• Macromolecular Research
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• v.8 no.5
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• pp.238-242
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• 2000

The new trisiloxane-bridged heterometallic dinuclear metallocenes, hexamethyltrisiloxanediyl(cyclopentadienyltitanium trichloride) (cyclopentadienylindenyl zirconium dichloride) , $C_3ITi-Cp(CH_3)_2Si-O-Si(CH_3)_2-O-Si(CH_3)_2-Cp-ZrIndCI_2$ (1) and hexamethyltrisiloxanediyl (cyclopentadienylindenylhafnium dichloride) (cyclopentadienylindenyl zirconium dichloride), $C_2IndHf-Cp(CH_3)_2Si-O-Si(CH_3)_2-Cp-ZrIndCl_2$ 2) connecting two dissimilar metallocenes were synthesized and used for ethylene polymerization in the presence of modified methylaluminoxane (MMAO) cocatalyst. The catalytic activity of heterometallic dinuclear metallocenes, 1 and 2 was lower than that of corresponding mononuclear metal-locene as well as two physically mixed catalysts, $CpTiCl_2/Cp_2ZrCl_2 and Cp_2HfCl_2/Cp_2ZrCl_2$. On the tither hand, MWD of PE obtained with 1 and 2 was remarkably broader ($M_w/M_n$) became up to 9.4) than those of PEs prepared with the corresponding mononuclear metallocenes and mixed catalysts. With analysis by GPC and CFC, it was found that PE produced by the heterometallic dinuclear metallocenes exhibited the definite bimodal GPC curves that should cause the broadening of MWD.

• Bulletin of the Korean Chemical Society
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• v.35 no.6
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• pp.1749-1753
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• 2014

Pseudo-first-order rate constants ($k_{obsd}$) have been measured spectrophotometrically for the nucleophilic substitution reaction of Y-substituted-phenyl picolinates (7a-f) with potassium ethoxide (EtOK) in anhydrous ethanol at $25.0{\pm}0.1^{\circ}C$. The plot of $k_{obsd}$ vs. [EtOK] curves upward while the plot of $k_{obsd}/[EtO^-]_{eq}$ vs. $[EtO^-]_{eq}$ is linear with a positive intercept in all cases. Dissection of $k_{obsd}$ into $k_{EtO^-}$ and $k_{EtOK}$ (i.e., the second-order rate constants for the reactions with the dissociated $EtO^-$ ion and ion-paired EtOK, respectively) has revealed that the ion-paired EtOK is more reactive than the dissociated $EtO^-$. The ${\sigma}^{\circ}$ constants result in a much better Hammett correlation than ${\sigma}^-$ constants, indicating that the reaction proceeds through a stepwise mechanism in which departure of the leaving group occurs after the rate-determining step (RDS). $K^+$ ion catalyzes the reaction by increasing the electrophilicity of the reaction center through formation of a cyclic transition state (TS). The catalytic effect decreases as the substituent Y becomes a stronger electron-withdrawing group (EWG). Development of a positive charge on the N atom of the picolinyl moiety through resonance interactions is responsible for the decreasing $K^+$ ion catalysis.

• Transactions of the Korean hydrogen and new energy society
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• v.7 no.1
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• pp.11-18
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• 1996

The Laves phase alloy hydrides have some promising properties as electrode materials in reversible metal hydride batteries. In this work, the hydrogen storage performance, crystallographic parameters, surface morphology, surface area and electrochemical characteristics of the non-stoichiometric $ZrMn_{0.3}V_{0.7}Ni_{1.4+{\alpha}}$, $ZrMn_{0.5}V_{0.5}Ni_{1.4+{\alpha}}$($\alpha$ =0.0, 0.2, 0.4, 0.6) alloys were examined. These as-cast alloys were found to have mainly a cubic C15-type Laves phase structure by X -ray diffraction analysis. The equilibrium pressure of the alloy were increased as $\alpha$ increased in both two types alloy. In case of $ZrMn_{0.5}V_{0.5}Ni_{1.4+{\alpha}}$ alloys, discharge efficiency and the rate capability of the alloy were decreased as $\alpha$ increased but, these values were increased in case of $ZrMn_{0.3}V_{0.7}Ni_{1.4+{\alpha}}$ alloys. The differences of these electrode properties observed were dependent on the reaction surface area and the catalytic activity of unit area of the each electrode.

