• Bulletin of the Korean Chemical Society
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• v.34 no.5
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• pp.1525-1529
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• 2013

Pseudo-first-order rate constants ($k_{obsd}$) have been measured spectrophotometrically for the nucleophilic substitution reactions of 2-pyridyl thionobenzoate (5b) with alkali-metal ethoxides (EtOM, $M^+=Li^+$, $Na^+$, $K^+$, and 18-crown-6-ether complexed $K^+$) in anhydrous ethanol at $25.0{\pm}0.1^{\circ}C$. The plots of $k_{obsd}$ vs. $[EtOM]_o$ curve upward regardless of the nature of the $M^+$ ions, while those of $k_{obsd}/[EtO^-]_{eq}$ vs. $[EtO^-]_{eq}$ are linear with a positive intercept. Dissection of $k_{obsd}$ into $k_{EtO^-}$ and $k_{EtOM}$ (i.e., the second-order rate constants for the reactions with the dissociated $EtO^-$ and ion-paired EtOM, respectively) has revealed that the ion-paired EtOM is more reactive than the dissociated $EtO^-$, and $M^+$ ions catalyze the reactions in the order $K^+$ < $Na^+$ < $Li^+$ < 18C6-complexed $K^+$. The plot of log $k_{EtOM}$ vs. $1/r_{Stokes}$ results in an excellent linear correlation, indicating that the reactions are catalyzed by the solvated $M^+$ ions but not by the bare $M^+$ ions. The reactions of 5b with EtOM have been concluded to proceed through a six-membered cyclic TS, in which the solvated $M^+$ ions increase the electrophilicity of the reaction center and the nucleofugality of the leaving group.

• Journal of the Korean Chemical Society
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• v.32 no.3
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• pp.260-266
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• 1988

The rate constants for the nucleophilic addition reactions of thioglycolic acid and cysteine to ${\beta},\;{\beta}$-dichlorostyrene derivatives(p-H, p-Cl, $p-CH_3,\;and\;p-OCH_3$) were photochemically determined at various pH and a rate equation which can be applied over a wide pH range was obtained. On the bases of rate equation, general base catalysis and substituent effect, the plausible addition reaction mechanism was proposed: Above pH 9.0, the reaction was initiated by the addition of sulfide anion, and in the range of pH 7.0 to 9.0, the neutral molecules and it's anions attacked to the double bond, competitively. However, below pH 7.0, only the neutral molecules of thioglycolic acid or cysteine added to the carbon-carbon double bond.

• Journal of the Korean Chemical Society
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• v.28 no.5
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• pp.284-292
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• 1984

This paper aims to predict the substituent and Lewis acid catalysis effect or reactivity on the regioselectivity of (4+2) cycloaddition reaction of the substituted-E-arene-diazocyanides and nitrosobenzenes. Frontier orbital theory (FMO) has been applied to thermal and catalyzed Diels-Alder reaction by means of CNDO/2 and EHT-SPD methods. It has been found that: (1) The above reaction is positive rho(${\rho}$) values in Hammett equation, so it takes normal electron demand reaction, and four-frontier orbitals and Anh methods are identical with experimental major regioisomer.(2) When electron withdrawing radicals are substituted HOMO and LUMO energies of dienophiles are reduced, and the reactivity is increased. (3) The major regioisomer is predicted as B type, as the Lewis acid makes complexes of dienophile, and polaries LUMO coefficients of dienophile in an opposite way. (4) The linear correlation of Hammett is indicated in the graph of stabilized energies(${\Delta}$E) and sigma(${\sigma}$).

• Journal of the Korean Chemical Society
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• v.33 no.1
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• pp.127-134
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• 1989

The rate constants of the nucleophilic addition reaction of 3-mercaptopropionic acid to the ${\beta},\;{\beta}$-diethoxycarbonylstryene derivatives (H, p-OCH$_3$, 3,4,5-(OCH$_3)_3$, 3,4-methylenedioxy) were determined by ultraviolet spectrophotometry, and rate equation which could be applied over a wide pH range was obtained. On the basis of pH-rate profile and the presence of general base catalysis, a plausible mechanism of this addition reaction was propound:Below pH 6.0 the reaction was initiated by the addition of neutral 3-mercaptopropionic acid molecule, and in the range of pH 6.0∼8.0, a neutral 3-mercaptopropionic acid molecule and a sulfide anion competitively attacked to the double bond. Above pH 8.0, the reaction proceeded through the addition of a sulfide anion.

• Polymer(Korea)
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• v.37 no.4
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• pp.462-469
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• 2013

Catechin (CTEC) is well-known as a very powerful antioxidant, containing the effects of anti-inflammation and skin wound healing. In this study, CTEC/${\beta}$-cyclodextrin (${\beta}$-CD) nanoparticles were incorporated into poly(vinyl alcohol) (PVA)/pectin (PT) hydrogel. The composite was designed for the induction of re-epithelializaton in skin wound. CTEC/${\beta}$-CD nanoparticles were prepared by a molecular complex method. The size of the CTEC nanoparticles formed in the hydrogel was in the range of $250{\pm}17.5$ nm. The incorporation efficiency of CTEC in the nanoparticles was 74%. The cumulative amounts of CTEC released from the hydrogel containing CTEC nanoparticles in the buffers of pH7.4 and 5.5 were $86.51{\pm}3.14%$ and $35.95{\pm}2.14%$ of total CTEC loaded in the hydrogel within 72 h, respectively. Also, in the wound healing test, the CTEC nanoparticles-loaded PVA/PT hydrogel showed faster healing of the wound made in rat dorsum than the CTEC gel.

