• The Korean Journal of Physiology and Pharmacology
• /
• 제5권1호
• /
• pp.87-92
• /
• 2001

Carbon monoxide (CO) binds to soluble guanylate cyclase to lead its activation and elicits smooth muscle relaxation. The vascular tissues have a high capacity to produce CO, since heme oxygenase-2 (HO-2) is constitutively expressed in endothelial and smooth muscle cells, and HO-1 can be greatly up-regulated by oxidative stress. Moreover, the substrate of HO, heme, is readily available for catalysis in vascular tissue. Although the activation of heme oxygenase pathway under various stress conditions may provide a defence mechanism in compromised tissues, the specific role of HO-1-derived CO in the control of aortic contractility still remains to be elucidated. The present study was done to determine the effect of HO-1 induction on the aortic contractility. Thus, the effects of incubation of aortic tissue with S-nitroso-N-acetylpenicillamine (SNAP) for 1 hr on the aortic contractile response to phenylephrine were studied. The preincubation with SNAP resulted in depression of the vasoconstrictor response to phenylephrine. This effect was restored by HO inhibitor or methylene blue but not by NOS inhibitor. The attenuation of vascular reactivity by preincubation with SNAP was also revealed in endothelium-free rings. $AlF4^--evoked$ contraction in control did not differ from that in SNP-treated group. These results suggest that increased production of CO was responsible for the reduction of the contractile response to phenylephrine in aortic ring preincubated with SNAP and this effect of SNAP was independent on endothelium.

• 대한화학회지
• /
• 제46권3호
• /
• pp.187-193
• /
• 2002

온도 (10, 15, 20, $25^{\circ}C$)와 압력(1, 200, 500, 1000 bar)변화에 따라 p-치환염화벤조일류 ($p-CH_3$, p-H, $p-NO_2$ )와 6-클로로퀴놀린(6-chloroquinoline)의 반응을 아세토니트릴 용매내에서 전기전도도법에 의하여 속도상수 ($k_2$)를 구하였다. 이로부터 여러활성화파라미터-활성화에너지(Ea, ${\Delta}V^{\neq}$, ${\Delta}H^{\neq}$,${\Delta}S^{\neq}$, ${\Delta}G^{\neq}$) 를 구하였으며 또한 기질의 치환기 효과에 따른 Hammentt 반응상수 p를 구하였다. 속도상수는 온도와 압력 증가에 따라 증가하였으며 친핵체인 6-chloroquinoline과 기질에 전자 받게 치환기 ($p-NO_2$)가 치환된 경우 더욱 증가하였다. 이 때 활성화부피(${\Delta}V^{\neq}$), 활성화엔트로피(${\Delta}S^{\neq}$)는 모두 음의 값으로 나타났으며 모든 압력 조건에 따라서 p는 양의 값을 나타내었다. 이러한 속도론적인 연구 결과 전반적인 반응은 $S_N2$반응메카니즘을 따르며, 압력이 증가함에 따라 결합형성이 진전되어지는 반응 메카니즘으로 진행 됨을 알 수 있었다.

