• Bulletin of the Korean Chemical Society
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• 제14권1호
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• pp.101-107
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• 1993

Ab initio calculations are carried out at the 6-311G$^{**}$ level for the $C_{2v}$ interactions of Be and Li atoms with acetylene molecule. The main contribution to the deep minima on the $^3B_2\;BeC_2H_2\;and\;^2B_2 LiC_2H_2$ potential energy curves is the b_2\;(2p(3b_2)-l{\pi}_g^*(4b_2))$ interaction, the $a_1\;(2s(6a_1)-I{\pi}_u(5a_1))$ interaction playing a relatively minor role. The exo deflection of the C-H bonds is basically favored, as in the $b_2$ interaction, due to steric crowding between the metal and H atoms, but the strong in-phase orbital interaction, or mixing, of the $a_1$ symmetry hydrogen orbital with the $5a'_1,\;6a'_1,\;and\;7a'_1$ orbitals can cause a small endo deflection in the repulsive complexes. The Be complex is more stable than the Li complex due to the double occupancy of the 2s orbital in Be. The stability and structure of the $MC_2H_2$ complexes are in general determined by the occupancy of the singly occupied frontier orbitals.

• 대한화학회지
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• 제29권1호
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• pp.23-30
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• 1985

${\pi}^{\ast}$-${\pi}^{\ast}$ 궤도간 상호작용에 관한 섭동식을 유도하였다. 섭동식으로부터 예측되는 ${\pi}$-${\pi}$와 ${\pi}^{\ast}$-${\pi}^{\ast}$ 상호작용간의 중요한 두가지 차이점은 : (ⅰ)에너지분리정도가 ${\pi}$-${\pi}$ 상호작용의 경우보다 ${\pi}^{\ast}$-${\pi}^{\ast}$의 경우가 더 컸으며, ( ii ) 상호작용에 의한 에너지 변화량은 ${\pi}$-${\pi}$ 상호작용의 경우보다 ${\pi}^{\ast}$-${\pi}^{\ast}$의 경우가 더 불안정화 되었다. 이러한 예측들은 실험결과들과 MO이론적 계산에 의하여 잘 밝혀졌다. 한편 STO-3G 및 INDO-LCBO 계산방법은 ${\pi}^{\ast}$-${\pi}^{\ast}$ 상호작용을 과소평가하고 있음을 알았으며 MO이론적 계산을 이용하여 이러한 ${\pi}^{\ast}$-${\pi}^{\ast}$상호작용을 적절히 표현하는 데는 split valence 기초함수를 사용하여야 함을 밝혔다.

• Journal of Astronomy and Space Sciences
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• 제33권2호
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• pp.93-99
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• 2016

A redback system is a binary system composed of a pulsar and a main sequence star. The inverse Compton (IC) scattering between the stellar soft photons and the relativistic pulsar wind will generate orbital-modulating GeV photons. We look for these IC emissions from redback systems. A multi-wavelength observation of an unassociated gamma-ray source, 3FGL J2039.6-5618, by Salvetti et al. (2015) detected an orbital modulation with a period of 0.2 days in both X-ray and optical cases. They suggested 3FGL J2039.6-5618 to be a new redback candidate. We analyzed the gamma-ray emission of 3FGL J2039.6-5618 using the data from the Fermi large area telescope (Fermi-LAT) and obtained the spectrum in different orbital phases. We propose that the spectrum has orbital dependency and estimate the characteristic energy of the IC emission from the stellar-pulsar wind interaction.

• Bulletin of the Korean Chemical Society
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• 제31권3호
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• pp.595-598
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• 2010

Ab initio and DFT molecular orbital calculations predict that acetyl radical reacts with acetylene through interactions primarily involving the SOMO of the radical and the in-plane ${\pi}$-bond of acetylene. An energy barrier (${\Delta}E_1$) of 39.6 kJ $mol^{-1}$ is predicted for the preferred anti arrangement of reactants at the CCSD(T)/cc-pVDZ//BHandHLYP/cc-pVDZ level of theory. NBO analysis reveals additional interactions between the radical SOMO and the nearby C-H ${\sigma}$-bond in acetylene worth about 10% of the total transition state interaction energy. This type of orbital interaction has not previously been observed in radical addition reactions involving C-C ${\pi}$-bonds.

