• Bulletin of the Korean Chemical Society
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• 제25권9호
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• pp.1307-1308
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• 2004

• Bulletin of the Korean Chemical Society
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• 제11권1호
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• pp.77-78
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• 1990

• Journal of Photoscience
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• 제7권3호
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• pp.87-95
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• 2000

As sunlight not always optimized for every terrestrial plant in terms of light quality, quantity and duration, some plants suffer detrimental effects of sunlight exposure under certain conditions. Photoinhibition of photosynthesis is a typical phenomenon representing harmful light effects, commonly observed in many photosynthetic organisms. It is generally accepted that functional, structural loss of photosystem II complex(PSII) is the primary event of photoinhibition. Accumulating data also suggest that singlet oxygen($^1$O$_2$) is the main toxic species directly involved in it. There are two different views on the specific site and mechanism of $^1$O$_2$ production in the photosynthetic membrane. One of them favors the PSII reaction center, where the primary charge pairs recombination occurs as a prerequisite for the generation of $^1$O$_2$, and the other inclines to photosensitized $^1$O$_2$ formation by a substance located outside PSII. This article describes how we, as the advocators of the latter concept, have arrived at the conclusion that $^1$O$_2$ immediately involved in PSII photodamage is largely generated from the Rieske center of the cytochrome b$_{6}$/f complex and diffuses into PSII, attacking the reaction center subunits.s.

• Journal of Photoscience
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• 제3권2호
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• pp.77-83
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• 1996

Photosensitization via the singlet oxygen ($^1O_2$) mechanism by the binuclear iron-sulfur center, denoted as [2Fe-2S], was investigated, using a highly purified ferredoxin (Fd) preparation from spinach leaves. Since the apoprotein of Fd contains a good number of amino acid residues that are readily reactive with $^1O_2$ and thus interfere with the detection of $^1O_2$ generated from [2Fe-2S], we attempted to deprive the $^1O_2$-sensitive residues of their $^1O_2$-scavenging capacity as much as possible by treating Fd with rose bengal plus 550 nm monochromatic light and thereby photooxidatively degrading these residues. The photochemically modified Fd was found to keep the structural integrity of its Fe-S group virtually unaffected by the treatment. By employing chemical trap method for measurement and examining the kinetic effects of azide and deuterium oxide on the reactions of $^1O_2$ with various trap compounds, we were able to demonstrate that [2Fe-2S] indeed acts as a photosensitizer via $^1O_2$. Further, the minimum quantum yield of $^1O_2$ production by [2Fe-2S] was estimated to be 0.0047.

• Journal of Ginseng Research
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• 제11권2호
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• pp.101-110
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• 1987

인삼(Panax ginseng C.A. Meyer) 엽소병에서 chorophyll의 bleaching 현상에 대한 생리적 반응기작을 조사, 분석한 결과 chorophyll의 bleaching 현상은 singlet oxygen ($^1O_2$)에 의한 photooxidation 과 catalase와 peroxidase의 inactivation에 의한 $H_2O_2$의 autooxidation이었다. Chorophyll의 bleaching 현상에 원인으로 추리된 $H_2O_2$를 농도별로 인삼잎 절편에 처리하였던 바, chorophyll의 함량과 chorophyll의 흡수스펙트럼은 자연광 처리시 유발된 bleaching 현상과 일치하였으며, saponin 첨가로 인하여 bleaching 현상은 현저히 촉진되었다.

• Bulletin of the Korean Chemical Society
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• 제13권2호
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• pp.166-172
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• 1992

Studies have been conducted to explore single electron transfer (SET) induced photocyclization reactions of N-(trimethylsilylmethoxyalkyl)phthalimides(alkyl=E thyl, n-propyl, n-butyl, n-pentyl, and n-octyl). Photocyclizations occur in methanol in high yields to produce cyclized products in which phthalimide carbonyl carbon is bonded to the carbon of side chain in place of the trimethylsilyl group. Mechanism for these photocyclizations involving intramolecular SET from oxygen in the $\alpha-silylmethoxy$ groups to the singlet excited state phthalimide moieties followed by desilylation of the intermediate $\alpha-silylmethoxy$ cation radicals and cyclization by radical coupling are proposed. In contrast, photoreaction of N-(trimethylsilylmethoxyethyl) phthalimide in acetone follows different reaction routes to produce two cyclized products in which carbon-carbon bond formation takes place between the phthalimide carbonyl carbon and the carbon $\alpha$ to silicon and oxygen atoms via triplet carbonyl hydrogen abstraction triplet carbonyl silyl group abstraction pathways. The normal singlet SET pathway dominates these triplet processes for photoreaction of this substance in methanol. The efficient and regioselective cyclization reactions observed for photolysis in methanol represent synthetically useful processes for construction of medium and large ring heterocyclic compounds.