• Korean Chemical Engineering Research
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• v.43 no.5
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• pp.566-570
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• 2005

The study on the hydrogenation and isomerization of unsaturated bicyclic hydrcarbon compounds using methylcyclopentadiene dimer (MCPD) was carried out. Exo compound was prepared through isomerization reaction after two hydrogenation reaction steps. In the first hydrogenation reaction which needs one mole of hydrogen, the formation rate of monomer was increased as dimer was decomposed at reaction temperature above $100^{\circ}C$. At first hydrogenation, DHDMCPD [dihydrodi(methylcyclopentadiene)] was formed and second hydrogenation was proceeded to produce THDMCPD [tetrahydrodi(methylcyclopentadiene)], the ratio of exo to endo THDMCPD was varied by the control of 2nd hydrogenation temperature. To improve the process, continuous 1st and 2nd hydrogenation conditions were established by using the 2nd stage heat controllable reactor. Also, catalytic activities were compared by the use of halogenized aluminum, metal halides and solid acids catalysts on the isomerization reaction from endo to exo THDMCPD.

• BMB Reports
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• v.35 no.1
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• pp.116-126
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• 2002

Nitric oxide (NO), synthesized from L-arginine by NO synthases, is a small, lipophilic, diffusible, highly reactive molecule with dichotomous regulatory roles in many biological events under physiological and pathological conditions. NO can promote apoptosis (pro-apoptosis) in some cells, whereas it inhibits apoptosis (anti-apoptosis) in other cells. This complexity is a consequence of the rate of NO production and the interaction with biological molecules such as metal ion, thiol, protein tyrosine, and reactive oxygen species. Long-lasting overproduction of NO acts as a pro-apoptotic modulator, activating caspase family proteases through the release of mitochondrial cytochrome c into cytosol, up-regulation of the p53 expression, and alterations in the expression of apoptosis-associated proteins, including the Bcl-2 family. However, low or physiological concentrations of NO prevent cells from apoptosis that is induced by the trophic factor withdrawal, Fas, $TNF{\alpha}$/ActD, and LPS. The anti-apoptotic mechanism is understood on the basis of gene transcription of protective proteins. These include: heat shock protein, hemeoxygenase, or cyclooxygenase-2 and direct inhibition of the apoptotic executive effectors caspase family protease by S-nitrosylation of the cysteine thiol group in their catalytic site in a cell specific way. Our current understanding of the mechanisms by which NO exerts both pro- and anti-apototic action is discussed in this review article.

• Bulletin of the Korean Chemical Society
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• v.32 no.2
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• pp.639-644
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• 2011

A simple and highly sensitive chemiluminescence method to determine norfloxacin (NFLX) has been proposed by measuring the chemiluminescence (CL) intensities using a flow injection (FI) system. The CL intensity of the luminol-$H_2O_2$ system is strongly enhanced by the addition of Cu (II) in alkaline condition. The CL intensity is substantially increased after the injection of NFLX into the luminol-$H_2O_2$-Cu (II) system. The enhancement effect is attributed to a catalytic effect of Cu (II) due to the interaction with NFLX which forms a complex with the catalyst. Under the optimal conditions, the sensitizing effect of the CL intensity is proportional to the concentration of NFLX in the range of $1.5{\times}10^{-9}-5.9{\times}10^{-7}molL^{-1}$ (r = 0.9994) with a detection limit ($3{\sigma}$) of $2.98{\times}10^{-10}molL^{-1}$. The proposed method had good reproducibility with the relative standard deviation (RSD, n = 5) of 1.6% for $1{\times}10^{-7}molL^{-1}$ of NFLX. The possible reaction mechanism of the CL reaction is also discussed. This method has been successfully applied for the determination of trace amount of NFLX in pharmaceutical preparations and serum samples.

