• Food Science and Preservation
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• v.9 no.2
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• pp.253-259
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• 2002

The antioxidative and free radical scavenging activity of water extracts of dandelion were investigated. Antioxidative and radical scavenging activity were assessed by means of different tests; inhibition of peroxidation on linoleic acid model system, scavenging DPPH radical, scavenging of hydroxyl radical by chemiluminescence assay, scavenging of superoxide anion radical by EPR spectroscopy and scavenging of hydrogen peroxide. The leaf extract showed strong antioxidant activity in linoleic acid system. The antioxidant activity of water extracts of dandelion increased with increasing concentrations of extracts. The scavenging activity of the dandelion extracts, on inhibition of the DPPH radical, was related to the reaction time. Hydroxyl radical were generated by lenten reaction and dandelion extract was found to scavenge OH˙in a concentration-dependent manner. The water extract of leaf had effective scavenging activities on hydrogen peroxide and superoxide anion radical. From the these data, it is evident that water extract of dandelion leaf is an effective scavenger for OH˙, O$_2$¨, DPPH˙, hydrogen peroxide. And, the antioxidative effect observed is believed to be partly due to this radical scavenger activity.

• Bulletin of the Korean Chemical Society
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• v.35 no.5
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• pp.1285-1293
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• 2014

Several interesting features in trajectory were observed in the direct dynamics study of formaldehyde dissociation above radical dissociation limit. The hydrogen atom deliberately placed on the radical dissociation path can turn around at some distance from C without completion of dissociation and return to HCO moiety, colliding with it just as in a radical-radical recombination and producing a highly energized molecule. Excursion of a hydrogen atom to a distance of 6-8 bohrs and migration of a hydrogen atom back and forth between C and O are two of the most interesting features exhibited by the energized molecule. A series of excursions is seen to lead to a different kind of dissociation resembling roaming-like dissociation characterized by high vibrational excitation of $H_2$ fragment. It is suggested that excursion occurs due to involvement of two different force field systems that exhibit discontinuity in 6-8 bohrs from HCO moiety. We argue that roaming is a non-zero impact parameter version of the excursion.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.9 s.240
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• pp.979-987
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• 2005

Numerical simulations were performed at atmospheric pressure in order to understand the effect of additives on flame speed, flame temperature, radical concentrations, $NO_x$ formation, and heat flux in freely propagating $CH_4-Air$ flames. The additives were both carbon dioxide and hydrogen chloride which had a combination of physical and chemical behavior on hydrocarbon flame. In the flame established with the same mole of methane and additive, hydrogen chloride significantly contributed toward the reduction of flame speed, flame temperature, $NO_x$ formation and heat flux by the chemical effect, whereas carbon dioxide mainly did so by the physical effect. The impact of hydrogen chloride on the decrease of the radical concentration was about $1.4\~3.0$ times as large as that of carbon dioxide. Hydrogen chloride had higher effect on the reduction of $EI_{NO}$ than carbon dioxide because of the chemical effect of hydrogen chloride. The reaction, $OH+HCl{\rightarrow}Cl+H_2O$, played an important role in the heat flux from flames added by hydrogen chloride instead of the reaction, $OH+H_2{\rightarrow}H+H_2O$ which was an important reaction in hydrocarbon flames.

• Journal of Soil and Groundwater Environment
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• v.6 no.1
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• pp.3-12
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• 2001