• 대한화학회지
• /
• 제47권3호
• /
• pp.206-212
• /
• 2003

온도(10, 15, 20, $25^{\circ}C$)와 압력(1, 200, 500, 1000 bar) 변화에 따라 p-치환염화벤조일류$(p-CH_3,\;p-H,\;p-NO_2)$와 퀴놀린 유도체(quinoline, 6-chloroquinoline)의 반응을 아세토니트릴 용매내에서 전기전도도법에 의하여 속도상수$(k_2)$를 구하였다. 이로부터 여러 활성화파라미터-활성화에너지$(Ea,\;{\Delta}V^{\neq},\;{\Delta}H^{\neq},\;{\Delta}S^{\neq}, \;{\Delta}G^{\neq})$를 구하였으며, 또한 Hammett반응상수 ${\rho}_X$와 기질의 치환기 효과에따른 ${\rho}_Y$를 구하였다. 속도상수는 온도와 압력 증가에 따라 증가하였으며, 친핵체인 quinoline과 기질에 전자 받게 치환기$(p-NO_2)$가 치환된 경우 더욱 증가 하였다. 이때 활성화부($({\Delta}V^{\neq})$, 활성화엔트로피$({\Delta}S^{\neq})$는 모두 음의 값으로 나타났으며, 모든 압력 조건에 따라서 친핵체의 치환기 효과 ${\rho}_X$는 음의 값을 ${\rho}_Y$는 양의 값을 나타내었다. 이러한 속도론적인 연구 결과 전반적인 반응은 $S_N2$ 반응메카니즘을 따르며, 압력이 증가함에 따라 결합형성이 진전되어지는 반응 메카니즘으로 진행됨을 알 수 있었다.

• 한국응용약물학회:학술대회논문집
• /
• 한국응용약물학회 1994년도 제2회 추계심포지움
• /
• pp.69-80
• /
• 1994

Although ureases play important roles in microbial nitrogen metabolism and in the pathogenesis of several human diseases, little is known of the mechanism of metallocenter biosynthesis in this Ni-Containing enzyme. Klebsiella aerogenes urease apo-protein was purified from cells grown in the absence of Ni. The purified apo-enzyme showed the same native molecular weight, charge, and subunit stoichiometry as the holo-enzyme. Chemical modification studies were consistent with histidinyl ligation of Ni. Apo-enzyme could not be activated by simple addition of Ni ions suggesting a requirement for a cellular factor. Deletion analysis showed that four accessory genes (ureD, ureE, ureF, and ureG) are necessary for the functional incorporation of the urease metallocenter. Whereas the $\Delta$ureD, $\Delta$ureF, and $\Delta$ureG mutants are inactive and their ureases lack Ni, the $\Delta$ureE mutants retain partial activity and their ureases possess corresponding lower levels of Ni. UreE and UreG peptides were identified by SDS-polyacrylamide gel comparisons of mutant and wild type cells and by N-terminal sequencing. UreD and UreF peptides, which are synthesized at ve교 low levels, were identified by using in vitro transcription/translation methods. Cotransformation of E. coli cells with the complementing plasmids confirmed that ureD and ureF gene products act in trans. UreE was purified and characterized. immunogold electron microscopic studies were used to localize UreE to the cytoplasm. Equilibrium dialysis studies of purified UreE with $^{63}$ NiC1$_2$ showed that it binds ～6 Ni in a specific manner with a $K_{d}$ of 9.6 $\pm$1.3 $\mu$M. Results from spectroscopic studies demonstrated that Ni ions are ligated by 5 histidinyl residues and a sixth N or O atom, consistent with participation of the polyhistidine tail at the carboxyl termini of the dimeric UreE in Ni binding. With these results and other known features of the urease-related gene products, a model for urease metallocenter biosynthesis is proposed in which UreE binds Ni and acts as a Ni donor to the urease apo-protein while UreG binds ATP and couples its Hydrolysis to the Ni incorporation process.ouples its Hydrolysis to the Ni incorporation process.s.

• 한국주조공학회지
• /
• 제6권1호
• /
• pp.12-19
• /
• 1986

This study was undertaken to understand the formation mechanism of the hard spots in high strength brass. To investigate the behavior of the hard spots in the isothermal liquid state with varying silicon content, the rapidly quenched specimens were obtained by suctioning the melt into the silica tube and water quenching. To examine the growth process of the hard spots with holding time, the unidirectional solidification technique was used. The results of this study are summarized as follows: 1) With the addition of Fe in order to get the effects of grain refinement in high strength brass, the two different type of Fe-rich phases are occurred, which are defined as dendritic and globular phase. The chemical composition of the globular phase was different from that of the dendritic phase in that the globular phase contained Si. 2) With increasing Si content, the Fe-rich phase had a tendency to form globular phase. 3) As the holding time increased in the liquid state, globular was also prone to coalesce. The further growth of globular phase to large size was due to reducing the interfacial energy. 4) The primary phase of copper alloy was nucleated preferentially on the dendritic phase. It was noticeable that the dendritic phase acted as a grain refiner. However, the agglomerate (hard spots) which was composed of the globular phase decreased the mechanical properties of high strength brass. 5) Once the hard spots formed in the high strength brass casting, it was very difficult to remove them. This is due to the fact that their meting temperature is higher than the pouring temperature of high strength brass.

