• Bulletin of the Korean Chemical Society
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• v.33 no.1
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• pp.48-54
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• 2012

The $[Fe_4S_4]^{2+}$ clusters with 2-, 3-, and 4-pyridinemethanethiolate (S2-Pic, S3-Pic, and S4-Pic, respectively) terminal ligands have been synthesized from the ligand substitution reaction of the $(^nBu_4N)_2[Fe_4S_4Cl_4]$ (I) cluster. The new $(^nBu_4N)_2[Fe_4S_4(SR)_4]$ (R = 2-Pic; II, 3-Pic; III, 4-Pic; IV) clusters were characterized by FTIR and UV-Vis spectroscopy. Cluster II was crystallized in the monoclinic space group C2/c with a = 24.530 (5) $\AA$, b = 24.636(4) $\AA$, c = 21.762(4) $\AA$, ${\beta}=103.253(3)^{\circ}$, and Z = 8. The X-ray structure of II showed two unique 2:2 site-differentiated $[Fe_4S_4]^{2+}$ clusters due to the bidentate-mode coordination by 2-pyridinemethanethiolate ligands. Cluster III was crystallized in the same monoclinic space group C2/c with a = 26.0740(18) $\AA$, b = 23.3195(16) $\AA$, c = 22.3720(15) $\AA$, ${\beta}=100.467(2)^{\circ}$, and Z = 8. The 3-pyridinemethanethiolate ligand of III was coordinated to the $[Fe_4S_4]^{2+}$ core as a terminal mode. Cluster IV with 4-pyridinemethanethiolate ligands was found to have a similar structure to the cluster III. Fully reversible $[Fe_4S_4]^{2+}/[Fe_4S_4]^+$ redox waves were observed from all three clusters by cyclic voltammetry measurement. The electrochemical potentials for the $[Fe_4S_4]^{2+}/[Fe_4S_4]^+$ transition decreased in the order of II, III and IV, and the reduction potential changes by the ligands were explained based on the structural differences among the complexes. The complex III was reacted with sulfonium salt of $[PhMeSCH_2-p-C_6H_4CN](BF_4)$ in MeCN to test possible radical-involving reaction as a functional model of the [$Fe_4S_4$]-SAM (S-adenosylmethionine) cofactor. However, the isolated reaction products of 3-pyridinemethanethiolate-p-cyanobenzylsulfide and thioanisole suggested that the reaction followed an ionic mechanism and the products formed from the terminal ligand attack to the sulfonium.

• Journal of the Korean Chemical Society
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• v.38 no.10
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• pp.719-725
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• 1994

Kinetic studies were carried out for substitution reaction of $cis-[Co(NH_3)_4Cl(OH_2)]^{2+}(\mu$ = 0.75) with GlyOR (R = $C_2H_5$, $CH_3$, H) in pH 5 buffer solution at $20^{\circ}C$ by UV/Vis-spectrophotometry. We obtained cis-[Co$(NH_3)_4$Cl(glyOR)]$^{2+}$ as product. The reaction turns out to be first order for Co(III) and GlyOR, respectively. The rate constants are obtained as 9.21, 11.66 and 15.33 l${\cdot}\;mol^{-1}{\cdot}sec^{-1}$ for GlyOEt, GlyOMt and GlyOH, respectively. The activation parameters $E_a,\;{\Delta}H^{\neq}\;and\;{\Delta}S^{\neq}$ for GlyOEt were obtained as 65.77, 63.35 kJ/mol and -53.51(e.u.), respectively and were obtained as 70.91, 68.50 kJ/mol and -38.42(e.u.) for GlyOMt. In case of GlyOH, respectable values of 79.72, 77.30 kJ/mol and -26.59(e.u.) were obtained. On the basis of kinetic data and the observed activation parameters, we propose that the proper mechanism involves $S_N$2 step.

• The Korea Journal of Herbology
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• v.30 no.5
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• pp.15-21
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• 2015

Objectives : Methicillin-resistantStaphylococcus aureus(MRSA) is a human pathogen. New antibacterial agents are needed to treat MRSA-related infections. This study investigated the antibacterial activity of EtOH 70% extracts ofTonghyeonipal-dan(THD) which prescription is composed of oriental medicine against MRSA.Methods : The antibacterial activity of THD was evaluated against MRSA strains by using the Disc diffusion method, broth microdilution method, Checkerboard dilution test, and Time-kill test; its mechanism of action was investigated by bacteriolysis, detergent or ATPase inhibitors were used.Results : The minimum inhibitory concentration (MIC) of THD is 1,000~2,000 μg/mL against MRSA. In the checkerboard dilution test, fractional inhibitory concentration index (FICI) of THD in combination with antibiotics indicated synergy or partial synergism againstS. aureus. Furthermore, a time-kill assay showed that the growth of the tasted bacteria was considerably inhibited after 24 h of treatment with the combination of THD with selected antibiotics. For measurement of cell membrane permeability, THD 500 μg/mL along with concentration of Triton X-100 (TX) and Tris-(hydroxymethyl) aminomethane (TRIS) were used. In the other hand, N,N-dicyclohexylcarbodimide (DCCD) and Sodium azide (NaN3) were used as an inhibitor of ATPase. TX, TRIS, DCCD and NaN3 cooperation againstS. aureusshowed synergistic action.Conclusions : Accordingly, antimicrobial activity of THD was affected by cell membrane and inhibitor of ATPase were assessed. These results suggest that THD has antibacterial activity, and that THD extract offers great potential as a natural antibiotic against MRSA.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.3
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• pp.429-436
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• 2013