• KSBB Journal
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• v.20 no.1 s.90
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• pp.46-49
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• 2005

Curdlan, a natural $\beta-1,3-glucan,$ has been studied as drug carrier due to its unique properties including its thermal gelling characters. In this study, curdlan was chemically acetylated for pH-sensitive drug delivery. Curdlan acetate microspheres(CAMs) were prepared by the solvent evaporation method. The size of the CAMs was below $200{\mu}m.$ The drug loading efficiency of microspheres was approximately $58.44\%$. In the swelling test, the CAMs showed pH-sensitive behavior. The swelling capacity of microspheres at pH 7.4 was much greater than at pH 1.4. Also, release rate of indomethacin(IND) at pH 7.4 from the CAMs was faster than that at pH 1.4. Therefore the CAMs have potential for the controlled release of IND over an extended period of time.

• Biotechnology and Bioprocess Engineering:BBE
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• v.11 no.6
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• pp.530-537
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• 2006

Recently isolated, Pseudomonas putida SN1 grows on styrene as its sole carbon and energy source through successive oxidation of styrene by styrene monooxygenase (SMO), styrene oxide isomerase (SOI), and phenylacetaldehyde dehydrogenase. For the production of (S)-styrene oxide, two knockout mutants of SN1 were constructed, one lacking SOI and another lacking both SMO and SOI. These mutants were developed into whole-cell biocatalysts by transformation with a multicopy plasmid vector containing SMO genes (styAB) of the SN1. Neither of these self-cloned recombinants could grow on styrene, but both converted styrene into an enantiopure (S)-styrene oxide (e.e. > 99%). Whole-cell SMO activity was higher in the recombinant constructed from the SOI-deleted mutant (130 U/g cdw) than in the other one (35 U/g cdw). However, the SMO activity of the former was about the same as that of the SOI-deleted SN1 possessing a single copy of the styAB gene that was used as host. This indicates that the copy number of styAB genes is not rate-limiting on SMO catalysis by whole-cell SN1.

• Preventive Nutrition and Food Science
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• v.19 no.4
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• pp.247-260
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• 2014

The impact of folate on health and disease, particularly pregnancy complications and congenital malformations, has been extensively studied. Mandatory folic acid fortification therefore has been implemented in multiple countries, resulting in a reduction in the occurrence of neural tube defects. However, emerging evidence suggests increased folate intake may also be associated with unexpected adverse effects. This literature review focuses on contemporary issues of concern, and possible underlying mechanisms as well as giving consideration the future direction of mandatory folic acid fortification. Folate fortification has been associated with the presence of unmetabolized folic acid (PteGlu) in blood, masking of vitamin $B_{12}$ deficiency, increased dosage for anti-cancer medication, photo-catalysis of PteGlu leading to potential genotoxicity, and a role in the pathoaetiology of colorectal cancer. Increased folate intake has also been associated with twin birth and insulin resistance in offspring, and altered epigenetic mechanisms of inheritance. Although limited data exists to elucidate potential mechanisms underlying these issues, elevated blood folate level due to the excess use of PteGlu without consideration of an individual's specific phenotypic traits (e.g. genetic background and undiagnosed disease) may be relevant. Additionally, the accumulation of unmetabolized PteGlu may lead to inhibition of dihydrofolate reductase and other enzymes. Concerns notwithstanding, folic acid fortification has achieved enormous advances in public health. It therefore seems prudent to target and carefully monitor high risk groups, and to conduct well focused further research to better understand and to minimize any risk of mandatory folic acid fortification.

• Journal of the Korean GEO-environmental Society
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• v.11 no.6
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• pp.31-37
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• 2010

In this study, optimization of MEK and Toluene removal was conducted by HTO(Hybrid Thermal Oxidation) system. HTO system has a multi-bed reaction plate and the plate consisted of wasted heat regeneration part and catalysis part. VOCs removal by HTO system was estimated by changing inlet flow rates with different valve changing times. Under $350^{\circ}C$ of combustion temperature, VOCs was fully converted and the equivalent conversion was 100%. The thermal oxidation efficiency, related to the amount of injected fuel into HTO system and the valve change time, was revealed at the level of 93.0~96.3%. In case of MEK removal by HTO system, the efficiency was ranged from 91.1 to 97.1%. Also, Toluene removal efficiency(93.2~97.4%) was good and stable with respect to the operating conditions. Considering above results, it was proved that HTO system could be a stable and compact system for VOCs, especially MEK and Toluene with high removal efficiency.

• 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.