• Title/Summary/Keyword: dimers

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Density Functional Theoretical Study on Intermolecular Interactions of 3,6-Dihydrazino-1,2,4,5-tetrazine Dimers

  • Hu, Yin;Ma, Hai-Xia;Li, Jun-Feng;Gao, Rong;Song, Ji-Rong
    • Bulletin of the Korean Chemical Society
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    • v.31 no.10
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    • pp.2897-2902
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    • 2010
  • Seven fully optimized geometries of 3,6-dihydrazino-1,2,4,5-tetrazine (DHT) dimers have been obtained with density functional theory (DFT) method at the B3LYP/$6-311++G^{**}$ level. The intermolecular interaction energy was calculated with zero point energy (ZPE) correction and basis set superposition error (BSSE) correction. The greatest corrected intermolecular interaction energy of the dimers is $-23.69\;kJ{\cdot}mol^{-1}$. Natural bond orbital (NBO) analysis is performed to reveal the origin of the interaction. Based on the vibrational analysis, the changes of thermodynamic properties from the monomers to dimer with the temperature ranging from 200.0 K to 800.0 K have been obtained using the statistical thermodynamic method. It was found that the hydrogen bonds dominantly contribute to the dimers, while the binding energies are not only determined by hydrogen bonding. The dimerization process can not occur spontaneously at given temperatures.

Dimerization of Fibril-forming Segments of α-Synuclein

  • Yoon, Je-Seong;Jang, Soon-Min;Lee, Kyung-Hee;Shin, Seok-Min
    • Bulletin of the Korean Chemical Society
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    • v.30 no.8
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    • pp.1845-1850
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    • 2009
  • We have performed replica-exchange molecular dynamics (REMD) simulations on the dimer formation of fibrilforming segments of $\alpha$-Synuclein (residues 71 - 82) using implicit solvation models with two kinds of force fields- AMBER parm99SB and parm96. We observed spontaneous formation of dimers from the extensive simulations, demonstrating the self-aggregating and fibril forming properties of the peptides. Secondary structure profile and clustering analysis showed that dimers with antiparallel $\beta$-sheet conformations, stabilized by well-defined hydrogen boding, are major species corresponding to global free energy minimum. Parallel dimers with partial $\beta$-sheets are found to be off-pathway intermediates. The relative instability of the parallel arrangements is due to the repulsive interactions between bulky and polar side chains as well as weaker backbone hydrogen bonds.

STM Study on c(4$\times$4) Reconstruction of Si(100)

  • Maeng, Jae-Yeol;Kim, Sehun
    • Proceedings of the Korean Vacuum Society Conference
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    • 2000.02a
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    • pp.151-151
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    • 2000
  • We have studied the atomic structure of Si(100)-c(4$\times$4) reconstruction using scanning tunneling microscopy(STM). The c(4$\times$4) reconstruction can be formed by annealing the hydrogen exposured surface at temperatures between 850 and 960 K. At this temperature ranges, adsorbed hydrogen atoms are all desorbed. Therefore, the c(4$\times$4) reconstruction is due to the Si dimers on surface. The filled and empty state images of the STM were interpreted in terms of Si dimers in c(4$\times$4) primitive cell forming the reconstruction. Based on the STM images and hydrogen adsorption experiment on c(4$\times$40 surface, we suggest that Si dimers in c(4$\times$40 unit cell are perpendicular ad-dimer to the underlying Si dimer rows.

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Reconstruction Change of Si(5 5 12) Induced by Selective Bi Adsorption (Bi의 선택적 흡착으로 유도된 Si(5 5 12) 표면의 재구조변화)

  • Cho Sang-Hee;Seo Jae-M.
    • Journal of the Korean Vacuum Society
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    • v.15 no.2
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    • pp.152-161
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    • 2006
  • In order to test the capacity of Si(5 5 12) as a potential template for nanowire fabrication, Bi/Si(5 5 12) system has been studied by STM. With Bi deposition, Si(5 5 12) has been transformed to Si(3 3 7) terrace. Initially Bi atoms selectively replace Si-dimers and Si-adatoms with Bi-dimers and Bi-adatoms, respectively. With extended Bi adsorption, Bi-dimers adsorb on the pre-adsorbed Bi-dimers and Bi-atoms. These dimers in the second layer form Bi-dimer pairs having relatively stable $p^3$ bonding, Finally, the Bi-dimer adsorbs on the Bi-dimers in the second layer and saturates. It can be deduced that both surface transformation to (3 3 7) and site-selective Bi adsorption are possible due to substrate-strain relaxation through inserting Bi atoms into subsurface of Si substrate.

