Jinheung Kim

A near-infrared fluorescent sensor for detection of cyanide in aqueous solution and its application for bioimaging

A new NIR fluorescent sensor based on an amine-substituted heptamethine cyanine dye displayed a highly selective fluorescence enhancement with cyanide in aqueous solutions, and was applied for the imaging of anthropogenic and biogenic cyanide.

Salicylimine-Based Fluorescent Chemosensor for Aluminum Ions and Application to Bioimaging

In this study, an assay to quantify the presence of aluminum ions using a salicylimine-based receptor was developed utilizing turn-on fluorescence enhancement. Upon treatment with aluminum ions, the fluorescence of the sensor was enhanced at 510 nm due to formation of a 1:1 complex between the chemosensor and the aluminum ions at room temperature. As the concentration of Al(3+) was increased, the fluorescence gradually increased. Other metal ions, such as Na(+), Ag(+), K(+), Ca(2+), Mg(2+), Hg(2+), Mn(2+), Co(2+), Ni(2+), Cu(2+), Zn(2+), Cd(2+), Pb(2+), Cr(3+), Fe(3+), and In(3+), had no such significant effect on the fluorescence. In addition, we show that the probe could be used to map intracellular Al(3+) distribution in live cells by confocal microscopy.

Axial ligand tuning of a nonheme iron(IV)–oxo unit for hydrogen atom abstraction

The reactivities of mononuclear nonheme iron(IV)–oxo complexes bearing different axial ligands, [FeIV(O)(TMC)(X)]n+ [where TMC is 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane and X is NCCH3 (1-NCCH3), CF3COO− (1-OOCCF3), or N3− (1-N3)], and [FeIV(O)(TMCS)]+ (1′-SR) (where TMCS is 1-mercaptoethyl-4,8,11-trimethyl-1,4,8,11-tetraazacyclotetradecane), have been investigated with respect to oxo-transfer to PPh3 and hydrogen atom abstraction from phenol OH and alkylaromatic CH bonds. These reactivities were significantly affected by the identity of the axial ligands, but the reactivity trends differed markedly. In the oxidation of PPh3, the reactivity order of 1-NCCH3 > 1-OOCCF3 > 1-N3 > 1′-SR was observed, reflecting a decrease in the electrophilicity of iron(IV)–oxo unit upon replacement of CH3CN with an anionic axial ligand. Surprisingly, the reactivity order was inverted in the oxidation of alkylaromatic CH and phenol OH bonds, i.e., 1′-SR > 1-N3 > 1-OOCCF3 > 1-NCCH3. Furthermore, a good correlation was observed between the reactivities of iron(IV)–oxo species in H atom abstraction reactions and their reduction potentials, Ep,c, with the most reactive 1′-SR complex exhibiting the lowest potential. In other words, the more electron-donating the axial ligand is, the more reactive the iron(IV)–oxo species becomes in H atom abstraction. Quantum mechanical calculations show that a two-state reactivity model applies to this series of complexes, in which a triplet ground state and a nearby quintet excited-state both contribute to the reactivity of the complexes. The inverted reactivity order in H atom abstraction can be rationalized by a decreased triplet-quintet gap with the more electron-donating axial ligand, which increases the contribution of the much more reactive quintet state and enhances the overall reactivity.

A Photocatalyst–Enzyme Coupled Artificial Photosynthesis System for Solar Energy in Production of Formic Acid from CO2

The photocatalyst-enzyme coupled system for artificial photosynthesis process is one of the most promising methods of solar energy conversion for the synthesis of organic chemicals or fuel. Here we report the synthesis of a novel graphene-based visible light active photocatalyst which covalently bonded the chromophore, such as multianthraquinone substituted porphyrin with the chemically converted graphene as a photocatalyst of the artificial photosynthesis system for an efficient photosynthetic production of formic acid from CO(2). The results not only show a benchmark example of the graphene-based material used as a photocatalyst in general artificial photosynthesis but also the benchmark example of the selective production system of solar chemicals/solar fuel directly from CO(2).

Label-free dual assay of DNA sequences and potassium ions using an aptamer probe and a molecular light switch complex

A homogeneous assay is reported using Ru(phen)(2)(dppz)(2+) and a K(+)-binding aptamer for the selective and sensitive detection of a target oligonucleotide and potassium ions, based on reduction in fluorescence emission according to the formation of the G-quadruplex structure from the aptamer in the presence of K(+).

