• Title/Summary/Keyword: NUC

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Kinetic Study on Aminolysis of 4-Pyridyl X-Substituted Benzoates: Effect of Substituent X on Reactivity and Reaction Mechanism

  • Lee, Jong-Pal;Bae, Ae-Ri;Um, Ik-Hwan
    • Bulletin of the Korean Chemical Society
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    • v.32 no.6
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    • pp.1907-1911
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    • 2011
  • A kinetic study is reported for nucleophilic substitution reactions of 4-pyridyl X-substituted benzoates 7a-e with a series of alicyclic secondary amines in H2O. The Br${\o}$nsted-type plot for the reactions of 4-pyridyl benzoate 7c is linear with ${\beta}_{nuc}$ = 0.71. The corresponding reactions of 2-pyridyl benzoate 6, which is less reactive than 7c, resulted in also a linear Br${\o}$nsted-type plot with ${\beta}_{nuc}$ = 0.77. The fact that the more reactive 7c results in a smaller ${\beta}_{nuc}$ value appears to be in accord with the reactivity-selectivity principle. The aminolysis of 7c has been suggested to proceed through a stepwise mechanism in which breakdown of the intermediate is the rate-determining step (RDS). The Hammett plot for the reactions of 7a-e with piperidine consists of two intersecting straight lines, i.e., ${\rho}_X$ = 1.47 for substrates possessing an electron-donating group (EDG) and ${\rho}_X$ = 0.91 for those possessing an electron-withdrawing group (EWG). In contrast, the corresponding Yukawa-Tsuno plot exhibits excellent linear correlation with ${\rho}_X$ = 0.79 and r = 0.56. Thus, it has been concluded that the nonlinear Hammett plot is not due to a change in the RDS but is caused by stabilization of the ground state of the substrates possessing an EDG through resonance interaction between the EDG and the C=O bond of the substrates.

Kinetic Study on Michael-type Reactions of 1-Phenyl-2-propyn-1-one with Alicyclic Secondary Amines: Effect of Medium on Reactivity and Mechanism

  • Hwang, So-Jeong;Park, Youn-Min;Um, Ik-Hwan
    • Bulletin of the Korean Chemical Society
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    • v.29 no.10
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    • pp.1911-1914
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    • 2008
  • Second-order rate constants (kN) have been measured for Michael-type addition reactions of a series of alicyclic secondary amines to 1-phenyl-2-propyn-1-one (2) in MeCN at 25.0 ${\pm}$ 0.1 ${^{\circ}C}$. All the amines studied are less reactive in MeCN than in $H_2O$ although they are more basic in the aprotic solvent by 7-9 p$K_a$ units. The Bronsted-type plot is linear with $\beta_{nuc}$ = 0.40, which is slightly larger than that reported previously for the corresponding reactions in $H_2O$ ($\beta_{nuc}$ = 0.27). Product analysis has shown that only E-isomer is produced. Kinetic isotope effect is absent for the reactions of 2 with morpholine and deuterated morpholine (i.e., $k^H/k^D$ = 1.0). Thus, the reaction has been concluded to proceed through a stepwise mechanism, in which proton transfer occurs after the rate-determining step. The reaction has been suggested to proceed through a tighter transition state in MeCN than in H2O on the basis of the larger $\beta_{nuc}$ in the aprotic solvent. The nature of the transition state has been proposed to be responsible for the decreased reactivity in the aprotic solvent.

Effects of Fermented Red Ginseng Extracts on Hyperglycemia in Streptozotocin-induced Diabetic Rats

  • Kim, Hyun-Jeong;Chae, In-Gyeong;Lee, Sung-Gyu;Jeong, Hyun-Jin;Lee, Eun-Ju;Lee, In-Seon
    • Journal of Ginseng Research
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    • v.34 no.2
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    • pp.104-112
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    • 2010
  • Fermented red ginseng (FRG) was prepared by inoculating 0.1% Lactobacillus fermentum NUC-C1 and fermenting them at $40^{\circ}C$ for 12 hours. The ginsenoside contents of FRG were increased compared with those of red ginseng (RG). Moreover, the levels of the ginsenosides Rg2, Rg3, and Rh2 in FRG increased significantly. In an oral glucose tolerance test (OGTT), blood glucose levels were lower in animals fed with RG and FRG extracts than in normal controls. In particular, FRG extracts in OGTT were superior to RG extracts. The antidiabetic effects of FRG in streptozotocin (STZ)-induced diabetic rats were investigated. Rats were divided into four groups: normal control, diabetes mellitus (DM), FRG administered at 100 mg/kg, and FRG administered at 200 mg/kg groups. FRG extracts were orally administered to each treatment group for 3 weeks, and blood glucose, insulin, and lipid levels of each group were determined. Orally administered FRG extracts significantly reduced blood glucose levels and increased plasma insulin levels in diabetic rats. Additionally, the activities of disaccharidases, including sucrase, lactase, and maltase, were decreased significantly in the FRG groups. FRG groups also had reduced triglyceride and total cholesterol levels, compared with the DM group. These results suggest that FRG may have antidiabetic effects in STZ-induced diabetic rats.

