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Sample records for activity kinetic studies

  1. Study of kinetics of degradation of cyclohexane carboxylic acid by acclimated activated sludge.

    PubMed

    Wang, Chunhua; Shi, Shuian; Chen, Hongyan

    2016-01-01

    Activated sludge contains complex microorganisms, which are highly effective biodegrading agents. In this study, the kinetics of biodegradation of cyclohexane carboxylic acid (CHCA) by an acclimated aerobic activated sludge were investigated. The results showed that after 180 days of acclimation, the activated sludge could steadily degrade >90% of the CHCA in 120 h. The degradation of CHCA by the acclimated activated sludge could be modeled using a first-order kinetics equation. The equations for the degradation kinetics for different initial CHCA concentrations were also obtained. The kinetics constant, kd, decreased with an increase in the CHCA concentration, indicating that, at high concentrations, CHCA had an inhibiting effect on the microorganisms in the activated sludge. The effects of pH on the degradation kinetics of CHCA were also investigated. The results showed that a pH of 10 afforded the highest degradation rate, indicating that basic conditions significantly promoted the degradation of CHCA. Moreover, it was found that the degradation efficiency for CHCA increased with an increase in temperature and concentration of dissolved oxygen under the experimental conditions. PMID:27191578

  2. A coupled observation - modeling approach for studying activation kinetics from measurements of CCN activity

    NASA Astrophysics Data System (ADS)

    Raatikainen, T.; Moore, R. H.; Lathem, T. L.; Nenes, A.

    2012-05-01

    This paper presents an approach to study droplet activation kinetics from measurements of CCN activity by the Continuous Flow Streamwise Thermal Gradient CCN Chamber (CFSTGC) and a comprehensive model of the instrument and droplet growth. The model, which can be downloaded from http://nenes.eas.gatech.edu/Experiments/CFSTGC.html , is evaluated against a series of experiments with ammonium sulfate calibration aerosol. Observed and modeled droplet sizes are in excellent agreement for a water vapor uptake coefficient ~0.2, which is consistent with theoretical expectations. The model calculations can be considerably accelerated without significant loss of accuracy by assuming simplified instrument geometry and constant parabolic flow velocity profiles. With these assumptions, the model can be applied to large experimental data sets to infer kinetic growth parameters while fully accounting for water vapor depletion effects and changes in instrument operation parameters such as the column temperature, flow rates, sheath and sample flow relative humidities, and pressure. When the effects of instrument operation parameters, water vapor depletion and equilibrium dry particle properties on droplet size are accounted for, the remaining variations in droplet size are most likely due to non-equilibrium processes such as those caused by organic surface films, slow solute dissociation and glassy or highly viscous particle states. As an example of model application, data collected during a research flight in the ARCTAS 2008 campaign are analyzed. The model shows that water vapor depletion effects can explain changes in the observed average droplet size.

  3. Study of the kinetic parameters for synthesis and hydrolysis of pharmacologically active salicin isomer catalyzed by baker's yeast maltase

    NASA Astrophysics Data System (ADS)

    Veličković, D. V.; Dimitrijević, A. S.; Bihelović, F. J.; Jankov, R. M.; Milosavić, N.

    2011-12-01

    One of the key elements for understanding enzyme reactions is determination of its kinetic parameters. Since transglucosylation is kinetically controlled reaction, besides the reaction of synthesis, very important is the reaction of enzymatic hydrolysis of created product. Therefore, in this study, kinetic parameters for synthesis and secondary hydrolysis of pharmacologically active α isosalicin by baker's yeast maltase were calculated, and it was shown that specifity of maltase for hydrolysis is approximately 150 times higher then for synthesis.

  4. Lipase-catalyzed synthesis of palmitanilide: Kinetic model and antimicrobial activity study.

    PubMed

    Liu, Kuan-Miao; Liu, Kuan-Ju

    2016-01-01

    Enzymatic syntheses of fatty acid anilides are important owing to their wide range of industrial applications in detergents, shampoo, cosmetics, and surfactant formulations. The amidation reaction of Mucor miehei lipase Lipozyme IM20 was investigated for direct amidation of triacylglycerol in organic solvents. The process parameters (reaction temperature, substrate molar ratio, enzyme amount) were optimized to achieve the highest yield of anilide. The maximum yield of palmitanilide (88.9%) was achieved after 24 h of reaction at 40 °C at an enzyme concentration of 1.4% (70 mg). Kinetics of lipase-catalyzed amidation of aniline with tripalmitin has been investigated. The reaction rate could be described in terms of the Michaelis-Menten equation with a Ping-Pong Bi-Bi mechanism and competitive inhibition by both the substrates. The kinetic constants were estimated by using non-linear regression method using enzyme kinetic modules. The enzyme operational stability study showed that Lipozyme IM20 retained 38.1% of the initial activity for the synthesis of palmitanilide (even after repeated use for 48 h). Palmitanilide, a fatty acid amide, exhibited potent antimicrobial activity toward Bacillus cereus. PMID:26672452

  5. Understanding long-time vacancy aggregation in iron: A kinetic activation-relaxation technique study

    NASA Astrophysics Data System (ADS)

    Brommer, Peter; Béland, Laurent Karim; Joly, Jean-François; Mousseau, Normand

    2014-10-01

    Vacancy diffusion and clustering processes in body-centered-cubic (bcc) Fe are studied using the kinetic activation-relaxation technique (k-ART), an off-lattice kinetic Monte Carlo method with on-the-fly catalog building capabilities. For monovacancies and divacancies, k-ART recovers previously published results while clustering in a 50-vacancy simulation box agrees with experimental estimates. Applying k-ART to the study of clustering pathways for systems containing from one to six vacancies, we find a rich set of diffusion mechanisms. In particular, we show that the path followed to reach a hexavacancy cluster influences greatly the associated mean-square displacement. Aggregation in a 50-vacancy box also shows a notable dispersion in relaxation time associated with effective barriers varying from 0.84 to 1.1 eV depending on the exact pathway selected. We isolate the effects of long-range elastic interactions between defects by comparing to simulations where those effects are deliberately suppressed. This allows us to demonstrate that in bcc Fe, suppressing long-range interactions mainly influences kinetics in the first 0.3 ms, slowing down quick energy release cascades seen more frequently in full simulations, whereas long-term behavior and final state are not significantly affected.

  6. Investigation of metal binding and activation of Escherichia coli glyoxalase I: kinetic, thermodynamic and mutagenesis studies.

    PubMed Central

    Clugston, Susan L; Yajima, Rieko; Honek, John F

    2004-01-01

    GlxI (glyoxalase I) isomerizes the hemithioacetal formed between glutathione and methylglyoxal. Unlike other GlxI enzymes, Escherichia coli GlxI exhibits no activity with Zn(2+) but maximal activation with Ni(2+). To elucidate further the metal site in E. coli GlxI, several approaches were undertaken. Kinetic studies indicate that the catalytic metal ion affects the k (cat) without significantly affecting the K (m) for the substrate. Inductively coupled plasma analysis and isothermal titration calorimetry confirmed one metal ion bound to the enzyme, including Zn(2+), which produces an inactive enzyme. Isothermal titration calorimetry was utilized to determine the relative binding affinity of GlxI for various bivalent metals. Each metal ion examined bound very tightly to GlxI with an association constant ( K (a))>10(7) M(-1), with the exception of Mn(2+) ( K (a) of the order of 10(6) M(-1)). One of the ligands to the catalytic metal, His(5), was altered to glutamine, a side chain found in the Zn(2+)-active Homo sapiens GlxI. The affinity of the mutant protein for all bivalent metals was drastically decreased. However, low levels of activity were now observed for Zn(2+)-bound GlxI. Although this residue has a marked effect on metal binding and activation, it is not the sole factor determining the differential metal activation between the human and E. coli GlxI enzymes. PMID:14556652

  7. Endogenous KCNE Subunits Govern Kv2.1 K+ Channel Activation Kinetics in Xenopus Oocyte Studies

    PubMed Central

    Gordon, Earl; Roepke, Torsten K.; Abbott, Geoffrey W.

    2006-01-01

    Kv2.1 is a voltage-gated potassium (Kv) channel that generates delayed rectifier currents in mammalian heart and brain. The biophysical properties of Kv2.1 and other ion channels have been characterized by functional expression in heterologous systems, and most commonly in Xenopus laevis oocytes. A number of previous oocyte-based studies of mammalian potassium channels have revealed expression-level-dependent changes in channel properties, leading to the suggestion that endogenous oocyte factors regulate channel gating. Here, we show that endogenous oocyte potassium channel KCNE ancillary subunits xMinK and xMiRP2 slow the activation of oocyte-expressed mammalian Kv2.1 channels two-to-fourfold. This produces a sigmoidal relationship between Kv2.1 current density and activation rate in oocyte-based two-electrode voltage clamp studies. The effect of endogenous xMiRP2 and xMinK on Kv2.1 activation is diluted at high Kv2.1 expression levels, or by RNAi knockdown of either endogenous subunit. RNAi knockdown of both xMiRP2 and xMinK eliminates the correlation between Kv2.1 expression level and activation kinetics. The data demonstrate a molecular basis for expression-level-dependent changes in Kv channel gating observed in heterologous expression studies. PMID:16326911

  8. Oxidation of flavonoids by hypochlorous acid: reaction kinetics and antioxidant activity studies.

    PubMed

    Krych-Madej, Justyna; Stawowska, Katarzyna; Gebicka, Lidia

    2016-08-01

    Flavonoids, plant polyphenols, ubiquitous components of human diet, are excellent antioxidants. Hypochlorous acid (HOCl), produced by activated neutrophils, is highly reactive chlorinating and oxidizing species. It has been reported earlier that flavonoids are chlorinated by HOCl. Here we show that flavonoids from flavonol subclass are also oxidized by HOCl, but only if the latter is in a large molar excess (≥ 10). The kinetics of this reaction was studied by stopped-flow spectrophotometry, at different pH. We found that flavonols were oxidized by HOCl with the rate constants of the order of 10(4)-10(5) M(-1) s(-1) at pH 7.5. Antioxidant activity of HOCl-modified flavonoids was measured by 2,2'-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) method. Slightly higher antioxidant activity, compared to parent compounds, was observed for flavonols after their reaction with equimolar or moderate excess of HOCl whereas flavonols treated with high molar excess of HOCl exhibited decrease in antioxidant activity. The mechanism of flavonoid reaction with HOCl at physiological pH is proposed, and biological consequences of this reaction are discussed. PMID:27225705

  9. Different antibacterial activity of novel theophylline-based ionic liquids - Growth kinetic and cytotoxicity studies.

    PubMed

    Borkowski, Andrzej; Ławniczak, Łukasz; Cłapa, Tomasz; Narożna, Dorota; Selwet, Marek; Pęziak, Daria; Markiewicz, Bartosz; Chrzanowski, Łukasz

    2016-08-01

    The aim of this study was to investigate novel theophylline-based ionic liquids and their cytotoxic effects towards model Gram-positive and Gram-negative bacteria (Bacillus cereus and Escherichia coli, respectively). Growth kinetics, respiratory rates and dehydrogenase activities were studied in the presence of ionic liquids at concentrations ranging from 10 to 1000mg/L. Additionally, the influence of ionic liquids on bacterial cells associated with specific interactions based on the structure of cell wall was evaluated. This effect was assessed by viability tests and scanning electron microscope observations. The obtained results confirmed that ionic liquids exhibit different levels of toxicity in relation to Gram-positive and Gram-negative bacteria. Those effects are associated with the chemical structure of the cationic species of the ionic liquids and their critical micelle concentration value. It was established that the presence of an alkyl or allyl group increased the toxicity, whereas the presence of an aryl group in the cation decreased the toxic effect of ILs. Results presented in this study also revealed unexpected effects of self-aggregation of E. coli cells. Overall, it was established that the studied ILs exhibited higher toxicity towards Gram-positive bacteria due to different interactions between the ILs and the cell membranes. These findings may be of importance for the design of ILs with targeted antimicrobial properties. PMID:27082812

  10. Adsorption of cellulase Aspergillus niger on a commercial activated carbon: kinetics and equilibrium studies.

    PubMed

    Daoud, Fatima Boukraa-Oulad; Kaddour, Samia; Sadoun, Tahar

    2010-01-01

    The adsorption kinetics of cellulase Aspergillus niger on a commercial activated carbon has been performed using a batch-adsorption technique. The effect of various experimental parameters such as initial enzyme concentration, contact time and temperature were investigated. The pseudo-first-order and pseudo-second-order kinetic models were used to describe the kinetic data which shows that the adsorption of the enzyme followed the pseudo-second-order rate expression and the rate constants were evaluated. The Langmuir and Freundlich adsorption isotherm models were applied to describe the equilibrium isotherms, and the isotherm constants were determined. It was found that Langmuir model was more suitable for our data. The activation energy of adsorption was also evaluated for the adsorption of enzyme onto activated carbon. It was found 11.37 kJ mol(-1). Thermodynamic parameters Delta G(0), Delta H(0) and DeltaS(0) were calculated, indicating that this process can be spontaneous and endothermic. The adsorption enthalpy and entropy were found 11.12 kJ mol(-1) and 0.084 kJ mol(-1)K(-1), respectively. At 30 degrees C and at pH 4.8, 1g activated carbon adsorbed about 1565 mg of cellulase, with a retention of 70% of the native enzyme activity up to five cycles of repeated batch enzyme reactions. PMID:19744839

  11. Active food packaging based on molecularly imprinted polymers: study of the release kinetics of ferulic acid.

    PubMed

    Otero-Pazos, Pablo; Rodríguez-Bernaldo de Quirós, Ana; Sendón, Raquel; Benito-Peña, Elena; González-Vallejo, Victoria; Moreno-Bondi, M Cruz; Angulo, Immaculada; Paseiro-Losada, Perfecto

    2014-11-19

    A novel active packaging based on molecularly imprinted polymer (MIP) was developed for the controlled release of ferulic acid. The release kinetics of ferulic acid from the active system to food simulants (10, 20, and 50% ethanol (v/v), 3% acetic acid (w/v), and vegetable oil), substitutes (95% ethanol (v/v) and isooctane), and real food samples at different temperatures were studied. The key parameters of the diffusion process were calculated by using a mathematical modeling based on Fick's second law. The ferulic acid release was affected by the temperature as well as the percentage of ethanol of the simulant. The fastest release occurred in 95% ethanol (v/v) at 20 °C. The diffusion coefficients (D) obtained ranged between 1.8 × 10(-11) and 4.2 × 10(-9) cm(2)/s. A very good correlation between experimental and estimated data was obtained, and consequently the model could be used to predict the release of ferulic acid into food simulants and real food samples. PMID:25369799

  12. Kinetics and equilibrium adsorption study of p-nitrophenol onto activated carbon derived from walnut peel.

    PubMed

    Liu, Xiaohong; Wang, Fang; Bai, Song

    2015-01-01

    An original activated carbon prepared from walnut peel, which was activated by zinc chloride, was modified with ammonium hydroxide or sodium hydroxide in order to contrast the adsorption property of the three different activated carbons. The experiment used a static adsorption test for p-nitrophenol. The effects of parameters such as initial concentration, contact time and pH value on amount adsorbed and removal are discussed in depth. The thermodynamic data of adsorption were analyzed by Freundlich and Langmuir models. The kinetic data of adsorption were measured by the pseudo-first-order kinetics and the pseudo-second-order kinetics models. The results indicated that the alkalized carbon samples derived from walnut peel had a better performance than the original activated carbon treated with zinc chloride. It was found that adsorption equilibrium time was 6 h. The maximum removal rate of activated carbon treated with zinc chloride for p-nitrophenol was 87.3% at pH 3,whereas the maximum removal rate of the two modified activated carbon materials was found to be 90.8% (alkalized with ammonium hydroxide) and 92.0% (alkalized with sodium hydroxide) at the same pH. The adsorption data of the zinc chloride activated carbon were fitted to the Langmuir isotherm model. The two alkalized activated carbon samples were fitted well to the Freundlich model. The pseudo-second-order dynamics equation provided better explanation of the adsorption dynamics data of the three activated carbons than the pseudo-first-order dynamics equation. PMID:26676011

  13. Gating Kinetics of the Cyclic-GMP-Activated Channel of Retinal Rods: Flash Photolysis and Voltage-Jump Studies

    NASA Astrophysics Data System (ADS)

    Karpen, Jeffrey W.; Zimmerman, Anita L.; Stryer, Lubert; Baylor, Denis A.

    1988-02-01

    The gating kinetics of the cGMP-activated cation channel of salamander retinal rods have been studied in excised membrane patches. Relaxations in patch current were observed after two kinds of perturbation: (i) fast jumps of cGMP concentration, generated by laser flash photolysis of a cGMP ester (``caged'' cGMP), and (ii) membrane voltage jumps, which perturb activation of the channel by cGMP. In both methods the speed of activation increased with the final cGMP concentration. The results are explained by a simple kinetic model in which activation involves three sequential cGMP binding steps with bimolecular rate constants close to the diffusion-controlled limit; fully liganded channels undergo rapid open-closed transitions. Voltage perturbs activation by changing the rate constant for channel closing, which increases with hyperpolarization. Intramolecular transitions of the fully liganded channel limit the kinetics of activation at high cGMP concentrations (>50 μ M), whereas at physiological cGMP concentrations (<5 μ M), the kinetics of activation are limited by the third cGMP binding step. The channel appears to be optimized for rapid responses to changes in cytoplasmic cGMP concentration.

  14. Adsorption of leather dye onto activated carbon prepared from bottle gourd: equilibrium, kinetic and mechanism studies.

    PubMed

    Foletto, Edson Luiz; Weber, Caroline Trevisan; Paz, Diego Silva; Mazutti, Marcio Antonio; Meili, Lucas; Bassaco, Mariana Moro; Collazzo, Gabriela Carvalho

    2013-01-01

    Activated carbon prepared from bottle gourd has been used as adsorbent for removal of leather dye (Direct Black 38) from aqueous solution. The activated carbon obtained showed a mesoporous texture, with surface area of 556.16 m(2) g(-1), and a surface free of organic functional groups. The initial dye concentration, contact time and pH significantly influenced the adsorption capacity. In the acid region (pH 2.5) the adsorption of dye was more favorable. The adsorption equilibrium was attained after 60 min. Equilibrium data were analyzed by the Langmuir, Freundlich, Dubinin-Radushkevich and Temkin isotherm models. The equilibrium data were best described by the Langmuir isotherm, with maximum adsorption capacity of 94.9 mg g(-1). Adsorption kinetic data were fitted using the pseudo-first-order, pseudo-second-order, Elovich and intraparticle diffusion models. The adsorption kinetic was best described by the second-order kinetic equation. The adsorption process was controlled by both external mass transfer and intraparticle diffusion. Activated carbon prepared from bottle gourd was shown to be a promising material for adsorption of Direct Black 38 from aqueous solution. PMID:23128640

  15. New library of aminosulfonyl-tagged Hoveyda–Grubbs type complexes: Synthesis, kinetic studies and activity in olefin metathesis transformations

    PubMed Central

    Borré, Etienne; Caijo, Frederic

    2010-01-01

    Summary Seven novel Hoveyda–Grubbs precatalysts bearing an aminosulfonyl function are reported. Kinetic studies indicate an activity enhancement compared to Hoveyda’s precatalyst. A selection of these catalysts was investigated with various substrates in ring-closing metathesis of dienes or enynes and cross metathesis. The results demonstrate that these catalysts show a good tolerance to various chemical functions. PMID:21165173

  16. Sorption of perfluorooctane sulfonate and perfluorooctanoate on activated carbons and resin: Kinetic and isotherm study.

    PubMed

    Yu, Qiang; Zhang, Ruiqi; Deng, Shubo; Huang, Jun; Yu, Gang

    2009-03-01

    Perfluorooctane sulfonate (PFOS) and perfluorooctanoate (PFOA) have increasingly attracted global concerns in recent years due to their global distribution, persistence, strong bioaccumulation and potential toxicity. The feasibility of using powder activated carbon (PAC), granular activated carbon (GAC) and anion-exchange resin (AI400) to remove PFOS and PFOA from water was investigated with regard to their sorption kinetics and isotherms. Sorption kinetic results show that the adsorbent size influenced greatly the sorption velocity, and both the GAC and AI400 required over 168h to achieve the equilibrium, much longer than 4h for the PAC. Two kinetic models were adopted to describe the experimental data, and the pseudo-second-order model well described the sorption of PFOS and PFOA on the three adsorbents. The sorption isotherms show that the GAC had the lowest sorption capacity both for PFOS and PFOA among the three adsorbents, while the PAC and AI400 possessed the highest sorption capacity of 1.04mmolg(-1) for PFOS and 2.92mmolg(-1) for PFOA according to the Langmuir fitting. Based on the sorption behaviors and the characteristics of the adsorbents and adsorbates, ion exchange and electrostatic interaction as well as hydrophobic interaction were deduced to be involved in the sorption, and some hemi-micelles and micelles possibly formed in the intraparticle pores. PMID:19095279

  17. Kinetic studies of the liquid-phase adsorption of a reactive dye onto activated lignite

    SciTech Connect

    Petrolekas, P.D.; Maggenakis, G.

    2007-02-14

    The kinetics of batch adsorption of a commercial reactive dye onto activated lignite has been investigated at temperatures of 26, 40, and 55{sup o}C, using aqueous solutions with initial dye concentrations in the range of 15-60 mg/L. An empirical single parameter relationship of the adsorbent loading versus the square root of contact time was proposed, which was determined to provide a very good description of the batch adsorption transients up to equilibrium. The data were also examined by means of the Elovich equation. The effect of the temperature and the initial dye concentration on the adsorption kinetics was analyzed, and the results were discussed by considering that intraparticle diffusion is the dominant mechanism.

  18. Kinetic studies on the adsorption of methylene blue onto vegetal fiber activated carbons

    NASA Astrophysics Data System (ADS)

    Cherifi, Hakima; Fatiha, Bentahar; Salah, Hanini

    2013-10-01

    The vegetable sponge of cylindrical loofa (CL), a natural product which grows in the north of Algeria, was used to prepare activated carbons. Two activated carbons, AC1 and AC2, by two physiochemical activation methods to be used for methylene blue removal from wastewater. The surface structure of AC1, AC2 and CL were analyzed by scanning electron microscopy. Adsorption isotherm of methylene blue onto the prepared activated carbons was determined by batch tests. The effects of various parameters such as contact time, initial concentration, pH, temperature, adsorbent dose and granulometry were investigated, at agitation rate 150 rpm. The results showed that the equilibrium uptake increased with increasing initial MB concentration. The maximum % removal of MB obtained was 99% at 50 °C for AC1 and 82% at 30 °C for AC2. The increase in initial pH in the ranges of 2-10 increases the yields removal of MB on AC2. The pseudo-first-order and pseudo-second-order kinetic models were applied to test the experimental data. The latter provided the best correlation of the experimental data compared to the pseudo-first-order model.

  19. Crystallization kinetics and molecular mobility of an amorphous active pharmaceutical ingredient: A case study with Biclotymol.

    PubMed

    Schammé, Benjamin; Couvrat, Nicolas; Malpeli, Pascal; Delbreilh, Laurent; Dupray, Valérie; Dargent, Éric; Coquerel, Gérard

    2015-07-25

    The present case study focuses on the crystallization kinetics and molecular mobility of an amorphous mouth and throat drug namely Biclotymol, through differential scanning calorimetry (DSC), temperature resolved X-ray powder diffraction (TR-XRPD) and hot stage microscopy (HSM). Kinetics of crystallization above the glass transition through isothermal and non-isothermal cold crystallization were considered. Avrami model was used for isothermal crystallization process. Non-isothermal cold crystallization was investigated through Augis and Bennett model. Differences between crystallization processes have been ascribed to a site-saturated nucleation mechanism of the metastable form, confirmed by optical microscopy images. Regarding molecular mobility, a feature of molecular dynamics in glass-forming liquids as thermodynamic fragility index m was determined through calorimetric measurements. It turned out to be around m=100, describing Biclotymol as a fragile glass-former for Angell's classification. Relatively long-term stability of amorphous Biclotymol above Tg was analyzed indirectly by calorimetric monitoring to evaluate thermodynamic parameters and crystallization behavior of glassy Biclotymol. Within eight months of storage above Tg (T=Tg+2°C), amorphous Biclotymol does not show a strong inclination to crystallize and forms a relatively stable glass. This case study, involving a multidisciplinary approach, points out the importance of continuing looking for stability predictors. PMID:26003417

  20. Kinetic and calorimetric study of the adsorption of dyes on mesoporous activated carbon prepared from coconut coir dust.

