• Title/Summary/Keyword: bonding mechanism

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Nucleophilic Substitution at a Carbonyl Carbon Atom (IX). Solvolysis of 2-Furoyl Chloride and 2-Thenoyl Chloride in Binary Mixtures (카르보닐탄소원자의 친핵성 치환반응 (제9보). 이성분 혼합용매에서 2-염화테노일 및 2-염화퓨로일의 가용매분해반응)

  • Son Jin-Eon;Sang-Kee Yoon;Ikchoon Lee
    • Journal of the Korean Chemical Society
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    • v.23 no.6
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    • pp.339-348
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    • 1979
  • The kinetics of the solvolysis of 2-furoyl chloride and 2-thenoyl chloride in $MeOH-H_2O,\;EtOH-H_2O,\;(Me)_2CO-H_2O,\;MeCN-H_2O$ and MeCN-MeOH has been investigated. The rates were faster in protic solvents than in aprotic solvents. This was caused by the bond breaking of leaving group through hydrogen-bonding solvation of protic solvents. In MeCN-M$\'{e}$OH the rate in MeOH rich solvents was faster than in MeCN rich solvents by the specific solvation of alcoholic hydrogen and there was a maximum rate of reaction at MeOH mole fraction of 0.8. The reaction rates of solvolysis were considerably slower than those of benzoyl chloride owing to the electron withdrawing effect of thienyl and furyl groups. It was concluded that solvolytic reaction proceeds via a dissociative $S_N2$ mechanism in which bond-breaking precedes bond-formation at the transition state.

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Effect of Low-temperature Thermal Treatment on Degree of Crystallinity of a Low Density Polyethylene: $^{1}H$ Nuclear Magnetic Resonance Study (저밀도 폴리에틸렌의 결정화도에 대한 저온 열처리 효과: 수소 핵자기공명 연구)

  • Lee, Chang-Hoon;Choi, Jae-Kon
    • Elastomers and Composites
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    • v.43 no.4
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    • pp.259-263
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    • 2008
  • An effect of low-temperature long-term thermal degradation on a degree of crystallinity of a low density polyethylene (LDPE) was investigated by using $^1H$ solid state nuclear magnetic resonance (SSNMR). Firstly, the long-term thermal treatment makes a color of LDPE from white to pale yellow which is indicative of thermal oxidation. Secondly, it makes the $^{1}H$ NMR spin-spin and spin-lattice relaxation times ($T_1$) to be long. Lastly, the degree of crystallinity of the semicrystalline aged-LDPE also decreases with thermal treatment. Above all, the $T_1$ increase is envisaged to be due to either a decrease of the amorphous regions governing overall spin-lattice relaxation mechanism in LDPEs or a dynamically restricted motion of specific molecular motions by intermolecular hydrogen bonding or crosslinking. However, since the decrease of crystallinity implies an increase of amorphous regions by the thermal treatment, the former case is contrast to our results. Accordingly, we concluded that the latter effect is responsible for the $T_1$ increase.

Proton implantation mechanism involved in the fabrication of SOI wafer by ion-cut process (Ion-cut에 의한 SOI웨이퍼 제조에서의 양성자조사기구)

  • 우형주;최한우;김준곤;지영용
    • Journal of the Korean Vacuum Society
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    • v.13 no.1
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    • pp.1-8
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    • 2004
  • The SOI wafer fabrication technique has been developed by using ion-cut process, based on proton implantation and wafer bonding techniques. It has been shown by TRIM simulation that 65 keV proton implantation is required for the standard SOI wafer (200 nm SOI, 400 nm BOX) fabrication. In order to investigate the optimum proton dose and primary annealing condition for wafer splitting, the surface morphologic change has been observed such as blistering and flaking. As a result, effective dose is found to be in the 6∼$9\times10^{16}$ $H^{+}/\textrm{cm}^2$ range, and the annealing at $550^{\circ}C$ for 30 minutes is expected to be optimum for wafer splitting. The depth distribution of implanted hydrogen has been experimentally confirmed by ERD and SIMS measurements. The microstructure evolution in the damaged layer was also studied by X-TEM analysis.

Study on the design of LEO Satellite System in Space Plasma Environment (우주 플라즈마 환경에서 저궤도 위성 시스템 설계에 관한 고찰)

  • Lim, S.B.;Hong, S.P.;Kim, T.Y.;Jang, J.W.;Choi, S.W.
    • Aerospace Engineering and Technology
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    • v.7 no.2
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    • pp.67-75
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    • 2008
  • The electrostatic charging/discharging mechanism and its effects, and the system design considerations in the space plasma environment are studied in this paper. The electrostatic discharge (ESD) effects are carefully taken into account for a design of the satellite system at the early stage of the development. Generally, the electrical design requirements are specified to protect the satellite system from the ESD effects in the electromagnetic compatibility specifications. Those requirements are included the grounding, the bonding, the shielding, the conductive coating, the electric interfacing and so on. The space charging is caused by the increasing of the voltage difference between the each locations on the satellite surface. If the space charging is continued up to threshold, it may be occurred the system failure. This phenomenon is depended on the mission of system, electrical and mechanical configuration, system operation, and orbit condition. Therefore the related requirements are properly tailored and concentrated into the safety design.