• Computers and Concrete
• /
• 제20권2호
• /
• pp.205-214
• /
• 2017

The Hydraulically driven test system and ${\Phi}100mm$ split Hopkinson pressure bar(SHPB) test device were employed to research the quasi-static and dynamic mechanical properties of concrete specimens which has been immersed for 60 days in sodium sulfate (group S1) and sodium chloride (group S2) solution, the evolution of their mass during corrosive period was explored at the same time, and the mechanism of performances lost was analyzed from the microscopic level by using scanning electron microscope. Results of the experimental indicated that: their law of mass both presents the trend of continuous rising during corrosive period, and it increases rapidly on the early days, the mass growth of group S1 and group S2 in first 7 days are 76.78% and 82.82% of their total increment respectively; during the corrosive period, the quasi-static compressive strength of specimens in two groups are significantly decreased, both of which present the trend of increase first and then decrease, the maximum growth rate of group S1 and group S2 are 7.52% and 12.71% respectively, but they are only 76.23% and 82.84% of specimens which under normal environment (group N) on day 60; after immersed for 60 days, there were different decrease to dynamic compressive strength and specific energy absorption, and so as their strain rate sensitivities. So the high salinity environment has a significant effect of weaken the quasi-static and dynamic mechanical performance of concrete.

• Corrosion Science and Technology
• /
• 제15권5호
• /
• pp.226-236
• /
• 2016

316L stainless steels have been widely used in many engineering fields, because of their high corrosion resistance and good mechanical properties. However, welding or aging treatment may induce intergranular corrosion and stress corrosion cracking etc. Since these types of corrosion are closely related to the formation of chromium carbide in grain boundaries, the alloys are controlled by methods such as the lowering of carbon content, solution heat treatment. This work focused on the intergranular corrosion mechanism of slightly-sensitized and Ultrasonic Nano-crystal Surface Modification (UNSM)-treated 316L stainless steel. Samples were sensitized for 1, 5, and 48 hours at $650^{\circ}C$ in $N_2$ gas atmosphere. Subsequently UNSM treatments were carried out on the surface of the samples. The results were discussed on the basis of the sensitization by chromium carbide and carbon segregation, the residual stress and grain refinement. Even though chromium carbide was not precipitated, the intergranular corrosion rate of 316L stainless steel was drastically increased with aging time, and it was confirmed that the increased intergranular corrosion rate of slightly-sensitized (not carbide formed) 316L stainless steel was due to the carbon segregation along the grain boundaries. However, UNSM treatment improved the intergranular corrosion resistance of aged stainless steels, and its improvement was due to the reduction of carbon segregation and the grain refinement of the outer surface, including the introduction of compressive residual stress.

