• Bulletin of the Korean Chemical Society
• /
• v.32 no.3
• /
• pp.964-972
• /
• 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
• /
• v.12 no.4
• /
• pp.429-433
• /
• 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
• /
• v.50 no.2
• /
• pp.92-97
• /
• 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.

• Journal of the Korean Ceramic Society
• /
• v.35 no.1
• /
• pp.5-10
• /
• 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.

• Korean Journal of Food Science and Technology
• /
• v.30 no.4
• /
• pp.983-987
• /
• 1998

Effects of sugars, temperature, pH and some chemicals on caramelization were investigated for improving of its reaction rates. Among the sugars tested, fructose showed the fastest reaction rate, followed by sucrose, glucose, starch syrup and maltose. As the reaction temperature increased from 80 to $110^{\circ}C$, the rate greatly increased by the range of $150{\sim}8000$ folds depending on sugars. It was indicated that pH 10 resulted in the highest reaction rate in the range of $pH{\;}4{\sim}10$. When several chemicals, such as phosphates and organic acid salts, were added to starch syrup, the rate increased by more than 10 folds, in particular effects of $K_2HPO_4$ and sodium salts of citrate, oxalate and succinate were significant.

• Journal of environmental and Sanitary engineering
• /
• v.18 no.4
• /
• pp.45-51
• /
• 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
• /
• 2005.10a
• /
• pp.83-87
• /
• 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

• Journal of Korean Society for Atmospheric Environment
• /
• v.10 no.2
• /
• pp.83-89
• /
• 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.

• Korean Journal of Crystallography
• /
• v.9 no.1
• /
• pp.44-47
• /
• 1998

A reduction/oxidation reaction between A1 metal powder and SiO2 powder was performed by Self-propagating High-temperature Synthesis (SHS) reaction induced by microwave energy to produce a composite of Al2O3 and Si powders by using a 2.45 GHz kitchen model microwave oven. A Microwave Hybrid Heating(MHH) method was applied by using SiC powders as a suscepting material to raise the temperature of the disk samples and the heat increase rate of over 100℃/min were obtained before the reaction. The reaction started around 850℃ and the heat increase rate jumped to over 200℃/min after the reaction took place.

• Journal of the Korean Ceramic Society
• /
• v.35 no.10
• /
• pp.1030-1039
• /
• 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.