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Identification of Oligosaccharides in Human Milk Bound onto the Toxin A Carbohydrate Binding Site of Clostridium difficile

  • Nguyen, Thi Thanh Hanh;Kim, Jong Woon;Park, Jun-Seong;Hwang, Kyeong Hwan;Jang, Tae-Su;Kim, Chun-Hyung;Kim, Doman
    • Journal of Microbiology and Biotechnology
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    • v.26 no.4
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    • pp.659-665
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    • 2016
  • The oligosaccharides in human milk constitute a major innate immunological mechanism by which breastfed infants gain protection against infectious diarrhea. Clostridium difficile is the most important cause of nosocomial diarrhea, and the C-terminus of toxin A with its carbohydrate binding site, TcdA-f2, demonstrates specific abolishment of cytotoxicity and receptor binding activity upon diethylpyrocarbonate modification of the histidine residues in TcdA. TcdA-f2 was cloned and expressed in E. coli BL21 (DE3). A human milk oligosaccharide (HMO) mixture displayed binding with TcdA-f2 at 38.2 respond units (RU) at the concentration of 20 μg/ml, whereas the eight purified HMOs showed binding with the carbohydrate binding site of TcdA-f2 at 3.3 to 14 RU depending on their structures via a surface plasma resonance biosensor. Among them, Lacto-N-fucopentaose V (LNFPV) and Lacto-N-neohexaose (LNnH) demonstrated tight binding to TcdA-f2 with docking energy of −9.48 kcal/mol and −12.81 kcal/mol, respectively. It displayed numerous hydrogen bonding and hydrophobic interactions with amino acid residues of TcdA-f2.

Mechanical property of Diglycldyl ether of bisphenol A-Methylene dianiline System with Succinonitrile (Diglycidyl ether of bisphenol A-Methylene dianiline-Succinonitrile계의 역학적 성질)

  • Cho, Sung-Woo;Shim, Mi-Ja;Kim, Sang-Wook
    • Korean Journal of Materials Research
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    • v.2 no.3
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    • pp.191-196
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    • 1992
  • The new epoxy resin, diglycidyl ether of bisphenol A(DGEBA)/4, 4'-methylene dianiline (MDA)/succinonitrile system, containing the reactive additive succionitrile was investigated through the impact test and the stress-strain test on the basis of the behavior of cure reaction and the cure mechanism. The new epoxy resin system, having the different succinonitrile contents, were cured at $80^{\circ}C$for 1.5 hour and then in order to cure completely at $150^{\circ}C$ for 1 hour. It was shown that as the succinonitrile content increased, impact strength was gradually increased, tensile strength was decreased, almost constantly Young's modulus was sustained and elongation was increased until the succinonitrile content was increased to 10phr, and then decreased. From the experimental results, it can be concluded that the chemical bonding length between the main chains was extended by adding the reactive additive succinonitrile. It was also found that the flexibility of epoxy resin was improved by adding the succinonitrile.

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The Adsorption of Alkyl Aldehydes on Cations Supported by Layer Silicate. Complex Formation Theory (Layer Silicate에 지지된 양이온상에서의 알킬알데히드의 흡착기구. 착물형성 이론)

  • Kim Jong Taik;Sohn Jong Rack
    • Journal of the Korean Chemical Society
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    • v.18 no.3
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    • pp.180-188
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    • 1974
  • Adsorption mechanism of alkyl aldehydes, acetaldehyde, acrolein, and crotonaldehyde on cations supported by layer silicates was studied by means of IR spectroscopy and X-ray. An analysis of four characteristic split bands in the region of $1720∼1580㎝^{-1}$ was made. The carbonyl stretching band which shifted about $130㎝^{-1}$ to lower frequencies was observed only for $Ni^{2+}$ and Al^{3+}$ but slightly with $Ca^{2+}$ at high sample temperature and was attributed to >C=O…M complex formation. A sharp band which appeared as a shoulder at 1722 for acetaldehyde and 1690 for acrolein and crotonaldehyde was responsible for the interaction of carbonyl with surface hydroxyl. The second broad band which appeared at about 1710~1660 was responsible for hydrogen bonding between carbonyl oxygen and cationic hydroxyl group. The third band which appeared at about 1640~1660 was attributed to induced >C=C< double bond due to the strong carbonyl interaction. This was supported by the interlamellar spacings obtained by X-ray diffractometry.

