• KSBB Journal
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• v.14 no.6
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• pp.639-642
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• 1999

Optimization of the chitosanoligosaccharide production was studied with chitosanase. The optimum conditions for the enzymic reaction have been determined. Enzyme stability was maintained above 90% after 6 days at pH 5.0. The optimum initial reaction rate was appeared in 1.0% of chitosan solution. The production yield of chitosanoligosaccharides was over at 0.4%~2.0% of chitosan. At 4.0% of chitosan solution, however, the production yield was decreased to 64.6%. To increase the yield, stepwise addition of substrate into the reactor was investigated. In this case, the yield was increased from 64.6% to 83.2% and the final concentrations of chitosanoligosaccharide was 12.26 mg/mL. By TLC analysis, most of the chitosanoligosaccharides produced were 3-5 mers.

• Bulletin of the Korean Chemical Society
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• v.17 no.2
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• pp.153-158
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• 1996

The synthesis of common skeleton of podosporin A and aureol was studied through cationic olefin cyclization as a key step. The generation of thermodynamic silyl enol ether or enol acetate under known conditions gave regioselectivity of 88:12. The enolate alkylation of 2,3-dimethylcyclohexanone with 2,5-dimethoxybenzyl bromide at the more substituted site via lithium enolate gave poor yield. In this case an organozincate or an ammonium enolate also proved to be ineffective or not practical in terms of yield. Side chain elongation of the substituted cyclohexanone 13 through Grignard reaction, Wittig reaction, or Shappiro reaction did not proceed because of steric hindrance and side reactions. However, Stille coupling reaction via enol triflate produced the desired product 18 in high yield. The advanced intermediate 22, which was efficiently synthesized from 18, produced 24 instead of the desired product under a cationic olefin cyclization condition, indicating that the cyclization occurred in a stepwise mannervia the organomercury intermediate 23.

• Proceedings of the Korean Geotechical Society Conference
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• 1991.10a
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• pp.289-311
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• 1991

Analysis of supported excavation system by Elasto-Plastic Isoparametric Finite Element Method and Elasto-Plastic Beam Method have been conducted for the simulation of stepwise underground excavation. Conventional methods, fixed Supported Beam and Spring Supported Beam method, also have been examined and compared with the results of elasto-plastic beam method and field data. Except unavoidable result of upward ground settlement near the top of retaining wall and relatively high bending moment of wall at each excavation level, satisfactory results have been derived using elasto-plastic isopara metric finite element method. The results from elasto-plastic beam analysis program, developed by the author, are proved to be fit field data in acceptable variance as shown in the paper. Displacement and bending moment, of the wall by conventional methods, both fixed supported beam and spring supported beam, are always underestimated than field data, and attention must be given that the diffence increases with deeper excavation depth and lower horizontal subgrade reaction of the ground.

• Bulletin of the Korean Chemical Society
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• v.34 no.11
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• pp.3372-3376
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• 2013

The kinetic studies on the reactions of ethyl methyl (2) and ethyl propyl (4) chlorothiophosphates with X-pyridines have been carried out in acetonitrile at $35.0^{\circ}C$. The free energy correlations with X show biphasic concave upwards with a break point at X = H (2) and 3-Ph (4), respectively. A stepwise mechanism with a rate-limiting leaving group expulsion from the intermediate is proposed based on the magnitudes of selectivity parameters for both substrates. The considerably large values of ${\beta}_X$ = 1.50(2) and 1.44(4) with strongly basic pyridines and relatively small values of ${\beta}_X$ = 0.43(2) and 0.36(4) with weakly basic pyridines are interpreted as a change of the attacking direction of the X-pyridines from a frontside to a backside attack toward the chloride leaving group.

• Bulletin of the Korean Chemical Society
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• v.35 no.8
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• pp.2371-2374
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• 2014

A kinetic study is reported on SNAr reaction of 1-fluoro-2,4-dinitrobenzene with a series of primary amines including hydrazine in $H_2O$ at $25.0^{\circ}C$. The plots of $k_{obsd}$ vs. [amine] are linear and pass through the origin, indicating that general-base catalysis by a second amine molecule is absent. The Br${\o}$nsted-type plot exhibits an excellent linear correlation with ${\beta}_{nuc}$ = 0.46 when hydrazine is excluded from the correlation. The reaction has been suggested to proceed through a stepwise mechanism, in which expulsion of the leaving group occurs after the rate-determining step (RDS). Hydrazine is ca. 10 times more reactive than similarly basic glycylglycine (i.e., the ${\alpha}$-effect). A five-membered cyclic intermediate has been suggested for the reaction with hydrazine, in which intramolecular H-bonding interactions would facilitate expulsion of the leaving group. However, the enhanced leaving-group ability is not responsible for the ${\alpha}$-effect shown by hydrazine because expulsion of the leaving group occurs after RDS. Destabilization of the ground-state of hydrazine through the electronic repulsion between the nonbonding electron pairs is responsible for the ${\alpha}$-effect found in the current $S_NAr$ reaction.

