. Detection limits of SBOD for Mg2+ and Cd2+ were calculated to be 3.8 µM and 2.9 µM, respectively. The binding modes of SBOD for Mg2+ and Cd2+ were determined to be 1:1 by ESI-MS and Job plot. Association mechanisms for SBOD to Mg2+ and Cd2+ were illustrated by ESI-MS, UV-vis, fluorescence spectroscopy, and calculations.

Proton Switch in the Secondary Coordination Sphere to Control Catalytic Events at the Metal Center: Biomimetic Oxo Transfer Chemistry of Nickel Amidate Complex.

High-valent metal-oxo species are key intermediates for the oxygen atom transfer step in the catalytic cycles of many metalloenzymes. While the redox-active metal centers of such enzymes are typically supported by anionic amino acid side chains or porphyrin rings, peptide backbones might function as strong electron-donating ligands to stabilize high oxidation states. To test the feasibility of this idea in synthetic settings, we have prepared a nickel(II) complex of new amido multidentate ligand. The mononuclear nickel complex of this N5 ligand catalyzes epoxidation reactions of a wide range of olefins by using mCPBA as a terminal oxidant. Notably, a remarkably high catalytic efficiency and selectivity were observed for terminal olefin substrates. We found that protonation of the secondary coordination sphere serves as the entry point to the catalytic cycle, in which high-valent nickel species is subsequently formed to carry out oxo-transfer reactions. A conceptually parallel process might allow metalloenzymes to control the catalytic cycle in the primary coordination sphere by using proton switch in the secondary coordination sphere.

A Benzothiazole-Based Fluorescence Turn-on Sensor for Copper(II).

A new benzothiazole-based chemosensor BTN (1-((Z)-(((E)-3-methylbenzo[d]thiazol-2(3H)-ylidene)hydrazono)methyl)naphthalen-2-ol) was synthesized for the detection of Cu2+. BTN could detect Cu2+ with "off-on" fluorescent response from colorless to yellow irrespective of presence of other cations. Limit of detection for Cu2+ was determined to be 3.3 µM. Binding ratio of BTN and Cu2+ turned out to be a 1:1 with the analysis of Job plot and ESI-MS. Sensing feature of Cu2+ by BTN was explained with theoretical calculations, which might be owing to internal charge transfer and chelation-enhanced fluorescence processes.

A New Reversible Colorimetric Chemosensor Based on Julolidine Moiety for Detecting F.

We synthesized an original reversible colorimetric chemosensor PDJ ((E)-9-((2-(6-chloropyridazin-3-yl)hydrazono)methyl)-2,3,6,7-tetrahydro-1H,5H-pyrido[3,2,1-ij]quinolin-8-ol) for the detection of F-. PDJ displayed a selective colorimetric detection to F- with a variation of color from colorless to yellow. Limit of detection of PDJ for F- was calculated as 12.1 µM. The binding mode of PDJ and F- turned out to be a 1:1 ratio using Job plot. Sensing process of F- by PDJ was demonstrated by 1H NMR titration and DFT calculation studies that suggested hydrogen bond interactions followed by deprotonation. Moreover, the practicality of PDJ was demonstrated via a reversible test with TFA (trifluoroacetic acid).

A naphthyl thiourea-based effective chemosensor for fluorescence detection of Ag+ and Zn2.

A naphthyl thiourea-based effective chemosensor HNC, (E)-2-(2-hydroxy-3-methoxybenzylidene)-N-(naphthalen-1-yl)hydrazine-1-carbothioamide, was synthesized. HNC showed quick responses toward Ag+ and Zn2+ through marked fluorescence turn-on in different solvent conditions, respectively. Binding proportions of HNC to Ag+ and Zn2+ were found to be 2:1 and 1:1, respectively. Detection limits of HNC for Ag+ and Zn2+ were calculated as 3.82 and 0.21 µM. Binding processes of HNC for Ag+ and Zn2+ were represented using Job's plot, DFT, 1 H NMR titration, and ESI-MS.

An Indole-Based Fluorescent Chemosensor for Detecting Zn2+ in Aqueous Media and Zebrafish.

An indole-based fluorescent chemosensor IH-Sal was synthesized to detect Zn2+. IH-Sal displayed a marked fluorescence increment with Zn2+. The detection limit (0.41 µM) of IH-Sal for Zn2+ was greatly below that suggested by the World Health Organization. IH-Sal can quantify Zn2+ in real water samples. More significantly, IH-Sal could determine and depict the presence of Zn2+ in zebrafish. The detecting mechanism of IH-Sal toward Zn2+ was illustrated by fluorescence and UV-visible spectroscopy, DFT calculations, 1H NMR titration and ESI mass.

Determination of Zinc Ion by a Quinoline-Based Fluorescence Chemosensor.

A novel fluorescence chemosensor XYQ for detecting Zn(II) was synthesized. XYQ showed fluorescence turn-on to Zn(II) with high sensitivity and selectivity in aqueous media among 19 metal ions. Its binding structure was demonstrated by ESI-MS, Job plot, and 1H NMR titration. The detection limit of XYQ to Zn(II) was 0.53 µM. It is much below WHO drinking water standard (76.0 µM). XYQ could be applied successfully to the test kit and real samples. The fluorescence turn-on process was possibly explained as a chelation-enhanced fluorescence (CHEF) effect with theoretical calculations.

A Thiourea-Containing Fluorescent Chemosensor for Detecting Ga3.

