Ye Won Choi

Dual-channel detection of Cu2+ and F− with a simple Schiff-based colorimetric and fluorescent sensor

A simple and easily synthesized colorimetric and fluorescent receptor 1, based on 4-diethylaminosalicylaldehyde moieties as a binding and signaling unit, has been synthesized and characterized. The receptor 1 has a selective colorimetric sensing ability for copper (II) ion by changing color from colorless to yellow in aqueous solution, and could be utilized to monitor Cu(II) over a wide pH range of 4-11. In addition, the detection limit (12μM) of 1 for Cu(2+) is much lower than that (30μM) recommended by WHO in drinking water, and its copper complex could be reversible simply through treatment with a proper reagent such as EDTA. Moreover, receptor 1 exhibited both a color change from colorless to yellow and fluorescence enhancement with a red shift upon addition to F(-) in DMSO. The recognition mechanism was attributed to the intermolecular proton transfer between the hydroxyl group of the receptor and the fluoride.

A highly selective and sensitive fluorescent turn-on Al3+ chemosensor in aqueous media and living cells: experimental and theoretical studies

A highly selective and sensitive fluorescent chemosensor (1) based on a 2-aminobenzoic acid Schiff base has been synthesized in one step. The binding properties of 1 with metal ions were investigated by fluorescence, UV-vis, 1H NMR and electrospray ionization mass spectra. This sensor exhibited enhanced fluorescence in the presence of Al3+ in aqueous solution and also in living cells. The sensing mechanism of 1 toward Al3+ was explained by DFT/TDDFT calculations. The binding constant was determined to be 3.1 × 108 M−1 which is one of the highest binding affinities among such simple Schiff bases for Al3+ in buffer solution. The calibration curve for the analytical performance of Al3+ was found to be linear over a concentration range with a very low detection limit of 290 nM (3σ).

Fluorescence ‘on–off–on’ chemosensor for the sequential recognition of Hg2+ and cysteine in water

A simple fluorescent chemosensor 1 for the sequential detection of Hg2+ and cysteine was developed by combination of benzene-1,2-diamine and 6-bromopyridine-2-carboxaldehyde. The sensor 1 exhibited an ‘on–off’ fluorescent quenching response in the presence of Hg2+, and could be applied for detection of Hg2+ with a good recovery in water samples. The sensing mechanism of 1 for Hg2+ was supported by theoretical calculations. Moreover, the resulting Hg2+–2·1 complex acted as an efficient ‘off–on’ sensor for cysteine, showing recovery of 1 from Hg2+–2·1 complex. Therefore, the sensor 1 can be employed as a practical fluorescent chemosensor for recognition of Hg2+ and cysteine in aqueous solution.

A highly selective fluorescent chemosensor based on a quinoline derivative for zinc ions in pure water

A new simple receptor 1 based on quinoline was synthesized as a water-soluble fluorescent ‘turn-on’ chemosensor for zinc ions. In 100% aqueous buffer solution, sensor 1 displayed a selective fluorescence enhancement (317-fold) at 536 nm with Zn2+. The detection limit (4.48 μM) of 1 for Zn2+ was far below the WHO guideline (76 μM) in drinking water. Importantly, sensor 1 could be used to detect and quantify Zn2+ in water samples. Moreover, the sensing ability of 1 for Zn2+ was supported by theoretical calculations. Thus, this sensor 1 has the ability to be a practical system for monitoring Zn2+ concentrations in aqueous samples.

Chromogenic naked-eye detection of copper ion and fluoride

A bi-functional colorimetric chemosensor 1, based on julolidine moiety and N-(2-aminoethyl)-5-nitropyridin-2-amine, has been synthesized and characterized. The sensor 1 has proven to be highly selective and sensitive to Cu2+ with a color change from colorless to yellow in aqueous solution. The sensing mechanism of 1 for Cu2+ was proposed to be the ligand-to-metal charge-transfer (LMCT), which was explained by theoretical calculations. It was also found that the 1–Cu2+ complex could be recycled simply through treatment with an appropriate reagent such as EDTA. Importantly, the sensor 1 could be used to detect and quantify Cu2+ in water samples. Moreover, 1 showed a selective colorimetric response toward fluoride due to the increase in the intramolecular charge transfer (ICT) band by a deprotonation process without any inhibition from other anions such as CH3COO− and CN−.

Distinction between Mn(III) and Mn(II) by using a colorimetric chemosensor in aqueous solution

A new colorimetric chemosensor for Mn(III) and Mn(II) was developed by combination of 2-(aminomethyl)aniline and 4-(diethylamino)-2-hydroxybenzaldehyde. This sensor 1 exhibited an obvious color change from pale yellow to reddish brown in the presence of Mn3+ in aqueous solution (buffer/CH3CN = 7 : 3), which was reversible with the addition of EDTA. Moreover, 1 could be used to detect and quantify Mn3+ in water samples, and as a practical, visible colorimetric test kits for Mn3+. Moreover, 1 could detect Mn2+ via the formation of 1–Mn3+ complex with longer reaction time. The resulting different reaction time of Mn(III) and Mn(II) with 1 was used to differentiate between Mn(III) and Mn(II). Finally, the sensing ability of 1 for Mn3+ was supported by theoretical calculations.