• Bulletin of the Korean Chemical Society
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• 제34권12호
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• pp.3795-3799
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• 2013

The second-order rate constants ($k_N$) have been measured spectrophotometrically for nucleophilic substitution reactions of Y-substituted-phenyl 2-methylbenzoates (6a-e) with a series of cyclic secondary amines in MeCN at $25.0{\pm}0.1^{\circ}C$. Comparison of the $k_N$ values for the reactions of 4-nitrophenyl 2-methylbenzoate (6d) with those reported previously for the corresponding reactions of 4-nitrophenyl 2-methoxybenzoate (5) reveals that 6d is significantly less reactive than 5, indicating that modification of 2-MeO in the benzoyl moiety of 5 by 2-Me (i.e., $5{\rightarrow}6d$) causes a significant decrease in reactivity. This supports our previous report that aminolysis of 5 proceeds through a six-membered cyclic intermediate, which is highly stabilized through intramolecular H-bonding interactions. The Br${\o}$nsted-type plot for the reactions of 6d with a series of cyclic secondary amines is linear with ${\beta}_{nuc}=0.71$, which appears to be a lower limit of ${\beta}_{nuc}$ for a stepwise mechanism with breakdown of an intermediate ($T^{\pm}$) being rate-determining step (RDS). The Br${\o}$nsted-type plot for the reactions of 6a-e with piperidine is curved, i.e., the slope of Br${\o}$nsted-type plot (${\beta}_{lg}$) decreases from -1.05 to -0.41 as the leaving-group basicity decreases. The nonlinear Br${\o}$nsted-type plot has been taken as evidence for a stepwise mechanism with a change in RDS (e.g., from the $k_2$ step to the $k_1$ process as the leaving-group basicity decreases). Dissection of $k_N$ into the microscopic rate constants associated with the reactions of 6a-e with piperidine (e.g., $k_1$ and $k_2/k_{-1}$ ratio) also supports the proposed mechanism.

• Molecules and Cells
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• 제41권4호
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• pp.331-341
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• 2018

L-pipecolic acid is a non-protein amino acid commonly found in plants, animals, and microorganisms. It is a well-known precursor to numerous microbial secondary metabolites and pharmaceuticals, including anticancer agents, immunosuppressants, and several antibiotics. Lysine cyclodeaminase (LCD) catalyzes ${\beta}$-deamination of L-lysine into L-pipecolic acid using ${\beta}$-nicotinamide adenine dinucleotide as a cofactor. Expression of a human homolog of LCD, ${\mu}$-crystallin, is elevated in prostate cancer patients. To understand the structural features and catalytic mechanisms of LCD, we determined the crystal structures of Streptomyces pristinaespiralis LCD (SpLCD) in (i) a binary complex with $NAD^+$, (ii) a ternary complex with $NAD^+$ and L-pipecolic acid, (iii) a ternary complex with $NAD^+$ and L-proline, and (iv) a ternary complex with $NAD^+$ and L-2,4-diamino butyric acid. The overall structure of SpLCD was similar to that of ornithine cyclodeaminase from Pseudomonas putida. In addition, SpLCD recognized L-lysine, L-ornithine, and L-2,4-diamino butyric acid despite differences in the active site, including differences in hydrogen bonding by Asp236, which corresponds with Asp228 from Pseudomonas putida ornithine cyclodeaminase. The substrate binding pocket of SpLCD allowed substrates smaller than lysine to bind, thus enabling binding to ornithine and L-2,4-diamino butyric acid. Our structural and biochemical data facilitate a detailed understanding of substrate and product recognition, thus providing evidence for a reaction mechanism for SpLCD. The proposed mechanism is unusual in that $NAD^+$ is initially converted into NADH and then reverted back into $NAD^+$ at a late stage of the reaction.

• 한국산학기술학회논문지
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• 제11권10호
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• pp.3621-3625
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• 2010

스컬 용융법으로 제조된 유색 큐빅지르코니아의 색향상을 위해서 $1200^{\circ}C$, $1400^{\circ}C$에서 10~60분으로 조건을 바꾸면서 진공열처리를 실시하였다. 진공열처리 시간과 온도가 증가함에 따라 준비된 3가지의 큐빅지르코니아는 점점 채도가 떨어지면서 파스텔톤의 바디 색을 유지하다가 궁극적으로 흑색으로 변화하였다. 일반적인 보석감정법과 XPS를 활용하여 이러한 색변화에 따른 물성의 정량적 변화와 메카니즘을 알아보았다. 열처리에 의한 색변화에 따른 경도와 밀도의 변화는 확인할 수 없었다. XPS에 의해서, 진공열처리에 따른 큐빅지르코니아의 색변화는 상안정제로 혼합된 $Y_2O_3$의 Y-O의 산화수 변화에 따른 현상임을 확인하였다.