A thiourea-based fluorescent chemosensor NADA, (E)-2-(4-(diethylamino)-2-hydroxybenzylidene)-N-(naphthalen-1-yl)hydrazine-1-carbothioamide, has been designed and synthesized. NADA could detect Ga3+ through a fluorescent turn-on with a low detection limit (0.29 µM). Importantly, NADA could effectively discriminate Ga3+ from Al3+ and In3+. The binding mechanism of NADA with Ga3+ was identified by ESI-mass, NMR titration, and DFT calculations.

An Acridine-Based Fluorescent Sensor for Monitoring ClO- in Water Samples and Zebrafish.

A novel acridine-based fluorescent chemosensor, BK ((E)-2-((acridine-9-ylimino)methyl)-N-benzhydrylhydrazine-1-carbothioamide), for monitoring ClO- was prepared. The sensor BK was synthesized by introducing a new synthetic route of making aldehyde group using formic hydrazide. Probe BK displayed notable fluorescence quenching in the presence of ClO- and showed a great selectivity over other guest analytes. The detection limit was calculated to be 7.65 µM. Additionally, BK was satisfactorily applied for sensing ClO- in water samples and zebrafish.

A visible chemosensor based on carbohydrazide for Fe(ii), Co(ii) and Cu(ii) in aqueous solution.

A colorimetric sensor with pyridyl and carbohydrazide components has been synthesized and visibly turns blue in the presence of Fe(ii). The colorless sensor also changes color when exposed to Co(ii) and Cu(ii), but its color becomes yellow. The sensor shows no visible response to other metal ions such Ca2+, Cr3+, Mn2+, Fe3+, Ni2+, Zn2+, Cd2+, Ag+, Hg2+, and Pb2+. The binding ratio of the sensor to Fe(ii), Co(ii), and Cu(ii) is 2 sensors to 1 metal ion. The binding constants of the sensor are: Fe(ii): 1.0 × 109 M-2, Co(ii): 2 × 109 M-2, and Cu(ii): 3.0 × 109 M-2. The sensor works well at neutral pH and micromolar concentrations of Fe(ii), Co(ii), and Cu(ii) can be detected in water samples. The sensor's color response to Cu(ii) is uniquely attenuated by glutathione.

A multiple target chemosensor for the sequential fluorescence detection of Zn2+ and S2- and the colorimetric detection of Fe3+/2+ in aqueous media and living cells.

A novel multiple target sensor, (E)-5-((4-(diethylamino)-2-hydroxybenzyldene)amino)-1H-imidazole-4-carboxamide (DHIC), was synthesized for fluorescence detection of Zn2+ and S2- and colorimetric detection of Fe3+/2+ in aqueous media. DHIC can operate as a turn "on-off" sequential fluorescent sensor for Zn2+ and S2-. Detection limits (1.59 µM and 8.03 µM) for Zn2+ and S2- are below the WHO standards (76.0 µM and 14.7 µM). The DHIC-Zn2+ complex could be reversibly reused with ethylenediaminetetraacetic acid. Importantly, DHIC could image sequentially Zn2+ and S2- in living cells. Moreover, DHIC displayed a discriminatory color change from pale yellow to orange yellow to Fe3+/2+. The detection limit of DHIC for Fe3+/2+ (0.73 µM and 1.11 µM) is far below the EPA drinking water standard (5.37 µM). The sensor DHIC could be applied to analyze Fe3+ in real samples.

Sequential Multiple-Target Sensor: In3+, Fe2+, and Fe3+ Discrimination by an Anthracene-Based Probe.

Indium is a nonphysiological toxic metal widely used in industry. While misunderstood, its toxicity is proposed to be linked to a perturbation of Fe3+ homeostasis through the binding of In3+ ions to essential iron metalloproteins such as transferrins. Therefore, the monitoring of In3+ and Fe3+ in biological environments is of prime interest for both basic research and diagnosis. Here we report the design of a salen-type anthracene-based probe able to selectively sense and discriminate In3+ and Fe2+/3+ ions by fluoro-colorimetry.

An Imidazo[1,5-α]Pyridine-Based Fluorometric Chemodosimeter for the Highly Selective Detection of Hypochlorite in Aqueous Media.

A new fluorometric chemodosimeter 2-amino-3-(((E)-3-(1-phenylimidazo[1,5-α]pyridin-3-yl)benzylidene)amino)maleonitrile (BPI-MAL) has been designed and synthesized for sensing hypochlorite. BPI-MAL showed a selective turn-on fluorescence for ClO- through hypochlorite-promoted de-diaminomaleonitrile reaction. It also could detect ClO- in the presence of various competitive anions including reactive oxygen species. Interestingly, sensor BPI-MAL was successfully applied as a fluorescent test kit for ClO- determination. The sensing property and mechanism of BPI-MAL toward ClO- were studied by fluorescence and UV-vis spectroscopy, NMR titration and DFT calculations.

A Novel Thiophene-Based Fluorescent Chemosensor for the Detection of Zn2+ and CN-: Imaging Applications in Live Cells and Zebrafish.

A novel fluorescent turn-on chemosensor DHADC ((E)-3-((4-(diethylamino)-2-hydroxybenzylidene)amino)-2,3-dihydrothiophene-2-carboxamide) has been developed and used to detect Zn2+ and CN-. Compound DHADC displayed a notable fluorescence increase with Zn2+. The limit of detection (2.55 ± 0.05 µM) for zinc ion was far below the standard (76 µM) of the WHO (World Health Organization). In particular, compound DHADC could be applied to determine Zn2+ in real samples, and to image Zn2+ in both HeLa cells and zebrafish. Additionally, DHADC could detect CN- through a fluorescence enhancement with little inhibition with the existence of other types of anions. The detection processes of compound DHADC for Zn2+ and CN- were demonstrated with various analytical methods like Job plots, 1H NMR titrations, and ESI-Mass analyses.