• Bulletin of the Korean Chemical Society
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• 제19권10호
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• pp.1073-1079
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• 1998

The potential energy surface (PES) of the non-identical SN2 reactions, F- + CH3Cl → FCH3 + Cl and (H2O)F + CH3Cl → FCH3 + Cl-(H2O), were investigated with ab initio MO calculations. The ab initio minimum energy reaction path (MERP) of the F- + CH3Cl → FCH3 + Cl- was obtained and it was expressed with an intermediate variable t. The ab initio PES was obtained near around t. Analytical potential energy function (PEF) was determined as a function of the t in order to reproduce the ab initio PES. Based on Morse-type potential energy function, a Varying Repulsive Cores Model (VRCM) was proposed for the description of the bond forming and the bond breaking which occur simultaneously during the SN2 reaction. The MERP calculated with the PEF is well agreed with the ab initio MERP and PEF could reproduce the ab initio PES well. The potential parameters for the interactions between the gas phase molecules in the reactions and water were also obtained. ST2 type model was used for the water.

• Bulletin of the Korean Chemical Society
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• 제16권10호
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• pp.915-923
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• 1995

The parameters for an empirical net atomic charge calculation method, Modified Partial Equalization of Orbital Electronegativity (MPEOE), were determined for the atoms in organosilicon compounds and zeolites. For the organosilicon family, the empirical parameters were determined by introducing both experimental and ab initio observables as constraints, these are the experimental and ab initio dipole moments, and the ab initio electrostatic potential of the organosilicon molecules. The Mulliken population was also introduced though it is not a quantum mechanical observable. For the parameter optimization of the atoms in the aluminosilicates, the dipole moments and the electrostatic potentials which calculated from the 6-31G** ab initio wave function were used as constraints. The empirically calculated atomic charges of the organosilicons could reproduce both the experimental and the ab inito dipole moments well. The empirical atomic charges of the aluminosilicates could reproduce the ab initio electrostatic potentials well also.

• 대한화학회지
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• 제43권4호
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• pp.378-383
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• 1999

파라-치환 피리딘의 치환기 효과를 조사하기 위하여 Ab initio 계산을 수행하였다. 여러 치환 피리딘의 최적화 된 구조로부터 정전기전위를 계산한 결과 피리딘의 질소 원자에서 최소값을 나타내었으며, 최소정전기전위 값은 Hammett 치환기 상수, ${\sigma}_p$ 및 ${\Delta}pKa$와 홀륭한 상관성이 있음을 알았다. 그 결과 최소정전기전위가 치환기 효과를 나타내는 척도로 사용될 수 있음을 알 수 있었다.

• Bulletin of the Korean Chemical Society
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• 제27권12호
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• pp.2028-2036
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• 2006

The combined ab initio and vibrational predissociation (VP) spectroscopic studies on methylammonium-$(water)_4$ complex aimed at understanding the hydration behavior of an amphiphilic ion core are described. The ab initio calculations predicted eleven low-energy isomers forming cyclic, tripod, chain, and caged structures, and their relative stabilities, total hydration energies and thermodynamic functions at 298 K and 150 K. The excellent correlation between the observed VP spectra and ab initio spectra for bonded N-H, bonded O-H and free O-H stretches suggested co-existence of five cyclic isomers and two non-cyclic isomers in ion beam at 150 K, consistent with the trends of calculated Gibbs free energies.

• 대한화학회지
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• 제42권1호
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• pp.1-8
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• 1998

티아졸 고리를 포함하는 lexitroposin에서, DNA minor groove의 염기쌍과 결합하는 부분인 티아졸의 분자정전기전위를 ab initio계산을 통해 구하였으며 protonate된 티아졸의 두 가지 가능한 형태에 대해 MNDO 및 ab initio방법으로 기하학적 구조를 최적화 하였다. 최적화된 구조에 대해 6-31G및 6-31G* basis set을 사용하여 양성자 친화도를 구하였으며 아울러 티아졸의 양성자 친화도에 미치는 치환기 효과를 알아보기 위해 전자를 주는 기와 전자를 끄는 기를 치환시킨 여러 치환 치아졸에 대해 양성자 친화도를 조사하였다. 그 결과 티아졸의 질소 원자가 DNA minor groove 쪽으로 배향되고 전자를 주는 기가 치환될 때 양성자 친화도가 증가됨을 알 수 있었다.

• Bulletin of the Korean Chemical Society
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• 제26권1호
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• pp.32-33
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• 2005

• Bulletin of the Korean Chemical Society
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• 제23권7호
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• pp.929-930
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• 2002

• Bulletin of the Korean Chemical Society
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• 제24권1호
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• pp.75-80
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• 2003

The structures and complexation energies of penta-O-alkylated 1b and penta-O-tert-butyl ester 1e of p-tert-butylcalix[5]arene and their simplified structures (2b and 2e) toward a series of alkyl ammonium guests have been calculated by a semi-empirical AM1 method. For AM1 calculations, complexation efficiencies of the simplified host 2e are very similar to the values of host 1e. The complexes of simplified host 2e with alkyl ammonium ions also have been optimized by ab initio HF/6-31G method. The calculated complexation efficiencies for 2e by ab initio method have been found to be bigger in magnitude than the values obtained by AM1 calculations for linear alkyl ammonium guests. Calculation results show that all of the calix[5]aryl derivatives investigated in this study have much better complexation ability toward ammonium cation without alkyl group compared with other alkyl ammonium guests. Ab initio calculations also well duplicate the molecular discriminating behaviors of calix[5]arene derivative 2e between butyl ammonium ions: $n-BuNH_3^+\;>\;iso-BuNH_3^+\;>\;sec-BuNH_3^+\;>\;tert-BuNH_3^+$.

• Bulletin of the Korean Chemical Society
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• 제24권6호
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• pp.837-842
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• 2003

In ab initio molecular dynamics, whenever information about the potential energy surface is needed for integrating the equations of motion, it is computed “on the fly” using electronic structure calculations. For Born-Oppenheimer methods, the electronic structure calculations are converged, whereas in the extended Lagrangian approach the electronic structure is propagated along with the nuclei. Some recent advances for both approaches are discussed.

• Journal of Photoscience
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• 제12권3호
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• pp.185-186
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• 2005

The electronic structure of photoskinsensitizing psoralens has been investigated by the ab initio calculations. The photocycloaddition reaction of 8-methoxypsoralen with thymine is studied as a model for the photosensitizing reaction of psoralen with DNA bases. The photocycloadduct was inferred to be a C4-cycloaddition product with the stereochemistry of Syn, H-H, Syn, H-T formed through [2+2] addition reaction between the 3,4-double bonds of 8-methoxypsoralen and 5,6-double bond of thymine base.