• Mass Spectrometry Letters
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• v.2 no.1
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• pp.24-27
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• 2011

Hyperthermal ion/surface collisions of bromotoluene radical cations were studied using perfluorinated (F-SAM) and hydroxyl-terminated (OH-SAM) self-assembled monolayer surfaces in a tandem mass spectrometer with BEEQ geometry. The isomers were differentiated by ion abundance ratios taken from surface-induced dissociation (SID). The dissociation rate followed the order of ortho > meta > para isomers. The peak abundance ratio of m/z 51 to m/z 65 showed the best result to discern the isomers. A dissociation channel leading to tolylium ion was suggested to be responsible for the pronounced isomeric differences. The capability of SID to provide high-energy activation with narrow internal energy distribution may have channeled the reaction into the specific dissociation pathway, also facilitating small differences in reaction rates to be effective in the spectral time window of this experiment. All of the molecular ions experiencing reactive collisions with the F-SAM surface undergo transhalogenation, in which a fluorine atom on the surface replaces the bromine in the incoming ions. This reactive collision was dependent on the laboratory collision energy occurring in ca. 40.75 eV range.

• Macromolecular Research
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• v.12 no.4
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• pp.325-335
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• 2004

Molecular weight distributions of poly(vinyl neo-decanoate) produced by the bulk polymerization of the monomer to low conversions were investigated to obtain values of the rate constants for the chain transfer to monomer ( $C_{M}$). The value of $C_{M}$ of 7.5($\pm$0.6)${\times}$10$^{-4}$ was obtained from a logarithmic plot of the number distribution at 5,25, and 5$0^{\circ}C$, which suggests that the activation energy for chain transfer is on the order of 20-25 kJ ㏖$^{-1}$ . These plots were linear between the number and weight-average degrees of polymerization, but not over the whole molecular weight range for which a significant signal was observed in the gel permeation chromatography (GPC) trace. Modeling suggests that the deviations observed at high molecular weights can be explained by branching of the chains through chain transfer to the polymer, with a branching density as low as 10$^{-5}$ , without affecting the slope at low values of the number of monomer unit, N. This deviation from the expected distribution of linear chains was used to estimate the branching densities at low conversion.ion.

• Macromolecular Research
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• v.13 no.5
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• pp.391-396
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• 2005

The polymerization of methyl methacrylate (MMA) was carried out using CuBr/bidentate phosphorus ligand catalyst systems. MMA polymerization with CuBr/phosphine-phosphinidene (PP) exhibited high conversion ($\~80\%$) in 5 h at $90^{\circ}C$ along with a linear increase of ln($[M]_0/[M]$) versus time, indicating constant concentration of the propagating radicals during the polymerization. The molecular weight of the prepared PMMA tended to increase with conversion, suggesting the living polymerization characteristic of the system. On the other hand, a large difference between the measured and theoretical molecular weight and a broad molecular weight distribution were observed, implicating possible incomplete control over the polymerization. This may have been caused by the low deactivation rate constant ($\kappa_{deact}$) of the system. The low $\kappa_{deact}$, would result in irreversible generation of radicals instead of reversible activation/deactivation process of ATRP. Polymerizations performed at different ligand to CuBr ratios and different monomer to initiator ratios did not afford better control over the polymerization, suggesting that the controllability of CuBr/phosphorus ligand system for ATRP is inherently limited.

• International Journal of Oral Biology
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• v.34 no.1
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• pp.15-20
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• 2009

In our present study, total methanol extracts prepared from B. platyphylla var. japonica showed a significant increase in cell proliferation upon the induction of oxidative stress by hydrogen peroxide or $\gamma$-ray irradiation. Total methanol extracts were fractionated into five separate preparations i.e. n-hexane, dichloromethane, ethylacetate, n-butanol and water fractions. Among these, the ethylacetate and butanol fractions of B. platyphylla var. japonica showed the highest protective effects against oxidative stress induced by hydrogen peroxide. These fractions also showed strong protective effects against $\gamma$-ray irradiation. When we evaluated the cytotoxicity of these fractions, the butanol fraction showed no effects in a colony formation assay. In addition, the butanol fraction showed a cell proliferation activation effect evidenced by significant increase in the colony formation of $\gamma$-ray irradiated cells. Both a radical scavenging activity and clonogenic activity assay suggested that the mechanism behind this protective effect against reactive oxygen species may be due to the radical scavenging and cell proliferation activity of B. platyphylla var. japonica extracts.

• Natural Product Sciences
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• v.27 no.2
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• pp.115-121
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• 2021

Lentinus edodes contains functional metabolites such as polysaccharopeptides, lectins, and secondary metabolites. Fermented soybean paste is representative fermented materials in Korea, and is gradually increasing due to various biological activities. In the present study, ethanol extracts of fermented products with/without L. edodes were designated as SPL and SP, and prepared to develop safer and therapeutic functional foods with antioxidant and anti-inflammatory activities for treatment of inflammatory disorders. SP and SPL extracts exhibited antioxidant effects via inhibiting radical activities. Inflammatory mediators, nitric oxide (NO), prostaglandin E₂ (PGE₂), interleukin (IL)-1β, IL-6, IL-8, tumor necrosis factor (TNF)-α, and inducible nitric oxide synthase (iNOS) production and nuclear factor-kappa B (NF-κB) activation were down-regulated by two extracts. SPL extract more strongly enhanced the antioxidant and anti-inflammatory activities than SP extract. Its' activities shown more longer fermentation period and more strong inhibitory effects. Taken together, our results suggested that fermented product with medicinal plant has synergic effect and SPL can be a potential candidate for treatment of inflammatory bowel diseases.

