• Journal of the Korean Chemical Society
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• v.26 no.6
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• pp.407-413
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• 1982

The rate constants of the nucleophilic addition of cysteine to 3,4-methylenedioxyphenylmethylene malononitrile were determined by UV Spectrophotometry and a rate equation which can be applied over wide pH range was obtained. On the basis of rate equation, it may be concluded that the rate constants were dependent upon only the concentration of hydroxide ion above pH 9.0, however, below pH 6.0, the reaction were initiated by the addition of neutral cysteine molecule to carbon-carbon double bond and at pH 7.0~9.0, the addition of a neutral cysteine molecule and it's anion occurred competitively.

• Journal of the Korean Chemical Society
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• v.17 no.5
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• pp.357-362
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• 1973

The polarographic behaviors of Pb(Ⅱ), Cd(Ⅱ) and Cu(Ⅱ) in histidine solutions were studied at ionic strength $({\mu})$ of 0.1 with the use of $NaClO_4$ as a supporting electrolyte. The formation constants of the mixed-ligand complexes of Pb(Ⅱ), Cd(Ⅱ) and Cu(Ⅱ) were calculated by Schaap's method in the presence of both histidine and hydroxide ion. The results of the electrode reactions in the systems are also discussed.

• Bulletin of the Korean Chemical Society
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• v.24 no.3
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• pp.306-310
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• 2003

Hydrolysis reactions of S-phenyl-S-vinyl-N-p-tosylsulfilimine (VSI) and its derivatives at various pH have been investigated kinetically. The hydrolysis reactions produced phenylvinylsulfoxide and p-toluene sulfonamide as the products. The reactions are first order and Hammett ρ values for pH 1.0, 6.0, and 11.0 are 0.82, 0.45, and 0.57, respectively. This reaction is not catalyzed by general base. The plot of k vs pH shows that there are three different regions of the rate constants $(k_t)$ in the profile.; At pH < 2 and pH > 10, the rate constants are directly proportional to the concentrations of hydronium and hydroxide ion catalyzed reactions, respectively. The rate constant remains nearly the same at 2 < pH < 10. On the bases of these results, the plausible hydrolysis mechanism and a rate equation have been proposed: At pH < 2.0, the reaction proceeds via the addition of water molecule to sulfur after protonation at the nitrogen atom of the sulfilimine, whereas at pH > 10.0, the reaction proceeds by the addition of hydroxide ion to sulfur directly. In the range of pH 2.0-10.0, the addition of water to sulfur of sulfilimine appears to be the rate controlling step.

• Bulletin of the Korean Chemical Society
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• v.20 no.10
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• pp.1213-1217
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• 1999

Hydrolysis reactions of 2-phenyl-4H,5H,6H-3-methyl-3-thiazinium perchlorate (PTP) and its derivatives at various pH have been investigated kinetically. The hydrolysis is quantitative, producing N-3-mercaptopropyl-N-methylbenzamide as the only product in the all pH ranges. The observed rate of hydrolysis of PTP was always of the first-order. For hydrolysis from PTP, Hammett ρvalues were 0.53, 0.84 and 1.13 for pH 5.0, 8.0, and 10.0, respectively. Bronsted βvalue was 0.53 for general base catalysis. This reaction is catalyzed by general w acetate concentration. However, as the amount of base becomes larger, the rate of hydrolysis reaction approaches the limiting values. The plot of log k vs. pH shows that the rate constants (kt) are two different regions in the profile; one part is directly proportional to hydroxide ion concentration and the other is not. On the bases of these result, the plausible hydrolysis mechanism and a reaction equation were proposed: Below pH 4.5, the hydrolysis was initiated by the addition of water to α-carbon. Above pH 9.0, the hydrolysis was proceeded by the addition of hydroxide ion to α-carbon. However, in the range of pH 4.5-8.0, these two reactions occured competitively.

• Carbon letters
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• v.8 no.4
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• pp.321-325
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• 2007

The oxygen and nitrogen enriched activated carbons were obtained from modification of commercial activated carbon by using nitric acid, sodium hydroxide and urea. Zeta-potentials of modified activated carbons were investigated in relation to copper ion adsorption. The structural properties of modified activated carbons were not so much changed, but the zeta-potentials and isoelectric points were considerably changed. The zeta-potential of nitric acid modified activated carbon was the most negative than other activated carbons in the entire pH region, and the $pH_{IEP}$ was shifted from pH 4.8 to 2.6, resulted in the largest copper ion adsorption capacities compare with other activated carbons in the range of pH 3~6.5. In case of urea modified activated carbon, copper ion adsorption was larger than that of the as-received activated carbon from pH 2 to pH 6.5 even though the $pH_{IEP}$ was shifted to pH 6.0, it was due to the coordination process operated between nitrogen functional groups and copper ion. The adsorption capacity of copper ion was much influenced by zeta-potential and $pH_{IEP}$ of carbon adsorbent.

