• Proceedings of the PSK Conference
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• 2003.04a
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• pp.263.2-263.2
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• 2003

There is now increasing evidence that free radicals and active oxygen species are involved in a variety of pathological events. Free radical-mediated cell damage and free radical attack on polyunsaturated fatty acids result in the formation of lipid radicals. These lipid radicals react readily with molecular oxygen to produce peroxy radicals responsible for initiating lipid peroxidation. The peroxidation of cellular membrane lipid can lead to cell necrosis and considered to ve implicated in a number of pathophysiological conditions including liver disease. (omitted)

• Clean Technology
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• v.26 no.3
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• pp.204-210
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• 2020

In this study, the ignition characteristics of bio jet fuel (Bio-7629, Bio-5172) produced by F-T process and petroleum-based jet fuel (Jet A-1) were compared and analyzed. The ignition delay time of each fuel was measured by means of a combustion research unit (CRU) and the results were explained through an analysis of the properties and composition of the fuel. The ignition delay time of Bio-5172 was the shortest while that of Jet A-1 was the longest because Jet A-1 had the highest surface tension and Bio-5172 had the lowest viscosity in terms of fuel properties that could affect the physical ignition delay time. As a result of the analysis of the constituents' type and ratio, 22.8% aromatic compounds in Jet A-1 could generate benzyl radical, which had low reactivity during the oxidation reaction, affecting the increase of ignition delay time. Both Bio-7629 and Bio-5172 were composed of paraffin only, with the ratio of n-/iso- being 0.06 and 0.80, respectively. The lower the degree of branching is in paraffin, the faster the isomerization of peroxy radical is produced during oxidation, which could determine the propagation rate of the ignition. Therefore, Bio-5172, composed of more n-paraffin, possesses shorter ignition delay time compared with Bio-7629.

• Korean Journal of Pharmacognosy
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• v.39 no.3
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• pp.260-264
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• 2008

Eight compounds were isolated from the EtOAc soluble fraction of Euphorbia supina MeOH extract as the radical scavengers for antioxidant activity. Their structures were identified as kaempferol (1), quercetin (2), juglanin (3), avicularin (4), astragalin (5), isoquercitrin (6), hyperin (7), and nicotiflorin (8) by spectroscopic analysis. The antioxidant activity was evaluated by the ORAC (oxygen radical absorbance capacity) assay, which measures scavenging activity against peroxy radicals induced by 2,2'-azobis (2-methylpropionamidine) dihydrochloride, and the ORAC value is expressed as relative trolox equivalent. Compounds 4, 6, and 7 exhibited potent antioxidant activity, whereas the other compounds showed weaker activity than trolox.

• Proceedings of the Korea Air Pollution Research Association Conference
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• 2003.11a
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• pp.315-316
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• 2003

대기중 광화학반응에서 생산되는 이차 생성물중의 하나인 $H_2O$$_2$(hydrogen peroxide)는 peroxy radicals간의 결합에 의해 생성된다. HO$_2$ + HO$_2$ $\longrightarrow$ $H_2O$$_2$+ $O_2$ 이렇게 생성된 $H_2O$$_2$는 대기중에서 주요 산화제로 작용하며, pH 4.5 이하 수용액 내에서 S(IV)를 S(VI)로 산화시켜 H$_2$SO$_4$(sulfuric acid)를 생성 한다. 또한 $H_2O$$_2$는 대기중에서 odd-hydrogen radicals(OH, HO$_2$, and RO$_2$)의 저장고 역할과 함께 odd-hydrogen radical의 생성과 소멸에 작용하여 대기의 산화력을 반영한다(Lee et al. 2000). (중략)

• Macromolecular Research
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• v.15 no.5
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• pp.418-423
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• 2007

A methacrylate copolymer based on isobornyl methacrylate (IBMA) and methyl methacrylate (MMA) was synthesized in an aqueous suspension via free-radical polymerization. The potential of this copolymer as a heat-resistant optical polymer is also discussed. 1,1,3,3-tetramethylbutyl peroxy-2-ethyl hexanoate and n-octyl mercaptan were used as the initiator and chain transfer agents, respectively. The effect of IBMA on the properties of the copolymer was investigated. The composition of the copolymer was analyzed using $^1H-NMR$, and the heat resistance by measuring the glass transition temperature, which exhibited a linear dependency on the IBMA content in the copolymer. Variation of the chain transfer content used in the synthesis step was effective for the optimization of the copolymer for practical use.

