• 대한화학회지
• /
• 제36권1호
• /
• pp.147-156
• /
• 1992

${\alpha}-{\beta}-,{\gamma}$-알루미나 및 MgO를 담체로 사용하여 담지된 납산화물 촉매를 제조하였다. 담지된 납산화물 촉매상에서 메탄의 $C^{2+}$ 탄화수소로의 전환반응은 MgO 담지촉매에서 $C^{2+}$ 선택도가 최대로 얻어졌으며, ${\gamma}$-알루미나 담지 PbO 촉매에서는 $CO_2$ 선택도가 높았다. 그리고 ${\alpha}$-알루미나 담지촉매에서는 중간정도의 활성이 얻어졌으며, ${\beta}$-알루미나 담지촉매에서는 활성이 거의 나타나지 않았다. 이러한 반응특성은 촉매의 격자산소의 활성에 크게 의존하였으며, 또한 격자 산소의 활성은 담체와 산화물간의 상호작용과 담체의 성질에 영향받았다. 특히 MgO 담지 촉매에서는 X-선 회절분석에서 여타의 담체에서보다 PbO 산화물의 (002)면의 피크 세기가 (111)면의 세기에 비해 훨씬 크게 나타난 것으로 볼 때 메탄의 Oxidative Coupling 반응에서의 표면산화물-담체 상호작용(SOSI)의 한 예로 여겨졌다.

• Journal of Microbiology and Biotechnology
• /
• 제13권4호
• /
• pp.501-508
• /
• 2003

Artificial coupling of one enzyme with another can provide an efficient means for the production of industrially important chemicals. Xylose reductase has been recently discovered to be useful in the reductive production of xylitol. However, a limitation of its in vitro or in vivo use is the regeneration of the cofactor NAD(P)H in the enzyme activity. In the present study, an efficient process for the production of xylitol from D-xylose was established by coupling two enzymes. A NADH-dependent xylose reductase (XR) from Pichia stipitis catalyzed the reduction of xylose with a stoichiometric consumption of NADH, and the resulting cofactor $NAD^+$ was continuously re-reduced by formate dehydrogenase (FDH) for regeneration. Using simple kinetic analyses as tools for process optimization, suitable conditions for the performance and yield of the coupled reaction were established. The optimal reaction temperature and pH were determined to be about $30^{\circ}C$ and 7.0, respectively. Formate, as a substrate of FDH, affected the yield and cofactor regeneration, and was, therefore, adjusted to a concentration of 20 mM. When the total activity of FDH was about 1.8-fold higher than that of XR, the performance was better than that by any other activity ratios. As expected, there were no distinct differences in the conversion yields of reactions, when supplied with the oxidized form $NAD^+$ instead of the reduced form NADH, as a starting cofactor for regeneration. Under these conditions, a complete conversion (>99%) could be readily obtained from a small-scale batch reaction.

• Bulletin of the Korean Chemical Society
• /
• 제35권3호
• /
• pp.833-838
• /
• 2014

The energy- and time-dependent branching to the competing dissociation paths are studied by theory for coupled unimolecular dissociations of the o-, m-, and p-chlorotoluene radical cations to $C_7{H_7}^+$ (benzylium and tropylium). There are four different paths to $C_7{H_7}^+$, three to the benzylium ion and one to the tropylium ion, and all of them are coupled together. The branching to the multiple paths leads to the multiexponential decay of reactant with the branching ratio depending on both internal energy and time. To gain insights into the multipath branching, we study the detailed kinetics as a function of time and internal energy on the basis of ab inito/RRKM calculations. The number of reaction steps to $C_7{H_7}^+$ is counted for each path. Of the three isomers, the meta mostly goes through the coupling, whereas the para proceeds with little or no coupling. In the beginning, some reactants with high internal energy decay fast to the benzylium ion without any coupling and others rearrange to the other isomers. Later on all three isomers dissociate to the products via long-lived intermediates. Thus, the reactant shows a multiexponential decay and the branching ratio varies with time as the average internal energy decreases with time. The reciprocal of the effective lifetime is taken as the rate constant. The resulting rate-energy curves are in line with experiments. The present results suggest that the coupling between the stable isomers is thermodynamically controlled, whereas the branching to the product is kinetically controlled.

