• Journal of the Korean Chemical Society
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• v.19 no.3
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• pp.179-185
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• 1975

A new mechanism is proposed for aromatic substitution, involving the formation of pseudo molecular complexes at the transition state. It accounts for the addition reactions of aromatic compounds with double bond reagents such as ozone, somium tetraoxide and carbene as well as all of the features of electrophilic substitution reactions. The pseudo molecular complex has been proved to be formed by quantum-chemical considerations using the simple Huckel method.

• Journal of the Korea Concrete Institute
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• v.29 no.4
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• pp.379-387
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• 2017

The objective of this study is to develop sustainable PVA fiber-reinforced cementitious composites (FRCCs) that could exhibit comparable strength level to normal PVA FRCCs with no recycled materials. To evaluate mechanical properties of the FRCCs, compressive, flexural and direct tensile tests were conducted. In addition to the test, to calculate amount of carbon dioxide ($CO_2$) emission at the stage of manufacturing the FRCCs, life cycle inventory data base (LCI DB) were referenced from domestic and Japan. From the test results, the mechanical properties such as compressive, flexural and direct tensile strengths were decreased as the replacement ratio of recycled materials increased. And it was determined that the amount of $CO_2$ emission was reduced for the specimens with higher water-binder ratio (W/B) and replacement ratios. It was also found that binder intensity ($B_i$) value was higher as replacement ratio of fly ash (FA) increased. This result means that larger amount of FA is need to deliver one unit of a given performance indicator (1 MPa of strength) of FRCCs compared to that of ordinary portland cement (OPC). As a result, it could be concluded that FRCCs with W/B 45% replaced by FA 25% and recycled sand (RS) 25% is desirable for both target performance and $CO_2$ emission.

• Journal of the Korean Applied Science and Technology
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• v.30 no.1
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• pp.160-165
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• 2013

In order to express the natural color in organic light emitting diode(OLED), red, green, and blue luminescent materials are needed. While lots of red and green emitters are searched actively, not many useful blue emitters are found yet. It is due to the high energy gap for the blue emission. This research is about a synthesis of the blue emitting compound with high emission efficiency and thermal stability, which starts with carbazole and anthracene. Carbazole with bulky substituent, tert-butyl group, is connected directly to electroluminescent and thermally stable anthracene. The distance between the hole transporting group and the electron transporting group are studied for the relevance to the luminescence.

• Journal of the Korean Chemical Society
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• v.36 no.1
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• pp.51-56
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• 1992

X-ray diffraction analysis and infrared spectrophotometry were used to investigate the crystal structures and the bonding characteristics in $Pb(Zr_{1-y}Ti_y)O_3$ (PNZT), which has a perovskite structure. As $Pb^{2+}$ of PZT was substituted by 8${\sim}$12 atom% $Nd^{3+}$ ion, the structures were changed to cubic from tetragonal and its transmission had maximum value. Transmission increased as the stretching force constant $(k_s)$ of unit cell increased. It is supposed that the electro-optic characteristics might occur due to electron-transition from HOMO to LUMO of titanium ion.

• Journal of Life Science
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• v.14 no.5
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• pp.752-760
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• 2004

The function of the [4Fe-4S] cluster containing iron (Fe-) protein in nitrogenase catalysis is to serve as the nucleotide-dependent electron donor to the MoFe protein which contains the sites for substrate binding and reduction. The ability of the Fe protein to function in this manner is dependent on its ability to adopt the appropriate conformation for productive interaction with the MoFe protein and on its ability to change redox potentials to provide the driving force required for electron transfer. The MgADP-bound (or off) conformational state of the nitrogenase Fe protein structure described reveals mechanisms for long-range communication from the nucleotide-binding sites to control affinity of association with the MoFe protein component. Two pathways, termed switches I and II, appear to be integral to this nucleotide signal transduction mechanism. In addition, the structure of the MgADP bound Fe protein provides the basis for the changes in the biophysical properties of the [4Fe-4S] observed when Fe protein binds nucleotides. The structures of the nitrogenase Fe protein with defined amino acid substitutions in the nucleotide dependent signal transduction pathways of the Switch I and Switch II have been determined by X-ray diffraction methods. These two pathways have been also implicated by site directed mutagenesis studies, structural analysis and analogies to other proteins that utilize similar nucleotide dependent signal transduction pathways. We have examined the validity of the assignment of these pathways in linking the signals generated by MgATP binding and hydrolysis to macromolecular complex formation and intermolecular electron transfer. The results provide a structural basis for the observed biophysical and biochemical properties of the Fe protein variants and interactions within the nitrogenase Fe protein-MoFe protein complex.