This study considers how the fatigue behavior and probabilistic properties of SAE1055 steel are related to its hardness level. SAE1055 steel was heat-treated using induction hardening. Five types of specimens were prepared (A: base material, B: through hardened material with HV390, C: through hardened material with HV510, D: through hardened material with HV700, and E: surface hardened material with HV700). Fatigue tests were performed under a stress ratio of R = -1 using a 4-point rotary bending fatigue tester. The fatigue behaviors were greatly influenced by the hardness, but the fatigue limit did not increase over a hardness of HV510. In addition, the effect of the hardness level on the failure mechanism was evaluated using a scanning electron microscope. The probabilistic properties of the fatigue life were investigated using a probabilistic S-N approach, and the effect of the hardness level on these properties was evaluated using a residue analysis.

• Atmosphere
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• v.31 no.1
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• pp.45-60
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• 2021

The synoptic structures and precipitation impact of extratropical cyclones (ETCs) influencing on the three adjacent megacities in East Asia, i.e., Beijing (Beijing ETCs), Seoul (Seoul ETCs) and Tokyo (Tokyo ETCs), are analyzed using ERA-interim reanalysis data from 1979 to 2018. Individual ETC tracks are identified with the automated tracking algorithm applied to 850-hPa relative vorticity field. Among four seasons, ETCs are the most frequent in spring. In this season, Beijing ETCs are mainly generated at the leeside of Altai-Sayan Mountains and primarily develop through interaction between the upper-level trough and lower-level cyclonic circulation. For Seoul ETCs, the leesides of Altai-Sayan Mountains (Seoul-N ETCs) and Tibetan Plateau (Seoul-S ETCs) are main genesis regions and the features of ETCs are different according to the genesis regions. While Seoul-N ETCs mainly develope by the same mechanism of Beijing ETCs, strong diabatic heating due to vapor transport is responsible for the genesis of Seoul-S ETCs. Tokyo ETCs are originated from the leesides of Tibetan Plateau and Kuroshio-Oyashio Extension regions, and strong diabatic heating as well as interaction between upper and lower levels determines the genesis of these ETCs. The precipitation impact resulting from ETCs become strong in the order of Beijing ETCs, Seoul-N ETCs, Seoul-S ETCs, and Tokyo ETCs and accounts for up to 40%, 27%, 52%, and 70% of regional precipitation, respectively.

• Journal of Pharmacopuncture
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• v.18 no.3
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• pp.32-41
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• 2015

Objectives: Condurango (Gonolobus condurango) extract is used by complementary and alternative medicine (CAM) practitioners as a traditional medicine, including homeopathy, mainly for the treatment of syphilis. Condurango bark extract is also known to reduce tumor volume, but the underlying molecular mechanisms still remain unclear. Methods: Using a cervical cancer cell line (HeLa) as our model, the molecular events behind condurango extract's (CE's) anticancer effect were investigated by using flow cytometry, immunoblotting and reverse transcriptase-polymerase chain reaction (RT-PCR). Other included cell types were prostate cancer cells (PC3), transformed liver cells (WRL-68), and peripheral blood mononuclear cells (PBMCs). Results: Condurango extract (CE) was found to be cytotoxic against target cells, and this was significantly deactivated in the presence of N-acetyl cysteine (NAC), a scavenger of reactive oxygen species (ROS), suggesting that its action could be mediated through ROS generation. CE caused an increase in the HeLa cell population containing deoxyribonucleic acid (DNA) damage at the G zero/Growth 1 (G0/G1) stage. Further, CE increased the tumor necrosis factor alpha ($TNF-{\alpha}$) and the fas receptor (FasR) levels both at the ribonucleic acid (RNA) and the protein levels, indicating that CE might have a cytotoxic mechanism of action. CE also triggered a sharp decrease in the expression of nuclear factor kappa-light-chain-enhancer of activated B cells ($NF-{\kappa}B$) both at the RNA and the protein levels, a possible route to attenuation of B-cell lymphoma 2 (Bcl-2), and caused an opening of the mitochondrial membrane's permeability transition (MPT) pores, thus enhancing caspase activities. Conclusion: Overall, our results suggest possible pathways for CE mediated cytotoxicity in model cancer cells.

