• Bulletin of the Korean Chemical Society
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• v.29 no.10
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• pp.1937-1940
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• 2008

The P1 duplex of Tetrahymena group I ribozyme is the important system for studying the conformational changes in folding of ribozyme. The formation of the P1 duplex between IGS and substrate RNA and the catalytic activity of ribozyme require a variety of metal ions such as $Mg^{2+}$ and $Mn^{2+}$. In order to investigate the effect of the $Mg^{2+}$ concentration on the conformation of the P1 duplex, the NMR study was performed as a function of $Mg^{2+}$ concentration. This study revealed that the less stable AU-rich region formed duplex at $50{^{\circ}C}$ under high $Mg^{2+}$ concentration condition but melts out under low $Mg^{2+}$ concentration condition. It was also found that in the active conformation under 10 mM $MgCl_2$ condition, the unstable central G${\cdot}$U wobble pair maintains the significant base pairing up to $50{^{\circ}C}$. This study provides the information of the unique feature of the P1 duplex structure and the roll of $Mg^{2+}$ ion on the formation of the active conformation.

• Bulletin of the Korean Chemical Society
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• v.32 no.8
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• pp.2584-2592
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• 2011

Nickel nanoparticle-poly(N-vinyl-2-pyrrolidone)/$TiO_2-ZrO_2$ composite (Ni-PVP/$TiO_2-ZrO_2$) was prepared by in situ polymerization method. The physical and chemical properties of Ni-PVP/$TiO_2-ZrO_2$ were investigated by XRD, FT-IR, BET, TGA, SEM and TEM techniques. The catalytic performance of this novel heterogeneous catalyst was determined for the Suzuki-Miyaura cross-coupling reaction between aryl halides and phenylboronic acid in the presence of methanol-water mixture as solvent. The effects of reaction temperature, the amount of catalyst, amount of support, solvent, and amount of metal for the synthesis of Ni-PVP/$TiO_2-ZrO_2$, were investigated as well as recyclability of the heterogeneous composite. The catalyst used for this synthetically useful transformation showed considerable level of reusability besides very good activity.

• Carbon letters
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• v.12 no.4
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• pp.185-193
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• 2011

Carbon nanotubes (CNTs) have developed into one of the most competitively researched nano-materials of this decade because of their structural uniqueness and excellent physical properties such as nanoscale one dimensionality, high aspect ratio, high mechanical strength, thermal conductivity and excellent electrical conductivity. Mass production and structure control of CNTs are key factors for a feasible CNT industry. Water and ethanol vapor enhance the catalytic activity for massive growth of vertically aligned CNTs. A shower system for gas flow improves the growth of vertically aligned single walled CNTs (SWCNTs) by controlling the gas flow direction. Delivery of gases from the top of the nanotubes enables direct and precise supply of carbon source and water vapor to the catalysts. High quality vertically aligned SWCNTs synthesized using plasma enhance the chemical vapor deposition technique on substrate with suitable metal catalyst particles. This review provides an introduction to the concept of the growth of vertically aligned SWCNTs and covers advanced topics on the controlled synthesis of vertically aligned SWCNTs.

• Carbon letters
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• v.13 no.2
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• pp.99-108
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• 2012

The sol-gel technique has been studied to fabricate a homogeneous Fe-Mo/MgO catalyst. Ambient effects (air, Ar, and $H_2$) on thermal decomposition of the citrate precursor have been systematically investigated to fabricate an Fe-Mo/MgO catalyst. Severe agglomeration of metal catalyst was observed under thermal decomposition of citrate precursor in air atmosphere. Ar/$H_2$ atmosphere effectively restricted agglomeration of bimetallic catalyst and formation of highly-dispersed Fe-Mo/MgO catalyst with high specific surface-area due to the formation of Fe-Mo nanoclusters within MgO support. High-quality thin-multiwalled carbon nanotubes (t-MWCNTs) with uniform diameters were achieved on a large scale by catalytic decomposition of methane over Fe-Mo/MgO catalyst prepared under Ar-atmosphere. The produced t-MWCNTs had outer diameters in the range of 4-8 nm (average diameter ~6.6 nm) and wall numbers in the range of 4-7 graphenes. The as-synthesized t-MWCNTs showed product yields over 450% relative to the utilized Fe-Mo/MgO catalyst, and indicated a purity of about 85%.

