• Journal of Ginseng Research
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• 제7권1호
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• pp.88-93
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• 1983

Studies were carried out to elucidate the protein stabilizing effect of ginseng. Malate dehydrogenase (EC 1.1.1.37) was used as a protein and the rate constant of the enzyme inactivation was determined under the heat denaturation condition. There was an optimum pH for the enzyme stability, the rate constant of the enzyme inactivation was minimum at BH 8.8. The rate constant was increased at lower and higher pH regions than the optimum pH. The inactivation reaction followed the Arrehnius law and the activation energy was measured as 36.8kcal/mole. The reaction rate was not affected by the enzyme concentration and thus it was assumed to be unimolecular first order reaction. The water extract of red ginseng decreased the rate constant of Malate dehydrogenate under heat inactivation condition to stabilize the enzyme activity. Purified ginseng saponin also stabilized the enzyme against heat inactivation.

• Bulletin of the Korean Chemical Society
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• 제1권1호
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• pp.30-35
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• 1980

The thermal decomposition reaction of ethyl bromide was studied in the temperature range of 724.5-$755.1^{\circ}K$. Pressure dependence of the reaction was observed in its fall-off region. A theoretical evaluation of the rate constants was carried out adopting RRKM formulation in the region and was compared with the experimental observation.The validity of theory was also reevaluated by using the observed results. The observed activation energy in this study and Arrhenius A-factor were 51.7 kcal/mole and $10^{12.5}$, respectively. The small A-factror in the study was discussed in terms of the formation of a tight activated complex and the molecular elimination as a prevalent reaction mode.

• Bulletin of the Korean Chemical Society
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• 제26권8호
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• pp.1177-1184
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• 2005

Ab initio quantum chemical molecular orbital calculations have been performed for the unimolecular decomposition of methacrylonitrile ($CH_3C(CN)=CH_2$), especially for HCN and $H_2$ molecular elimination channels. Structures and energies of the reactants, products, and relevant species along the individual reaction pathways were determined by MP2 gradient optimization and MP4 single point energy calculations. Direct four-center elimination of HCN and three-center elimination of H2 channels were identified. In addition, H or CN migration followed by HCN or H2 elimination channels via the methylcyanoethylidene intermediate was also identified. Unlike the case of crotonitrile previously studied, in which the dominant decomposition process was the direct three-center elimination of HCN, the most important reaction pathway should be the direct threecenter elimination of $H_2$ in the case of methacrylonitrile.

• Bulletin of the Korean Chemical Society
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• 제10권3호
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• pp.262-269
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• 1989

The gas phase thermal decomposition of 1-bromo-3-chloropropane in the presence of radical inhibitor was studied by using the conventional static system. The mechanism of unimolecular elimination channel is shown below. [...] In this scheme, the total molecular dissociation rate constant, ($k_1\;+\;k_2$), for the decomposition of $BrCH_2CH_2CH_2Cl$ was determined by pyrolyzing the $BrCH_2CH_2CH_2Cl$ in the temperature range of $380-420^{\circ}C$ and in the pressure range of 10∼100 torr. To obtain $k_3\;and\;k_4,\;and\;to\;obtain\;k_1\;and\;k_2$ independently, the thermal decompositions of allyl chloride and allyl bromide were also studied. The Arrhenius parameters for each step are as follows; $log\;A_{\infty}\;=\;14.20(sec^{-1}),\;E_a$ = 56.10(kcal/mol) for reaction path 1; $log\;A_{\infty}\;=\;12.54(sec^{-1}),\;E_a$ = 49.75(kcal/mol) for reaction path 2; $log\;A_{\infty}\;=\;13.41(sec^{-1}),\;E_a$ = 50.04(kcal/mol) for reaction path 3; $log\;A_{\infty}\;=\;12.43(sec^{-1}),\;E_a$ = 52.78(kcal/mol) for reaction path 4; Finally, the experimentally observed pressure dependence of the rate constants in each step is compared with the theoretically predicted values that are obtained by the RRKM calculations.

• Bulletin of the Korean Chemical Society
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• 제17권12호
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• pp.1147-1149
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• 1996

The trans (2a)-cis (2b) isomerization of [Me2Al(μ-NHtBu)]2 (2) has been studied by 1H NMR spectroscopy. The equilibrium has been observed to follow reversible first order kinetics with ΔH0=2.22±0.07 kJmol-1 and ΔS0=2.85±0.07 JK-1mol-1. The activation parameters for the conversion 2a→2b are ΔH1=49.7±2.3 kJmol-1 and ΔS1=-126.3±0.2 JK-1mo1-1 and for the reverse reaction 2b→2a are ΔH-1=47.5±2.3 kJmol-1 and ΔS-1=-129.1±0.5 JK-1mol-1. The isomerization is markedly accelerated in the presence of Lewis bases. A crossover experiment indicates that the isomer interconversion is a unimolecular process. The large negative entropies of activation suggest either the existence of a sterically congested intermediate or the participation of solvent in the isomerization process.

