• Journal of Microbiology
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• v.33 no.3
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• pp.215-221
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• 1995

S. coelicolor A3(2) cells were treated with various redox-cycling agents on nutrient agar plates and examined for their effect on the growth and differentiation. When treated with plumbagin, severe effect on cell viability was observed at concentrations above 250 $\mu$M. However, the surviving colonies differentiated normally. When treated with 100 $\mu$M paraquat, growth rate was decreased and morphological differentiation was inhibited, while the survival rate was maintained at about 100% even at 5 mM paraquat. Menadione or lawsone did not cause any visible changes at concentrations up to 1 mM. The effect of paraquat was also observed when it was added to nutrient agar plate before spore inoculation. Paraquat had also observed when it was added to nutrient agar plate before spore inoculation. Paraquat had no effect on colonies growing on R2YE agar plates. Among the components of R2YE medium selectively added to nutrient agar medium, CaCl$_2$ was found to have some protective function from the inhibitory effect of paraquat. As a first step to study the mechanism of the inhibitory effect of paraquat on differentiation, resistant mutants which sporulate well in the presence of paraquat were screened following UV mutagenesis. Three paraquat-resistant mutants were isolated with a frequency of 3 $\times$10${-5}$. Their mutation sites were determined by genetic crossings. All three mutations were mapped to a single locus near arg4 at about 1 o'clock on the genetic map of S. coelicolor A3(2).

• The Korean Journal of Pharmacology
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• v.27 no.2
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• pp.155-166
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• 1991

In order to evaluate a potential role of mitochondria in the mediation of toxicity of paraquat (PQ), submitochondrial particle and microsome of mouse liver were compared by oxygen radical generation and lipid peroxidation. With NADH in submitochondrial particle and NADPH in microsome as electron donors, PQ stimulated production of superoxide anion and $H_2O_2$ in both fractions. Under the same conditions, PQ enhanced the generation of ethylene from methional suggestiong stimulation of OH production by PQ. But these effects by PQ were somewhat lower in submitochondrial particle than in microsome. In addition, lipid peroxidation(measured as MDA production) was stimulated by PQ in both fractions. The stimulation of lipid peroxidation in both fractions seemed to occur by the same mechanism probably through perferryl ion. This was supported by the following findings: i) The lipid peroxidation in both fractions was partially inhibited by SOD and completely inhibited by DETAPAC(an iron chelator) but not by catalase or OH scavenger. ii) Addition of $ADP-Fe^{3+}$ further increased PQ-induced lipid peroxidation but decreased ethylene production from methional suggesting no correlation between OH production and lipid peroxidation. The redox-cycling of PQ in mitochondria appeared to be linked to NADH dehydrogenase, not to CoQ since all of the observed stimulations by PQ in submitochondrial particle were inhibited by p-hydroxymercuribenzoate(a NADH dehydrogenase inhibitor) but not affected by other respiratory chain blockers. The above results demonstrate that redox-cycling properties of PQ leading to oxygen radical generation and lipid peroxidation can also occur in mitochondria in the same manner as in microsome. Therefore, the observed actions of PQ in mitochondria suggest that mitochondria may also contribute to toxicity of this drug in vivo.

• Journal of Electrochemical Science and Technology
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• v.9 no.3
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• pp.220-228
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• 2018

This study introduced a carbon-free electrode for $Li-O_2$ cells with the aim of suppressing the side reactions activated by carbon material. Micro-particles of poly(3,4-ethylenedioxythiophene) (PEDOT), a conducting polymer, were used as the base material for the air electrode of $Li-O_2$cells. The PEDOT micro-particles were treated with $H_2SO_4$ to improve their electronic conductivity, and LiBr and CsBr were used as the redox mediators to facilitate the dissociation of there action products in the electrode and reduce the over-potential of the $Li-O_2$ cells. The capacity of the electrode employing PEDOT micro-particles was significantly enhanced via $H_2SO_4$ treatment, which is attributed to the increased electronic conductivity. The considerable capacity enhancement and relatively low over-potential of the electrode employing $H_2SO_4$-treated PEDOT micro-particles indicate that the treated PEDOT micro-particles can act as reaction sites and provide storage space for the reaction products. The cyclic performance of the electrode employing $H_2SO_4$-treated PEDOT micro-particles was superior to that of a carbon electrode. The results of the Fourier-transform infrared spectroscopic analysis showed that the accumulation of residual reaction products during cycling was significantly reduced by introducing the carbon-free electrode based on $H_2SO_4$-treated PEDOT micro-particles, compared with that of the carbon electrode. The cycle life was improved owing to the effect of the redox mediators. The refore, the use of the carbon -free electrode combined with redox mediators could realize excellent cyclic performance and low over-potential simultaneously.