• 콘크리트학회논문집
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• 제14권2호
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• pp.231-238
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• 2002

콘크리트 교량 바닥판은 건조수축 및 온도변화 등에 의하여 초기 1차균열이 발생하고, 사용기간 동안 반복되는 차량하중의 크기와 철근 간격 등에 의하여 초기 균열이 이방향 균열로 점차 발전하게 된다. 그러나 현재 사용되고 있는 대부분의 균열 예측식이 일방향 부착-슬립이론에 기초하고 있기 때문에 철근과 보강재의 간격에 따라 변화되는 교량 바닥판의 균열폭을 예측하고 보강된 바닥판의 사용성을 평가하기에는 많은 어려움이 있다. 따라서 본 연구에서는 시험결과에 기초하여 성능향상된 바닥판의 균열 메카니즘을 구명하였으며, 이로부터 사용성을 평가할 수 있는 새로운 균열예측식을 제안하였다. 제안된 균열예측식은 기존 균열식에 비하여 예측결과가 우수한 것으로 나타났으나, 철근 항복 이후 철근과 보강재의 변형률이 급격히 증가할 때 오차범위가 커지는 것으로 나타나 추가적인 연구가 필요한 것으로 판단된다. 따라서 보다나은 균열예측을 위해서는 피로 하중하에서의 철근 항복이후에 대한 추가적인 연구가 필요한 것으로 판단된다.

• Bulletin of the Korean Chemical Society
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• 제35권8호
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• pp.2448-2452
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• 2014

Second-order rate constants ($k_N$) have been measured spectrophotometrically for $S_NAr$ reactions of Y-substituted-phenoxy-2,4-dinitrobenzenes (1a-1g) with hydrazine and glycylglycine in 80 mol % $H_2O$/20 mol % DMSO at $25.0{\pm}0.1^{\circ}C$. Hydrazine is 14.6-23.4 times more reactive than glycylglycine. The magnitude of the ${\alpha}$-effect increases linearly as the substituent Y becomes a stronger electron-withdrawing group (EWG). The Br${\o}$nsted-type plots for the reactions with hydrazine and glycylglycine are linear with ${\beta}_{lg}=-0.21$ and -0.14, respectively, which is typical for reactions reported previously to proceed through a stepwise mechanism with expulsion of the leaving group occurring after rate-determining step (RDS). The Hammett plots correlated with ${\sigma}^{\circ}$ constants result in much better linear correlations than ${\sigma}^-$ constants, indicating that expulsion of the leaving group is not advanced in the transition state (TS). The reaction of 1a-1g with hydrazine has been proposed to proceed through a five-membered cyclic intermediate ($T_{III}$), which is structurally not possible for the reaction with glycylglycine. Stabilization of the intermediate $T_{III}$ through intramolecular H-bonding interaction has been suggested as an origin of the ${\alpha}$-effect exhibited by hydrazine.

• 한국지반환경공학회 논문집
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• 제10권7호
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• pp.167-177
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• 2009

본 연구에서는 터널 붕괴붕락의 유형 중 국부 암괴하중에 의한 숏크리트 라이닝의 파괴특성을 유한요소 해석을 통해 고찰하였다. 우선, 기존 터널 라이닝 파괴특성을 보다 체계적으로 파악하기 위하여 암반과 숏크리트체 강성비와 부착강도의 특성에 변화를 주어 총 9가지의 조건을 설정하였다. 각 조건에 대한 블록낙하실험(falling block test)환경에서 수치해석을 수행하여 파괴양상을 고찰해 보고 기존의 이론적 파괴 메카니즘과 비교/평가하여 보았다. 결과적으로, 기존 문헌에서 언급된 4가지 파괴모드(점착파괴(adhesive failure), 직접전단파괴(direct shear failure), 휨인장파괴(flexural failure) 및 휨전단파괴(punching shear failure))가 모두 구현되긴 하였으나, 점착파괴는 항상 타 파괴유형과 동반되어 나타나며, 별도의 파괴유형으로 분류하는 것은 부적절하다고 판단되었다. 또한 기존 관련 연구에서는 터널공학의 주요개념인 아칭효과에 대해 고려치 않고 단순보 개념하에서 라이닝의 파괴특성을 고찰하였으며, 굴착에 의해 부가되는 라이닝의 초기 축력을 고려치 않고 있다. 이에 대해 터널특성에 부합된 경계조건들을 고려하여 신규 라이닝 파괴모드를 재 고찰하였으며, 곡률이 있는 터널 라이닝조건에서는 크게 두 가지 파괴유형으로 분류할 수 있는 것으로 파악되었다.