• 한국환경농학회지
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• 제12권3호
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• pp.264-280
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• 1993

The environmental pollutions were a serious problem in Korea recently. So many researcher have studied the effect of environmental pollution on plants and agro-ecosystem, but the basic mechanisms of environmental stresses were various. One of the important mechanisms was oxidative stress caused by active toxic oxygen. The toxic oxygen was generated by several stresses, abnormal temperature, many xenobiotics, air pollutants, water stress, fugal toxin, etc. In the species of toxic oxygen which is primary inducer of oxidative stresses, superoxide, hydrogen peroxide, hydroxyl radical and singlet oxygen were representative species. The scavenging systems were divided into two groups. One was nonenzymatic system and the other enzymatic system. Antioxidants such as glutathione, ascorbic acid, and carotenoid, have the primary function in defense mechanisms. Enzymatic system divided into two groups; First, direct interaction with toxic oxygen(eg. superoxide dismutase). Second, participation in redox reaction to maintain the active antioxidant levels(eg. glutathione reductase, ascorbate peroxidase, etc.).

• Bulletin of the Korean Chemical Society
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• 제24권7호
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• pp.916-920
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• 2003

Photoreactions of N-(2,4-dibromonaphthyl)arenecarboxamides in basic medium result in the intramolecular substituted products, 2-aryl-8-bromonaphthoxazoles in moderate yields and further photoreactions of the products afford the reduced products, 2-arylnaphthoxazoles. These reactions are straightforward for syntheses of naphthoxazole derivatives. Since the intramolecular photosubstitution of the bromoarenecarboxamide by the oxygen of its amide group is more effective than the photoreduction of the substituted product, 2-aryl-8- bromonaphthoxazole in basic medium, the intramolecular substituted product, 2-aryl-8-bromonaphthoxazole can be isolated. A charge-transfered excited singlet state of an imidol form of the 2-bromoarenecarboxamide is involved in the photosubstitution, whereas an excited triplet state of the 2-aryl-8-bromonaphthoxzole is closely involved in the photoreduction.

• Bulletin of the Korean Chemical Society
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• 제6권5호
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• pp.291-295
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• 1985

The efficiency of photosensitization of methyl linoleate (ML) oxidation by N-acetyl-L-trypophan(NAT) and 3-methyl indole(scatole) was markedly enhanced by increased concentration of ML in ethanol solution. The fluorescence intensities of sensitizers were observed to be quenched by ML, indicating that ML interacts with the indole excited singlet state. The inhibition of photosensitization by azide demonstrated a possible role of singlet oxygen in the photosensitization. The steady state kinetic treatment of azide inhibition of photosensitization was expected to show linear increase of reciprocal yield of ML oxidation product vs. reciprocal ML concentration at constant azide concentration, but the actual slope was nonlinear. This indicates another competing reaction involved in the photosensitization, As a possible competing reaction, electron transfer from ML to the excited sensitizer was proposed, since the measured fluorescence quenching rate constant closely resembled electron transfer rate constant determined from ML concentration dependence of oxidation product formation.

• 한국식품저장유통학회지
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• 제20권5호
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• pp.684-690
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• 2013

이 연구의 목적은 소리쟁이 뿌리로부터 얻어진 다양한 용매 추출물의 항산화 활성과 광 피해 억제 효과를 확인하는 것이다. 항산화 활성은 총 페놀 함량 분석과 DPPH 라디칼 소거능, ABTS 라디칼 소거능, 단일항산소 억제 효과로 확인하였다. DPPH 라디칼 소거 활성을 나타내는 $IC_{50}$ 값은 0.005~0.093 mg/mL를 나타내어 소리쟁이 뿌리 추출물의 DPPH 소거 활성이 우수하다는 것을 알 수 있었다. 특히 에틸아세테이트 추출물이 0.005 mg/mL로 높은 DPPH 라디칼 소거 활성을 나타내었는데, 비교 물질로 주로 사용되는 ascorbic acid의 0.010 mg/mL 보다 높은 우수한 항산화력을 가지는 것을 확인하였다. 단일항산소 억제 효과를 나타내는 $QC_{50}$ 값은 부탄올과 에틸아세테이트 추출물의 경우 각각 0.464, 0.365 mg/mL을 나타내어 높은 소거 활성을 보였으며, 대장균 및 DNA와 같은 생체기관의 피해로부터 이들 추출물의 광 피해 억제 효과를 시험한 결과 강한 빛에 의해 야기되는 활성산소의 피해로부터 생물체를 보호해주는 것을 알 수 있었다. 총 페놀 함량도 에틸아세테이트와 부탄올 추출물에서 높은 수준을 나타내었다. 결론적으로 소리쟁이 뿌리의 추출물은 생물체의 산화적 스트레스로부터 야기되는 활성산소를 억제하는 중요한 역할을 하며, 보다 심도 깊은 연구를 진행한다면 새로운 생물 소재로 활용성이 높을 것으로 사료된다.