    PubMed

    Macedo, Jeremias de Souza; da Costa Júnior, Nivan Bezerra; Almeida, Luis Eduardo; Vieira, Eunice Fragoso da Silva; Cestari, Antonio Reinaldo; Gimenez, Iara de Fátima; Villarreal Carreño, Neftali Lênin; Barreto, Ledjane Silva

    2006-06-15

    Mesoporous activated carbon has been prepared from coconut coir dust as support for adsorption of some model dye molecules from aqueous solutions. The methylene blue (MB) and remazol yellow (RY) molecules were chosen for study of the adsorption capacity of cationic and anionic dyes onto prepared activated carbon. The adsorption kinetics was studied with the Lagergren first- and pseudo-second-order kinetic models as well as the intraparticle diffusion model. The results for both dyes suggested a multimechanism sorption process. The adsorption mechanisms in the systems dyes/AC follow pseudo-second-order kinetics with a significant contribution of intraparticle diffusion. The samples simultaneously present acidic and basic sites able to act as anchoring sites for basic and acidic dyes, respectively. Calorimetric studies reveal that dyes/AC interaction forces are correlated with the pH of the solution, which can be related to the charge distribution on the AC surface. These AC samples also exhibited very short equilibrium times for the adsorption of both dyes, which is an economically favorable requisite for the activated carbon described in this work, in addition to the local abundance of the raw material. PMID:16497318

  1. Kinetic activation-relaxation technique.

    PubMed

    Béland, Laurent Karim; Brommer, Peter; El-Mellouhi, Fedwa; Joly, Jean-François; Mousseau, Normand

    2011-10-01

    We present a detailed description of the kinetic activation-relaxation technique (k-ART), an off-lattice, self-learning kinetic Monte Carlo (KMC) algorithm with on-the-fly event search. Combining a topological classification for local environments and event generation with ART nouveau, an efficient unbiased sampling method for finding transition states, k-ART can be applied to complex materials with atoms in off-lattice positions or with elastic deformations that cannot be handled with standard KMC approaches. In addition to presenting the various elements of the algorithm, we demonstrate the general character of k-ART by applying the algorithm to three challenging systems: self-defect annihilation in c-Si (crystalline silicon), self-interstitial diffusion in Fe, and structural relaxation in a-Si (amorphous silicon). PMID:22181304

  2. Adsorption of methylene blue onto activated carbon produced from tea (Camellia sinensis L.) seed shells: kinetics, equilibrium, and thermodynamics studies*

    PubMed Central

    Gao, Jun-jie; Qin, Ye-bo; Zhou, Tao; Cao, Dong-dong; Xu, Ping; Hochstetter, Danielle; Wang, Yue-fei

    2013-01-01

    Tea (Camellia sinensis L.) seed shells, the main byproduct of the manufacture of tea seed oil, were used as precursors for the preparation of tea activated carbon (TAC) in the present study. A high yield (44.1%) of TAC was obtained from tea seed shells via a one-step chemical method using ZnCl2 as an agent. The Brunauer-Emmett-Teller (BET) surface area and the total pore volumes of the obtained TAC were found to be 1 530.67 mg2/g and 0.782 6 cm3/g, respectively. The equilibrium adsorption results were complied with Langmuir isotherm model and its maximum monolayer adsorption capacity was 324.7 mg/g for methylene blue. Adsorption kinetics studies indicated that the pseudo-second-order model yielded the best fit for the kinetic data. An intraparticle diffusion model suggested that the intraparticle diffusion was not the only rate-controlling step. Thermodynamics studies revealed the spontaneous and exothermic nature of the sorption process. These results indicate that tea seed shells could be utilized as a renewable resource to develop activated carbon which is a potential adsorbent for methylene blue. PMID:23825151

  3. Kinetic studies of Thermobifida fusca Cel9A active site mutant enzymes.

    PubMed

    Zhou, Weilin; Irwin, Diana C; Escovar-Kousen, Jose; Wilson, David B

    2004-08-01

    Thermobifida fusca Cel9A-90, an unusual family 9 enzyme, is a processive endoglucanase containing a catalytic domain closely linked to a family 3c cellulose binding domain (Cel9A-68) followed by a fibronectin III-like domain and a family 2 cellulose binding domain. To study its catalytic mechanism, 12 mutant genes with changes in five conserved residues of Cel9A-68 were constructed, cloned, and expressed in Escherichia coli. The purified mutant enzymes were assayed for their activities on (carboxymethyl)cellulose, phosphoric acid-swollen cellulose, bacterial microcrystalline cellulose, and 2,4-dinitrophenyl beta-D-cellobioside. They were also tested for ligand binding, enzyme processivity, and thermostability. The results clearly show that E424 functions as the catalytic acid, D55 and D58 are both required for catalytic base activity, and Y206 plays an important role in binding, catalysis, and processivity, while Y318 plays an important role in binding of crystalline cellulose substrates and is required for processivity. Several amino acids located in a loop at the end of the catalytic cleft (T245-L251) were deleted from Cel9A-68, and this enzyme showed slightly improved filter paper activity and binding to BMCC but otherwise behaved like the wild-type enzyme. The FnIII-like domain was deleted from Cel9A-90, reducing BMCC activity to 43% of the wild type. PMID:15274620

  4. Application of zeolite-activated carbon macrocomposite for the adsorption of Acid Orange 7: isotherm, kinetic and thermodynamic studies.

    PubMed

    Lim, Chi Kim; Bay, Hui Han; Neoh, Chin Hong; Aris, Azmi; Abdul Majid, Zaiton; Ibrahim, Zaharah

    2013-10-01

    In this study, the adsorption behavior of azo dye Acid Orange 7 (AO7) from aqueous solution onto macrocomposite (MC) was investigated under various experimental conditions. The adsorbent, MC, which consists of a mixture of zeolite and activated carbon, was found to be effective in removing AO7. The MC were characterized by scanning electron microscopy (SEM), energy dispersive X-ray, point of zero charge, and Brunauer-Emmett-Teller surface area analysis. A series of experiments were performed via batch adsorption technique to examine the effect of the process variables, namely, contact time, initial dye concentration, and solution pH. The dye equilibrium adsorption was investigated, and the equilibrium data were fitted to Langmuir, Freundlich, and Tempkin isotherm models. The Langmuir isotherm model fits the equilibrium data better than the Freundlich isotherm model. For the kinetic study, pseudo-first-order, pseudo-second-order, and intraparticle diffusion model were used to fit the experimental data. The adsorption kinetic was found to be well described by the pseudo-second-order model. Thermodynamic analysis indicated that the adsorption process is a spontaneous and endothermic process. The SEM, Fourier transform infrared spectroscopy, ultraviolet-visible spectral and high performance liquid chromatography analysis were carried out before and after the adsorption process. For the phytotoxicity test, treated AO7 was found to be less toxic. Thus, the study indicated that MC has good potential use as an adsorbent for the removal of azo dye from aqueous solution. PMID:23653315

  5. Equilibrium and kinetic studies of adsorption of phosphate onto ZnCl2 activated coir pith carbon.

    PubMed

    Namasivayam, C; Sangeetha, D

    2004-12-15

    Phosphate removal from aqueous solution was investigated using ZnCl(2)-activated carbon developed from coir pith, an agricultural solid waste. Studies were conducted to delineate the effect of contact time, adsorbent dose, phosphate concentration, pH, and temperature. The adsorption equilibrium data followed both Langmuir and Freundlich isotherms. Langmuir adsorption capacity was found to be 5.1 mg/g. Adsorption followed second-order kinetics. The removal was maximum in the pH range 3-10. pH effect and desorption studies showed that adsorption occurred by both ion exchange and chemisorption mechanisms. Adsorption was found to be spontaneous and endothermic. Effect of foreign ions on adsorption shows that perchlorate, sulfate, and selenite decreased the percent removal of phosphate. PMID:15533408

  6. Magnetic resonance and kinetic studies of the mechanism of membrane-bound sodium and potassium ion- activated adenosine triphosphatase.

    PubMed

    Grisham, C M; Mildvan, A S

    1975-01-01

    EPR and water proton relaxation rate (1/T1) studies of partially (40%) and "fully" (90%) purified preparations of membrane-bound (Na+ + K+) activated ATPase from sheep kidney indicate one tight binding site for Mn2+ per enzyme dimer, with a dissociation constant (KD = 0.88 muM) in agreement with the kinetically determined activator constant, identifying this Mn2+-binding site as the active site of the ATPase. Competition studies indicate that Mg2+ binds at this site with a dissociation constant of 1 mM in agreement with its activator constant. Inorganic phosphate and methylphosphonate bind to the enzyme-Mn2+ complex with similar high affinities and decrease 1/T1 of water protons due to a decrease from four to three in the number of rapidly exchanging water protons in the coordination sphere of enzyme-bound Mn2+. The relative effectiveness of Na+ and K+ in facilitating ternary complex formation with HPO2-4 and CH3PO2-3 as a function of pH indicates that Na+ induces the phosphate monoanion to interact with enzyme-bound Mn2+. Thus protonation of an enzyme-bound phosphoryl group would convert a K+-binding site to a Na+-binding site. Dissociation constants for K+ and Na+, estimated from NMR titrations, agreed with kinetically determined activator constants of these ions consistent with binding to the active site. Parallel 32Pi-binding studies show negligible formation (less than 7%) of a covalent E-P complex under these conditions, indicating that the NMR method has detected an additional noncovalent intermediate in ion transport. Ouabain, which increases the extent of phosphorylation of the enzyme to 24% at pH 7.8 and to 106% at pH 6.1, produced further decreases in 1/T1 of water protons. Preliminary 31P- relaxation studies of CH3PO2-3 in the presence of ATPase and Mn2+ yield an Mn to P distance (6.9 +/- 0.5 A) suggesting a second sphere enzyme-Mn-ligand-CH3PO2-3 complex. Previous kinetic studies have shown that T1+ substitutes for K+ in the activation of the enzyme

  7. Treatment of dairy wastewater by commercial activated carbon and bagasse fly ash: Parametric, kinetic and equilibrium modelling, disposal studies.

    PubMed

    Kushwaha, Jai Prakash; Srivastava, Vimal Chandra; Mall, Indra Deo

    2010-05-01

    Present study reports treatment of synthetic dairy wastewater (SDW) in terms of chemical oxygen demand (COD) removal by means of adsorption onto activated carbon-commercial grade (ACC) and bagasse fly ash (BFA). Optimum conditions for SDW treatment were found to be: initial pH approximately 4.8, adsorbent dose of 20g/l for ACC and 10g/l for BFA and contact time approximately 8h. Pseudo-second-order kinetic model was found to fit the kinetic data and Redlich-Peterson isotherm model was generally found to best represent the equilibrium data for SDW treatment by ACC and BFA. The change in entropy and enthalpy for SDW adsorption onto ACC and BFA were estimated as 125.85kJ/molK and 91.53kJ/mol; and 25.71kJ/molK and 17.26kJ/mol, respectively. The negative values of change in Gibbs free energy indicate the feasibility and spontaneous nature of the adsorptive treatment. PMID:20097555

  8. Iron Impregnated Activated Carbon as an Efficient Adsorbent for the Removal of Methylene Blue: Regeneration and Kinetics Studies

    PubMed Central

    Shah, Irfan; Adnan, Rohana; Wan Ngah, Wan Saime; Mohamed, Norita

    2015-01-01

    In this study, iron impregnated activated carbon (FeAC) was synthesized following an oxidation and iron impregnation of activated carbon (AC). Both the AC and FeAC were characterized by pHZPC and FTIR spectroscopy. The removal of Methylene Blue (MB) by AC and FeAC was examined under various experimental conditions. The FeAC showed up to 95% (higher than AC) MB removal in the pH range of 7–10. Although the reaction kinetics was pseudo–second order, the overall rate was controlled by a number of processes such as film diffusion, pore diffusion and intraparticle diffusion. The activation energy values for the MB uptake by AC and FeAC (21.79 and 14.82 kJ/mol, respectively) revealed a physisorption process. In the regeneration study, FeAC has shown consistently ≥ 90% MB removal even up to 10 repeated cycles. The reusable characteristic of the spent FeAC improved the practical use of activated carbon and can be a breakthrough for continuous flow system applications where it can work effectively without any significant reduction in its performance. PMID:25849291

  9. Equilibrium and kinetics study on the adsorption of perfluorooctanoic acid from aqueous solution onto powdered activated carbon.

    PubMed

    Qu, Yan; Zhang, Chaojie; Li, Fei; Bo, Xiaowen; Liu, Guangfu; Zhou, Qi

    2009-09-30

    Powdered activated carbon (PAC) was applied to remove perfluorooctanoic acid (PFOA) from the aqueous PFOA solution in this study. Contact time, adsorbent dose and temperature were analyzed as the effect factors in the adsorption reaction. The contact time of maximum PFOA uptake was around 1h while the sorption removal efficiency increased with the PAC concentrations. And the process of adsorption increased from 303 K to 313 K and then decreased from 313 K to 323 K. Among four applied models, the experimental isotherm data were discovered to follow Langmuir isotherm model more closely. Thermodynamically, adsorption was endothermic because enthalpy, entropy and Gibbs constants were 198.5 kJ/mol, 0.709 kJ/mol/K and negative, respectively, which also indicated that the adsorption process was spontaneous and feasible. From kinetic analysis, the adsorption was suggested to be pseudo-second-order model. The adsorption of PFOA on the PAC was mainly controlled by particle diffusion. PMID:19395160

  10. Liquefaction chemistry and kinetics: Hydrogen utilization studies

    SciTech Connect

    Rothenberger, K.S.; Warzinski, R.P.; Cugini, A.V.

    1995-12-31

    The objectives of this project are to investigate the chemistry and kinetics that occur in the initial stages of coal liquefaction and to determine the effects of hydrogen pressure, catalyst activity, and solvent type on the quantity and quality of the products produced. The project comprises three tasks: (1) preconversion chemistry and kinetics, (2) hydrogen utilization studies, and (3) assessment of kinetic models for liquefaction. The hydrogen utilization studies work will be the main topic of this report. However, the other tasks are briefly described.

  11. Mechanism of O2 activation by cytochrome P450cam studied by isotope effects and transient state kinetics.

    PubMed

    Purdy, Matthew M; Koo, Laura S; de Montellano, Paul R Ortiz; Klinman, Judith P

    2006-12-26

    The early steps in dioxygen activation by the monooxygenase cytochrome P450cam (CYP101) include binding of O2 to ferrous P450cam to yield the ferric-superoxo form (oxyP450cam) followed by an irreversible, long-range electron transfer from putidaredoxin to reduce the oxyP450cam. The steady state kinetic parameter kcat/Km(O2) has been studied by a variety of probes that indicate a small D2O solvent isotope effect (1.21 +/- 0.08), a very small solvent viscosogen effect, and a 16O/18O isotope effect of 1.0147 +/- 0.0007. This latter value, which can be compared with the 16O/18O equilibrium isotope effect of 1.0048 +/- 0.0003 measured for oxyP450cam formation, is attributed to a primarily rate-limiting outer-sphere electron transfer from the heme iron center as O2 that has prebound to protein approaches the active site cofactor. The electron transfer from putidaredoxin to oxyP450cam was investigated by rapid mixing at 25 degrees C to complement previous lower-temperature measurements. A rate of 390 +/- 23 s-1 (and a near-unity solvent isotope effect) supports the view that the long-range electron transfer from reduced putidaredoxin to oxyP450cam is rapid relative to dissociation of O2 from the enzyme. P450cam represents the first enzymatic reaction of O2 in which both equilibrium and kinetic 16O/18O isotope effects have been measured. PMID:17176102

  12. A comparative study of rhodopsin function in the great bowerbird (Ptilonorhynchus nuchalis): Spectral tuning and light-activated kinetics.

    PubMed

    van Hazel, Ilke; Dungan, Sarah Z; Hauser, Frances E; Morrow, James M; Endler, John A; Chang, Belinda S W

    2016-07-01

    Rhodopsin is the visual pigment responsible for initiating the phototransduction cascade in vertebrate rod photoreceptors. Although well-characterized in a few model systems, comparative studies of rhodopsin function, particularly for nonmammalian vertebrates are comparatively lacking. Bowerbirds are rare among passerines in possessing a key substitution, D83N, at a site that is otherwise highly conserved among G protein-coupled receptors. While this substitution is present in some dim-light adapted vertebrates, often accompanying another unusual substitution, A292S, its functional relevance in birds is uncertain. To investigate functional effects associated with these two substitutions, we use the rhodopsin gene from the great bowerbird (Ptilonorhynchus nuchalis) as a background for site-directed mutagenesis, in vitro expression and functional characterization. We also mutated these sites in two additional rhodopsins that do not naturally possess N83, chicken and bovine, for comparison. Both sites were found to contribute to spectral blue-shifts, but had opposing effects on kinetic rates. Substitutions at site 83 were found to primarily affect the kinetics of light-activated rhodopsin, while substitutions at site 292 had a larger impact on spectral tuning. The contribution of substitutions at site 83 to spectral tuning in particular depended on genetic background, but overall, the effects of substitutions were otherwise surprisingly additive, and the magnitudes of functional shifts were roughly similar across all three genetic backgrounds. By employing a comparative approach with multiple species, our study provides new insight into the joint impact of sites 83 and 292 on rhodopsin structure-function as well as their evolutionary significance for dim-light vision across vertebrates. PMID:26889650

  13. Biochemical methods for studying kinetic regulation of Arf1 activation by Sec7

    PubMed Central

    Richardson, Brian C.; Fromme, J. Christopher

    2015-01-01

    The Arf family of small GTPases regulates vesicular transport at several locations within the cell, and is in turn regulated by guanine nucleotide exchange factors (GEFs) via a conserved catalytic domain, termed the Sec7 domain. The catalytic activity of the Sec7 domain is well characterized in the context of a few GEFs acting at the periphery of the cell. This chapter describes techniques used to extend biochemical analysis of activity to the much larger GEFs acting on the Arf family in the core secretory pathway, using the activity of S. cerevisiae Sec7 on Arf1, regulating export from the trans-Golgi network (TGN), as a model. Complete methods for purification to near-homogeneity of all proteins required, including several Sec7 constructs and multiple relevant small GTPases, are detailed. These are followed by methods for quantification of the nucleotide exchange activity of Sec7 in a physiologically relevant context, including modifications required to dissect the signal integration functions of Sec7 as an effector of several other small GTPases, and methods for identifying stable Sec7-small GTPase interactions in the presence of membranes. These techniques may be extended to analysis of similar members of the Sec7 GEF subfamily in other species and acting elsewhere in the secretory pathway. PMID:26360031

  14. Kinetic and sensitive analysis of tyrosinase activity using electron transfer complexes: in vitro and intracellular study.

    PubMed

    Zhu, Xianglong; Hu, Juan; Zhao, Zhenghuan; Sun, Mingjun; Chi, Xiaoqin; Wang, Xiaomin; Gao, Jinhao

    2015-02-18

    Tyrosinase is an important marker of human diseases such as the neurodegeneration associated with Parkinson's disease and melanoma. Sensitive detection of tyrosinase activity in vitro and inside cells is of great significance to medical diagnostics and skin disorder treatments. With unique photophysical properties, semiconductor quantum dots (QDs) are employed as photoluminescent platforms for various biosensing, in particular for the detection of enzyme activities. In this work, QDs are functionalized with tyrosine and zwitterionic molecules to construct a nanometer-scale scaffold (QD-Tyr conjugate), and this is used to test tyrosinase activity in vitro and inside cells. Tyrosinase oxidizes tyrosine to dopachrome and switches on the electron-transfer access, which relates to fluorescence quenching. High quenching efficiency is achieved by shortening the distance between the electron donors and acceptors, which is attributed to the small size of the conjugated tyrosine. Enzymatic process curves reveal the enhanced enzymatic activity on the conjugated nanoparticle substrate, which leads to highly sensitive detection of tyrosinase (as low as 1 nM). It is also demonstrated that QD-Tyr conjugates can sensitively probe intracellular tyrosinase in melanoma cells, which promises great potential in disease monitoring and medical diagnostics. PMID:25285706

  15. An investigation into the crystallization tendency/kinetics of amorphous active pharmaceutical ingredients: A case study with dipyridamole and cinnarizine.

    PubMed

    Baghel, Shrawan; Cathcart, Helen; Redington, Wynette; O'Reilly, Niall J

    2016-07-01

    Amorphous drug formulations have great potential to enhance solubility and thus bioavailability of BCS class II drugs. However, the higher free energy and molecular mobility of the amorphous form drive them towards the crystalline state which makes them unstable. Accurate determination of the crystallization tendency/kinetics is the key to the successful design and development of such systems. In this study, dipyridamole (DPM) and cinnarizine (CNZ) have been selected as model compounds. Thermodynamic fragility (mT) was measured from the heat capacity change at the glass transition temperature (Tg) whereas dynamic fragility (mD) was evaluated using methods based on extrapolation of configurational entropy to zero [Formula: see text] , and heating rate dependence of Tg [Formula: see text] . The mean relaxation time of amorphous drugs was calculated from the Vogel-Tammann-Fulcher (VTF) equation. Furthermore, the correlation between fragility and glass forming ability (GFA) of the model drugs has been established and the relevance of these parameters to crystallization of amorphous drugs is also assessed. Moreover, the crystallization kinetics of model drugs under isothermal conditions has been studied using Johnson-Mehl-Avrami (JMA) approach to determine the Avrami constant 'n' which provides an insight into the mechanism of crystallization. To further probe into the crystallization mechanism, the non-isothermal crystallization kinetics of model systems were also analysed by statistically fitting the crystallization data to 15 different kinetic models and the relevance of model-free kinetic approach has been established. The crystallization mechanism for DPM and CNZ at each extent of transformation has been predicted. The calculated fragility, glass forming ability (GFA) and crystallization kinetics are found to be in good correlation with the stability prediction of amorphous solid dispersions. Thus, this research work involves a multidisciplinary approach to

  16. Adsorption behavior of activated carbon derived from pyrolusite-modified sewage sludge: equilibrium modeling, kinetic and thermodynamic studies.

    PubMed

    Chen, Yao; Jiang, Wenju; Jiang, Li; Ji, Xiujuan

    2011-01-01

    Activated carbon was developed from sewage sludge using pyrolusite as an additive. It was demonstrated that the removal efficiency of two synthetic dyes (Tracid orange GS and Direct fast turquoise blue GL) by the produced adsorbent was up to 97.6%. The activated carbon with pyrolusite addition had 38.2% higher surface area, 43.8% larger micropore and 54.4% larger mesopore production than ordinary sludge-based activated carbons. Equilibrium adsorption isotherms and kinetics were also investigated based on dyes adsorption tests. The experimental data were analyzed by the Langmuir and Freundlich models of adsorption, and the results fitted well to the Langmuir isotherm. The kinetic data have been analyzed using pseudo-first-order, pseudo-second-order and intraparticle diffusion equation. The experimental data fitted very well with pseudo-second-order kinetic model. Activation energies for the adsorption processes ranged between 8.7 and 19.1 kJ mol 1. Thermodynamic parameters such as standard free energy (deltaG0), standard enthalpy (deltaH0) and standard entropy (deltaS0) were evaluated. The adsorption of these two dyes on the activated carbon was found to be a spontaneous and endothermic process in nature. PMID:22097045

  17. Activated carbon derived from carbon residue from biomass gasification and its application for dye adsorption: Kinetics, isotherms and thermodynamic studies.

    PubMed

    Maneerung, Thawatchai; Liew, Johan; Dai, Yanjun; Kawi, Sibudjing; Chong, Clive; Wang, Chi-Hwa

    2016-01-01

    In this work, activated carbon (AC) as an effective and low-cost adsorbent was successfully prepared from carbon residue (or char, one of the by-products from woody biomass gasification) via physical activation. The surface area of char was significantly increased from 172.24 to 776.46m(2)/g after steam activation at 900°C. The obtained activated carbons were then employed for the adsorption of dye (Rhodamine B) and it was found that activated carbon obtained from steam activation exhibited the highest adsorption capability, which is mainly attributed to the higher surface area and the abundance of hydroxyl (-OH) and carboxyl (-COOH) groups on the activated carbon surface. Moreover, it was also found that the adsorption capability significantly increased under the basic condition, which can be attributed to the increased electrostatic interaction between the deprotonated (negatively charged) activated carbon and dye molecules. Furthermore, the equilibrium data were fitted into different adsorption isotherms and found to fit well with Langmuir model (indicating that dye molecules form monolayer coverage on activated carbon) with a maximum monolayer adsorption capability of 189.83mg/g, whereas the adsorption kinetics followed the pseudo-second-order kinetics. PMID:26512858

  18. Kinetic and Spectroscopic Studies of Bicupin Oxalate Oxidase and Putative Active Site Mutants

    PubMed Central

    Moomaw, Ellen W.; Hoffer, Eric; Moussatche, Patricia; Salerno, John C.; Grant, Morgan; Immelman, Bridget; Uberto, Richard; Ozarowski, Andrew; Angerhofer, Alexander

    2013-01-01

    Ceriporiopsis subvermispora oxalate oxidase (CsOxOx) is the first bicupin enzyme identified that catalyzes manganese-dependent oxidation of oxalate. In previous work, we have shown that the dominant contribution to catalysis comes from the monoprotonated form of oxalate binding to a form of the enzyme in which an active site carboxylic acid residue must be unprotonated. CsOxOx shares greatest sequence homology with bicupin microbial oxalate decarboxylases (OxDC) and the 241-244DASN region of the N-terminal Mn binding domain of CsOxOx is analogous to the lid region of OxDC that has been shown to determine reaction specificity. We have prepared a series of CsOxOx mutants to probe this region and to identify the carboxylate residue implicated in catalysis. The pH profile of the D241A CsOxOx mutant suggests that the protonation state of aspartic acid 241 is mechanistically significant and that catalysis takes place at the N-terminal Mn binding site. The observation that the D241S CsOxOx mutation eliminates Mn binding to both the N- and C- terminal Mn binding sites suggests that both sites must be intact for Mn incorporation into either site. The introduction of a proton donor into the N-terminal Mn binding site (CsOxOx A242E mutant) does not affect reaction specificity. Mutation of conserved arginine residues further support that catalysis takes place at the N-terminal Mn binding site and that both sites must be intact for Mn incorporation into either site. PMID:23469254

  19. Kinetic studies of adsorption of thiocyanate onto ZnCl2 activated carbon from coir pith, an agricultural solid waste.