Reactions of 〔(2-N, N-Dimethylaminomethyl)phenyl〕methylvinychlorosilane with t-BuLi: Synthesis and Characterization of Five Isomeric 1,3-Disilacyclobutanes.

  • Lee, Myeong Yu;Jo, Hyeon Mo;Lee, Su Heung;Kim, Jang Hwan
    • Bulletin of the Korean Chemical Society
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    • v.22 no.6
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    • pp.593-596
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    • 2001
  • The reaction of [(2-N,N-dimethylaminomethyl) pheny] methylvinychlorosiane with t-BuLi in hexane solvent gave dimers, five isomeric 1,3-disilacyslobutanes which were weparated and charaterized. In trapping experiments with various trapping agents, no corresponding silene-trapping aduct was observed. We suggest that more important species for the formation of five isomeric dimers might be the zwitterionic species generated by virtue of intramolecular donor atom rather than the silene.

Ab initio Study on Structures, Energies and Vibrations of Methylammonium-(water)$_n$ (n=1-3) Complexes

  • Kim, Gwang Yeon;Jo, Yung In;Bu, Du Wan
    • Bulletin of the Korean Chemical Society
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    • v.22 no.6
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    • pp.597-604
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    • 2001
  • The reaction of [(2-N,N-dimethylaminomethyl) pheny] methylvinychlorosiane with t-BuLi in hexane solvent gave dimers, five isomeric 1,3-disilacyslobutanes which were weparated and charaterized. In trapping experiments with various trapping agents, no corresponding silene-trapping aduct was observed. We suggest that more important species for the formation of five isomeric dimers might be the zwitterionic species generated by virtue of intramolecular donor atom rather than the silene.

Liquid Crystalline Properties of Dimers Having o-, m- and p- Positional Molecular Structures

  • Park, Joo-Hoon;Choi, Ok-Byung;Lee, Hwan-Myung;Lee, Jin-Young;Kim, Sung-Jo;Cha, Eun-Hee;Kim, Dong-Hyun;Ramaraj, B.;So, Bong-Keun;Kim, Kyung-Hwan;Lee, Soo-Min;Yoon, Kuk-Ro
    • Bulletin of the Korean Chemical Society
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    • v.33 no.5
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    • pp.1647-1652
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    • 2012
  • With the objective to design and synthesis of Schiff's base symmetrical liquid crystal dimmers and to study the effect of molecular structure variation ($o-ortho$, $m-meta$, $p-para$) and change in alkoxy terminal chain length on mesomorphic properties of liquid crystals, We have synthesized Schiff base dimers from dialdehyde derivative containing 2-hydroxy-1,3-dioxypropylene as short spacer with aniline derivatives having different lengths of terminal alkoxy chains ($n$ = 5, 7, 9). The chemical structure of the final products was characterized by proton nuclear magnetic resonance ($^1H$ NMR) spectroscopy and fourier transform infrared (FT-IR) spectroscopy. The mesomorphic properties and optical textures of the resultant dimers were characterized by differential scanning calorimetry (DSC) and polarized optical microscopy (POM). The existence of smectic A phase transition was confirmed by the observation of batonnets and fan shaped textures in optical microscopy when compound were heated from crystalline phase. All of the dimers of this series, with the exception of $\mathbf{2S_5}$ -ortho, -meta, -para, were thermotropic liquid crystal. The compound $\mathbf{2S_9}$ -meta was monotropic, while the rest were enantiotropic. It was found that the change in terminal alkoxy chain length has pronounced effect on the mesomorphic properties. The temperature range of smectic A phase window widens with increasing alkoxy chain length.

Theoretical Studies of Hydrogen Bonded Dimers AM1 Study of Hydrogen-Bonding Energies of MeOH-solvent Binary Systems (水素結合 이합체에 關한 理論的인 硏究, 메탄올-溶妹 이성분계에 대한 水素結合 에너지의 AM1 的 硏究)

  • Shi Choon Kim;Myoung Ok Park
    • Journal of the Korean Chemical Society
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    • v.32 no.3
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    • pp.249-259
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    • 1988
  • The solvent effects of MeOH-solvent dimers were studied via AM1 Hamiltonian and supermolecule methods. Methanol, ethanol, acetone, dimethylsulfoxide, N,N-dimethylformamide, tetrahydrofuran, dioxane, and acetonitrile were considered as solvent molecules. Optimized geometries, electron densities, molecular energies, and hydrogen-bonding energies of monomers and dimers were calculated. We found that the stabilization energies contributed to the hydrogen-bonding were decreased in the order of dimethylsulfoxide > ethanol > N,N-dimethylformamide > acetone > methanol > tatrahydrofuran > dioxane > acetonitrile, and this order was explained by using the change of electron density and energy partition functions.

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