• Journal of Marine Bioscience and Biotechnology
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• v.2 no.4
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• pp.257-262
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• 2007

Squid viscera oil was investigated by pretreatment method for enhancing the commercial value. Transeterification was performed to reduce rancidity of the oil, off-flavor was removed by using activated carbon adsorption. Analysis using ATD (Automatic Thermal Desorber) and GC/MG shows the efficacy of off-flavor removement. The rates of Transesterification employing inorganic catalyst and biocatalyst were tested, respectively. With stepwise addition of ethanol, the most efficiency of the reaction was achieved by inorganic catalyst. The efficiency of the reaction was estimated by acid value corresponding to rancidity of reaction product.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.264.2-264.2
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• 2013

Molecular layer deposition (MLD) is sequential, self-limiting surface reaction to form conformal and ultrathin polymer film. This technique generally uses bifunctional precursors for stepwise sequential surface reaction and entirely organic polymer films. Also, in comparison with solution-based technique, because MLD is vapor-phase deposition based on ALD, it allows epitaxial growth of molecular layer on substrate and is especially good for surface reaction or coating of nanostructure such as nanopore, nanochannel, nanwire array and so on. In this study, polyurea film that consisted of phenylenediisocyanate and phenylenediamine was formed by MLD technique. In situ Fourier Transform Infrared (FTIR) measurement on high surface area SiO2 substrate was used to monitor the growth of polyurethane and polyurea film. Also, to investigate orientation of chemical bonding formed polymer film, plan-polarized grazing angle FTIR spectroscopy was used and it showed epitaxial growth and uniform orientation of chemical bones of polyurea films.

• Bulletin of the Korean Chemical Society
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• v.21 no.11
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• pp.1090-1094
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• 2000

A reaction between germanium (Ge) and the ligand, o-chlorophenylfluorone (o-CPF) has been carried out. The reaction sensitive at pH 4.5 in the presence of triton x-100 was selective in the presence of EDTA. The spectral correction technique was ap plied to the analysis of the reaction instead of single wavelength spectrophotometry because the absorption of excess of o-CPF was not negligible. An updated determination of the properties of the Ge(IV)-o-CPF complex is given, which involved the complex ratio, stepwise absorptivity and stability constant of the complex. In present work, the results show that the complex $Ge(o-CPF)_3was$ formed and its cumulative stability constant was 1.09 ${\times}$1016 . For sample analysis, the detection limit of germanium was 0.01 mg/L, and the recoveries were between 96.4% and 102%, with relative standard deviations of less than 6.5%.

• Bulletin of the Korean Chemical Society
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• v.33 no.10
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• pp.3253-3257
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• 2012

Second-order rate constants for the reactions of phenyl Y-substituted-phenyl carbonates 5a-g with Z-substituted-phenoxides ($k_{Z-PhO^-}$) have been measured spectrophotometrically in 80 mol % $H_2O$/20 mol % DMSO at $25.0{\pm}0.1^{\circ}C$. 4-Nitrophenyl phenyl carbonate (5e) is up to 235 times more reactive than 4-nitrophenyl benzoate (4e). The Br$\o$nsted-type plot for the reactions of 5e with Z-substituted-phenoxides is linear with ${\beta}_{nuc}=0.54$, which is typical for reactions reported previously to proceed through a concerted mechanism. Hammett plots correlated with ${\sigma}^o$ and ${\sigma}^-$ constants for the reactions of 5a-f with 4-chlorophenoxide exhibit highly scattered points. In contrast, the Yukawa-Tsuno plot results in an excellent linear correlation with ${\rho}_Y=1.51$ and r = 0.52, indicating that the leaving-group departure occurs at the rate-determining step (RDS). A stepwise mechanism, in which leaving-group departure occurs at RDS, has been excluded since the incoming 4-$ClPhO^-$ is more basic and a poorer nucleofuge than the leaving Y-substituted-phenoxides. Thus, the reaction has been concluded to proceed through a concerted mechanism. Our study has shown that the modification of the nonleaving group from benzoyl to phenyloxycarbonyl causes a change in the reaction mechanism (i.e., from a stepwise mechanism to a concerted pathway) as well as an increase in the reactivity.

• Bulletin of the Korean Chemical Society
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• v.29 no.10
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• pp.1911-1914
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• 2008

Second-order rate constants (kN) have been measured for Michael-type addition reactions of a series of alicyclic secondary amines to 1-phenyl-2-propyn-1-one (2) in MeCN at 25.0 ${\pm}$ 0.1 ${^{\circ}C}$. All the amines studied are less reactive in MeCN than in $H_2O$ although they are more basic in the aprotic solvent by 7-9 p$K_a$ units. The Bronsted-type plot is linear with $\beta_{nuc}$ = 0.40, which is slightly larger than that reported previously for the corresponding reactions in $H_2O$ ($\beta_{nuc}$ = 0.27). Product analysis has shown that only E-isomer is produced. Kinetic isotope effect is absent for the reactions of 2 with morpholine and deuterated morpholine (i.e., $k^H/k^D$ = 1.0). Thus, the reaction has been concluded to proceed through a stepwise mechanism, in which proton transfer occurs after the rate-determining step. The reaction has been suggested to proceed through a tighter transition state in MeCN than in H2O on the basis of the larger $\beta_{nuc}$ in the aprotic solvent. The nature of the transition state has been proposed to be responsible for the decreased reactivity in the aprotic solvent.