• The Transactions of The Korean Institute of Electrical Engineers
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• v.59 no.10
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• pp.1832-1838
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• 2010

Aging of transformer insulating material in natural ester insulating oil is compared to that in conventional transformer oil. Aging of insulating paper and insulating oil have been studied by performing accelerated thermal aging test. Sealed aging test vessels containing cooper, laminated core, Kraft paper and insulating oil(natural oil or mineral oil) were aged at $140^{\circ}C$ for 500, 1000, 1500 and 2000 hours. Insulating oils after aging are investigated with total acid number, breakdown voltage and viscosity. Also, degradation of insulating paper after aging is determined using breakdown voltage and mechanical strength. Accelerated aging studies demonstrate a slower aging rate for natural ester insulating oil compared to the rate for conventional mineral oil.

• Natural Product Sciences
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• v.4 no.1
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• pp.45-50
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• 1998

Seven triterpenoid saponins such as oleanolic acid 28-O-{\beta}-D-glucopyranosyl$ ester, hederagenin $28-O-{\beta}-D-glucopyranosyl$ ester, chikusetsusaponin IVa, udosaponin A, salsoloside C, udosaponins F and C were isolated from the aerial parts of Aralia continentalis, among which two $28-O-{\beta}-D-glucopyranosyl$ esters of oleanolic acid and hederagenin are isolated for the first tome from this plant. These results suggested that the chemical components of Korean Dokwhal are practically identical to those of japanese Udo supporting the chemotaxonomical point of view.

• Proceedings of the PSK Conference
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• 2003.04a
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• pp.135.1-135.1
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• 2003

We have previously reported three new oleanene-type glycosides and kudzusaponin $A_3$ methyl ester and subproside II methyl ester from the roots of Echinosophora koreensis. Further study has now led to the isolation of three known oleanen-type glycosides. sophoraflavoside I, azukisaponin V, and kudzusaponin $SA_3$ as their methyl esters. The structures of theses compounds were characterized by spectroscopic and chemical methods.

• Journal of the Korean Magnetic Resonance Society
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• v.20 no.2
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• pp.41-45
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• 2016

Chemical investigation of a marine-derived fungus, Penicillium sp. 108YD020, resulted in the discovery of six bile acid derivatives, glycocholic acid (1), glycocholic acid methyl ester (2), cholic acid (3), glycochenodeoxycholic acid (4), glycodeoxycholic acid methyl ester (5), and cholic acid methyl ester (6). The structures of six bile acid derivatives 1-6 were determined by the detailed analysis of 1D, 2D NMR and LC-MS data, along with chemical methods and literature data analysis.

• Journal of Plant Biology
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• v.39 no.4
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• pp.273-278
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• 1996

Arabidopsis mutants deficient in flavonoid and sinapate ester (tt4 and fah1-7, respectively) were evaluated in vivo and in vitro to study the possible role of flavonoid compounds in pollen tube growth. In vivo, we investigated pollen tube growth in the pistils of the mutants and wild type(Ler). The growth of pollen tubes was significantly different among the three genotypes. In the fal1-7 pistils, the tubes grew to a greater length relative to those of the wild type or tt4. To examine in vitro pollen tube growth, a solid medium was devised for pollen germination and subsequent growth. In vitro, the identical result was obtained; fahl-7 pollens developed the longest tubes and elongated most rapidly. Therefore, the growth response of pollen tubes to phenolic compounds was examined by adding quercetin or sinapate ester in various concentrations to the media. Quercetin enhanced both germination rate and tube growth in the pollens of the mutants and the wild type, especially in tt4. In contrast, sinapate ester inhibits pollen germination and pollen tube growth in three genotypes. These results suggest that flavonoids and related phenolic compounds have physiological role in the plant reproductive system.

• Journal of Electrical Engineering and Technology
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• v.12 no.6
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• pp.2333-2341
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• 2017

Mineral oils are commonly used as transformer insulation oils but these oils are obtained from non-renewable and non-sustainable sources, which is highly undesirable. For this reason, natural ester oils are now being used in replacement of mineral oils because of their good biodegradability, high cooling stability, good oxidation stability and excellent insulation performance. Nanotechnology has gained prominence in both academic and industrial fields over the years and it has been shown in previous studies that nanoscale materials are useful for transformers due to their favourable dielectric properties. The objective of this study is to compare the AC breakdown voltage and viscosity of natural ester oil with three types of nanofluids. The natural ester oil-based nanofluids are prepared by mixing palm fatty acid ester (PFAE) oil with three types of nanoparticles at a concentration of 0.01 g/l: (1) $Fe_3O_4$ conductive nanoparticles, (2) $TiO_2$ semi-conductive nanoparticles and (3) $Al_2O_3$ insulating nanoparticles. The AC breakdown voltage of the oil samples is analysed using Weibull statistical analysis and the results reveal that the PFAE oil-based $Fe_3O_4$ nanofluid gives exceptional dielectric performance compared to other oil samples, whereby the AC breakdown voltage increases by 43%. It can be concluded that the PFAE oil-based $Fe_3O_4$ nanofluid is a promising dielectric liquid to substitute mineral oils.

