• BMB Reports
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• 제49권3호
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• pp.135-136
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• 2016

Small interfering RNAs (siRNAs) have been developed to intentionally repress a specific gene expression by directing RNA-induced silencing complex (RISC), mimicking the endogenous gene silencer, microRNAs (miRNAs). Although siRNA is designed to be perfectly complementary to an intended target mRNA, it also suppresses hundreds of off-targets by the way that miRNAs recognize targets. Until now, there is no efficient way to avoid such off-target repression, although the mode of miRNA-like interaction has been proposed. Rationally based on the model called "transitional nucleation" which pre-requires base-pairs from position 2 to the pivot (position 6) with targets, we developed a simple chemical modification which completely eliminates miRNA-like off-target repression (0%), achieved by substituting a nucleotide in pivot with abasic spacers (dSpacer or C3 spacer), which potentially destabilize the transitional nucleation. Furthermore, by alleviating steric hindrance in the complex with Argonaute (Ago), abasic pivot substitution also preserves near-perfect on-target activity (∼80-100%). Abasic pivot substitution offers a general means of harnessing target specificity of siRNAs to experimental and clinical applications where misleading and deleterious phenotypes from off-target repression must be considered.

• 대한화학회지
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• 제34권2호
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• pp.184-188
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• 1990

치환 phenacyl bromide와 imidazole과의 반응 및 phenacyl bromide와 치환imidazole과의 반응속도를 전기전도도법으로 측정하였다. 반응속도는 phenacyl bromide의 전자 끄는기에 의하여 촉진되었으며 이 반응은 linear free energy relationship과 isokinetic relationship에 잘 맞았다. 반응속도와 imidazole의 pKa사이에는 Bronsted rule이 잘 적용되었으나 2-methylimidazole의 경우에는 위치장애현상으로 인해 여기서 벗어났다. Acetonitrile 용매하에서는 methanol 용매하에서보다 Kirkwood식에서 예상되는 것보다 훨씬 빠르게 반응속도가 관찰되었다.

• Fibers and Polymers
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• 제2권2호
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• pp.86-91
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• 2001

Liquid crystalline (LC) poly(ethylene terephthalate-co-2(3)-chloro-1,4-phenylene terephthalate) [copoly(ET/CPT)] was prepared using poly(ethylene terephthalate) (PET) as a flexible spacer, terephthalic acid (TPA), and chlorohydroquinone diacetate (CHQDA). All reactions involved in the copolymerization were investigated using some model compounds: TAP was used for acidolysis, diphenylethyl terephthalate (DPET) for interchange reaction between PET chains, and 야-o-chlorophenyl terephthalate (DOCT) and di-m-chlorophenyl terephthalate (DMCT) for interchange reaction between PET and rigid rodlike segments. Activation energies obtained for the acidolysis of PET with TPA and for interchange reaction of PET with DPET, DOCT, and DMCT were 19.8 kcal/mol, 26.5 kcal/mole, and 45.9 kcal/mole, respectively. This result supports that the copolymerization proceeds through the acidolysis of PET with TPA first and subsequent polycondensation between carboxyl end group and CHQDA or acetyl end group, which is formed from the reaction of CHQDA and TPA. Also, it was found that ester-interchange reaction can be influenced by the steric hindrance. Copoly(ET/CPT)s obtained has ethylene acetate end groups formed from acetic acid hydroxy ethylene end groups and showed almost the random sequence distribution for all compositions.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 1999년도 하계종합학술대회 논문집
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• pp.275-278
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• 1999

We have grown vertically aligned carbon nanotubes in a large area of Co-Ni codeposited Si substrates by the thermal CVD using $C_2$H$_2$gas. Since the discovery of carbon nanotubes, Synthesis of carbon nanotubes for mass production has been achieved by several methods such as laser vaporization, arc discharge, and pyrolysis. In particular, growth of vertically aligned nanotubes is of technological importance for applications to FED. Recently, vertically aligned carbon nanotubes have been grown on glass by PECVD. Aligned carbon nanotubes can be also grown on mesoporous silica and Fe patterned porous silicon using CVD. Despite such breakthroughs in the growth, the growth mechanism of the alignment are still far from being clearly understood. Furthermore, FED has not been clearly demonstrated yet at a practical level. Here, we demonstrate that carbon nanotubes can be vertically aligned on catalyzed Si substrate when the domain density reaches a certain value. We suggest that steric hindrance between nanotubes at an initial stage of the growth forces nanotubes to align vertically and then nanotubes are further grown by the cap growth mechanism.

• Bulletin of the Korean Chemical Society
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• 제31권9호
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• pp.2613-2617
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• 2010

Chloroprene is a chlorine substituent of 1,3-butadiene. Butadiene rubber (BR) and chloroprene rubber (CR) composites were thermally aged at 60, 70, 80, and $90^{\circ}C$ for 2 - 185 days in a convection oven and changes of the crosslink densities by the accelerated thermal aging were investigated. The crosslink densities increased as the aging time elapsed and as the aging temperature became higher. Degrees of the crosslink density changes of the BR composite were on the whole larger than those of the CR one except the short-term thermal aging at 60 and $70^{\circ}C$. The crosslink densities abnormally increased after themal aging at high temperatures for a long time. Activation energies for the crosslink density changes of the rubber composites tended to increase with increase of the aging time and the variation showed a local minimum. The activation energies of the CR composite were lower than those of the BR one. The experimental results were explained with a role of ligand of chlorine atom of CR in a zinc complex, steric hindrance by chlorine atom of CR, and oxidation of rubber chain.

