• Journal of the Korean Chemical Society
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• v.53 no.6
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• pp.640-652
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• 2009

We have performed mPW1PW91 calculations to investigate the conformational characteristics and hydrogen bonds of p-tert-butylcalix[4]arene (1), p-tert-butylcalix[5]arene (2), calix[6]arene (3) and p-tertbutylcalix[6]arene (4). The structures of the different conformers of 1-3 were optimized by using mPW1PW91/6-31+G(d,p) method. The relative stability of the four conformers of 1 is in the following order: cone (most stable) > partial-cone > 1,2-alternate > 1,3-alternate. The relative stability of the conformers of 2 is in the following order: cone (most stable) > 1,2-alternate > partial-cone > 1,3-alternate. The relative stability of the various conformers of 3 is in the following order: cone (pinched: most stable) > partial-cone > cone (winged) - 1,2-alternate - 1,2,3-alternate > 1,4-alternate > 1,3-alternate > 1,3,5-alternate. The structures of the various conformers of 4 were optimized by using the mPW1PW91/6-31G(d,p) method followed by single point calculation of mPW1PW91/6-31+G(d,p). The relative stability of the conformers of 4 is in the following order: cone (pinched) > 1,2-alternate > cone (winged) > 1,4-alternate - partial-cone > 1,2,3-alternate > 1,3,5-alternate > 1,3-alternate. The primary factor affecting the relative stabilities of the various conformers of the 1-4 are the number and strength of the intramolecular hydrogen bonds. The hydrogen-bond distances are discussed based on two different calculation methods (B3LYP and mPW1PW91).

• Bulletin of the Korean Chemical Society
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• v.27 no.4
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• pp.508-514
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• 2006

In this study, we have performed ab initio computer simulations to investigate the conformational and complexation characteristics of the trimethyl ether of p-tert-butylmonodeoxycalix[4]arene (6) with a potassium ion. The structures of different conformers of 6 and their potassium complexes were optimized by using ab initio RHF/6-31G and B3LYP/6-31G(d,p) methods. The relative stability of the various conformers of the uncomplexed 6 is in following order: cone (most stable) > 1-partial-cone ~ 2i-partial-cone > 2-partial-cone ~ 1,3-alternate > 3i-partial-cone. However, the relative stability of the conformational complexes of 6 with $K^+$ is in the following order: 2-partial cone ~ 1,3-alternate > cone > 3-partial cone > 1-partial cone (least stable). The highest binding strengths of 2-partial-cone and 1,3-alternate complexes originate from two strong cation-$\pi$ interactions and two strong cation-oxygen interactions in the complex of 6+$K^+$. Due to the cation-$\pi$ interactions, the calculated C-C bond distances in the arenes of the $K^+$-complexes are about 0.0048 $\AA$ longer than the values of their isolated hosts.

• 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.25 no.1
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• pp.55-58
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• 2004

In this study we have performed ab initio computer simulations to investigate the conformational characteristics of the tetramethoxycalix[4]arenes (1 and 2). The structures of four types (cone, partial cone, 1,2-alternate, and 1,3-alternate) of conformers for each compound have been optimized using ab initio RHF/6-31G and 6-31$G^{**}$ methods. General trends in relative stabilities of tetramethyl ether derivatives of calix[4]arene 1 and p-tert-butylcalix[4]arene 2 are similar and decrease in following order: partial cone (most stable) > cone > 1,3-alternate > 1,2-alternate. The calculated results of the most stable conformation of partial cone structure agree with the reported NMR experimental observations.

• Journal of the Chungcheong Mathematical Society
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• v.23 no.4
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• pp.609-616
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• 2010

We characterize extreme rays of the cone $\mathbb{T}$ of all positive semi-definite block matrices whose partial transposes are also positive semi-definite. We also construct an algorithm checking whether a given PPTES generates an extreme ray in the cone $\mathbb{T}$ or not. Using this algorithm, we give an example of $4{\otimes}4$ PPT entangle state of the type (5, 5), which generates extreme ray of the cone $\mathbb{T}$.