A Kinetic Study on Aminolysis of Benzyl 2-Pyridyl Thionocarbonate and t-Butyl 2-Pyridyl Thionocarbonate: Effects of Polarizability and Steric Hindrance on Reactivity and Reaction Mechanism

  • Kim, Min-Young;Bae, Ae Ri;Um, Ik-Hwan
    • Bulletin of the Korean Chemical Society
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    • v.34 no.8
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    • pp.2325-2329
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    • 2013
  • Second-order rate constants $k_N$ have been measured for reactions of benzyl 2-pyridyl thionocarbonate (4b) and t-butyl 2-pyridyl thionocarbonate (5b) with a series of cyclic secondary amines in MeCN at $25.0{\pm}0.1^{\circ}C$. The $k_N$ values for the reactions of 4b and 5b have been compared with those reported previously for the corresponding reactions of benzyl 2-pyridyl carbonate (4a) and t-butyl 2-pyridyl carbonate (5a) to investigate the effect of changing the electrophilic center from C=O to C=S on reactivity and reaction mechanism. The thiono compound 4b is more reactive than its oxygen analogue 4a. The Br${\o}$nsted-type plots for the reactions of 4a and 4b are linear with ${\beta}_{nuc}=0.57$ and 0.37, respectively. The reactions of 4a were previously reported to proceed through a concerted mechanism, while those of 4b in this study have been concluded to proceed through a stepwise mechanism with formation of an intermediate being the rate-determining step on the basis of the ${\beta}_{nuc}$ value of 0.37. Enhanced polarizability upon changing the C=O in 4a by C=S has been suggested to be responsible for the reactivity order and the contrasting reaction mechanisms. In contrast, the reactivity of 5a and 5b is similar, but they are much less reactive than 4a and 4b. Furthermore, the reactions of 5a and 5b have been concluded to proceed through the same mechanism (i.e., a concerted mechanism) on the basis of linear Bronsted-type plots with ${\beta}_{nuc}=0.45$ or 0.47. It has been concluded that the strong steric hindrance exerted by the t-Bu in 5a and 5b causes a decrease in their reactivity and forces the reactions to proceed through a concerted mechanism.

A Wide Dynamic Range NUC Algorithm for IRCS Systems

  • Cai, Li-Hua;He, Feng-Yun;Chang, Song-Tao;Li, Zhou
    • Journal of the Korean Physical Society
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    • v.73 no.12
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    • pp.1821-1826
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    • 2018
  • Uniformity is a key feature of state-of-the-art infrared focal planed array (IRFPA) and infrared imaging system. Unlike traditional infrared telescope facility, a ground-based infrared radiant characteristics measurement system with an IRFPA not only provides a series of high signal-to-noise ratio (SNR) infrared image but also ensures the validity of radiant measurement data. Normally, a long integration time tends to produce a high SNR infrared image for infrared radiant characteristics radiometry system. In view of the variability of and uncertainty in the measured target's energy, the operation of switching the integration time and attenuators usually guarantees the guality of the infrared radiation measurement data obtainted during the infrared radiant characteristics radiometry process. Non-uniformity correction (NUC) coefficients in a given integration time are often applied to a specified integration time. If the integration time is switched, the SNR for the infrared imaging will degenerate rapidly. Considering the effect of the SNR for the infrared image and the infrared radiant characteristics radiometry above, we propose a-wide-dynamic-range NUC algorithm. In addition, this essasy derives and establishes the mathematical modal of the algorithm in detail. Then, we conduct verification experiments by using a ground-based MWIR(Mid-wave Infared) radiant characteristics radiometry system with an Ø400 mm aperture. The experimental results obtained using the proposed algorithm and the traditional algorithm for different integration time are compared. The statistical data shows that the average non-uniformity for the proposed algorithm decreased from 0.77% to 0.21% at 2.5 ms and from 1.33% to 0.26% at 5.5 ms. The testing results demonstrate that the usage of suggested algorithm can improve infrared imaging quality and radiation measurement accuracy.

Deformation of the Reference Korean Voxel Model and Its Effect on Dose Calculation (표준한국인 체적소 모델 HDRK-Man의 외형 보정 및 선량 산출에 미치는 영향 평가)

  • Jeong, Jong-Hwi;Cho, Sung-Koo;Cho, Kun-Woo;Kim, Chan-Hyeong
    • Journal of Radiation Protection and Research
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    • v.33 no.4
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    • pp.167-172
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    • 2008
  • Recently a high-quality voxel model of a Korean adult male was constructed at Hanyang University by using very high resolution serially-sectioned anatomical images of a cadaver, which was provided by the Korean Institute of Science and Technology Information (KISTI). Most existing voxel phantoms are developed based on an individual in the supine posture. This study converted the HDRK-Man voxel model into surface model and adjusted the flattened back of the HDRK-Man to a normal shape in the upright posture using 3D graphic softwares such as $3D-DOCTOR^{TM}$, $Rapidform^{(R)}$2006, $Rhinoceros^{(R)}$4.0, $MAYA^{(R)}$8.5. The effective doses of adjusted model were compared with those of unadjusted model for some standard irradiation geometries (i.e., AP, PA, LLAT, RLAT). In general, the differences were not very large and, among those, the largest difference was found for the PA radiation geometry, as expected. These methodologies can be used for the development of various deformed posture models of HDRK-Man in the later stage of this project.