• Bulletin of the Korean Chemical Society
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• 제32권3호
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• pp.857-862
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• 2011

Kinetic studies of the reactions of N-methyl-Y-${\alpha}$-bromoacetanilides with substituted X-benzylamines have been carried out in dimethyl sulfoxide at $25.0^{\circ}C$. The Hammett plots for substituent X variations in the nucleophiles (log $k_N$ vs ${\sigma}_X$) are slightly biphasic concave upwards/downwards, while the Bronsted plots (log $k_N$ vs $pK_a$) are biphasic concave downwards with breakpoints at X = H. The Hammett plots for substituent Y variations in the substrates (log $k_N$ vs ${\sigma}_Y$) are biphasic concave upwards/downwards with breakpoints at Y = H. The cross-interaction constant $\rho_{XY}$ values are all negative: $\rho_{XY}$ = -0.32 for X = Y = electron-donating; -0.22 for X = electron-withdrawing and Y = electron-donating; -1.80 for X = electron-donating and Y = electronwithdrawing; -1.43 for X = Y = electron-withdrawing substituents. Deuterated kinetic isotope effects are primary normal ($k_H/k_D$ > 1) for Y = electron-donating, while secondary inverse ($k_H/k_D$ < 1) for Y = electronwithdrawing substituent. The proposed mechanisms of the benzylaminolyses of N-methyl-Y-${\alpha}$-bromoacetanilides are a concerted mechanism with a five membered ring TS involving hydrogen bonding between hydrogen (deuterium) atom in N-H(D) and oxygen atom in C = O for Y = electron-donating, while a concerted mechanism with an enolate-like TS in which the nucleophile attacks the ${\alpha}$-carbon for Y = electronwithdrawing substituents.

• 대한화학회지
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• 제17권4호
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• pp.247-255
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• 1973

$Li^{+},\;Na^{+},\;K^{+}, Ca^{2+},\;Ni^{2+},\;Al^{3+}$, 과 $F^{3+}$의 陽이온을 포화시킨 Wyoning montmorillonite에 acetone, methyl-ethyl ketone. diethyl ketone을 加熱用 i.r. gas cell 內에서 各各 다른 壓力아래 吸着시켜 $4000{\sim}1200cm^{-1}$에서spectra를 얻었다.두가지 형태의 C=O결합변화가$1713cm^{-1}$과 $1690cm^{-1}$ 나타났으며 이들은 陽이온의 水酸基 및 吸着水와 그리고 表面水酸基와 水素結合을 일으키는 결과로 나타났다. OH 吸收 spectra의 强度는 陽이온의 水酸基의 resonance 理論을 뒷받침해 주었다. coordinate bond를 일으키는 경향은 計算한 C=O기의 酸素의 formal charge의 크기와 잘 맞았다.

• Nuclear Engineering and Technology
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• 제49권4호
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• pp.734-743
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• 2017

In order to investigate the swelling behavior and fuel-cladding interaction mechanism of U-10Zr alloy metallic fuel at very low burnup, an irradiation experiment was concisely designed and conducted on the China Mianyang Research Reactor. Two types of irradiation samples were designed for studying free swelling without restraint and the fuel-cladding interaction mechanism. A new bonding material, namely, pure aluminum powder, was used to fill the gap between the fuel slug and sample shell for reducing thermal resistance and allowing the expansion of the fuel slug. In this paper, the concise irradiation rig design is introduced, and the neutronic and thermal-hydraulic analyses, which were carried out mainly using MCNP (Monte Carlo N-Particle) and FLUENT codes, are presented. Out-of-pile tests were conducted prior to irradiation to verify the manufacturing quality and hydraulic performance of the rig. Nondestructive postirradiation examinations using cold neutron radiography technology were conducted to check fuel cladding integrity and swelling behavior. The results of the preliminary examinations confirmed the safety and effectiveness of the design.

• 한국기계가공학회지
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• 제18권2호
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• pp.1-6
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• 2019

With the increase in number of the athletic population and elderly demographic, the demand for orthopedic splints, which are used to support a damaged body, has rapidly increased. Current splints mainly consist of inner and outer parts, which are multiple fabrics covered with polyurethane and nonwoven fabrics, respectively. However, the laminated materials with directly applied pre-polymer coating lead to a high defect rate because of the uneven thickness on the surface. Thus, this study proposes an indirect coating method using a precise clearance controller, which enables the even application of the coating material on multiple inner parts while maintaining a constant thickness. In addition, a roll-to-roll (R2R) technique is applied instead of the sewing mechanism to bond the inner and outer materials together and enhance the productivity in the final stage. In the advanced methods, there is a storage tank that contains polyurethane, a clearance controller, and pairs of rollers in the upper and lower rows. To improve the quality of the products and optimize the equipment, three controllable factors are determined: the viscosity of polyurethane, angle of the gap controller and number of pairs of rollers in the R2R system.