• Journal of Microbiology and Biotechnology
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• v.26 no.7
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• pp.1224-1233
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• 2016

The present study assessed the effects of an aqueous extract of Acanthopanax koreanum root (AE) and of AE following fermentation by lactic acid bacteria (Lactobacillus plantarum and Bifidobacterium bifidum) (AEF) on human skin fibroblast HS68 cells exposed to ultraviolet B (UVB) irradiation and oxidative stress. AEF effectively antagonized the senescence-associated β-galactosidase staining and upregulation of p53 and p21^Cip1/WAF1 induced by UVB or H₂O₂ treatment in HS68 cells. It also exhibited excellent antioxidant activities in radical scavenging assays and reduced the intracellular level of reactive oxygen species induced by UVB or H₂O₂ treatment. The antioxidant and antisenescent activities of AEF were greater than those of nonfermented A. koreanum extract. AEF significantly repressed the UVB- or H₂O₂-induced activities of matrix metalloproteinase (MMP)-1 and -3, overexpression of MMP-1, and nuclear factor κB (NF-κB) activation. This repression of NF-κB activation and MMP-1 overexpression was attenuated by a mitogen-activated protein kinase activator, suggesting that this AEF activity was dependent on this signaling pathway. Taken together, these data indicated that AEF-mediated antioxidant and anti-photoaging activities may produce anti-wrinkle effects on human skin.

• Journal of the Korean Applied Science and Technology
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• v.37 no.5
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• pp.1100-1105
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• 2020

We investigated the driving force and the required charges for spontaneous reduction of metal nanoparticles (NPs) on a scotch tape induced by mechanochemical activation. The charges were analyzed based on anodic stripping voltammetry (ASV) of silver, which is proportional to the number of charge identities on the tape. The results supported that the driving force is mechanochemical radicals rather than ions in the light of the high charge density on the tape.

• Bulletin of the Korean Chemical Society
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• v.35 no.3
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• pp.839-844
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• 2014

The gas-phase radical-radical reaction $O(^3P)$ + $C_2H_5$ (ethyl) ${\rightarrow}$ $H(^2S)$ + $CH_3CHO$(acetaldehyde) was investigated by applying a combination of vacuum-ultraviolet laser-induced fluorescence spectroscopy in a crossed beam configuration and ab initio calculations. The two radical reactants $O(^3P)$ and $C_2H_5$ were respectively produced by photolysis of $NO_2$ and supersonic flash pyrolysis of the synthesized precursor azoethane. Doppler profile analysis of the nascent H-atom products in the Lyman-${\alpha}$ region revealed that the average translational energy of the products and the average fraction of the total available energy released as translational energy were $5.01{\pm}0.72kcalmol^{-1}$ and 6.1%, respectively. The empirical data combined with CBS-QB3 level ab initio theory and statistical calculations demonstrated that the title exchange reaction is a major channel and proceeds via an addition-elimination mechanism through the formation of a short-lived, dynamical addition complex on the doublet potential energy surface. On the basis of systematic comparison with several exchange reactions of hydrocarbon radicals, the observed small kinetic energy release can be explained in terms of the loose transition state with a product-like geometry and a small reverse activation barrier along the reaction coordinate.

• Korean Chemical Engineering Research
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• v.47 no.4
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• pp.441-445
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• 2009

Effect of temperature on membrane degradation in PEMFCs was studied. After cell operation at different temperatures($60{\sim}90^{\circ}C$) under accelerating degradation conditions(OCV, anode dry, cathode RH 65%) for 144 h, cell performance decreased from 12 to 35%. The results of FER in effluent water showed that this decrease in cell performance was caused by membrane degradation by the attack of $H_2O_2$ or oxygen radicals(${\cdot}OH$, $HO_2{\cdot}$) and that resulted in increase in gas crossover for radical formation. Radical formation on the electrode was confirmed by ESR. Activation energy of 66.2 kJ/mol was obtained by Arrhenius plot used to analyze the effect of temperature on membrane degradation. Increase of cell temperature enhanced gas crossover rate, radical formation rate and membrane degradation rate.

• YAKHAK HOEJI
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• v.34 no.4
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• pp.267-276
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• 1990

To achieve a better understanding of antioxidant action manifested by malotilate, the dithiol malonates, we monitored the oxy radical-scavenging system against the chronic hepatic damage induced by $CCl_4$ alone or in combination with ethanol. Malotilate was given orally at a dose of 100 mg/kg/day and $CCl_4$ 1.5 ml/kg was injected subcutaneously twice a week for 4 weeks. In each group receiving ethanol, drinking water was replaced by 20% aqueous solution or glucose, isocaloric amounts of ethanol, as a control of ethanol was diluted in its drinking water. Each rat was killed as a starved state at 18 hours after the period of the experiment, four weeks. The results were summarized as follows: 1) Malotilate inhibited the rate of generation of superoxide radicals, the accumulation of lipoperoxides, and promoted the synthesis of glutathione in the liver. 2) Malotilate stimulated the enhancement of activity of superoxide dismutase in hepatic mitochondria. 3) Malotilate had no effects on the hepatic $H_2O_2$ contents. 4) Malotilate showed the increase of catalase activity in the liver poisoned with $CCl_4$, and also gave a tendency to increase it in the liver intoxicated with ethanol. Thus, our data suggested that the activation of hepatic antioxidant system in the presence of malotilate would play a role in protecting liver against the toxic effects of oxy radical and/or lipid peroxides under the hepatotoxic conditions induced by $CCl_4$ with or without ethanol. However, the effects of malotilate against the ethanol-induced hepatotoxicity appear to be insignificant.