Antioxidant and Anti-inflammatory Activities of Ethanol Extracts from Medicinal Herb Mixtures (단일 생약재 및 생약복합제 에탄올추출물의 항산화 및 항염증 활성)

  • Lee, Sung-Gyu;Jeong, Hyun-Jin;Lee, Eun-Ju;Kim, Jong-Boo;Choi, Sang-Won
    • Korean Journal of Food Science and Technology
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    • v.43 no.2
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    • pp.200-205
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    • 2011
  • In this study, antioxidant and anti-inflammatory effects of ethanol extracts from medicinal herb mixtures were investigated in vitro. Contents of total polyphenols in ethanol extracts from Houttuynia cordata Thunb. (HC), Carthamus tinctorius L. (CT), and MIX-2 (Houttuynia cordata Thunb., Acanthopanax gracilistylus Smith, Carthamus tinctorius L., Kalopanax pictus) were 58.98, 60.79 and 57.74 mg/g respectively. Radical scavenging activities of the ethanol extracts were examined using ${\alpha},{\alpha}$-diphenyl-${\beta}$-picrylhydrazyl radicals and 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) assay. Anti-inflammatory effects of ethanol extracts from medicinal herbs composites were examined using 5-lipoxygenase (5-LO), cyclooxygenase-2 (COX-2) and nitric oxide (NO) inhibition assays. The ethanol extracts from medicinal herb mixtures showed higher 5-LO and COX-2 inhibition activities than those from single medicinal herbs. The ethanol extracts from medicinal herb mixtures also showed strong anti-inflammatory activity through inhibition of NO production.

Antioxidant and Anti-inflammatory Activities of Extracts from Korean Traditional Medicinal Prescriptions (한방처방제추출물의 항산화 및 항염증 활성)

  • Lee, Sung-Gyu;Lee, Eun-Ju;Park, Woo-Dong;Kim, Jong-Boo;Choi, Sang-Won
    • Korean Journal of Food Science and Technology
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    • v.43 no.5
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    • pp.624-632
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    • 2011
  • Water and ethanol extracts of 16 different Korean traditional oriental prescriptions used widely for prevention of degenerative arthritis were prepared and their total phenolic and total flavonoid contents were quantified. Additionally, antioxidant and anti-inflammatory activities of water, ethanol and enzyme-treated extracts were determined by in vitro assays. Total phenolic and total flavonoid contents of three extracts from the 16 different medicinal prescriptions varied from 10.03-78.03 and 0-16.24 mg/g, respectively. Among the three extracts of 16 different medicinal prescriptions tested, 'Mahangeuigamtang' showed the potent full term for DPPH ($RC_{50}$=71.26, 27.33, 63.00 ${\mu}g/mL$) and full term for ABTS ($RC_{50}$=21.11, 27.45, 152.11 ${\mu}g/mL$) radical scavenging activities, and its water and ethanol extracts exhibited significant cyclooxygenase-2 (COX-2) inhibitory activity (49.10 and 69.06%, respectively). Ethanol and enzyme-treated extracts of 'Euieuiintang' exerted the strongest COX-2 inhibitory activity (68.23 and 75.05%, respectively). 'Mahangeuigamtang' and 'Euieuiintang' may be useful as potential therapeutic agents for treatment of degenerative diseases, such as inflammation and aging.

Reactions of 4-Nitrophenyl 2-Thiophenecarboxylates with R2NH/R2NH2+ in 20 mol % DMSO (aq). Effects of 5-Thienyl Substituent and Base Strength

  • Pyun, Sang Yong;Cho, Bong Rae
    • Bulletin of the Korean Chemical Society
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    • v.34 no.7
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    • pp.2036-2040
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    • 2013
  • Reactions of 4-nitrophenyl 2-thiophenecarboxylate (1a-e) with $R_2NH/R_2NH{_2}^+$ in 20 mol % DMSO (aq) have been studied kinetically. The $2^{nd}$ order kinetics, ${\beta}_{nuc}$ = 0.88-0.98, and linear Hammett and Yukawa-Tsuno plots observed for these reactions indicate an addition-elimination mechanism in which the $2^{nd}$ step is rate limiting. The ${\beta}_{nuc}$ value increased with a stronger electron-withdrawing 5-thienyl substituent, the Hammett plots are linear except for X = MeO, and Yukawa-Tsuno plots are linear with ${\rho}$ = 0.79-1.32 and r = 0.28-0.93, respectively. The ${\rho}$ value increased and r value decreased with a stronger nucleophile, indicating an increase in the electron density at the C=O bond and a decrease in the resonance demand. These results have been interpreted with enhanced N-C bond formation in the transition state with the reactivity increase.