Kwon Hee Bok

Highly selective and sensitive colorimetric chemosensor for detection of Co2+ in a near-perfect aqueous solution

A new simple and easy-to-make colorimetric chemosensor 1 was designed and synthesized by combination of 4-diethylaminosalicylaldehyde and diethylenetriamine. In a near-perfect aqueous solution, sensor 1 showed a selective color change from colorless to yellow in the presence of Co2+ with a 1 : 1 stoichiometric system. To investigate the sensing mechanism of 1 for Co2+, UV-vis spectroscopy, ESI-mass and theoretical calculations were conducted. The detection limit (0.65 μM) of 1 for Co2+ was comparable to the Federal-State Toxicology and Risk Analysis Committee (FSTRAC) guideline in drinking water (0.68 μM). Practically, 1 functioned as a visible test strip with a silica plate and could be used to quantify Co2+ in real water samples. Therefore, probe 1 could be a good alternative method for on-site and real time screening of Co2+.

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 Dual-Channel Chemosensor Based on Chemodosimeter Approach for Detecting Cyanide in Aqueous Solution: a Combination of Experimental and Theoretical Studies

A new colorimetric and fluorescent receptor 1 for the detection of CN− has been simply developed. Receptor 1 showed selectively colorimetric and fluorometric responses to CN− in a near-perfect aqueous solution, respectively. This sensor displayed an obvious color change from yellow to colorless upon selective binding with CN−. In addition, it could function as an “OFF-ON type” fluorescent response through a nucleophilic addition mechanism. The binding mode of receptor 1 with CN− was proposed to be 1:1, based on Job plot, 1H NMR titration and ESI-mass spectrometry analysis. Moreover, the sensing mechanism for CN− was theoretically supported by DFT and TD-DFT calculations.

A fluorescence “turn-on” chemosensor for Hg2+ and Ag+ based on NBD (7-nitrobenzo-2-oxa-1,3-diazolyl)

A new fluorescent sensor 1 was prepared by bridging a 7-nitrobenzo-2-oxo-1,3-diazolyl (NBD) fluorophore with a dimethyl ethylene amine group via an ethylamine spacer. Distinct “turn-on” fluorescence changes of 1 were observed upon the addition of Hg2+ and Ag+ in the aqueous solution. The sensor 1 showed high sensitivity toward Hg2+ and Ag+ with detection limits of 0.05 μM and 0.12 μM, respectively. Moreover, the sensing abilities of 1 for Hg2+ and Ag+ were successfully carried out in real water samples, and 1 functioned as fluorescent test strip with silica plate. The sensing mechanisms of 1 with Hg2+ and Ag+ were studied by using photophysical experiments, NMR titration, and ESI-mass spectrometry analysis. Moreover, turn-on fluorescence of 1 toward Hg2+ and Ag+ caused by photo-induced electron transfer (PET) was explained by density functional theory (DFT) calculations.

Synthesis, Characterization, and Catalytic Activities of A Nickel(II) Monoamido‐Tetradentate Complex: Evidence For NiIII–Oxo and NiIV–Oxo Species

A new mononuclear nickel(II) complex, [NiII (dpaq)Cl] (1), containing a tetradentate monoamido ligand, dpaq (dpaq=2-[bis(pyridin-2-ylmethyl)amino]-N-(quinolin-8-yl)acetamide), has been synthesized and characterized by IR spectroscopy, elemental analysis, and UV/Vis spectroscopy. The structure of the nickel complex has been determined by X-ray crystallography. This nonheme NiII complex 1 catalyzed the epoxidation reaction of a wide range of olefins with meta-chloroperoxybenzoic acid (m-CPBA) under mild conditions. Olefin epoxidation using this catalytic system has been proposed to involve a new reactive NiIV -oxo (4) species, based on the evidence from a PPAA (peroxyphenylacetic acid) probe, Hammett studies, H218 O exchange experiments, and ESI mass spectroscopic analysis. Moreover, the nature of solvent significantly influenced partitioning between heterolytic and homolytic O-O bond cleavage of the Ni-acylperoxo intermediate (2). The O-O bond of 2 proceeded predominantly through heterolytic cleavage in a protic solvent, such as CH3 OH. These results suggest that possibly a NiIV -oxo species is a common reactive intermediate in protic solvents. The two active oxidants, namely NiIV -oxo (3) and NiIII -oxo (4), which are responsible for stereospecific olefin epoxidation and radical-type oxidations, respectively, operate in aprotic solvents.

Synthesis, Characterization, and Efficient Catalytic Activities of a Nickel(II) Porphyrin: Remarkable Solvent and Substrate Effects on Participation of Multiple Active Oxidants

A new nickel(II) porphyrin complex, [NiII (porp)] (1), has been synthesized and characterized by 1 H NMR, 13 C NMR and mass spectrometry analysis. This NiII porphyrin complex 1 quantitatively catalyzed the epoxidation reaction of a wide range of olefins with meta-chloroperoxybenzoic acid (m-CPBA) under mild conditions. Reactivity and Hammett studies, H218 O-exchange experiments, and the use of PPAA (peroxyphenylacetic acid) as a mechanistic probe suggested that participation of multiple active oxidants NiII -OOC(O)R 2, NiIV -Oxo 3, and NiIII -Oxo 4 within olefin epoxidation reactions by the nickel porphyrin complex is markedly affected by solvent polarity, concentration, and type of substrate. In aprotic solvent systems, such as toluene, CH2 Cl2 , and CH3 CN, multiple oxidants, NiII -(O)R 2, NiIV -Oxo 3, and NiIII -Oxo 4, operate simultaneously as the key active intermediates responsible for epoxidation reactions of easy-to-oxidize substrate cyclohexene, whereas NiIV -Oxo 3 and NiIII -Oxo 4 species become the common reactive oxidant for the difficult-to-oxidize substrate 1-octene. In a protic solvent system, a mixture of CH3 CN and H2 O (95:5), the NiII -OOC(O)R 2 undergoes heterolytic or homolytic O-O bond cleavage to afford NiIV -Oxo 3 and NiIII -Oxo 4 species by general acid catalysis prior to direct interaction between 2 and olefin, regardless of the type of substrate. In this case, only NiIV -Oxo 3 and NiIII -Oxo 4 species were the common reactive oxidant responsible for olefin epoxidation reactions.