• Bulletin of the Korean Chemical Society
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• 제18권9호
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• pp.976-981
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• 1997

The magnetic susceptibilities of molybdenum ions with 4d1 electronic configuration in the octahedral crystal field were calculated on the basis of ligand field theory. The experimental magnetic susceptibilities for molybdenum ions, which are stabilized at the octahedral site in the perovskite lattice of Ba2ScMoⅤO6 and Sr2YMoⅤO6, were compared with the theoretical ones. We have tried to fit their temperature dependence of magnetic susceptibility with ligand field parameters, spin-orbit coupling constant ζSO, and orbital reduction parameter κ according to intermediate field coupling and strong field theory. Strong field coupling theory could not explain experimental curves without unrealistically large axial ligand field, since it ignores the mixing up between different state via spin-orbit interaction and ligand field. On the other hand, the intermediate field coupling theory could successfully reproduce experimental data in octahedral and trigonal ligand field. The fitting result demonstrates not only the fact that spin-orbit interaction is primarily responsible for the variation of magnetic behavior but also the fact that effective orbital overlap, enhanced by cubic crystal structure, reduces significantly orbital angular momentum as indicated by κ parameter.

• 대한화학회지
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• 제27권5호
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• pp.330-339
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• 1983

N개의 $\sigma$결합으로 분리되어 있는 분자내 두 비결합 궤도함수(nonbonding orbital)간의 상호작용을 PMO론적으로 고찰하기 위하여 질소, 산소 및 황화합물에 대하여 반경험적인 CNDO/2 및 ab initio(STO-3G 수준) 계산을 수행하였다. 각 사슬형 및 고리형 화합물에 대한 기저준위의 에너지, orbital 상호작용에 의한 에너지준위 분리 및 상호작용 에너지 변화에 대한 계산 결과는 섭동론적 에너지항으로 만족스럽게 설명될 수 있었다. 질소 및 산소화합물에서는 through-space 상호작용 에너지항으로서 계산결과가 만족스럽게 설명될 수 있었다. 이 경우 N이 홀수인 계에서는 n-준위가 n+준위보다 안정화되었고 N이 짝수인 계에서는 n+준위가 n-준위보다 안정화되었다. 이 때의 에너지 분리는 홀수계에서 더 큰 결과를 보였다. 그러나 cis-ethylene diamine과 o-phenylene diamine(Table 4의 구조 VI)에서는 through-space 상호작용의 기여가 무시될 수 없었고 그 결과 홀수계에서 에너지 준위의 순서가 뒤바뀌게 되었으며 에너지분리도 짝수계에서 더 큰 결과를 보였다. 끝으로 황화합물에서는 항상 through-space 상호작용의 기여가 무시될 수 없었다. 이 결과는 3주기 원소인 황의 크기가 2주기 원소인 질소 및 산소보다 크다는 사실과 일치하고 있다.

• 대한의생명과학회지
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• 제1권1호
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• pp.89-94
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• 1995

B(a)P와 cytochrome P-450의 heme부분은 구조가 평면이므로 겹침 상호작용이 가능하다. 가능성이 큰 겹침 상호작용모형을 결정하기 위해 이들 분자에 대해 MO계산을 행하였다. 이 경우 궤도함수 상호작용이 가장 중요하므로, 프론티어궤도함수의 eigen vetor값이 크며 상호 결합성을 보여야 한다. 이를 바탕으로 다섯가지 가능성이 있는 모형을 선택한 수 MN2와 MO방법을 실행하였다. 이중 B(a)P의 4, 5, 6번 위치와 heme group의 Y탄소와 III pyrrole환이 포개어지는 형태가 가장 안전하였다.

