• KSBB Journal
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• v.23 no.6
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• pp.519-524
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• 2008

Monacolin-K is a strong anti-hypercholesterolemic agent produced by Monascus sp. via polyketide pathway. High-yielding mutants of monacolin-K were developed through rational screening strategies adopted based on understanding of monacolin-K biosynthetic pathway. Through the experiments for investigating various amino acids as putative precursors for the monacolin-K biosynthesis, it was found that production level of monacolin-K was remarkably increased when optimum amount of cysteine was supplemented into the production medium. We suggested that these phenomena might be related to the special roles of SAM (S-adenosyl methionine), a putative methyl group donor in the biosynthetic pathway of monacolin-K, demonstrating close interrelationship between SAM-synthesizing primary metabolism and monacolin-K synthesizing secondary metabolism. Namely, increase in the intracellular amount of SAM derived from the putative precursor, cysteine which was extracellularly supplemented into the production medium might contribute to the significant enhancement in the monacolin-K biosynthetic capability of the highly mutated producers. On the basis of these assumptions derived from the above fermentation results, we decided to construct efficient expression vectors harboring SAM synthetase gene (metK) cloned from A. nidulans, with the hope that increased intracellular level of SAM could lead to further enhancement in the monacolin-K production through overcoming a rate-limiting step associated with monacolin-K biosynthesis. Hence, in order to overcome the plausible rate-limiting step associated with monacolin-K biosynthesis by increasing intracellular level of SAM, we transformed the producer mutants with an efficient expression vector harboring gpdA promoter of the producer microorganism, and metK gene. Notably, from the resulting various transformants, we were able to screen a very high-yielding transformant which showed approximately 3.3 fold higher monacolin-K productivity than the parallel nontransformed mutants in shake flask cultures performed under the identical fermentation conditions.

• Bulletin of the Korean Chemical Society
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• v.30 no.9
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• pp.2077-2082
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• 2009

The conformational and electronic properties of 2-cyano-3-(thiophen-2-yl)acrylic acid (TCA) in analogues used as sensitizers in dye-sensitized solar cells was examined using density functional theory (DFT) and natural bond orbital analysis methods. A relaxed potential energy surface scan was performed on NKX-2677 by rotating the C-C bond between the thiophene and cyanoacrylic acid which yielded activation energy barriers of about 13 kcal/mol for both E and Z configurations. The most stable conformation of all the analogues was E-180 except for NKX-2587 which has an electrostatic repulsion between the oxygen of the coumarin and the nitrogen of the cyanoacrylic acid. The increase in the electron delocalization between the thiophene and cyanoacrylic acid influences the stability for most of the analogues. But for NKX-2600, even though there was a greater deviation from the planarity of TCA, the stability was mainly due to the presence of a weak hydrogen bond between the hydrogen of the methyl group of the amine located in the donor moiety and the nitrogen of the cyanoacrylic acid. The vertical excitation energies of the analogues containing TCA were calculated by time-dependent DFT method. There were slight differences in its vertical excitation energies but the oscillator strengths vary significantly especially in the case of NKX-2600.

• Journal of Photoscience
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• v.10 no.1
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• pp.9-20
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• 2003

