• Bulletin of the Korean Chemical Society
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• 제16권11호
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• pp.1028-1032
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• 1995

The structure and electronic properties of the Si(100) surface is studied using the atom superposition and electron delocalization method. The energy released when the symmetric dimer surface is reconstructed to form the buckled dimer surface with p(2X2) symmetry is calculated to be 0.99 eV per dimer in the case of ideal clean surfaces. This indicates that the surface dimer buckling is intrinsic from the viewpoint of thermodynamics. The relaxation energy, when water is adsorbed on the clean symmetric dimer surface to form the buckled dimer surface, is 2.25 eV per dimer for appropriate coverages. These results show that H2O molecule could induce a reconstruction of the surface structure through adsorption. The buckling of the surface dimer is, therefore, more favorable under the existence of water vapour. This conclusion supports the recently obtained experimental observations by Chander et al.

• 대한화학회지
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• 제40권11호
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• pp.686-691
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• 1996

Viologen 유도체를 합성하여 이들의 electrochromic(전기변색) 특성을 조사했다. 1, 1'-diethyl-4, 4'-bipiridinium dibromide(EV), 1, 1'-dipropyl-4, 4'-bipyridinium dibromide(PV), 1, 1'-dibuthyl-4, 4'-pyridinium dibromide(BV), 1-ethyl-1'-butyl-4, 4'-bipyridinium dibromide(EBV)를 대상으로 하여 propylene carbonate/methanol 용액내에서 전기변색성을 검토하였다. 또한 전장하에서 EV와 EBV의 cation radical은 dimer를 형성하는 것을 알 수 있었다.

• 한국자기공명학회:학술대회논문집
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• 한국자기공명학회 2002년도 International Symposium on Magnetic Resonance
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• pp.90-90
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• 2002

Syndecans, transmembrane heparan sulfate proteoglycans, are coreceptors with integrin in cell adhesion process. It forms a ternary signaling complex with protein kinase C and phosphatidylinositol 4,5 bisphosphate (PIP2) for integrin signaling. NMR data indicates that cytoplasmic domain of syndecan-4 (4L) undergoes a conformational transition in the presence of PIP2, forming oligomeric conformation. The structure based on NMR data demonstrated that syndecan-4L itself forms a compact intertwined symmetric dimer with an unusual clamp shape for residues Leu$^{186}$ -Ala$^{195}$ . The molecular surface of the syndecan-4L dimer is highly positively charged. In addition, no inter-subunit NOEs in membrane proximal amino acid resides (Cl region) has been observed, demonstrating that the Cl region is mostly unstructured in syndecan-4L dimmer. However, the complex structure in the presence of PIP2 induced a high order multimeric conformation in solution. In addition, phosphorylation of cytoplasmic domain induces conformational change of syndecan-4, resulting inhibition of PKC signaling. The NMR structural data strongly suggest that PIP2 promotes oligomerization of syndecan-4 cytoplasmic domain for PKC activation and further induces structural reorganization of syndecan for mediating signaling network in cell adhesion procedure.

• 대한금속재료학회지
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• 제47권1호
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• pp.32-37
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• 2009

Molecular dynamic simulations on the structural evolution of the Si(001) vicinal surfaces, which are tilted with respect to [100] and [110] directions were performed by using the empirical Tersoff potential. Tersoff potential was implemented at LAMMPS code and confirmed to describe the properties of Si. When the steps are generated along [100] direction, symmetric dimer rows formed with respect to the step edges. On the other hand, when the steps are generated along [110] direction, alternating dimer rows form with respect to the step edges. The configurational differences between the two vicinal surfaces were discussed in terms of the surface diffusion and the possibility of preventing step bunching for the (001) vicinal surface tilted along [100] direction was suggested.

• 공업화학
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• 제22권4호
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• pp.358-366
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• 2011

선상의 액정 dimer 동족체인 ${\alpha},{\omega}$-(4-사이아노아조벤젠-4'-옥시)알케인(CATWETn, n = 2~10, 유연격자 중의 메틸렌 단위들의 수)을 합성함과 동시에 이들의 열방성 액정 거동을 검토하였다. n이 3, 6인 dimer들은 단방성 네마틱 상을 형성하는 반면 다른 유도체들은 양방성 네마틱 상을 형성하였다. Dimer들의 네마틱액체 전이온도와 상 전이시의 엔트로피 변화는 n의 함수로서 커다란 홀수-짝수 효과를 나타냈다. 이러한 상 전이 거동은 유연격자의 홀수-짝수의 변화에 의한 유연격자의 평균적인 형태변화의 견지에서 합리적으로 설명된다. CATWETn이 나타내는 네마틱 상의 열적 안정성과 질서도 그리고 홀수-짝수 효과는 메톡시, 니트로 그리고 펜틸기로 치환된 dimer에 대해 보고된 결과와 유사한 경향을 나타내는 반면 monomesogenic 화합물인 1-{4-(4'-사이아노페닐아조)펜옥시}알킬브롬 그리고 곁사슬형 액정 고분자인 폴리[1-{4-(4'-사이아노페닐아조)펜옥시알킬옥시}에틸렌]에 대해 보고된 결과와 현저히 달랐다. 이들의 결과를 Imirie에 의한 'virtural trimer model'의 견지에서 검토하였다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2009년도 제38회 동계학술대회 초록집
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• pp.364-364
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• 2010