• Journal of the Korean Geotechnical Society
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• v.28 no.3
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• pp.67-75
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• 2012

This paper presents an environment-friendly sand cementation method by precipitating calcium carbonate using plant extracts. The plant extracts contain urease like $Sporosarcina$ $pasteurii$, which can decompose urea into carbonate ion and ammonium ion. It can cause cementation within sand particles where carbonate ions decomposed from urea combine with calcium ions dissolved from calcium chloride or calcium hydroxide to form calcium carbonate. Plant extracts, urea and calcium chloride or calcium hydroxide were blended and then mixed with Nakdong River sand. The mixed sand was compacted into a cylindrical specimen and cured for 3 days at room temperature ($18^{\circ}C$). Unconfined compression test, SEM and XRD analyses were carried out to evaluate three levels of urea concentration and two different calcium sources. As urea concentration increased, the unconfined compressive strength increased up to 10 times those without plant extracts because calcium carbonate precipitated more, regardless of calcium source. It was also found that the strength of specimen using calcium chloride was higher than that of specimen using calcium hydroxide.

• Journal of the Korean Recycled Construction Resources Institute
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• v.10 no.4
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• pp.600-608
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• 2022

This study investigates the effect of layered double hydroxide (LDH) on the healing performance of self-healing concrete by assessing the chloride penetration resistance of self-healing cement mortars using electrical chloride ion migration-diffusion test. Test results show that both mortars containing healing materials only and mortars containing healing materials and Ca-Al LDH together mostly had higher migration-diffusion coefficients right after cracking, but the migration-diffusion coefficients decreased more than that of OPC with increasing healing ages, and thus, they yielded higher healing capacities than OPC. Also, mortars containing Ca-Al LDH together with healing materials showed higher reduction of their migration-diffusion coefficients, and thus, higher healing capacities than mortars containing healing materials only. This suggests that as the self-healing product increases on the crack surface, the binding of chloride ions by LDH inside the crack increases.

• Korean Journal of Soil Science and Fertilizer
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• v.28 no.2
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• pp.105-113
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• 1995

Adsorption experiments of heavy metal cations by Fe- and Al-hydroxides was conducted to obtain clear information on their adsorption mechanisms. The adsorption isothermal curves of heavy metal cations by Fe- and Al-hydroxides conformed to Langmuir's equation. Increasing the crystallinity degree of Fe- and Al-hydroxides tended to decrease the adsorption capacity and binding energy of heavy metal cations. At the same crystallinity degree, Al-hydroxide showed higher adsorption capacity and energy for the heavy metal cations than Fe-hydroxide. The adsorption capacity and energy of heavy metal cations were directly related to CEC, specific surface area and charge density of hydroxides, and the sequence was in the order of $Cu^{+{+}}$ > $Zn^{+{+}}$ > $Cd^{+{+}}$. The adsorption mechanism of $M^{+{+}}$ form of heavy metal could be presumed as the specific adsorption of $M^{+{+}}$ and the desorption of two $H^+$ from the surface aquo($OH_2$) and/or hydroxo(-OH) group for each mole of $M^{+{+}}$ adsorbed. A ring structure between $M^{+{+}}$ and two surface aquo and/or hydroxo groups was postulated. Nonspecific adsorption involved the adsorption of $MCl^+$ and the desorption of one H+ from the surface aquo and/or hydroxo groups for each mole of $M^{+{+}}$ adsorbed. A single bond structure in which $MCl^+$ replaced one $H^+$ from the surface aquo and/or hydroxo groups was postulated. The ratio of specific to nonspecific adsorption increased with increasing pH.

• Journal of Applied Biological Chemistry
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• v.56 no.3
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• pp.171-177
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• 2013

Efficient extraction of total proteins from soil microorganisms is tedious because of small quantity. In this regard, an improved method for extraction of whole cell proteins is developed from soil microorganisms, Saccharomyces cerevisiae and Pichia pastoris. of which the cell wall are very strong. Pretreatment with NH4OH prior to the final extraction using NaOH/SDS was tried under the basis that ammonium ion was possible to enhance the permeability and/or to weaken the yeast cell walls. The pre-treatment of yeast cells with NH4OH drastically enhanced the protein extraction when it was compared with control (without NH4OH pre-treatment). At the pre-treatment of 0.04 N NH4OH at pH 9.0, about 3 fold of proteins was obtained from p. pastoris. Ammonium hydroxide appears to penetrate into the yeast cell walls more readily at basic pH. The effect of NH4OH pretreatment was pH dependent. The methods developed in this experiment might be applicable for an effective extraction of yeast proteins for the purpose of biochemical studies, especially proteomic analysis.

• Korean Chemical Engineering Research
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• v.44 no.5
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• pp.476-482
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• 2006

This paper studied the recovery of organic acid from organic acid salt by using bipolar membrane electrodialysis. Acetic acid and lactic acid was used as for organic acid. Organic acid concentration, sodium hydroxide concentration and pH values were measured at various current density. Organic acid salt was effectively converted to organic acid and sodium hydroxide. Based on the experimental results, mathematical models were developed, in which time changes in ion balance were considered. Model predictions of organic acid concentration, sodium hydroxide concentration and pH values were in good agreement with the experimental data.