• Bulletin of the Korean Chemical Society
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• v.25 no.6
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• pp.847-851
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• 2004

The complexation characteristics of tetramethyl (1) and tetraethyl esters (2) of p-tert-butylcalix[4]arene with alkali metal cations have been investigated by ab initio calculation. The structures of endo- or exocomplexation of the hosts in cone conformation with alkali metal ions have been optimized using HF/6-31G method followed by B3LYP/6-31G(d) single point calculation. B3LYP/6-31G(d) calculations suggest that exo-complexation efficiencies of sodium ion to the cavity of lower rim of hosts 1 and 2 are 27.1 and 25.8 kcal/mol better than that of potassium ion, respectively. The exo-complexation efficiencies of potassium ion to the cavity of lower rim of hosts 1 and 2 are 33.3 and 31.5 kcal/mol better than the endo-complexation inside the upper rim (four aromatic rings) as expected from the experimental results. B3LYP/6-31G(d) calculation of the ethyl ester 2 shows 29.5 and 30.8 kcal/mol better exo-complexation efficiency for both sodium and potassium ions than the methyl ester 1.

• BMB Reports
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• v.36 no.3
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• pp.243-250
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• 2003

In this paper we investigate (using AM1 semi-empirical as well as HF methods at the STO-3G, 3-21G, 6-31G, 6-$31G^*$ and 6-31+$G^{**}$ level) the conformations, geometrical parameters, Mulliken charges, and solvation effects of the triphosphate form of AZT (AZTTP), as well as the thymidine nucleotide (dTTP) structure. Our calculated geometrical parameters and Mulliken charges, with and without solvation effects, are correlated with recent experimental results.

• Bulletin of the Korean Chemical Society
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• v.25 no.4
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• pp.553-556
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• 2004

In this study we have performed ab initio computer simulations to investigate the conformational characteristics of the tetraethyl (1) and triethyl ester (2) of p-tert-butylcalix[4]arene. The structures of different conformational isomers for each compound have been optimized using ab initio RHF/6-31G methods. After optimization, B3LYP/6-31+G(d,p) single point calculations of the final structures are done to include the effect of electron correlation and the basis set with diffuse function and polarization function. Relative stability of tetraethyl ester (1) of p-tert-butylcalix[4]arene is in following order: cone (most stable) > partial cone > 1,3- alternate > 1,2-alternate isomer. Relative stability of triethyl ester (2) of p-tert-butylcalix[4]arene is in following order: cone (most stable) > 2-partial cone > 1-partial cone > 3-partial cone ~ 1,3-alternate ~ 1,2- alternate isomer.

• Bulletin of the Korean Chemical Society
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• v.32 no.5
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• pp.1685-1691
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• 2011

The molecular structures of thiacalix[4]biscrown-5 (1) and p-tert-butylthiacalix[4]biscrown-5 (2) and their alkali-metal-ion complexes were optimized using the DFT BLYP/6-31G(d) and mPW1PW91/6-31G(d,p) (hybrid HF-DF) calculations. The total electronic energies, the normal vibrational modes, and the Gibbs free energies of the mono- and di-topic complexes of each host with the sodium and potassium ions were analyzed. The $K^+$-complexes exhibited relatively stronger binding efficiencies than $Na^+$-complexes for both the monoand di-topic complexes of 1 and 2 comparing the efficiencies of the sodium and potassium complexes with an anisole and phenol. The mPW1PW91/6-31G(d,p) calculated distances between the oxygen atoms and the alkali metal ions were reported in the alkali-metal-ion complexes ($1{\cdot}Na^+$, $1{\cdot}2Na^+$, $1{\cdot}K^+$, $1{\cdot}2K^+$, $2{\cdot}Na^+$, $2{\cdot}Na^+$, $2{\cdot}K^+$, $2{\cdot}2K^+$). The BLYP/6-31G(d) calculated IR spectra of the host 1 and its mono-topic alkali-metal-ion complexes are compared.

• Journal of the Korean Chemical Society
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• v.53 no.5
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• pp.521-529
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• 2009

Molecular structures of the various conformers for the 1,3-dimethoxy-p-tert-butylthiacalix[4] crown-5-ether (3) were optimized by using DFT B3LYP/6 - 31 + G(d,p) and mPW1PW91/6 - 31 + G(d,p) (hybrid HF-DF) calculation methods. We have analyzed the energy differences and structures of eight in/out orientations (cone_oo, cone_oi, pc_oo, pc_io, pc_oi, pc_ii, 13a_oo, 13a_io) of two methoxy groups in three major conformations (cone, partial-cone and 1,3-alternate). The 13a_oo (out-out orientation of the 1,3-alternate conformer) is calculated to be the most stable among eight different conformations of 3, and in accord with the experimental result. The ordering of relative stability resulted from the mPW1PW91/6 - 31 + G(d,p) calculation method is following: 13a_oo > 13a_io$\sim$pc_io$\sim$cone_oo > cone_oi$\sim$pc_oo$\sim$pc_oi > pc_ii.