• 대한환경공학회지
• /
• 제28권5호
• /
• pp.535-542
• /
• 2006

본 연구에서는 일반 토양 중에 존재하는 망간산화물의 하나인 버네사이트(birnessite)를 이용한 1-naphthol의 산화-공유결합 반응에 의한 제거 특성을 다양한 반응조건(반응시간, 버네사이트 주입량 및 pH 등)에서 회분식 실험을 통하여 조사하였다. 버네사이트에 의한 1-naphthol의 제거효율은 모든 반응조건에서 우수하였으며, 생성되는 반응산물은 1-naphthol의 산화-공유결합 반응에 의한 중합체임을 반응 후 상등액에 대한 UV-vis. 흡광 분석 및 질량분석기를 이용한 분자량 분석을 통해 확인하였다. 버네사이트 첨가량에 따른 1-naphthol의 산화 변환 실험 결과는 유사-일차 반응속도 식을 적용하여 반응 속도 상수, k를 구하였으며, 이 유사-일차 속도상수를 버네사이트의 비표면적으로 표준화하여 도출한 반응속도상수($k_{surf}$)는 $9.31{\times}10^{-4}(L/m^2{\cdot}min)$이었다. 또한, 버네사이트에 의한 1-naphthol의 산화 변환 효율은 수용액의 pH에 영향을 받았으며, pH가 10에서 4로 감소하면서 유사-일차 반응속도 상수는 $0.129min^{-1}$에서 $0.187min^{-1}$로 증가하였다.

• Nuclear Engineering and Technology
• /
• 제53권3호
• /
• pp.833-841
• /
• 2021

During the postulated severe accident of nuclear reactor, eutectic reaction leads to low-temperature melting of fuel cladding and early failure of core structure. In order to model eutectic melting with the moving particle semi-implicit (MPS) method, the eutectic reaction model is developed to simulate the eutectic reaction phenomenon. The coupling of mass diffusion and phase diagram is applied to calculate the eutectic reaction with the uniform temperature. A heat transfer formula is proposed based on the phase diagram to handle the heat release or absorption during the process of eutectic reaction, and it can combine with mass diffusion and phase diagram to describe the eutectic reaction with temperature variation. The heat transfer formula is verified by the one-dimensional melting simulations and the predicted interface position agrees well with the theoretical solution. In order to verify the eutectic reaction models, the eutectic reaction of uranium and iron in two semi-infinite domains is simulated, and the profile of solid thickness decrease over time follows the parabolic law. The modified MPS method is applied to calculate Transient Reactor Test Facility (TREAT) experiment, the penetration rate in the simulations are agreeable with the experiment results. In addition, a hypothetical case based on the TREAT experiment is also conducted to validate the eutectic reaction with temperature variation, the results present continuity with the simulations of TREAT experiment. Thus the improved method is proved to be capable of simulating the eutectic reaction in the severe accident.

• Bulletin of the Korean Chemical Society
• /
• 제32권spc8호
• /
• pp.2970-2972
• /
• 2011

One-pot homo- and cross-coupling reactions of arenediazonium tosylate salts bearing a halogen group have been exploited for the synthesis of biaryls and polyaryls under mild conditions. $Pd(OAc)_2$ has proven to be an efficient catalyst for the successful dual transformation of diazonium salts into p-quaterphenyl (3).

• KSBB Journal
• /
• 제8권2호
• /
• pp.110-114
• /
• 1993

Vinblastine, an anticancer agent was produced by chemical coupling of two different monomeric indole alkaloids, vinblastine and catharanthine in the presence of ferric ion. Vindoline was efficiently extracted from the leaves of vinca (Cafharanthus roseus) by using supercritical carbon dioxide, whereas catharanthine was chemically extracted from the in vitro cultured hairy roots. The extracted crude monomeric precursors were purified by a two-step preparative TLC. The coupling reaction was carried out in the 0.1M glycine buffer(pH 2.0, 5ml) containing 40mM FeC13 with purified vindoline(0.3mg) and catharanthine(0.3mg) at 4$^{\circ}C$. The production yields (weight %) of vinblastine and 3', 4'-anhy-drovinblastine in the products were 23.2 and 26.0, respectively. The produced vinblastine was confirmed by FAB-MS.

