• 대한화학회지
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• 제57권3호
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• pp.311-315
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• 2013

The geometry structures of hexa-coordinated [NiLX]X complexes ($X=Cl^-,\;Br^-,\;I^-$) {L = 8,9,18,19-tetrahydro-7H,17H-dibenzo[f,o] [1,5,9,13]dioxadiaza cyclohexadecine-8,18-diol} are optimized by density functional theory (DFT) using B3LYP/LANL2DZ. The calculated geometric parameters are in good agreement with the corresponding experimental values. Calculation results about these complexes show that dipole moment decreases, and the energy levels of HOMOs descend from iodo-complex to chloro-complex. The energy levels of HOMOs descend gently from iodo-complex to chloro-complex, while the energy levels of LUMOs in the present complexes are almost similar; therefore the energy gapes between HOMOs and LUMOs increased from iodo-complex to chloro-complex.

• 대한화학회지
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• 제53권3호
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• pp.257-265
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• 2009

$Cu^{+}$ 및 $Cu^{2+}$와 proline의 결합형태에 따른 구조 및 금속 친화도를 DFT(Density Functional Theory) 방법으로 조사하였다. 금속-proline의 결합과 여러 결합형태에 따른 에너지 순서는 $Cu^{+}$-Proline및 $Cu^{2+}$-proline 착화합물에서 서로 매우 상이함을 알았다. $Cu^{+}$-Proline의 경우, 바닥상태의 구조는 $Cu^{+}$가 중성 proline의 카르보닐 산소 및 이미노기 질소에 배위된 두 자리 배위를 하며, 이에 비해 $Cu^{2+}$-Proline 의 바닥상태의 구조는 zwitter이온 형태 proline의 카르복시기의 두 산소 사이에 chelation을 형성하는 구조임을 확인하였다. 가장 안정한 $Cu^{+}$-Proline 착화합물에서 proline의 금속 이온 친화도는 6-311++G(d,p) 수준에서 76.0 kcal/mol로 계산되었으며, proline의 $Cu^{2+}$ 이온 친화도는 258.5 kcal/mol로 나타났다.

• Bulletin of the Korean Chemical Society
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• 제33권11호
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• pp.3797-3804
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• 2012

We present calculations for valine (Val) - $(H_2O)_n$ (n = 0-5) to examine the effects of microsolvating water on the relative stability of the zwitterionic vs. canonical forms of Val. We calculate the structures, energies and Gibbs free energies of the conformers at B3LYP/6-311++G(d,p), wB97XD/6-311++G(d,p) and MP2/aug-cc-pvdz level of theory. We find that five water molecules are needed to stabilize the zwitterionic form of Val. By calculating the barriers of the canonical ${\leftrightarrow}$ zwitterionic pathways of Val - $(H_2O)_5$ conformers, we suggest that both forms of Val - $(H_2O)_5$ may be observed in low temperature gas phase.

• Bulletin of the Korean Chemical Society
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• 제33권9호
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• pp.2861-2866
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• 2012

Results of the comparisons of various density functional theory (DFT) methods with different basis sets for predicting the molecular geometry of TPOP24N-Oxide macrocycle, an oxoporphyrin N-oxide, are reported in this paper. DFT methods, including M06-2X, B3LYP, LSDA, B3PW91, PBEPBE, and BPV86, are examined. Different basis sets, such as 6-$31G^*$, 6-31+G (d, p), 6-311+G (d, p), and 6-311++G (d, p), are also considered. The M06-2X/6-$31G^*$ level is superior to all other density functional methods used in predicting the geometry of TPOP24N-Oxide. The geometries of regioisomeric chlorin N-oxide and oxoporphyrin N-oxide are reported using M06-2X/6-$31G^*$ method. The geometry effects of oxoporphyrin and chlorin N-oxide regioisomers are increased ${\beta}-{\beta}$ bond lengths by N-oxidation because the bond overlap index due to charge transfers is decreased. In N-oxidation ring (II, III), angles that include ${\beta}-{\beta}$ bond length increase as the bond overlap index of ${\beta}-{\beta}$ bond is decreased by N-oxidation. The potential energy surfaces of chlorin N-oxide and oxoporphyrin N-oxide are explored by M06-2X/6-$31G^*$, and single-point calculations are performed at levels up to M06-2X/6-311++G (d, p). Total and relative energies are then calculated. The results indicate that chlorin 24 N-oxides are more stable than chlorin 22 N-oxides in chlorin N-oxide regioisomers. Moreover, TPOP24N-Oxide is less stable than TPOP22N-Oxide.

