Tae Geun Jo

A diaminomaleonitrile based selective colorimetric chemosensor for copper(II) and fluoride ions

A new and simple colorimetric receptor 1, based on 2,3-diaminomaleonitrile and julolidine moieties, has been synthesized and characterized. 1 showed a selective colorimetric sensing ability for copper(II) ions by changing color from yellow to colorless, and could be utilized to monitor Cu2+ over a wide pH range of 4–12. The detection limit of 1 (2.1 μM) for Cu2+ ions is much lower than that recommended by WHO in drinking water (30 μM). Moreover, the receptor 1 can also detect fluoride by color change from yellow to orange, distinguishing the fluoride ions effectively from anions such as CH3COO− and CN−. It was also found that the 1–F− complex was reversibly bound and could be simply reverted back through treatment with a proper reagent such as HCl. The sensing mechanism for F− was theoretically supported by DFT and TD-DFT calculations.

A highly sensitive benzimidazole-based chemosensor for the colorimetric detection of Fe(II) and Fe(III) and the fluorometric detection of Zn(II) in aqueous media

A new dual chemosensor 1 for the colorimetric detection of Fe2+/3+ and the fluorometric detection of Zn2+ has been developed and characterized. The sensor 1 has proven to be highly selective to Fe2+/3+ with a color change from colorless to dark green in a near-perfect aqueous solution. 1 had low detection limits (1.21 μM for Fe3+ and 1.18 μM for Fe2+), which are lower than the World Health Organization guideline (5.36 μM) for drinking water. Moreover, 1 showed a selective detecting ability for Zn2+ by ‘OFF–ON’ fluorescent response in aqueous solution. The detection limit (1.05 μM) of 1 for Zn2+ was much lower than World Health Organization guideline (76 μM) for drinking water. Interestingly, it could be recycled simply through treatment with an appropriate reagent such as EDTA (ethylenediaminetetraacetic acid). The sensing mechanism of 1 for Zn2+ was explained by the theoretical calculations. In particular, the sensor 1 could be used to quantify iron and zinc in water samples.

A highly selective fluorescent sensor for the detection of Al3+ and CN− in aqueous solution: biological applications and DFT calculations

A new “turn-on fluorescence type” chemosensor 1 (N′1,N′2-bis((E)-2-hydroxybenzylidene)oxalohydrazide) with a simple structure was devised and synthesized. In aqueous solution, receptor 1 could efficiently detect both Al3+ and CN− at two different wavelengths. The limit of detection for Al3+ (2.0 μM) is below the World Health Organization (WHO) guideline for drinking water (7.41 μM). To utilize for practical and biological applications, the ability of 1 for monitoring Al3+ was tested in real water samples and living cells. In addition, 1 showed a highly selective fluorescence enhancement for CN− in the presence of other anions without any interference. The sensing mechanisms of 1 for Al3+ and CN− were supported by theoretical calculations.

A new Schiff-based chemosensor for chromogenic sensing of Cu2+, Co2+ and S2− in aqueous solution: experimental and theoretical studies

A new Schiff-based multifunctional colorimetric chemosensor 1 was developed for the detection of various analytes (Cu2+, Co2+ and S2−). Sensor 1 could simply monitor Cu2+ and Co2+via the naked eye in an aqueous environment. The quite low detection limits were found to be 0.19 μM for Cu2+ and 0.18 μM for Co2+, which were much lower than the values recommended by the World Health Organization (WHO) for Cu2+ (31.5 μM) and Environmental Protection Agency (EPA) for Co2+ (17 μM). Importantly, 1 showed high preferential selectivity for Cu2+ and Co2+ over competitive metal ions. For practical applications, the sensing abilities of 1 for detecting Cu2+ and Co2+ were examined in real water samples. In addition, 1 exhibited high selectivity for S2− even in the presence of other anions without any interference. Moreover, the sensing mechanisms of 1 toward Cu2+, Co2+ and S2− were explained by theoretical calculations.

