• Title, Summary, Keyword: kinetics

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Investigation of Cure Kinetics and Storage Stability of the o-Cresol Novolac Epoxy Nanocomposites with Pre-intercalated Phenolic Hardeners

  • Hwang, Tae-Yong;Lee, Jae-Wook;Lee, Sang-Min;Nam, Gi-Joon
    • Macromolecular Research
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    • v.17 no.2
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    • pp.121-127
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    • 2009
  • The cure kinetics of the epoxy-layered, silicate nanocomposites were studied by differential scanning calorimetry under isothermal and dynamic conditions. The materials used in this study were o-cresol novolac epoxy resin and phenol novolac hardener, with organically modified layered silicates. Various kinetic parameters, including the reaction order, activation energy, and kinetic rate constants, were investigated, and the storage stability of the epoxy-layered silicate nanocomposites was measured. To synthesize the epoxy-layered silicate nanocomposites, the phenolic hardener underwent pre-intercalation by layered silicate. From the cure kinetics analyses, the organically modified layered silicate decreased the activation energy during cure reaction in the epoxy/phenolic hardener system. In addition, the storage stability of the nanocomposite with the pre-intercalated phenolic hardener was significantly increased compared to that of the nanocomposite with direct mixing of epoxy, phenolic hardener, and layered silicate. This was due to the protective effect of the reaction between onium ions and epoxide groups.

Physiological characterization of kinetics and action mechanism of vibrio hemolysin

  • Choe, Young-Chool;Jeong, Cajin
    • Journal of Microbiology
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    • v.33 no.4
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    • pp.289-294
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    • 1995
  • The action mechanism of hemolysin rendering virulency of Vibrio anguilarum has not clarified as yet, even though there were several possible factors explained. We have studied hemolytic kinetics performed by hemolysin from V. anguillarum strain V7 as well as binding of hemolysin to RBC membrane. Maximal rate of hemolysis and duration of lag phase were directly and inversly correlated to the concentration of hemolysin used. Hemolysin molecules are known to bind consumptively with proper diameter, while other protectants with smaller diameter could not. In conclusion, hemolysin should bind irreversibly to RBC membrane exert hemolysis distorting osmotic pressure. The binding could be hindered by spatial structure of the RBC surfacem which might be caused by sialic acid.

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Oxidation Kinetics of Pitch Based Carbon Fibers

  • Roh, Jae-Seung
    • Carbon letters
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    • v.9 no.2
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    • pp.121-126
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    • 2008
  • High modulus pitch based carbon fibers (HM) were exposed to isothermal oxidation using tube furnace in carbon dioxide gas to study the oxidation kinetics under the temperature of $800-1100^{\circ}C$. The kinetic equation $f=1-{\exp}(-at^b)$ was introduced and the constant b was obtained in the range of 1.02~1.42. The oxidation kinetics were evaluated by the reaction-controlling regime (RCR) depending upon the apparent activation energies with the conversion increasing from 0.2 to 0.8. The activation energies decrease from 24.7 to 21.0 kcal/mole with the conversion increasing from 0.2 to 0.8, respectively. According to the RCR, the reaction was limited by more diffusion controlling regime for the HM fibers with the conversion increasing. Therefore, it seems that the oxidation which is under the diffusion controlling regime takes place continuously from the skin to the core of the fiber.

Helicobacter pylori Urease May Exist in Two Forms: Evidence from the Kinetic Studies

