• Journal of Soil and Groundwater Environment
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• v.26 no.1
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• pp.54-64
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• 2021

The chemical warfare agents (CWAs) have been developed for offensive or defensive purposes and used as chemical weapons in war and terrorism. The CWAs are exposed to the natural environment, transported through the water system and then eventually contaminate soil and groundwater. Therefore, effective decontamination technology to remediate CWAs are needed. The CWAs are extremely dangerous and prodution is strictly prohibited, therefore, it is difficult to use CWAs even in experimental purpose. In this study, 2,4-dichlorophenoxyacetic acid (2,4-D) was chosen as a model representative CWA because it is a simulant of anti-plant CWAs and one of the major component of agent orange. The optimum degradation conditions such as oxidant:activator ratio were determined. The effects of hydroxylamine and chelating agents such as citric acid (CA), oxalic acid (OA), malic acid (MA), and EDTA addition to increase Fe2+ activation were also investigated. Scavenger experiments using tert-butyl alcohol (TBA) and ethanol confirmed that although both sulfate (SO4•-) and hydroxyl radical (•OH) existed in Fe2+-persulfate system, sulfate radical was the predominant radical. To promote the Fe2+ activator effect, the effect of hydroxylamine as a reducing agent was investigated. In chelating agents assisted Fe2+-persulfate oxidation, the addition of 2 mM of CA and MA enhanced 2,4-D degradation. In contrast, EDTA and OA inhibited the 2,4-D removal due to steric hindrance effect.

• Journal of Microbiology and Biotechnology
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• v.6 no.3
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• pp.173-178
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• 1996

Synergic effects among endo-xylanase, $\beta$-xylosidase, and acetyl xylan esterase of Bacillus stearothermophilus in the hydrolysis of xylan were studied by using birchwood, oat spelt, and acetylated xylan as substrates. Synergism between endo-xylanase and $\beta$-xylosidase was observed on all three substrates tested, indicating that $\beta$-xylosidase enhanced the production of xylose by relieving the end-product inhibition upon endo-xylanase conferred by xylooligomers. Endo-xylanase and $\beta$-xylosidase also showed synergism with acetyl xylan esterase in the hydrolysis of birchwood and acetylated xylan, while no synergic effect was detected in oat spelt xylan hydrolysis. Thus, the hydrolysis of xylan containing acetic acid side chains required the action of acetyl xylan esterase, which eliminated the steric hindrance of the side chains, leading to the better hydrolysis by endo-xylanase and $\beta$-xylosidase , and the acetyl xylan esterase activity was also enhanced by endo-xylanase and $\beta$-xylosidase for the latter enzymes provided acetyl xylan esterase with shorter xylan oligomers, the better substrate for the enzyme.

• Macromolecular Research
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• v.8 no.1
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• pp.26-33
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• 2000

A series of pH/temperature sensitive polymers were synthesized by copolymerizing N-isopro-pyl acrylamide(NIPAAm) and acrylic acid(AAc) . The influence of polyelectrolyte between poly(allyl amine) (PAA) and poly(L-lysine)(PLL) on the lower critical solution temperature(LCST) of pH/temperature sensitive polymer was compared in the range of pH 2∼12. The LCST of PNIPAAm/water in aqueous poly(NIPAAm-co-AAc) solution was determined by cloud point measurements. A polyelectrolyte complex was prepared by mixing poly(NIPAAm-co-AAc) with poly(allyl amine) (PAA) or poly(L-lysine) (PLL) solutions as anionic and cationic polyelectrolytes, respectively. The effect of polyelectrolyte complex formation on the conformation of PLL was studied as a function of temperature by means of circular dichroism(CD). The cloud points of PNIPAAm in the aqueous copolymers solutions were stongly affected by pH, the presence of polyelectrolyte solute, AAc content, and charge density. The polyelectrolyte complex was formed at neutral condition. The influence of more hydrophobic PLL as a polyelectrolyte on the cloud point of PNIPAAm in the aqueous copolymer solution was stronger than that of poly(allyl amine)(PAA). Although polymer-polymer complex was formed between poly(NIPAAm-co-AAc) and PLL, the conformational change of PLL did not occur due to steric hinderance of bulky N-isopropyl groups of PNIPAAm.

