• Analytical Science and Technology
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• v.8 no.4
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• pp.655-661
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• 1995

The electrochemical reduction of coumarin derivatives in 0.1M TEAP acetonitrile solution was investigated by the direct current, differential pulse polarography, cyclic voltammetry and controlled potential coulometry. The electrochemical reduction of 7-acetoxy-4-bromomethyl-coumarin(ABMC) was proceeded as an irreversible three steps(-0.58, -1.63 and -2.25 volts) of electrochemical transfer before chemical reaction. The solution color turned to yellow after the carboxyl group was reduced at 2nd step(-1.63 volts vs. Ag-AgCl) and the change in color was independant to the bromo group. Upon the basis of the results on the products analysis and the interpretaton of polarograms, a possible electrochemical reaction mechanism was suggested.

• Bulletin of the Korean Chemical Society
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• v.15 no.9
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• pp.724-729
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• 1994

The effect of oxygen for the HF chemical laser performance has been theoretically investigated. Due to the inhibition mechanism of $O_2$ in $H_2$/$F_2$ chain reaction, the rate for the formation of HF is reduced by the addition of $O_2$. As the concentration of $O_2$ in the reaction mixture increases, the pulse power and temperature of the system becomes lower, while total output energy does not change significantly. But addition of $O_2$ makes the system easy to be controlled and the composition of $H_2$+$F_2$ can be high at constant total pressure. With this system, it is possible to obtain higher output energy than oxygen free environment.

• Bulletin of the Korean Chemical Society
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• v.20 no.6
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• pp.643-647
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• 1999

Hydropalladium carboxylates, formed from π-allylpalladium chloride dimer plus carboxylic acids, have been shown to catalyze cyclization of structurally diverse enediynes to form the corresponding six- or five-membered rings depending upon the reaction conditions. Some enediynes having an Oxygen linker in an appropriate position under the similar condition yielded the corresponding cyclopropanation products in highly stereoselective manner. A study using deuterated formic acid has proven that the alkylpalladium intermediates formed in our conditions were reduced by the pendant formate ligand. The dienediyne 10 yielded only the tricyclic product 12 in 67% yield, although it was expected to frrm the cyclic product 11. All these cyclizations seemed to occur via the corresponding alkylpalladium intermediates I. which could proceed to the corresponding cyclic products depending on the reaction conditions and the substrates. The study using ceuterated formic acid could provide an important information to understand the present cyclization mechanism. Overall the present study could play an important role in developing new synthetic methodologies for constructing complex polycyclic compounds.

• Biomedical Science Letters
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• v.15 no.2
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• pp.153-160
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• 2009

Photodynamic therapy(PDT) is a treatment utilizing the generation of singlet oxygen and other reactive oxygen species(ROS), which selectively accumulate in target cells. The aim of present work is to investigate the photodynamic therapy mechanism of 9-HpbD-a-mediated PDT in HeLa cell lines. We studied the general reactive oxygen species(G-ROS) activation after 9-HpbD-a PDT using fluorescence stain with $H_2DCF-DA$. G-ROS activation observed after 9-HpbD-a PDT and higher activation condition was 1 hour after PDT at 0.5 ${\mu}g/ml$ 9-HpbD-a concentration. Sodium azide and reduced glutathione(the singlet oxygen quencher) could protect HeLa cells from cell death induced by 9-HpbD-a PDT. But D-mannitol(the hydroxyl radical scavenger) could not protect cell death. Singlet oxygen played a decisive role in 9-HpbD-a PDT induced HeLa cell death. Type II reaction was the main type of ROS formation at 9-HpbD-a PDT.

• 한국전산유체공학회:학술대회논문집
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• 2002.05a
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• pp.115-120
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• 2002

A two-dimensional direct numerical simulations was peformed to investigate the flame structure of $CH_4/N_2$-Air counterflow nonpremixed flame interacting with a single vortex. The detailed transport properties and a modified 16-step augmented reduced mechanism based on Miller and Bowman's detailed reaction mechanism were adopted in this calculation. To quantify the strain on flame induced by a vortex, a scalar dissipation rate (SDR) is introduced. Results show that the fuel- and air-side vortex cause an unsteady extinction. In this case, the flame interacting with a vortex is extinguished in much larger SDR than steady flame. It was also found that air- side vortex extinguishes a flame more rapidly than fuel -side vortex.

