• Journal of the Korean Chemical Society
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• v.30 no.3
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• pp.265-272
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• 1986

Kinetic studies for the methanolysis of tert-butyl halides (t-BuCl, t-BuBr, t-BuI) were carried out in MeOH-1,1,2,2-tetrachloroethane mixtures. The solvatochromic comparison method was used with six indicators to analyze solvent effects on the ionizations of tert-butyl halides. It was shown that the cooperative effect of solvent polarity-polarizability was the most important factor influenced on the methanolysis rates of tert-butyl halides, but the electrophilic assistance for halide leaving group and the nucleophilic assistance for tert-butylium ion were considerably influential, too. And it was found that the electrophilic assistance caused by hydrogen bonding and the nucleophilic assistance for carbon center were stronger for more basic leaving group ($I^-) and more polarizable leaving group(t-BuCl

• Transactions of the Korean hydrogen and new energy society
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• v.27 no.4
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• pp.378-385
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• 2016

In this study, we synthesized a biocatalyst consisting of glucose oxidase (GOx), polyethyleneimine (PEI) and carbon nanotube (CNT) with addition of glutaraldehyde (GA)(GA/[GOx/PEI/CNT])for fabrication of glucose sensor. Main bonding of the GA/[GOx/PEI/CNT] catalyst was formed by crosslinking of functional end groups between GOx/PEI and GA. Catalytic activity of GA/[GOx/PEI/CNT] was quantified by UV-Vis and electrochemical measurements. As a result of that, high immobilization ratio of 199% than other catalyst (with only physical adsorption) and large sensitivity value of $13.4{\mu}A/cm^2/mM$ was gained. With estimation of the biosensor stability, it was found that the GA/[GOx/PEI/CNT] kept about 88% of its initial activity even after three weeks. It shows GA minimized the loss of GOx and improved sensing ability and stability compared with that using other biocatalysts.

• Carbon letters
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• v.4 no.1
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• pp.1-9
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• 2003

Recently, the control of pore-characteristics of nano-porous materials has been studied extensively because of their unique applications, which includes size-selective separation, gas adsorption/storage, heterogeneous catalysis, etc. The most widely adopted techniques for controlling pore characteristics include the utilization of pillar effect by metal oxide and of templates such as zeolites. More recently, coordination polymers constructed by transition metal ions and bridging organic ligands have afforded new types of nano-porous materials, porous metal-organic framework(porous MOF), with high degree and uniformity of porosity. The pore characteristics of these porous MOFs can be designed by controlling the coordination number and geometry of selected metal, e.g transition metal and rare-earth metal, and the size, rigidity, and coordination site of ligand. The synthesis of porous MOF by the assembly of metal ions with di-, tri-, and poly-topic N-bound organic linkers such as 4,4'-bipyridine(BPY) or multidentate linkers such as carboxylates, which allow for the formation of more rigid frameworks due to their ability to aggregate metal ions into M-O-C cluster, have been reported. Other porous MOF from co-ligand system or the ligand with both C-O and C-N type linkage can afford to control the shape and size of pores. Furthermore, for the rigidity and thermal stability of porous MOF, ring-type ligand such as porphyrin derivatives and ligands with ability of secondary bonding such as hydrogen and ionic bonding have been studied.

• Biotechnology and Bioprocess Engineering:BBE
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• v.11 no.4
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• pp.357-363
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• 2006

Monolithic molecularly imprinted columns were designed and prepared by an in-situ thermal-initiated copolymerization technique for rapid separation of tryptophan and N- CBZ-phenylalanine enantiomers. The influence of polymerization conditions and separation conditions on the specific molecular recognition ability for enantiomers and diastereomers was investigated. The specious molecular recognition was found to be dependent on the stereo structures and the arrangement of functional groups of the imprinted molecule and the cavities in the molecularly imprinted polymer (MIP). Moreover, hydrogen bonding interactions and hydrophobic interactions played an important role in the retention and separation. Compared to conventional MIP preparation procedures, the present method is very simple, and its macroporous structure has excellent separation properties.

• Journal of Korea Technical Association of The Pulp and Paper Industry
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• v.33 no.2
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• pp.1-7
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• 2001

Use of high yield pulp and recycled fiber as raw materials and water system closure result in higher fines content and buildup of organic and inorganic contaminants in white water. These are detrimental for the effectiveness of chemical additives including retention aids. Thus it is imperative to employ a retention systems that maintains its efficiency in closed papermaking system for reducing fresh water consumption. The performance of four different microparticle retention systems including cationic polyacrylamide (C-PAM)/bentonite, highly charged cationic starch (HCS)/silica, C-PAM/micropolymer, cationic guar gum (CGG)/silica was evaluated and compared at three different levels of papermaking system closure. Buildup of detrimental substances in a closed white water system increased cationic demand and finally reduced the performance of retention systems. Cationic starch and guar gums maintained their effectiveness in retention in closed white water systems contaminated with anionic trashes because of their structural rigidity and hydrogen bonding ability. Particularly, cationic guar gums, due its stiffness of molecular structure, appeared perform better than catinonic starch.

