• Bulletin of the Korean Chemical Society
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• v.29 no.10
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• pp.1920-1926
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• 2008

We investigated the C-H bond activation mechanism of aldimine by the [RhCl$(PPH_3)_3$] model catalyst using DFT B3LYP//SBKJC/6-31G*/6-31G on GAMESS. Due to their potential utility in organic synthesis, C-H bond activation is one of the most active research fields in organic and organometallic chemistry. C-H bond activation by a transition metal catalyst can be classified into two types of mechanisms: direct C-H bond cleavage by the metal catalyst or a multi-step mechanism via a tetrahedral transition state. There are three structural isomers of [RhCl$(PH_3)_2$] coordinated aldimine that differ in the position of chloride with respect to the molecular plane. By comparing activation energies of the overall reaction pathways that the three isomeric structures follow in each mechanism, we found that the C-H bond activation of aldimine by the [RhCl$(PH_3)_3$] catalyst occurs through the tetrahedral intermediate.

• Preventive Nutrition and Food Science
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• v.12 no.4
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• pp.251-258
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• 2007

Thermal resistance and heat activation characteristics of Clostridium botulinum ATCC 25763 spores were evaluated. The effects of nisin and pH on the activation and subsequent germination were also investigated. Spores of C. botulinum were not inactivated by heat treatments up to $92^{\circ}C$ for 2 hr. Heat treatment at $85^{\circ}C$ for 90 min was selected as the optimal activation condition based on monitoring subsequent germination. L-alanine alone or in combination with L-cysteine was not sufficient to germinate the spores of this strain. Tryptone-Peptone- Glucose-Yeast extract (TPGY) broth supplemented with L-alanine was used as a suitable germination medium. Decreasing pH of activation suspension increased the degree of phase darkening, i.e., germination. In addition, the presence of nisin during activation increased the degree of phase darkening. The majority of spore populations were dormant at a pH of less than 2.8, and these populations required heat activation to increase the culturability on TPGY agar medium. However, extended heating in the presence of nisin at pH 2.8 decreased the spore count; however, heat activation was less necessary at pH 3.4, compared at pH 2.8.

• Bulletin of the Korean Chemical Society
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• v.24 no.6
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• pp.829-831
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• 2003

Various theoretical studies of σ-bond activation of organic molecules by transition metal complexes arereviewed. In the homolytic σ-bond activation, the d orbital energy level of the central metal is an importantfactor, as well known. At the same time, the electron-withdrawing substituent which stabilizes the sp3 orbitalaccelerates the homolytic σ-bond activation. In the heterolytic C-H σ-bond activation of RH by $MXL_n$, the XHbond formation is an important driving force, where $MRL_n$ and HX are formed as products. The heterolytic σ-bond activation is also understood in terms of the electrophilic attack of the metal center to the substrate.

• Bulletin of the Korean Chemical Society
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• v.32 no.spc8
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• pp.2865-2866
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• 2011

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.07a
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• pp.346-349
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• 2002

High Power and high dose ion implantation is essentially needed to make power MOSFET devices based on SiC wafers, because the diffusivities of the impurities such as Al, N, p, B in SiC crystal are very low. In addition, it is needed high temperature annealing for electrical activation of the implanted species. Due to the very high annealing temperature, the surface morphology after electrical activation annealing becomes very rough. We have found the different surface morphologies between implanted and unimplanted region. The unimplanted region showed smoother surface morphology It implies that the damage induced by high energy ion implantation affects the roughening mechanism. Some parts of Si-C bonding are broken in the damaged layer, s\ulcorner the surface migration and sublimation become easy. Therefore the macrostep formation will be promoted. N-type 4H-SiC wafers, which were Al ion implanted at acceleration energy ranged from 30kev to 360kev, were activated at 1600$^{\circ}C$ for 30min. The pre-activation annealing for damage relaxation was performed at 1100-1500$^{\circ}C$ for 30min. The surface morphologies of pre-activation annealed and activation annealed were characterized by atomic force microscopy(AFM).