During ozonation process, the hydroxyl radical generation rates were measured under different experimental conditions (ozone feed rate, nitrobenzene concentration, hydroxyl radical scavenger, pH, HO$_2$O$_2$/O$_3$ etc.) Nitrobenzene could be decomposed by hydroxyl radical rather than ozone only and nitrobenzene decomposition rate was expressed with functions of ozone and nitrobenzene concentration. The rate was decreased as the hydroxyl radical scavenger concentration was increased, and all results were followed pseudo first-order reaction. Using a competitive method, hydroxyl radical generation rate was measured with probe compound and scavenger. It was proportional to ozone concentration, and 0.24mo1 of hydroxyl radical was produced with 1mol of ozone. Under different pH conditions, hydroxyl radical generation rates were measured (pH 10.2 (0.91Ms$^{-1}$ ) > pH 7.3 (0.72Ms$^{-1}$ ) > pH 5.6 (0.67Ms$^{-1}$ ) > pH 3.4 (0.63Ms$^{-1}$ )) showing higher generation rate at high pH values. Addition of hydrogen peroxide promoted the generation rate of hydroxyl radical. Considering the results of pH experiments and addition of hydrogen peroxide experiments, the hydroxyl radical generation rate was 1.6 times higher in hydrogen peroxide solution than in high pH solution, indicating addition of hydrogen peroxide is better promoter to produce the hydroxyl radical in ozonation. These results could be applied to AOPs to remediate the contaminated wastewater and groundwater.

• Applied Chemistry for Engineering
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• v.33 no.3
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• pp.322-327
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• 2022

Fucoidans were degraded by hydrogen peroxide under the electron beam (2.5 MeV) with various radiation doses (5 kGy, 10 kGy, 15 kGy, and 20 kGy) at room temperature. The degradation property was analyzed with a gel permeation chromatography (GPC-MALLS) method. An average molecular weight of fucoidan decreased from 99,956 at the irradiation dose of 0 kGy to 6,725 at the irradiation dose of 20 kGy. The solution viscosity of fucoidans showed a similar pattern to the molecular weight change. The number of chain breaks per molecule (N) increased with increasing the irradiation dose and concentration of hydrogen peroxide. The radiation yield of scission value markedly increased with increasing the irradiation dose up to 15 kGy. Also a 10% hydrogen peroxide concentration was more efficient than that of 5%. The structures of degraded fucoidan samples were studied with Fourier transform infrared spectroscopy (FT-IR). The results showed that the degradation process did not significantly change the chemical structure or the content of sulfate group. The sulfur content of each sample was determined with an Elemental Analyzer. With increasing the concentration of hydrogen peroxide, the ratios of sulfur/carbon, hydrogen/carbon, and nitrogen/carbon slightly decreased. The antioxidant activities of fucoidans were investigated based on hydroxyl radical scavenging activities. The ability of fucoidan to inhibit the hydroxyl radical scavenging activity was depended on its molecular weight.

• Journal of Welding and Joining
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• v.29 no.1
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• pp.99-106
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• 2011

Joint strength between a solder ball and a pad on a substrate is one of the major factors which have effects on electronic device reliability. The effort to improve solder joint strength via surface cleaning, heat treatment and solder composition change have been in progress. This paper will discuss the method of solder ball joint strength improvement using LF hydrogen radical cleaning treatment and focus on the effects of surface treatment condition on the solder ball shear strength and interfacial reactions. In the joint without radical cleaning, voids were observed at the interface. However, the specimens cleaned by hydrogen-radical didn't have voids at the interface regardless of cleaning time. The shear strength between the solder ball and the pad was increased over 120%(about 800gf) when compared to that without the radical treatment (680gf) under the same reflow condition. Especially, at the specimen treated for 5minutes, ball shear strength was considerably increased over 150%(1150gf). Through the observation of fracture surface and cross-section microstructure, the increase of joint strength resulted from the change of fracture mode, that is, from the solder ball fracture to IMC/Ni(P) interfacial fracture. The other cases like radical treated specimen for 1, 3, 7, 9min. showed IMC/solder interfacial fracture rather than fracture in the solder ball.

• Proceedings of the Korea Air Pollution Research Association Conference
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• 2002.04a
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• pp.111-112
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• 2002

대기 중에 존재하는 hydrogen peroxide($H_2O$$_2$)는 특별한 source를 통해 배출되기보다는 오존이 광분해 되어 수증기와 반응하여 생성된 hydroperoxy radical (HO$_2$)의 self-reaction이나, 대기 중으로 배출된 VOCs의 산화 과정과 같은 광화학적 기원으로 생성된다. 이렇게 생성된 $H_2O$는 오존(O$_3$), hydroxy radical(OH)과 함께 대기 중으로 배출되는 물질과 반응하여 그 농도를 감소시키는 산화제를 역할을 한다. (중략)

