• Title/Summary/Keyword: acceptor reaction

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A Study for Mechanism and Oxidation Reaction of Substituted Benzyl Alcohols by 2,2'-Bipyridinium Chlorochromate (2,2'-Bipyridinium Chlorochromate에 의한 치환 벤질 알코올류의 산화반응과 메카니즘에 관한 연구)

  • Kim, Young-Sik;Park, Young-Cho
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.13 no.7
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    • pp.3252-3260
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    • 2012
  • 2,2'-Bipyridinium chlorochromate[$C_{10}H_8N_2HCrO_3Cl$] was synthesized by the reaction of 2,2'- bipyridine with chromium(VI) trioxide in 6M HCl. The structure was characterized by IR and ICP analysis. The oxidation of benzyl alcohol using 2,2'-bipyridinium chlorochromate in various solvents showed that the reactivity increased with the increase in the order of the dielectric constant(${\varepsilon}$), in the order: cyclohexene< chloroform$p-CH_3$, H, m-Br, $m-NO_2$) in N,N'-dimethylformamide. Electron-donating substituents accelerated the reaction, whereas electron acceptor groups retarded the reaction. The Hammett reaction constant(${\rho}$) was -0.64(303K). The oxidation reactivity of alcohols can be a useful factor to study about physical properties such as thermal stability, when the polysilsesquioxane solution is ready for an applying coating agent. The observed experimental data was used to rationalized the hydride ion transfer in the rate-determining step.

A Study for Kinetics and Oxidation Reaction of Substituted Benzyl Alcohols using Cr(VI)-Heterocyclic Complex(Cr(VI)-Isoquinoline) (Cr(VI)-헤테로고리 착물(Cr(VI)-Isoquinoline)를 이용한 치환 벤질 알코올류의 산화반응과 속도론에 관한 연구)

  • Park, Young-Cho;Kim, Young-Sik
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.14 no.11
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    • pp.6000-6007
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    • 2013
  • Cr(VI)-heterocyclic complex[Cr(VI)-isoquinoline] was synthesized by the reaction between of heterocyclic compound(isoquinoline) and chromium trioxide, and characterized by IR and ICP analysis. The oxidation of benzyl alcohol using Cr(VI)-isoquinoline in various solvents showed that the reactivity increased with the increase of the dielectric constant(${\varepsilon}$), in the order : cyclohexene$CH_3$, m-Br, m-$NO_2$). Electron- donating substituents accelerated the reaction, whereas electron acceptor groups retarded the reaction. The Hammett reaction constant(${\rho}$) was -0.69(308K). The observed experimental data have been ratiolized. The hydride ion transfer causes the prior formation of a chromate ester in the rate-determining step.

A Study for Kinetics and Oxidation Reaction of Alcohols by Cr(VI)-4-(Dimethylamino)pyridine (크롬(VI)-4-(Dimethylamino)pyridine에 의한 알코올류의 산화반응과 반응속도에 관한 연구)

  • Kim, Young-Sik;Park, Young-Cho;Kim, Young Jun
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.14 no.1
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    • pp.499-505
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    • 2013
  • Cr(VI)-4-(dimethylamino)pyridine[4-(dimethylamino)pyridinium chlorochromate] was synthesized by the reaction of 4-(dimethylamino)pyridine with chromium trioxide in 6M-HCl, and characterized by IR, ICP. The oxidation of benzyl alcohol using 4-(dimethylamino)pyridinium chlorochromate in various solvents showed that the reactivity increased with the increase of the dielectric constant(${\varepsilon}$), in the order: cyclohexene$H_2SO_4$ solution), 4-(dimethylamino)pyridinium chlorochromate oxidized benzyl alcohol and its derivatives(p-$OCH_3$, m-$CH_3$, H, m-$OCH_3$, m-Cl, m-$NO_2$) smoothly in DMF. Electron-donating substituents accelerated the reaction, whereas electron acceptor groups retarded the reaction. The Hammett reaction constant(${\rho}$) was -0.68(303K). The observed experimental data was used to rationalize the hydride ion transfer in the rate-determining step.