• Journal of Ginseng Research
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• v.34 no.3
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• pp.198-204
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• 2010

Korean ginseng (Panax ginseng C.A. Meyer) preserved in syrup, known as ginseng Jung Kwa (GJK), is a popular traditional snack in Korea. We investigated the effects of heat processing time on total phenolic content and antioxidant capacity of GJK. Water extract was prepared from GJK with different heat processing times, 3 hours (GJK-3), 6 hours (GJK-6), or 12 hours (GJK-12), with sonication for 2 hours. The GJK extract contained total phenolic content in the following order: GJK-12 (2.28%)>GJK-6 (1.57%)>GJK-3 (1.29%). Both the peroxy and hydroxyl radical-scavenging activity and cellular antioxidant capacity of GJK extract was significantly enhanced with increasing heat processing time. The hydroxyl radical-scavenging activity of GJK-12 extract was greater than that of the GJK-3 and GJK-6 extracts, consistent with metal chelating capacity and reducing capacity. In a cellular model, the GJK extract effectively reduced 2,2'-azobis(2-amidinopropane) dihydrochloride, $Cu^{2+}$-, and $H_2O_2$-induced oxidative stress, with GJK-12 and GJK-6 extracts demonstrating greater cellular antioxidant capacity than the GJK-3 extract. These results suggest that heat processing time can contribute to the antioxidant capacity of GJK and that GJK extract may have the potential to be used as an effective dietary antioxidant to prevent oxidative stress-related diseases.

• Elastomers and Composites
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• v.55 no.1
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• pp.51-58
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• 2020

In this study, the thermal oxidation of raw natural rubber (NR) was investigated under controlled conditions by optical image and fourier transform infrared (FT-IR) analysis. The thermal oxidation was performed on a transparent thin film of raw NR coated on a KBr window in a dark chamber at 80℃ under low humidity conditions to completely exclude moisture and restrict light oxidation. Images of the thin film of raw NR were obtained before and after thermal oxidation. FT-IR absorption spectra were measured in the transmission mode at different thermal exposure times. The thermal oxidation of NR was examined by the changes in the absorption peaks at 3449, 1736, 1447, 1377, 1242, 1072, and 833 cm^-1, which corresponded to a hydroxyl group (-OH), a carbonyl group (-C=O) from an aldehyde and a ketone, a methylene group (-CH₂-), a methyl group (-CH₃), a carbon-oxygen single bond (-C-O) from an epoxide, a carbon-oxygen bond (-C-O) from an ether, an alcohol, a peroxide, or a cyclic peroxide, and a cis-methine group (cis-CCH₃=CH-), respectively. In the initial stage of thermal oxidation, two different types of free radicals were produced quickly and randomly by the homolytic cleavage of a double bond and allylic hydrogen abstraction. Aldehydes and ketones were formed from chain scissions of the double bonds and alcohols were produced from allylic hydrogen abstraction at the methylene or methyl groups. Two reactions seemed to proceed competitively with each other. At a later stage, oxidative crosslinks seemed to dominate through the combination of free radicals such as an allyl radical (CH=CHCH₂·), alkoxy radical (RO·), and peroxy radical (ROO·) and the reaction of a hydroperoxide (-ROOH) with a double bond. The image obtained after thermal oxidation showed hardening without cracks. Based on these observations, a plausible two-step mechanism was suggested for chain hardening caused by the thermal oxidation.

