• Korean Chemical Engineering Research
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• v.45 no.4
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• pp.345-350
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• 2007

During PEMFC operation, OCV(open circuit voltage) and low humidity conditions accelerate the degradation of perfluorosulfonic acid membrane. There have been no studies that clearly explain why these conditions accelerate the membrane degradation. In this study, the hydrogen permeability through the membrane, I-V polarization of MEA, fluoride emission rate(FER) and $H_2O_2$ concentration in condensed water were measured during cell operation under OCV and low relative humidity(RH). The experimental results were evaluated with oxygen radical mechanism the most commonly known for membrane degradation. It seems that low RH of anode is a good condition for $H{\cdot}$ radical formation on the Pt catalyst and the OCV condition accelerate the $H{\cdot}$ to form $HO_2{\cdot}$ radical attacking the polymer membrane.

• Journal of Food Hygiene and Safety
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• v.17 no.2
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• pp.106-116
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• 2002

The 70% ethanol extract of Alpinia officinarum and its major flavonoid, galangin showed strong antioxidative effect on the lipid peroxidation of ethyl linolate with Fenton's reagent and free radical scavenging effect to DPPH radical generation. However, they did not reveal any pro-oxidant effect on bleomycin-Fe(III) dependent DNA degradation. They also showed the protective effect against $H_2O$$_2$, KO$_2$ or UV-induced cytotoxicity in mammalian cells. They also showed the suppressive effect of DNA damage induced by $H_2O$$_2$ or KO$_2$ with dose-dependent manner in single cell gel electrophoresis(SCGE) assay. On the other hand, they have an anticlastogenic effect against adriamycin-induced micronucleated reticulocyte in peripheral blood of mice. These results suggest that the mechanism of inhibition by 70% ethanol extract of Alpinia officinarum and galangin against reactive oxygen species (ROS)-induced genotoxicity or cytotoxicity is due, at least partly, to their antioxidative and free radical scavenging properties without pro-oxidant effect. All these results indicate that 70% ethanol extract of Alpinia officinarum and galangin may be useful for protection against ROS-induced cytotoxicity and DNA damage.

• Journal of the Korean Society of Food Science and Nutrition
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• v.31 no.1
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• pp.109-116
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• 2002

This study was performed to investigate the effect of kimchi intake on antiaging characteristics in liver of senescence-accelerated mouse (SAM) in terms of free radical production and anti-oxidative enzyme activities. Two hundred twenty SAM were divided into four groups and fed kimchi diet for 12 months. Experimental groups were kimchi free AIN-76 diet (control) group, Korean cabbage kimchi diet (KCK) group, mustard leaf added (30%) Korean cabbage kimchi diet (MKCK) group, and mustard leaf kimchi diet (MLK) group. Amount of freez-dried kimchi added to the diet was 5% that is equivalent to 50 g of fresh kimchi. Concentrations of total free radical, OH radical, $H_2O$$_2$in the liver significantly increased as aged (p<0.05). But those free radical concentrations from kimchi diet groups were lower than those of control (p<0.05). Among kimchi groups, MKCK and MLK groues showed greater inhibiting effect than KCK. Antioxidant enzyme activities of Cu, Zn-SOD, Mn-SOD, GSH-px, catalase and GSH/GSSG in kimchi groups were significantly increased (P

• Journal of the Korean Society of Food Science and Nutrition
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• v.40 no.7
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• pp.1053-1062
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• 2011

Reactive oxygen species (ROS), including singlet oxygen (${O_2}^1$), superoxide anion radical ($O_2{\cdot}^-$), hydroxyl radical ($HO{\cdot}$), peroxyl radical ($ROO{\cdot}$), hydrogen peroxide ($H_2O_2$), and hypochlorous (HOCl), are generated as byproducts of normal cellular metabolism. ROS induce damage to many biological molecules, such as lipids, proteins, carbohydrates, and DNA. It is widely believed that some degenerative diseases caused by ROS can be prevented by the high intake of fruits and vegetables due to their antioxidant activities. Recently, research on natural antioxidants has become increasingly active in various fields. Several assays have been developed to measure the total antioxidant capacity of antioxidants in fruits and vegetables in vitro. These assays include those for DPPH radical scavenging activity, SOD-like activity, total polyphenol content, oxygen radical absorbance capacity, reducing power, trolox equivalent antioxidant capacity (ABTS assay), single-cell gel electrophoresis (comet assay), and a cellular antioxidant activity assay. Because different antioxidant compounds may act through different mechanisms in vitro, no single assay can fully evaluate the total antioxidant capacity of foods. Due to the complexity of the composition of foods, it is important to be able to measure antioxidant activity using biologically relevant assays. In this review, recently used assays were selected for extended discussion, including a comparison of the advantages and disadvantages of each assay and their application to fruits and vegetables.

