• Bulletin of the Korean Chemical Society
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• 제32권3호
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• pp.964-972
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• 2011

This work investigated the difference between $Fe^{2+}$ autoxidation-induced and Fenton-type cleavage of pBR322 plasmid DNA. $^{\cdot}OH$ generation reactions in the absence and presence of $H_2O_2$ under various conditions were also investigated. Although both the $Fe^{2+}$ autoxidation and Fenton-type reactions showed DNA cleavage and $^{\cdot}OH$ generation, there were significant differences in their efficiencies and reaction rates. The rate and efficiency of the cleavage reaction were higher in the absence of 1.0 mM of $H_2O_2$ than in its presence in 20 mM phosphate buffer. In contrast, the $^{\cdot}OH$ generation reaction was more prominent in the presence of $H_2O_2$ and showed a pH-independent, fast initial reaction rate, but the rate was decreased in the absence of $H_2O_2$ at across the entire tested pH range. Studies using radical scavengers on DNA cleavage and $^{\cdot}OH$ generation reactions in both the absence and presence of $H_2O_2$ confirmed that both reactions spontaneously involved the active oxygen species $^{\cdot}OH$, ${O_2}^{\cdot-}$, $^1O_2$ and $H_2O_2$, indicating that a similar process may participate in both reactions. Based on the above observations, a new mechanism for the $Fe^{2+}$ autoxidation-induced DNA cleavage reaction is proposed.

• Bulletin of the Korean Chemical Society
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• 제12권4호
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• pp.429-433
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• 1991

The photoinduced electron transfer reactions of N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD) in various polar solvents were studied by measuring time-resolved fluorescence. The temperature dependence on the fluorescence decay rate in acetonitrile, methanol, ethanol and buthanol was carried out to obtain the activation energy and Arrehnius factor for the photoinduced electron transfer reaction. It was found that as the dielectric constant of the solvent increases, the activation energy and the reaction rate increase. This implys that the Arrehnius factor is important in controlling the photoinduced electron transfer reaction rate. In water, TMPD exists in three forms (cationic, protonated and neutral forms) due to the high dielectric constant and strong proton donating power of water. The photoinduced electron transfer reaction was found to be very fast (< 50 ps) and also the long liverd component in the fluorescence decay profile attributable to the photoexcited protonated form of TMPD was observed. Probably, the reaction pathway and the reaction coordinate seem to be different depending on the solvents studied here.

• Elastomers and Composites
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• 제50권2호
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• pp.92-97
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• 2015

A study on reaction kinetics for a PTMG/TDI prepolymer with 2,2'-dichloro-4,4'-methylenedianiline (MOCA), of which formulations may be generally used for fabricating high performance polyurethane elastomers, was peformed using non-isothermal differential scanning calorimetry (DSC). A number of thermograms were obtained at several constant heating rates, and analysed using Flynn-Wall-Ozawa (FWO) isoconversional method for activation energy, $E_a$ and extended-Avrami equation for reaction order, n. Urea formation reaction of the present system was observed to occur through the simple exothermic reaction process in the temperature range of $100{\sim}130^{\circ}C$ for the heating rate of $3{\sim}7^{\circ}C/min$. and could be well-fitted with generalized sigmoid function. Though activation energy was nearly constant as $53.0{\pm}0.5kJ/mol$, it tended to increase a little at initial stage, but it decreases at later stage by the transformation into diffusion-controlled reaction due to the increased viscosity. Reaction order was evaluated as about 2.8, which was somewhat higher than the generally well-known $2^{nd}$ order values for the various urea reactions. Both the reaction order and reaction rate explicitly increased with temperature, which was considered as the indication of occurring the side reactions such as allophanate or biuret formation.

• 한국세라믹학회지
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• 제35권1호
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• pp.5-10
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• 1998

Mullitization in a multicomponent oxide system(alumina-kaolin-quartz-feldspar-talc) was studied as a function of sintering temperature from 1200 to 1500$^{\circ}C$ based upon a quantitative X-ray diffraction analysis. In the present study mullite grew as wiskers and its formation reaction showed characteristic there stages as follows In the first stage(1255-1295$^{\circ}C$) an appreciable mullitization(nucleation) occurred while corun-dum dissolution into glass (increasing glass content ) limited the rate of the reaction. At 1295-1335$^{\circ}C$ (second state) the reaction was significantly enhanced with a considerable glass consumption and with no appreciable change in corundum content. Finally (above 1335$^{\circ}C$) the reaction rate was attenuated re-markably with an apparent decrease in glass consumption rate. The impingement of mullite whiskers by oth-er whiskers and crystals was speculated to cause mullite growth in thickness direction with a slow growth rate resulting in the diminished reaction rate in the final stage.