• Proceedings of the Korean Magnestics Society Conference
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• 2002.12a
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• pp.100-101
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• 2002

자성가넷 박막은 가시광선 영역에서 큰 값의 페러데이 회전각을 갖고, 광흡수가 적어 우수한 자기광학 특성을 나타내는 재료로 널리 알려져 있다.[1]. 또한 가넷에 Bi를 치환하면 성능지수가 크게 증가하는 것이 알려져 있으므로 현재 연구개발의 초점이 Bi치환 가넷 박막에 모아지고 있다. 가넷박막을 제조하는 방법에 있어 종래에는 스퍼터링법, LPE법, 열분해법 등으로 연구되어 왔으나, 스퍼터링법과 LPE법의 경우 공정이 복잡하고 고가의 장치가 필요한 단점이 있으며, 열분해법의 경우에는 잔존하는 일부 분해가스로 인하여 박막이 다공질화 될 우려가 있다.[2]. (중략)

• Journal of the Korean Chemical Society
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• v.29 no.6
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• pp.565-574
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• 1985

The rates of reaction between 4-substituted-2,6-dinitrochlorobenzenes with para-substituted anilines in methanol-acetonitrile mixtures were measured by conductometry. It was observed that the rate constant increases in the order of X = 4-$NO_2 {\gg}4-CN {\gg}4- CF_3$, where X is a substituent in the substrate. The rate constant also increases in the order of Y = p-O$CH_3{\gg}p- CH_3{\gg}H {\gg}p-Cl{\gg}m- NO_2$, where Y is a substituent in the aniline ring. Kinetic studies in the methanol-acetonitrile solvent system with various nucleophiles showed that the N-C bond forming step is making a great contribution to the overall second order rate constant. The electrophilic catalysis by methanol probably consists of the hydrogen bonding between alcoholic hydrogen and leaving chloride in the transition state. The nucleophilic catalysis by methanol may be ascribed to the formation of hydrogen bonds between alcoholic oxygen and hydrogens of amines in the transition state. All these experimental facts are supporting the operation of $S_N$Ar machanism with the second step being the rate determining. This mechanism can be successfully fitted to the PES model.

• Journal of the Korean Chemical Society
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• v.33 no.1
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• pp.31-36
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• 1989

The second-order rate constants for the nucleophilic substitution reactions of para-substituted benzyl nitrates with para-substituted anilines in acetonitrile were conductometrically determined. Hammett ${\rho}$x and ${\rho}$y values and Bronsted ${\beta}$ values were obtained from these kinetic data. The reactions of Benzyl nitrates with the series of anilines showed linear Hammett plots with negative slopes. For the change of substituents in the benzyl nitrates, nonlinear Hammett plots with a concave upwards curve were obtained. We applied the potential energy surface and the quantum mechanical models in order to examine the transition state variations caused by changes in substituents on the nucleophile and the substrate. The results showed that the reaction was proceeded via the $S_{N}2$-type reaction mechanism in which the extent of bond-formation was greatly changed depending on the property of the substituents in substrate.

• Journal of the Korean Chemical Society
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• v.55 no.3
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• pp.392-399
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• 2011

Two conformations of benzoic acid derivatives ($NH_2$, OH, H, F, Cl, CN, NO, $NO_2$) have been investigated at MP2, DFT and HF level using the 6-311++G(d,p) basis set. It was found that the cis isomers are more stable. Hydrogen bonding formation of benzoic acids has been estimated from stabilization energies. The calculated hydrogen-bonding energies of dimers showed a cooperative interaction in the cyclic ones. It was found that an electron-releasing group (ERG) into the phenyl rings resulted in the formation of more stable hydrogen bonding. Red shift of O-H bond was found from -565.3 to -589.3 for dimers. The natural bond orbital (NBO) analysis was applied to characterize nature of the interaction.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 1998.11a
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• pp.195-200
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• 1998

토양내에 있어 중금속의 총량 분석만으로는 오염 토양에 대한 환경 평가를 위한 충분한 자료가 되지 못한다. 또한 중금속의 토양내 위해성은 중금속과 토양과의 화학적 상호작용에 의해 결정되기 때문에 중금속의 화학적 형태를 규명하는 것은 토양 환경에 있어서 그들의 이동성과 거동 특성을 평가하는데 중요한 자료가 된다. 연속 추출법은 구봉 광산의 광미로 부터 Cd, Cu, Pb을 화학적 형태에 따라 분리하고, 인위적으로 중금속을 포화시킨 광미와 두밭토양에 있어 중금속의 토양내 거동 특성을 예측하기 위하여 이용되었다. 광미중 Pb의 대부분은 Fe-Mn oxide, carbonate의 결합 형태로 존재하였으며, Cu와 Cd은 각각 71.8%와 42.9%가 유기물, carbonate의 결합형태로 존재하였다. 상당량의 Cd(94.9%), Cu(95.1%), 그리고 Pb(85.8%)은 토양내 잠재적으로 이동 가능한 형태로 존재하였다. 유성과 논산의 밭토양 에 가해진 Cd는 대부분 이동성이 가장 높은 치환태로 존재하였으며, 유성과 논산 토양에서 각각 67.9%와 93.2%가 치환태로 존재하였다. 토양에 가해진 Cd, Cu, Pb은 대부분 이동이 용이한 형태로 존재하였으며, 토양과의 결합세기는 Pb > Cu > Cd 순으로 감소하였다.