• Applied Biological Chemistry
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• v.47 no.3
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• pp.293-299
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• 2004

Antioxidant activity of ethanolic extract of two giant embryonic rices, Nampung giant embryonic rice and Hwachung giant embryonic rice, were investigated mainly focusing on their ability to inhibit lipid peroxidation and scavenge reactive oxygen species in comparison with those of general rice. The results showed that germination process increased reducing power, inhibitory activity on lipid peroxidation and scavenging ability either on superoxide or hydroxyl radicals. Among the cultivars tested, increase in antioxidative action was found to be most prominent for Hwachung giant embryonic rice cultivar. For scavenging of superoxide radicals, the extract from Nampung giant embryonic rice has the most potent activity, however, increasing rate of scavenging activity by germination process was also found to be the greatest for Hwachung giant embryonic rice. We found that the scavenging mechanism for superoxide radicals was attributed to the direct scavenging of the radicals. The scavenging of hydroxyl radicals, the most toxic oxygen radical to biological system, by the rice extracts were also examined, and the results showed that either overall activity or the increasing rate of the activity to scavenge hydroxyl radicals by germination process was the greatest for Hwachung giant embryonic rice. Moreover, the results suggested that the scavenging action to hydroxyl radicals might be mediated by direct quenching of the radicals, not by chelating $Fe^{2+}$. Further studies showed that the antioxidant action of the rice extracts tested in vitro was also operative for suppressing ROS production induced in TPA-stimulated HL-60 cells.

• Journal of the Korean Chemical Society
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• v.55 no.5
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• pp.741-745
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• 2011

Well-resolved vibronic emission spectra were recorded in the visible region from the corona discharge of precursor alkylbenzenes in a technique of corona excited supersonic expansion using a pinhole-type glass nozzle. From the observed spectra, we found the evidence of the presence of benzyl-type radicals generated by dissociation of C-C or C-H bonds of alkyl group. After identification of benzyl-type radicals formed in the corona discharge, we suggest that energy densities in alkyl chain play a crucial role in determining the bond dissociation during corona excitation.

• Journal of the Korean Magnetic Resonance Society
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• v.21 no.1
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• pp.1-6
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• 2017

Enhancements in NMR sensitivity have been the main driving force to extend the boundaries of NMR applications. Recently, techniques to shift the thermally populated nuclear spin states are employed to gain high NMR signals. Here, we introduce a technique called photochemically induced dynamic nuclear polarization (photo-CIDNP) and discuss its progresses in enhancing the solution-state NMR sensitivity.

• Textile Coloration and Finishing
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• v.4 no.2
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• pp.64-68
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• 1992

The charge-transfer(CT) complexes derived from phenothiazine as donor and quinonoid compounds as accepters were evaluated as coloring matter. Light fastness of the intermolecular charge-transfer(CT) complex dyes as well as absorption wavelength is an important factor when the complexes are applied to coloring matters. The photofading mechanism of CT complex dyes of phenothiazine and accepters were examined. The addition of effective radical scavenger, antioxidant and photostabilizer gave a remarkable enhancement of the photostability of CT dyes.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2010.06a
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• pp.188-188
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• 2010

Recently, there has been increased incessantly an interest in research area on energy material for electronic and electric energy generation applications. The proposed material takes an unobtrusive operation into the simple displacing mechanism using chemical impact material. However, this material makes up a radical design, based on the operation of the stoichiometry ratio on the material architecture.

• Journal of the Korean Chemical Society
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• v.15 no.6
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• pp.359-366
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• 1971

The extended Huckel calculations on five organic accelerators of vulcanization have been carried out. Various MO quantities e.g., electron populations and AO coefficients, are used to explain accelerator reactivity of the compounds. Results of these analyses lead us to support free radical mechanism of acceleration in vulcanization.