• Bulletin of the Korean Chemical Society
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• v.18 no.11
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• pp.1166-1172
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• 1997

[FeⅢ(BLPA)DBC]BPh4, a new functional model for the catechol dioxygenases, has been synthesized, where BLPA is bis((6-methyl-2-pyridyl)methyl)(2-pyridylmethyl)amine and DBC is 3,5-di-tert-butylcatecholate dianion. The BLPA complex has a structural feature that iron center has a six-coordinate geometry with N4O2 donor set. It exhibits EPR signals at g=5.5 and 8.0 which are typical values for the high-spin FeⅢ (S=5/2) complex with axial symmetry. The BLPA complex reacts with O2 within a few hours to afford intradiol cleavage (75%) and extradiol cleavage (15%) products which is very unique result of all [Fe(L)DBC] complexes studied. The iron-catecholate interaction of BLPA complex is significantly stronger, resulting in the enhanced covalency of the metal-catecholate bonds and low energy catecholate to FeⅢ charge transfer bands at 583 and 962 nm in CH3CN. The enhanced covalency is also reflected by the isotropic shifts exhibited by the DBC protons, which indicate increased semiquinone character. The greater semiquinone character in the BLPA complex correlates well with its high reactivity towards O2. Kinetic studies of the reaction of the BLPA complex with 1 atm O2 in CH3OH and CH2Cl2 under pseudo-first order conditions show that the BLPA complex reacts with O2 much slower than the TPA complex, where TPA is tris(2-pyridylmethyl)amine. It is presumably due to the steric effect of the methyl substituent on the pyridine ring. Nevertheless, both the high specificity and the fast kinetics can be rationalized on the basis of its low energy catecholate to FeⅢ charge transfer bands and large isotropic NMR shifts for the BLPA protons. These results provide insight into the nature of the oxygenation mechanism of the catechol dioxygenases.

• Journal of the Korean Society of Propulsion Engineers
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• v.18 no.5
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• pp.95-100
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• 2014

In hypersonic aircraft, increase of aerodynamic heat and engine heat leads heat loads in airframe. It could lead structural change of aircraft's component and malfunctioning. Endothermic fuels are liquid hydrocarbon fuels which are able to absorb the heat load by undergoing endothermic reactions. In this study, exo-tetrahydrodicyclopentadiene was selected as a model endothermic fuel and experiments on endothermic properties were investigated with pore structure controlled zeolite catalyst using metal deposition. We secured the catalyst that had better endothermic performance than commercial catalyst. The object of this study is inspect catalyst properties which have effect on heat absorption improvement. Synthetic catalyst could be applied to system that use exo-THDCP as endothermic fuel instead of other commercial catalyst.

• Proceedings of the Ginseng society Conference
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• 2002.10a
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• pp.317-334
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• 2002

Ginsenosides are metabolized (deglycosylated) by intestinal bacteria to active forms after oral administration. 20(S)-Protopanaxadiol $20-O-{\beta}-D-glucopyranoside$ (M1) and 20(S)-protopanaxatriol (M4) are the main intestinal bacterial metabolites (IBMs) of protopanaxadiol- and protopanaxatriol-type glycosides. M1 was selectively accumulated into the liver soon after its intravenous (i.v.) administration to mice, and mostly excreted as bile; however, some M1 was transformed to fatty acid ester (EMl) in the liver. EM1 was isolated from rats in a recovery dose of approximately $24mol\%.$ Structural analysis indicated that EM1 comprised a family of fatty acid mono-esters of M1. Because EM1 was not excreted as bile as Ml was, it was accumulated in the liver longer than M1. The in vitro cytotoxicity of M1 was attenuated by fatty acid esterification, implying that esterification is a detoxification reaction. However, esterified M1 (EM1) inhibited the growth of B16 melanoma more than Ml in vivo. The in vivo antitumor activity paralleled with the pharmacokinetic behavior. In the case of M4, orally administered M4 was absorbed from the small intestine into the mesenteric lymphatics followed by the rapid esterification of M4 with fatty acids and its spreading to other organs in the body and excretion as bile. The administration of M4 prior to tumor injection abrogated the enhanced lung metastasis in the mice pretreated with 2-chloroadenosine more effectively than in those pretreated with anti-asialo GMl. Both EM1 and EM4 did not directly affect tumor growth in vitro, whereas EM1 promoted tumor cell lysis by lymphocytes, particularly non-adherent splenocytes, and EM4 stimulated splenic NK cells to become cytotoxic to tumor cells. Thus, the esterification of IBM with fatty acids potentiated the antitumor activity of parental IBM through delay of the clearance and through immunostimulation. These results suggest that the fatty acid conjugates of IBMs may be the real active principles of ginsenosides in the body.