• Molecules and Cells
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• v.28 no.6
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• pp.545-551
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• 2009

Mitogen-activated protein kinases (MAPK) affect the activation of activator protein-1 (AP-1), which plays an important role in regulating a range of cellular processes. However, the roles of these signaling factors on hydrogen peroxide ($H_2O_2$)-induced cell death are unclear. This study examined the effects of $H_2O_2$ on the activation of MAPK and AP-1 by exposing the cells to $H_2O_2$ generated by either glucose oxidase or a bolus addition. Exposing BJAB or Jurkat cells to $H_2O_2$ affected the activities of MAPK differently according to the method of $H_2O_2$ exposure. $H_2O_2$ increased the AP-1-DNA binding activity in these cells, where continuously generated $H_2O_2$ led to an increase in mainly the c-Fos, FosB and c-Jun proteins. The c-Jun-$NH_2$-terminal kinase (JNK)-mediated activation of c-Jun was shown to be related to the $H_2O_2$-induced cell death. However, the suppression of $H_2O_2$-induced oxidative stress by either JNK inhibitor or c-Jun specific antisense transfection was temporary in the cells exposed to glucose oxidase but not to a bolus $H_2O_2$. This was associated with the disruption of death signaling according to the severe and prolonged depletion of reduced glutathione. Overall, these results suggest that $H_2O_2$ may decide differently the mode of cell death by affecting the intracellular redox state of thiol-containing antioxidants, and this depends more closely on the duration exposed to $H_2O_2$ than the concentration of this agent.

• Journal of the Korean Chemical Society
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• v.48 no.3
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• pp.327-330
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• 2004

• Korean Journal of Materials Research
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• v.13 no.1
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• pp.31-35
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• 2003

The intensity is measured as functions of both distance from filament to substrate and $CH_3$OH/($CH_3$OH＋$H_2$O) ratio by OES(Optical Emission Spectroscopy) to investigate the effects of activation species such as $H_{\alpha}$, $H_{\beta}$, H$\Upsilon\;C_3$, CH on diamond film growth.$ H_{\alpha}$ increases as $CH_3$OH composition decreases, while CH increases as $CH_3$OH composition increases. The intensity of $H_{\alpha}$ decreases as the distance increases and that of CH increases as the distance increases. The intensities of other activation species of $H_{\beta}$, H$\Upsilon\;C_3$, do not vary as a function of measured position distance. It varies randomly. It means that various parameters for depositing diamond thin film can be explained by the intensity(density) change of activation species, as a function of the distance of the filament.

• Korean Journal of Food Science and Technology
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• v.12 no.3
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• pp.209-215
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• 1980

Proteases from papaya latex were partially purified by ammonium sulfate precipitation and separated into two fractions (Fraction I and II ) by carboxymethyl cellelose column chromatography. Each fraction, mixture of the two fractions, and crude extract of the papaya latex at pH 7.0 were inactivated at the range of $60{\sim}90^{\circ}C$ and thermal properties of the enzymes were investigated. In the thermal inactivation of fraction I, the enthalpy of activation was 89.5 kJ/mol; the entropy of activation, -44.0 J/mol K; the free energy of activation, 104.6 kJ/mol; z-value, $25^{\circ}C$. For fraction II, the enthalpy of activation was 96.5 kJ,/mol; the entropy of activation, -22.0 J/mol K; the free energy of activation, 104.0 kJ/mol; z-value, $23^{\circ}C$. For the mixture of fraction I and II, the enthalpy of activation was 90.9 kJ/mol; the entropy of activation, -38.8 J/mol·K; the free energy of activation, 104.2 kJ/mol; z-value, $24.6^{\circ}C$. For crude extract, the enthalpy of activation was 113.8 kJ/mol; the entropy of activation, 22.0 J/mol·K; the free energy of activation, 106.2 kJ/mol; z-value, $23.2^{\circ}C$. It was indicated that the fraction I was more heat-stable than the fraction II and this suggested that the thermal stability of the proteases in papaya latex is probably due to the fraction I.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2003.11a
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• pp.13-16
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• 2003

There is no study that application of the maturity using H.B.C and H.S.C. Also activation energy has different values according to the cement, admixture and water-cement ratio. Therefore to make accurate explanation for the effect of temperature on concrete strength development properties, it is necessary that activation energy value according to the kind of cement is reviewed. This study compares and estimates equivalent age using activation energy value obtained by this experiment and Freiesleben activation energy value with compressive strength of concrete. As the result of this study, activation energy value obtained by this study has more accurate explanation of temperature's influence on concrete strength development than Freiesleben activation energy value.