• 한국식품과학회지
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• 제30권4호
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• pp.983-987
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• 1998

Caramel화 반응에 당의 종류, 온도, pH 및 첨가물질이 미치는 영향을 조사하여 반응속도 향상을 위한 반응조건을 찾고자 하였다. 그 결과 당의 종류로는 fructose가 가장 빠른 반응속도를 보였고 그 다음은 sucrose-glucose-starch syrup-maltose의 순이었다. 반응 온도를 $80^{\circ}C$에서 $110^{\circ}C$로 상승시켰을 때 당의 종류에 따라 $150{\sim}8000$배의 속도향상이 있었으며 반응 pH는 $pH{\;}4{\sim}10$ 범위에서 pH 10이 가장 높은 반응을 보였다. 인산염과 유기산염을 첨가했을 때 $K_2HPO_4$와 citrate, oxalate, succinate의 sodium염들이 반응촉진 효과가 있음이 밝혀졌다.

• 환경위생공학
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• 제18권4호
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• pp.45-51
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• 2003

This study was conducted to remove the color in dyeing wastewater by ozone oxidation process, and the results were summarized as follows ; The 18.3％ of BOD and 56.3％ TOC were removed as decreasing with pH 1 in dyeing wastewater, containing the polyester reducing process. It showed that terephthalic acid was precipitated at low pH. The color of dyeing wastewater was removed by the first order reaction, and the reaction rate constants at pH 3, 7, 12 were investigated $0.234{\;}min^{-1},{\;}0.215{\;}min^{-1}{\;}and{\;}0.201{\;}min^{-1}$ respectively. It showed that color was more effectively removed with direct reaction of ozone than radical reaction(non-direct reaction). As increasing of the water temperature, the reaction rate constants were increased slightly. It indicated that activity of ozone was improved at high water temperature.

• 한국가스학회:학술대회논문집
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• 한국가스학회 2005년도 추계학술발표회 논문집
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• pp.83-87
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• 2005

The kinetics of the direct synthesis of DME was studied under different conditions over a temperature range of $220\~280^{\circ}C$, syngas ratio $1.2\~ 3.0$ All experiment were carried out over hybrid catalyst, composed to a methanol synthesis catalyst (Cu/ZnO/$Al_2O_3$) and a dehydration Catalyst ($\gamma$-Al_2O_3$) The observed reaction rate qualitatively follows a Langmiur-Hinshellwood type of reaction mechanism. Such a mechanism is considered with three reaction, methanol synthesis, methanol dehydration and water gas shift reaction. From a surface reaction with dissociative adsorption of hydrogen, methanol and water, individual reaction rate was determined

• 한국대기환경학회지
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• 제10권2호
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• pp.83-89
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• 1994

The reaction of sulfur dioxide with cupric oxide was investigated over a temperature range of 300-50$0^{\circ}C$, and the regenaration reaction was studied using cupric sulfate and hydrogen over a temperature range of 240-35$0^{\circ}C$ in a fixed bed reactor. The experimental results showed that the efficiencies for elimination and regenaration reactions were maximum at 45$0^{\circ}C$ and at 30$0^{\circ}C$ respectively. In both cases the experimental data could be interpreted properly by shrinking unreacted core model while the chemical reaction is rate controlling step. The reaction rate constants were determined to be 24.88 exp(-6724/RT) (cm/min) for elimination reaction, and 0.0165 exp(-2047/RT)(cm/min ) for regeneration reaction.

• 한국결정학회지
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• 제9권1호
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• pp.44-47
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• 1998

가정용 2.45GHz 마이크로파 오븐을 사용하여 A1 금속분말과 SiO2 분말간에 SHS방법에 의하여 산화/환원 반응을 통한 Al2O3 분말과 Si분말간의 복합체를 얻을 수 있었다. 분말간의 반응을 일으키기 위한 온도까지 승온시키기 위하여는 SiC 분말을 susceptor로 이용한 마이크로파 복합가열(Microwave Hybrid Heating)방법을 사용하여 분당 100℃의 승온 속도로 가열하였으며 반응은 850℃ 근처에서 일어났으며 가열 속도는 반응이 시작되면서 분당 200℃ 이상의 온도상승이 일어나면서 원하는 반응을 얻을 수 있었다.

• 한국세라믹학회지
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• 제35권10호
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• pp.1030-1039
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• 1998

In fly ash-lime system the effects of reaction condition amounts of gypsum and cement and CaO/SiO2 ratio on the hydrates by hydrothermal reaction were investigated. The tobermorite phases were not observed in hy-drothermal reaction of fly ash lime because of the hydrate rate was very slow. The compressive strength and the hydration rate increased with increasing the amount of gypusm and cement and the optimum amounts of gypsumo and cement were 5wt and 20wt% respectively. The specimen which CaO/SiO2 ratio is 0.85 was shown the maximum compressive strength and the tobermorite phase within reaction time 2 hours.