• 공업화학
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• 제3권1호
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• pp.156-171
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• 1992

Chitin was isolated from crab shell. Chitosan, which was prepared by the deacetylation of chitin, was acylated to obtain N-acetyl(regenerated chitin), N-propionyl, N-butyryl, N-hexanoyl, N-decanoyl and N-maleated chitosans and their metal ion adsorption characteristics of N-acylchitosans were investigated. In order to enhance the adsorptivity, their porous beads were prepared and their adsorptivity with respect to the porosity and the adsorptivities for metal ions($Cu^{2+}$, $Ni^{2+}$, $CO^{2+}$, $Mn^{2+}$, $Ag^{+}$)were investigated. Their metal ion adsorptivities were remarkably imporved compared to those of chitin. As the larger acyl groups were introduced, adsorptivity increased, but that of N-decanoyl chitosan showed some decrease because of steric hindrance of the bulky N-decanoyl group. N-Maleated chitosan containing carboxyl group showed highly improved adsorptivity, and N-acylchitosans showed the good selective adsorption in the mixed metal ions($Cu^{2+}$, $Ni^{2+}$, $CO^{2+}$, $Mn^{2+}$ and $Ag^{+}$). They also showed excellent adsorption characteristics as chelating polymers.

• 한국표면공학회지
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• 제24권1호
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• pp.1-17
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• 1991

Understanding of the detailed reaction mechanisms during MOVPE and ALE is essential to further improve the properties of the grown crystals and the controllability of the growth parameters. The unified models for the detailed reaction paths are not available at this stage. The study, however, has been advanced to the extent that consensus on some of the reaction paths can be drawn from the scattered data. Metalakyls such as TMGa and TMIn seem to nearly fully decompose in the gas phase through homogeneous reaction at the typical MOVPE growth temperature. Hydrides such as AsH3 and PH3, on the contrary. seem to decompose heterogeneously onthe substrate surfaces as well as homogeneously in the gas phase. However, at lower temperatures, where ALE crystals are typically grown, the growth process is strongly dependent on the surface reactions. It seems that steric hindrance effects which the radicals reaching the substrate exhibit on the surface the growth rate a function of the metalalkyle supply durations. In addition, dydrogens released from hydrides seem to play an essential role in removing carbons leberated from the metalalkyls. High growth temperatures also seem to be effective in desorbing carbons from surface. The understanding of the reaction mechanisms was possible though diverse appraaches utilizing many ex-situ and in-situ diagnostic techniques and genuine experimental designs. It is the purpose of this paper to review and discuss many of these efforts and to draw some possible conclusions from them.

• 한국표면공학회지
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• 제24권1호
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• pp.1.1-1.1
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• 1991

Understanding of the detailed reaction mechanisms during MOVPE and ALE is essential to further improve the properties of the grown crystals and the controllability of the growth parameters. The unified models for the detailed reaction paths are not available at this stage. The study, however, has been advanced to the extent that consensus on some of the reaction paths can be drawn from the scattered data. Metalakyls such as TMGa and TMIn seem to nearly fully decompose in the gas phase through homogeneous reaction at the typical MOVPE growth temperature. Hydrides such as AsH3 and PH3, on the contrary. seem to decompose heterogeneously onthe substrate surfaces as well as homogeneously in the gas phase. However, at lower temperatures, where ALE crystals are typically grown, the growth process is strongly dependent on the surface reactions. It seems that steric hindrance effects which the radicals reaching the substrate exhibit on the surface the growth rate a function of the metalalkyle supply durations. In addition, dydrogens released from hydrides seem to play an essential role in removing carbons leberated from the metalalkyls. High growth temperatures also seem to be effective in desorbing carbons from surface. The understanding of the reaction mechanisms was possible though diverse appraaches utilizing many ex-situ and in-situ diagnostic techniques and genuine experimental designs. It is the purpose of this paper to review and discuss many of these efforts and to draw some possible conclusions from them.

• 한국물환경학회지
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• 제21권2호
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• pp.205-210
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• 2005

There has been a growing interest in NF membrane for drinking water treatment, because it can remove simultaneously both hardness and hazardous micro pollutants such as pesticides and THM precursors. In this work, a hollow fiber NF membrane known as a composite membrane was employed for the rejection properties of both hydrophilic solutes and micro organic pollutants, where the former was used to evaluate the molecular sieving effect of this membrane and the latter was employed for the investigation of solute-membrane interaction as hydrophobic materials. This membrane effectively rejected the hydrophilic solutes and the permeation of them was mainly controlled by the molecular sieving effects such as molecular weight and molecular width. In the case of all micro organic pollutants, the rejections were varied from 42.2% for Simazine to 91.6% for Malathion, and the parameters related to the steric hindrance could significantly play an important role in the rejection. In the batch type adsorption experiments, all micro organic pollutants were entrapped mildly on the membrane in spite of lower degree compared with that of aromatic compounds, and they were correlated with log K.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제49권8호
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• pp.451-454
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• 2000

We have grown vertically aligned carbon nanotubes in a large area of Co-Ni codeposited Si substrates by the thermal CVD usign $C_2H_2$ gas. Since the discovery of carbon nanotubes, growth of carbon nanotubes has been achieved by several methods such as laser vaporization, arc discharge, and pyrolysis. In particular, growth of vertically aligned nanotubes is important to flat panel display applications. Recently, vertically aligned carbon nanotubes have been grown on glass by PECVD. Aligned carbon nanotubes can be also grown on mesoporous silica and Fe patterned porous silicon using CVD. In this paper, we demonstrate that carbon nanotubes can be vertically aligned on catalyzed Si substrate when the domain density of catalytic particles reaches a certain value. We suggest that steric hindrance between nanotubes at an initial stage of the growth forces nanotubes to align vertically and each nonotubes are grown in bundle.