• Mass Spectrometry Letters
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• 제13권3호
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• pp.49-57
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• 2022

During electrospray ionization mass spectrometry (ESI-MS) analysis of proteins, the addition of supercharging agents allows for adjusting the maximal charge state, affecting the charge state distribution, and increases the number of ions reaching the detector thus, improving signal detection. We postulate that in di-substituted arene isomers, molecules with higher polarizability values should generate greater interactions and hence elicit higher signal intensities. Polarizability is an electronic parameter which has been demonstrated to predict many chemical interactions. Many properties can be predicted based on charge polarization. Molecular polarizability is a vital descriptor for explaining intermolecular interactions. We employed DFT (density functional/Hartree-Fock hybrid model, B3LYP)-derived descriptors and computed molecular polarizability for ten disubstituted arene reagents, each set made up of three (ortho, meta, para) isomers, with reported use as supercharging reagents during ESI experiments. The atomic electronic inputs were ionization potential (IP), electron affinity (EA), electronegativity (𝛘), hardness (η), chemical potential (µ), and dipole moment (D). We determined that the para isomers showed the highest polarizability values in nine of the ten sets. There was no difference between the ortho and meta isomers. Polarizability also increased with increasing complexity of the substituents on the benzene ring. Polarizability correlated positively with IP, EA, 𝛘, η, and D but correlated negatively with chemical potential. This DFT study predicts that the para isomers of di-substituted arene isomers should elicit the strongest ESI responses. An experimental comparison of the three isomers, especially of larger supercharging molecules, could be carried out to establish this premise.

• Bulletin of the Korean Chemical Society
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• 제35권8호
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• pp.2311-2316
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• 2014

Conformations and vibrational frequencies of the racemic (2RS,3RS)-5-amino-3-(4-phenylpiperazin-1-yl)-1,2,3,4-tetrahydronaphthalen-2-ol-(I) [(2RS,3RS)-(I)], a precursor of benzovesamicol analogues, have been carried out using various DFT methods (M06-2X, B3LYP, B3PW91, PBEPBE, LSDA, and B3P86) with basis sets of 6-31G(d), 6-31+G(d,p), 6-311+G(d,p), 6-311++G(d,p), cc-pVTZ, and TZVP. The LSDA/6-31G(d) level of theory shows the best performance in reproducing the X-ray powder structure. However, the PBEPBE/cc-pVTZ level of theory is the best method to predict the vibrational frequencies of (2RS,3RS)-(I). The potential energy surfaces of racemic pairs (2RS,3RS)-(I) and -(II) are obtained at the LSDA/6-31G(d) level of theory in the gas phase and in water. The results indicate that (2RS,3RS)-(I) are more stable by ~0.75 kcal/mol in energy than (2RS,3RS)-(II) in water, whereas conformer AIIg and BIIg are more stable by ~0.04 kcal/mol than AIg in gas phase. In particular, the hydrogen bond distances between the N of piperazine and the OH of tetrahydronaphthalen become longer in gas, compared with those in the water phase. Vibrational frequencies calculated at the PBEPBE/cc-pVTZ level of theory in the gas phase are larger than those in water, whereas their intensities in the gas phase are weaker than those in water.

• 폴리머
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• 제34권1호
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• pp.69-73
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• 2010

Effects of reaction time and temperature on the isomerization and dehydrobromination reactions of brominated butyl rubber were investigated. The structural composition of brominated butyl rubber was determined by Fourier transform infrared spectroscopy (FT-IR) and proton nuclear magnetic resonance spectroscopy($^1H$-NMR), Density functional theory (DFT) was used to study on the isomerization and dehydrobromination mechanisms of model compounds. The geometries for model compounds of 3-bromo-5,5,7,7-tetramethyl-2(2',2',4',4'-tetramethyl)pentyl-1-octylene (3BrOE), 1-bromo-5,5,7,7-tetramethyl-2(2',2',4',4'-tetramethyl)pentyl-2-octylene (1Br2OE) and 5,5,7,7-tetramethyl-2(2',2', 4',4'-tetramethyl)pentyl-1,3-octadiene (CD) had been optimized by using density functional theory at B3LYP/3-21G and B3LYP/6-31G levels. The predicted energy of 3BrOE lies higher than that of 1Br2OE which suggests that 1Br2OE configuration is more stable than the 3BrOE configuration. Compared with the energy barrier, the pathway of dehydrobromination is less competitive than that of isomerization. This is qualitatively consistent with the experimental results.

