• Bulletin of the Korean Chemical Society
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• 제4권3호
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• pp.123-127
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• 1983

The crystal structure of metoclopramide, $C_14H_22ClN_3O_2$, has been determined by X-ray diffraction techniques using diffractometer data obtained by the ${\omega}-2{\theta}$ scan technique with Mo $K\alpha$ radiation from a crystal with space group symmetry $P{\overline{1}}$ and unit cell parameters a = 7.500(1), b = 8.707(2), c = 13.292(2) ${\AA}$; ${\alpha}$ = 101.70(2), ${\beta}$ = 81.20(2), and ${\gamma}$ = $114.90(l)^{\circ}$. The sructure was solved by direct methods and refined by full-matrix least-squares to a final R = 0.055 for the 1524 observed reflections. The bent overall-conformation of the molecule seems to be determined mainly by the bifurcated intramolecular hydrogen bond from the amide nitrogen atom to the methoxy oxygen and the amine nitrogen atoms. The crystal packing consists of the hydrogen bonds, ${\pi}-{\pi}$ interaction and hydrophobic interaction.

• 한국생물공학회:학술대회논문집
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• 한국생물공학회 2001년도 추계학술발표대회
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• pp.671-674
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• 2001

정제, 농축된 free CGTase 는 pH 6.0 - 7.0의 범위에서 안정하였으며, $70^{\circ}C$정도의 고온에서도 안정한 특성을 가지고 있었으며, CGTase의 고정화를 위한 방법으로서 CNBr-activated sepharose 4B에 의한 고정화가 가장 높은 효율올 나타내는 것으로 결정되었다. 고정화의 최적조건은 $30^{\circ}C$, 60rpm, pH 6.0의 phosphate buffer 하에서 9 시간 동안 고정화하는 것이었고, CNBr-activated sepharose 4B를 이용한 고정화의 경우 실험에 사용된 다른 모든 이온교환 수지에서 얻어진 효율에 비해 월등한 효과를 보였다.

• Bulletin of the Korean Chemical Society
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• 제33권1호
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• pp.153-158
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• 2012

The hydrogenation of $AlB_2$-type BaGaGe exhibits a metal to insulator (MI) transition, inducing a puckering distortion of the original hexagonal [GaGe] layers. We investigate the electronic structure changes associated with the hydrogen-induced MI transition, using extended H$\ddot{u}$ckel tight-binding band calculations. The results indicate that hydrogen incorporation in the precursor BaGaGe is characterized by an antibonding interaction of $\pi$ on GaGe with hydrogen 1s and the second-order mixing of the singly occupied antibonding $\pi^*$ orbital into it, through Ga-H bond formation. As a result, the fully occupied bonding $\pi$ band in BaGaGe changes to a weakly dispersive band with Ge pz (lone pair) character in the hydride, which becomes located just below the Fermi level. The Ga-Ge bonds within a layered polyanion are slightly weakened by hydrogen incorporation. A rationale for this is given.

• Bulletin of the Korean Chemical Society
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• 제23권10호
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• pp.1459-1462
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• 2002

The kinetics of the addition of X-substituted benzylamines (BA) to Y-substituted Benzylideneacetylacetones (BAA) have been investigated in acetonitrile at $25.0^{\circ}C$. The reaction is studied under pseudo-first-order conditions by keeping a large excess of BA over BAA. The addition of BA to BAA occurs in a single step in which the addition of BA to $C_\alpha$ of BAA and proton transfer from BA to $C_\beta$ of BAA take place concurrently with a four-membered cyclic transition state structure. The magnitude of the Hammett ($p_X$) and Bronsted ($\beta_x$) coefficients are rather small suggesting an early tansition state (TS). The sign and magnitude of the cross-interaction constant, $p_{XY}$ (= -0.49), is comparatible to those found in the normal bond formation processes in the $S_N2$ and addition reactions. The normal kinetic isotope effect ($K_H/K_D$ > 1.0) and relatively low $\Delta$H^{${\neq}$}$ and large negative $\Delta$S^{${\neq}$}$ values are also consistent with the mechanism proposed.

• 대한화학회지
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• 제18권4호
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• pp.223-238
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• 1974

염화포름산 알킬의 할로겐화 이온 교환반응을 반응속도론적으로 연구하고, 이의 전자 구조적 특성을 CNDO/2 MO계산으로 연구하였으며 이로부터 구조와 반응성 간의 관계를 논의하였다. 염화포름산 알킬의 에너지면에서의 가장 안정한 입체배치가 알킬기와 염소원자 사이가 서로 트랜스인 입체배치임을 알았으며, 결합주위의 회전장애가 {\pi}-전자 비편재화에 기인됨을 밝혔다. 염화포름산 알킬은 하전분리가 심한 극성물질이며, 이것이 카르보닐 산소와 알콕시 산소의 효과 및 염소의 효과에 기인됨을 밝혔다. 반응속도에 미치는 용매효과는 $(CH_3)_2CO>CH_3CN{\gg}MeOH$순으로 반응성이 감소되는 작용을 나타냈으며, 친핵성도는 양성자성 용매중에서 $I^->Br^->Cl^-$, 비양자성 용매 중에서 $Cl^->Br^->I^-$이었으며 알킬기의 기여는 $CH_3->C_2H_5->i-C_3H_7-$순이었다. 초기상태와 천이상태의 안정화 기여를 기초로 용매효과를 해석하였으며 초기상태 탈용매화의 특성으로 친핵성도를 논의하였다. 이 반응에 대하여 가장 유리한 메카니즘을 첨가-제거 메카니즘으로 제안하였다. 염화포름산 알킬의 반응성을 결정하는 구조적 요인은 하전, C-Cl 결합에 대하여 ${\alpha}^{\ast}$인 LUMO의 에너지준위 및 이 MO에서 C-Cl결합의 반결합세기임을 밝혔다.