    PubMed

    Namasivayam, C; Sangeetha, D

    2005-09-01

    The adsorption of thiocyanate onto ZnCl2 activated carbon developed from coir pith was investigated to assess the possible use of this adsorbent. The influence of various parameters such as agitation time, thiocyanate concentration, adsorbent dose, pH and temperature has been studied. Adsorption followed second-order rate kinetics. Two theoretical adsorption isotherms, namely, Langmuir and Freundlich were used to describe the experimental results. The Langmuir adsorption capacity (Q0) was found to be 16.2 mg g(-1) of the adsorbent. The per cent adsorption was maximum in the pH range 3.0-7.0. pH effect and desorption studies showed that ion exchange and chemisorption mechanism are involved in the adsorption process. Thermodynamic parameters such as DeltaG0, DeltaH0 and DeltaS0 for the adsorption were evaluated. The negative values of DeltaH0 confirm the exothermic nature of adsorption. Effects of foreign ions on the adsorption of thiocyanate have been investigated. Removal of thiocyanate from ground water was also tested. PMID:16083768

  20. Structure-Activity Relationship Studies of Isomeric 2,4-Diaminoquinazolines on β-Amyloid Aggregation Kinetics.

    PubMed

    Mohamed, Tarek; Shakeri, Arash; Tin, Gary; Rao, Praveen P N

    2016-05-12

    A library of isomeric 2,4-diaminoquinazoline (DAQ) derivatives were synthesized and evaluated for antiaggregation potential toward Aβ40/42. Structure-activity relationship data identified compound 3k (N (4)-(4-bromobenzyl)quinazoline-2,4-diamine) with a 4-bromobenzyl substituent as the most potent inhibitor (Aβ40 IC50 = 80 nM) and was almost 18-fold more potent compared to the reference agent curcumin (Aβ40 IC50 = 1.5 μM). The corresponding N (2)-isomer 4k (N (2)-(4-bromobenzyl)quinazoline-2,4-diamine) was also able to prevent Aβ aggregation (Aβ40 IC50 = 1.7 μM). However, compound 4k exhibited superior inhibition of Aβ42 aggregation (Aβ42 IC50 = 1.7 μM) compared to compound 3k (Aβ42 IC50 = 14.8 μM) and was ∼1.8-fold more potent compared to curcumin (Aβ42 IC50 = 3.1 μM). These results were supported by Aβ aggregation kinetics investigations and transmission electron microscopy studies, which demonstrate the suitability of DAQ ring system to develop antiamyloid agents as pharmacological tools to study Aβ aggregation. PMID:27190601

  1. Kinetic study on biomass gasification

    SciTech Connect

    Bingyan, X.; Chuangzhi, W.; Zhengfen, L.; Guang, Z.X. )

    1992-09-01

    An experimental apparatus, with the features of fast heating rate and continuous record of reaction parameters, was developed to study kinetics of fast pyrolysis. The temperature effects, at a range of 400 C to 900 C, on pyrolysis rate, products profile, gas quality and quantity, and so on, were studied and the results are listed and analyzed. The effect of secondary reaction of gas phase at 700 C was tested and the regression result is expressed in an experimental formula. Based on the experimental results, the three-stage-reaction mechanism module is suggested. The kinetic expression to calculate gas formation rate is concluded as: d{alpha}/dt = A exp({minus}E/RT)(1 {minus} {alpha}){sup n}. The kinetic parameters of A, E, and n at different temperatures are given in the paper.

  2. Nanoporous activated carbon fluidized bed catalytic oxidations of aqueous o, p and m-cresols: kinetic and thermodynamic studies.

    PubMed

    Karthikeyan, S; Sekaran, G; Gupta, V K

    2013-07-01

    Nanoporous activated carbon prepared from rice husk through precarbonisation at 400 °C and phosphoric acid activation at 800 °C was used as fluidized bed in Fenton oxidation of the o, p and m-cresols in aqueous solution. The efficiencies of homogeneous Fenton oxidation, fluidized Fenton oxidation and aerobic biological oxidation systems for the removal of o, p and m-cresols in aqueous solution have been compared. The kinetic constants and the thermodynamic parameters for the homogeneous Fenton, heterogeneous Fenton and aerobic biological oxidations of o, p and m-cresols in synthetic wastewater were determined. The degradation of cresols in synthetic wastewater was confirmed using FT-IR, (1)H-NMR and UV-visible spectroscopy. PMID:23292221

  3. Supramolecular polymer transformation: a kinetic study.

    PubMed

    Baram, Jonathan; Weissman, Haim; Rybtchinski, Boris

    2014-10-16

    Investigation of supramolecular kinetics is essential for elucidating self-assembly mechanisms. Recently, we reported on a noncovalent system involving a bolaamphiphilic perylene diimide dimer that is kinetically trapped in water but can rearrange into a different, more ordered assembly in water/THF mixtures ( Angew. Chem. Int. Ed. 2014 , 53 , 4123 ). Here we present a kinetic mechanistic study of this process by employing UV-vis spectroscopy. The transformation exhibits a rapid decrease in the red-shifted absorption band, which is monitored in order to track the kinetics at different temperatures (15-50 °C) and concentrations. Fitting the data with the 1D KJMA (Kolmogorov-Johnson-Mehl-Avrami) model affords the activation parameters. The latter as well as seeding experiments indicates that the transformation occurs without the detachment of covalent units, and that hydration dynamics plays a significant role in nucleation, with entropic factors being dominant. Switching off the transformation, and the formation of off-pathway intermediates were observed upon heating to temperatures above 55 °C. These insights into kinetically controlled supramolecular polymer transformations provide mechanistic information that is needed for a fundamental understanding of noncovalent processes, and the rational design of noncovalent materials. PMID:25238603

  4. Deterministic Modelling of BAK Activation Kinetics

    NASA Astrophysics Data System (ADS)

    Grills, C.; Chacko, A.; Crawford, N.; Johnston, P. G.; Fennell, D. A.; O'Rourke, S. F. C.

    2009-08-01

    The molecular mechanism underlying mitochondrial BAK activation during apoptosis remains highly controversial. Two seemingly conflicting models have been proposed. In the activation model, BAK requires so-called activating BH3 only proteins (aBH3) to initiate its conformation change. In the other, displacement from inhibitory pro-survival BCL-2 proteins (PBPs) and monomerization of BAK by PBP restricted dissociator BH3-only proteins (dBH3) is sufficient. To better understand the kinetic implications of these models and reconcile these conflicting but highly evidence-based models, we have employed dynamical systems analysis to explore the kinetics underlying BAK activation as a non-linear reaction system. Our findings accommodate both pure agonism and dissociation as mutually exclusive mechanisms capable of initiating BAK activation. In addition we find our work supports a modelling based approach for predicting resistance to therapeutically relevant small molecules BH3 mimetics.

  5. Kinetic studies on the oxidation of oxyhemoglobin by biologically active iron thiosemicarbazone complexes: relevance to iron-chelator-induced methemoglobinemia.

    PubMed

    Basha, Maram T; Rodríguez, Carlos; Richardson, Des R; Martínez, Manuel; Bernhardt, Paul V

    2014-03-01

    The oxidation of oxyhemoglobin to methemoglobin has been found to be facilitated by low molecular weight iron(III) thiosemicarbazone complexes. This deleterious reaction, which produces hemoglobin protein units unable to bind dioxygen and occurs during the administration of iron chelators such as the well-known 3-aminopyridine-2-pyridinecarbaldehyde thiosemicarbazone (3-AP; Triapine), has been observed in the reaction with Fe(III) complexes of some members of the 3-AP structurally-related thiosemicarbazone ligands derived from di-2-pyridyl ketone (HDpxxT series). We have studied the kinetics of this oxidation reaction in vitro using human hemoglobin and found that the reaction proceeds with two distinct time-resolved steps. These have been associated with sequential oxidation of the two different oxyheme cofactors in the α and β protein chains. Unexpected steric and hydrogen-bonding effects on the Fe(III) complexes appear to be the responsible for the observed differences in the reaction rate across the series of HDpxxT ligand complexes used in this study. PMID:24317633

  6. Following atomistic kinetics on experimental timescales with the kinetic Activation Relaxation Technique

    DOE PAGESBeta

    Mousseau, Normand; Beland, Laurent K; Brommer, Peter; El-Mellouhi, Fedwa; Joly, Jean-Francois; N'Tsouaglo, Gawonou Kokou; Restrepo, Oscar; Trochet, Mickael

    2015-01-01

    The properties of materials, even at the atomic level, evolve on macroscopic time scales. Following this evolution through simulation has been a challenge for many years. For lattice-based activated diffusion, kinetic Monte Carlo has turned out to be an almost perfect solution. Various accelerated molecular dynamical schemes, for their part, have allowed the study on long time scale of relatively simple systems. There is still a need, however, for methods able to handle complex materials such as alloys and disordered systems. Here, we review the kinetic Activation Relaxation Technique (k-ART), one of a handful of off-lattice kinetic Monte Carlo methods,more » with on-the-fly cataloging, that have been proposed in the last few years.« less

  7. Kinetic study and mechanism of Niclosamide degradation.

    PubMed

    Zaazaa, Hala E; Abdelrahman, Maha M; Ali, Nouruddin W; Magdy, Maimana A; Abdelkawy, M

    2014-11-11

    A spectrophotometric kinetic study of Niclosamide alkaline degradation as a function of drug concentration, alkaline concentration and temperature has been established utilizing double divisor-ratio spectra spectrophotometric method. The developed method allowed determination of Niclosamide in presence of its alkaline degradation products; namely; 2-chloro-4-nitro aniline (DEG I) and 5-chloro salicylic acid (DEG II) with characterization of its degradation mechanism. It was found that degradation kinetic of Niclosamide followed pseudo-first order under the established experimental conditions with a degradation rate constant (k) of 0.0829 mol/h and half life (t1/2) of 8.35 h. The overall degradation rate constant as a function of the temperature under the given conditions obeyed Arrhenius equation where the activation energy was calculated to be 3.41 kcal/mol. PMID:24892546

  8. Kinetic study and mechanism of Niclosamide degradation

    NASA Astrophysics Data System (ADS)

    Zaazaa, Hala E.; Abdelrahman, Maha M.; Ali, Nouruddin W.; Magdy, Maimana A.; Abdelkawy, M.

    2014-11-01

    A spectrophotometric kinetic study of Niclosamide alkaline degradation as a function of drug concentration, alkaline concentration and temperature has been established utilizing double divisor-ratio spectra spectrophotometric method. The developed method allowed determination of Niclosamide in presence of its alkaline degradation products; namely; 2-chloro-4-nitro aniline (DEG I) and 5-chloro salicylic acid (DEG II) with characterization of its degradation mechanism. It was found that degradation kinetic of Niclosamide followed pseudo-first order under the established experimental conditions with a degradation rate constant (k) of 0.0829 mol/h and half life (t1/2) of 8.35 h. The overall degradation rate constant as a function of the temperature under the given conditions obeyed Arrhenius equation where the activation energy was calculated to be 3.41 kcal/mol.

  9. CURRENT AND KINETIC HELICITY OF LONG-LIVED ACTIVITY COMPLEXES

    SciTech Connect

    Komm, Rudolf; Gosain, Sanjay

    2015-01-01

    We study long-lived activity complexes and their current helicity at the solar surface and their kinetic helicity below the surface. The current helicity has been determined from synoptic vector magnetograms from the NSO/SOLIS facility, and the kinetic helicity of subsurface flows has been determined with ring-diagram analysis applied to full-disk Dopplergrams from NSO/GONG and SDO/HMI. Current and kinetic helicity of activity complexes follow the hemispheric helicity rule with mainly positive values (78%; 78%, respectively, with a 95% confidence level of 31%) in the southern hemisphere and negative ones (80%; 93%, respectively, with a 95% confidence level of 22% and 14%, respectively) in the northern hemisphere. The locations with the dominant sign of kinetic helicity derived from Global Oscillation Network Group (GONG) and SDO/HMI data are more organized than those of the secondary sign even if they are not part of an activity complex, while locations with the secondary sign are more fragmented. This is the case for both hemispheres even for the northern one where it is not as obvious visually due to the large amount of magnetic activity present as compared to the southern hemisphere. The current helicity shows a similar behavior. The dominant sign of current helicity is the same as that of kinetic helicity for the majority of the activity complexes (83% with a 95% confidence level of 15%). During the 24 Carrington rotations analyzed here, there is at least one longitude in each hemisphere where activity complexes occur repeatedly throughout the epoch. These ''active'' longitudes are identifiable as locations of strong current and kinetic helicity of the same sign.

  10. A Kinetic Model of Active Extensile Bundles

    NASA Astrophysics Data System (ADS)

    Goldstein, Daniel; Chakraborty, Bulbul; Baskaran, Aparna

    Recent experiments in active filament networks reveal interesting rheological properties (Dan Chen: APS March Meeting 2015 D49.00001). This system consumes ATP to produce an extensile motion in bundles of microtubules. This extension then leads to self generated stresses and spontaneous flows. We propose a minimal model where the activity is modeled by self-extending bundles that are part of a cross linked network. This network can reorganize itself through buckling of extending filaments and merging events that alter the topology of the network. We numerically simulate this minimal kinetic model and examine the emergent rheological properties and determine how stresses are generated by the extensile activity. We will present results that focus on the effects of confinement and network connectivity of the bundles on stress fluctuations and response of an active gel.

  11. Lipoic acid and dihydrolipoic acid. A comprehensive theoretical study of their antioxidant activity supported by available experimental kinetic data.

    PubMed

    Castañeda-Arriaga, Romina; Alvarez-Idaboy, J Raul

    2014-06-23

    The free radical scavenging activity of lipoic acid (LA) and dihydrolipoic acid (DHLA) has been studied in nonpolar and aqueous solutions, using the density functional theory and several oxygen centered radicals. It was found that lipoic acid is capable of scavenging only very reactive radicals, while the dehydrogenated form is an excellent scavenger via a hydrogen transfer mechanism. The environment plays an important role in the free radical scavenging activity of DHLA because in water it is deprotonated, and this enhances its activity. In particular, the reaction rate constant of DHLA in water with an HOO(•) radical is close to the diffusion limit. This has been explained on the basis of the strong H-bonding interactions found in the transition state, which involve the carboxylate moiety, and it might have implications for other biological systems in which this group is present. PMID:24881907

  12. A study on the morphology and catalytic activity of gold nanoparticles by the kinetic Monte Carlo simulation

    NASA Astrophysics Data System (ADS)

    He, Xiang; Chen, Zhao-Xu

    2016-05-01

    We studied the thermal-stability of supported Au nanoparticles on the substrates of different binding strength to gold by Monte Carlo simulations. It has been revealed that the stable Au morphology is determined by the temperature and the binding strength. When heated on the strongly-binding substrates, the Au nanoparticles would wet the substrate completely and form monolayer. The stable Au layered structure of few layers can be formed by the incomplete wetting of clusters on the intermediate-binding substrates. The simulation results are in good agreement with pertinent experimental and theoretical results. Based on the simulation results and experimental observations, we find the strong linkage between the top edge sites and the activity TOF of low-temperature CO oxidation. We conclude that the top edges sites of Au layered structures are possible reactive sites. This study may provide new perspective for controlling morphology and understanding catalytic activity of supported metallic clusters.

  13. Plant cytosolic pyruvate kinase: a kinetic study.

    PubMed

    Podestá, F E; Plaxton, W C

    1992-11-20

    The kinetic properties of cytosolic pyruvate kinase (PKc) from germinating castor oil seeds (COS) have been investigated. From experiments in which the free Mg2+ concentration was varied at constant levels of either the complexed or free forms of the substrates it was determined that the true substrates are the free forms of both phosphoenolpyruvate (PEP) and ADP. This conclusion is corroborated by the quenching of intrinsic PKC tryptophan fluorescence by free PEP and ADP. Mg2+ is bound as the free bivalent cation but is likely released as MgATP. The fluorescence data, substrate interaction kinetics, and pattern of inhibition by products and substrate analogues (adenosine 5'-O-(2-thiodiphosphate) for ADP and phenyl phosphate for PEP) are compatible with a sequential, compulsory-ordered, Tri-Bi type kinetic reaction mechanism. PEP is the leading substrate, and pyruvate the last product to abandon the enzyme. The dissociation constant and limiting Km for free PEP (8.2 to 22 and 38 microM, respectively) and the limiting Km for free ADP (2.9 microM) are considerably lower than those reported for the non-plant enzyme. The results indicate that COS PKc exists naturally in an activated state, similar to the fructose 1,6-bisphosphate-activated yeast enzyme. This deduction is consistent with a previous study (F.E. Podestá and W.C. Plaxton (1991) Biochem. J. 279, 495-501) that failed to identify any allosteric activators for the COS PKc, but which proposed a regulatory mechanism based upon ATP levels and pH-dependent alterations in the enzyme's response to various metabolite inhibitors. As plant phosphofructokinases display potent inhibition by PEP, the overall rate of glycolytic flux from hexose 6-phosphate to pyruvate in the plant cytosol will ultimately depend upon variations in PEP levels brought about by the regulation of PKc. PMID:1445948

  14. Rheological studies of tautomerization kinetics in supercooled glibenclamide drug.

    PubMed

    Wojnarowska, Z; Wang, Y; Sokolov, A P; Paluch, M

    2012-12-01

    Rheological measurements have been applied to study the tautomerization of the pharmaceutically active compound glibenclamide. The rate constant and activation energy of the imidic-acid-amide transformation have been successfully determined by monitoring the evolution of shear viscosity. The kinetic parameters from rheological measurements agree reasonably well with the data previously obtained from dielectric spectroscopy. The present Brief Report demonstrates that rheology can provide a fast and precise way to characterize the reaction kinetics of tautomerization. PMID:23368084

  15. Rheological studies of tautomerization kinetics in supercooled glibenclamide drug

    NASA Astrophysics Data System (ADS)

    Wojnarowska, Z.; Wang, Y.; Sokolov, A. P.; Paluch, M.

    2012-12-01

    Rheological measurements have been applied to study the tautomerization of the pharmaceutically active compound glibenclamide. The rate constant and activation energy of the imidic-acid-amide transformation have been successfully determined by monitoring the evolution of shear viscosity. The kinetic parameters from rheological measurements agree reasonably well with the data previously obtained from dielectric spectroscopy. The present Brief Report demonstrates that rheology can provide a fast and precise way to characterize the reaction kinetics of tautomerization.

  16. Rhealogical studies of tautomerization kinetics in supercooled glibenclamide drug

    SciTech Connect

    Wojnarowska, S; Wang, Yangyang; Sokolov, Alexei P; Paluch, Marian W

    2012-01-01

    Rheological measurements have been applied to study the tautomerization of the pharmaceutically active compound glibenclamide. The rate constant and activation energy of the imidic-acid-amide transformation have been successfully determined by monitoring the evolution of shear viscosity. The kinetic parameters from rheological measurements agree reasonably well with the data previously obtained from dielectric spectroscopy. The present Brief Report demonstrates that rheology can provide a fast and precise way to characterize the reaction kinetics of tautomerization.

  17. Adsorption of Trametes versicolor laccase to soil iron and aluminum minerals: enzyme activity, kinetics and stability studies.

    PubMed

    Wu, Yue; Jiang, Ying; Jiao, Jiaguo; Liu, Manqiang; Hu, Feng; Griffiths, Bryan S; Li, Huixin

    2014-02-01

    Laccases play an important role in the degradation of soil phenol or phenol-like substance and can be potentially used in soil remediation through immobilization. Iron and aluminum minerals can adsorb extracellular enzymes in soil environment. In the present study, we investigated the adsorptive interaction of laccase, from the white-rot fungus Trametes versicolor, with soil iron and aluminum minerals and characterized the properties of the enzyme after adsorption to minerals. Results showed that both soil iron and aluminum minerals adsorbed great amount of laccase, independent of the mineral specific surface areas. Adsorbed laccases retained 26-64% of the activity of the free enzyme. Compared to the free laccase, all adsorbed laccases showed higher Km values and lower Vmax values, indicating a reduced enzyme-substrate affinity and a lower rate of substrate conversion in reactions catalyzed by the adsorbed laccase. Adsorbed laccases exhibited increased catalytic activities compared to the free laccase at low pH, implying the suitable application of iron and aluminum mineral-adsorbed T. versicolor laccase in soil bioremediation, especially in acid soils. In terms of the thermal profiles, adsorbed laccases showed decreased thermal stability and higher temperature sensitivity relative to the free laccase. Moreover, adsorption improved the resistance of laccase to proteolysis and extended the lifespan of laccase. Our results implied that adsorbed T. versicolor laccase on soil iron and aluminum minerals had promising potential in soil remediation. PMID:24225344

  18. On fast reactor kinetics studies

    SciTech Connect

    Seleznev, E. F.; Belov, A. A.; Matveenko, I. P.; Zhukov, A. M.; Raskach, K. F.

    2012-07-01

    The results and the program of fast reactor core time and space kinetics experiments performed and planned to be performed at the IPPE critical facility is presented. The TIMER code was taken as computation support of the experimental work, which allows transient equations to be solved in 3-D geometry with multi-group diffusion approximation. The number of delayed neutron groups varies from 6 to 8. The code implements the solution of both transient neutron transfer problems: a direct one, where neutron flux density and its derivatives, such as reactor power, etc, are determined at each time step, and an inverse one for the point kinetics equation form, where such a parameter as reactivity is determined with a well-known reactor power time variation function. (authors)

  19. Kinetic studies of ICF implosions

    SciTech Connect

    Kagan, Grigory; Herrmann, H. W.; Kim, Y. -H.; Schmitt, M. J.; Hakel, P.; Hsu, S. C.; Hoffman, N. M.; Svyatsky, D.; Baalrud, S. D.; Daligault, J. O.; Sio, H.; Zylstra, A. B.; Rosenberg, M. J.; Rinderknecht, H. G.; Johnson, M. Gatu; Frenje, J. A.; Seguin, F. H.; Li, C. K.; Petrasso, R. D.; Albright, B. J.; Taitano, W.; Kyrala, G. A.; Bradley, P. A.; Huang, C. -K.; McDevitt, C. J.; Chacon, L.; Srinivasan, B.; McEvoy, A. M.; Joshi, T. R.; Adams, C. S.

    2016-01-01

    Here, kinetic effects on inertial confinement fusion have been investigated. In particular, inter-ion-species diffusion and suprathermal ion distribution have been analyzed. The former drives separation of the fuel constituents in the hot reacting core and governs mix at the shell/fuel interface. The latter underlie measurements obtained with nuclear diagnostics, including the fusion yield and inferred ion burn temperatures. Basic mechanisms behind and practical consequences from these effects are discussed.

  20. Kinetic studies of ICF implosions

    NASA Astrophysics Data System (ADS)

    Kagan, Grigory; Herrmann, H. W.; Kim, Y.-H.; Schmitt, M. J.; Hakel, P.; Hsu, S. C.; Hoffman, N. M.; Svyatsky, D.; Baalrud, S. D.; Daligault, J. O.; Sio, H.; Zylstra, A. B.; Rosenberg, M. J.; Rinderknecht, H. G.; Gatu Johnson, M.; Frenje, J. A.; Séguin, F. H.; Li, C. K.; Petrasso, R. D.; Albright, B. J.; Taitano, W.; Kyrala, G. A.; Bradley, P. A.; Huang, C.-K.; McDevitt, C. J.; Chacon, L.; Srinivasan, B.; McEvoy, A. M.; Joshi, T. R.; Adams, C. S.

    2016-05-01

    Kinetic effects on inertial confinement fusion have been investigated. In particular, inter-ion-species diffusion and suprathermal ion distribution have been analyzed. The former drives separation of the fuel constituents in the hot reacting core and governs mix at the shell/fuel interface. The latter underlie measurements obtained with nuclear diagnostics, including the fusion yield and inferred ion burn temperatures. Basic mechanisms behind and practical consequences from these effects are discussed.