• Bulletin of the Korean Chemical Society
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• v.14 no.6
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• pp.704-708
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• 1993

The intramolecular charge transfer (ICT) phenomena of the photoexcited 2-biphenylcarboxylic acid (2BPCA) and 4-biphenylcarboxylic acid (4BPCA) have been investigated in some surfactant micellar solutions. The ICT emission of 4BPCA and 2BPCA in aqueous solution at sufficiently low pH (1-3) has been observed to be markedly quenched and blue-shifted upon addition of a cationic surfactant, cetyltrimethylammonium chloride (CTAC) in contrast to little change in anionic sodium dodecyl sulfate (SDS) and neutral Brij 35. An anionic emission band has been observed to be enhanced at expense of the ICT emission as a function of the concentration of CTAC. These results with the micellar effects on the fluorescence decay kinetics of 4BPCA suggest that formation of the ICT state of the excited acids is inhibited by CTAC-induced proton transfer as well as the decrease in the polarity and/or hydrogen-bonding ability of the micellar microenvironment entrapping the acids.

• Bulletin of the Korean Chemical Society
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• v.7 no.6
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• pp.458-461
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• 1986

The fluorescence intensity of khellin-dimethylfumarate C$_4$-cycloadduct (KDF) is very sensitive to temperature and to the nature of solvents, especially hydrogen-bonding ability. The fluorescence quantum yields of KDF in ethanol and isopentane at 77K are 0.73 and 0.54, respectively, both of which are much larger than the room temperature values. The phosphorescence lifetime is very long and decreases with decreasing the solvent polarity. The phosphorescence and fluorescence quantum yield ratio is very small and decreases with decreasing solvent polarity. The solvent relaxation plays an important role in the excited states of KDF. The internal conversion is a major decay process of the excited singlet state of KDF in all the solvents used at room temperature.

• Journal of the Korean Chemical Society
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• v.39 no.2
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• pp.94-102
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• 1995

S-Hydroxypropyl(PH) ${\beta}$-cyclodextrin(hydrophilic), dialkyl(DA)-cyclodextrin(hydrophobic), trifluoroacetyl(TA) ${\gamma}$-cyclodextrin(intermediate) stationary phases were used for gas chromatographic separation of racemic alcohols and their derivatives. All the alcohols used for this experiment were derivatived by using trifluoro acetic anhydride, acetic anhydride, or trichloro acetic anhydride. It is apparent that the enantioselectivity of the enantiomeric pairs was very dependent on the type of acylation reagent. The best experimental condition of optical resolution of the alcohols and their derivatives was different on the polarity of the solute molecules. The chiral separation was also studied depending on temperature, polarity of the column, and hydrogen bonding ability and steric effect between the alchols and CD stationary phase. The chiral recognition mechanism is dependent not upon the kinds of the chiral stationay phases but upon the derivatization of the racemic alchols.

• Biomedical Science Letters
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• v.11 no.4
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• pp.487-492
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• 2005

The baculovirus/insect cell expression system is of great value in the study of structure-function relationships in mammalian glucose-transport proteins by site-directed mutagenesis and for the large-scale production of these proteins for mechanistic and biochemical studies. Spodoptera frugiperda Clone 21 (Sf2l) cells grow well on TC-100 medium that contains $0.1\%$ D-glucose as the major carbon source, strongly suggesting the presence of endogenous glucose transporters. However, very little is known about the properties of the endogenous sugar transporter(s) in Sf2l cells, although a saturable transport system for hexose uptake has been previously revealed in the Sf cells. In order to further examine the substrate and inhibitor recognition properties of the Sf2l cell transporter, the ability of hexoses to inhibit 2-deoxy-D-glucose (2dGlc) transport was investigated by measuring inhibition constants $(K_i)$. The $K_i's$ for reversible inhibitors were determined from plots of uptake versus inhibitor concentration. Transport was effectively inhibited by D-mannose and D-glucose. Of the hexoses tested, L-glucose had the least effect on 2dGlc transport in the Sf2l cells, indicating that the transport is stereoselective. Unlike the human HepG2 type glucose transport system, D-mannose had a somewhat greater affinity for the Sf2l cell transporter than D-glucose, implying that the hydroxyl group at the C-2 position is not necessary for strong binding. However, epimerization at the C-4 position of D-glucose (D-galactose) resulted in a dramatic decrease in affinity of the hexose for the Sf2l cell transporter. Such a lowering of affinity might be the result of the involvement of the C-4 hydroxyl in hydrogen bonding. It is therefore suggested that Sf2l cells were found to contain an endogenous sugar transport activity that in several aspects resembles the human HepG2 type glucose transporter, although the insect and human transporters do differ in their affinity for cytochalasin B.

• Applied Biological Chemistry
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• v.25 no.4
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• pp.224-231
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• 1982

${\alpha}-Tocopherol$ was found to be a fluorescent probe in determination of the phasetransition temperature of liposome. Since this was a discovery of a new aspect of ${\alpha}-tocopherol$ as an important biochemical molecule, its molecular spectroscopic characterization was carried out in order to obtain some informations on its spectral and, structural properties in various media, anticipating that the compound may entertain a wide applications in biochemical systems as a spectroscopic probe. Two species of α${\alpha}-tocopherol$, monomer and dimer, were found to exist in organic media, especially in solvents of nonhydrogen bonding ability. Monomer with maximum UV-absorption around $(291{\sim}294nm)$ is highly fluorescent, while dimer which is formed by intermolecular hydrogen bonds and absorbes with spectral peak at 298nm is nonfluorescent. ${\alpha}-tocopherol$ incorporated to liposome exhibits emission property quite different from that in various organic media showing broad and red-shifted fluorescence excitation and emission spectra. This spectral abnormality is to be interpreted to arise from chromanolate-type ion, H-dissociated ${\alpha}-tocopherol$.