• Proceedings of the Korean Environmental Sciences Society Conference
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• 1998.10a
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• pp.1-1
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• 1998

Advanced (Chemical) oxidation processes (AOP) differ from most conventional ones in that hydroxyl radical(OH.) is considered to be the primary oxidant. Hydroxyl radicalcan react non-selectively with a great number of organic and inorganic chemicals. The typical rate constants of true hydroxyl radical reactions are in the range of between 109 to 1012 sec-1. Many processes are possible to generate hydroxyl radical. These include physical and chemical methods and their combinations. Physical means involves the use of high energy radiation such as gamma ray, electron beam, and acoustic wave. Under an applied high energy radiation, water molecules can be decomposed to yield hydroxyl radicals or aqueous electrons. Chemical means include the use of conventional oxidants such as hydrogen peroxide and ozone, two of the most efficient oxidants in the presence of promoter or catalyst. Hydrogen peroxide in the presence of a catalyst such as divalent iron ions can readily produce hydroxyl radicals. Ozone in the presence of specific chemical species such as OH- or hydrogen peroxide, can also generate hydroxyl radicals. Finally the combination of chemical and physical means can also yield hydroxyl radicals. Hydrogen peroxide in the presence of acoustic wave or ultra violet beam can generate hydroxyl radicals. The principles for hydroxyl radical generation will be discussed. Recent case studied of AOP for water treatment and other environmental of applications will be presented. These include the treatment of contaminated soils using electro-Fenton, lechate treatment with conventional Ponton, treatment of coal for sulfur removal using sonochemical and the treatment of groundwater with enhanced sonochemical processes.

• Bulletin of the Korean Chemical Society
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• v.5 no.1
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• pp.16-21
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• 1984

The relative Arrhenius parameters for t-butoxy radical decomposition (log $A_d$, $E_d$) and hydrogen abstraction of t-butoxy radical from hydrogen donor (log $A_d$, $E_d$) by competitive method were obtained as follows: for cyclohexane; log $A_a/A_d$ = -4.17 mole/l and $E_d-E_a$ = 9.01 kcal/mole, for isobutane; log $A_a/A_d$ = -5.70 mole/l and $E_e-E_a$= 11.0 kcal/mole. From the reported Arrhenius parameters for t-Butoxy radical decomposition reactions the parameters for t-Butoxy radical reactions with isobutane and cyclohexane are estimated to be log $A(l/mol{\cdot}sec)$ = 8.4, $E_a$ = 4.3 kcal/mol and $log A (l/mol{\cdot}sec)= 9.9,\;E_a$ = 6.3 kcal/mol, respectively.

• The Korean Journal of Food And Nutrition
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• v.35 no.4
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• pp.259-267
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• 2022

The purpose of this study was to evaluate the antioxidative activities of jeolpyun containing Cnidium officinale M extract (2%, 4%, 6%, 8%) by total polyphenol contents, electron donating ability on 2,2-diphenyl-1-picrylhydrazyl (DPPH), scavenging ability of superoxide anion radical and decomposing ability of hydrogen peroxide. In chromaticity analysis, the brightness significantly decreased with increasing Cnidium officinale M extract content. Jeolpyun containing 8% Cnidium officinale M extract revealing the highest value for the redness and the yellowness, 1.07, 12.70, respectively. The total polyphenol contents of jeolpyun containing 8% Cnidium officinale M extract were the highest content of 4,213 ㎍ gallic acid equivalent (GAE)/mL. The total polyphenol contents revealed significant difference (p<0.05). Jeolpyun containing 8% Cnidium officinale M extract revealing the highest electron donating ability (83.55%). The electron donating abilities were significantly related at p<0.05. The scavenging abilities of superoxide anion radical for jeolpyun containing 4% Cnidium officinale M extract revealed the highest ability (0.01676). There was no significant difference. The hydrogen peroxide decomposing ability for jeolpyun containing 8% Cnidium officinale M extract revealed the most hydrogen peroxide decomposing ability (-0.193) and the hydrogen peroxide decomposing ability revealed a significant difference (p<0.05).