  1. Synthesis and properties of Fe3O4-activated carbon magnetic nanoparticles for removal of aniline from aqueous solution: equilibrium, kinetic and thermodynamic studies

    PubMed Central

    2013-01-01

    In this study, powder activated carbon (PAC) and magnetic nanoparticles of iron (III) oxide were used for synthesis of Fe3O4-activated carbon magnetic nanoparticles (AC-Fe3O4 MNPs) as an adsorbent for the removal of aniline. The characteristics of adsorbent were evaluated by SEM, TEM, XRD and BET. Also, the impact of different parameters such as pH, contact time, adsorbent dosage, aniline initials concentration and solution temperature were studied. The experimental data investigated by Langmuir and Freundlich adsorption isotherms and two models kinetically of pseudo first-order and pseudo second-order. The results indicated that the adsorption followed Langmuir and pseudo second-order models with correlation r2 > 0.98 and r2 > 0.99, respectively. The equilibrium time was obtained after 5 h. According to Langmuir model, the maximum adsorption capacity was 90.91 mg/g at pH = 6, and 20°C. The thermodynamic parameters indicated that adsorption of aniline on magnetic activated carbon was exothermic and spontaneous. This synthesized AC-Fe3O4 MNPs due to have advantages such as easy and rapid separation from solution could be applied as an adsorbent effective for removal of pollutants such as aniline from water and wastewater. PMID:23414171

  2. Comparative evaluation of adsorption kinetics of diclofenac and isoproturon by activated carbon.

    PubMed

    Torrellas, Silvia A; Rodriguez, Araceli R; Escudero, Gabriel O; Martín, José María G; Rodriguez, Juan G

    2015-01-01

    Adsorption mechanism of diclofenac and isoproturon onto activated carbon has been proposed using Langmuir and Freundlich isotherms. Adsorption capacity and optimum adsorption isotherms were predicted by nonlinear regression method. Different kinetic equations, pseudo-first-order, pseudo-second-order, intraparticle diffusion model and Bangham kinetic model, were applied to study the adsorption kinetics of emerging contaminants on activated carbon in two aqueous matrices. PMID:26301850

  3. Spectrophotometric evaluation of surface morphology dependent catalytic activity of biosynthesized silver and gold nanoparticles using UV-vis spectra: A comparative kinetic study

    NASA Astrophysics Data System (ADS)

    Ankamwar, Balaprasad; Kamble, Vaishali; Sur, Ujjal Kumar; Santra, Chittaranjan

    2016-03-01

    The development of eco-friendly and cost-effective synthetic protocol for the preparation of nanomaterials, especially metal nanoparticles is an emerging area of research in nanotechnology. These metal nanoparticles, especially silver can play a crucial role in various catalytic reactions. The biosynthesized silver nanoparticles described here was very stable up to 6 months and can be further exploited as an effective catalyst in the chemical reduction of 4-nitrophenol to 4-aminophenol. The silver nanoparticles were utilized as an efficient surface-enhanced Raman scattering (SERS) active substrate using Rhodamine 6G as Raman probe molecule. We have also carried out systematic comparative studies on the catalytic efficiency of both silver and gold nanoparticles using UV-vis spectra to monitor the above reaction spectrophotometrically. We find that the reaction follows pseudo-first order kinetics and the catalytic activity can be explained by a simple model based on Langmuir-Hinshelwood mechanism for heterogeneous catalysis. We also find that silver nanoparticles are more efficient as a catalyst compare to gold nanoparticles in the reduction of 4-nitrophenol to 4-aminophenol, which can be explained by the morphology of the nanoparticles as determined by transmission electron microscopy.

  4. Ribonuclease activity of vaccinia DNA topoisomerase IB: kinetic and high-throughput inhibition studies using a robust continuous fluorescence assay.

    PubMed

    Kwon, Keehwan; Nagarajan, Rajesh; Stivers, James T

    2004-11-30

    Vaccinia type I DNA topoisomerase exhibits a strong site-specific ribonuclease activity when provided a DNA substrate that contains a single uridine ribonucleotide within a duplex DNA containing the sequence 5' CCCTU 3'. The reaction involves two steps: attack of the active site tyrosine nucleophile of topo I at the 3' phosphodiester of the uridine nucleotide to generate a covalent enzyme-DNA adduct, followed by nucleophilic attack of the uridine 2'-hydroxyl to release the covalently tethered enzyme. Here we report the first continuous spectroscopic assay for topoisomerase that allows monitoring of the ribonuclease reaction under multiple-turnover conditions. The assay is especially robust for high-throughput screening applications because sensitive molecular beacon technology is utilized, and the topoisomerase is released during the reaction to allow turnover of multiple substrate molecules by a single molecule of enzyme. Direct computer simulation of the fluorescence time courses was used to obtain the rate constants for substrate binding and release, covalent complex formation, and formation of the 2',3'-cyclic phosphodiester product of the ribonuclease reaction. The assay allowed rapid screening of a 500 member chemical library from which several new inhibitors of topo I were identified with IC(50) values in the range of 2-100 microM. Three of the most potent hits from the high-throughput screening were also found to inhibit plasmid supercoil relaxation by the enzyme, establishing the utility of the assay in identifying inhibitors of the biologically relevant DNA relaxation reaction. One of the most potent inhibitors of the vaccinia enzyme, 3-benzo[1,3]dioxol-5-yl-2-oxoproprionic acid, did not inhibit the closely related human enzyme. The inhibitory mechanism of this compound is unique and involves a step required for recycling the enzyme for steady-state turnover. PMID:15554707

  5. Kinetic energy budgets during the life cycle of intense convective activity

    NASA Technical Reports Server (NTRS)

    Fuelberg, H. E.; Scoggins, J. R.

    1978-01-01

    Synoptic-scale data at three- and six-hour intervals are employed to study the relationship between changing kinetic energy variables and the life cycles of two severe squall lines. The kinetic energy budgets indicate a high degree of kinetic energy generation, especially pronounced near the jet-stream level. Energy losses in the storm environment are due to the transfer of kinetic energy from grid to subgrid scales of motion; large-scale upward vertical motion carries aloft the kinetic energy generated by storm activity at lower levels. In general, the time of maximum storm intensity is also the time of maximum energy conversion and transport.

  6. Kinetic studies of elementary chemical reactions

    SciTech Connect

    Durant, J.L. Jr.

    1993-12-01

    This program concerning kinetic studies of elementary chemical reactions is presently focussed on understanding reactions of NH{sub x} species. To reach this goal, the author is pursuing experimental studies of reaction rate coefficients and product branching fractions as well as using electronic structure calculations to calculate transition state properties and reaction rate calculations to relate these properties to predicted kinetic behavior. The synergy existing between the experimental and theoretical studies allow one to gain a deeper insight into more complex elementary reactions.

  7. sup 1 H and sup 31 P nuclear magnetic resonance and kinetic studies of the active site structure of chloroplast CF sub 1 ATP synthase

    SciTech Connect

    Devlin, C.C.; Grisham, C.M. )

    1990-07-03

    The interaction of nucleotides and nucleotide analogues and their complexes with Mn{sup 2+} bound to both the latent and dithiothreitol-activated CF{sub 1} ATP synthase has been examined by means of steady-state kinetics, water proton relaxation rate (PRR) measurements, and {sup 1}H and {sup 31}P nuclear relaxation measurements. Titration of both the latent and activated Mn{sup 2+}-CF{sub 1} complexes with ATP, ADP, P{sub i}, Co(NH{sub 3}){sub 4}ATP, Co(NH{sub 3}){sub 4}ADP, and Co(NH{sub 3}){sub 4}AMPPCP leads to increases in the water relaxation enhancement, consistent with enhanced metal binding and a high ternary complex enhancement. Steady-state kinetic studies are consistent with competitive inhibition of CF{sub 1} by Co(NH{sub 3}){sub 4}AMPPCP with respect to CaATP. {sup 1}H and {sup 31}P nuclear relaxation measurements in solutions of CF{sub 1} and Co(NH{sub 3}){sub 4}AMPPCP were used to determine the conformation of the bound substrate analogue and the arrangement with respect to this structure of high- and low-affinity sites for Mn{sup 2+}. The bound nucleotide analogue adopts a bent conformation, with the low-affinity sites for Mn{sup 2+}. The bound nucleotide analogue adopts a bent conformation, with the low-affinity Mn{sup 2+} site situated between the adenine and triphosphate moieties and the high-affinity metal site located on the far side of the triphosphate chain. The low-affinity metal forms a distorted inner-sphere complex with the {beta}-P and {gamma}-P of the substrate. The distances from Mn{sup 2+} to the triphosphate chain are too large for first coordination sphere complexes but are appropriate for second-sphere complexes involving, for example, intervening hydrogen-bonded water molecules or residues from the protein.

  8. Sorption of water alkalinity and hardness from high-strength wastewater on bifunctional activated carbon: process optimization, kinetics and equilibrium studies.

    PubMed

    Amosa, Mutiu K

    2016-08-01

    Sorption optimization and mechanism of hardness and alkalinity on bifunctional empty fruit bunch-based powdered activation carbon (PAC) were studied. The PAC possessed both high surface area and ion-exchange properties, and it was utilized in the treatment of biotreated palm oil mill effluent. Batch adsorption experiments designed with Design Expert(®) were conducted in correlating the singular and interactive effects of the three adsorption parameters: PAC dosage, agitation speed and contact time. The sorption trends of the two contaminants were sequentially assessed through a full factorial design with three factor interaction models and a central composite design with polynomial models of quadratic order. Analysis of variance revealed the significant factors on each design response with very high R(2) values indicating good agreement between model and experimental values. The optimum operating conditions of the two contaminants differed due to their different regions of operating interests, thus necessitating the utility of desirability factor to get consolidated optimum operation conditions. The equilibrium data for alkalinity and hardness sorption were better represented by the Langmuir isotherm, while the pseudo-second-order kinetic model described the adsorption rates and behavior better. It was concluded that chemisorption contributed majorly to the adsorption process. PMID:26752149

  9. Activated sludge acclimatisation kinetics to non-ionic surfactants.

    PubMed

    Carvalho, G; Novais, J M; Pinheiro, H M

    2003-01-01

    The biodegradation of surfactants is a frequent and complex problem in domestic and industrial wastewater treatment processes. In addition to the resulting metabolites being sometimes refractory, the complete biodegradation of many of the most employed non-ionic surfactants requires long hydraulic retention times and the presence of specialised bacterial consortia. Preliminary acclimatisation tests highlighted the importance of the sludge acclimatisation state to a specific surfactant substrate for biotreatment efficiency. This paper reports on studies aimed at quantifying activated sludge acclimatisation and memory retention levels when subjected to changes in the type of surfactant included in the feed. Several transitions were tested, namely from an alkylphenol ethoxylate to a linear alkyl ethoxylate and the reverse, and between alkyl ethoxylates with different hydrophobic and hydrophilic molecular chain lengths. The kinetic results showed that sludge activation and memory loss were more dynamic for primary biodegradation It was found that the sludge was harder to adapt to alkylphenol ethoxylate than to alkyl ethoxylate. The former also apparently introduced an inhibitory effect, resulting in very slow degradation kinetics when imposed to alkyl ethoxylate acclimatised sludge. When replacing an alkyl ethoxylate with another surfactant of the same family, a longer ethoxylate chain reduced the degradation rates. This effect was further enhanced by simultaneously increasing the hydrophobic chain length of the substrate. The acclimatisation kinetic after the replacement of an alkyl ethoxylate by a longer counterpart was slower than the reverse case, and memory was also more easily lost. PMID:12641258

  10. Michaelis-Menten Kinetics and the Activation Energy Relate Soil Peroxidase Kinetics to the Lignin Chemistry

    NASA Astrophysics Data System (ADS)

    Triebwasser-Freese, D.; Tharayil, N.; Preston, C. M.; Gerard, P.

    2013-12-01

    Recently, it has been suggested that lignin exhibit a turnover rate of less than 6 years, suggesting that the enzymatic mechanisms mediating the decay of lignin are less understood. One factor that could be affecting the mean residence time of lignin in the soil is the catalytic efficiency of soil oxidoreductase enzymes. We characterized the spatial and seasonal transitions in the Michaelis-Menten kinetics and activation energy of the soil oxidoreductase enzyme, peroxidase, across three ecosystems of differing litter chemistries- pine, deciduous forest, and a cultivated field- and associate it to the soil lignin chemistries. To interpret the combined effect of Vmax and Km, the two parameters were integrated into one term which we defined as the catalytic efficiency. Generally, the peroxidases in pine soils exhibited the highest Vmax and Km, resulting in the lowest catalytic efficiency, followed by that in the deciduous soils. Meanwhile, the agricultural soils which exhibited the lowest Vmax and Km contained the highest catalytic efficiency of peroxidase. Through linear regression analysis of the kinetic parameters to the soil lignin chemistry, we discerned that the catalytic efficiency term best associated to the lignin monomer ratios (C/V, P/V, and SCV/V). The Activation Energy of peroxidase varied by depth, and seasons across the ecosystems. However, the Activation Energy of peroxidase did not relate to the lignin chemistry or quantity. Collectively, our results show that although the peroxidase Vmax and Km in the phenolic-poor soils are low, the degradation efficiency of peroxidases in this soils can be equivalent or exceed that of phenolic-rich soils. This study, through the characterization of Michaelis-Menten kinetics, provides a new insight into the mechanisms that could moderate the decomposition of lignin in soils.

  11. Kinetic smog-chamber studies on halogen activation from a simulated salt pan, using dry and wet NaCl/NaBr surfaces

    NASA Astrophysics Data System (ADS)

    Bleicher, Sergej; Balzer, Natalja; Zetzsch, Cornelius; Buxmann, Joelle; Platt, Ulrich

    2010-05-01

    Field experiments and laboratory studies have shown that atomic Br and Cl are released from sea-salt aerosol and saline soils. This halogen release is based on the uptake of gaseous HOX by aqueous, acidified salt surfaces. Br and Cl play an important role in atmospheric ozone depletion and the destruction of hydrocarbons. Furthermore, Secondary Organic Aerosol (SOA) and HUmic LIke Substances (HULIS) may take part in these reaction cycles by halogenation and production of volatile organic halogen compounds. Aerosol smog-chamber facilities (coolable to -25°C) enable us to simulate the halogen release mechanism under arctic tropospheric conditions. Mechanistic and kinetic studies are carried out to investigate the influence of SOA and HULIS on halogen cycles and to determine halogenated gaseous and solid organic products. The present laboratory measurements study halogen activation from salt surfaces, which are similar to typical salt pan environments. In these experiments we placed different artificial salt mixtures with NaCl/NaBr ratios up to 300:1 on a Teflon pan located in a Teflon chamber with a volume of 3.5 m3. Under clean air conditions we inject ozone and a mixture of non-methane hydrocarbons with well-known reactivities against OH and Cl and irradiated the chamber with a solar simulator. Beside the usual observing instruments like an ozone monitor and a gas chromatograph we used Differential Optical Absorption Spectroscopy (DOAS) in a White cell with a light path up to 320 m to observe various gas-phase species including BrO radicals. A dry air / dry salt pan environment showed no ozone depletion and no halogen activation. At relative humidity above 50%, a rapid ozone depletion (4.7 h half-life) was observed, which is much faster than for pure NaCl under the same conditions (77 h). Furthermore, the mixed salt was acidified with H2SO4 to a pH value of 4.3, no difference in ozone depletion and halogen activation was observed at this point. The DOAS

  12. Oxidation and hydrolysis kinetic studies on UN

    NASA Astrophysics Data System (ADS)

    Rao, G. A. Rama; Mukerjee, S. K.; Vaidya, V. N.; Venugopal, V.; Sood, D. D.

    1991-11-01

    The reaction of oxygen and water vapour with UN microspheres containing 0.78 and 10.9 mol% UO 2 as impurity was studied under non-isothermal heating conditions in a thermobalance under different partial pressures of oxygen, a fixed pressure of water vapour in argon, and in air. Uranium mononitride was ultimately converted to U 3O 8, with the formation of UO 2 and U 2N 3 as intermediates. The end product of pyrohydrolysis was UO 2. The kinetic parameters were evaluated and the mechanism of the reaction was suggested. Different kinetic models were used to explain the oxidation behaviour of UN.

  13. Kinetic Study on Pyrolysis of Oil Palm Frond

    NASA Astrophysics Data System (ADS)

    Soon, V. S. Y.; Chin, B. L. F.; Lim, A. C. R.

    2016-03-01

    The pyrolysis of oil palm frond is studied using thermogravimetric analysis (TGA) equipment. The present study investigates the thermal degradation behaviour and determination of the kinetic parameters such as the activation energy (EA ) and pre-exponential factor (A) values of oil palm frond under pyrolysis condition. The kinetic data is produced based on first order rate of reaction. In this study, the experiments are conducted at different heating rates of 10, 20, 30, 40 and 50 K/min in the temperature range of 323-1173 K under non-isothermal condition. Argon gas is used as an inert gas to remove any entrapment of gases in the TGA equipment.

  14. Interactions of xanthines with activated carbon. I. Kinetics of the adsorption process

    NASA Astrophysics Data System (ADS)

    Navarrete Casas, R.; García Rodriguez, A.; Rey Bueno, F.; Espínola Lara, A.; Valenzuela Calahorro, C.; Navarrete Guijosa, A.

    2006-06-01

    Because of their pharmaceutical and industrial applications, we have studied the adsorption of xanthine derivates (caffeine and theophylline) by activated carbon. To this end, we examined kinetic, equilibrium and thermodynamic aspects of the process. This paper reports the kinetics results. The experimental results indicate that the process was first order in C and the overall process was assumed to involve a single, reversible adsorption-desorption process obeying a kinetic law postulated by us.

  15. Isotherm and kinetics study of malachite green adsorption onto copper nanowires loaded on activated carbon: artificial neural network modeling and genetic algorithm optimization.

    PubMed

    Ghaedi, M; Shojaeipour, E; Ghaedi, A M; Sahraei, Reza

    2015-05-01

    In this study, copper nanowires loaded on activated carbon (Cu-NWs-AC) was used as novel efficient adsorbent for the removal of malachite green (MG) from aqueous solution. This new material was synthesized through simple protocol and its surface properties such as surface area, pore volume and functional groups were characterized with different techniques such XRD, BET and FESEM analysis. The relation between removal percentages with variables such as solution pH, adsorbent dosage (0.005, 0.01, 0.015, 0.02 and 0.1g), contact time (1-40min) and initial MG concentration (5, 10, 20, 70 and 100mg/L) was investigated and optimized. A three-layer artificial neural network (ANN) model was utilized to predict the malachite green dye removal (%) by Cu-NWs-AC following conduction of 248 experiments. When the training of the ANN was performed, the parameters of ANN model were as follows: linear transfer function (purelin) at output layer, Levenberg-Marquardt algorithm (LMA), and a tangent sigmoid transfer function (tansig) at the hidden layer with 11 neurons. The minimum mean squared error (MSE) of 0.0017 and coefficient of determination (R(2)) of 0.9658 were found for prediction and modeling of dye removal using testing data set. A good agreement between experimental data and predicted data using the ANN model was obtained. Fitting the experimental data on previously optimized condition confirm the suitability of Langmuir isotherm models for their explanation with maximum adsorption capacity of 434.8mg/g at 25°C. Kinetic studies at various adsorbent mass and initial MG concentration show that the MG maximum removal percentage was achieved within 20min. The adsorption of MG follows the pseudo-second-order with a combination of intraparticle diffusion model. PMID:25699703

  16. Isotherm and kinetics study of malachite green adsorption onto copper nanowires loaded on activated carbon: Artificial neural network modeling and genetic algorithm optimization

    NASA Astrophysics Data System (ADS)

    Ghaedi, M.; Shojaeipour, E.; Ghaedi, A. M.; Sahraei, Reza

    2015-05-01

    In this study, copper nanowires loaded on activated carbon (Cu-NWs-AC) was used as novel efficient adsorbent for the removal of malachite green (MG) from aqueous solution. This new material was synthesized through simple protocol and its surface properties such as surface area, pore volume and functional groups were characterized with different techniques such XRD, BET and FESEM analysis. The relation between removal percentages with variables such as solution pH, adsorbent dosage (0.005, 0.01, 0.015, 0.02 and 0.1 g), contact time (1-40 min) and initial MG concentration (5, 10, 20, 70 and 100 mg/L) was investigated and optimized. A three-layer artificial neural network (ANN) model was utilized to predict the malachite green dye removal (%) by Cu-NWs-AC following conduction of 248 experiments. When the training of the ANN was performed, the parameters of ANN model were as follows: linear transfer function (purelin) at output layer, Levenberg-Marquardt algorithm (LMA), and a tangent sigmoid transfer function (tansig) at the hidden layer with 11 neurons. The minimum mean squared error (MSE) of 0.0017 and coefficient of determination (R2) of 0.9658 were found for prediction and modeling of dye removal using testing data set. A good agreement between experimental data and predicted data using the ANN model was obtained. Fitting the experimental data on previously optimized condition confirm the suitability of Langmuir isotherm models for their explanation with maximum adsorption capacity of 434.8 mg/g at 25 °C. Kinetic studies at various adsorbent mass and initial MG concentration show that the MG maximum removal percentage was achieved within 20 min. The adsorption of MG follows the pseudo-second-order with a combination of intraparticle diffusion model.

  17. Kinetic isotope effects for concerted multiple proton transfer: a direct dynamics study of an active-site model of carbonic anhydrase II.

    PubMed

    Smedarchina, Zorka; Siebrand, Willem; Fernández-Ramos, Antonio; Cui, Qiang

    2003-01-01

    The rate constant of the reaction catalyzed by the enzyme carbonic anhydrase II, which removes carbon dioxide from body fluids, is calculated for a model of the active site. The rate-determining step is proton transfer from a zinc-bound water molecule to a histidine residue via a bridge of two or more water molecules. The structure of the active site is known from X-ray studies except for the number and location of the water molecules. Model calculations are reported for a system of 58 atoms including a four-coordinated zinc ion connected to a methylimidazole molecule by a chain of two waters, constrained to reproduce the size of the active site. The structure and vibrational force field are calculated by an approximate density functional treatment of the proton-transfer step at the Self-Consistent-Charge Density Functional Tight Binding (SCC-DFTB) level. A single transition state is found indicating concerted triple proton transfer. Direct-dynamics calculations for proton and deuteron transfer and combinations thereof, based on the Approximate Instanton Method and on Variational Transition State Theory with Tunneling Corrections, are in fair agreement and yield rates that are considerably higher and kinetic isotope effects (KIEs) that are somewhat higher than experiment. Classical rate constants obtained from Transition State Theory are smaller than the quantum values but the corresponding KIEs are five times larger. For multiple proton transfer along water bridges classical KIEs are shown to be generally larger than quantum KIEs, which invalidates the standard method to distinguish tunneling and over-barrier transfer. In the present case, a three-way comparison of classical and quantum results with the observed data is necessary to conclude that proton transfer along the bridge proceeds by tunneling. The results suggest that the two-water bridge is present in low concentrations but makes a substantial contribution to proton transport because of its high

  18. The kinetics of ER fusion protein activation in vivo

    PubMed Central

    Wilson, Catherine H.; Gamper, Ivonne; Perfetto, Alessandra; Auw, Jeremy; Littlewood, Trevor D.; Evan, Gerard I.

    2014-01-01

    Reversibly switchable proteins are powerful tools with which to explore protein function in vitro and in vivo. For example, the activity of many proteins fused to the hormone-binding domain of the modified estrogen receptor (ERTAM) can be regulated by provision or removal of 4-hydroxytamoxifen (4-OHT). Despite the widespread use of ERTAM fusions in vivo, inadequate data are available as to the most efficacious routes for systemic tamoxifen delivery. In this study, we have used two well-characterised ERTAM fusion proteins, both reversibly activated by 4-OHT, to compare the effectiveness and kinetics of 4-OHT delivery in mice in vivo by either tamoxifen in food or by intraperitoneal injection. Our data indicate that dietary tamoxifen offers an effective, facile and ethically preferable means for long term activation of ERTAM fusion proteins in vivo. PMID:24662815

  19. Thermodynamics, Kinetics, and Activation energy Studies of the sorption of chromium(III) and chromium(VI) to a Mn3O4 nanomaterial

    PubMed Central

    Cantu, Yvette; Remes, Abril; Reyna, Alejandra; Martinez, Denise; Villarreal, Jahaziel; Ramos, Hilda; Trevino, Samantha; Tamez, C.; Martinez, A.; Eubanks, T.; Parsons, J. G.

    2014-01-01

    In this study, a manganese oxide, Mn3O4 was used to remove chromium(III) and chromium(VI) from aqueous solutions. The Mn3O4 nanomaterial was synthesized through a precipitation method, and was characterized using XRD, which confirmed the material had a crystal structure similar to hausmannite. In addition, using Scherrer’s equation it was determined that the nanomaterial had an average grain size of 19.5 ± 1.10 nm. A study of the effects of pH on the binding of chromium(III) and chromium(VI) showed that the optimum binding pH was 4 and 3 respectively. Batch isotherm studies were performed to determine the binding capacity of chromium(III), which was determined to be 18.7 mg/g, 41.7 mg/g, and 54.4 mg/g respectively for 4°C, 21°C, and 45°C. Chromium(VI) on the other hand had lower binding capacities of 2.5 mg/g, 4.3 mg/g, and 5.8 mg/g for 4°C, 21°C, 45°C, respectively. Thermodynamic studies performed indicated the sorption process was for the most part controlled by physisorption. The ΔG for the sorption of chromium(III) and Chromium(VI) ranged from −0.9 to −13 kJ/mol, indicating a spontaneous reaction was occurring. The enthalpy indicated a endothermic reaction was occurring during the binding and show ΔH values of 70.6 and 19.1 kJ.mol for chromium(III) and Chromium(VI), respectively. In addition, ΔS for the reaction had positive values of 267 and 73 J/mol for chromium(III) and chromium(VI) which indicate a spontaneous reaction. In addition, the sorption process was found to follow pseudo second order kinetic and the activation energy studies indicated the binding process occurred through chemisorption. PMID:25097453

  20. Kinetics of small particle activation in supersaturated vapors

    SciTech Connect

    McGraw, R.; Wang, J.