• The Journal of Advanced Prosthodontics
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• 제4권2호
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• pp.103-108
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• 2012

PURPOSE. Debonding of a composite resin core of the fiber post often occurs at the interface between these two materials. The aim of this study was to evaluate the effects of different surface treatment methods on bond strength between fiber posts and composite core. MATERIALS AND METHODS. Sixty-four fiber posts were picked in two groups (Hetco and Exacto). Each group was further divided into four subgroups using different surface treatments: 1) silanization; 2) sandblasting; 3) Treatment with 24% $H_2O_2$, and 4) no treatment (control group). A cylindrical plexiglass matrix was placed around the post and filled with the core resin composite. Specimens were stored in 5000 thermal cycles between $5^{\circ}C$ and $55^{\circ}C$. Tensile bond strength (TBS) test and evaluation using stereomicroscope were performed on the specimen and the data were analyzed using two-way ANOVA, Post Hoc Scheffe tests and Fisher's Exact Test (${\alpha}$=.05). RESULTS. There was a significant difference between the effect of different surface treatments on TBS ($P$ <.001) but different brands of post ($P$=.743) and interaction between the brand of post and surface treatment ($P$=.922) had no significant effect on TBS. Both silanization and sandblasting improved the bonding strength of fiber posts to composite resin core, but there were not any significant differences between these groups and control group. CONCLUSION. There was not any significant difference between two brands of fiber posts that had been used in this study. Although silanization and sandblasting can improve the TBS, there was not any significant differences between surface treatments used.

• Elastomers and Composites
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• 제47권1호
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• pp.54-64
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• 2012

본 연구에서는 polar 한 silica 와 non-polar 한 고무사이의 친화력을 증대시키기 위하여 SBR 분자 주쇄에 acrylonitrile 을 도입시킨 acrylonitirle functionalized emulsion SBR 의 물성에 관하여 연구하였다. Acrylonitrile의 nitrile group 은 silica 표면의 silanol group 과 H-bond 를 형성할 수 있음으로 polar 한 silica 표면에 흡착되는 가교촉진제를 줄이고 가황반응을 촉진시키는 것으로 판단된다. SBR 및 AN-SBR 에 PEG 를 적용한 컴파운드의 경우 PEG 와 silica 표면의 silanol group 과의 상용성이 높아 가교촉진제가 polar 한 silica 표면에 흡착됨을 줄여 가교시간이 단축된 것으로 판단된다. 기계적 물성에서 AN-SBR 컴파운드는 SBR 1721 컴파운드 대비 100%, 300%에서 높은 모듈러스 값을 나타내었다. 이러한 결과는 AN-SBR 의 높은 분자량 및 nitrile group 의 도입에 따른 가교도의 상승에 의한 결과로 판단된다. 동적점탄특성 결과에서 AN-SBR 컴파운드는 SBR 1721 컴파운드 대비 $60^{\circ}C$ 에서 낮은 tan ${\delta}$ 값을 나타내었으며, 이는 nitrile group 과 silica 사이의 친화력에 따른 filler-rubber interaction의 향상에 의해 반복변형에 의한 energy dissipation 이 낮은 것으로 판단된다.

• Bulletin of the Korean Chemical Society
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• 제26권12호
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• pp.1965-1968
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• 2005

Extended H$\ddot{u}$ckel molecular calculations have been used to analyze how the magnitude of exchange coupling is influenced by the structural distortions in a series of dinuclear six-coordinate copper(II) complexes bridged by the planar bis-bidentate oxalate anion. Copper(II) ions have distorted octahedral surroundings, one being axially elongated and the other compressed. The magnetic interaction is strong in the former complexes and very weak in the latter. This is interpreted as resulting from a switching of magnetic spin orbitals due to the structural distortions (bond elongation or compression) of the copper sites.

• Bulletin of the Korean Chemical Society
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• 제30권12호
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• pp.3006-3010
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• 2009

We have performed long time REMD simulation on 15-19 residues of human calcitonin hormone (DFNKF) which is known to form highly ordered amyloid fibril. The simulation started from randomly oriented multiple DFNKF strand. Using all-atom level simulations with the generalized Born solvation (GB) model (param99MOD3), we observed spontaneous formation of ${\beta}$-sheet for tetramer. Interestingly, the current simulation gives anti-parallel sheet as a major conformation, consistent with experiments. The major interaction stabilizing the anti-parallel sheet seems to be the inter-strand hydrogen bond.

• Bulletin of the Korean Chemical Society
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• 제1권3호
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• pp.109-112
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• 1980

Ultraviolet spectrophotometric investigations were carried out on monoalkylbenzene-iodine systems in carbon tetrachloride. The results reveal the formation of one-to-one molecular complexes. On the basis of the equilibrium constants for these complexes of representative monosubstituted benzenes, the following order of increasing stability is obtained: i-propyl- ${\Delta}$H, ${\Delta}$G and ${\Delta}$S for the interaction of a number of monoalkyl substituted benzenes with iodine have been determined. In general, it can be said that as ${\Delta}$H becomes increasingly negative, corresponding decreases in the ${\Delta}$G and the ${\Delta}$S values are observed, and these variations are linear. The thermodynamic constants become increasingly negative with increasing monoalkyl substitution of the aromatic donor nucleus. The complex bond is therefore weak, and its formation is accompanied by relatively small entropy changes. Thus, analysis of these findings is discussed.