• Bulletin of the Korean Chemical Society
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• v.33 no.2
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• pp.663-669
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• 2012

The nucleophilic substitution reactions of dibutyl chlorophosphate (3) with substituted anilines ($XC_6H_4NH_2$) and deuterated anilines ($XC_6H_4ND_2$) are investigated kinetically in acetonitrile at $55.0^{\circ}C$. The obtained deuterium kinetic isotope effects (DKIEs; kH/kD) are secondary inverse ($k_H/k_D$ = 0.86-0.97) with the strongly basic anilines while primary normal ($k_H/k_D$ = 1.04-1.10) with the weakly basic anilines. The DKIEs, steric effects of the two ligands, activation parameters, cross-interaction constants, variation trends of the kH/kD values with X, and mechanism are discussed for the anilinolyses of the nine ($R_1O$)($R_2O$)P(=O)Cl-type chlorophosphates. A concerted mechanism is proposed with a backside nucleophilic attack transition state for the strongly basic anilines and with a frontside attack involving a hydrogen-bonded four-center-type transition state for the weakly basic anilines on the basis of the magnitudes, secondary inverse and primary normal, and variation trends of the $k_H/k_D$ values with X.

• Biotechnology and Bioprocess Engineering:BBE
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• v.6 no.4
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• pp.269-273
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• 2001

This study presents a new formulation method for improving DNA transfection effi-ciency using a fusogenic peptide and polyethylene glycol-grafted polyethylenimine. Succinimidyls succinate polyethylene glycol (PEG-SSA) was conjugated with polyethylenimine(PEL). PEL is well known for a good endosomal escaping and DNA condensign agent. The positively charged syn-thetic fusogenic peptide, KALA was coated on the negatively charged PEG-g-PEI/DNA and PEI/DNA complexes. The KALA/PEI/ DNA complexes exhibited aggregation behavior at higher KALA coating amount with an effective diameter of around 1,000 nm. However, the LALA/PEG-g-PEI/DNA complexes were 100-300 nm in size with a surface zeta-potential (ζ)value of about +20mV. The conjugated PEG molecules suppressed any KALA-mediated inter-particle aggregation, and thereby improved the transfection efficiency, Consequently, the transfection efficiency of the KALA/PEG-g-PEI/DNA complexes was obtained by utilizing both the fusogenic activity of KALA and the steric repulsion effect of PEC.

• BMB Reports
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• v.49 no.3
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• pp.135-136
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• 2016

Small interfering RNAs (siRNAs) have been developed to intentionally repress a specific gene expression by directing RNA-induced silencing complex (RISC), mimicking the endogenous gene silencer, microRNAs (miRNAs). Although siRNA is designed to be perfectly complementary to an intended target mRNA, it also suppresses hundreds of off-targets by the way that miRNAs recognize targets. Until now, there is no efficient way to avoid such off-target repression, although the mode of miRNA-like interaction has been proposed. Rationally based on the model called "transitional nucleation" which pre-requires base-pairs from position 2 to the pivot (position 6) with targets, we developed a simple chemical modification which completely eliminates miRNA-like off-target repression (0%), achieved by substituting a nucleotide in pivot with abasic spacers (dSpacer or C3 spacer), which potentially destabilize the transitional nucleation. Furthermore, by alleviating steric hindrance in the complex with Argonaute (Ago), abasic pivot substitution also preserves near-perfect on-target activity (∼80-100%). Abasic pivot substitution offers a general means of harnessing target specificity of siRNAs to experimental and clinical applications where misleading and deleterious phenotypes from off-target repression must be considered.