    2010-08-29

    We examine the nucleated (with barrier) activation of perfectly wetting (zero contact angle) particles ranging from bulk size down to one nanometer. Thermodynamic properties of the particles, coated with liquid layers of varying thickness and surrounded by vapor, are analyzed. Nano-size particles are predicted to activate at relative humidity below the Kelvin curve on crossing a nucleation barrier, located at a critical liquid layer thickness such that the total particle size (core + liquid layer) equals the Kelvin radius (Fig. 1). This barrier vanishes precisely as the critical layer thickness approaches the thin layer limit and the Kelvin radius equals the radius of the particle itself. These considerations are similar to those included in Fletcher's theory (Fletcher, 1958) however the present analysis differs in several important respects. Firstly, where Fletcher used the classical prefactor-exponent form for the nucleation rate, requiring separate estimation of the kinetic prefactor, we solve a diffusion-drift equation that is equivalent to including the full Becker-Doering (BD) multi-state kinetics of condensation/evaporation along the growth coordinate. We also determine the mean first passage time (MFPT) for barrier crossing (Wedekind et al., 2007), which is shown to provide a generalization of BD nucleation kinetics especially useful for barrier heights that are considerably lower than those typically encountered in homogeneous vapor-liquid nucleation, and make explicit comparisons between the MFPT and BD kinetic models. Barrier heights for heterogeneous nucleation are computed by a thermo-dynamic area construction introduced recently to model deliquescence and efflorescence of small particles (McGraw and Lewis, 2009). In addition to providing a graphical representation of the activation process that offers new insights, the area construction provides a molecular approach that avoids explicit use of the interfacial tension. Typical barrier profiles for

  1. Biosorptive uptake of ibuprofen by steam activated biochar derived from mung bean husk: Equilibrium, kinetics, thermodynamics, modeling and eco-toxicological studies.

    PubMed

    Mondal, Sandip; Bobde, Kiran; Aikat, Kaustav; Halder, Gopinath

    2016-11-01

    The present study explores the use of steam activated mung bean husk biochar (SA-MBHB) as a potential sorbent for the removal of non-steroidal and anti-inflammatory drug ibuprofen from aqueous solution. SA-MBHB was characterized by SEM, FTIR, BET, TGA, point of zero charge (pHPZC) and UV-Vis spectrophotometer. The relation between removal percentages of ibuprofen and parameters such as adsorbent dose (0.05 g-250 g), contact time (5 min-210 min), pH (2-10), speed of agitation (40-280 rpm), temperature (293-308 K) and initial ibuprofen concentration (5-100 ppm) was investigated and optimized by a series of batch sorption experiments. The optimized conditions achieved were: adsorbent dose 0.1 g/L, agitation speed 200 rpm, pH 2, initial ibuprofen concentration 20 mg L(-1), equilibrium time 120 min and temperature 20 °C for more than 99% adsorptive removal of ibuprofen. The equilibrium adsorption data were well fitted into the Langmuir isotherm model while kinetic data suggested the removal process to follow pseudo second order reaction. The adsorption phenomena were optimized and simulated by using response surface methodology (RSM) and artificial neural network (ANN). Effect of process variables viz. dose, agitation speed and pH on the sorbed amount of IBP was studied through a 2(3) full factorial central composite design (CCD). The comparative analysis was done for ibuprofen removal by constructing ANN model training using same experimental matrix of CCD. The growth of Scenedesmus abundans was also observed to be affected by the IBP solution whereas the biochar treated with IBP solution did not significantly affect the growth of the Scenedesmus abundans. The results revealed that SA-MBHB could be a cost-effective, efficient and non-hazardous adsorbent for the removal of ibuprofen from aqueous solution. PMID:27544645

  2. Tyrosinase inhibition kinetic studies of standardized extract of Berberis aristata.

    PubMed

    Biswas, Rajarshi; Mukherjee, Pulok K; Chaudhary, Sushil K

    2016-06-01

    The stem bark and wood of Berberis aristata DC (Daruharidra) are one of the principal ingredients of traditional skin lighting and exfoliating scrub preparation in India. The standardised extract of B. aristata was screened to evaluate their in vitro antityrosinase activity and inhibition kinetics. Phytochemical and pharmacological studies were carried out with different solvent fractions of the methanol extract of B. aristata (MEBA). RP-HPLC analysis was used to determine the berberine content in extract and fractions of B. aristata. MEBA showed maximum berberine content. Extract and fractions of B. aristata contain the maximum amount of alkaloids than other constituents. In tyrosinase inhibition assay, MEBA was found to possess highest dose-dependent monophenolase and moderate diphenolase activity. The enzyme kinetic study revealed that MEBA possessed mixed type inhibition of monophenolase activity of tyrosinase. These bioactivities indicate that the MEBA has antihyperpigmentation potential in human skin. PMID:26212353

  3. Effect of surfactant on hydrolysis products accumulation and short-chain fatty acids (SCFA) production during mesophilic and thermophilic fermentation of waste activated sludge: kinetic studies.

    PubMed

    Zhang, Peng; Chen, Yinguang; Zhou, Qi

    2010-09-01

    In the presence of surfactant sodium dodecylbenzene sulfonate (SDBS) the hydrolysis products accumulation and the short-chain fatty acids (SCFA) production during waste activated sludge fermentation under mesophilic and thermophilic conditions was compared with that at room temperature. In order to understand the mechanism of significant amounts of mesophilic and thermophilic hydrolysis products and SCFA observed in the presence of surfactant, the kinetic models at different SDBS dosages were developed. It was found that SDBS increased the mesophilic and thermophilic hydrolysis rate significantly, and the maximum specific utilization of hydrolysis products increased at low SDBS and decreased at high one. However, the observed maximum specific utilization of SCFA decreased seriously with SDBS increase. In the presence of SDBS the decay rate of acidogenic bacteria not only was lower than that in the absence of SDBS but decreased with the increase of SDBS under either mesophilic or thermophilic conditions. PMID:20409704

  4. Studies of combustion kinetics and mechanisms

    SciTech Connect

    Gutman, D.

    1993-12-01

    The objective of the current research is to gain new quantitative knowledge of the kinetics and mechanisms of polyatomic free radicals which are important in hydrocarbon combustion processes. The special facility designed and built for these (which includes a heatable tubular reactor coupled to a photoionization mass spectrometer) is continually being improved. Where possible, these experimental studies are coupled with theoretical ones, sometimes conducted in collaboration with others, to obtain an improved understanding of the factors determining reactivity. The decomposition of acetyl radicals, isopropyl radicals, and n-propyl radicals have been studied as well as the oxidation of methylpropargyl radicals.

  5. Kinetic and physical characterization of force generation in muscle: a laser temperature-jump and length-jump study on activated and contracting rigor fibers.

    PubMed

    Davis, J S; Harrington, W F

    1993-01-01

    Experiments are presented that probe the mechanism of contraction in normal activated muscle fibers and in heated rigor fibers. In activated fibers we subdivide the partial recovery of isometric tension during the Huxley-Simmons phase 2 into temperature-independent and temperature-dependent steps termed, respectively, phase 2fast and phase 2slow. Evidence is presented to show that phase 2fast arises from the perturbation of a damped elastic element in the cross-bridge and that phase 2slow is the manifestation of an endothermic, order-disorder transition responsible for de novo tension generation. These responses are common to both frog and rabbit fibers. The only difference between animals is that the kinetics of phase 2slow appears to scale with the working temperature of the muscle and not absolute temperature. Rigor fibers heated above the working temperature of the muscle contract. Tension generation is, as with activated fibers, endothermic. Tension transients following a laser temperature-jump of activated and heated rigor fibers are virtually indistinguishable on the basis of either the form or magnitude of the response. In length-jump experiments, tension recovery by heated rigor fibers consists of three exponentials with a tension-dependent rate for the medium speed step. Preliminary data indicate that the rigor cross-bridge operates over a distance of between 13.5 and 18 nm. Collectively, these data imply that tension generation in muscle arises from accessible conformational states in the proteins of the cross-bridge alone. ATP hydrolysis in active fibers and the heating of rigor fibers simply serve to shift these intrinsic conformational equilibria towards tension generation. PMID:8109364

  6. Modeling high adsorption capacity and kinetics of organic macromolecules on super-powdered activated carbon.

    PubMed

    Matsui, Yoshihiko; Ando, Naoya; Yoshida, Tomoaki; Kurotobi, Ryuji; Matsushita, Taku; Ohno, Koichi

    2011-02-01

    The capacity to adsorb natural organic matter (NOM) and polystyrene sulfonates (PSSs) on small particle-size activated carbon (super-powdered activated carbon, SPAC) is higher than that on larger particle-size activated carbon (powdered-activated carbon, PAC). Increased adsorption capacity is likely attributable to the larger external surface area because the NOM and PSS molecules do not completely penetrate the adsorbent particle; they preferentially adsorb near the outer surface of the particle. In this study, we propose a new isotherm equation, the Shell Adsorption Model (SAM), to explain the higher adsorption capacity on smaller adsorbent particles and to describe quantitatively adsorption isotherms of activated carbons of different particle sizes: PAC and SPAC. The SAM was verified with the experimental data of PSS adsorption kinetics as well as equilibrium. SAM successfully characterized PSS adsorption isotherm data for SPACs and PAC simultaneously with the same model parameters. When SAM was incorporated into an adsorption kinetic model, kinetic decay curves for PSSs adsorbing onto activated carbons of different particle sizes could be simultaneously described with a single kinetics parameter value. On the other hand, when SAM was not incorporated into such an adsorption kinetic model and instead isotherms were described by the Freundlich model, the kinetic decay curves were not well described. The success of the SAM further supports the adsorption mechanism of PSSs preferentially adsorbing near the outer surface of activated carbon particles. PMID:21172719

  7. Kinetic discrimination in T-cell activation.

    PubMed Central

    Rabinowitz, J D; Beeson, C; Lyons, D S; Davis, M M; McConnell, H M

    1996-01-01

    We propose a quantitative model for T-cell activation in which the rate of dissociation of ligand from T-cell receptors determines the agonist and antagonist properties of the ligand. The ligands are molecular complexes between antigenic peptides and proteins of the major histocompatibility complex on the surfaces of antigen-presenting cells. Binding of ligand to receptor triggers a series of biochemical reactions in the T cell. If the ligand dissociates after these reactions are complete, the T cell receives a positive activation signal. However, dissociation of ligand after completion of the first reaction but prior to generation of the final products results in partial T-cell activation, which acts to suppress a positive response. Such a negative signal is brought about by T-cell ligands containing the variants of antigenic peptides referred to as T-cell receptor antagonists. Results of recent experiments with altered peptide ligands compare favorably with T-cell responses predicted by this model. PMID:8643643

  8. Performance and kinetics of LiFePO4-carbon bi-material electrodes for hybrid devices: A comparative study between activated carbon and multi-walled carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Varzi, Alberto; Ramirez-Castro, Claudia; Balducci, Andrea; Passerini, Stefano

    2015-01-01

    Activated Carbon (AC) and multi-walled carbon nanotubes (CNT) are investigated as components of LiFePO4 (LFP)-based bi-material electrodes for hybrid devices. Firstly, the influence of their different morphological and porosimetric characteristics is correlated to the electrochemical performance. Furthermore, kinetic aspects are carefully studied (by means of galvanostatic cycling and cyclic voltammetry), in order to address the processes which determine the power performance. The results indicate that, independently from the carbon, under high current loads the electrode kinetics are limited by the transport of reactant to the LFP particles. In such conditions CNT allow, better than AC, rapid electrons and Li+ ions flow through the open network established in the electrode, thus enabling superior high rate performance, especially during pulsed operation.

  9. A new robust kinetic assay for DAP epimerase activity.

    PubMed

    Hor, Lilian; Peverelli, Martin G; Perugini, Matthew A; Hutton, Craig A

    2013-10-01

    DAP epimerase is the penultimate enzyme in the lysine biosynthesis pathway. The most versatile assay for DAP epimerase catalytic activity employs a coupled DAP epimerase-DAP dehydrogenase enzyme system with a commercial mixture of DAP isomers as substrate. DAP dehydrogenase converts meso-DAP to THDP with concomitant reduction of NADP(+) to NADPH. We show that at high concentrations, accumulation of NADPH results in inhibition of DAPDH, resulting in spurious kinetic data. A new assay has been developed employing DAP decarboxylase that allows the reliable characterisation of DAP epimerase enzyme kinetics. PMID:23838343

  10. Application of granular activated carbon/MnFe2O4 composite immobilized on C. glutamicum MTCC 2745 to remove As(III) and As(V): Kinetic, mechanistic and thermodynamic studies

    NASA Astrophysics Data System (ADS)

    Podder, M. S.; Majumder, C. B.

    2016-01-01

    The main objective of the present study was to investigate the efficiency of Corynebacterium glutamicum MTCC 2745 immobilized on granular activated carbon/MnFe2O4 (GAC/MnFe2O4) composite to treat high concentration of arsenic bearing wastewater. Non-linear regression analysis was done for determining the best-fit kinetic model on the basis of three correlation coefficients and three error functions and also for predicting the parameters involved in kinetic models. The results showed that Fractal-like mixed 1,2 order model for As(III) and Brouser-Weron-Sototlongo as well as Fractal-like pseudo second order models for As(V) were proficient to provide realistic description of biosorption/bioaccumulation kinetic. Applicability of mechanistic models in the current study exhibited that the rate governing step in biosorption/bioaccumulation of both As(III) and As(V) was film diffusion rather than intraparticle diffusion. The evaluated thermodynamic parameters ΔG0, ΔH0 and ΔS0 revealed that biosorption/bioaccumulation of both As(III) and As(V) was feasible, spontaneous and exothermic under studied conditions.

  11. Application of granular activated carbon/MnFe₂O₄ composite immobilized on C. glutamicum MTCC 2745 to remove As(III) and As(V): Kinetic, mechanistic and thermodynamic studies.

    PubMed

    Podder, M S; Majumder, C B

    2016-01-15

    The main objective of the present study was to investigate the efficiency of Corynebacterium glutamicum MTCC 2745 immobilized on granular activated carbon/MnFe2O4 (GAC/MnFe2O4) composite to treat high concentration of arsenic bearing wastewater. Non-linear regression analysis was done for determining the best-fit kinetic model on the basis of three correlation coefficients and three error functions and also for predicting the parameters involved in kinetic models. The results showed that Fractal-like mixed 1,2 order model for As(III) and Brouser-Weron-Sototlongo as well as Fractal-like pseudo second order models for As(V) were proficient to provide realistic description of biosorption/bioaccumulation kinetic. Applicability of mechanistic models in the current study exhibited that the rate governing step in biosorption/bioaccumulation of both As(III) and As(V) was film diffusion rather than intraparticle diffusion. The evaluated thermodynamic parameters ΔG(0), ΔH(0) and ΔS(0) revealed that biosorption/bioaccumulation of both As(III) and As(V) was feasible, spontaneous and exothermic under studied conditions. PMID:26322840

  12. Kinetic studies on novel plasminogen activators. Demonstration of fibrin enhancement for hybrid enzymes comprising the A-chain of plasmin (Lys-78) and B-chain of tissue-type plasminogen activator (Ile-276) or urokinase (Ile-159).

    PubMed Central

    Fears, R; Dodd, I; Ferres, H; Robinson, J H

    1990-01-01

    The activation of plasminogen by two novel hybrid enzymes, constructed from the A-chain of plasmin and the B-chains of tissue-type plasminogen activator (t-PA) or urokinase, was compared with the activation by the parent enzymes. Basal kinetic constants for 'Lys-plasminogen' (human plasminogen with N-terminal lysine) and 'Glu-plasminogen' (human plasminogen with N-terminal glutamic acid) activation were similar to those of the parent activators. The Km for plasminogen turnover for both hybrid enzymes was considerably decreased in the presence of both soluble fibrin and a mimic, a CNBr digest of fibrinogen. These enhancements and the related apparent negative co-operativity are similar to the behaviour of t-PA itself. The results are discussed with regard to the molecular features involved in the mechanism of fibrin stimulation. PMID:2139324

  13. Kinetic and spectroscopic studies on nitrogenase

    SciTech Connect

    Gutheil, W.G.

    1989-01-01

    A detailed procedure and description of the apparatus used for the purification of sodium dithionite obtained from commercial sources is presented with yields 98+% pure material with yields of 25-35%. The effect of the purified dithionite on nitrogenase specific activities was determined and found to be insignificant. Mass spectra analysis of the P{sub i} obtained from nitrogenase catalyzed labeled ATP hydrolysis indicated that nitrogenase acts as a normal ATPase catalyzing nucleophilic attack at the {lambda} phosphorus atom of ATP. Recovered ATP was analyzed for positional isotope exchange (PIX) by {sup 31}P NMR. A numerical model to quantitatively interpret these results in terms of the currently available information on the kinetics of nitrogenase catalyzed ATP hydrolysis was developed. CD monitored titrations of the oxidized Fe protein at 360 nm with MgADP and MgATP are presented. Data were analyzed by fitting to models where cooperativity was allowed or not allowed. Analytical and numerical solutions for non cooperative and cooperative models were implemented. Statistical analysis of the data are presented and discussed as supporting non cooperative vs. cooperative behavior between the nucleotide binding sites. The thermodynamic analysis and incorporation of redox data allow a proposed model of the interactions between the ligand binding sites and the redox center of this protein to be presented. Several complete spectral titrations with various nucleotide analogs are also presented.

  14. Fast and slow activation kinetics of voltage-gated sodium channels in molluscan neurons.

    PubMed

    Gilly, W F; Gillette, R; McFarlane, M

    1997-05-01

    Whole cell patch-clamp recordings of Na current (I(Na)) were made under identical experimental conditions from isolated neurons from cephalopod (Loligo, Octopus) and gastropod (Aplysia, Pleurobranchaea, Doriopsilla) species to compare properties of activation gating. Voltage dependence of peak Na conductance (gNa) is very similar in all cases, but activation kinetics in the gastropod neurons studied are markedly slower. Kinetic differences are very pronounced only over the voltage range spanned by the gNa-voltage relation. At positive and negative extremes of voltage, activation and deactivation kinetics of I(Na) are practically indistinguishable in all species studied. Voltage-dependent rate constants underlying activation of the slow type of Na channel found in gastropods thus appear to be much more voltage dependent than are the equivalent rates in the universally fast type of channel that predominates in cephalopods. Voltage dependence of inactivation kinetics shows a similar pattern and is representative of activation kinetics for the two types of Na channels. Neurons with fast Na channels can thus make much more rapid adjustments in the number of open Na channels at physiologically relevant voltages than would be possible with only slow Na channels. This capability appears to be an adaptation that is highly evolved in cephalopods, which are well known for their high-speed swimming behaviors. Similarities in slow and fast Na channel subtypes in molluscan and mammalian neurons are discussed. PMID:9163364

  15. Kinetics of water vapor diffusion in activated carbon

    NASA Astrophysics Data System (ADS)

    Kurmasheva, D. M.; Kapralov, P. O.; Travkin, V. D.; Artemov, V. G.; Tikhonov, V. I.; Volkov, A. A.

    2014-05-01

    We describe an experimental method for studying rapid processes of water vapor sorption by fine-dispersed and porous materials. The concentration of gas-phase water molecules is detected during adsorption by a laser-diode spectrometer. The kinetic pressure curves are recorded in a time window of 10-1 to 103 s and are analyzed using analogy of the diffusion flow with the electric current in a branched RC circuit. The proposed model establishes the relation between the kinetics curves being measured and the structural parameters of the medium.

  16. A Model for the Interfacial Kinetics of Phospholipase D Activity on Long-Chain Lipids

    PubMed Central

    Majd, Sheereen; Yusko, Erik C.; Yang, Jerry; Sept, David; Mayer, Michael

    2013-01-01

    The membrane-active enzyme phospholipase D (PLD) catalyzes the hydrolysis of the phosphodiester bond in phospholipids and plays a critical role in cell signaling. This catalytic reaction proceeds on lipid-water interfaces and is an example of heterogeneous catalysis in biology. Recently we showed that planar lipid bilayers, a previously unexplored model membrane for these kinetic studies, can be used for monitoring interfacial catalytic reactions under well-defined experimental conditions with chemical and electrical access to both sides of the lipid membrane. Employing an assay that relies on the conductance of the pore-forming peptide gramicidin A to monitor PLD activity, the work presented here reveals the kinetics of hydrolysis of long-chain phosphatidylcholine lipids in situ. We have developed an extension of a basic kinetic model for interfacial catalysis that includes product activation and substrate depletion. This model describes the kinetic behavior very well and reveals two kinetic parameters, the specificity constant and the interfacial quality constant. This approach results in a simple and general model to account for product accumulation in interfacial enzyme kinetics. PMID:23823233

  17. KINETIC STUDIES OF SIMULATED POLLUTED ATMOSPHERES

    EPA Science Inventory

    The kinetics and reaction mechanisms of several important atmospheric contaminants - SO2, formaldehyde, nitrous acid, and the nitrosamines - were assessed to help quantify some key aspects of the chemistry of polluted atmospheres. The reactions and lifetimes of excited sulfur dio...

  18. Effect of temperature on Candida antartica lipase B activity in the kinetic resolution of acebutolol

    NASA Astrophysics Data System (ADS)

    Rajin, Mariani; Kamaruddin, A. H.

    2016-06-01

    Thermodynamic studies of free Candida antartica lipase B in kinetic resolution of acebutolol have been carried out to characterize the temperature effects towards enzyme stability and activity. A decreased in reaction rate was observed in temperature above 40oC. Thermodynamic studies on lipase deactivation exhibited a first-order kinetic pattern. The activation and deactivation energies were 39.63 kJ/mol and 54.90 kJ/mol, respectively. The enthalpy and entropy of the lipase deactivation were found to be 52.12 kJ/mol and -0.18 kJ/mol, respectively.

  19. Enzyme kinetics and interaction studies for human JNK1β1 and substrates activating transcription factor 2 (ATF2) and c-Jun N-terminal kinase (c-Jun).

    PubMed

    Figuera-Losada, Mariana; LoGrasso, Philip V

    2012-04-13

    c-Jun N-terminal kinase (JNK) is a stress signal transducer linked to cell death, and survival. JNK1 has been implicated in obesity, glucose intolerance, and insulin resistance. In this study we report the kinetic mechanism for JNK1β1 with transcription factors ATF2 and c-Jun along with interaction kinetics for these substrates. JNK1β1 followed a random sequential mechanism forming a ternary complex between JNK-substrate-ATP. K(m) for ATF2 and c-Jun was 1.1 and 2.8 μM, respectively. Inhibition studies using adenosine 5'-(β,γ-methylenetriphosphate) and a peptide derived from JNK interacting protein 1 (JIP1) supported the proposed kinetic mechanism. Biolayer interferometry studies showed that unphosphorylated JNK1β1 bound to ATF2 with similar affinity as it did to c-Jun (K(D) = 2.60 ± 0.34 versus 1.00 ± 0.35 μM, respectively). The presence of ATP increased the affinity of unphosphorylated JNK1β1 for ATF2 and c-Jun, to 0.80 ± 0.04 versus 0.65 ± 0.07 μM, respectively. Phosphorylation of JNK1β1 decreased the affinity of the kinase for ATF2 to 11.0 ± 1.1 μM and for c-Jun to 17.0 ± 7.5 μM in the absence of ATP. The presence of ATP caused a shift in the K(D) of the active kinase for ATF2 to 1.70 ± 0.25 μM and for c-Jun of 3.50 ± 0.95 μM. These results are the first kinetic and biochemical characterization of JNK1β1 and uncover some of the differences in the enzymatic activity of JNK1β1 compared with other variants and suggest that ATP binding or JNK phosphorylation could induce changes in the interactions with substrates, activators, and regulatory proteins. PMID:22351776

  20. Kinetics and mechanism studies of p-nitroaniline adsorption on activated carbon fibers prepared from cotton stalk by NH4H2PO4 activation and subsequent gasification with steam.

