• Korean Journal of Materials Research
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• v.13 no.6
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• pp.347-351
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• 2003

II-Ⅵ ZnO compound semiconductor thin films were grown on $\alpha$-Al$_2$O$_3$(0001) single crystal substrate by radical beam assisted molecular beam epitaxy and the optical properties were investigated. Zn(6N) was evaporated using Knudsen cell and O radical was assisted at the partial pressure of 1$\times$10$^{4}$ Torr and radical beam source of 250-450 W RF power. In $\theta$-2$\theta$ x-ray diffraction analysis, ZnO thin film with 500 nm thickness showed only ZnO(0002)and ZnO(0004) peaks is believed to be well grown along c-axis orientation. Photoluminescence (PL) measurement using He-Cd ($\lambda$=325 nm) laser is obtained in the temperature range of 9 K-300 K. At 9 K and 300 K, only near band edge (NBE) is observed and the FWHM's of PL peak of the ZnO deposited at 450 RF power are 45 meV and 145 meV respectively. From no observation of any weak deep level peak even at room temperature PL, the ZnO grains are regarded to contain very low defect density and impurity to cause the deep-level defects. The peak position of free exciton showed slightly red-shift as temperature was increased, and from this result the binding energy of free exciton can be experimentally determined as much as $58\pm$0.5 meV, which is very closed to that of ZnO bulk. By van der Pauw 4-point probe measurement, the grown ZnO is proved to be n-type with the electron concentration($n_{e}$ ) $1.69$\times$10^{18}$$cm^3$, mobility($\mu$) $-12.3\textrm{cm}^2$/Vㆍs, and resistivity($\rho$) 0.30 $\Omega$$\cdot$cm.

• Proceedings of the Korea Air Pollution Research Association Conference
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• 2003.05b
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• pp.231-232
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• 2003

과산화수소(hydrogen peroxide, $H_2O$$_2$)는 광화학적 2차 생성물이며, 대기의 산화상태를 알려주는 지시자의 역할을 한다. 과산화수소는 HO$_2$ radical의 self-reaction 으로 생성된다. HO$_2$+ HO$_2$+ M $H_2O$$_2$ + M (1) OH나 HO$_2$ radical은 NOx나 hydrocarbon 과 같은 대표적인 오존 전구물질들을 산화시킨다. 대기 내 수명이 불과 1초 이내인 OH나 HO$_2$ radical을 직접 측정하기란 어려우므로 수명이 1~2 일 정도인 $H_2O$$_2$를 측정하여 이들 radical의 대기 내 농도를 추정할 수 있다. (중략)

• Natural Product Sciences
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• v.9 no.4
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• pp.245-248
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• 2003

A phytochemical investigation on the methanolic extract of Cosmos caudatus has led to the isolation of quercetin $3-O-{\beta}-D-arabinofuranoside$ (1), quercetin $3-O-{\beta}-D-rhamnoside$ (2), quercetin $3-O-{\alpha]-D-glucoside$ (3) and quercetin (4). These compounds were shown to be the antioxidative constituents of the plant when evaluated using the ferric thiocyanate (FTC) and thiobarbituric acid (TBA), and radical scavengers based on the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging assays.

• Archives of Pharmacal Research
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• v.23 no.3
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• pp.237-239
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• 2000

The antioxidant activity of Artemisia montana was determined by measuring the radical scavenging effect on 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical and inhibitory activity against free radical generation of hepatocytes ($AC_2$F). The methanol extract of A. montana showed strong radical scavenging activity at a concentration of $10.1{\mu}g/m{\ell}$, and thus fractionated by solvent extraction. Esculetin and luteolin 7-O-rutinoside (scolymoside) were isolated as the active principles from the EtOAc and interphase fractions, respectively. The antioxidant activity of these compounds were comparable to that of L-ascorbic acid.

• Journal of Environmental Science International
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• v.22 no.12
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• pp.1561-1569
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• 2013

This study carried out a laboratory scale plasma reactor about the characteristics of chemically oxidative species (${\cdot}OH$, $H_2O_2$ and $O_3$) produced in dielectric barrier discharge plasma. It was studied the influence of various parameters such as gas type, $1^{st}$ voltage, oxygen flow rate, electric conductivity and pH of solution for the generation of the oxidant. $H_2O_2$ and $O_3$.) $H_2O_2$ and $O_3$ was measured by direct assay using absorption spectrophotometry. OH radical was measured indirectly by measuring the degradation of the RNO (N-Dimethyl-4-nitrosoaniline, indicator of the generation of OH radical). The experimental results showed that the effect of influent gases on RNO degradation was ranked in the following order: oxygen > air >> argon. The optimum $1^{st}$ voltage for RNO degradation were 90 V. As the increased of $1^{st}$ voltage, generated $H_2O_2$ and $O_3$ concentration were increased. The intensity of the UV light emitted from oxygen-plasma discharge was lower than that of the sun light. The generated hydrogen peroxide concentration and ozone concentration was not high. Therefore it is suggested that the main mechanism of oxidation of the oxygen-plasma process is OH radical. The conductivity of the solution did not affected the generation of oxidative species. The higher pH, the lower $H_2O_2$ and $O_3$ generation were observed. However, RNO degradation was not varied with the change of the solution pH.

