• 공업화학
• /
• 제25권2호
• /
• pp.227-232
• /
• 2014

전자빔조사와 과산화수소를 사용하여 알지네이트(sodium alginate, SA)를 저분자화 시키는데 1.0, 2.5 MeV의 전자빔 에너지가 이용되었으며, 저분자화 수율($G_s$), 분자량의 제어를 위해 2.5 ~ 20 kGy의 조사량, 0 ~ 4.5%의 과산화수소의 양을 조절하였다. 전자빔조사에 의한 저분자화 알지네이트(depolymerized sodium alginate, DSA)는 주로 1,4-glicoside결합이 끊어지며, C2-C3결합이 끊어지며 생기는 약간의 formate 말단을 가지며, 전자빔 조사 저분자화 저분자 알지네이트 말단(end group)의 화학적 구조가 단순하며, 고분자 알지네이트와 유사한 구조를 가짐을 알 수 있었다. 도입된 전자빔의 에너지와 조사량이 증가하면 알지네이트의 분자량은 감소하였으며, 알지네이트의 농도(2.0w/v%)로 높을 때 저분자화수율이 높았다. 특히 2% 알지네이트 수용액에 20 kGy (2MeV)의 조사량과 1.5% 과산화수소를 도입하였을 때 가장 큰 저분자화 수율($7.919{\times}10^4mol/J$)을 얻을 수 있었다.

• 대한화학회지
• /
• 제15권3호
• /
• pp.109-116
• /
• 1971

The mechanical degradation of poly (${\alpha}$-methyl styrene) in several mixed solvents (toluene-n-butyl alcohol, toluene-sec-butyl alcohol, toluene-kerosene, toluene-methyl ethyl ketone), from $1^{\circ}C to $45^{\circ}C$, was studied using the capillary flow method. The velocity constant of scission reaction (k) and the limited degree of polymerization (g) were compared at the same value of [${\eta}$] at each temperatures. As results, mechanical degradation of polymer in dilute mixed solutions is affected by composition of solvents around the polymer chains.

• Fibers and Polymers
• /
• 제5권3호
• /
• pp.225-229
• /
• 2004

The effect of UV and $^60{Co}$ gamma radiations on the physical and mechanical properties of nylon 6 mono-filaments with different draw ratios has been studied. Specimens were exposed to either up to 25 Mrad of gamma or up to 168 hrs of intense UV irradiation. The results show that nylon mono-filaments exposed to gamma rays, with much higher quantum energy than UV, undergo a larger extent of molecular chain scission. Higher irradiation dose also results in the production of insoluble, macroscopic three-dimensional cross-linked network structure. The amorphous regions with a lower density of cohesive energy (lower molecular orientation) show a higher extent of cross linking reaction whereas amorphous regions with a higher density of cohesive energy (higher orientation) show higher extent of chain scission reaction, irrespective of UV ray or gamma ray irradiation.

• 대한약학회:학술대회논문집
• /
• 대한약학회 2003년도 Proceedings of the Convention of the Pharmaceutical Society of Korea Vol.1
• /
• pp.255.1-255.1
• /
• 2003

During our research program to find DNA strand-scission agents from higher plants, the MeOH extracts of the wood bark of Mucunar birdwoodiana Tutcher. (Leguminosae) exhibited the most potent activity with an IC$\^$50/ value of 4.9 $\mu\textrm{g}$/$m\ell$. Thus, detailed laboratory investigation was performed, and led to the isolation of the known compounds, catechin(1) and epicatechin(2) as the active principles. (omitted)

• 폴리머
• /
• 제31권4호
• /
• pp.278-282
• /
• 2007

컴퓨터 하드디스크 윤활제로 사용되고 있는 perfluoropolyether(PFPE)의 다양한 분해 거동을 살펴보았다. PFPE의 열분해는 $170\;^{\circ}C$에서 시작하여 $450\;^{\circ}C$에서 완전 분해가 일어나며 마모된 하드디스크 슬라이드의 재질인 $Al_2O_3{\cdot}TiC$가 윤활제와 접촉하는 경우, Lewis acid 촉매분해에 의하여 주사슬의 methylene oxide(fluoride)의 절단에 의한 급격한 분해반응과 methylene(fluoride)와 hydroxy 말단기의 열분해로 인하여 $300\;^{\circ}C$에서 분해가 완료됨을 확인하였다. PFPE에 UV가 조사되면 광 분해 영향으로 Lewis acid 촉매분해와는 달리 methylene oxide (fluoride)의 절단 보다는 methylene(fluoride)와 말단기의 절단이 더 촉진되며 이때 생성된 라디칼의 2차 반응에 의한 chain extension에 의하여 PFPE의 분자량이 증가됨을 확인하였다.

• 공업화학
• /
• 제27권6호
• /
• pp.659-663
• /
• 2016

알켄 또는 알킨의 산화 반응이 루테늄 지르코니아 불균일 촉매에 의해 매우 선택적이며 효율적으로 전환되었다. 절단반응을 통해, C-C 이중 결합은 알데히드 관능기로, 삼중 결합은 다이케톤 또는 카르복시산으로 전환되었는데, 다양한 기질들이 $30^{\circ}C$에서 $PhI(OAc)_2$ 산화제와 dichloromethane 및 물(각각 5 mL와 0.5 mL)의 혼합 용매 조건에서 반응이 수행되었다. 사용된 촉매 $Ru(OH)_x/ZrO_2$는 이 절단 반응에 대해 기존의 다른 루테늄 기반 불균일 또는 균일 촉매들보다 더 좋은 활성과 선택성을 보였다. 반응이 진행되는 동안, 제조된 촉매의 기계적인 물성은 안정적이었고, 금속의 침출은 전혀 보이지 않았다. 불포화된 탄화수소들의 산화적 절단에 대해, 합성된 촉매는 여러 번 재사용해도 그 촉매의 성능을 그대로 유지하였다.