• Composites Research
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• v.34 no.5
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• pp.277-282
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• 2021

Graphene oxide can be reduced to graphene under supercritical fluid condition even without using a specific reducing agent or applying a high thermal process. In this study, a process for converting graphene oxide into graphene was studied under supercritical fluid conditions in methanol and ethanol solvents. When the structure of asprepared graphene was analyzed by using FE-SEM and XRD, the reduction of graphene oxide in supercritical fluid condition was more affected by the change of solvent than other variables such as concentration of graphene oxide and reaction time. The use of ethanol showed better results for the reduction than the use of methanol. The graphene prepared in this study was mixed with epoxy resin up to 20 wt.% to make composites, and the thermal conductivity of the composites were analyzed. Thermal conductivity of the composite increased proportionally with graphene loadings. The graphene prepared in supercritical ethanol condition was more effective on the thermal conductivity of the composite.

• Journal of the Korean institute of surface engineering
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• v.54 no.2
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• pp.96-101
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• 2021

NaNbO₃:Eu³⁺ phosphor thin films were grown on quartz substrates by radio-frequency magnetron sputtering at a growth temperature of 100 ℃, with subsequent annealing at temperatures of 800, 900, and 1000 ℃. The effects of annealing temperature on the structural, morphological, and optical properties of the thin films were investigated. The NaNbO₃:Eu³⁺ sputtering target was synthesized by a solid-state reaction of raw materials Na₂CO₃, Nb₂O₅, and Eu₂O₃. The X-ray diffraction patterns exhibited that the thin films had two mixed phases of NaNbO₃ and Eu₂O₃. Surface morphologies were investigated by using field emission-scanning electron microscopy and indicated that the grains of the thin film annealed at 1000 ℃ showed irregular shapes with an average size of approximately 300 nm. The excitation spectra of Eu³⁺-doped NaNbO₃ thin film consisted of a strong charge transfer band centered at 304 nm in the range of 240-350 nm and two weak peaks at 395 and 462 nm, respectively, resulting from the ⁷F₀→⁵L₆ and ⁷F₀→⁵H₂ transitions of Eu³⁺ ions. The emission spectra under excitation at 304 nm exhibited an intense red band centered at 614 nm and two weak bands at 592 and 681 nm. As the annealing temperature increased from 800 ℃ to 1000 ℃, the intensities of all the emission bands and the band gap energies gradually increased. These results indicate that the higher annealing temperature enhance the luminescent properties of NaNbO₃:Eu³⁺ thin films.

• Journal of Applied Biological Chemistry
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• v.64 no.4
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• pp.375-382
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• 2021

Biorenovation is a microbial enzyme-based structural modification of component compounds in natural products and synthetic compounds including plant extracts with the potential benefits of improved biological activities compared with its reaction substrates. In this study, we investigated the anti-inflammatory activity of Distylium racemosum leaf extract and D. racemosum leaf biorenovation extract (DLB). As a result, DLB inhibited nitric oxide, prostaglandin E2, and inflammatory cytokines including tumor necrosis factor-α, interleukin-6, interleukin-1β at non-toxic concentrations. In addition, DLB significantly inhibited inducible nitric oxide synthase and cyclooxygenase-2 on LPS-treated RAW 264.7 macrophages. Based on these results, we suggest that the DLB could be used as a potent anti-inflammatory agents. It also suggests that the application of biological evolution has potential usefulness to increase the practical value of natural products.