• 한국전기화학회:학술대회논문집
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• 2001.06a
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• pp.37-42
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• 2001

The electrooxidation of methanol was studied using Pt, PtNi(1.1 and 3:1), PtRuNi and PtRu(1:1) alloy nanoparticles in sulfuric acid solution for application to a direct methanol fuel cell. The PtNi and PtRuNi alloys showed excellent catalytic activities compared to those of pure Pt and PtRu. The role of Ni in the electrocatalytic activity was investigated using cyclic voltammetry (CV), chronoamperometry (CA), X-ray photoelectron spectroscopy (XPS). The XPS data confirm that the chemical states of Pt are exclusively metal as well as the presence of metallic Ni, NiO, $Ni(OH)_2$, NiOOH, metallic Ru, $RuO_2$, and $RuO_3$. Negative shifts of the binding energies of Pt for the PtNi alloy nanoparticles were determined by XPS measurements. This can be explained based by assuming that the enhanced activities of PtNi alloys for methanol electrooxidation were caused by the oxide states of Ni and by the change in the electronic structure of Pt component in the alloys.

• Journal of Microbiology and Biotechnology
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• v.8 no.3
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• pp.270-276
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• 1998

Extracellular ${\alpha}$-glucosidase was purified to homogeneity from moderately thermophilic Bacillus sp. DG0303. The thermostable ${\alpha}$-glucosidase was purified by ammonium sulfate fractionation, ion-exchange chromatography, preparative polyacrylamide gel electrophoresis (PAGE), and electroelution. The molecular weight of the enzyme was estimated to be 60 kDa by SDS-PAGE. The optimum temperature for the action of the enzyme was at $60^{\circ}C$. It had a half-life of 35 min at $60^{\circ}C$. The enzyme was stable at the pH range of 4.5~7.0 and had an optimum pH at 5.0. The enzyme preparation did not require any metal ion for activity. The thermostable ${\alpha}$-glucosidase hydrolyzed the ${\alpha}$-1,6-linkages in isomaltose, isomaltotriose, and panose, and had little or no activity with maltooligosaccharides and other polysaccharides. The $K_m$ (mM) for p-nitrophenyl-${\alpha}$-D-glucopyranoside (pNPG), panose, isomaltose, and isomaltotriose were 4.6, 4.7, 40.8, and 3.7 and the $V_{max}$(${\mu}mol{\cdot}min^-1$$mg^-1$) for those substrates were 5629, 1669, 3410, and 1827, respectively. The N-terminal amino acid sequence of the enzyme was MERVWWKKAV. Based on its substrate specificity and catalytic properties, the enzyme has been assigned to be an oligo-1,6-glucosidase.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.384.1-384.1
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• 2014