• Natural Product Sciences
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• v.15 no.4
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• pp.234-240
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• 2009

Phytochemical investigation of the MeOH extract of the aerial parts of Bistorta manshuriensis resulted in the isolation of two cerebrosides, two lactams, six phenolic compounds and seven flavonoids. Their chemical structures were characterized by spectroscopic methods to be pinelloside (1), soyacerebroside I (2), pterolactam (3), 5-hydroxypyrrolidine-2-one (4), vanillic acid (5), caffeic acid methyl ester (6), protocatechuic acid (7), caffeic acid (8), 3,5-di-O-caffeoyl quinic acid methyl ester (9), chlorogenic acid methyl ester (10), avicularin (11), afzelin (12), quercetin (13), isoorientin (14), quercetin 3-O-${\beta}$-D-glucoside (15), quercitrin (16), and luteolin (17). The isolated compounds (1 - 4, 7, 12, 14) were isolated for the first time from this plant source and the compounds 1 - 4, 9 and 10 were first reported from the genus Bistorta. Compound 17 exhibited moderate cytotoxicity and compound 6 exhibited weak cytotoxicity against four human cancer cell lines in vitro using an SRB bioassay.

• Natural Product Sciences
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• v.14 no.1
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• pp.37-46
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• 2008

From the 70% EtOH extract of the roots of Astragalus membranaceus (Leguminosae), fifteen saponins were isolated and identified as astragaloside I (1), isoastragaloside II (2), astragaloside II (3), agroastragaloside I (4), cyclogaleginoside B (5), cycloaraloside A (6), brachyoside B (7), agroastragaloside II (8), astragaloside III (9), astragaloside IV (10), astramembranoside A (11), astramembranoside B (12), cylocanthoside E (13), cyclounifolioside B (14) and azukisaponin V methyl ester (15) by spectroscopic methods. Ten compounds 1 - 3, 5 - 7, 9 - 11 and 14 have cycloastragenol as an aglycon, and four compounds 4, 8 , 12, and 13 have cyclocanthogenin as an aglycon. The hairy roots of A. membranaceus were shown to produce previously unreported cycloartane-type saponins such as agroastragalosides I (4) and II (8) and cycloastragenol $3-O-{\beta}-D-xyloside$ (5), together with the known saponins. This is the first report of these saponins (4, 5, and 8) from the intact plant. Although the occurrence of the oleanane-type triterpene saponin, azukisaponin V methyl ester (15), in Astragalus plants has been demonstrated by others, this is the first report of the azukisaponin V methyl ester (15) from the Astragalus plants.

• Bulletin of the Korean Chemical Society
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• v.19 no.6
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• pp.689-695
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• 1998

Carbobenzoxy-alanyl-thiaarginine benzyl ester and carbobenzoxy-alanyl-thialysine benzyl ester were synthesized in solution. Kinetic studies were carried out using three different analytical methods, semi-classical method, progress curve analysis and competitive spectrophotometry. In competitive spectrophotometry, carbobenzoxy-valyl-glycyl-arginyl-p-nitroaniline was used as a detector. Kinetic constants such as $K_m$ and $V_{max}$ measured by competitive spectrophotometry are almost the same as those values measured by semi-classical method. Colorimetric Ellman's assays showed the thio-peptido mimetics to be a suitable substrates for trypsin. Kinetic studies with trypsin gave $K_m$ of 2.33 mM and $k_{cat}$ of $1.50{\times}10^5\;min^{-1}$ for carboxy-alanyl-thiaarginine benzyl ester and $K_m$ of $3.41{\times}10^{-3}\; Mm\; and\; k_{cat}\; of\; 520{\times}102\; min^{-1}$ for carbobenzoxy-alanyl-thialysine benzyl ester, respectively. Kinetic constants $(K_m=2.04{\times}10^{-2}\; mM, K_{cat}=4.42{\times}10^3 \;min^{-1})$ for natural substrate, carbobenzoxy-alanyl-lysine benzyl ester, were also evaluated by competitive spectrophotometry in order to compare the mode of binding on trypsin.

• Korean Journal of Pharmacognosy
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• v.19 no.2
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• pp.99-101
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• 1988

3, 4-Dihydroxybenzoic acid and it's artefact ethyl ester obtained from Acanthopanax senticosus Max. were tested ex vivo and found to show mild inhibitory activities against rat platelet aggregation.