• International Journal of Concrete Structures and Materials
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• v.8 no.2
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• pp.173-182
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• 2014

An experimental investigation was carried out to evaluate the mechanical properties of concrete mixtures in which coarse aggregate was partially (30, 50 or 70 %) replaced with pre-washed municipal solid waste incineration (MSWI) bottom ash. Results indicated that bottom ash reduced the compressive strength, elastic modulus, and levels of heavy metals in leachate when used as a replacement for gravel, and that the maximum amount of MSWI bottom ash in concrete should not exceed 50 %. To analyze the effect mechanism of bottom ash in concrete, the degree of hydration and the following pozzolanic reaction characterized by the pozzolanic activity index, and the porosity distribution in cement mortar. The study indicates that improved properties of concrete are not solely later strength gain and reduced levels of heavy metals in leachate but also the progression of pozzolanic reactions, where a dense structure contains a higher proportion of fine pores that are related to durability.

• Transactions of the Korean hydrogen and new energy society
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• v.31 no.5
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• pp.467-479
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• 2020

Various researches are being conducted to reduce greenhouse gases generated by the consumption of traditional energy resources. This study was conducted to numerically analyze the combustion characteristics and N-S reaction behavior with respect to the H₂ content of syngas composed of CO and H₂ in pressurized air combustion. A non-premixed opposed flow flame model was applied a modified detailed mechanism with S-chemistry was developed based on GRI 3.0 to simulate the syngas reaction. As the hydrogen content increased, the flame thickness increased due to the fast reactivity of hydrogen. In the rich region, NO and SO₂ were reduced by reaction with H radical and H bonding of NO was suppressed by the formation of HOSO.

• Resources Recycling
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• v.29 no.6
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• pp.35-40
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• 2020

In this study were carried out basic experiments mainly to investigate important reaction mechanism, the reaction temperature, time and the addition amount of Zn in recycling of waste cemented carbide by the zinc bath process. As a result, it was required that the Zn bath reaction was heated more than at 800℃ to accelerate reaction of melted Zn and Co inside of wasted cemented carbide. Furthermore, thickness of the waste cemented carbide was reduced linearly according to increase of reaction time at 700℃ for 0.5~2h in the zinc bath reaction. Also the zinc bath reaction was examined that heating in lower than at 800℃ for 3h and then heated more than at 900℃ for 1h(above 3.0×10 torr-2 vaccum) was suitable to reduce vapour loss amount of Zn in the zinc bath process.

• Bulletin of the Korean Chemical Society
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• v.21 no.12
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• pp.1217-1221
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• 2000

L-alanine dehydrogenase from Bacillus subtilis exhibits allosteric kinetic properties in the presence of $ZN^{2+}$. $ZN^{2+}$ induces the binding of substrate (L-alanine) to be cooperative at pH 8.0. The effect of pH variation between pH 7.0 and pH 10.0 on the inhibition by $ZN^{2+}$ correlates with the pH effect on the $K_m$ values for L-alanine within these pH range indicating that $ZN^{2+}$ and substrate compete for the same site. No such cooperativity is induced by $ZN^{2+}$ when the reaction is carried out at pH 10. At this higher pH, $ZN^{2+}$ binds with the enzyme with lower affinity and noncompetitive with respect to L-alanine. Inhibition of L-alanine dehydrogenase by $ZN^{2+}$ depends on the ionic strength. Increase in KCI concentration reduced the inhibition, but allosteric property in $ZN^{2+}$ binding is conserved. A model for the regulatory mechanism of L-alanine dehydrogenase as a noncooperative substrate-cooperative cofactor allosteric enzyme, which is compatible in both concerted and the sequential allosteric mechanism, is proposed.

• Journal of Soil and Groundwater Environment
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• v.27 no.1
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• pp.25-30
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• 2022

Mackinawite (FeS), as a ubiquitous reduced iron mineral, is known as a key controller of redox reactions in anaerobic subsurface environment. The reaction of FeS with redox-sensitive toxic element such as arsenic is substantially affected by pH conditions of the given environments. In this study, the interaction of As(V) with FeS was studied under strict anaerobic conditions with various pH conditions. The pH-dependent arsenic removal tests were conducted under wide ranges of pH conditions and X-ray absorption spectroscopy (XAS) was applied to investigate the reaction mechanisms under pH 5, 7, and 9. The removal efficiency of FeS for As(V) showed the higher removal of As(V) under low pH conditions and its removal efficiency decreased with increasing pH, and no As(V) reduction was observed in 1 g/L FeS solution. However, XAS analysis indicated the reduction of As(V) to As(III) occurred during reaction between FeS and As(V). The reduced form of As(III) was particularly identified as an arsenic sulfide mineral (As₂S₃) in all pH conditions (pH 5, 7, and 9). As₂S₃ precipitation was more pronounced in pH 5 where the solubility of FeS is higher than in other pH conditions. The linear combination fitting results of XAS demonstrated that As(V) removal mechanism is concerted processes of As₂S₃ precipitation and surface complexation of both arsenic species.