Optimization of Glycosyl Aesculin Synthesis by Thermotoga neapolitana β-Glucosidase Using Response-surface Methodology (반응표면분석법을 이용한 Thermotoga neapolitana β-glucosidase의 당전이 활성을 통한 glycosyl aesculin 합성 최적화)

  • Park, Hyunsu;Park, Young-Don;Cha, Jaeho
    • Journal of Life Science
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    • v.27 no.1
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    • pp.38-43
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    • 2017
  • Glycosyl aesculin, a potent anti-inflammatory agent, was synthesized by transglycosylation reaction, catalyzed by Thermotoga neapolitana ${\beta}-glucosidase$, with aesculin as an acceptor. The key reaction parameters were optimized using response-surface methodology (RSM) and $2{\mu}g$ of the enzyme. As shown by a statistical analysis, a second-order polynomial model fitted well to the data (p<0.05). The response surface curve for the interaction between aesculin and other parameters revealed that the aesculin concentration and reaction time were the primary factors that affected the yield of glycosyl aesculin. Among the tested factors, the optimum values for glycosyl aesculin production were as follows: aesculin concentration of 9.5 g/l, temperature of $84^{\circ}C$, reaction time of 81 min, and pH of 8.2. Under these conditions, 61.7% of glycosyl aesculin was obtained, with a predicted yield of 5.86 g/l. The maximum amount of glycosyl aesculin was 6.02 g/l. Good agreement between the predicted and experimental results confirmed the validity of the RSM. The optimization of reaction conditions by RSM resulted in a 1.6-fold increase in the production of glycosyl aesculin as compared to the yield before optimization. These results indicate that RSM can be effectively used for process optimization in the synthesis of a variety of biologically active glycosides using bacterial glycosidases.

Solvation in Mixed Solvent (III). Solvatochromic Analysis for the Solvent Effect of Binary Mixed Solvent (혼합용매에서의 용매화 (제3보). 이성분 혼합용매 중에서 용매효과에 대한 분광용매화 분석)

  • Lee, Ik-Choon;La, Sang-Mu;Lee, Bon-Su;Sohn, Se-Chul
    • Journal of the Korean Chemical Society
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    • v.28 no.4
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    • pp.210-216
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    • 1984
  • Solvatochromic comparison methods were applied to determine Taft's solvent parameters, ${\pi}^{\ast}$(solvent polarity-polarizability), ${\alpha}$(solvent hydrogen bond donor acidity) and ${\beta}$ (solvent hydrogen bond acceptor basicity) for MeOH-MeCN solvent mixtures. Swain's solvent parameters A(anion solvation scale) and B(cation solvation scale) were also determined by least square fitting of kinetic data in the same binary solvent mixtures. It was found that: (i)${\beta}$ depends on the basicity of the solvent and increases with the MeOH content owing to the increase in polymeric structure of methanol; (ii) ${\pi}^{\ast}$depends on the dipole moment of the solvent and increases with the MeCN content of the solvent; (iii) ${\alpha}$ increases rapidly with the MeOH content as the hydrogen bond donor acidity of the solvent mixtures increases. Taft's reaction constants a and s and Swain's reaction constants a and b were determined for the reactions reported from our laboratory previously using solvent parameters determined in this work. No meaningful inter-relationship was found between the two set of reaction parameters, but a good linear correlation was found between the ratios a/s and a/b. Solvent effect on the reaction mechanism, substituent effect and leaving group ability were examined in the light of these reaction constants ratios.

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A Study for Kinetics and Oxidation Reaction of Substituted Benzyl Alcohols Using (C10H8N2H)2Cr2O7 ((C10H8N2H)2Cr2O7를 이용한 치환 벤질 알코올류의 산화반응과 반응속도에 관한 연구)

  • Park, Young Cho;Kim, Young Sik;Kim, Soo Jong
    • Applied Chemistry for Engineering
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    • v.28 no.5
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    • pp.597-600
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    • 2017
  • $(C_{10}H_8N_2H)_2Cr_2O_7$ was synthesized by reacting 4,4'-bipyridine and chromium (VI) trioxide. The structure of the product was characterized with FT-IR (infrared spectroscopy) and elemental analysis. The oxidation of benzyl alcohol using $(C_{10}H_8N_2H)_2Cr_2O_7$ in various solvents showed that the reactivity increased with the increase of the solvent dielectric constant, in the order of DMF (N,N'-dimethylformamide) > acetone > chloroform > cyclohexane. In the presence of DMF, an acidic catalyst such as $H_2SO_4$ $(C_{10}H_8N_2H)_2Cr_2O_7$ oxidized benzyl alcohol (H) and its derivatives ($p-OCH_3$, $m-CH_3$, $m-OCH_3$, m-Cl, $m-NO_2$). Electron donating substituents accelerated the reaction rate, whereas electron acceptor groups retarded the reaction rate. Hammett reaction constant (${\rho}$) was -0.70 (308 K). The observed experimental data were used to rationalize the hydride ion transfer in the rate determining step.