• Bulletin of the Korean Chemical Society
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• v.27 no.5
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• pp.663-666
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• 2006

Carnosine, homocarnosine and anserine might act as anti-oxidants and free radical scavengers in vivo. In the present study, the protective effects of carnosine and related compounds on the $H_2O_2$-mediated cytochrome c modification were studied. Carnosine, homocarnosine and anserine significantly inhibited the oligomerization of cytchrome c induced by $H_2O_2$. All three compounds also inhibited the formation of carbonyl compound and dityrosine during the incubation of cytochrome c with $H_2O_2$. These compounds effectively inhibited the peroxidase activity in the cytchrome c treated with $H_2O_2$. The results suggested that carnosine, homocarnosine, and anserine might protect cytochrome c against $H_2O_2$-mediated oxidative damage through a free radical scavenging.

• Journal of the Korean Society of Food Science and Nutrition
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• v.29 no.1
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• pp.106-110
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• 2000

We investigated the active oxygen scavenging activity and active compound from Humulus japonicus. The ethyl acetate and butanol fraction exhibited strong scavenging effects on hydroxyl radical. Furthermore active compound was isolated and purified using Amberlite XAD-2 column chromatography and preparative HPLC from ethyl acetate fracton, and major compound was identified as a luteolin-7-O-$\beta$-D-glucoside by the MS, UV, 1H-NMR and 13C-NMR analyses. Luteolin-7-O-$\beta$-D-glucoside exhibited strong scavenging effect on active oxygens such as superoxide radical, hydroxyl radical and hydrogen peroxide.

• Korean Journal of Pharmacognosy
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• v.41 no.3
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• pp.180-184
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• 2010

The antioxidant activity of Desmodium oldhami (Leguminosae) was determined by measuring the radical scavenging effect on DPPH (1,1-diphenyl-2-picrylhydrazyl). The methanolic extract of D. oldhami showed the strong antioxidant activity. Five compounds, kaempferol-3-O-rhamnopyranoside (afzeline) (1), quercetin-3-O-[$\alpha$-L-rhamnopyranosyl($1{\rightarrow}6$)-$\beta$-Dglucopyranoside] (rutin) (2), kaempferol-3-O-glucopyranoside (astragalin) (3), genistein-7-O-$\beta$-D-glucopyranoside (genistin) (4), kaempferol-3-O-rutinoside (5) were isolated from the active ethyl acetate soluble fraction of D. oldhami through repeated silica gel and Sephadex LH-20 column chromatography. Among them, compound 2 showed the most significant antioxidative effect on DPPH free radical scavenging test. Compounds 1-5 are reported for the first time from this plant.

• The Plant Pathology Journal
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• v.21 no.3
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• pp.283-287
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• 2005

Since the discovery of generation of $O_2^-$ in plant, many evidence for the oxidative burst (OXB) has been accumulated in various combinations of plant and pathogen or elicitor systems. $O_2^-$ generating system responsible for the OXB was coupled with oxidation of reduced nicotinamide adenine dinucleotide phosphate (NADPH) in microsomal fraction isolated from sliced aged potato tuber slices which were treated by hyphal wall components elicitor from Phytophthora infestans (HWC). We developed new assay method for quantitative measurement of oxygen radical $O_2^-$ by using electron spin resonance (ESR) analysis during elicitor­induced OXB on the surface of plant tissues. The ESR analysis using an $O_2^-$ trapper, Tiron (1,2-dihydroxy-3,5­benzenedisulfonic acid), provided a convenient assay for detecting only $O_2^-$ during elicitor-induced OXB producing various active oxygen species (AOS) on plant tissue surface. Tiron was oxidized to Tiron semiquinon radical by $O_2^-$. Quantity of the radical signal was measured by specific spectra on ESR spectroscopy. The level of $O_2^-$ was high in from surface of potato tuber tissue treated with hyphal cell wall elicitor (HWC) from Phytophthora infestans. There was no secondary OXB induction by $H_2O_2$ treatment in plant.

• Archives of Pharmacal Research
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• v.22 no.1
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• pp.81-85
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• 1999

Nine flavonoids (1-9) were isolated from the leaves of Morus alba (Moraceae). The structures of compounds were determined to be kaempferol-3-O-$\beta$-glucopyranoisde (astragalin, 1) kaempferol-3-O-(6"-O-acetyl)-$\beta$-D-glucopyranoside (2), quercetin-3-O-(6"-O-acetyl)-$\beta$-D-glucopyranoside (3), quercetin-3-O-$\beta$-D-glucopyranoside (4), kaempferol-3-O-$\alpha$-L-rhamnopyranosyl-(1 6)-$\beta$-D-glucopyranoside (5), quercetin-3-O-$\alpha$-L-rhamnopyranosyl-(1 6)-$\beta$-D-glucopyranoside (rutin, 6), quercetin-3-O-$\beta$-D-glucopyranosyl-(1 6)-$\beta$-D-glucopyranoside (7), quercetin-3,7-di-O-$\beta$-D-glucopyranoside (8) and quercetin (9) on th basis of spectroscopic and chemical studies. Compounds 7 and 9 exhibited significant radical scavenging effect on 1,1-diphenyl-2-picryl-hydrazyl radical.