• Journal of Electrochemical Science and Technology
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• v.14 no.2
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• pp.152-161
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• 2023

Vanadium redox flow batteries (VRFBs) have been considered one of promising power sources for large scale energy storage systems (ESS) because of their excellent cycle performance and good safety. However, VRFBs still have a few challenging issues, such as poor Coulombic efficiency due to vanadium crossover between catholyte and anolyte, although recent efforts have shown promise in electrochemical performance. Herein, the vanadium complexes with various glyme ligands have been examined as active materials to suppress vanadium crossover between catholyte and anolyte, thus improving the Coulombic efficiency of VRFBs. The conventional Nafion membrane has a channel size of ca. 10 Å, whereas vanadium cation species are small compared to the Nafion membrane channel. For this reason, vanadium cations can permeate through the Nafion membrane, resulting in significant vanadium crossover during cycling, although the Nafion membrane is a kind of ion-selective membrane. In this regard, various glyme additives, such as 1,2-dimethoxyethane (monoglyme), diethylene glycol dimethyl ether (diglyme), and tetraethylene glycol dimethyl ether (tetraglyme) have been examined as complexing agents for vanadium cations to increase the size of vanadium-ligand complexes in electrolytes. Since the size of vanadium-glyme complexes is proportional to the chain length of glymes, the vanadium permeability of the Nafion membrane decreases with increasing the chain length of glymes. As a result, the vanadium complexes with tetraglyme shows the excellent electrochemical performance of VRFBs, such as stable capacity retention (90.4% after 100 cycles) and high Coulombic efficiency (98.2% over 100 cycles).

• Korean Chemical Engineering Research
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• v.56 no.6
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• pp.890-894
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• 2018

In this study, methylene blue which is one of dye materials was introduced as active material for aqueous redox flow battery. The redox potential of methylene blue was shifted to negative direction as pH increased. The full-cell performance was evaluated by using methylene blue as the negative active material and vanadium as the positive active material with acid supporting electrolytes. The cell voltage of methylene $blue/V^{4+}$ is very low (0.45 V). In addition, the maximum solubility of methylene blue in water is only 0.12 M. Therefore, the cell test was performed with very low concentration (0.0015 M methylene blue, $0.15M\;V^{4+}$) at first time. Cut-off voltage range was 0 to 0.8 V and $1mA{\cdot}cm^{-2}$ current density was adopted during cycling. As a result, current efficiency (CE) was 99.67%, voltage efficiency (VE), 88.83% and energy efficiency (EE) was 85.87% and discharge capacity was ($0.0500Ah{\cdot}L^{-1}$) at 4 cycle. In addition, the cell test was performed with increased concentration (0.1 M methylene blue, $0.15M\;V^{4+}$) with $10mA{\cdot}cm^{-2}$ current density, leading to higher discharge capacity ($3.8122Ah{\cdot}L^{-1}$) with similar efficiency (CE=99%, VE=85%, EE=85% at 4 cycle).

• Journal of Microbiology and Biotechnology
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• v.16 no.3
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• pp.386-390
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• 2006

A green fluorescent protein-based Pseudomonas putida reporter was successfully constructed and shown to be capable of detecting oxidative stress. In this whole-cell reporter, the promoter of the paraquat-inducible ferredoxin-$NADP^+$ reductase (fpr) was fused to a promoterless gfp gene on a broad-host-range promoter probe vector. Pseudomonas putida KT2440 harboring this reporter plasmid exhibited an increased level of gfp expression in the presence of redox-cycling agents (paraquat and menadione), hydrogen peroxide, and potential environmental pollutant chemicals such as toluene, paint thinner, gasoline, and diesel. Induction of fpr in the presence of these chemicals was confirmed using Northern blot analysis.

• Microbiology and Biotechnology Letters
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• v.28 no.1
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• pp.1-7
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• 2000

The bacterial strain JW-2 which conferred resistance against paraquat (1,1'-dimethyl-4,4'-bipyridinium dichloride) was isolated from soil. The strain was identified as an Ochrobactrum anthropi based on its morphological, physiological, biological and fatty acid composition, and was designated as Ochrobactrum anthropi JW-2. We compard paraquat resistance of O. anthropi JW-2 with Escherichia coli J105. In the presence of 100mM paraquat, E. coli JM105 was not grown whereas the growth rate of O. anthropi was about 70% of control. We compared the sensitivity of O. anthropi JW-2 and E. coli J105 to redox-cycling compounds such as paraquat, plumbagin or menadione, which are known to exacebate wuperoxide generation. O. anthropi JW-2 did not show cross-resistance to plumbagin or menadione. superoxide dismutase activity was increased in paraqunt-treated E. coli JM105 while it was not increased in O.anthropi JW-2. These results suggest that the mechanism of paraquat resistance in O.anthropi JW-2 is probably due to selectively decreased permeability toward paraquat by membrane protein.