  • Gang, Jin-Gu;Yun, Soon-Kyu;Hwang, Se-Young
    • Journal of Microbiology and Biotechnology
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    • v.19 no.12
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    • pp.1565-1568
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    • 2009
  • Purified Helicobacter pylori urease displayed a sigmoid curve in the plot of velocity versus [S] at urea concentrations less than 0.1mM. Under conditions where preservatives, glycerol, or polyethylene glycol (PEG) were added to the enzyme reaction, the substrate hydrolysis was consistent with Michaelis-Menten kinetics, with a $K_m$ of $0.21\;{\pm}\;0.06\;mM$ and a $V_{max}$ of $1,200\;{\pm}\;300\;{\mu}mol\;min^{-1}\;mg^{-1}$. However, at saturating substrate concentrations, the kinetic parameters of H. pylori urease were unaffected by the presence of the preservatives, and enzyme catalysis conformed to Michaelis-Menten kinetics. The Hill coefficients of the enzyme-catalyzed urea hydrolysis in the presence and absence of PEG were 1 and 2, respectively. Based on these findings, we suggest that H. pylori urease may exist in aggregated and dissociated forms, each with intact function but differing kinetics that may be of importance in maximizing urea breakdown at varying urea concentrations in vivo.

Estimation of Nitrite Concentration in the Biological Nitritation Process Using Enzymatic Inhibition Kinetics

  • GIL, KYUNG-IK;EUI-SO CHOI
    • Journal of Microbiology and Biotechnology
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    • v.12 no.3
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    • pp.377-381
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    • 2002
  • Recently, interests to remove nitrogen in the nitritation process have increased because of its economical advantages, since it could be a short-cut process to save both oxygen for nitrification and carbon for denitrification compared to a typical nitrification. However, the kinetics related with the nitritation process has not yet been fully understood. Furthermore, many useful models which have been successfully used for wastewater treatment processes cannot be used to estimate effluent nitrite concentration for evaluating performance of the nitritation process, since the process rate equations and population of microorganisms for nitrogen removal in these models have been set up only for the condition of full nitrification. Therefore, the present study was conducted to estimate an effluent nitrite concentration in the nitritation process with a concept of enzymatic inhibition kinetics based on long-term laboratory experiments. Using a nonlinear least squares regression method, kinetic parameters were accurately determined. By setting up a process rate equation along with a mass balance equation of the nitrite-oxidizing step, an effluent nitrite concentration in the nitritation process was then successfully estimated.

Kinetics of Initial Water Vapor Adsorption by Inonotus obliquus Mushroom Powders

  • Lee, Min-Ji;Seog, Eun-Ju;Lee, Jun-Ho
    • Preventive Nutrition and Food Science
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    • v.12 no.2
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    • pp.111-114
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    • 2007
  • Water vapor adsorption kinetics of Inonotus mushroom powders were investigated in temperature and water activity ranges of 20 to 40$^{\circ}C$ and 0.30 to 0.81, respectively. Initial water vapor adsorption rate of mushroom powders increased with increases in temperature and water activity. The temperature dependency of water activity followed the Clausius-Clapeyron equation. The net isosteric heat of sorption increased with an increase in water activity. Water vapor adsorption kinetics of the mushroom powders can be well described by a simple empirical model. Temperature dependency of the reaction rate constant followed the Arrhenius relationship. The activation energy ranged from 56.86 to 91.35 kJ/mol depending on water activity. Kinetic compensation relationship was observed between k$_o$ and E$_a$ with the isokinetic temperature of 790.27 K.

Kinetics of Water Vapor Adsorption by Chitosan-based Nanocomposite Films

  • Seog, Eun-Ju;Zuo, Li;Lee, Jun-Ho;Rhim, Jong-Whan
    • Food Science and Biotechnology
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    • v.17 no.2
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    • pp.330-335
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    • 2008
  • Water vapor adsorption kinetics of 3 different types of chitosan-based films, i.e., control chitosan, chitosan/montmorillionite (Na-MMT), and chitosan/silver-zeolite (Ag-Ion) nanocomposite films, were investigated at temperature range of $10-40^{\circ}C$. In all the films, water vapor is initially adsorbed rapidly and then it comes slowly to reach equilibrium condition. Reasonably good straight lines were obtained with plotting of 1/($m-m_0$) vs. l/t. It was found that water vapor adsorption kinetics of chitosan-based films was accurately described by a simple empirical model and the rate constant of the model followed temperature dependence according to Arrhenius equation. Arrhenius kinetic parameters ($E_a$ and $k_o$) for water vapor adsorption by chitosan-based films showed a kinetic compensation effect between the parameters with the isokinetic temperature of 315.52 K.