대면적 그래핀을 합성하는 방법으로 주로 화학기상증작법, SiC 기판을 고온 열처리하는 방법 그리고 최근에는 고체소스를 활용하여 그래핀을 합성하는 방법 등이 보고되고 있다. 이에, 본 연구에서는 폴리머 용액들을 원하는 기판에 스핀코팅하여 건조시킨 후, 후 열처리 공정을 통해 그래핀을 합성하고 물성을 평가해보았다. 그래핀 합성을 위해서 사용된 폴리머 탄소원은 Vinyl계 폴리머 용액으로, polystyrene (PS), polyacrylonitrile (PAN), 그리고 polymethylmetacrylate (PMMA) 등으로 2wt%의 폴리머 용액을 $SiO_2$기판에 스핀 코팅을 하고, 그 위에 Nickel이나 Copper와 같은 catalytic metal을 capping layer로 증착하고, 고진공에서 후열처리 공정에 의해 그래핀을 성장하였다. 이때, 탄소원으로 쓰인 PS, PMMA 폴리머는 pristine graphene 합성을 위해, PAN 폴리머는 질소가 도핑된(n-type) 그래핀 합성을 위해 사용되었다. 그래핀의 물성은 폴리머 종류, 코팅된 두께, 촉매 금속층 종류와 두께, 그리고 후열처리 공정 온도와 시간에 따라서 조절이 가능하였다. 우리는 Raman spectroscopy, AFM, SEM 등을 활용하여 그래핀의 층수, 결함, 표면양상 등을 평가하였고, 또한 전사된 그래핀을 기반으로 제작된 FET의 게이트 전압에 따른 I-V 곡선을 측정하여 캐리어 종류 및 전하 이동도 등을 평가하였다. 더욱 상세한 내용은 프레젠테이션에서 논하겠다.

• Applied Chemistry for Engineering
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• v.3 no.4
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• pp.717-721
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• 1992

Mechanical mixtures of vanadium molybdate and copper molybdate catalysts prepared by coprecipitation method, and those of $MoO_3$ and $V_2O_5$ were used to study the synergistic effects between each metal oxide for the selective oxidation of acrolein. The catalytic activity results revealed that the conversion of acrolein and yield of acrylic acid were increased with the mixture catalysts and it could be explained by a remote control mechanism. Thermal gravimetric analysis confirmed the evolution of lattice oxygen in the mixture catalysts.

• Macromolecular Research
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• v.13 no.6
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• pp.491-498
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• 2005

Fluorene-containing, spiro-type, conjugated polymers were synthesized via the cyclopolymerization of dipropargylfluorenes (2-substituted, X=H, Br, Ac, $ NO_{2}$) with various transition metal catalysts. The polymerization of dipropargylfluorenes proceeded well using Mo-based catalysts to give a high polymer yield. The catalytic activities of the Mo-based catalysts were found to be more effective than those of W-based catalysts. The palladium (II) chloride also increased the polymer yield of the polymerization. The polymer structure of poly(dipropargylfluorene)s was characterized by such instrumental methods as NMR ($^{1}H_{-}$, $^{13}C_{-}$), IR, UV-visible spectroscopies, and elemental analysis as having the conjugated polymer backbone bearing fluorene moieties. The $^{13}C_{-}$NMR spectral data on the quaternary carbon atoms in polymers indicated that the conjugated cyclopolymers have the six-membered rings majorly. The poly(dipropargylfluorene) derivatives were completely soluble in halogenated and aromatic hydrocarbons such as methylene chloride, chloroform, benzene, toluene, and chlorobenzene. The poly(dipropargylfluorene) derivatives were thermally more stable than poly(dipropargylfluorene) itself, and X-ray diffraction analyses revealed that the polymers are mostly amorphous. The photoluminescence peaks of the polymers were observed at about 457-491 nm, depending on the substituents of fluorene moieties.

• Journal of the Korean Chemical Society
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• v.30 no.1
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• pp.101-104
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• 1986

Dialdehydes such as adipaldehyde, glutaraldehyde, and succinaldehyde were readily reduced to give their corresponding 1,6-hexanediol, 1,5-pentanediol, and 1,4-butanediol in good yields in the presence of catalytic amount of hexarhodium hexadecacarbonyl or iron pentacarbonyl in water and methoxyethanol or ethanol at 180$^{\circ}C$ for 4 hr under carbon monoxide atmosphere. Under the same reaction conditions, diketones such as 2,5-hexanedione, 2,4-pentanedione, and 2,3-butanedione afforded their corresponding 2,5-hexanediol, 2,4-pentanediol and 2,3-butanediol in moderate yields. For double hydrohydroxymethylation of dialdehydes or diketones, rhodium or iron carbonyl complexes are more effective than others. Particularly, benzoquinone gave hydroquinone quantitatively.