• Proceedings of the Korean Society of Applied Pharmacology
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• 1992.05a
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• pp.41-41
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• 1992

새로이 합성된 1,4-Naphthoquinone(1,4-NQ) 화합물의 세포독성의 확인과 그 작용기전을 규명코져 본 실험을 수행하였다. 분리된 흰쥐 간세포를 1,4-NQ유도체들과 반응 시켰을때 이들 중 YC 001과 YC 008은 독성을 나타냈으나 YC 012는 독성율 나타내지 아니하였다. 세포독성은 세포치사, lactate dehydrogenase 유출 및 산소소비의 억제등으로 확인하였다. 세포 독성의 기전은 mitochondria에서의 전자흐름 차단작용과 microsome에서 redox-cycling 기전에 의한 산소리디칼 생성의 두가지에 대하여 검토하였다. 분리된 mitochondria를 YC 001과 YC 008은 반응 시켰을때 mitochondria의 호흡은 완전히 억제되었다. 그러나 YC 012는 전혀 작용을 나타내지 아니하였다. 이는 간세포에 대한 독성작용과 일치하는 결과이며 따라서 mitochondria에 대한 억제 작용은 이들의 세포독성에 주요한 요인이라고 추측되었다.

• Proceedings of the KIEE Conference
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• 1996.07c
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• pp.1703-1706
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• 1996

The purpose of this study is to research and develop polypyrrole(PPy) positive for thin film rechargeable lithium battery. We investigated cyclic voltammetry, AC impedance response and charge/discharge cycling of PPy/SPE/Li cells as a function of temperature. The redox capacity of $PPy/CF_{3}SO_{3}$ film was the most large. The discharge capacity of PPy/SPE/Li cell with $PPy/CF_{3}SO_{3}$ film was higher than those of $PPy/ClO_{4}$ and $PPy/AsF_6$ films at all cycles. The energy density of PPy/SPE/Li cells during 1st cycle was 73, 90 and 101Wh/kg at $25^{\circ}C$, $45^{\circ}C$ and $60^{\circ}C$, respectively. The improvement of energy density is due to reduction of charge-transfer resistance associated doping-undoping process in PPy film with Increasing temperature. $PPy/CF_{3}SO_{3}$ film shows a good property on charge/discharge cycling in PEO-$LiClO_4$-PC-EC electrolyte.

• Proceedings of the Korea Crystallographic Association Conference
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• 2002.11a
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• pp.16-16
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• 2002

The presently commercialized lithium-ion batteries use layer structured LiCoO₂ cathodes. Because of the high cost and toxicity of cobalt, an intensive search for new cathode materials has been underway in recent years. Recently, a concept of a one-to-one solid state mixture of LiNO₂ and LiMnO₂, i.e., Li[Ni/sub 0.5/Mn/sub 0.5/]O₂, was adopted by Ohzuku and Makimura to overcome the disadvantage of LiNiO₂ and LiMnO₂. Li[Ni/sub 0.5/Mn/sub 0.5/]O₂ has the -NaFeO₂ structure, which is characteristic of the layered LiCoO₂ and LiNiO₂ structures and shows excellent cycleability with no indication of spinel formation during electrochemical cycling. Layered Li[Ni/sub x/Co/sub 1-2x/Mn/sub x/]O₂ (x = 0.5 and 0.475) materials with high homogeneity and crystallinity were synthesized using a mechanical alloying method. The Li[Ni/sub 0.475/Co/sub 0.05/Mn/sub 0.475/]O₂ electrode delivers a high discharge capacity of 187 mAh/g between 2.8 and 4.6 V at a high current density of 0.3 mA/㎠(30 mA/g) with excellent cycleability. The charge/discharge and differential capacity vs. voltage studies of the Li[Ni/sub x/Co/sub 1-2x/Mn/sub x/]O₂ (x = 0.5 and 0.475) materials showed only one redox peak up to 50 cycles, which indicates that structural phase transitions are not occurred during electrochemical cycling. The magnitude of the diffusion coefficients of lithium ions for Li[Ni/sub x/Co/sub 1-2x/Mn/sub x/]O₂(x = 0.5 and 0.475) are around 10/sup -9/ ㎠/s measured by the galvanostatic intermittent titration technique (GITT).