    PubMed

    Li, Kunquan; Li, Ye; Zheng, Zheng

    2010-06-15

    Activated carbon fibers (ACFs) were prepared for the removal of p-nitroaniline (PNA) from cotton stalk by chemical activation with NH(4)H(2)PO(4) and subsequent physical activation with steam. Surface properties of the prepared ACFs were performed using nitrogen adsorption, FTIR spectroscopy and SEM. The influence of contact time, solution temperature and surface property on PNA adsorption onto the prepared ACFs was investigated by conducting a series of batch adsorption experiments. The kinetic rates at different temperatures were modeled by using the Lagergren-first-order, pseudo-second-order, Morris's intraparticle diffusion and Boyd's film-diffusion models, respectively. It was found that the maximum adsorption of PNA on the ACFs was more than 510 mg/L, and over 60% adsorption occurred in first 25 min. The effect of temperature on the adsorption was related to the contacting time and the micropore structure of the adsorbents. And the increase of micropore surface area favored the adsorption process. Kinetic rates fitted the pseudo-second-order model very well. The pore diffusion played an important role in the entire adsorption period, and intraparticle diffusion was the rate-limiting step in the beginning 20 min. The Freundlich model provided a better data fitting as compared with the Langmuir model. The surface micrograph of the ACF after adsorption showed a distinct roughness with oval patterns. The results revealed that the adsorption was in part with multimolecular layers of coverage. PMID:20202747

  1. [Methodologic aspects of body water kinetic dynamic studies].

    PubMed

    Lobachik, V I; Chupushtanov, S A; Pishchulina, G N; Voronov, S F; Nosovskiĭ, A M

    1998-01-01

    In studying the level of hydration and liquid phases (LPs) in a space mission there use the stable and/or radioactive isotopes. The investigations are unique, the methods are adequate but not adapted in full measure to the challenges of the problem under study. The methodical approaches to the study of the dynamics of water metabolism are not available. Repeated introduction of the markers for these purposes is not acceptable. Another problem associates with taking the markers orally. In this case, a concentration of the markers will depend on the absorption and excretion processes. Prior to, during and in the readaptation period these functions will be different, making a correlation of the accumulated data difficult. There advances a possible version of solving these problems, namely, to use for the dynamic studies the residual contents of the markers in the LPs after single injection. However, this approach calls for investigating the kinetics of markers in weightlessness or during its ground-based simulation. The kinetics of tritium water has been studied in 6 volunteers under conditions of the 5-day bedrest and in 9 healthy men during free motor activity. There determined the characteristics of marker kinetics in a healthy man during his routine living activities. Under bedrest conditions there have been noted slowing-down of the rate and a decrease in the degree of marker accumulation in the body after its single injection, the shift of a period of relative stabilization of marker content in LP to the more late dates of experiment, slowing-down of the marker excretion rate from the body. PMID:9858979

  2. Spectroscopic, thermodynamic, kinetic studies and oxidase/antioxidant biomimetic catalytic activities of tris(3,5-dimethylpyrazolyl)borate Cu(II) complexes.

    PubMed

    Shaban, Shaban Y; Ramadan, Abd El-Motaleb M; Ibrahim, Mohamed M; Mohamed, Mahmoud A; van Eldik, Rudi

    2015-08-21

    A series of copper(ii) complexes, viz. [Tp(MeMe)Cu(Cl)(H2O)] (), [Tp(MeMe)Cu(OAc)(H2O)] (), [Tp(MeMe)Cu(NO3)] () and [Tp(MeMe)Cu(ClO4)] () containing tris(3,5-dimethylpyrazolyl)borate (KTp(MeMe)), have been synthesized and fully characterized. The substitution reaction of with thiourea was studied under pseudo-first-order conditions as a function of concentration, temperature and pressure in methanol and acetonitrile as solvents. Two reaction steps that both depended on the nucleophile concentration were observed for both solvents. Substitution of coordinated methanol is about 40 times faster than the substitution of chloride. In acetonitrile, the rate constant for the displacement of coordinated acetonitrile was more than 20 times faster than the substitution of chloride. The reported activation parameters indicate that both reaction steps follow a dissociative mechanism in both solvents. On going from methanol to acetonitrile, the rate constant for the displacement of the solvent becomes more than 200 times faster due to the more labile acetonitrile, but the substitution mechanism remained to have a dissociative character. The antioxidant activities of were evaluated for superoxide dismutase (SOD), glutathione-s-transferase (GST0 and glutathione reduced (GSH-Rd) activity. and were found to show (p < 0.05) the highest antioxidant activity in comparison to and , which can be ascribed to the geometric configuration as well as the nature of the co-ligand. showed catechol oxidase activity with turnover numbers of 20 min(-1) and a coordination affinity for 3,5-DTBC of K1, = 31 mM(-1). K1 is rather large and seems to be typical for faster biomimetic models, and also for the enzyme itself (25 mM(-1)). The reaction rate depended linearly on the complex concentration, indicating a first-order dependence on the catalyst concentration. PMID:26172408

  3. A kinetic study on pantetheinase inhibition by disulfides.

    PubMed

    Pitari, G; Maurizi, G; Ascenzi, P; Ricci, G; Duprè, S

    1994-11-15

    The mammalian enzyme pantetheinase, which hydrolyzes pantetheine to pantothenic acid and cysteamine, is inhibited by many thiol reagents and activated by thiols. Two thiol groups of different reactivity and accessibility are involved in the catalytic process [Ricci, G., Nardini, M., Chiaraluce, R., Duprè, S. & Cavallini, D. (1986) Biochim. Biophys. Acta 870, 82-91]. The inhibition kinetics by some natural and synthetic disulfides [pantethine, cystamine, 5,5'-dithiobis(2-nitrobenzoic acid), 4,4'-dithiodipyridine and oxidized mercaptoethanol] has been studied by two experimental approaches, either by monitoring activity after incubation of the enzyme with the inhibitor or by determining the progress curves in the presence of substrate and inhibitor. Data reported here indicate that pantetheinase reacts irreversibly with various disulfides in a time-dependent manner with the formation of a mixed disulfide apparently preceeded by a conformational change, giving a modified E* form with new kinetic parameters. This modified form may be further competitively inhibited by disulfides interacting with the enzyme at the active site. PMID:7957261

  4. Antioxidant potential of curcumin-related compounds studied by chemiluminescence kinetics, chain-breaking efficiencies, scavenging activity (ORAC) and DFT calculations.

    PubMed

    Slavova-Kazakova, Adriana K; Angelova, Silvia E; Veprintsev, Timur L; Denev, Petko; Fabbri, Davide; Dettori, Maria Antonietta; Kratchanova, Maria; Naumov, Vladimir V; Trofimov, Aleksei V; Vasil'ev, Rostislav F; Delogu, Giovanna; Kancheva, Vessela D

    2015-01-01

    This study compares the ability to scavenge different peroxyl radicals and to act as chain-breaking antioxidants of monomers related to curcumin (1): dehydrozingerone (2), zingerone (3), (2Z,5E)-ethyl 2-hydroxy-6-(4-hydroxy-3-methoxyphenyl)-4-oxohexa-2,5-dienoate (4), ferulic acid (5) and their corresponding C 2-symmetric dimers 6-9. Four models were applied: model 1 - chemiluminescence (CL) of a hydrocarbon substrate used for determination of the rate constants (k A) of the reactions of the antioxidants with peroxyl radicals; model 2 - lipid autoxidation (lipidAO) used for assessing the chain-breaking antioxidant efficiency and reactivity; model 3 - oxygen radical absorbance capacity (ORAC), which yields the activity against peroxyl radicals generated by an azoinitiator; model 4 - density functional theory (DFT) calculations at UB3LYP/6-31+G(d,p) level, applied to explain the structure-activity relationship. Dimers showed 2-2.5-fold higher values of k A than their monomers. Model 2 gives information about the effects of the side chains and revealed much higher antioxidant activity for monomers and dimers with α,β-unsaturated side chains. Curcumin and 6 in fact are dimers of the same monomer 2. We conclude that the type of linkage between the two "halves" by which the molecule is made up does not exert influence on the antioxidant efficiency and reactivity of these two dimers. The dimers and the monomers demonstrated higher activity than Trolox (10) in aqueous medium (model 3). A comparison of the studied compounds with DL-α-tocopherol (11), Trolox and curcumin is made. All dimers are characterized through lower bond dissociation enthalpies (BDEs) than their monomers (model 4), which qualitatively supports the experimental results. PMID:26425195

  5. Antioxidant potential of curcumin-related compounds studied by chemiluminescence kinetics, chain-breaking efficiencies, scavenging activity (ORAC) and DFT calculations

    PubMed Central

    Slavova-Kazakova, Adriana K; Angelova, Silvia E; Veprintsev, Timur L; Denev, Petko; Fabbri, Davide; Dettori, Maria Antonietta; Kratchanova, Maria; Naumov, Vladimir V; Trofimov, Aleksei V; Vasil’ev, Rostislav F

    2015-01-01

    Summary This study compares the ability to scavenge different peroxyl radicals and to act as chain-breaking antioxidants of monomers related to curcumin (1): dehydrozingerone (2), zingerone (3), (2Z,5E)-ethyl 2-hydroxy-6-(4-hydroxy-3-methoxyphenyl)-4-oxohexa-2,5-dienoate (4), ferulic acid (5) and their corresponding C 2-symmetric dimers 6–9. Four models were applied: model 1 – chemiluminescence (CL) of a hydrocarbon substrate used for determination of the rate constants (k A) of the reactions of the antioxidants with peroxyl radicals; model 2 – lipid autoxidation (lipidAO) used for assessing the chain-breaking antioxidant efficiency and reactivity; model 3 – oxygen radical absorbance capacity (ORAC), which yields the activity against peroxyl radicals generated by an azoinitiator; model 4 – density functional theory (DFT) calculations at UB3LYP/6-31+G(d,p) level, applied to explain the structure–activity relationship. Dimers showed 2–2.5-fold higher values of k A than their monomers. Model 2 gives information about the effects of the side chains and revealed much higher antioxidant activity for monomers and dimers with α,β-unsaturated side chains. Curcumin and 6 in fact are dimers of the same monomer 2. We conclude that the type of linkage between the two “halves” by which the molecule is made up does not exert influence on the antioxidant efficiency and reactivity of these two dimers. The dimers and the monomers demonstrated higher activity than Trolox (10) in aqueous medium (model 3). A comparison of the studied compounds with DL-α-tocopherol (11), Trolox and curcumin is made. All dimers are characterized through lower bond dissociation enthalpies (BDEs) than their monomers (model 4), which qualitatively supports the experimental results. PMID:26425195

  6. Active heterotrophic biomass and sludge retention time (SRT) as determining factors for biodegradation kinetics of pharmaceuticals in activated sludge.

    PubMed

    Majewsky, Marius; Gallé, Tom; Yargeau, Viviane; Fischer, Klaus

    2011-08-01

    The present study investigates the biodegradation of pharmaceutically active compounds (PhACs) by active biomass in activated sludge. Active heterotrophs (X(bh)) which are known to govern COD removal are suggested as a determining factor for biological PhAC removal as well. Biodegradation kinetics of five polar PhACs were determined in activated sludge of two wastewater treatment plants which differed in size, layout and sludge retention time (SRT). Results showed that active fractions of the total suspended solids (TSS) differed significantly between the two sludges, indicating that TSS does not reveal information about heterotrophic activity. Furthermore, PhAC removal was significantly faster in the presence of high numbers of heterotrophs and a low SRT. Pseudo first-order kinetics were modified to include X(bh) and used to describe decreasing PhAC elimination with increasing SRT. PMID:21652206

  7. Kinetic studies of stress-corrosion cracking

    NASA Technical Reports Server (NTRS)

    Noronha, P. J.

    1977-01-01

    Use of time-to-failure curves for stress-corrosion cracking processes may lead to incorrect estimates of structural life, if material is strongly dependent upon prestress levels. Technique characterizes kinetics of crackgrowth rates and intermediate arrest times by load-level changes.

  8. Triacylglycerol kinetics in endotoxic rats with suppressed lipoprotein lipase activity

    SciTech Connect

    Bagby, G.J.; Corll, C.B.; Martinez, R.R.

    1987-07-01

    Hypertriglyceridemia observed in animals after bacterial endotoxin administration and some forms of sepsis can result from increased hepatic triacylglycerol (TG) output or decreased TG clearance by extrahepatic tissues. To differentiate between these two possibilities, TG and free fatty acid (FFA) kinetics were determined in control and endotoxin-injected rats 18 h after treatment. Plasma TG and FFA kinetics were assessed by a constant intravenous infusion with (9,10-/sup 3/H)palmitate-labeled very low-density lipoprotein and (1-/sup 14/C)palmitate bound to albumin, respectively. In addition, lipoprotein lipase (LPL) activity was determined in heart, skeletal muscle, and adipose tissue as well as in postheparin plasma of functionally hepatectomized, adrenalectomized, and gonadectomized rats. Plasma FFA acid concentrations were slightly increased in endotoxin-treated rats but their turnover did not differ from control. Endotoxin-treated rats had a threefold increase in plasma TG concentrations and decreased heart, skeletal muscle, and post-heparin plasma LPL activity. Plasma TG turnover was decreased, indicating that hypertriglyceridemia was not due to an increased TG output by the liver. Instead, the endotoxin-induced increase in plasma TG concentration was consequence of the 80% reduction in TG metabolic clearance rate. Thus, suppression of LPL activity in endotoxic animals impairs TG clearance resulting in hypertriglyceridemia. Furthermore, endotoxin administration reduced the delivery of TG-FFA to extrahepatic tissues because hepatic synthesis and secretion of TG from plasma FFA was decreased and LPL activity was suppressed.

  9. DEVELOPMENT OF QUANTITATIVE STRUCTURE-ACTIVITY RELATIONSHIPS FOR PREDICTING BIODEGRADATION KINETICS

    EPA Science Inventory

    Results have been presented on the development of a structure-activity relationship for biodegradation using a group contribution approach. sing this approach, reported results of the kinetic rate constant agree within 20% with the predicted values. dditional compound studies are...

  10. Large-scale epitaxial growth kinetics of graphene: A kinetic Monte Carlo study

    SciTech Connect

    Jiang, Huijun; Hou, Zhonghuai

    2015-08-28

    Epitaxial growth via chemical vapor deposition is considered to be the most promising way towards synthesizing large area graphene with high quality. However, it remains a big theoretical challenge to reveal growth kinetics with atomically energetic and large-scale spatial information included. Here, we propose a minimal kinetic Monte Carlo model to address such an issue on an active catalyst surface with graphene/substrate lattice mismatch, which facilitates us to perform large scale simulations of the growth kinetics over two dimensional surface with growth fronts of complex shapes. A geometry-determined large-scale growth mechanism is revealed, where the rate-dominating event is found to be C{sub 1}-attachment for concave growth-front segments and C{sub 5}-attachment for others. This growth mechanism leads to an interesting time-resolved growth behavior which is well consistent with that observed in a recent scanning tunneling microscopy experiment.

  11. Diffusion of point defects in crystalline silicon using the kinetic activation-relaxation technique method

    NASA Astrophysics Data System (ADS)

    Trochet, Mickaël; Béland, Laurent Karim; Joly, Jean-François; Brommer, Peter; Mousseau, Normand

    2015-06-01

    We study point-defect diffusion in crystalline silicon using the kinetic activation-relaxation technique (k-ART), an off-lattice kinetic Monte Carlo method with on-the-fly catalog building capabilities based on the activation-relaxation technique (ART nouveau), coupled to the standard Stillinger-Weber potential. We focus more particularly on the evolution of crystalline cells with one to four vacancies and one to four interstitials in order to provide a detailed picture of both the atomistic diffusion mechanisms and overall kinetics. We show formation energies, activation barriers for the ground state of all eight systems, and migration barriers for those systems that diffuse. Additionally, we characterize diffusion paths and special configurations such as dumbbell complex, di-interstitial (IV-pair+2I) superdiffuser, tetrahedral vacancy complex, and more. This study points to an unsuspected dynamical richness even for this apparently simple system that can only be uncovered by exhaustive and systematic approaches such as the kinetic activation-relaxation technique.

  12. Insights into Coupled Folding and Binding Mechanisms from Kinetic Studies.

    PubMed

    Shammas, Sarah L; Crabtree, Michael D; Dahal, Liza; Wicky, Basile I M; Clarke, Jane

    2016-03-25

    Intrinsically disordered proteins (IDPs) are characterized by a lack of persistent structure. Since their identification more than a decade ago, many questions regarding their functional relevance and interaction mechanisms remain unanswered. Although most experiments have taken equilibrium and structural perspectives, fewer studies have investigated the kinetics of their interactions. Here we review and highlight the type of information that can be gained from kinetic studies. In particular, we show how kinetic studies of coupled folding and binding reactions, an important class of signaling event, are needed to determine mechanisms. PMID:26851275

  13. Reactivity of organic micropollutants with ozone: A kinetic study

    SciTech Connect

    Brambilla, A.; Bolzacchini, E.; Meinardi, S.

    1995-12-01

    Studies about the chemical reactivity of compounds widely used in the environment are needed. The chemical reactivity of triazines (simazine, atrazine, terbutylazine) and phenylureas (linuron and diuron) was studied. The kinetics of the oxidation of the triazines and phenylureas with ozone at pH 3 and the kinetics of the saturation of the solution with ozone were evaluated. These data may be useful for the prediction of the persistency of these compuonds in the environment and for the treatment of wastewaters contaminated with these compounds. The solution was presaturated with ozone before the addition of the substrate, and the reaction constants for the pseudo first order kinetics -d[substrate]/dt = k{sub app} [substrate] at 298{degree}K were obtained, assuming a steady state concentration of ozone of 1.91 10{sup -4} mol L{sup -1} for the phenylureas and of 3.03 10{sup -4} and L{sup -1} for the triazines. The data obtained were: atrazine k = 6.86 (L mol{sup -1}s{sup -1}); simazine: 9.26; t-butylazine 7.26; linuron 11.00; diuron 43.90. The activation parameters for the reaction of simazine were {Delta}H{sup =} = 9.35 kcal mol{sup -1} and {Delta}S{sup =} = -22.3 cal mol{sup -1} {degree}K{sup -1} and for the reaction of diuron were {Delta}H{sup =} = 16.83 Kcal mol{sup -1}, {Delta}S{sup =} = 5.696 cal mol{sup -1} {degree}K{sup -1}.

  14. Thermogravimetric kinetic study of agricultural residue biomass pyrolysis based on combined kinetics.

    PubMed

    Wang, Xun; Hu, Mian; Hu, Wanyong; Chen, Zhihua; Liu, Shiming; Hu, Zhiquan; Xiao, Bo

    2016-11-01

    Pyrolytic kinetic of an agricultural residue (AR) feedstock, a mixture of plants (cotton, wheat, rich, corn) stems, was investigated based on combined kinetics. The most suitable mechanism for AR one-step pyrolysis was f(α)=(1-α)(1.1816)α(-1.8428) with kinetic parameters of: apparent activation energy 221.7kJ/mol, pre-exponential factor 4.17E16s(-1). Pyrolysis of AR feedstock could not be described by one-step reaction attributes to heterogeneous features of pyrolysis processes. Combined kinetics three-parallel-reaction (CK-TPR) model fitted the pyrolysis experimental data very well. Reaction mechanisms for pseudo hemicelluloses, cellulose, lignin in CK-TPR model was f(α)=(1-α)(1.6244)α(-0.3371)[-ln(1-α)](-0.0515), f(α)=(1-α)(1.0597)α(-0.6909)[-ln(1-α)](0.9026) and f(α)=(1-α)(2.9577)α(-4.7719), respectively. Apparent activation energy of three pseudo components followed the order of Elignin(197.3kJ/mol)>Ecellulose(176.3kJ/mol)>Ehemicelluloses (151.1kJ/mol). Mechanism of hemicelluloses pyrolysis could be further expressed as f(α)=(1-α)(1.4). The pyrolytic mechanism of cellulose met the Nucleation well. However, mechanism of lignin pyrolysis was complex, which possibly was the combined effects of Nucleation, Diffusion, Geometrical contraction, and Power law. PMID:27521788

  15. Pharmacodynamic properties of faropenem demonstrated by studies of time-kill kinetics and postantibiotic effect.

    PubMed

    Boswell, F J; Andrews, J M; Wise, R

    1997-03-01

    The pharmacodynamic properties of faropenem, a new oral penem antibiotic, were investigated by studying time-kill kinetics and postantibiotic effect. Time-kill kinetics were employed against strains of Bacteroides fragilis, Escherichia coli, Staphylococcus aureus, Haemophilus influenzae, Moraxella catarrhalis and Streptococcus pyogenes. The postantibiotic effects of faropenem were studied using strains of E. coli, S. aureus, H. influenzae and Streptococcus pneumoniae. The time-kill kinetic data demonstrated that faropenem has bactericidal activity. Faropenem exhibited a significant postantibiotic effect against all strains except H. influenzae. PMID:9096193

  16. Kinetic Study of Denatonium Sorption to Smectite Clay Minerals

    PubMed Central

    Crosson, Garry S.; Sandmann, Emily

    2013-01-01

    Abstract The denatonium cation, as a benzoate salt, is the most bitter cation known to modern society and is frequently added to consumer products to reduce accidental and intentional consumption by humans and animals. Denatonium can enter the environment by accidental discharges, potentially rendering water supplies undrinkable. Interactions of denatonium with soil components (i.e., smectite minerals) ultimately control the environmental fate of denatonium, but the current literature is devoid of studies that evaluate denatonium sorption to smectite minerals. This study investigated the mechanism and kinetics of denatonium sorption to smectite clay minerals as a function of smectite type, temperature, pH and ionic strength. Uptake by synthetic mica montmorillonite (Syn-1), Wyoming montmorillonite (SWy-2), and Texas montmorillonite (STx-1b) at 305K was rapid, with equilibrium being reached within 2 min for all clays. Complete removal of denatonium was observed for STx-1b at pH 6.9, while partial removal was observed for Syn-1 and SWy-2. Kinetic behavior of SWy-2 and Syn-1 is consistent with a pseudo–second-order model at 305K. An activation energy of +25.9 kJ/mol was obtained for sorption to Syn-1 and was independent of temperature between 286K and 338K. Activation-free energy (ΔG*), activation enthalpy (ΔH*), and activation entropy (ΔS*) for Syn-1 were found to be +62.91 kJ/mol, +23.36 kJ/mol, and −0.130 kJ/(K·mol), respectively. Sorption capacities at pH 3.6, 6.9, and 8.2 were constant at 1.3×10−2 g denatonium/g clay; however, the kinetic rate constant increased by 56%, going from acidic to basic solution conditions. Distribution coefficients were negatively correlated with ionic strength, suggesting cation exchange. Collectively, results suggested that smectite minerals can serve as efficient sinks for denatonium cations. This is much-needed information for agencies developing regulations regarding denatonium usage and for water treatment

  17. Kinetic Study of Denatonium Sorption to Smectite Clay Minerals.

    PubMed

    Crosson, Garry S; Sandmann, Emily

    2013-06-01

    The denatonium cation, as a benzoate salt, is the most bitter cation known to modern society and is frequently added to consumer products to reduce accidental and intentional consumption by humans and animals. Denatonium can enter the environment by accidental discharges, potentially rendering water supplies undrinkable. Interactions of denatonium with soil components (i.e., smectite minerals) ultimately control the environmental fate of denatonium, but the current literature is devoid of studies that evaluate denatonium sorption to smectite minerals. This study investigated the mechanism and kinetics of denatonium sorption to smectite clay minerals as a function of smectite type, temperature, pH and ionic strength. Uptake by synthetic mica montmorillonite (Syn-1), Wyoming montmorillonite (SWy-2), and Texas montmorillonite (STx-1b) at 305K was rapid, with equilibrium being reached within 2 min for all clays. Complete removal of denatonium was observed for STx-1b at pH 6.9, while partial removal was observed for Syn-1 and SWy-2. Kinetic behavior of SWy-2 and Syn-1 is consistent with a pseudo-second-order model at 305K. An activation energy of +25.9 kJ/mol was obtained for sorption to Syn-1 and was independent of temperature between 286K and 338K. Activation-free energy (ΔG*), activation enthalpy (ΔH*), and activation entropy (ΔS*) for Syn-1 were found to be +62.91 kJ/mol, +23.36 kJ/mol, and -0.130 kJ/(K·mol), respectively. Sorption capacities at pH 3.6, 6.9, and 8.2 were constant at 1.3×10(-2) g denatonium/g clay; however, the kinetic rate constant increased by 56%, going from acidic to basic solution conditions. Distribution coefficients were negatively correlated with ionic strength, suggesting cation exchange. Collectively, results suggested that smectite minerals can serve as efficient sinks for denatonium cations. This is much-needed information for agencies developing regulations regarding denatonium usage and for water treatment professionals who may

  18. Pulsed laser kinetic studies of liquids under high pressure

    SciTech Connect

    Eyring, E.M.

    1992-09-22

    A laser flash photolysis kinetic study of 2,2{prime}-bipyridine bidentate chelating ligands with one claw in the first coordination sphere of a molybdenum carbonyl complex has been completed at pressures up to 150 MPa. The reaction mechanism for thermal ring closure is found from activation volumes to change from associative interchange to dissociative interchange as substituents on the 2,2{prime}-bipyridine ligands become bulkier. In a similar study of more rigid, substituted phenanthroline bidentate ligands it was found that substituent bulkiness had little effect on the thermal ring closure mechanism. Stability constants for lithium ion complexes with crown ethers in a room temperature molten salt, fluorescence quantum yields for cresyl violet and several other dyes in solution, and the oxidation of alcohols by OsO{sub 4} have also been investigated.

