• Korean Membrane Journal
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• v.8 no.1
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• pp.31-35
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• 2006

Pervaporation of water/2,2,2-trifluoroethanol (TFEA) mixtures was performed using a NaY zeolite membrane which was prepared by a hydrothermal synthesis. Pervaporation with a zeolite membrane is one of the economic separation technologies for liquid mixtures including organic/water solutions. The effects of a TFEA feed concentration and a temperature were studied on the permeation flux and the separation factor. Not only the water flux increased significantly with the increase of the operating temperature, but also the TFEA flux through the NaY zeolite membrane rapidly increased with the increase of the temperature at the feed concentration below 0.8 mole fraction of TFEA.

• Macromolecular Research
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• v.12 no.4
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• pp.374-378
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• 2004

The biodegradable and biocompatible poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), a copolymer of microbial polyester, was fabricated as nanofibrous mats by electrospinning. Image analysis of the electrospun nanofibers fabricated from a 2 wt% 2,2,2-trifluoroethanol solution revealed a unimodal distribution pattern of fiber diameters with an observed average diameter of ca. 185 nm. The fiber diameter of electrospun fabrics could be controlled by adjusting the electro spinning parameters, including the solvent composition, concentration, applied voltage, and tip-to-collector distance. Chondrocytes derived from rabbit ear were cultured on a PHBV cast film and an electrospun PHBV nano-fibrous mat. After incubation for 2 h, the percentages of attached chondrocytes on the surfaces of the flat PHBV film and the PHBV nanofibrous mat were 19.0 and 30.1 %, respectively. On the surface of the electrospun PHBV fabric, more chondrocytes were attached and appeared to have a much greater spreaded morphology than did that of the flat PHBV cast film in the early culture stage. The electro spun PHBV nanofabric provides an attractive structure for the attachment and growth of chondrocytes as cell culture surfaces for tissue engineering.

• Macromolecular Research
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• v.17 no.7
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• pp.522-527
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• 2009

A photocrosslinkable polyphosphazene was used for molecular imprinting. We synthesized polyphosphazene (3) having urea groups for complexation with N-carbobenzyloxyglycin (Z-Gly-OH, template) and chalcone groups for cross-linking reaction. As substituents, 4-hydroxycha1cone (1) and N-(4-hydroxyphenyl)-N'-ethylurea (2) were prepared. Choloro groups of poly(dichlorophosphazene) were replaced by the sequential treatment with sodium salts of compounds 1 and 2, and trifluoroethanol. The template molecule was complexed with the urea groups on the polymer chains via hydrogen bonding. A thin polymer film was prepared by casting a solution of the complex of polymer 3 and the template in dimethylformamide on a quartz cell and irradiated with 365 nm UV light to yield a cross-linked film with a thickness of about $16{\mu}m$. The template molecules in the film were removed by Soxhlet extraction with methanol/acetic acid. The control polymer film was prepared in the same manner for the preparation of the imprinted polymer film, except that the template and triethylamine were omitted. In the rebinding test, the imprinted film exhibited much higher recognition ability for the template than the control polymer. We also investigated the specific recognition ability of the imprinted polymer for the template and its structural analogues. The rebinding tests were conducted using Z-Glu-OH, Z-Asp($O^tBu$)-OH, and Z-Glu-OMe. The imprinted film showed higher specific recognition ability for the template and the lowest response for Z-Asp($O^tBu$)-OH.

• Journal of the Korean Chemical Society
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• v.27 no.2
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• pp.95-101
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• 1983

The pseudo-first order rate constants have been obtained for the solvolysis of benzoyl cyanide in various aqueous solvent mixtures and ethanol-trifluoroethanol mixtures at 1, 5, 10, 15 and $20^{\circ}C$. Values of n in the Kivinen polt, m values of Grunwald-Winstein polt, $\beta$ values of Leffler relationship and values of m and l in the extended Grunwald-Winstein polt have been calculated and studied the transition state variation caused by solvent changes using the More O'Ferrall polt and quantum mechanical approach. It has been shown that the reaction proceed via the associative $S_N2$ mechanism, using the transition state parameters and quantum mechanical model approach.

