• Korean Journal of Microbiology
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• v.28 no.2
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• pp.151-157
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• 1990

The maximum nitrogen fixation activity of the associative, microaerobic and acid tolerant bacteria, Azospirillum amazonense Kp1 was obtained with 0.2Kpa of $O_{2}$ and showed a reversible inhibition by the higher concentrations. Ammonium treatment caused a gradual inhibition of the activity up to 350mM. The nitrogenase systems were purified by gradient chromatography on DEAE-52 cellulose, heat treatment and preparative PAGE. The MoFe protein showed molecular weight of 210,000 including two nonidentical subunits with apparent molecular weights of 55,000 and 50,000 and an isoelectricpoint of 5.2 and contained 2, 24 and 28 atoms of Mo, Fe and acid labile S per molecule. The Fe protein revealed molecular weight of 66,000 including two types of subunits with molecular weights of 35,000 and 31,000 and an isoelectric point of 4.6, and contained 4 atoms of Fe and 6 atoms of S per molecule. The maximum specific nitrogenase activity attained 2,200 and 1,700nM $C_2H_4mg^{-1} min^{-1}$, respectively for MoFe and Fe proteins at pH7 and $35^{\circ}C$. The activity was lost after 10 and 30 days under the cold room ($4^{\circ}C$) condition for Fe and MoFe proteins, respectively.

• Applied Chemistry for Engineering
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• v.2 no.2
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• pp.127-137
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• 1991

The dissociation and partial oxidation of $CH_3OH$ on polycrystalline $MoO_3$ powder catalyst were studied using thermal desorption spectrometry(TDS) under high vacuum condition. $CH_3OH$ was dissociatively adsorbed on $MoO_3$ in the forms of surface methoxy($-OCH_3$) and atomic hydrogen(-H). $CH_3OH$ desorbed at 425 K via the re-association of methoxy and adsorbed hydrogen atom, and HCHO desorbed at 545 K through the bond breakage of C-H in methoxy. Water TDS spectra showed two desorption peaks, that is, ${\alpha}$-peak at 428 K and ${\beta}$-peak at 586 K. It was suggested that ${\alpha}$-peak was due to the hydroxyl formed on $MoO_3$ surface during the dissociation of $CH_3OH$, and that ${\beta}$-peak was from the association of lattice oxygen and surface hydrogen atom formed by the bond breakage of C-H in methoxy. Pre-adsorbed oxygen on the surface of $MoO_3$ catalyst increased the amount of adsorption of $CH_3OH$ by promoting the dissociation of $CH_3OH$ on the surface, whereas pre-adsorbed water decreased the amount of adsorption of $CH_3OH$ by blocking of adsorption sites for $CH_3OH$.

• Applied Chemistry for Engineering
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• v.5 no.4
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• pp.609-615
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• 1994

Partial oxidation of ethylene over 10wt% $Ag/{\alpha}-Al_2O_3$ catalyst was studied with a pulse reactor which was connected directly to a G. C. When ethylene was injected after oxygen injection at the temperature where molecular adsorption of oxygen is difficult ethylene oxide was evolved. From the results, it is suggested that adsorbed atomic oxygen is related with the evolution of ethylene oxide. The selectivity to ethylene oxide decreased with the decrease of the amounts of adsorbed oxygen and bulk oxygen. Ethylene oxide was either decomposed to ethylene and adsorbed oxygen or isomerized to acetaldehyde. However, the isomerization of ethylene oxide to acetaldehyde was strongly suppressed by the preadsorbed oxygen.

• Journal of the Korean Magnetics Society
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• v.25 no.4
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• pp.106-110
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• 2015

We have studied electronic and magnetic structure of 2 kinds of diiron molecules using OpenMX method based on density functional method. The calculated density of states of diiron-2 is similar with that of diiron-4 because of equal number of 6 ligand atoms. The calculated total energy with antiferromagnetic spin configuration is lower than those of ferromagnetic configurations for both of them. The exchange interaction J of diiiron-4 between $Fe^{+3}$ atoms is one order larger than that of diiron-2, and the calculated J matches well with the experimental one. That comes from the short distance of Fe-O and the high O 2p energy levels. It derives a strong super exchange interaction. The angle of diiron-4 between Fe atoms is bigger than that of diiron-2. It also derives a strong super exchange interaction because of the ${\sigma}$-bond between Fe and O atoms.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.5 no.4
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• pp.370-377
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• 1995

The recombination of oxygen and nitrogen atoms on the surfaces of two coating m materials of the Space Shuttle Orbiter (SSO), a reaction cured glass (RCG) and a spinel (C742), was investigated. The recombination probability, $\gamma$, i.e., the probability that atoms im p pinging on the surface will recombine, was measured in a diffusion reactor. Value of $\gamma$ for oxy g gen atom on C742 ($3 {\times} 10^{-2}$) was much higher than that on RCG ($4 {\times} 10^{-4}$) at the tempera t ture of SSO re-entry (ca. 1000K). The higher value of $\gamma$ on C742 indicates a higher number d density of active sites than RCG. It suggests the possibility of designing less active surfaces by i inducing the desorption at lower temperature.