  19. Ultrasonic enhancement of the simultaneous removal of quaternary toxic organic dyes by CuO nanoparticles loaded on activated carbon: Central composite design, kinetic and isotherm study.

    PubMed

    Dashamiri, Somayeh; Ghaedi, Mehrorang; Dashtian, Kheibar; Rahimi, Mahmood Reza; Goudarzi, Alireza; Jannesar, Ramin

    2016-07-01

    Copper oxide nanoparticles loaded on activated carbon (CuO-NPs-AC) were prepared and fully analyzed and characterized with FE-SEM, XRD and FT-IR. Subsequently, this novel material was used for simultaneous ultrasound-assisted adsorption of brilliant green (BG), auramine O (AO), methylene blue (MB) and eosin yellow (EY) dyes. Problems regard to dyes spectra overlap in quaternary solution of this dyes were omitted by derivative spectrophotometric method. The best pH in quaternary system was studied by using one at a time method to achieved maximum dyes removal percentage. Subsequently, sonication time, adsorbent dosage and initial dyes concentrations influence on dyes removal was optimized by central composite design (CCD) combined with desirability function approach (DFA). Desirability score of 0.978 show optimum conditions set at sonication time (4.2 min), adsorbent mass (0.029 g), initial dyes concentration (4.5 mg L(-1)). Under this optimum condition the removal percentage for MB, AO, EY and BG dyes 97.58, 94.66, 96.22 and 94.93, respectively. The adsorption rate well fitted by pseudo second-order while adsorption capacity according to the Langmuir model as best equilibrium isotherm model for BG, MB, AO and EY was 20.48, 21.26, 22.34 and 21.29 mg g(-1), respectively. PMID:26964982

  20. Planning a Kinetic and Mechanistic Study with Cerium (IV)

    ERIC Educational Resources Information Center

    Hanna, Samir B.; And Others

    1976-01-01

    Presents a kinetic study that utilizes a method for varying the concentrations of the possible Ce(IV) species and computing the concentration distribution of the sulfato and hydroxo species of Ce(IV). (MLH)

  1. A rapid and sensitive method for kinetic study and activity assay of DNase I in vitro based on a GO-quenched hairpin probe.

    PubMed

    Xu, Wei; Xie, Zhenhua; Tong, Chunyi; Peng, Lan; Xiao, Changhui; Liu, Xuanming; Zhu, Yonghua; Liu, Bin

    2016-05-01

    As a waste-management endonuclease, DNase I has been suggested to be one of the deoxyribonucleases responsible for DNA fragmentation during apoptosis. We report here an alternative fluorescence method for DNase I assay with high accuracy and sensitivity by applying a DNA/GO (graphene oxide) probe. The method with a detection limit of 1 U mL(-1) was then applied to investigate the effects of external factors including antibiotics and heavy metal ions on DNase I. The results demonstrated that gentamicin sulfate was a strong inhibitor with an IC50 value of 0.57 ± 0.12 mM. The investigated heavy metal ions showed an inhibitory effect on DNase I activity in a concentration dependent manner with IC50 values of 0.04 μg/mL (Hg(2+)), 0.10 μg/mL (Pb(2+)), 1.35 μg/mL (Cd(2+)), 1.20 μg/mL (As(2+)), and 1.80 μg/mL (Cu(2+)). Finally, the new method was applied to detect DNase levels in complicated tumor tissue and cell samples and the results showed that DNase levels increased in tumor tissues compared with that of adjacent tissue. From the above results, we conclude that the method can be widely used for high - throughput assay of DNase I in biological samples as well as drug screening in vitro. Graphical Abstract The schematic of real-time monitoring of DNase I using GO - quenched hairpin probe as the substrate. The process of nucleotide digestion catalyzed by DNase I produces short fragments of hairpin probe and accordingly causes a significant increase in fluorescence. At first, GO can absorb the hairpin probes and quenched their fluorescence. When there is DNase I, the DNase can cleave the double strands of DNA. Fluorescence is restored due to the significantly weaker binding ability of small DNA fragments to GO compared with long DNA fragments. So, we can detect the increase in fluorescence to study the activity of DNase. PMID:27038057

  2. Catalytic deactivation on methane steam reforming catalysts. 2. Kinetic study

    SciTech Connect

    Agnelli, M.E.; Ponzi, E.N.; Yeramian, A.A.

    1987-08-01

    The kinetics of methane steam reforming reaction over an alumina-supported nickel catalyst was investigated at a temperature range of 640-740/sup 0/C in a flow reactor at atmospheric pressure. The experiments were performed varying the inlet concentration of methane, hydrogen, and water. A kinetic scheme of the Houghen-Watson type was satisfactorily proposed assuming the dissociative adsorption of CH/sub 4/ as the rate-limiting step, but this kinetic scheme can be easily replaced by a first-order kinetics (r/sub CH/4/sub / = kapparho/sub CH/4/sub /) for engineering purposes. Catalyst activation with H/sub 2/ and N/sub 2/ mixtures or with the reactant mixture results in the same extent of reaction.

  3. Probing the Effect of the Non-Active-Site Mutation Y229W in New Delhi Metallo-β-lactamase-1 by Site-Directed Mutagenesis, Kinetic Studies, and Molecular Dynamics Simulations

    PubMed Central

    Shi, Yun; Hu, Feng; Lao, Xingzhen; Gao, Xiangdong; Zheng, Heng; Yao, Wenbing

    2013-01-01

    New Delhi metallo-β-lactmase-1 (NDM-1) has attracted extensive attention for its high catalytic activities of hydrolyzing almost all β-lactam antibiotics. NDM-1 shows relatively higher similarity to subclass B1 metallo-β-lactmases (MβLs), but its residue at position 229 is identical to that of B2/B3 MβLs, which is a Tyr instead of a B1-MβL-conserved Trp. To elucidate the possible role of Y229 in the bioactivity of NDM-1, we performed mutagenesis study and molecular dynamics (MD) simulations. Although residue Y229 is spatially distant from the active site and not contacting directly with the substrate or zinc ions, the Y229W mutant was found to have higher kcat and Km values than those of wild-type NDM-1, resulting in 1∼7 fold increases in kcat/Km values against tested antibiotics. In addition, our MD simulations illustrated the enhanced flexibility of Loop 2 upon Y229W mutation, which could increase the kinetics of both substrate entrance (kon) and product egress (koff). The enhanced flexibility of Loop 2 might allow the enzyme to adjust the geometry of its active site to accommodate substrates with different structures, broadening its substrate spectrum. This study indicated the possible role of the residue at position 229 in the evolution of NDM-1. PMID:24339993

  4. Pulsed laser kinetic studies of liquids under high pressure

    SciTech Connect

    Eyring, E.M.

    1991-11-25

    A high pressure apparatus constructed for measuring the rates of reactions in liquids under pressures ranging from 1 atm to 2000 atm has been used to measure the complexation kinetics of molybdenum hexacarbonyl reacting with 2,2-bipyridine, 4,4{prime}-dimethyl-2-2{prime}-bipyridine and 4,4{prime}-diphenyl-2-2{prime} bipyridine in toluene. Pentacarbonyl reaction intermediates are created by a 10 nsec flash of frequency tripled Nd:YAG laser light. Measured activation volumes for chelate ligand ring closure indicate a change in mechanism from associative interchange to dissociative interchange as steric hindrance increases. A similar high pressure kinetics study of molybdenum carbonyl complexation by several substituted phenanthrolines is now well advanced that indicates that with the more rigid phenanthroline ligands steric effects from bulky substituents have less effect on the ring closure mechanism than in the case of the bipyridine ligands. An experimental concentration dependence of the fluorescence quantum yield of cresyl violet has been harmonized with previously published contradictory reports. Fluorescence of cresyl violet in various solvents and in micellar systems has also been systematically explored.

  5. Pyrolysis of microalgae residues--A kinetic study.

    PubMed

    Bui, Hau-Huu; Tran, Khanh-Quang; Chen, Wei-Hsin

    2016-01-01

    Pyrolysis of residues from the oil extraction process of two types of microalgae, Chlamydomonas (C. sp. JSC4) and Chlorella sorokiniana (C. Sorokiniana CY1) was studied by means of a thermogravimetric analyzer. Five pseudo-components (hemicellulose, cellulose, lignin, lipid and protein) model with n=1 or n#1 was assumed for a kinetic analysis of the collected pyrolysis data. The model with n#1 resulted in a slightly better fit quality and reasonable kinetic parameters. The calculated activation energy of hemicellulose, cellulose, lignin, lipid, protein was 115.12-117.12 kJ/mol, 181.67-198.30 kJ/mol, 61.74-62.75 kJ/mol, 104.93-114.14 kJ/mol and 90.75-99.31 kJ/mol, respectively, for C. sp. JSC4; and 113.12-117.12 kJ/mol, 218.73-28.79 kJ/mol, 64.77-66.39 kJ/mol, 131.97-143.63 kJ/mol and 108.03-118.13 kJ/mol, respectively, for C. Sorokiniana CY1. PMID:26342785

  6. Kinetic and thermodynamic studies of sulforaphane adsorption on macroporous resin.

    PubMed

    Yuanfeng, Wu; Lei, Zhang; Jianwei, Mao; Shiwang, Liu; Jun, Huang; Yuru, You; Lehe, Mei

    2016-08-15

    The adsorption equilibrium, kinetic and thermodynamic of sulforaphane (SF) adsorption onto macroporous resin in aqueous phase were studied. The SP850 resin was screened as the appropriate resin for SF purification. From the equilibrium studies, the Redlich-Peterson model was found to be the best for description of the adsorption behavior of SF onto SP850 resin, followed by the Freundlich model and the Langmuir model. Batch equilibrium experiments demonstrated that, in the examined temperature range, the equilibrium adsorption capacity of SP850 resin decreased with increasing adsorption temperature. Thermodynamics studies indicated that the adsorption of SF was a physical, exothermic, and spontaneous process. The adsorption kinetics revealed that the pseudo-second-order kinetic model was suitable to characterize the kinetics of adsorption of SF onto SP850. Finally, the intra-particle diffusion model demonstrated that SF diffused quickly into macropores, and that diffusion slowed down in the meso- and micropores. PMID:27391585

  7. Kinetic studies with N2-phenylguanines and with L-thymidine indicate that herpes simplex virus type-1 thymidine kinase and thymidylate kinase share a common active site.

    PubMed

    Maga, G; Focher, F; Wright, G E; Capobianco, M; Garbesi, A; Bendiscioli, A; Spadari, S

    1994-08-15

    It is known that the Herpes simplex virus type 1 (HSV-1)-encoded thymidine kinase (TK) co-purifies with an associated thymidylate kinase (TMPK) activity and that thymidylate (TMP) inhibits the phosphorylation of thymidine by the HSV-1 TK. Here we demonstrate that: (i) TMP phosphorylation catalysed by the viral TMPK is competitively inhibited by thymidine (TdR) with a Ki equal to its Km as substrate for the viral TK; (ii) L-thymidine (L-TdR), the enantiomer of the naturally occurring D-TdR and a substrate for the HSV-1 TK [Spadari, Maga, Focher, Ciarrocchi, Manservigi, Arcamone, Capobianco, Caruso, Colonna, Iotti and Garbesi (1992) J. Med. Chem. 35, 4214-4220], is a powerful inhibitor of the HSV-1 TMPK activity with a Ki value identical with its Km as a substrate for the viral TK; (iii) both viral TK and TMPK activities are inhibited, in a competitive way and with identical Ki values, by novel, non-substrate inhibitors of HSV-1 TK, N2-phenylguanines; (iv) L-TdR is phosphorylated to L-TMP by the viral TK, but L-TMP is not phosphorylated to L-TDP by the viral TMPK activity; and (v) L-TMP inhibits competitively and with identical potencies the phosphorylation of TdR and TMP catalysed respectively by the HSV-1 TK and TMPK activities. In conclusion, our data demonstrate that both TK and TMPK activities encoded by HSV-1 share a common active site which is very tolerant in accepting modified nucleosides, but cannot readily accommodate modified nucleoside monophosphates. PMID:8068016

  8. Kinetic studies with N2-phenylguanines and with L-thymidine indicate that herpes simplex virus type-1 thymidine kinase and thymidylate kinase share a common active site.

    PubMed Central

    Maga, G; Focher, F; Wright, G E; Capobianco, M; Garbesi, A; Bendiscioli, A; Spadari, S

    1994-01-01

    It is known that the Herpes simplex virus type 1 (HSV-1)-encoded thymidine kinase (TK) co-purifies with an associated thymidylate kinase (TMPK) activity and that thymidylate (TMP) inhibits the phosphorylation of thymidine by the HSV-1 TK. Here we demonstrate that: (i) TMP phosphorylation catalysed by the viral TMPK is competitively inhibited by thymidine (TdR) with a Ki equal to its Km as substrate for the viral TK; (ii) L-thymidine (L-TdR), the enantiomer of the naturally occurring D-TdR and a substrate for the HSV-1 TK [Spadari, Maga, Focher, Ciarrocchi, Manservigi, Arcamone, Capobianco, Caruso, Colonna, Iotti and Garbesi (1992) J. Med. Chem. 35, 4214-4220], is a powerful inhibitor of the HSV-1 TMPK activity with a Ki value identical with its Km as a substrate for the viral TK; (iii) both viral TK and TMPK activities are inhibited, in a competitive way and with identical Ki values, by novel, non-substrate inhibitors of HSV-1 TK, N2-phenylguanines; (iv) L-TdR is phosphorylated to L-TMP by the viral TK, but L-TMP is not phosphorylated to L-TDP by the viral TMPK activity; and (v) L-TMP inhibits competitively and with identical potencies the phosphorylation of TdR and TMP catalysed respectively by the HSV-1 TK and TMPK activities. In conclusion, our data demonstrate that both TK and TMPK activities encoded by HSV-1 share a common active site which is very tolerant in accepting modified nucleosides, but cannot readily accommodate modified nucleoside monophosphates. PMID:8068016

  9. Sorption kinetic studies of ammonium from aqueous solution on different inorganic and organic media.

    PubMed

    Kucić, Dajana; Cosić, Ivana; Vuković, Marija; Briski, Felicita

    2013-01-01

    In this study, the sorption of ammonium from aqueous solution onto activated carbon, natural zeolite, peat and potting soil was studied by performing batch kinetic sorption experiments. The activated carbon wasn't efficiently removing ammonium at concentrations higher than 50 mg L(-1). Sorption isotherms of ammonium on zeolite, peat and potting soil were determined at 25 degrees C and 200 rpm with the initial concentration of 50-7000 mg L(-1). Equilibrium data were fitted by Freundlich, Langmuir and Temkin isotherm and parameters were evaluated according these models. Langmuir model gives better fit to experimental data than Freundlich and Temkin models. Maximum adsorption capacities were for activated carbon 0.631 mg g(-1), zeolite 58 mg g(-1), peat 595 mg g(-1) and for potting soil 575 mg g(-1). The equilibrium kinetic data were analyzed using adsorption kinetic models: the pseudo-first and second-order equations and were found to follow the pseudo-second-order kinetic model. A comparison between linear and non-linear regression method for estimating the adsorption and kinetics parameters was examined. The obtained results showed that non-linear method may be a better way to determine the kinetic parameters. Thermodynamic studies showed exothermic and endothermic nature of the adsorption of NH4(+) on inorganic and organic adsorbents, respectively. From present results it can be seen that zeolite, peat and potting soil are good adsorbents for removal ammonium from aqueous solution. PMID:23841339

  10. Enhanced Enzyme Kinetic Stability by Increasing Rigidity within the Active Site*

    PubMed Central

    Xie, Yuan; An, Jiao; Yang, Guangyu; Wu, Geng; Zhang, Yong; Cui, Li; Feng, Yan

    2014-01-01

    Enzyme stability is an important issue for protein engineers. Understanding how rigidity in the active site affects protein kinetic stability will provide new insight into enzyme stabilization. In this study, we demonstrated enhanced kinetic stability of Candida antarctica lipase B (CalB) by mutating the structurally flexible residues within the active site. Six residues within 10 Å of the catalytic Ser105 residue with a high B factor were selected for iterative saturation mutagenesis. After screening 2200 colonies, we obtained the D223G/L278M mutant, which exhibited a 13-fold increase in half-life at 48 °C and a 12 °C higher T5015, the temperature at which enzyme activity is reduced to 50% after a 15-min heat treatment. Further characterization showed that global unfolding resistance against both thermal and chemical denaturation also improved. Analysis of the crystal structures of wild-type CalB and the D223G/L278M mutant revealed that the latter formed an extra main chain hydrogen bond network with seven structurally coupled residues within the flexible α10 helix that are primarily involved in forming the active site. Further investigation of the relative B factor profile and molecular dynamics simulation confirmed that the enhanced rigidity decreased fluctuation of the active site residues at high temperature. These results indicate that enhancing the rigidity of the flexible segment within the active site may provide an efficient method for improving enzyme kinetic stability. PMID:24448805

  11. Cytokine-release kinetics of platelet-rich plasma according to various activation protocols

    PubMed Central

    Roh, Y. H.; Kim, W.; Park, K. U.

    2016-01-01

    Objectives This study was conducted to evaluate the cytokine-release kinetics of platelet-rich plasma (PRP) according to different activation protocols. Methods Two manual preparation procedures (single-spin (SS) at 900 g for five minutes; double-spin (DS) at 900 g for five minutes and then 1500 g for 15 minutes) were performed for each of 14 healthy subjects. Both preparations were tested for platelet activation by one of three activation protocols: no activation, activation with calcium (Ca) only, or calcium with a low dose (50 IU per 1 ml PRP) of thrombin. Each preparation was divided into four aliquots and incubated for one hour, 24 hours, 72 hours, and seven days. The cytokine-release kinetics were evaluated by assessing PDGF, TGF, VEGF, FGF, IL-1, and MMP-9 concentrations with bead-based sandwich immunoassay. Results The concentration of cytokine released from PRP varied over time and was influenced by various activation protocols. Ca-only activation had a significant effect on the DS PRPs (where the VEGF, FGF, and IL-1 concentrations were sustained) while Ca/thrombin activation had effects on both SS and DS PRPs (where the PDGF and VEGF concentrations were sustained and the TGF and FGF concentrations were short). The IL-1 content showed a significant increase with Ca-only or Ca/thrombin activation while these activations did not increase the MMP-9 concentration. Conclusion The SS and DS methods differed in their effect on cytokine release, and this effect varied among the cytokines analysed. In addition, low dose of thrombin/calcium activation increased the overall cytokine release of the PRP preparations over seven days, relative to that with a calcium-only supplement or non-activation. Cite this article: Professor J. H. Oh. Cytokine-release kinetics of platelet-rich plasma according to various activation protocols. Bone Joint Res 2016;5:37–45. DOI: 10.1302/2046-3758.52.2000540 PMID:26862077

  12. Study on kinetic model of microwave thermocatalytic treatment of biomass tar model compound.

    PubMed

    Anis, Samsudin; Zainal, Z A

    2014-01-01

    Kinetic model parameters for toluene conversion under microwave thermocatalytic treatment were evaluated. The kinetic rate constants were determined using integral method based on experimental data and coupled with Arrhenius equation for obtaining the activation energies and pre-exponential factors. The model provides a good agreement with the experimental data. The kinetic model was also validated with standard error of 3% on average. The extrapolation of the model showed a reasonable trend to predict toluene conversion and product yield both in thermal and catalytic treatments. Under microwave irradiation, activation energy of toluene conversion was lower in the range of 3-27 kJ mol(-1) compared to those of conventional heating reported in the literatures. The overall reaction rate was six times higher compared to conventional heating. As a whole, the kinetic model works better for tar model removal in the absence of gas reforming within a level of reliability demonstrated in this study. PMID:24231266

  13. Modeling and Classification of Kinetic Patterns of Dynamic Metabolic Biomarkers in Physical Activity.

    PubMed

    Breit, Marc; Netzer, Michael; Weinberger, Klaus M; Baumgartner, Christian

    2015-08-01

    The objectives of this work were the classification of dynamic metabolic biomarker candidates and the modeling and characterization of kinetic regulatory mechanisms in human metabolism with response to external perturbations by physical activity. Longitudinal metabolic concentration data of 47 individuals from 4 different groups were examined, obtained from a cycle ergometry cohort study. In total, 110 metabolites (within the classes of acylcarnitines, amino acids, and sugars) were measured through a targeted metabolomics approach, combining tandem mass spectrometry (MS/MS) with the concept of stable isotope dilution (SID) for metabolite quantitation. Biomarker candidates were selected by combined analysis of maximum fold changes (MFCs) in concentrations and P-values resulting from statistical hypothesis testing. Characteristic kinetic signatures were identified through a mathematical modeling approach utilizing polynomial fitting. Modeled kinetic signatures were analyzed for groups with similar behavior by applying hierarchical cluster analysis. Kinetic shape templates were characterized, defining different forms of basic kinetic response patterns, such as sustained, early, late, and other forms, that can be used for metabolite classification. Acetylcarnitine (C2), showing a late response pattern and having the highest values in MFC and statistical significance, was classified as late marker and ranked as strong predictor (MFC = 1.97, P < 0.001). In the class of amino acids, highest values were shown for alanine (MFC = 1.42, P < 0.001), classified as late marker and strong predictor. Glucose yields a delayed response pattern, similar to a hockey stick function, being classified as delayed marker and ranked as moderate predictor (MFC = 1.32, P < 0.001). These findings coincide with existing knowledge on central metabolic pathways affected in exercise physiology, such as β-oxidation of fatty acids, glycolysis, and glycogenolysis. The presented modeling approach

  14. Modeling and Classification of Kinetic Patterns of Dynamic Metabolic Biomarkers in Physical Activity

    PubMed Central

    Breit, Marc; Netzer, Michael

    2015-01-01

    The objectives of this work were the classification of dynamic metabolic biomarker candidates and the modeling and characterization of kinetic regulatory mechanisms in human metabolism with response to external perturbations by physical activity. Longitudinal metabolic concentration data of 47 individuals from 4 different groups were examined, obtained from a cycle ergometry cohort study. In total, 110 metabolites (within the classes of acylcarnitines, amino acids, and sugars) were measured through a targeted metabolomics approach, combining tandem mass spectrometry (MS/MS) with the concept of stable isotope dilution (SID) for metabolite quantitation. Biomarker candidates were selected by combined analysis of maximum fold changes (MFCs) in concentrations and P-values resulting from statistical hypothesis testing. Characteristic kinetic signatures were identified through a mathematical modeling approach utilizing polynomial fitting. Modeled kinetic signatures were analyzed for groups with similar behavior by applying hierarchical cluster analysis. Kinetic shape templates were characterized, defining different forms of basic kinetic response patterns, such as sustained, early, late, and other forms, that can be used for metabolite classification. Acetylcarnitine (C2), showing a late response pattern and having the highest values in MFC and statistical significance, was classified as late marker and ranked as strong predictor (MFC = 1.97, P < 0.001). In the class of amino acids, highest values were shown for alanine (MFC = 1.42, P < 0.001), classified as late marker and strong predictor. Glucose yields a delayed response pattern, similar to a hockey stick function, being classified as delayed marker and ranked as moderate predictor (MFC = 1.32, P < 0.001). These findings coincide with existing knowledge on central metabolic pathways affected in exercise physiology, such as β-oxidation of fatty acids, glycolysis, and glycogenolysis. The presented modeling approach

  15. Rapid kinetic studies and structural determination of a cysteine proteinase mutant imply that residue 158 in caricain has a major effect upon the ability of the active site histidine to protonate a dipyridyl probe.