• Journal of Photoscience
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• v.7 no.2
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• pp.67-71
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• 2000

A quantum-chemical investigation on the conformations and electronic properties of trans(diphenyl-diheterocyclic) ethenes(t-PHEs) as building block for fully $\pi$-conjuated polymer are performed in order to display the effects of heterocyclic ring substitution. Structures for the molecules, t-PHEs were fully optimized by using semiempirical AM1, PM3 methods, and ab initio HF methods, with 6-31G basic set. The potential energy curves with respect to the change of single are obtained by using ab initio HF/6-31G basic set. The curves are not similar shapes in the molecules with respect to heterocyclic rings. It is shown that the steric repulsion interactions between phenyl ring and heterocyclic ring are subjected to different type with the respect to each heterocyclic ring. Electronic properties of the molecules were molecules were obtained by applying the optimized structures and selected geometries to the extended Huckel method. To investigate the change of HOMO-LUMO gap with respedt to the torsion angle, we select the optimized structures. By using the results, the dependency of conjugation for the energy gaps is analyzed. For t-PHE the energy gap increase up to 0.52 eV compared with its planar structure. In the cases of t-PHE and t-PHE, the energy gap increase by 1.29 and 1.15 eV, respectively, compared with its planar structure.

• Journal of the Korean Chemical Society
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• v.41 no.3
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• pp.123-129
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• 1997

In order to consider the reduced mass effects on the out-of-plane ring inversion vibration of 1,3-CHD, the vector-based computer program has been written and the kinetic energy expansion function for the large amplitude ring inversion vibration has been calculated using this program. The structural parameters for the calculations have been determined from the ab initio HF/6-31G** calculation. The potential energy function for the out-of-plane ring inversion vibration of 1,3-CHD has been determined from the kinetic energy expansion function and previously reported low-frequency Raman data. The vibrational Hamiltonian calculation including kinetic energy expansion function made it possible to determine the more reliable out-of-plane potential energy function for the ring inversion of 1,3-CHD.

• Bulletin of the Korean Chemical Society
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• v.24 no.1
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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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• v.19 no.1
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• pp.110-114
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• 1998

The hydrogen-bonding interactions between thioacetamide (TA) and urea derivatives such as tetramethylurea (TMU) and dimethyldiphenylurea (DMDPU) have been studied using near-infrared absorption spectroscopy. Thermodynamic parameters for the interactions between TA and urea derivatives were determined by analyzing the $v^{as}_{N-H}$+Amide Ⅱ combination band of TA at 1970 nm. The ΔH° values, indicating the intrinsic strength of hydrogen bonding, are - 23.0 kJ/mole and - 19.8 kJ/mol for TMU and DMDPU, respectively. This is well explained by the inductive effects of substituents. Ab initio molecular orbital calculations for the proton affinity of TMU, N,N-dimethylformamide (DMF), and N,N-dimethylacetamide (DMA) in gas phase have been carried out at HF/3-21G ad HF/6-31G(d) levels, showing that the proton affinity of TMU is larger than that of DMA, which agrees well the experimental results.

• Bulletin of the Korean Chemical Society
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• v.31 no.12
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• pp.3553-3560
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• 2010

A new hydrazone derivative compound has been synthesized and characterized by IR, $^1H$-NMR, $^{13}C$-NMR and UV-vis. spectroscopy techniques, elemental analysis and single-crystal X-ray diffraction (XRD). The new compound crystallizes in monoclinic space group C2/c. In addition to the crystal structure from X-ray experiment, the molecular geometry, vibrational frequencies and frontier molecular orbitals analysis of the title compound in the ground state have been calculated by using the HF/6-31G(d, p), B3LYP/6-311G(d, p) and B3LYP/6-31G(d, p) methods. The computed vibrational frequencies are used to determine the types of molecular motions associated with each of the observed experimental bands. To determine conformational flexibility, molecular energy profile of (1) was obtained by semi-empirical (AM1) calculation with respect to a selected degree of torsional freedom, which was varied from $-180^{\circ}$ to $+180^{\circ}$ in steps of $10^{\circ}$. Molecular electrostatic potential of the compound was also performed by the theoretical method.