• Bulletin of the Korean Chemical Society
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• v.30 no.2
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• pp.383-388
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• 2009

Rates of solvolyses of diphenyl thiophosphorochloridate ($(PhO)_2$PSCl, 1) in ethanol, methanol, and aqueous binary mixtures incorporating ethanol, methanol, acetone and 2,2,2-trifluoroethanol (TFE) are reported. For four representative solvents, studies were made at several temperatures and activation parameters were determined. The 30 solvents gave a reasonably precise extended Grunwald-Winstein plot, correlation coefficient (R) of 0.989. The sensitivity values (l = 1.29 and m = 0.64) of diphenyl thiophosphorochloridate ($(PhO)_2$PSCl, 1) were similar to those obtained for diphenyl phosphorochloridate ($(PhO)_2$POCl, 2), diphenylphosphinyl chloride ($Ph_2$POCl, 3) and diphenylthiophosphinyl chloride ($Ph_2$PSCl, 4). As with the previously studied of 3~4 solvolyses, an $S_N$ pathway is proposed for the solvolyses of diphenyl thiophosphorochloridate (1). The activation parameters, ${\Delta}H^{\neq}\;(=11.6{\sim}13.9\;kcal{\cdot}mol^{-1})\;and\;{\Delta}S^{\neq}\; (=\;-32.1\;{\sim}\;-42.7\;cal{\cdot}mol^{-1}{\cdot}K^{-1})$, were determined, and they were in line with values expected for an $S_N$2 reaction. The large kinetic solvent isotope effects (KSIE, 2.44 in MeOH/MeOD and 3.46 in $H_2O/D_2$O) are also well explained by the proposed $S_N$2 mechanism.

• Bulletin of the Korean Chemical Society
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• v.34 no.2
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• pp.615-621
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• 2013

Solvolyses of isobutyl chloroformate (4) in 43 binary solvent mixtures including highly aqueous media, water, $D_2O$, $CH_3OD$, 2,2,2-trifluoroethanol (TFE) as well as aqueous 1,1,1,3,3,3-hexafluoro-isopropanol (HFIP) solvents were performed at $45^{\circ}C$, in order to further investigate the recent results of D'Souza, M. $J^1$. et al.; solvolyses of 4 are found to be consistent with the proposed mechanism ($Ad_E$). The variety of solvent systems was extended to comprise highly ionizing power solvent media ($Y_{Cl}$ > 2.7 excepted for aqueous fluorinated solvents and pure TFE solvent) to investigate whether a mechanistic change occurs as solvent compositions are varied. However, in case of 18-solvent ranges having aqueous fluorinated solvent systems (TFE-$H_2O$ and HFIP-$H_2O$) and/or having $Y_{Cl}$ > 2.7 solvent systems, the solvent effect on reactivity for those of 4 are evaluated by the multiple regression analysis as competition with $S_N2$ - type mechanism. And in pure TFE and 97 w/w % HFIP solvents with high $Y_{Cl}$ and weak $N_T$, these solvolyses are understood as reactions which proceed through an ionization ($S_N1$) pathway.

• Proceedings of the Membrane Society of Korea Conference
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• 2005.11a
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• pp.133-147
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• 2005

In order to investigate applicability for 2,2,2-trifluoroethyl methacrylate (TFEMA) produced by esterification of 2,2,2-trifluoroethanol(TFEA) and methacrylic acid(MA) using pervaporation membrane, poly(vinyl alcohol) (PVA) composite membranes were prepared with glutaraldehyde(GA) onto porous polyethersulfone(PES) support. The degree of crosslinking and thickness of PVA coating layer were analyzed by swelling test and SEM(scanning electron microscopy), respectively. Pervaporation test was done with two feed mixures; TFEA/water, MA/water. The pervaporation data were obtained as a function of content of crosslinking agent, feed composition, and operating temperature, respectively. In case of TFEA-water(90/10 wt%) feed mixture at $80^{\circ}C$, the optimized membrane showed the high permeation flux of 1.5 $kg/m^2hr$ and separation factor of 320. In case of MA-water(90/10 wt%) feed mixture, the membranealso showed high permeation flux of 2.3 $kg/m^2hr$ and separation factor of 740 in same conditions.