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Nanotechnology in the Surface Treatment of Titanium Implant. (임상가를 위한 특집 2 - 티타늄 임플란트 표면처리에서의 나노테크놀로지)

  • Oh, Seung-Han
    • The Journal of the Korean dental association
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    • v.48 no.2
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    • pp.106-112
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    • 2010
  • Tissue engineering has been enhanced by advance in biomaterial nature, surface structure and design. In this paper, I report specifically vertically aligned titania ($TiO_2$) nanotube surface structuring for optimization of titanium implants utilizing nanotechnology. The formation, mechanism, characteristics of titania nanotubes are explained and emerging critical role in tissue engineering and regenerative medicine is reviewed. The main focus of this paper is on the unique 3 dimensional tubular shaped nanostructure of titania and its effects on creating epochal impacts on cell behavior. Particularly, I discuss how different cells cultured on titania nanotube are adhered, proliferated, differentiated and showed phenotypic functionality compared to those cultured on flat titanium. As a matter of fact, the presence of titania nanotube surface structuring on titanium for dental applications had an important effect improving the proliferation and mineralization of osteoblasts in vitro, and enhancing the bone bonding strength with rabbit tibia over conventional titanium implants in vivo. The nano-features of titania nanotubular structure are expected to be advantageous in regulating many positive cell and tissue responses for various tissue engineering and regenerative medicine applications.

A Study on alumina Sintering through the Oxidation of AI Powder. (Al 분말의 산화에 의한 $Al_2O_3$ 소결에 관한 연구)

  • 박정현;안주삼;김해두
    • Journal of the Korean Ceramic Society
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    • v.19 no.3
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    • pp.179-186
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    • 1982
  • This research is to aim at the study of sintering mechanism through the observation of microstructure by scanning electron microscopy, after the mixture of 30wt% $Al_2O_3$ (White Alundum) powder is fired in air at the temperature range of 1350~150$0^{\circ}C$ in order to sinter $Al_2O_3$-Al through the oxidation of Al powder. The results obtained in this experiment are as follows: 1. While the compressive strength of $Al_2O_3$(WA) body fired at $1450^{\circ}C$ for 5hrs in air is 150kg/$\textrm{cm}^2$, that of Al-$Al_2O_3$ body fired at 135$0^{\circ}C$, $1400^{\circ}C$ for 5hrs in air is 1100kg/$\textrm{cm}^2$, 1600kg/$\textrm{cm}^2$ respectively, and the higher the firing temperature, the more the compressive strength increases. These results from the sintering effect between $Al_2O_3$(WA) grains and surrounding Al-oxidation layer. 2. While the compressive strength of Al2O3(WA) body fired at 150$0^{\circ}C$ for 5hrs in air is 250kg/$\textrm{cm}^2$, the compressive strength of Al-$Al_2O_3$body fired under the same condition is 2050kg/$\textrm{cm}^2$ and water absorption 9.0%, porosity 23.3%, bulk density 2.60gr/$cm^3$. It is assumed that these results come from not only the grain growth of oxidized Al grains but also the increase of bonding strength between $Al_2O_3$(WA) grains.

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Synthesis and Structural Studies of an Organic Complex and its Association with BSA

  • Meng, Fa-Yan;Yu, Sheng-Rong;Liang, Li-Xi;Zhong, Xue-Ping;Wang, Li;Zhu, Jin-Mei;Lin, Cui-Wu
    • Bulletin of the Korean Chemical Society
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    • v.32 no.7
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    • pp.2253-2259
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    • 2011
  • The self-assembly of one novel organic complex based on chlorogenic acid (HCA) and 2,2'-bipyridine (2,2'-bipy) has been synthesized and characterized. The complex achieved by hydrogen-bonding interactions, adopted a 1:1 stoichiometry in a solid state. The proton transfer occurred from the carboxyl oxygen to the aromatic nitrogen atom to form salts CA${\cdot}$(2,2'-Hbipy), the 2,2'-Hbipy molecule individually occupies the pseudo-tetragonum that is formed with CA. In this paper, the interactions of CA${\cdot}$(2,2'-Hbipy) with bovine serum albumin (BSA) were studied by fluorescence spectrometry. For CA${\cdot}$(2,2'-Hbipy), HCA and 2,2'-bipy, the average quenching constants for BSA were $2.4384{\times}10^4$, $4.653{\times}10^3$, and $3.059{\times}10^3\;L{\cdot}mol^{-1}$, respectively. The mechanism for protein fluorescence quenching is apparently governed by a static quenching process. The Stern-Volmer quenching constants and corresponding thermodynamic parameters ${\Delta}$H, ${\Delta}$G and ${\Delta}$S were calculated. The binding constants and the number of binding sites were also investigated. The conformational changes of BSA were observed from synchronous fluorescence spectra.