• Molecules and Cells
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• v.21 no.3
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• pp.395-400
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• 2006

Glutathione S-transferase P1 (GSTP1) plays an important role in detoxification and the metabolism of xenobiotics. Here we show that GSTP1 also regulates the MEKK1-MKK7 signaling pathway. Over-expression of GSTP1 in HEK293 cells inhibited both ${\Delta}MEKK1$- and etoposide-induced apoptosis, and inhibited procaspase-3 activation and PARP cleavage. MEKK1- induced apoptosis requires both its kinase activity and proteolytic cleavage. ${\Delta}MEKK1$ activity was inhibited by over-expression of GSTP1 in vivo and MEKK1 kinase activity was also inhibited by GSTP1 in vitro when assayed with bacterially-expressed MKK7(KM) protein as substrate. GSTP1 inhibition of etoposide-induced cell apoptosis was mainly due to its ability to suppress MEKK1 kinase activity. The glutathione-conjugating activity of GSTP1 was essential for the above effects. These findings provide insight into the mechanism by which GSTP1 protects cells from genotoxin-induced apoptosis.

• The Korean Journal of Physiology and Pharmacology
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• v.22 no.5
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• pp.539-546
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• 2018

Botulinum toxin type A (BoNT/A) has been used therapeutically for various conditions including dystonia, cerebral palsy, wrinkle, hyperhidrosis and pain control. The substantia gelatinosa (SG) neurons of the trigeminal subnucleus caudalis (Vc) receive orofacial nociceptive information from primary afferents and transmit the information to higher brain center. Although many studies have shown the analgesic effects of BoNT/A, the effects of BoNT/A at the central nervous system and the action mechanism are not well understood. Therefore, the effects of BoNT/A on the spontaneous postsynaptic currents (sPSCs) in the SG neurons were investigated. In whole cell voltage clamp mode, the frequency of sPSCs was increased in 18 (37.5%) neurons, decreased in 5 (10.4%) neurons and not affected in 25 (52.1%) of 48 neurons tested by BoNT/A (3 nM). Similar proportions of frequency variation of sPSCs were observed in 1 and 10 nM BoNT/A and no significant differences were observed in the relative mean frequencies of sPSCs among 1-10 nM BoNT/A. BoNT/A-induced frequency increase of sPSCs was not affected by pretreated tetrodotoxin ($0.5{\mu}M$). In addition, the frequency of sIPSCs in the presence of CNQX ($10{\mu}M$) and AP5 ($20{\mu}M$) was increased in 10 (53%) neurons, decreased in 1 (5%) neuron and not affected in 8 (42%) of 19 neurons tested by BoNT/A (3 nM). These results demonstrate that BoNT/A increases the frequency of sIPSCs on SG neurons of the Vc at least partly and can provide an evidence for rapid action of BoNT/A at the central nervous system.

• Environmental Analysis Health and Toxicology
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• v.20 no.3 s.50
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• pp.209-213
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• 2005

Due to steady increase of childhood asthma, exposure to air toxics including PAHs have been thought as an etiology for the asthma. PAHs -involvement in airway inflammation, such as IgE production, is the potential mechanism of the PAHs-induced asthma. Cytochrome P450s (CYPs), particularly CYP1A1 is known enzyme to metabolite PAHs and to be induced by PAHs. The CYP1A1 expression has been emphasized as an biomarker for PAHs - exposure. The present study was performed to clarify the etiology of childhood asthma with PAHs-exposure using mRNA expression of CYP1A1 . The study Objects were Korean children who were asthma patients (cases) or other hospital controls (N=20; age,3 $\~$ 16; boys,56$\%$). As result, we detected expression of the CYP1A1 in all peripheral blood specimens which were collected from the subjects. Moreover, we found approx. 300 fold-higher expression of the CYP1A1 in the cases than that in the controls (p(<)0.01). When we considered age which was related to Asthma, the above significant trend was somewhat diluted, however, the relation between asthma and the Cypih i expression waL stronger than that between asthma and age (chi square,7.99 vs. 3.34). Therefore, our study supports that PAHs induce or worse childhood asthma and suggests application of expression of the CYP1A1 as an initiation or progress biomarker for PAHs - induced childhood asthma.

• Journal of Korean Society for Atmospheric Environment
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• v.11 no.E
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• pp.31-43
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• 1995

Natural emissions of NOx from soils were measured at an agricultural corn field during 3 weeks of growing season in summer (from May to June) 1995. This experiment was conducted in an effort to characterize the role of soil NOx on tropospheric ozone formation in rural atmosphere, and understand the natural NOx emission mechanism with respect to soil parameters. NO fluxes were ranged from 3.1 ng Nm$^{-2}s^{-1}$ to 259.0 ng Nm$^{-2}s^{-1}$, and average NO flux during experimental period was found to be 47.6 $\pm$ 50.6 ng Nm$^{-2}s^{-1}$ with 732 number of data. Diurnal variation of NO flux was shown clearly with daytime maximum and nighttime minimum. NO fluxes were correlated with soil temperature. Exponential soil temperature dependency of NO fluxes was found with 0.0160$^{circ}C^{-1} of k and r^2=0.508$, which agrees well to the value estimated at corn fields in eastern United States. The significant increases of NO fluxes from agricultural soil were detected after applying N fertilizers to soil. THe mechanisms attributed to this are enhanced biological nitrification and denitrification. In the view of rural ozone formation, the roles of natural NO emissions are very essential, especially in NOx - limited region such as southern United States.