• Bulletin of the Korean Chemical Society
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• v.2 no.1
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• pp.12-16
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• 1981

Alkyl and alkenyl substituent effects on nonbonded interactions of hexatriene were examined using CNDO/2 method. The results showed that: (1) rapid rate of thermal electrocyclization of 3-vinyl hexa-1, 3, 5-triene is due to increased overlap population between atom pair reacting resulting from strong electron repelling interaction of vinly group on the triene moiety; (2) stability of a conformer is determined by additive effect of composite ${\pi}$ structures; (3) a substituent on positions 2 and 3 increases the HOMO AO coefficient of sites 1 and 4 considerably and activates interactions with these sites.

• 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.

• Proceedings of the Korean Society of Plant Pathology Conference
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• 2003.10a
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• pp.64.2-64
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• 2003

Twenty-seven monogenic rice lines harboring major resistant gene for blast were screened to analyze their resistance spectrum to Korean blast fungus population using 190 isolates collected from 1985 to 2002. Especially, the monogenic line containing Pi-9 gene was screened using 320 isolates. Based on the monogenic lines-blast isolate interactions, the 27 rice lines were classified into 9 groups. The chinese rice cultivar LTH showed susceptible to all the tested isolates. Those lines IRBLz-Fu, ERBL5-M and IRBL9-W harboring Pi-z, Pi-5, and Pi-9, respectively showed broader spectrum of resistance than those rice lines having Pi-19, Pi-7 etc. Interestingly, the Pi-9 gene(IRBL9-W) showed resistance to most isolates collected before 2000, but it showed susceptible reactions to 5％ and 20％ of blast fungus population in 2001 and 2002, respectively. Population of virulent isolates to Pi-ta, Pi-b, and Pi-7 also were increased in 2002 compared to those before 2000.

• Macromolecular Research
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• v.12 no.3
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• pp.251-257
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• 2004

The nature of the nematic liquid crystal (LC) alignment induced by the rubbed polyimide (PI) alignment layers (ALs) and the electro-optical (EO) properties of the LC cells are expected to depend on the chemical and physical features of the PI. By employing five pyromellitic dianhydride (PMDA)-type PIs having different functionalities, we have studied the effects of the PI's structure and chemistry on the alignment characteristics and the cell's EO properties. Increasing the flexibility of the PI increases the pretilt angle and tends to improve the alignment stability. On the other hand, the rigid, fluorinated PI displays poor stability for LCs and induces a less stable/uniform LC alignment and, subsequently, a small pre tilt angle. It also transpired that fluorination of the PI deteriorated the voltage-transmittance characteristics and the voltage holding ratio; increasing the flexibility of the PI structure improves these EO properties. The finding that the qualitative trends for the PI's functionalities are similar for both the alignment and EO properties suggests that the EO properties are closely related to the alignment characteristics, which are determined by short-range interactions between LC and PI molecules.

• Bulletin of the Korean Chemical Society
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• v.34 no.7
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• pp.2148-2154
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• 2013

Three push-pull organic semiconductors, TPA-$Th_3$-MMN (1), TPA-ThTT-MMN (2), and TPA-ThDTT-MMN (3), comprising a triphenylamine donor and a methylene malononitrile acceptor linked by various ${\pi}$-conjugated thiophene units were synthesized, and the effects of the ${\pi}$-conjugated bridging unit on the photovoltaic characteristics of solution-processed small-molecule organic solar cells based on these semiconductors were investigated. Planar bridging units with extended ${\pi}$-conjugation effectively facilitated intermolecular ${\pi}-{\pi}$ packing interactions in the solid state, resulting in enhanced $J_{sc}$ values of the SMOSCs fabricated with bulk heterojunction films.

• Journal of the Korean Chemical Society
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• v.24 no.2
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• pp.101-107
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• 1980

Composite ${\pi}$-structure analysis has been proposed for predicting relative isomer stabilities based on nonbonded effects: all the possible crowded ${\pi}$-structures are identified for each isomer, and the systems are represented by abbreviated notation of $(n{\pi}/m)$ : then using simple rules and additivity of the nonbonded effects, the order of stability can be determined. A number of examples are given in support of this analytical procedure.

• Bulletin of the Korean Chemical Society
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• v.31 no.3
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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.

• BMB Reports
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• v.49 no.7
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• pp.355-356
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• 2016

The THO/TREX complex consists of several conserved subunits and is required for mRNA export. In metazoans, THO/TREX binds a subset of mRNAs during RNA splicing, and facilitates their nuclear export. How THO/TREX selects RNA targets is, however, incompletely understood. In our recent study, we reported that THO is loaded onto Piwi-interacting RNA (piRNA) precursor transcripts independent of splicing, and facilitates convergent transcription in Drosophila ovary. The precursors are later processed into mature piRNAs, small noncoding RNAs that silence transposable elements (TEs). We observed that piRNAs originating from dual-strand clusters, where precursors are transcribed from both strands, were specifically affected by THO mutation. Analysis of THO-bound RNAs showed enrichment of dual-strand cluster transcripts. Interestingly, THO loading onto piRNA precursors was dependent on Cutoff (Cuff), which comprises the Rhino-Deadlock-Cutoff (RDC) complex that is recruited to dual-strand clusters by recognizing H3K9me3 and licenses convergent transcription from he cluster. We also found that THO mutation affected transcription from dual-strand clusters. Therefore, we concluded that THO/TREX is recruited to dual-strand piRNA clusters, independent of splicing events, via multi-protein interactions with chromatin structure. Then, it facilitates transcription likely by suppressing premature termination to ensure adequate expression of piRNA precursors.

• Molecules and Cells
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• v.27 no.6
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• pp.667-671
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• 2009

Visfatin (Nampt/PBEF) plays a pivotal role in the salvage pathway for $NAD^+$ biosynthesis. Its potent inhibitor, FK866, causes cellular $NAD^+$ levels to decline, thereby inducing apoptosis in tumor cells. In an effort to improve the solubility and binding interactions of FK866, we designed and synthesized IS001, in which a ribose group is attached to the FK866 pyridyl ring. Here, we report the crystal structure of rat visfatin in complex with IS001. Like FK866, IS001 is positioned at the dimer interface, and all of the residues that interact with IS001 are involved in hydrophobic or ${\pi}-{\pi}$-stacking interactions. However, we were unable to detect any strong interactions between the added ribose ring of IS001 and visfatin, which implies that a bulkier modifying group is necessary for a tight interaction. This study provides additional structure-based information needed to optimize the design of visfatin inhibitors.

• Bulletin of the Korean Chemical Society
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• v.35 no.1
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• pp.250-252
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• 2014

Lipoprotein-associated phospholipase A2 (Lp-$PLA_2$) is a crucial enzyme in atherosclerosis as a potential drug target. The most remarkable Lp-$PLA_2$ inhibitory drug is Darapladib. We determined the binding pose of Darapladib to Lp-$PLA_2$ through docking study. Darapladib formed two hydrogen bonding interactions with the side chain of Tyr160 and Gln352 and several pi-pi interactions with aromatic and aliphatic hydrophobic residues of Lp-$PLA_2$. It is known that the dietylpropan-amine moiety of Darapladib has influence on the improvement of its oral bioavailability and we supposed this in our docking results.