• Journal of Microbiology and Biotechnology
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• 제17권11호
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• pp.1789-1796
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• 2007

A ${\beta}$-glucosidase with the molecular mass of 160,000 Da was purified to homogeneity from cell extract of a cellulolytic bacterium, Cellulomonas uda CS1-1. The kinetic parameters ($K_m$ and $V_{max}$) of the enzyme were determined with pNP-cellooligosccharides (DP 1-5) and cellobiose. The molecular orbital theoretical studies on the cellulolytic reactivity between the pNP-cellooligosaccharides as substrate (S) molecules and the purified ${\beta}$-glucosidase (E) were conducted by applying the frontier molecular orbital (FMO) interaction theory. The results of the FMO interaction between E and S molecules verified that the first stage of the reaction was induced by exocyclic cleavage, which occurred in an electrophilic reaction based on a strong charge-controlled reaction between the highest occupied molecular orbital (HOMO) energy of the S molecule and the lowest occupied molecular orbital (LUMO) energy of the hydronium ion ($H_3O^+$), more than endocyclic cleavage, whereas a nucleophilic substitution reaction was induced by an orbital-controlled reaction between the LUMO energy of the oxonium ion ($SH^+$) protonated to the S molecule and the HOMO energy of the $H_2O_2$ molecule. A hypothetic reaction route was proposed with the experimental results in which the enzymatic acid-catalyst hydrolysis reaction of E and S molecules would be progressed via $SN_1$ and $SN_2$ reactions. In addition, the quantitative structure-activity relationships (QSARs) between these kinetic parameters showed that $K_m$ has a significant correlation with hydrophobicity (logP), and specific activity has with dipole moment, respectively.

• Bulletin of the Korean Chemical Society
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• 제6권5호
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• pp.277-279
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• 1985

Orbital interactions of the types, ${\sigma}-{\pi},\;{\sigma}^*-{\pi},\;{\sigma}-{\pi}^*\;and\;{\sigma}^*-{\pi}^*$ are investigated for the rotamers of ${\alpha}$-X-acetones (X = F and Cl) using STO-3G method of calculation. It was found that the interactions are possible only in gauche forms, and the ${\sigma}^*-{\pi}^*$ interactions are in general greater than the $\sigma-\pi$ interactions due to the greater overlap, in spite of the greater energy gap involved; the greater ${\sigma}^*-{\pi}^*$ interaction causes greater lowering of ${\pi}^*$ level relative to the lowering of ${\sigma}$ in the ${\sigma}-{\pi}$ interaction so that both ${\sigma}-{\pi}^*$ and $n-{\pi}^*$ interactions are enhanced in the gauche forms. The extra stability of the gauche form and the red shift in the $n-{\pi}^*$ transition are thus found to be natural corollaries of the greater ${\sigma}^*-{\pi}^*$ interaction in the gauche forms.

• Interdisciplinary Bio Central
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• 제2권2호
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• pp.6.1-6.5
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• 2010

Fragment molecular orbital (FMO) method provides a novel tool for ab initio calculations of large biomolecules. This method overcomes the size limitation difficulties in conventional molecular orbital methods and has several advantages compared to classical force field approaches. While there are many features in this method, we here focus on explaining the issues related to protein-ligand binding: FMO method provides useful interaction-analysis tools such as IFIE, CAFI and FILM. FMO calculations can provide not only binding energies, which are well correlated with experimental binding affinity, but also QSAR descriptors. In addition, FMO-derived charges improve the descriptions of electrostatic properties and the correlations between docking scores and experimental binding affinities. These calculations can be performed by the ABINIT-MPX program and the calculation results can be visualized by its proper BioStation Viewer. The acceleration of FMO calculations on various computer facilities is ongoing, and we are also developing methods to deal with cytochrome P450, which belongs to the family of drug metabolic enzymes.