• Archives of Pharmacal Research
• /
• 제26권2호
• /
• pp.124-127
• /
• 2003

Four known prenylated flavonoids, artonins E (1) and O (2), artobiloxanthone (3), and cycloartobiloxanthone (4), were isolated from the stem bark of Artocarpus kemando by bioassayguided fractionation using the DNA strand-scission and the KB cytotoxicity assays as monitors. Compounds 1 and 3 exhibited strong DNA strand-scission activity, and all four compounds were found to be cytotoxic.

• Elastomers and Composites
• /
• 제51권1호
• /
• pp.1-9
• /
• 2016

Characterization of the UV oxidation for raw natural rubber (NR) was investigated in controlled conditions through image and FT-IR analysis. The UV oxidation was performed on a thin film of natural rubber coated on a KBr window at 254 nm and room temperature to exclude the thermal oxidation. Before or after exposure to UV light, image of the NR thin film was observed at a right or tilted angle. FT-IR absorption spectra were measured in transmission mode with the UV irradiation time. The UV oxidation of NR was examined by the changes of absorption peaks at 3425, 1717, 1084, 1477, 1377, and $833cm^{-1}$ which were assigned to hydroxyl group (-OH), carbonyl group (-C=O), carbon-oxygen bond (-C-O), methylene group $(-CH_2-)$, methyl group $(-CH_3)$, and cis-methine group $(cis-CCH_3=CH-)$, respectively. During the initial exposure period, the results indicated that the appearance of carbonyl group was directly related to the reduction of cis-methine group containing carbon-carbon double bond (-C=C-). Most of aldehydes or ketones from carbon-carbon double bonds were formed very fast by chain scission. A lot of long wide cracks with one orientation at regular intervals which resulted in consecutive chain scission were observed by image analysis. During all exposure periods, on the other hand, it was considered that the continuous increment of hydroxyl and carbonyl group was closely related to the decrement of methylene and methyl group in the allylic position. Therefore, two possible mechanisms for the UV oxidation of NR were suggested.

• Archives of Pharmacal Research
• /
• 제24권4호
• /
• pp.327-332
• /
• 2001

The antifibrotic effects of hot water extract (WEC), intracellular biopolymer (IPC) and extracellular biopolymers (EPC) from mycelial liquid culture of Cordyceps militaris on liver fibrosis were studied. Liver fibrosis was induced by a bile duct ligation and scission (BDL/S) operation, duration of 4 weeks in rats. In BDL/S rats, the levels of aspartate transaminase (AST), alanine transaminase (ALT), alkaline phosphatase (ALP), total bilirubin in serum and hydroxyproline content in liver were dramatically increased. The WEC or IPC treatment (30mg/kg/day for 4 weeks, p.o.) in BDL/S rats reduced the serum AST, ALT and ALP levels significantly (p<0.01). The EPC treatment (30 mg/kg /day for 4 weeks, p.o.) reduced the serum ALT, AST and ALP levels significantly (p<0.01). Malondialdehyde contents in liver treated with WEC, IPC or EPC were significantly reduced (p <0.05). But Liver hydroxyproline content was decreased only in EPC treated BDL/S rats to 55% that of BDL/S control rats (p < 0.01). The morphological characteristics and expression of alpha smooth muscle like actin in fibrotic liver, which appeared in BDL/S control group were improved in EPC treated fibrotic liver. These results indicate that IPC (30 mg/kg /day for 4 weeks, p.o.) has an antifibrotic effect on fibrotic rats induced by BDL/S.

• Elastomers and Composites
• /
• 제54권2호
• /
• pp.110-117
• /
• 2019

The characterization of the ozone oxidation for raw natural rubber (NR) was investigated under controlled conditions through image and fourier transform infrared (FT-IR) analysis. The ozone oxidation was performed on a transparent thin film of raw NR coated on a KBr window in a dark chamber at $40^{\circ}C$ under low humidity conditions to completely exclude thermal, moisture, or light oxidation. The ozone concentration was set at 40 parts per hundred million (pphm). Before or after exposure to ozone, the image of the thin film for raw NR was observed at a right or tilted angle. FT-IR absorption spectra were measured in the transmission mode according to ozone exposure time. The ozone oxidation of NR was determined by the changes in the absorption peaks at 1736, 1715, 1697, and $833cm^{-1}$, which were assigned to an aldehyde group (-CHO), a ketone group (-COR), an inter-hydrogen bond between carbonyl group (-C=O) from an aldehyde or a ketone and an amide group (-CONH-) of protein, and a cis-methine group ($is-CCH_3=CH-$, respectively. During ozone exposure period, the results indicated that the formation of the carbonyl group of aldehyde or ketone was directly related to the decrement of the double bond of cis-1,4-polyisoprene. Only carbonyl compounds such as aldehydes or ketones seemed to be formed through chain scission by ozone. Long thin cracks with one orientation at regular intervals, which resulted in consecutive chain scission, were observed by image analysis. Therefore, one possible two-step mechanism for the formation of aldehyde and ketone was suggested.