Synthesis of 6-Alkyl-3-Chromonealdehyde(2,2-dialkyl)hydrazone Derivatives for Green Light Emitting Materials (녹색발광 6-알킬-3-크로몬알데히드(2,2-디알킬)하이드라존 유도체의 합성)

  • Chung, Pyung-Jin;Chang, Hong-Joon
    • Applied Chemistry for Engineering
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    • v.21 no.4
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    • pp.424-429
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    • 2010
  • 6-Alkyl-3-chromonealdehyde (2,2-dialkyl)hydrazone derivatives were synthesized by dehydration condensation. They are green-emitting materials for organic light emitting device (OLED) composed of electron acceptor of 6-alkyl-3-chromonealdehydes and electron donor of 2,2-dialkylhydrazones in a conjugated structure. The structural properties of reaction products were analyzed by FT-IR and $^1H$-NMR spectroscopy. The thermal stabilities and reactivities were measured by melting points and yields. The UV-visibles and PL properties were also determined by excitation spectra and emission spectra, respectively.

Significant Substituent Effects on Pyridinolysis of Aryl Ethyl Chlorophosphates in Acetonitrile

  • Adhikary, Keshab Kumar;Lee, Hai Whang
    • Bulletin of the Korean Chemical Society
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    • v.35 no.5
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    • pp.1460-1464
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    • 2014
  • The substituent effects on the pyridinolysis (XC5H4N) of Y-aryl ethyl chlorophosphates are investigated in acetonitrile at $35.0^{\circ}C$. The two strong ${\pi}$-acceptor substituents, X = 4-Ac and 4-CN in the X-pyridines, exhibit large positive deviations from the Hammett plots but little positive deviations from the Br$\ddot{o}$nsted plots. The substituent Y effects on the rates are really significant and the Hammett plots for substituent Y variations in the substrates invariably change from biphasic concave downwards via isokinetic at X = H to biphasic concave upwards with a break point at Y = 3-Me as the pyridine becomes less basic. These are interpreted to indicate a mechanistic change at the break point from a stepwise mechanism with a rate-limiting bond formation (${\rho}_{XY}$ = -6.26) for Y = (4-MeO, 4-Me, 3-Me) to with a rate-limiting leaving group expulsion from the intermediate (${\rho}_{XY}$ = +5.47) for Y = (4-Me, H, 3-MeO). The exceptionally large magnitudes of ${\rho}_{XY}$ values imply frontside nucleophilic attack transition state.

A Mechanistic Study on the Nucleophilic Addition Reactions of Benzylamines to the Activated Olefins

  • Oh, Hyuck-Keun
    • Bulletin of the Korean Chemical Society
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    • v.29 no.6
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    • pp.1195-1198
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    • 2008
  • Kinetic studies of the additions of benzylamines to a noncyclic dicarbonyl group activated olefin, methyl $\alpha$-acetyl-$\beta$ -phenylacrylates (MAP), in acetonitrile at 30.0 ${^{\circ}C}$ are reported. The rates are lower than those for the cyclic dicarbonyl group activated olefins. The addition occurs in a single step with concurrent formation of the $C_\alpha$ -N and $C_\beta$ -H bonds through a four-center hydrogen bonded transition state. The kinetic isotope effects ($k_H/k_D$ > 1.0) measured with deuterated benzylamines ($XC_6H_4CH_2ND_2$) increase with a stronger electron acceptor substituent ($\delta\sigma$ X > 0) which is the same trend as those found for other dicarbonyl group activated series (1-4). The sign and magnitude of the cross-interaction constant, ρXY, is comparable to those for the normal bond formation processes in the $S_N2$ and addition reactions. The relatively low ${\Delta}H^\neq$ and large negative ${\Delta}S^\neq$ values are also consistent with the mechanism proposed.

Purification and Characterization of an Extracellular Levansucrase from Zymomonas mobilis ZM1(ATCC 10988). (Zymomonas mobilis ZM1이 생산하는 균체외 Levansucrase의 정제 및 특성)

  • 송기방;서정우;주현규;이상기
    • Microbiology and Biotechnology Letters
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    • v.26 no.4
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    • pp.309-315
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    • 1998
  • An extracellular levansucrase, which catalyzes the formation of levan from sucrose, from the culture broth of Zymomonas mobilis ZM1 was purified by conventional column purification methods. The final purification yield was 18.3 fold of the crude enzyme from Z. mobilis, with 16.5 % of the enzyme recovered in the preparation step. The molecular weight of the enzyme was estimated to be 91,000 by Superose 12 gel filtration, and 45,000 by SDS-PAGE, indicating that levansucrase is a dimer. The optimum pH for the enzyme activity was around pH 4.0 for sucrose hydrolysis, and was around pH 5.0 for levan formation. The enzyme was inhibited by some metal ions, such as Hg$\^$2+/ and Cu2$\^$2+/, and 50% of inhibition was observed with 5mM EDTA. The enzyme activity was enhanced by the presence of detergent Triton X-100, but inhibited by SDS completely The enzyme catalyzes the liberation of reducing sugars, oligosacccharides and the formation of fructose polymer(levan). The enzyme also catalyzes the transfructosylation reaction of fructose moiety from sucrose to various sugar acceptor molecules, including sugar alcohols.

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