• Bulletin of the Korean Chemical Society
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• v.29 no.7
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• pp.1374-1378
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• 2008

Using DFT B3LYP/6-31+G(d,p)//B3LYP/6-31G(d,p) calculation method, stable molecular structures were optimized for the p-tert-butylcalix[4]arene functionalized at lower rim by cage-annulated crown ether (1) in two different conformers and their potassium-ion complexes. Cone conformer of free host 1 was slightly more stable than partial-cone conformer. For two different kinds of complexation mode, the potassium ion in benzene-rings (bz) pocket showed comparable complexation efficiency with the cation in cage-annulated crown-ether (cr) for the cone and partial-cone conformers of 1. The complex (1${\bullet}K^+$) in the cr-binding mode for the partial-cone conformer was more stable than the cone conformer for B3LYP/6-31G(d,p) geometry optimization. However, $1_{(cone)}{\bullet}K^+$(cr) showed lower single-point energy than the $1_{(pc)}{\bullet}K^+$(cr) for B3LYP/6- 31+G(d,p) calculation method.

• Bulletin of the Korean Chemical Society
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• v.28 no.12
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• pp.2310-2314
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• 2007

Stable molecular conformations were calculated for the p-tert-butylcalix[4]arene crown ether bridged at the lower rim with pyridyl unit (1) in the various conformers and their potassium-ion complexes. The structures of three distinct conformations have been optimized using DFT B3LYP/6-31G(d,p) method. Relative stability of free host 1 is in following order: cone (most stable) > partial-cone > 1,3-alternate conformer. For two different kinds of complexation mode, the potassium cation in the crown-ether moiety (cr) has much better complexation efficiency than in the benzene-rings (bz) pocket for all three kinds of conformation of host molecule 1. The relative stability of complex (1+K+) in the cr-binding mode is in following order: partial-cone (most stable) ~ cone > 1,3-alternate conformer.

• Bulletin of the Korean Chemical Society
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• v.29 no.10
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• pp.1893-1897
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• 2008

We have performed DFT calculations to investigate the conformational characteristics and hydrogen bonds of the p-tert-butylcalix[5]arene (1) and p-tert-butylcalix[4]arene (2). The structures of different conformers of 1 were optimized by using B3LYP/6-31+G(d,p) method. The relative stability of the various conformers of 1 is in the following order: cone (most stable) > 1,2-alternate > partial-cone > 1,3-alternate. The relative stability of four conformers of 2 is in the following order: cone (most stable) > partial-cone > 1,2-alternate > 1,3-alternate. The primary factor affecting the relative stabilities of the various conformers of the 1 and 2 are the number and strength of the intramolecular hydrogen bonds. The hydrogen-bond distances are discussed based on different calculation methods.

• Bulletin of the Korean Chemical Society
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• v.23 no.6
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• pp.891-896
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• 2002

The structures and energies of p-tert-butylcalix[4]crown-6-ether(1) in various conformers and their alkyl ammonium complexes have been calculated by ab initio HF/6-31G quantum mechanics method. We have tried to obtain the relative affinity of partial-cone and 1,3-alternate conformers of 1 for alkyl ammonium guests by comparison with its cone-shaped analogue. We have also calculated the relative complexation efficiency of these host-guest complexes focusing on the binding sites of $crown-\sigma-enther$ moiety or benzene-rings pocket of the host molecule 1. These calculations revealed that the crown moiey has better complexation efficiency than upper rim part of calyx[4]arene that is in similar trend to the cone-shaped complexes.

• Bulletin of the Korean Chemical Society
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• v.15 no.6
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• pp.483-488
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• 1994

Tetra acyl esters of p-tert-butylcalix[4]arene and calix[4]arene, including acetyl, propionyl, butyryl and isobutyryl, are synthesized and their conformations are inferred from $^1H-NMR$ and $^{13}C-NMR$ spectra. The conformer distribution is affected by the presence of t-butyl group, whereas the acylation products of p-t-butylcalix[4]arene are the cone conformers, those of calix[4]arene are mostly partial cone and/or 1,3-alternate conformers. The conformational outcome is also affected by the method of preparation, the NaH-induced reaction is prefered to the acid-induced reaction for cone and partial cone. Interestingly, 1,2-alternate conformer was isolated in 14% yield from the butyrylation of calix[4]arene.