• Journal of the Korean Chemical Society
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• v.34 no.4
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• pp.345-351
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• 1990

Optical isomers of DABS-amino acids have been separated in a reversed phae high performance liquid chromatography by adding Cu (Ⅱ)-L-Proline chelate to the mobile phase. The retention behaviors for the DABS-amino acids are discussed in terms of pH of the mobile phase and the concentrations of acetonitrile, Cu (Ⅱ) complex, and buffer. The selectivity of the optical isomers of DABS-amino acids increases with the pH of the mobile, and the concentration of the chelate, but decreases with concentration of the oganic modifier. The concentration of buffer does not affect the optical separation selectivity. A separation mechanism is illustrated by cis and trans formation based on the steric effect of the ligand exchange reaction between DABS-amino acids and the copper chelate.

• Bulletin of the Korean Chemical Society
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• v.32 no.12
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• pp.4361-4365
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• 2011

The nucleophilic substitution reactions of bis(N,N-dimethylamino) phosphinic chloride (3) with substituted anilines ($XC_6H_4NH_2$) and deuterated anilines ($XC_6H_4ND_2$) are investigated kinetically in acetonitrile at $65.0^{\circ}C$. The anilinolysis rate of 3 is rather slow to be rationalized by the conventional stereoelectronic effects. The magnitudes of ${\rho}_X$ (= -6.42) and ${\beta}_X$ (= 2.27) values are exceptionally great. The deuterium kinetic isotope effects (DKIEs; $k_H/k_D$) are secondary inverse ($k_H/k_D$ = 0.69-0.96). A concerted $S_N2$ mechanism involving a backside attack is proposed on the basis of secondary inverse DKIEs and the variation trend of the $k_H/k_D$ values with X. The anilinolyses of six phosphinic chlorides in MeCN are briefly reviewed by means of DKIEs, steric effects of the two ligands, positive charge of the reaction center phosphorus atom, and selectivity parameters to obtain systematic information on phosphoryl transfer reaction mechanism.

• Journal of Korean Society on Water Environment
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• v.21 no.2
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• pp.205-210
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• 2005

There has been a growing interest in NF membrane for drinking water treatment, because it can remove simultaneously both hardness and hazardous micro pollutants such as pesticides and THM precursors. In this work, a hollow fiber NF membrane known as a composite membrane was employed for the rejection properties of both hydrophilic solutes and micro organic pollutants, where the former was used to evaluate the molecular sieving effect of this membrane and the latter was employed for the investigation of solute-membrane interaction as hydrophobic materials. This membrane effectively rejected the hydrophilic solutes and the permeation of them was mainly controlled by the molecular sieving effects such as molecular weight and molecular width. In the case of all micro organic pollutants, the rejections were varied from 42.2% for Simazine to 91.6% for Malathion, and the parameters related to the steric hindrance could significantly play an important role in the rejection. In the batch type adsorption experiments, all micro organic pollutants were entrapped mildly on the membrane in spite of lower degree compared with that of aromatic compounds, and they were correlated with log K.

• Bulletin of the Korean Chemical Society
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• v.31 no.11
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• pp.3272-3278
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• 2010

Synthesis and structural characterization of peripherally ferrocene-substituted zinc phthalocyanine (ZnPc-Fc) were carried out for efficient far-red/near-IR performance in dye-sensitized nanostructured $TiO_2$ solar cells. Incorporating ferrocene into phthalocyanine strongly improved the dye solubility in polar organic solvents, and reduced surface aggregation due to the steric effect of bulky ferrocene substituents. The involvement of electron transfer reaction pathways between ferrocene and phthalocyanine in ZnPc-Fc was evidenced by completely quenched fluorescence from S1 state (< 0.08% vs ZnPc). Strong absorption bands at 542 and 682 nm were observed in the transient absorption spectroscopy of ZnPc-Fc in DMSO, which was excited at a 670 nm laser pulse with a 15 ps full width at half maximum. Also, the excited state absorption signals at 450 - 600 and 750 - 850 nm appeared from the formation of charge separated state of phthalocyanine's anion. The lifetime of the charge separate state in ZnPc-Fc was determined to be $170{\pm}8$ ps, which was almost 17 times shorter than that of the ZnPc.