Neutron beam test of CsI crystal for dark matter search

Abstract We have studied the response of Tl- and Na-doped CsI crystals to nuclear recoils and γs below 10 keV . The response of CsI crystals to nuclear recoil was studied with mono-energetic neutrons produced by the 3 H ( p , n ) 3 He reaction. This was compared to the response to Compton electrons scattered by 662 keV γ-ray. Pulse shape discrimination between the response to these γs and nuclear recoils was studied, and quality factors were estimated. The quenching factors for nuclear recoils were derived for both CsI(Na) and CsI(Tl) crystals.Abstract We have studied the response of Tl- and Na-doped CsI crystals to nuclear recoils and γs below 10 keV . The response of CsI crystals to nuclear recoil was studied with mono-energetic neutrons produced by the 3 H ( p , n ) 3 He reaction. This was compared to the response to Compton electrons scattered by 662 keV γ-ray. Pulse shape discrimination between the response to these γs and nuclear recoils was studied, and quality factors were estimated. The quenching factors for nuclear recoils were derived for both CsI(Na) and CsI(Tl) crystals.

Effects of niobium doping on microstructures and ferroelectric properties of bismuth titanate ferroelectric thin films

Abstract Bi 4 Ti 3 O 12 thin films doped with 3 mol.% niobium were prepared on Pt/Ti/SiO 2 /Si substrates by sol–gel method. The niobium-doped Bi 4 Ti 3 O 12 (Nb–BiTiO) films annealed at 700 °C for 30 min in oxygen showed randomly oriented layered perovskite structures and was composed of plate-like and rod-like grains with no crack. The remanent polarization (2 P r ) and coercive field (2 E c ) of the Nb–BiTiO film annealed at 700 °C were 28 μC/cm 2 and 110 kV/cm, respectively. In addition, the film showed good switching endurance under bipolar pulse at least up to 4.5×10 10 cycles. Substitution of Nb in BiTiO thin films was effective for reducing the oxygen vacancies and generating good ferroelectric properties.

Ferroelectric properties of vanadium-doped Bi4Ti3O12 thin films deposited by a sol–gel method

We report the enhancement of ferroelectric properties in vanadium-doped Bi4Ti3O12 (BIT) thin films deposited by a sol–gel method. Compared to the undoped BIT, V-doped BIT (BTV) showed higher polarizations and a better fatigue resistance as reported in ceramic systems recently [Noguchi et al., Appl. Phys. Lett. 78, 1903 (2001)]. BTV showed a remanent polarization (2Pr) of 15.9 μC/cm2, higher than the value for BIT, 12.5 μC/cm2. The polarization of the BTV thin film capacitor decreased by 19%, while that of the BIT decreased by 23% after the fatigue test with 4×1010 switching cycles.

Selective fluorescence assay of aluminum and cyanide ions using chemosensor containing naphthol

The selective assay of aluminum and cyanide ions is reported using fluorescence enhancement and quenching of a phenol–naphthol based chemosensor (PNI) in aqueous and nonaqueous solvents, respectively. PNI gave no significant fluorescence in water. The binding properties of PNI with metal ions were investigated by UV-vis, fluorescence, and electrospray ionization mass spectrometry in a Bis–Tris buffer solution. The addition of aluminum ions switches on the fluorescence of the sensor PNI in water, comparable to relatively very low fluorescence changes in the presence of various other metal ions. The complex stability constant (Ka) for the stoichiometric 1 : 1 complexation of PNI with aluminium ions was obtained by fluorimetric titrations and NMR experiments. However, upon treatment with cyanide ions, the fluorescence of PNI was selectively turned off and the yellow solution of PNI turned to red in methanol. Other comparable anions, such as F−, Cl−, Br−, I−, CH3COO−, and H2PO4−, afforded no apparent fluorescence quenching. The interaction of PNI with cyanide ions was studied by NMR experiments.

Screening and Characterization of High-Affinity ssDNA Aptamers against Anthrax Protective Antigen

The protective antigen (PA) of Bacillus anthracis is a secreted protein that functions as a critical virulence factor. Protective antigen has been selected as a biomarker in detecting bacterial infection. The in vitro selection method, systematic evolution of ligands by exponential enrichment (SELEX), was used to find single-stranded DNAs that were tightly bound to PA. After 8 rounds of the SELEX process with PA, 4 different oligonucleotides (referred to as aptamers) that contain a 30-residue ssDNA sequence were identified. Dissociation constant (Kd) values with Cy3-attached aptamers were determined via fluorophotometry to be within a nanomolar range. The authors attempted to visualize the detection of PA using an aptamer-based enzyme-linked immunosorbent assay method, which has proven to be successful within a nanomolar Kd value range. Furthermore, 2 of the 4 aptamers exhibited specificity to PA against bovine serum albumin and bovine serum. The results of this study demonstrate the analytical potential of an oligonucleotide-based biosensor for a wide variety of applications, particularly in diagnosing disease through specific protein biomarkers.