• Nutritional Sciences
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• v.4 no.2
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• pp.79-84
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• 2001

The influence of Rhodiola extract on tissue antioxidant status, plasma lipid levels, cholesterol contents of liver and fores were investigated in rats find oxidized linoleic acid. Groups of five-week old male Sprague-Dawley rats fed ad libitum with a diet containing 20% oxidized linoleic acid with or without 300 mg/kg body weight freeze-dried Rhodiola water extract. The antioxidant effect of dietary Rhodiola extract supplementation on the peroxidation potential of rats was investigated. The microsomal thiobarbiruric acid reactive substance (TBARS) contents were changed significantly by Rhodiola extract supplementation. Hepatic Catalase activities were increased in Rhodiola supplemented rats, whereas hepatic Manganese Superoxide Dismutase (MnSOD) or Copper Zinc Superoxide Dismutase (CuZnSOD) were not elevated. In addition, plasma cholesterol lowering effect was observed along with the stimulated excretion of cholesterol through the feces were observed with Rhodiola feeding. Supplementation with Rhodiola extract did not alter high density lipoprotein (HDL) cholesterol. These results support that Rhodiola extract may be effective in protection against oxidative stress, and prevention and treatment of blood dyslipidemia. It demonstntes that Rhodiola extract has a potential to exert anti-atherogenic properties antioxidative capacities .

• Advances in Traditional Medicine
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• v.8 no.3
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• pp.266-278
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• 2008

Erythrina stricta, a deciduous tree widely used traditionally in indigenous system of medicine for various ailments such as rheumatism, fever, leprosy, epilepsy etc. The leaves of Erythrina stricta was extracted with ethanol (70%) and used for the evaluation of various in vitro antioxidant assays which includes H - donor activity, nitric oxide scavenging, superoxide anion scavenging, reducing ability, hydroxyl radical, hydrogen peroxide scavenging, total phenolic content, total flavonoid content, total antioxidant activity by thiocyanate and phosphomolybdenum method, metal chelating, $\beta$-carotene bleaching, total peroxy radical assays. The pro-oxidant activity was measured using bleomycin-dependent DNA damage. Ex vivo models like lipid peroxidation and erythrocyte haemolysis were also used to study the antioxidant property of the extract. The various antioxidant activities were compared with suitable standard antioxidants such as ascorbic acid, butylated hydroxyl toluene, $\alpha$-tocopherol, curcumin, quercetin and Trolox. The generation of free radicals viz. $O_2^{{\cdot}-}$, $OH^{\cdot}$, $H_2O_2$, $NO^{\cdot}$ and peroxyl radicals were effectively scavenged by the ethanolic extract of Erythrina stricta. In all the methods, the extract offered strong antioxidant activity in a concentration dependent manner. The total phenolic content, flavonoid content and total antioxidant activity in Erythrina stricta were determined as microgram (g) pyrocatechol, quercetin and $\alpha$-tocopherol equivalent/mg respectively. The extract did not exhibit any prooxidant activity when compared with ascorbic acid. The results obtained in the present study clearly indicates that Erythrina stricta scavenges free radicals and reduces lipid peroxidation, ameliorating the damage imposed by oxidative stress in different disease conditions and serve as a potential source of natural antioxidant.

• Journal of the Korean Chemical Society
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• v.16 no.1
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• pp.40-45
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• 1972

An electron spin resonance study has been made on lysozyme in. frozen aqueous solutions irradiated with $_{60}Co$ r-rays in air at $77^{circ}K.$ Water resonances are dominant when the concentration and the temperature are both below 20% and $130^{circ}K$ respectively. More solute radicals are produced in the solution of higher concentration. Majority of the solute radicals results from direct hit of the radiation. The same types of radicals are induced at $77^{circ}K$ whether the substances are irradiated in the dry state or in frozen aqueous solution. Based on these results, it is assumed that the number of ESR centers produced by the secondary intermolecular radical reacions and stabilized in aqueous solutions may depend on the concentration of the solution, and the presence of water may facilitate the secondary radical reactions occuring in the solute molecules after heat treatment. Majority of the solute radicals above around $193^{circ}K$ are believed to react with oxygen to form peroxytype radicals. However, when the solution is subiected to heat-treatment at $265^{circ}K$ after irradiation at $195^{circ}K$ the peroxy-type resonance was not observed, suggestin that an appreciable amount of oxygen is condensed into the ice, at $77^{circ}K.$ in addition to the oxygen that has already been dissolved in solution and react with solute free radicals during the process of heat-treatment. When the solution contains $H_2O_2$, no water resonance but $HO_2$, type resonance was observed probably indicating that the radiation-induced OH radicals are trapped in $H_2O_2$ aggregates and react readily with $H_2O_2$ molecules to poroduce $HO_2$ type radicals even at $77^{circ}K.$.