• Journal of the Korean Chemical Society
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• v.18 no.4
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• pp.223-238
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• 1974

CNDO/2 MO theoretical studies and kinetic studies of halide exchange reactions for alkylchloroformates have been carried out in order to investigate structure-reactivity relationship of alkylchloroformates. From the result of energetics, it was concluded that the most stable configuration of alkylchloroformate is that in which alkyl group and chlorine are trans to each other, and that the hindered rotation about the bond between the carbonyl carbon and alkoxy-oxygen bond is attributed to the ${\pi}-$electron delocalization. It has been found that the large charge separation is due to -M effect of carbonyl and alkoxy oxygens and-I effect of chlorine. The order of rates in solvents studied was $(CH_3)_2 > CO > CH_3CN{\gg}MeOH.$$I^->Br^->Cl^-$ in protic solvent, and of Cl^->Br^- >I^-$ in dipolar aprotic solvents. Alkyl group contribution has the decreasing order of $CH_3-> C_2H-{\gg}i-C_3H_7-.$ The solvent effect has been interpreted on the basis of initial and final state contribution. A transition state model has been suggested, and it has been proposed that the most favorable mechanism is the addition-elimination. From the results of activation parameters and electronic properties, an energy profile has been proposed. Structural factors determining reactivities of alkylchloroformates have been shown to be charge, energy level of ${\alpha}^*LUMO$ to C-Cl bond and ${\alpha}^{\ast} $antibonding strength with respect to C-Cl bond in this MO. Charge and polarizability of nucleophile, and the interaction of these effects with solvent structures are also found to be important.

• Journal of the Korean Chemical Society
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• v.32 no.4
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• pp.342-350
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• 1988

An experimental investigation is made to determine the mechanism of the aquation of $[Co(en)_2Cl_2]^+$ in $Hg^{2+}$ aqueous solution. The progress of reaction is followed UV/vis-spectrophotometrically by a measurment of the absorbance at a specific wavelength of Co(III) complex as a function of time. The aquation of cis-$[Co(en)_2Cl_2]^+$ and trans-$[Co(en)_2Cl_2]^+$ has been found to be first order and second order with respect to the concentration of $Hg^{2+}$ catalyst, respectively. It has been found that the reaction rate for aquation of the trans-form is faster than that of cis-form, and that the product of either cis-form or trans-form is always in the mixture ratio of 97 % to 3 %. Plausible reaction mechanism is proposed for the reaction system on the basis of kinetic data and activation parameters. Theoretical rate equation derived from the proposed mechanism is consistent with the observed one.

• Journal of the Korean Chemical Society
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• v.39 no.4
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• pp.275-280
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• 1995

The electron transfer reactions between cis-[Co(en)2(NO2)2]+ and rac-[Co(Y)]2-(Y=EDTA, PDTA, CyDTA) have been investigated in the presence of hydrogen ion. From the kinetic data, it has been found that electron transfer reactions between cis-[Co(en)2(NO2)2]+ and rac-[Co(Y)]2- proceed via inner-sphere pathway by catalysis of hydogen ion. The stereoselectivity in the electron transfer reactions between optically active △-cis-[Co(en)2(NO2)2]+ and rac-[Co(Y)]2- produced 6.0, 2.9, 3.0% e.e.(e.e.=enantiomeric excess) of △-[Co(EDTA)]-, △-[Co(PDTA)]- and △-[Co(CyDTA)]-, respectively. Based upon this observation, it seems that △-cis-[Co(en)2(NO2)2]+ is associated with rac-[Co(Y)]2- at first, and followed by the electron transfer reaction. Therefore, it was suggested that stereoselective electron transfer reaction between △-cis-[Co(en)2(NO2)2]+ and rac-[Co(Y)]2- proceed through both inner-sphere by the proton catalysis and outer-sphere with ionic association.