A Colorimetric and Fluorescent Chemosensor for the Selective Detection of Cu2+ and Zn2+ Ions

A new bi-functional chemosensor 1 based on 3,5-dichlorosalicylaldehyde and 2-(methylthio)aniline has been synthesized. It can detect Cu2+ with a color change from pale yellow to dark yellow in aqueous solution. The selective mechanism of 1 for Cu2+ was proposed to be the enhancement of the intramolecular charge transfer (ICT) band, which was explained by theoretical calculations. The sensor 1 could be used to detect and quantify Cu2+ in water samples. In addition, the sensor 1 displayed “turn-on” fluorescence response only to Zn2+, based on an effect of chelation-enhanced fluorescence (CHEF). Therefore, 1 can serve as a ‘single sensor for two different targets’ with dual modes.

A single colorimetric sensor for multiple targets: the sequential detection of Co2+ and cyanide and the selective detection of Cu2+ in aqueous solution

A new highly selective and multifunctional chemosensor 1 for the detection of Co2+, Cu2+ and CN−, based on 4-diethylaminosalicyl aldehyde and thiophene-2-carbohydrazide moieties, was designed and synthesized. 1 could simultaneously detect both Co2+ and Cu2+ by changing its color from colorless to yellow in aqueous solution. The binding modes of 1 to Co2+ and Cu2+ were determined to be a 2 : 1 complexation stoichiometry through job plot and ESI-mass spectrometry analysis. The detection limits (0.19 μM and 0.13 μM) of 1 for Co2+ and Cu2+ were lower than the DEP guideline (1.7 μM) of Co2+ and the WHO guideline (31.5 μM) of Cu2+ for drinking water. Importantly, 1 could detect and quantify Co2+ and Cu2+ in real water samples. Moreover, the resulting Co2+-2·1 complex sensed cyanide through naked-eye, showing recovery from Co2+-2·1 to 1. The sensing mechanisms of Cu2+ by 1 were explained by theoretical calculations.

A single fluorescent chemosensor for multiple targets of Cu2+, Fe2+/3+ and Al3+ in living cells and a near-perfect aqueous solution

A sulfonate-based chemosensor 1 was designed and synthesized for sensing various analytes: Cu2+, Fe2+/3+ and Al3+. Sensor 1 showed a high selectivity and sensitivity for the analytes in a near-perfect aqueous medium. Cu2+ and Fe2+/3+ could be monitored by fluorescence quenching of 1. It had sufficiently low detection limits (1.25 μM for Cu2+ and 3.96 μM for Fe3+), which were below the recommended levels of the World Health Organization for Cu2+ (31.5 μM) and the Environmental Protection Agency for Fe3+ (5.37 μM). 1 showed the high preferential selectivity for Cu2+ and Fe3+ in the presence of competitive metal ions without any interference. Importantly, pyrophosphate could be used to distinguish Fe3+ from Cu2+. In addition, this sensor could monitor Al3+ through fluorescence emission change. Moreover, 1 was successfully applied to quantify and image Al3+ in water samples and living cells. Based on photophysical studies and theoretical calculations, the sensing mechanisms of 1 for Cu2+ and Al3+ were explained, respectively.

A novel displacement-type colorimetric chemosensor for the detection of Cu2+ and GSH in aqueous solution

A new and simple colorimetric chemosensor 1 was developed for the sequential detection of Cu2+ and glutathione (GSH) in aqueous solution. Receptor 1 detected Cu2+ ions by changing its color from colorless to yellow. Based on UV-vis titrations, Job plot, and ESI-mass spectrometry analysis, the sensing mechanism for Cu2+ was proposed to be the enhancement of the intramolecular charge transfer band, which was further explained by theoretical calculations. The detection limit of 1 for Cu2+ (3.89 μM) was below the World Health Organization (WHO) guideline for drinking water (31.5 μM). Moreover, the resulting 1–Cu2+ complex could sequentially sense GSH, showing recovery of 1 from the complex.

A colorimetric F− chemosensor with high selectivity: experimental and theoretical studies

A new and simple colorimetric receptor 1, based on the combination of 2-amino-4-methylphenol moiety and julolidine moiety, has been designed and synthesized. 1 showed a selective colorimetric sensing ability toward F− ion by changing color from yellow to orange, and could be utilized to monitor F− without any inhibition by competitive anions such as CH3COO− and CN−. Based on Job plot, ESI-mass spectrometry and the 1H NMR titration, the binding mode of 1 for F− was proposed to be 1:1. Moreover, the sensing mechanism for F− was theoretically supported by DFT and TD-DFT calculations.Graphical Abstract