• 대한화학회지
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• 제40권5호
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• pp.327-332
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• 1996

이성분혼합용매내에서 Methyl-, Phenyl Chloroformate와 1-adamantyl 유도체들의 가용매분해반응속도를 여러 온도와 압력하에서 전도도방법에 의하여 측정하였다. 이들 속도상수로부터 활성화 부피(${\Delta}V_o^{\neq}$), 활성화 엔탈피(${Delta}H^{\neq}$), 활성화 엔크로피 (${\Delta}S^{\neq}$) 값을 구하였다. 이때 모든 혼합물내에서 ${\Delta}V_o^{\neq}$와 ${\Delta}V_s^{\neq}$는 음의 값을 나타내었으며, ${\Delta}H^{\neq}$는 양의 값을 얻었다. 이 현상을 용매구조변화에 대하여 논의하였다. 또한 활성화 부피와 활성화 엔트로피 값들을 플로트하여 본 반응에 대한 반응 경향성을 조사하였다. 이들 결과로부터 Methyl-, Phenyl Chloroformate와 1-adamantyl fluoroformate(알코올수용액)는 이분자반응이, 1-adamantyl fluoromate(TFE수용액)와 1-adamantyl tosylate는 일분자반응이 일어나는 것으로 추정할 수 있었다.

• Environmental Engineering Research
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• 제12권5호
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• pp.211-217
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• 2007

Polycyclic aromatic hydrocarbon growth from cyclopentadiene (CPD) pyrolysis was investigated using a laminar flow reactor operating in a temperature range of 600 to $950^{\circ}c$. Major products from CPD pyrolysis are benzene, indene and naphthalene. Formation of observed products from CPD is explained as follows. Addition of the cyclopentadienyl radical to a CPD $\pi$-bond produces a resonance-stabilized radical, which further reacts by one of three unimolecular channels: intramolecular addition, C-H bond $\beta$-scission, or C-C bond $\beta$-scission. The intramolecular addition pathway produces a 7-norbornenyl radical, which then decomposes to indene. Decomposition by C-H bond $\beta$-scission produces a biaryl intermediate, which then undergoes a ring fusion sequence that has been proposed for dihydrofulvalene-to-naphthalene conversion. In this study, we propose C-C bond $\beta$-scission pathway as an alternative reaction channel to naphthalene from CPD. As preliminary computational analysis, Parametric Method 3 (PM3) molecular calculation suggests that intramolecular addition to form indene is favored at low temperatures and C-C bond $\beta$-scission leading to naphthalene is predominant at high temperatures.

• 청정기술
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• 제16권3호
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• pp.198-205
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• 2010

염화탄화수소 열분해와 생성물분포 특성을 고찰하기 위해 등온 관형 반응기를 이용해 두 가지 실험을 수행하였다. 첫 번째는 반응분위기에 따른 열분해 특성을 파악하기 위해 $H_2$ 또는 Ar 반응분위기에서 dichloromethane ($CH_2Cl_2$) 분해율과 생성물분포 특성을 고찰하였다. Ar 반응분위기($CH_2Cl_2$/Ar 반응계)에서 보다 $H_2$ 반응분위기($CH_2Cl_2/H_2$ 반응계)에서 $CH_2Cl_2$ 분해율이 더 높았다. 이는 반응성 기체인 $H_2$ 분위기에서 $CH_2Cl_2$ 분해를 촉진시키며 수소 첨가 탈염소반응을 통해 탈염소화된 탄화수소화합물을 생성시키며, 다환방향족탄화수소 (polycyclic aromatic hydrocarbon: PAH)와 soot 생성을 억제하기 때문이다. $CH_2Cl_2/H_2$ 반응계에서 주요생성물로 탈염소화합물인 $CH_3Cl,\;CH_4,\;C_2H_6,\;C_2H_4,\;HCl$ 등이 생성되었으며, 미량 생성물로 chloroethylene이 검출되었다. $CH_2Cl_2$/Ar 반응계에서는 탄소물질수지가 낮았으며 특히 반응온도 $750^{\circ}C$ 이상에서 탄소물질 수지가 더 낮게 나타났다. 주요 생성물로는 chloroethylene과 HCl이 검출되었으며, 미량 생성물로는 $CH_3Cl$과 $C_2H_2$이 검출되었다. 고온 Ar 반응분위기에서 $CH_4$ 주입에 따른 chloroform($CHCl_3$) 분해와 생성물분포 특성을 비교 고찰하였다. $CHCl_3$ 분해율을 비교해 보면 $CH_4$을 주입할 경우($CHCl_3/CH_4/Ar$ 반응계)가 $CH_4$을 주입하지 않았을 경우($CHCl_3$/Ar 반응계)보다 분해율이 낮았다. 이는 $CHCl_3$가 분해되면서 생성되는 활성도가 큰 이중라디칼(diradical)인 :$CCl_2$가 첨가물로 주입된 $CH_4$와 반응하여 소모됨으로써 $CHCl_3$ 분해율이 상대적으로 감소되기 때문이다. Ar 반응분위기에서 $CH_4$ 첨가 여부에 따라 $CHCl_3$이 분해되면서 생성되는 생성물 분포는 큰 차이를 나타내고 있었다. 앞에서 고찰된 각 반응계에서 분해율 비교와 생성물 분포특성을 고려하고 열화학이론 및 반응속도론을 기초로 주요 반응경로를 제시하였다.