• Journal of the Korean Chemical Society
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• v.30 no.2
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• pp.195-200
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• 1986

MO studies have been carried out on 1,5-hydrogen shifts between tautomeric forms (6${\pi}$ system) of ${\beta}$-diketones, ${\beta}$-thioxoketones and ${\beta}$-dithioketones by determining transition state and analyzing structural stability effects on the activation barriers using MNDO method. The barrier was found to increase with the stability of the ground state having greater charge separation and with the increase (less stabilization) in the one electron energy ${\Delta}(2\sum\limits^{occ}{\varepsilon}i)^{\neq}$ in the activation process.

• Journal of the Korean Chemical Society
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• v.16 no.6
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• pp.334-340
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• 1972

CNDO/2 calculations have been carried out on methyl chloro-thiol-, methyl chloro-thiono-, and methyl chloro-dithio-formates. Results show that the trans is the stable configuration for these compounds. It was found that sulfur atom has much less tendency to use its lone pair electrons for ${\pi}$ bond formation compared with oxygen, and that thiolformates are stabilized by hyperconjugation of methyl hydrogens. The order of solvolytic reactivity was found to follow the order of cation stability, which is consistent with the $S_N1$ mechanism proposed for these compounds.

• Korean Journal of Crystallography
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• v.13 no.2
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• pp.57-62
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• 2002

Time-of-flight impact-collision ion scattering spectroscopy (TOF-ICISS) was applied to study the geometrical structure of epitaxially grown TiO layers on a MgO(001) surface. The hetero-epitaxial TiO layer was deposited by thermal evaporation of titanium onto the MgO(001) surface and subsequent exposure to oxygen at 400℃. The well-ordered TiO structure was confirmed with the 1×1 RHEED pattern. TOF-ICISS results revealed that the TiO layer was formed at the on-top sites of the MgO(001) substrate and that the lateral lattice constant of TiO layer was the same as that of the MgO substrate. The surface of the deposited epitaxial TiO layer was smooth without the three dimensional islands.

• Journal of the Korean Chemical Society
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• v.22 no.1
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• pp.7-11
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• 1978

The reactions of 2,4-dinitroiodobenzene with para subtituted anilines in acetonitrile-methanol binary solvent mixtures have been studied. Rate constants for reactions in methanol rich solvents are greater than for reactions in acetonitrile rich solvents. Kinetic results show that the bond formation step is rate determining in the solvent system studied. The solvent effect can be explained by stabilization of the transition state by formation of hydrogen bond between oxygen atom of methanol and hydrogen atom of aniline.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.211-211
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• 2013

나노 크기의 공간에서의 물질의 이동은 표면의 환경에 의해 영향을 받을 수 있다. 소수성그래핀과 친수성 실리콘 기판 사이의 계면에서의 물의 확산은 호기심을 자극할 뿐만 아니라 그래핀 소자의 특성을 좌우하는 전하도핑(charge doping) 현상을 이해하는데 중요한 모델이 된다. 본 연구에서는 라만 분광법과 원자 힘 현미경을 사용하여 그래핀/SiO2 계면 사이의 물의 확산 현상과 그에 따른 정공 밀도 변화를 탐구하였다. 열처리 된 그래핀은 기판과의 상호 작용에 의해 높은 밀도의 정공(electron hole)으로 도핑 되어 있으며, 이를 물에 담지 하였다. 본 실험에서는 이차원 라만 분광법을 통해 물 속에 담겨진 그래핀의 정공 밀도의 공간적인 분포를 확산 시간에 따라 조사하였다. 물의 확산은 시료에 따라 수 시간에서 수 일의 시간대에 걸쳐 그래핀 가장자리에서 중앙으로 이루어진다는 사실을 확인하였다. 또한 물의 계면 확산으로 인하여 전하 밀도가 감소한다는 사실은 열처리 된 그래핀의 정공 도핑을 유발하는 산소가 계면에 존재한다는 것을 증명한다.