Recent studies on the photoreactivity of l,4-unsaturated systems have changed some ideas that were firmly established in this area of research for many years. Thus, we have described the first examples of 2-aza-di-$\pi$-methane (2-ADPM) rearrangements promoted by triplet-sensitization and by single electron transfer (SET) using electron-acceptor sensitizers. These reactions afford N-vinylaziridine and cyclopropylimine photoproducts in the first examples of di-$\pi$-methane processes that yield three-membered ring heterocycles. l-Aza-1,4-dienes also undergo SET-promoted l-aza-di-$\pi$-methane (l-ADPM) rearrangements via radical-cation intermediates using electron acceptor sensitizers. In some cases, alternative cyclizations yielding different carbocycles and heterocycles have been observed. The l-ADPM and di-$\pi$-methane (DPM) reactions also occur via radical-anion intermediates on irradiation using electron donor sensitizers. On the other hand, the photoreactivity reported for $\beta$,${\gamma}$-unsaturated aldehydes for many years was decarbonylation to the corresponding alkenes. However, our studies demonstrate that these compounds undergo the oxa-di-$\pi$-methane (ODPM) rearrangement with high chemical and quantum efficiency. A comparison of the photochemical reactivity of $\beta$,${\gamma}$-unsaturated aldehydes and corresponding methyl ketones has shown that the ketones do not undergo the ODPM rearrangement while the corresponding aldehydes are reactive by this pathway. Monosubstituted $\beta$,${\gamma}$-unsaturated aldehydes at C-2 undergo the ODPM rearrangement yielding the corresponding cyclopropane carbaldehydes diastereoselectively. Finally, we have described the first examples of reactions, similar to the well know Norrish Type I process, which take place in the triplet excited state of $\beta$,${\gamma}$-unsaturated carbonyl compounds by excitation of the C-C double bond instead of the carbonyl group.

• Polymer(Korea)
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• v.25 no.4
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• pp.558-567
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• 2001

The syntheses of thermal latent catalysts have been carried out by modifying the substituent of pyrazinium salts. The thermal latent properties and cure behaviors of difunctional epoxy resin (diglycidylether of bisphenol-A, DGEBA) with 1 wt% of catalyst as an initiator were investigated by dynamic DSC method. As a result, the synthesized catalysts showed the good latent thermal properties in epoxy system. With increasing the basicity of substituted catalyst, the cure temperature and activation energy of epoxy system were increased, whereas the activity was decreased. This was probably due to the fact that the activity and cure behavior were controlled by ring strain and basicity of substituent. Consequently, the catalyst activity modified by methyl group as an electron donor was decreased in increasing of basicity in an initiation step of epoxy cure system. This is due to a decreasing of stabilities of both leaving group of pyrazinium salts and benzyl cation. However, the catalyst activity modified by cyano group as an electron acceptor was increased in increasing the stability of benzyl cation resulting from organic effects and resonance.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.63 no.1
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• pp.25-34
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• 2018

This study was conducted to investigate the germination and proteome profile characteristics of wheat seeds treated under various concentrations of abscisic acid (ABA). After-ripening, the seeds of three wheat cultivars (Baegjoong, Keumkang, and Uri) showing different levels of dormancy were used. Germination index and germination rate of the cultivars was higher than 0.95% and 98%, respectively, and these were not significantly different under 0, 10, 30, and $50{\mu}M$ ABA at 7 d after germination. However, the growth of the shoot and radicle was significantly inhibited at 10, 30, and $50{\mu}M$ ABA compared to that at $0{\mu}M$ ABA. Mean ABA content of the embryos of seeds germinated at 0 and $50{\mu}M$ ABA for 7 d was 0.8 and $269.0ngmg^{-1}DW$, respectively. Proteins extracted from embryos germinated for 4 d were analyzed by two-dimensional gel electrophoresis, and proteins showing a difference of 1.5-fold or greater in their spot volume relative to that of $0{\mu}M$ ABA were identified. The expression of four protein spots increased at $50{\mu}M$ ABA and two protein spots were detected only at $50{\mu}M$ ABA; these six proteins were all identified as globulin types. Conversely, the expression of three protein spots decreased at $50{\mu}M$ ABA and were identified as cytosolic glutamine sysnthetase, isocitrate dehydrogenase, and S-adenosylmethionine synthetase 2. In conclusion, ABA did not inhibit the germination rate regardless of pre-harvest sprouting characteristics of the cultivars. However, the growth of the shoot and radicle was significantly inhibited by ABA, most likely through the down regulation of glutamine, methyl group donor, and polyamines biosynthesis, among others, while accompanied by globulin accumulation in the embryos.