• Journal of Adhesion and Interface
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• v.2 no.3
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• pp.16-24
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• 2001

The curing behavior of a phenolic resin (F/p: 1.3, 1.9, 2.5 for resol resin, F/P: 0.5, 0.7, 0.9 for novolac resin) has been studied by FT-IR spectroscopy. In this study is to synthesis of resol and novolac type phenolic resin with different F/P molar ratios and to compare the level of cure at different curing temperature conditions ($130^{\circ}C$, $160^{\circ}C$, $180^{\circ}C$ for resol resin, $160^{\circ}C$, $170^{\circ}C$, $180^{\circ}C$ for novolac resin) for 3, 5, 7, 10, 20, and 60 (min.), respectively. The conversion (${\alpha}$) was determined by the ratio of the peak area with time to the peak area of non-baked phenolic QH ($3300cm^{-1}$) at spectra. It is concluded that the initial curing rate of resol and novolac resin was increased as the molar ratio of formaldehyde/phenol increased and as the curing temperature of resin increased. According to the analysis was by the homogenous first-order model, the initial curing rate of resol and novolac resin was increased as the molar ratio of formaIdehyde/phenol increased at specific curing temperature.

• Elastomers and Composites
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• v.42 no.1
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• pp.47-54
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• 2007

Reaction kinetics of polyurethane elastomers (PU) were studied using dynamic DSC and TGA for three PU samples of general purpose (Sample A), high temperature cross-likable CASE purpose with MOCA (Sample B), and RT cross-likable CASE purpose grade (Sample C). From DSC results, sample with MOCA(Sample B) showed lower shift of peak temperature, while showing broader thermograms than those of general purpose grade (Sample A). On the other hand, RT cross-linkable PU grade (Sample C) showed an interesting double mode reaction patterns, i.e., a lower temperature reaction at about $70\;^{\circ}C$, and a higher temperature reaction in the range of $140{\sim}170\;^{\circ}C$, indicating that it requires 2-step reaction process in order to complete the reaction. Once the cross-linking reaction completed, however, TGA results showed that all the samples would be considered to have similar chemical structures, showing similar decomposition processes. Sample C, especially, had showed decomposition properties of both Sample A and Sample B. Formation activation energies calculated from Kissinger method showed 10.39, 65.85, 36.52(Low $T_p$) and 18.21(High $T_p$) kcal/mol, while decomposition activation energies were 31.94, 30.84, 24.16 kcal/mol, respectively.

• Food Science and Preservation
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• v.24 no.6
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• pp.778-785
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• 2017

This study was conducted to develop a predictive model for the growth of Escherichia coli strain RC-4-D isolated from red kohlrabi sprout seeds. We collected E. coli kinetic growth data during red kohlrabi seed sprouting under isothermal conditions (10, 15, 20, 25, and $30^{\circ}C$). Baranyi model was used as a primary order model for growth data. The maximum growth rate (${\mu}max$) and lag-phase duration (LPD) for each temperature (except for $10^{\circ}C$ LPD) were determined. Three kinds of secondary models (suboptimal Ratkowsky square-root, Huang model, and Arrhenius-type model) were compared to elucidate the influence of temperature on E. coli growth rate. The model performance measures for three secondary models showed that the suboptimal Huang square-root model was more suitable in the accuracy (1.223) and the suboptimal Ratkowsky square-root model was less in the bias (0.999), respectively. Among three secondary order model used in this study, the suboptimal Ratkowsky square-root model showed best fit for the secondary model for describing the effect of temperature. This model can be utilized to predict E. coli behavior in red kohlrabi sprout production and to conduct microbial risk assessments.

• Korean Journal of Food Science and Technology
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• v.37 no.5
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• pp.850-855
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• 2005

Model was developed to predict the growth of Listeria monocytogenes in raw pork. Experiment condition for model development was full 5-by-7 factorial arrangements of temperature (0, 5, 10, 15, and $20^{\circ}C$) and time (0, 1, 2, 3, 18, 48, and 120 hr). Gompertz values A, C, B, and M, and growth kinetics, exponential growth rate (EGR), generation time (GT), lag phase duration (LPD), and maximum population density (MPD) were calculated based on growth increased data. GT and LPD values gradually decreased, whereas EGR value gradually increased with increasing temperature. Response surface analysis (RSA) was carried out using Gompertz B and M values, to formulate equation with temperature being main control factor. This equation was applied to Gompertz equation. Experimental and predictive values for GT, LPD, and EGR, compared using the model, showed no significant differences (p<0.01). Proposed model could be used to predict growth of microorganisms for exposure assessment of MRA, thereby allowing more informed decision-making on potential regulatory actions of microorganisms in raw pork.