• 대한한방소아과학회지
• /
• 제35권4호
• /
• pp.96-111
• /
• 2021

Objectives The purpose of this study is to look for pathological mechanism of disease development caused by Taedok, by studying whether stress and diet in pregnant ICR mice affect the intestinal flora and IgA (Immunoglobulin A) concentration. Methods The mice were divided into 4 groups (n=5 per group) based on the concept of Taedok: the control group (G1), stress group (G2), capsaicin diet group (G3), high fat diet group (G4). We collected and analyzed intestinal flora from maternal feces and cecal flora from neonatal mice by group. Then, IgA concentration in the maternal feces and sIgA (secretory Immunoglobulin A) concentration in the cecal contents of newborn mice were analyzed. In addition, serum corticosterone was analyzed before and after stress application. Results Changes in maternal intestinal flora and neonatal mice cecal flora by stress and diet were observed. There were no significant changes in the IgA concentration in maternal feces and the sIgA concentration in the cecal contents of neonatal mice. No significant changes compared to the control group were observed between groups before and after applying stress. However, when comparing within one subject, a significant increase was confirmed after stress application in the stress group (G2). Conclusions Based on the results, we observed stress and diet in pregnant mice affect the intestinal flora of maternal and neonatal. We were able to interpret the pathological mechanism of Taedok based on the principle of interaction between mother and newborn intestinal flora.

• 한국방재학회:학술대회논문집
• /
• 한국방재학회 2008년도 정기총회 및 학술발표대회
• /
• pp.413-416
• /
• 2008

Recently, the results of vital tissue test showed that nitrosodimethylamine (NDMA) as a disinfection by-product (DBP), could be regarded as a carcinogen because a tumor was observed in organs. U.S.EPA indicated 0.7 ng/L as exposure concentration of NDMA based on a risk assessment target with a lifetime cancer risk of $10^{-6}$. Several recent studies have shown that UV oxidation could remove NDMA. However, UV oxidation is uneconomical and can reform NDMA after treating. In addition, the treatment mechanism of adsorption has not been founddue to the uncertainty of NDMA pathway. In addtion, NDMA has a radioisotope $^{14}C$-labeled which can be analyzed at low concentration of NDMA by Liquid Scintillation Counter (LSC). This study has investigated NDMA determination using LSC at an extremely low range from 1 to 100 ng/L and NDMA removal by powdered activated carbon (PAC) adsorption. For $^{14}C$-NDMA by LSC, the highest correlation over 99% between count number and NDMA concentrationwas obtained with possibility of $^{14}C$-NDMA concentration up to 1 ng/L. In the presence of PAC ranging from 50 to 10,000 mg/L, $^{14}C$-NDMA was removed from 18% to 97% for Sigma-Aldrich corporation (S-A co.) and from 9% to 93% by PAC for Daejung corporation (Dj co.). Hence it was found that the removal efficiency by PAC adsorption could vary depending on PAC types from different companies. For PAC adsorption capacity of $^{14}C$-NDMA using the Freundlich isotherm, $K_f$ and 1/n of PAC from S-A co. were $2.67\times10^{-3}$ ng/mg and 1.009, while those of PAC from Dj co. were $1.30\times10^{-3}$ ng/mg and 0.994, respectively. Thus, PAC from S-A co. showed twice higher adsorption capacity than Dj co.

• 대한화학회지
• /
• 제29권5호
• /
• pp.465-471
• /
• 1985

메탄올-아세토니트릴, 메탄올-아세톤, 에탄올-아세토니트릴 및 에탄올-아세톤의 이성분 혼합용매에서 2-염화 안트라퀴논 카르보닐의 가용매분해반응 속도상수를 전기전도도법으로 측정하였다. 메탄올-아세토니트릴 이성분 혼합용매계에서는 메탄올의 몰분율 $X_{MeOH}$ = 0.73∼0.81에서, 메탄올-아세톤 이성분 혼합용매계에서는 메탄올의 몰분율 $X_{MeOH}$ = 0.83에서 각각 최대 반응속도 현상이 나타났다. Kivinen 관계식과 Grunwald-Winstein 관계식등의 적용으로 부터 본 반응이 $S_N2$형태의 반응메카니즘으로 진행함을 알 수 있었다. Taft의 분광용매화 관계식의 적용으로 부터 메탄올-아세토니트릴 및 메탄올-아세톤 혼합용매계에서는 용매의 수소결합주게효과(${\alpha}$)와 극성-편극성 효과가 중요하게 작용함을 알 수 있었으며, 에탄올의 이성분 혼합용매계에서는 용매의 수소결합주게 효과만 이 반응에 크게 기여함을 알 수 있었다.