Nonclassical Chemical Kinetics for Description of Chemical Fluctuation in a Dynamically Heterogeneous Biological System

  • Lim, Yu-Rim;Park, Seong-Jun;Lee, Sang-Youb;Sung, Jae-Young
    • Bulletin of the Korean Chemical Society
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    • v.33 no.3
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    • pp.963-970
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    • 2012
  • We review novel chemical kinetics proposed for quantitative description of fluctuations in reaction times and in the number of product molecules in a heterogeneous biological system, and discuss quantitative interpretation of randomness parameter data in enzymatic turnover times of ${\beta}$-galactosidase. We discuss generalization of renewal theory for description of chemical fluctuation in product level in a multistep biopolymer reaction occurring in a dynamically heterogeneous environment. New stochastic simulation results are presented for the chemical fluctuation of a dynamically heterogeneous reaction system, which clearly show the effects of the initial state distribution on the chemical fluctuation. Our stochastic simulation results are found to be in good agreement with predictions of the analytic results obtained from the generalized master equation.

Kinetics of the Formation of Metalloporphyrins and the Catalytic Effect of Lead Ions and Hydrogen Ions

  • Qi, Yong;Pan, Ji Gang
    • Bulletin of the Korean Chemical Society
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    • v.35 no.11
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    • pp.3313-3318
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    • 2014
  • The reaction mechanism of Lead ions catalyzing complexation reactions between TIPP and metal ions was investigated by researching the kinetics of the formation of metalloporphyrins by UV/Vis-spectra, and verified by exploring the formation of metalloporphyrins catalyzed by acetic acid. Kinetics studies suggested that the fluctuations of reaction rate indicated the formation of metalloporphyrin was step-wise, including the pre-equilibrium step (the coordination of the pyrrolenine nitrogens to $Mn^+$) and the rate-controlling step (the deprotonation of the pyrrole proton). In the pre-equalization step, a sitting-atop (SAT) structure formed first with the complexation between larger radius of $Pb^{2+}$ and TIPP, changed the activation, then $Pb^{2+}$ left with the smaller radius of metal ions attacking from the back of the porphyrin ring center. In the rate-controlling step, two pyrrole protons dissociated to restore a stable structure. This was verified by adding acetic acid at different reaction times.

Kinetics and Mechanism of Ruthenium(III) Catalyzed Oxidation of Butanone and Uncatalyzed Oxidation of Cychlohexanone by Cerium(IV) in Acid Sulphate Medium

  • Sharma, Priyamvada;Hemkar, Shalini;Khandelwal, C.L.;Sharma, P.D.
    • Journal of the Korean Chemical Society
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    • v.56 no.1
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    • pp.28-33
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    • 2012
  • The kinetics of ruthenium(III) chloride catalyzed oxidation of butanone and uncatalyzed oxidation of cyclohexanone by cerium(IV) in sulphuric acid medium have been studied. The kinetic rate law(I) in case of butanone conforms to the proposed mechanism. $$-\frac{1}{2}\frac{d[Ce^{IV}]}{dt}=\frac{kK[Ru^{III}][butanone]}{1+K[butanone]}$$ (1). However, oxidation of cyclohexanone in absence of catalyst accounts for the rate eqn. (2). $$-\frac{1}{2}\frac{[Ce^{IV}]}{dt}=\frac{(k_1+k_1K^'[H^+])[Ce^{IV}][Cyclohexanone]}{1+K_3[HSO_4^-]}$$ (2) Kinetics and activation parameters have been evaluated conventionally. Kinetically preferred mode of reaction is via ketonic and not the enolic forms.