• Applied Chemistry for Engineering
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• v.3 no.1
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• pp.24-34
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• 1992

Recent studies dealing with the fundamental understanding and applications of bimetallic catalysts are discussed. Bimetallic catalysts have had a major industrial impact, specifically for the reforming of petroleum naphtha, for the hydrogen reduction of carbon monoxide, and for the three way catalytic converter system. The action of the bimetallic catalysts in these reactions may be interpreted in terms of ensembles, electronic influences and surface structure. Various combinations of metal pairs have been considered in order to evaluate the role played by the added metals. For catalyst selectivity control, the possibility of surface enrichment of one element has been recognised. More generally, the influence of preparative variables on the formation of supported catalysts has been clarified, In particular by temperature programmed reduction (TPR). Information on the structure of bimetallic catalysts has been obtained with chemical probes, such as chemisorption and reaction rate measurement and physical probes, such as extended X-ray absorption fine structure (EXAFS), scanning transmission electron microscopy (STEM) and Xe-NMR.

• Applied Chemistry for Engineering
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• v.20 no.1
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• pp.28-33
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• 2009

Carbon nanotube supported molybdenum carbide catalysts were prepared as a function of various preparation conditions and characterized, and their catalytic activities were compared through electrochemical oxidation of methanol. To overcome the low activity of a transition metal catalyst, carbon nanotube was used as a support, and the amount and the kind of precursors, acid treatment method, and carburization temperature were varied for the catalyst preparation. ICP-AES, XRD and TEM were used for the catalyst characterization. Based on the various preparation methods of carbon nanotube supported molybdenum carbide catalysts ($Mo_2C/CNT$), the size and the amount of supported catalysts could be controlled, and their effects on the electrochemical oxidation could be explained.

• Applied Chemistry for Engineering
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• v.30 no.6
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• pp.652-658
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• 2019

Direct hydrazine fuel cells (DHFCs) have been considered to be one of the promising fuel cells because hydrazine as a liquid fuel possesses several advantages such as no emission of CO₂, relatively high energy density and catalytic activity over platinum group metal (PGM)-free anode catalysts. Judging from plenty of research works, however, regarding key components such as electrocatalysts as well as their physicochemical properties, it becomes quite necessary to understand better the underlying processes in DHFCs for the long term stability. Herein, we highlight recent studies of DHFCs in terms of a systematic approach for developing cost-effective and stable anode catalysts and electrode structures that incorporate mass transport characteristics of hydrazine, water and gas bubbles.

• Transactions of the Korean hydrogen and new energy society
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• v.26 no.4
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• pp.339-346
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• 2015

The synthesis of Fischer-Tropsch (FT) oil is the catalytic hydrogenation of CO to give a range of products, which can be used for the production of high-quality diesel fuel, gasoline and linear chemicals. This studied catalyst was prepared Cobalt-supported alumina and silica by the incipient wet impregnation of the nitrates of cobalt, promoter and organic solvent with supports. Cobalt catalysts were calcined at $350^{\circ}C$ before being loaded into the FT reactors. After the reduction of catalyst has been carried out under $450^{\circ}C$ for 24h, FT reaction of the catalyst has been carried out at GHSV of 4,000/hr under $200^{\circ}C$ and 20atm. From these experimental results, we have obtained the results as following; In case of $SiO_2$ catalysts, the activity of 12wt% $Cobalt-SiO_2$ synthesized by organic solvent was about 2 or 3 times higher than the activity of 12wt% $Cobalt-SiO_2$ catalyst synthesized without organic solvent. In particular, the activity of the $Cobalt-SiO_2$ catalyst prepared in the presence of an organic solvent P was two to three times higher than that of the $Cobalt-SiO_2$ catalyst prepared without the organic solvent. Effect of Cr and Cu metal as a promoter was found little. 200 h long-term activity test was performed with a $Co/SiO_2$ catalyst prepared in the presence of an organic solvent of Glyoxal solution.