• Journal of the Korean Magnetic Resonance Society
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• v.8 no.2
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• pp.127-138
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• 2004

We obtained the chemical shifts of amide protons (NHs) in helical peptides at various temperatures and trifluoroethanol (TFE) concentrations using 2-dimensional NMR spectroscopy. These NH chemical shifts and their temperature dependence exhibited characteristic periodicity of 3-4 residues per cycle along the helix, where downfield shifted NHs showed larger temperature dependence. In an attempt to understand these observations, we focused on hydrogen bonding changes in the peptides and examined the validity of two possible explanations: (1) changes in intermolecular hydrogen bonding caused by differential solvation of backbone carbonyl groups by TFE, and (2) changes in intramolecular hydrogen bonding due to disproportionate variations in the hydrogen bonding within the peptide helix. Interestingly, the slowly exchanging NHs, which were on the hydrophobic side of the helix, showed consistently larger temperature dependences. This could not be explained by the differential solvation assumption, because the slowly exchanging NHs would become more labile if the preceding carbonyl groups were preferentially solvated by TFE. We suggest that the disproportionate changes in intramolecular hydrogen bonding better explain both the temperature dependence and the exchange behavior observed in this study.

• Bulletin of the Korean Chemical Society
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• v.19 no.3
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• pp.349-353
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• 1998

Solvolysis rates of substituted 2-aryl-1,1-dimethylethyl bromides (1) were determined in a variety of solvents such as aqueous mixtures of ethanol, acetone, 2,2,2-trifluoroethanol, and also mixtures of ethanol and TFE at 25 ℃, 35 ℃, and 45 ℃. The solvent effects were analyzed in terms of Winstein-Grunwald equation. The solvent effects of 1-4-MeO failed to give a single linear correlation against either Y or YCl (YBr), but exhibited a wide split pattern which could not be related to the solvent nucleophilicity. On the other hand 1-4-CH3 and 1-H gave a fairly good linearity. In the case of 1-4-MeO, a fairly good linearity was observed against YΔ defined from the solvolysis of 4-methoxyneophyl tosylate. It is assumed that resonance interaction between reaction site and aryl-π-system operates to give charge delocalization regardless of the different solvolysis mechanisms. The Hammett-Brown treatment of the solvolytic rate constant of compounds 1 was obtained non-linear two separated lines of - 1.06 to - 1.46, suggesting of mechanistic changeover from kc-ks to kΔ on going from electron-withdrawing to electron-donating substituents as a basis of 4-CH3 group.

• Bulletin of the Korean Chemical Society
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• v.24 no.4
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• pp.431-436
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• 2003

Solvolytic rate constants at 25℃ are reported for solvolyses of cinnamyl bromide (1) in binary mixtures of water with acetone, ethanol, methanol, methanol-d, and 2,2,2-trifluoroethanol. Product selectivities are reported for solvolyses of 1 in aqueous ethanol and methanol. Rate ratios in solvents of the same $Y_{Br}$ value and different nucleophilicity provide measures of the minimum extent of nucleophilic solvent assistance (e.g. $[k_{40EW}/k_{97TFE}]$Y = 2.88, EW = ethanol-water). With use of the extended Grunwald-Winstein equation, the l and m values are similar to the values of 0.43 and 0.88 obtained for the solvolyses of 1 using the equation (see below) which includes a parameter (I) for solvation of aromatic rings. The magnitude of l and m values associated with a change of solvent composition predicts the $S_{N1}$ reaction mechanism rather than an $S_{N2}$ channel. Product selectivities (S), defined by S = [ether product]/[alcohol product]×[water]/[alcohol solvent] are related to four rate constants for reactions involving one molecule of solvent as nucleophile and another molecule of solvent as general base catalyst. A linear relationship between 1/S and molar ratio of solvent is derived theoretically and validated experimentally for solvolyses of the above substrates from water up 75% 1/S = $(k_{wa}/k_{aw})$([alcohol solvent]/[water]) + $k_{ww}/k_{aw}$ alcohol-water. The results are best explained by product formation from a “free” carbocation intermediate rather than from a solvent-separated ion pair.