• Journal of Marine Life Science
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• v.6 no.1
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• pp.1-8
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• 2021

In marine ecosystems, the biosynthesis and catabolism of dimethylsulfoniopropionate (DMSP) by marine bacteria is critical to microbial survival and the ocean food chain. Furthermore, these processes also influence sulfur recycling and climate change. Recent studies using emerging genome sequencing data and extensive bioinformatics analysis have enabled us to identify new DMSP-related genes. Currently, seven bacterial DMSP lyases (DddD, DddP, DddY, DddK, DddL, DddQ and DddW), two acrylate degrading enzymes (DddA and DddC), and four demethylases (DmdA, DmdB, DmdC, and DmdD) have been identified and characterized in diverse marine bacteria. In this review, we focus on the biochemical properties of DMSP cleavage enzymes with special attention to DddD, DddA, and DddC pathways. These three enzymes function in the production of acetyl coenzyme A (CoA) and CO₂ from DMSP. DddD is a DMSP lyase that converts DMSP to 3-hydroxypropionate with the release of dimethylsulfide. 3-Hydroxypropionate is then converted to malonate semialdehyde by DddA, an alcohol dehydrogenase. Then, DddC transforms malonate semialdehyde to acetyl-CoA and CO₂ gas. DddC is a putative methylmalonate semialdehyde dehydrogenase that requires nicotinamide adenine dinucleotide and CoA cofactors. Here we review recent insights into the structural characteristics of these enzymes and the molecular events of DMSP degradation.

• Journal of Powder Materials
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• v.26 no.4
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• pp.282-289
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• 2019

Ti has received considerable attention for aerospace, vehicle, and semiconductor industry applications because of its acid-resistant nature, low density, and high mechanical strength. A common precursor used for preparing Ti materials is $TiCl_4$. To prepare high-purity $TiCl_4$, a process based on the removal of $VOCl_3$ has been widely applied. However, $VOCl_3$ removal by distillation and condensation is difficult because of the similar physical properties of $TiCl_4$ and $VOCl_3$. To circumvent this problem, in this study, we have developed a process for $VOCl_3$ removal using Cu powder and mineral oil as purifying agents. The effects of reaction time and temperature, and ratio of purifying agents on the $VOCl_3$ removal efficiency are investigated by chemical and structural measurements. Clear $TiCl_4$ is obtained after the removal of $VOCl_3$. Notably, complete removal of $VOCl_3$ is achieved with 2.0 wt% of mineral oil. Moreover, the refined $TiCl_4$ is used as a precursor for the synthesis of Ti powder. Ti powder is fabricated by a thermal reduction process at $1,100^{\circ}C$ using an $H_2-Ar$ gas mixture. The average size of the Ti powder particles is in the range of $1-3{\mu}m$.

• Journal of Powder Materials
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• v.26 no.3
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• pp.231-236
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• 2019

Ni hydroxides ($Ni(OH)_2$) are synthesized on Ni foam by varying the hexamethylenetetramine (HMT) concentration using an electrodeposition process for pseudocapacitor (PC) applications. In addition, the effects of HMT concentration on the $Ni(OH)_2$ structure and the electrochemical properties of the PCs are investigated. HMT is the source of amine-based $OH^-$ in the solution; thus, the growth rate and morphological structure of $Ni(OH)_2$ are influenced by HMT concentration. When $Ni(OH)_2$ is electrodeposited at a constant voltage mode of -0.85 V vs. Ag/AgCl, the cathodic current and the number of nucleations are significantly reduced with increasing concentration of HMT from 0 to 10 mM. Therefore, $Ni(OH)_2$ is sparsely formed on the Ni foam with increasing HMT concentration, showing a layered double-hydroxide structure. However, loosely packed $Ni(OH)_2$ grains that are spread on Ni foam maintain a much greater surface area for reaction and result in the effective utilization of the electrode material due to the steric hindrance effect. It is suggested that the $Ni(OH)_2$ electrodes with HMT concentration of 7.5 mM have the maximum specific capacitance (1023 F/g), which is attributed to the facile electrolyte penetration and fast proton exchange via optimized surface areas.

• Journal of Ocean Engineering and Technology
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• v.32 no.6
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• pp.466-473
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• 2018

This paper presents an estimation method for the static configuration of a steel lazy wave riser (SLWR) using the dynamic relaxation method applied to estimate the configuration of structures with strong geometric non-linearity. The lumped mass model is introduced to reflect the flexible structural characteristics of the riser. In the lumped mass model, the tensions, shear forces, buoyancy, self-weights, and seabed reaction forces at nodal points are considered in order to find the static configuration of the SLWR. The dynamic relaxation method using a viscous damping formulation is applied to the static configuration analysis. Fictitious masses are defined at nodal points using the sum of the largest direct stiffness values of nodal points to ensure the numerical stability. Various case studies were performed according to the bending stiffness and size of the buoyancy module using the dynamic relaxation method. OrcaFlex was employed to validate the accuracy of the developed numerical method.