• 한국원자력학회:학술대회논문집
• /
• 한국원자력학회 1997년도 추계학술발표회논문집(1)
• /
• pp.70-75
• /
• 1997

A CASMO/ORIGEN coupling utility program was developed to predict the composition of all the fission products in spent PWR fuels. The coupling program reads the CASMO output file, modifies the ORIGEN cross section library and reconstructs the ORIGEN input file at each depletion step. In ORIGEN, the burnup equation is solved for actinides and fission products based on the fission reaction rates and depletion flux of CASMO. A sample calculation has been performed using a 14$\times$14 PWR fuel assembly and the results are given in this paper.

• Macromolecular Research
• /
• 제14권3호
• /
• pp.272-286
• /
• 2006

Dendritic hyperbranched poly(methyl methacrylate)s (PMMA)s, whose branched architectures resemble the 'dendron' part(s) of dendrimer, were synthesized by an iterative methodology consisting of two reactions in each iteration process: (a) a coupling reaction of u-functionalized, living, anionic PMMA having two tert-butyldimethylsilyloxymethylphenyl(SMP) groups with benzyl bromide(BnBr)-chain-end-functionalized PMMA, and (b) a transformation reaction of the introduced SMP groups into BnBr functionalities. These two reactions, (a) and (b), were repeated three times to afford a series of dendron-like, hyperbranched (PMMA)s up to third generation. Three dendron-like, hyperbranched (PMMA)s different in branched architecture were also synthesized by the same iterative methodology using a low molecular weight, functionalized 1,1-diphenylalkyl anion prepared from sec-BuLi and 1,1-bis(3-tert-butyldime-thylsilyloxymethylphenyl)ethylene in the reaction step (b) in each iterative process. Furthermore, structurally similar, dendron-like, hyperbranched block copolymers could be successfully synthesized by the iterative methodology using $\alpha$-functionalized, living, anionic poly(2-(perfluorobutyl) ethyl methacrylate) (PRfMA) in addition to $\alpha$-functionalized, living PMMA. Accordingly, the resulting block copolymers were comprised of both PMMA and PRfMA segments with different sequential orders. After the block copolymers were cast into films and annealed, their surface structures were characterized by angle-dependent XPS and contact angle measurements. All three samples showed significant segregation and enrichment of PRfMA segments at the surfaces.

• 콘크리트학회논문집
• /
• 제29권1호
• /
• pp.43-51
• /
• 2017

현행 규정에 따르면, 세장비 4 미만의 연결보에 대각철근을 사용하도록 규정하고 있다. 그러나 대각선 다발철근 상세는 보 내부의 철근 배근작업을 어렵게 만들고, 이는 또한 시공불량으로 이어질 수 있다. 본 연구에서는 고강도 철근(SD500 및 SD600)으로 보강된 콘크리트 연결보에 관한 실험결과를 나타내었다. 연결보 제작시 시공성을 향상시키기 위하여, 본 연구에서는 헤드바를 갖는 대구경 철근을 사용하였다. 배근상세 및 세장비를 변수로 하여, 2가지의 실규모 연결보를 제작 및 실험하였다. 전단벽을 연결하는 보의 실제 거동특성을 모사하기 위하여, 링크 조인트를 갖는 철골 구조물을 반력바닥에 설치하였다. 실험 결과, 연결보와 전단벽 접합부에서의 균열 및 철근이 항복되면서, 점차 연결보 중앙부로 손상이 진전되는 것으로 나타났다. 연결보는 FEMA 450-1의 설계변위에 대한 전단벽 층간변위 규정에 요구되는 변형능력을 충분히 갖는 것으로 나타났다. 그러나 고강도 철근으로 보강된 연결보의 상세설계를 위해서는, 다양한 세장비가 연결보의 구조거동에 미치는 영향에 관한 연구가 필요하다.