• Bulletin of the Korean Chemical Society
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• 제33권8호
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• pp.2711-2718
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• 2012

The alkylation of the ambident enolates of a methyl glycinate Schiff base with ethyl chloride was studied at B3LYP and MP2 levels with $6-31+G^*$ basis set. The free (E)-enolates and (Z)-enolate are similar in energy and geometry. The transition states for the alkylation of the free (E)/(Z)-enolate with ethyl chloride have similar energy barriers of ~13 kcal/mol. However, with a lithium ion, the (E)-enolate behaves as an ambident enolate and makes a cyclic lithium-complex in bidentate pattern which is more stable by 11-23 kcal/mol than the (Z)-enolate-lithium complexes. And the TS for the alkylation of (E)-enolate-lithium complex coordinated with one methyl ether is lower in energy than those from (Z)-enolate-lithium complexes by 4.3-7.3 kcal/mol. Further solvation model (SCRF-CPCM) and reaction coordinate (IRC) were studied. This theoretical study suggests that the alkylation of ambident enolates proceeds with stable cyclic bidentate complexes in the presence of metal ion and solvent.

• Bulletin of the Korean Chemical Society
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• 제33권10호
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• pp.3343-3348
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• 2012

The possible ways for increasing the antioxidant properties of vitamin E have been investigated with density function theory. The effect of replacing three methyl groups of vitamin E with various substituents such as electron donating and electron withdrawing groups on the antioxidant properties of vitamin E were investigated. Also the effects of the reducing the number of atoms in the heterocyclic ring and replacing the oxygen heteroatom with other heteroatoms on the antioxidant properties of vitamin E were investigated. The novel structures that obtained from replacing methyl groups with substituents such as $NH_2$, OH, COOH and NHMe have greater antioxidant activity than vitamin E. Obtained results reveal that novel structure that obtained with replacing O with NH hetroatom would be a better antioxidant than vitamin E. The results reveal that reducing the number of atoms in the heterocyclic ring is a better way to synthesize novel antioxidants.

• EDISON SW 활용 경진대회 논문집
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• 제3회(2014년)
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• pp.1-13
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• 2014

Potential Energy Surface(PES)를 양자 계산을 통해 알아내는 것은 화학 반응을 이해하는 데에 큰 도움이 된다. 이를테면 Transition State(TS)의 configuration을 알 수 있고, 따라서 reaction path와 활성화 에너지 값을 예측하여, 진행시키고자 하는 화학반응의 이해를 도울 수 있다. 하지만 PES를 그리기 위해서는 해당 분자의 다양한 configuration에 대한 singlet point energy 계산이 필요하기 때문에, 계산적인 측면에서 많은 비용을 요구한다. 따라서 product와 reactant의 구조와 같은 critical point의 정보를 이용하여 최소한의 configuration을 sampling하여 전체 PES를 재구성하는 기계학습 알고리즘을 개발하여 다차원 PES 상에서의 화학반응의 예측을 가능하게 하고자 한다. 본 연구에서는 Barbaralane의 두 안정화 된 구조의 critical point로 하여 이 주변을 random normal distribution하여, B3LYP/6-31G(d) level의 DFT 계산을 통해 relaxed scanning하여 구조와 에너지를 구하였으며, 이 정보를 Support Vector Regression(SVR) 알고리즘을 적용하여 PES를 재구현하였으며, 반응경로와 TS의 구조 그리고 활성화 에너지를 구하였다. 또한 본 기계학습 알고리즘을 바닥상태에서 일어나는 반응이 아닌, 들뜬 상태와 전자 구조가 변하는 화학반응, avoid crossing, conical intersection과 같은 Non-adiabatic frame에서 일어나는 현상에 적용 가능성을 논하고자 한다.