Defects existing on the clean Si(5 5 12)-$2{\times}1$, composed of one-dimensional(1-D) structures such as honeycomb (H) chain, $\pi$-bonded ($\pi$) chains, dimer-adatom (D-A) row, and tetramer (T) row, have been investigated by scanning tunneling microscopy (STM). It is found that the defects can be classified to two categories: One is originated from phase boundaries in D-A and T rows having $2{\times}$ periodicities, by which buckling directions are reversed, and the other is caused by missing atoms on $\pi$ chains, D-A rows, and T rows. All these defects are symmetric with respect to the [6 6 $\bar{5}$] direction, which is due to one-dimensional symmetry along the [1 $\bar{1}$ 0] direction. Especially it is worth noticing that on H chains none of such defects exist, which implies that the H chain is energetically the most stable among 1-D structures existing on Si(5 5 12)-$2{\times}1$.

• 대한화학회지
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• 제42권2호
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• pp.177-183
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• 1998

C2-손대칭 리간드(chiral ligand)의 한 종류인 (+)-11S,12S-bis [2,2'-(diphenylphosphino)benzanilido]-9,10-dihydro-9,10-ethanoanthracene과 백금과 코발트를 포함하는 착물과 각각 반응시켜, 세 종류의 새로운 착물인 $\pi$-allyl Pt(+)-11S,12S-bis[2'-(diphenylphosphino)benzanilido]-9,10-dihydro-9,10-ethanoanthracene perchlorate, $\pi$-allyl Pt(+)-11S,12S-bis[2,2'-(diphenylphosphino)benzanilido]-9,10-dihydro-9,10-ethanoanthracene chloride, (${\eta}$5-cyclopentadienyl) Co -(+)-11S,12S-bis[2,2'-(diphenylphosphino)benzanilido]-9,10-dihydro-9,10-ethanoanthracene를 얻었다. 그리고 (${\eta}$3-cyclohexenyl) Pd 착물과 대칭리간드인 1,2-bis(diphenylphosphino)ethane 과 반응시켜 새로운 착물, (${\eta}$3-cyclohexenyl) Pd1,2-bis(diphenylphosphino)ethane perchlorate를 생성하였다. 이들 착물은 NMR-, IR-, Mass-spectrometer, 원소분석등의 각종 화학분석기기에 의해 각각 확인되었다.

• BMB Reports
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• 제40권2호
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• pp.239-246
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• 2007

Riboflavin synthase from Escherichia coli is a homotrimer of 23.4 kDa subunits and catalyzes the formation of one molecule each of riboflavin and 5-amino-6-ribitylamino- 2,4(1H,3H)-pyrimidinedione by the transfer of a 4-carbon moiety between two molecules of the substrate, 6,7- dimethyl-8-ribityllumazine. Each subunit comprises two closely similar folding domains. Recombinant expression of the N-terminal domain is known to provide a $C_2$-symmetric homodimer. In this study, the binding properties of wild type as well as two mutated proteins of N-terminal domain of riboflavin synthase with various ligands were tested. The replacement of the amino acid residue A43, located in the second shell of riboflavin synthase active center, in the recombinant N-terminal domain dimer reduces the affinity for 6,7-dimethyl-8-ribityllumazine. The mutation of the amino acid residue C48 forming part of activity cavity of the enzyme causes significant $^{19}F$ NMR chemical shift modulation of trifluoromethyl derivatives of 6,7-dimethyl-8-ribityllumazine in complex with the protein, while substitution of A43 results in smaller chemical shift changes.

• 공업화학
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• 제21권2호
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• pp.230-237
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• 2010

선상의 액정 다이머 동족체들인 ${\alpha},{\omega}$-비스(4-니트로아조벤젠-4'-카보닐옥시)알칸들(NATWESn, n = 2~8, 10, 유연격자 중의 메틸렌 단위들의 수)을 합성함과 동시에 이들의 열적 거동을 검토하였다. 모든 다이머들은 쌍방성 네마틱 상들을 형성하였다. 다이머들의 네마틱 상에서 액체 상으로의 전이온도들, 그리고 상 전이시의 엔트로피 변화는 n의 함수로서 커다란 홀수-짝수 효과를 나타냈다. 이러한 거동은 유연격자의 홀수-짝수의 변화에 의한 유연격자의 평균적인 형태변화의 견지에서 합리적으로 설명된다. NATWESn이 나타내는 네마틱 상의 열적 안정성과 질서도, 그리고 홀수-짝수의 크기는 니트로아조벤젠 그룹을 폴리메틸렌 유연격자를 통하여 에테르 결합으로 도입시켜 얻은 대칭 다이머들의 결과들과 거의 유사한 반면 모노메소겐 화합물들인 4-{4'-(니트로페닐아조펜옥시}알카노일 클로라이드들, 그리고 곁사슬형 액정 고분자인 폴리[1-{4-(4'-니트로페닐아조)펜옥시카보닐알카노일옥시}에틸렌]들의 결과들에 비해 판이하였다. 이들의 결과를 Imrie에 의한 'irtual trimer model'의 견지에서 검토하였다.