• Korean Journal of Food Science and Technology
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• v.32 no.1
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• pp.161-167
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• 2000

The protease produced by a newly isolated Aspergillus wentti from Korean traditional Meju was purified and characterized. The optimal medium composition and culture conditions for maximum protease production were ; bran :1% glucose solution =1 : 1, pH 9.0, $30^{\circ}C$, and 4 days of fermentation. Protease was purified by QAE-Sephadex, SP-Sephadex ion exchange chromatography and Sephadex G-100 chromatography. The specific activity and the purification fold of the purified enzyme were 213 unit/mg protein and 27.3, respectively. The molecular weight of purified protease was found to be 32 kDa by SDS-PAGE. Km and Vmax value's for hammastein milk casein were $3.049{\times}10^{-4}\;M\;and\;151.1\;{\mu}g/min$, respectively. Kinetic parameters showed that the enzyme has higher affinity to casein than isolated soybean protein, hemoglobin and bovine serum albumin. Optimal pH and temperature for reaction of the purified enzyme were 9.0 and $50^{\circ}C$, respectively. The enzyme was stable at pH 4.0-11.0, below $40^{\circ}C$, and the activity was not stimulated by metal ions. 1mM phenylmethylsulfonyl fluoride inhibited the enzyme activity by 98.5%. It means that the enzyme is one of serine protease.

• Korean Journal of Food Science and Technology
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• v.16 no.2
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• pp.211-217
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• 1984

To study affinity of proteolytic enzymes to soy proteins, the physicochemical and functional properties of enzymatically modified protein products, kinetic parameters and degree of hydrolysis were measured using trypsin, alcalase (serine type protease) and pronase. Bacterial alcalase and pronase showed much greater affinity to soy protein than animal intestinal trypsin. This effect was very significant when unheated soy isolate was used as a substrate. Specific activities of these enzymes decreased with the increment of substrate concentration (over 2.0%, w/v) when heat denatured soy protein was used as a substrate. However, the decrease in specific activity was negligible at substrate concentrations lower than 2.0%. Polyacrylamide gel electrophoretic results showed that the pattern of 2S protein band changed distinctly in alcalase hydrolysis as compared with those of trypsin and pronase. Protein solubilities of alcalase and pronase hydrolyzates increased by 25-30%, at their pI (pH 5.0) over the control. Virtually no change was observed in solubility by trypsin hydrolysis. Heat coagulability and calcium-tolerance of the protein increased by enzymatic hydrolysis. No clear tendency, however, was observed for emulsion properties, foam expansion and the amount of free -SH groups. The enzyme treatment considerably decreased foam stability.

• Korean Journal of Food Science and Technology
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• v.10 no.1
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• pp.52-56
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• 1978

The mechanism of cooking rice was investigated using a japonica type rice variety, Akibare, of 50%, 70% and 90% polishing degrees. The hardness of rice cooked at various cooking temperatures ($90^{\circ}-120^{\circ}C$) was measured with a Texturometer. The cooking rate followed the equation of a first-order reaction. The reaction rate constants were in the increasing order of 50%, 70% and 90% polished rice. The temperature coefficient of the reaction rate constant at cooking temperatures of ($90^{\circ}-100^{\circ}C$) was about 2 in all rice samples. The activation energies of cooking at temperatures below $100^{\circ}C$ and above $100^{\circ}C$ were about 17,000 and 9,000 cal/mole, respectively. The polishing degrees and water soaking time of rice did not affect the activation energy of cooking; however, the lower polishing degrees and shorter soaking increased the cooking time The experimental results suggested that the cooking process of rice comprises two mechanisms: At temperatures below $100^{\circ}C$ the cooking rate is controlled by the reaction rate of rice constituents with water, and at temperatures above $100^{\circ}C$, it is controlled by the rate of diffusion of water through the cooked portion (or layer) toward the interface of uncooked core in which the reaction is occurring.