    PubMed

    Katerelos, N A; Goodenough, P W

    1996-11-26

    Cysteine proteinases are endopeptidases whose catalytic activity depends upon the nucleophilicity of the active site cysteine thiol group. An ion pair forms with an active site histidine. The presence in some cysteine proteinases of an aspartic acid close to the ion pair has been used as evidence of a "catalytic triad" as found in the serine proteinases. In these enzymes, the correct alignment of serine, histidine, and aspartate residues controls catalysis. However, the absence of the homologous aspartate residue in the mammalian cysteine proteinases cathepsins B and H argues against this pivotal role for aspartic acid. Instead, an Asn, physically close to the histidine in cysteine proteinases, has been proposed as a member of the catalytic triad. Protein engineering is being used to investigate these questions. In this study, the Asp158Glu mutant of the plant cysteine proteinase caricain was analyzed by stopped-flow rapid kinetics. The probe that was used was 2,2'-dipyridyl disulfide (2 PDS), and the profile of k versus pH gave results more closely allied to a small molecule active site model than the normal profile with cysteine proteinases. Multiple pKa's identified in the profile are as follows: pK1 = 3.4 (Cys 25), pK2 = 3.6, pK3 = 7.0, and pK4 = 8.6 (His 158). The structure of the enzyme with the bound inhibitor E64 was solved (R factor of 19.3%). Although the distance between the imadazolium and the surrounding charged amino acids is only slightly changed in the mutant, the reduced steady state activity and narrower pH range can be related to changes in the hydrogen-bonding capacity of the imadazolium. PMID:8942638

  16. Kinetic studies on the tensile state of water in trees.

    PubMed

    Tributsch, Helmut; Cermak, Jan; Nadezhdina, Nadezhda

    2005-09-22

    The solar-powered generation and turnover of tensile, cohesive water in trees is described as a kinetic phenomenon of irreversible thermodynamics. A molecular kinetic model for tensile water formation and turnover is presented, which is found to be mathematically equivalent with an autocatalytic reaction (Brusselator). It is also shown to be consistent with the van der Waals equation for real liquid-gas systems, which empirically considers intermolecular forces. It can therefore be used to explain both the irreversible thermodynamics and the kinetics of the tensile liquid state of water. A nonlinear bistable evaporation behavior of tensile water is predicted, which has not yet been experimentally characterized in trees. Conventional sap flow techniques in combination with infrared imaging of heat flow around a local heat source were used to study the dynamics and energetics of water transport of trees during the eclipse of August 11, 1999. The evaporative "pulling force" in a tree was demonstrated with infrared techniques and shown to respond within seconds. While the ambient temperature during the eclipse did not drop by more than 2 degrees C, evaporative water transport was reduced by a factor of up to 2-3. The expected hysteresis (with an up to 50% decrease in energy-conversion-related entropy production) was measured, reflecting a bistable mode of conversion of solar energy into tensile water flow. This nonlinear (autocatalytic) phenomenon, together with tensile molecular order, damped the oscillating behavior of xylem tensile water, and its occasional all-or-none rupture (cavitation) can thus be explained by the nonlinear nature of intermolecular forces active in the water conduit/parenchyma environment. This characterizes the physical chemistry and energetics of tensile water in trees as an active-solar-energy-driven self-organizing process. Water is handled in the form of microcanonical ensembles and transformed into a stretched, metastable icelike state

  17. Kinetic Studies of the Solvolysis of Two Organic Halides

    ERIC Educational Resources Information Center

    Duncan, J. A.; Pasto, D. J.

    1975-01-01

    Describes an undergraduate organic chemistry laboratory experiment which utilizes the solvolysis of organic halides to demonstrate first and second order reaction kinetics. The experiment also investigates the effect of a change of solvent polarity on reaction rate, common-ion and noncommon-ion salt effects, and the activation parameters of a…

  18. Single-molecule kinetics under force: probing protein folding and enzymatic activity with optical tweezers

    NASA Astrophysics Data System (ADS)

    Wong, Wesley

    2010-03-01

    Weak non-covalent bonds between and within single molecules govern many aspects of biological structure and function (e.g. DNA base-paring, receptor-ligand binding, protein folding, etc.) In living systems, these interactions are often subject to mechanical forces, which can greatly alter their kinetics and activity. My group develops and applies novel single-molecule manipulation techniques to explore and quantify these force-dependent kinetics. Using optical tweezers, we have quantified the force-dependent unfolding and refolding kinetics of different proteins, including the cytoskeletal protein spectrin in collaboration with E. Evans's group [1], and the A2 domain of the von Willebrand factor blood clotting protein in collaboration with T. Springer's group [2]. Furthermore, we have studied the kinetics of the ADAMTS13 enzyme acting on a single A2 domain, and have shown that physiolgical forces in the circulation can act as a cofactor for enzymatic cleavage, regulating hemostatic activity [2]. References: 1. E. Evans, K. Halvorsen, K. Kinoshita, and W.P. Wong, Handbook of Single Molecule Biophysics, P. Hinterdorfer, ed., Springer (2009). 2. X. Zhang, K. Halvorsen, C.-Z. Zhang, W.P. Wong, and T.A. Springer, Science 324 (5932), 1330-1334 (2009).

  19. Tissue cholinesterases. A comparative study of their kinetic properties.

    PubMed

    Dave, K R; Syal, A R; Katyare, S S

    2000-01-01

    The substrate saturation and temperature-dependent kinetic properties of soluble and membrane-bound forms of acetylcholinestarase (AChE) from brain and butyrylcholinesterase (BChE) from heart and liver were examined. In simultaneous studies these parameters were also measured for AChE in erythrocyte membranes and for BChE in the serum from rat and humans. For both soluble and membrane-bound forms of the enzyme from the three tissues, two components were discernible. In the brain, Km of component I (high affinity) and component II (low affinity) was somewhat higher in membrane-bound form than that of the soluble form components, while the Vmax values were significantly higher by about five fold. In the heart, Km of component II was lower in membrane-bound form than in the soluble form, while Vmax for both the components was about four to six fold higher in the membrane-bound form. In the liver, Vmax was marginally higher for the two components of the membrane-bound enzyme; the Km only of component I was higher by a factor of 2. In the rat erythrocyte membranes three components of AChE were present showing increasing values of Km and Vmax. In contrast, in the human erythrocyte membranes only two components could be detected; the one corresponding to component II of rat erythrocyte membranes was absent. In the rat serum two components of BChE were present while the human serum was found to possess three components. Component I of the human serum was missing in the rat serum. Temperature kinetics studies revealed that the Arrhenius plots were biphasic for most of the systems except for human serum. Membrane binding of the enzyme resulted in decreased energy of activation with shift in phase transition temperature (Tt) to near physiological temperature. PMID:10739108

  20. Microfluidic rheology of active particle suspensions: Kinetic theory.

    PubMed

    Alonso-Matilla, Roberto; Ezhilan, Barath; Saintillan, David

    2016-07-01

    We analyze the effective rheology of a dilute suspension of self-propelled slender particles confined between two infinite parallel plates and subject to a pressure-driven flow. We use a continuum kinetic model to describe the configuration of the particles in the system, in which the disturbance flows induced by the swimmers are taken into account, and use it to calculate estimates of the suspension viscosity for a range of channel widths and flow strengths typical of microfluidic experiments. Our results are in agreement with previous bulk models, and in particular, demonstrate that the effect of activity is strongest at low flow rates, where pushers tend to decrease the suspension viscosity whereas pullers enhance it. In stronger flows, dissipative stresses overcome the effects of activity leading to increased viscosities followed by shear-thinning. The effects of confinement and number density are also analyzed, and our results confirm the apparent transition to superfluidity reported in recent experiments on pusher suspensions at intermediate densities. We also derive an approximate analytical expression for the effective viscosity in the limit of weak flows and wide channels, and demonstrate good agreement between theory and numerical calculations. PMID:27375827

  1. Towards a quantitative kinetic theory of polar active matter

    NASA Astrophysics Data System (ADS)

    Ihle, T.

    2014-06-01

    A recent kinetic approach for Vicsek-like models of active particles is reviewed. The theory is based on an exact Chapman- Kolmogorov equation in phase space. It can handle discrete time dynamics and "exotic" multi-particle interactions. A nonlocal mean-field theory for the one-particle distribution function is obtained by assuming molecular chaos. The Boltzmann approach of Bertin, et al., Phys. Rev. E 74, 022101 (2006) and J. Phys. A 42, 445001 (2009), is critically assessed and compared to the current approach. In Boltzmann theory, a collision starts when two particles enter each others action spheres and is finished when their distance exceeds the interaction radius. The average duration of such a collision, τ0, is measured for the Vicsek model with continuous time-evolution. If the noise is chosen to be close to the flocking threshold, the average time between collisions is found to be roughly equal to τ0 at low densities. Thus, the continuous-time Vicsek-model near the flocking threshold cannot be accurately described by a Boltzmann equation, even at very small density because collisions take so long that typically other particles join in, rendering Boltzmann's binary collision assumption invalid. Hydrodynamic equations for the phase space approach are derived by means of a Chapman-Enskog expansion. The equations are compared to the Toner-Tu theory of polar active matter. New terms, absent in the Toner-Tu theory, are highlighted. Convergence problems of Chapman-Enskog and similar gradient expansions are discussed.

  2. Host natural suppressor activity regulates hemopoietic engraftment kinetics in antibody-conditioned recipient mice

    SciTech Connect

    Sadelain, M.W.; Green, D.R.; Wegmann, T.G. )

    1990-03-01

    Resistance to semi-allogeneic or syngeneic hemopoietic stem cell engraftment can be reduced by treating the unirradiated host with anti-class I MHC antibody. In our previous studies we showed a direct correlation between such resistance and the level of natural suppressor (NS) activity in the host. Thus newborn mice that have high NS activity are very resistant to marrow engraftment, as are adults pretreated with CFA that increases NS activity in the bone marrow. We have now devised a method that allows us to follow hemopoietic engraftment kinetics within the marrow cavity itself by assaying individual CFU-granulocyte/macrophage progenitor cells for their host or donor origin over the immediate post-transplant period. By using this method, we find a close correlation between the rate of marrow engraftment and reduction in host NS activity. Marrow engraftment does not correlate with the reduction of either total host bone marrow cellular content or CFU-granulocyte/macrophage progenitor cell levels. NS activity is mediated by Thy-1-, partially radiosensitive, nylon wool nonadherent cells without NK activity. Adoptively transferred Thy-1-, irradiated spleen cells containing NS activity induced by pretreatment with CFA delayed engraftment kinetics in the marrow cavity. Thus hemopoietic engraftment in the marrow cavity appears to be controlled by an inhibitory regulatory activity that is reflected in the in vitro NS assay. These studies suggest new regulatory targets for selective host conditioning to eliminate resistance to marrow transplantation.

  3. Multiple heating rate kinetic parameters, thermal, X-ray diffraction studies of newly synthesized octahedral copper complexes based on bromo-coumarins along with their antioxidant, anti-tubercular and antimicrobial activity evaluation

    NASA Astrophysics Data System (ADS)

    Patel, Ketan S.; Patel, Jiten C.; Dholariya, Hitesh R.; Patel, Kanuprasad D.

    2012-10-01

    Series of new Cu(II) complexes were synthesized by classical thermal technique. The biologically potent ligands (L) were prepared by refluxing 6-brom 3-acetyl coumarin with aldehydes in the presence of piperidine in ethanol. The Cu(II) complexes have been synthesized by mixing an aqueous solution of Cu(NO3)2 in 1:1 molar ratios with ethanolic bidentate ligands and Clioquinol. The structures of the ligands and their copper complexes were investigated and confirmed by the elemental analysis, FT-IR, 1H NMR, 13C NMR, mass spectral and powder X-ray diffraction studies respectively. Thermal behaviour of newly synthesized mixed ligand Cu(II) complexes were investigated by means of thermogravimetry, differential thermogravimetry, differential scanning calorimetry, electronic spectra and magnetic measurements. Dynamic scan of DSC experiments for Cu(II) complexes were taken at different heating rates (2.5-20 °C min-1). Kinetic parameters for second step degradation of all complexes obtained by Kissinger's and Ozawa's methods were in good agreement. On the basis of these studies it is clear that ligands coordinated to metal atom in a monobasic bidentate mode, by Osbnd O and Osbnd N donor system. Thus, suitable octahedral geometry for hexa-coordinated state has been suggested for the metal complexes. Both the ligands as well as its complexes have been screened for their in vitro antioxidant, anti-tubercular and antimicrobial activities. All were found to be significant potent compared to parent ligands employed for complexation.

  4. Activity determination, kinetic analyses and isoenzyme identification of gamma glutamyltransferase in human neutrophils.

    PubMed

    Sener, Azize; Yardimci, Turay

    2005-05-31

    Gamma-glutamyltransferase (GGT, EC 2.3.2.2) which hydrolyzes glutathione (GSH), is required for the maintenance of normal intracellular GSH concentration. GGT is a membrane enzyme present in leukocytes and platelets. Its activity has also been observed in human neutrophils. In this study, GGT was purified from Triton X-100 solubilized neutrophils and its kinetic parameters were determined. For kinetic analyses of transpeptidation reaction, gamma-glutamyl p-nitroanilide was used as the substrate and glycylglycine as the acceptor. Apparent K(m) values were determined as 1.8 mM for gamma-glutamyl p-nitroanilide and 16.9 mM for glycylglycine. The optimum pH of GGT activity was 8.2 and the optimum temperature was 37 degrees C. It had thermal stability with 58 % relative activity at 56 degrees C for 30 min incubation. L-serine, in the presence of borate, was detected as the competitive inhibitor. Bromcresol green inhibited neutrophil GGT activity as a noncompetitive inhibitor. The neutrophils seem to contain only the isoenzyme that is present in platelets. We characterized the kinetic properties and compared the type of the isoenzyme of neutrophil GGT with platelet GGT via polyacrylamide gel electrophoresis (PAGE) under a standard set of conditions. PMID:15943911

  5. Degradation of reactive blue 19 by needle-plate non-thermal plasma in different gas atmospheres: Kinetics and responsible active species study assisted by CFD calculations.

    PubMed

    Sun, Yu; Liu, Yanan; Li, Rui; Xue, Gang; Ognier, Stéphanie

    2016-07-01

    This study investigated the degradation of a model organic compound, reactive blue (RB-19), in aqueous solution using a needle-plate non-thermal plasma (NTP) reactor, which was operated using three gas atmospheres (Ar, air, O2) at room temperature and atmospheric pressure. The relative discharge and degradation parameters, including the peak to peak applied voltage, power, ozone generation, pH, decolorization rates, energy density and the total organic carbon (TOC) reduction were analyzed to determine the various dye removal efficiencies. The decolorization rate for Ar, air and O2 were 59.9%, 49.6% and 89.8% respectively at the energy density of 100 kJ/L. The best TOC reduction was displayed by Ar with about 8.8% decrease, and 0% with O2 and air atmospheres. This phenomenon could be explained by the formation of OH• and O3 in the Ar and O2 atmospheres, which are responsible for increased mineralization and efficient decolorization. A one-dimension model was developed using software COMSOL to simulate the RB-19-ozone reaction and verify the experiments by comparing the simulated and experimental results. It was determined that ozone plays the most important role in the dye removal process, and the ozone contribution rate ranged from 0.67 to 0.82. PMID:27124311

  6. Thermodynamic and kinetic behaviors of trinitrotoluene adsorption on powdered activated carbons

    SciTech Connect

    Lee, J.W.; Hwang, K.J.; Shim, W.G.; Moon, I.S.

    2006-07-01

    Regulations on the removal of trinitrotoluene (TNT) from wastewater have become increasingly more stringent, demanding faster, less expensive, and more efficient treatment. This study focuses on the adsorption equilibrium and kinetics of TNT on powered activated carbons (PAC). Three types of PACs (i.e., wood based, coal based, and coconut-shell based) were studied as functions of temperature and pH. Thermodynamic properties including Gibbs free energy, enthalpy, and entropy, were evaluated by applying the Van't Hoff equation. In addition, the adsorption energy distribution functions which describe heterogeneous characteristics of porous solid sorbents were calculated by using the generalized nonlinear regularization method. Adsorption kinetic studies were carried out in batch adsorber under important conditions such as PAC types, temperature, pH, and concentration. We found that fast and efficient removal of TNT dissolved in water can be successfully achieved by PAC adsorption.

  7. Diffusion barriers in the kinetics of water vapor adsorption/desorption on activated carbons

    SciTech Connect

    Harding, A.W.; Foley, N.J.; Thomas, K.M.; Norman, P.R.; Francis, D.C.

    1998-07-07

    The adsorption of water vapor on a highly microporous coconut-shell-derived carbon and a mesoporous wood-derived carbon was studied. These carbons were chosen as they had markedly different porous structures. The adsorption and desorption characteristics of water vapor on the activated carbons were investigated over the relative pressure range p/p{degree} = 0--0.9 for temperatures in the range 285--313 K in a static water vapor system. The adsorption isotherms were analyzed using the Dubinin-Serpinski equation, and this provided an assessment of the polarity of the carbons. The kinetics of water vapor adsorption and desorption were studied with different amounts of preadsorbed water for set changes in pressure relative to the saturated vapor pressure (p/p{degree}). The adsorption kinetics for each relative pressure step were compared and used to calculate the activation energies for the vapor pressure increments. The kinetic results are discussed in relation to their relative position on the equilibrium isotherm and the adsorption mechanism of water vapor on activated carbons.

  8. Effect of the porous structure of activated carbon on the adsorption kinetics of gold(I) cyanide complex

    NASA Astrophysics Data System (ADS)

    Ibragimova, P. I.; Grebennikov, S. F.; Gur'yanov, V. V.; Fedyukevich, V. A.; Vorob'ev-Desyatovskii, N. V.

    2014-06-01

    The effect the porous structure of activated carbons obtained from furfural and coconut shells has on the kinetics of [Au(CN)2]- ion adsorption is studied. Effective diffusion coefficients for [Au(CN)2]- anions in transport and adsorbing pores and mass transfer coefficients in a transport system of the pores and in microporous zones are calculated using the statistical moments of the kinetic curve.

  9. Comparative study of gyrokinetic, hybrid-kinetic and fully kinetic wave physics for space plasmas

    NASA Astrophysics Data System (ADS)

    Told, D.; Cookmeyer, J.; Muller, F.; Astfalk, P.; Jenko, F.

    2016-06-01

    A set of numerical solvers for the linear dispersion relations of the gyrokinetic (GK), the hybrid-kinetic (HK), and the fully kinetic (FK) model is employed to study the physics of the KAW and the fast magnetosonic mode in these models. In particular, we focus on parameters that are relevant for solar wind oriented applications (using a homogeneous, isotropic background), which are characterized by wave propagation angles averaging close to 90°. It is found that the GK model, while lacking high-frequency solutions and cyclotron effects, faithfully reproduces the FK {{Alfv\\acute{e}n}} wave physics close to, and sometimes significantly beyond, the boundaries of its range of validity. The HK model, on the other hand, is much more complete in terms of high-frequency waves, but owing to its simple electron model it is found to severely underpredict wave damping rates even on ion spatial scales across a large range of parameters, despite containing full kinetic ion physics.

  10. Nucleation pathway and kinetics of phase-separating active Brownian particles.

    PubMed

    Richard, David; Löwen, Hartmut; Speck, Thomas

    2016-06-28

    Suspensions of purely repulsive but self-propelled Brownian particles might undergo phase separation, a phenomenon that strongly resembles the phase separation of passive particles with attractions. Here we employ computer simulations to study the nucleation kinetics and the microscopic pathway active Brownian disks take in two dimensions when quenched from the homogeneous suspension to propulsion speeds beyond the binodal. We find the same qualitative behavior for the nucleation rate as a function of density as for a passive suspension undergoing liquid-vapor separation, suggesting that the scenario of an effective free energy also extends to the kinetics of phase separation. We study the transition in more detail through a committor analysis and find that transition states are best described by a combination of cluster size and the radial polarization of particles in the cluster. PMID:27126952

  11. Combining an Optical Resonance Biosensor with Enzyme Activity Kinetics to Understand Protein Adsorption and Denaturation

    PubMed Central

    Wilson, Kerry A.; Finch, Craig A.; Anderson, Phillip; Vollmer, Frank; Hickman, James J.

    2014-01-01

    Understanding protein adsorption and resultant conformation changes on modified and unmodified silicon dioxide surfaces is a subject of keen interest in biosensors, microfluidic systems and for medical diagnostics. However, it has been proven difficult to investigate the kinetics of the adsorption process on these surfaces as well as understand the topic of the denaturation of proteins and its effect on enzyme activity. A highly sensitive optical whispering gallery mode (WGM) resonator was used to study a catalytic enzyme’s adsorption processes on different silane modified glass substrates (plain glass control, DETA, 13F, and SiPEG). The WGM sensor was able to obtain high resolution kinetic data of glucose oxidase (GO) adsorption with sensitivity of adsorption better than that possible with SPR. The kinetic data, in combination with a functional assay of the enzyme activity, was used to test hypotheses on adsorption mechanisms. By fitting numerical models to the WGM sensograms for protein adsorption, and by confirming numerical predictions of enzyme activity in a separate assay, we were able to identify mechanisms for GO adsorption on different alkylsilanes and infer information about the adsorption of protein on nanostructured surfaces. PMID:25453976

  12. Chemical kinetic studies on dry sorbents. Final report. [Sodium bicarbonate

    SciTech Connect

    Davis, W.T.; Keener, T.C.

    1982-02-15

    The scope of this research investigation has included a review of potential additives suitable for dry flue-gas desulfurization (FGD) and a bench scale laboratory study to determine the chemical kinetics for the reaction of five different sorbents with sulfur dioxide. The sorbents chosen included sodium bicarbonate (NaHCO/sub 3/), soda ash (Na/sub 2/CO/sub 3/), trona, lime (CaO) and hydrated lime (Ca(OH)/sub 2/). This study has shown that: (1) The reaction rate increases with temperature for soda ash and calcium oxide. The reaction temperature has an inverse effect on sodium bicarbonate and trona due, primarily, to the simultaneous thermal activation reaction. The calcium hydroxide-SO/sub 2/ reaction increased up to 550/sup 0/F, and then decreased, due to uneven gas flow distribution. (2) The reaction rates for soda ash, calcium oxide and calcium hydroxide were increased by decreasing their particle size. This effect was not confirmed for sodium bicarbonate and trona where reaction temperature was the most important reaction parameter. (3) Reaction with soda ash was found to be limited by the presence of an impervious ash layer which prevented interparticle gaseous diffusion. Calcium oxide and calcium hydroxide were found to be limited by a slow chemical reaction rate. Results on the rate-limiting steps for sodium bicarbonate and trona were inconclusive because of the simultaneous thermal activation reaction. (4) The effect of thermal activation was to increase the reaction rate for sodium bicarbonate and trona at lower temperatures. This effect was less pronounced at higher temperatures. (5) Results obtained for nitric oxide show limited adsorption for the five sorbents tested as compared to the finding for sulfur dioxide.

  13. ANALYTICAL METHODS FOR KINETIC STUDIES OF BIOLOGICAL INTERACTIONS: A REVIEW

    PubMed Central

    Zheng, Xiwei; Bi, Cong; Li, Zhao; Podariu, Maria; Hage, David S.

    2015-01-01

    The rates at which biological interactions occur can provide important information concerning the mechanism and behavior of these processes in living systems. This review discusses several analytical methods that can be used to examine the kinetics of biological interactions. These techniques include common or traditional methods such as stopped-flow analysis and surface plasmon resonance spectroscopy, as well as alternative methods based on affinity chromatography and capillary electrophoresis. The general principles and theory behind these approaches are examined, and it is shown how each technique can be utilized to provide information on the kinetics of biological interactions. Examples of applications are also given for each method. In addition, a discussion is provided on the relative advantages or potential limitations of each technique regarding its use in kinetic studies. PMID:25700721

  14. Analytical methods for kinetic studies of biological interactions: A review.

    PubMed

    Zheng, Xiwei; Bi, Cong; Li, Zhao; Podariu, Maria; Hage, David S

    2015-09-10

    The rates at which biological interactions occur can provide important information concerning the mechanism and behavior of these processes in living systems. This review discusses several analytical methods that can be used to examine the kinetics of biological interactions. These techniques include common or traditional methods such as stopped-flow analysis and surface plasmon resonance spectroscopy, as well as alternative methods based on affinity chromatography and capillary electrophoresis. The general principles and theory behind these approaches are examined, and it is shown how each technique can be utilized to provide information on the kinetics of biological interactions. Examples of applications are also given for each method. In addition, a discussion is provided on the relative advantages or potential limitations of each technique regarding its use in kinetic studies. PMID:25700721

  15. Activity and kinetic properties of phosphotransacetylase from intestinal sulfate-reducing bacteria.

    PubMed

    Kushkevych, Ivan V

    2015-01-01

    Phosphotransacetylase activity and the kinetic properties of the enzyme from intestinal sulfate-reducing bacteria Desulfovibrio piger and Desulfomicrobium sp. has never been well-characterized and has not been studied yet. In this paper, the specific activity of phosphotransacetylase and the kinetic properties of the enzyme in cell-free extracts of both D. piger Vib-7 and Desulfomicrobium sp. Rod-9 intestinal bacterial strains were presented at the first time. The microbiological, biochemical, biophysical and statistical methods in this work were used. The optimal temperature and pH for enzyme reaction was determined. Analysis of the kinetic properties of the studied enzyme was carried out. Initial (instantaneous) reaction velocity (V0), maximum amount of the product of reaction (Pmax), the reaction time (half saturation period, τ) and maximum velocity of the phosphotransacetylase reaction (Vmax) were defined. Michaelis constants (Km) of the enzyme reaction (3.36 ± 0.35 mM for D. piger Vib-7, 5.97 ± 0.62 mM for Desulfomicrobium sp. Rod-9) were calculated. The studies of the phosphotransacetylase in the process of dissimilatory sulfate reduction and kinetic properties of this enzyme in intestinal sulfate-reducing bacteria, their production of acetate in detail can be perspective for clarification of their etiological role in the development of the humans and animals bowel diseases. These studies might help in predicting the development of diseases of the gastrointestinal tract, by providing further details on the etiology of bowel diseases which are very important for the clinical diagnosis of these disease types. PMID:25781158

  16. Kinetic Study of the Heck Reaction: An Interdisciplinary Experiment

    ERIC Educational Resources Information Center

    Gozzi, Christel; Bouzidi, Naoual

    2008-01-01

    The aim of this experiment is to study and calculate the kinetic constant of a Heck reaction: the arylation of but-3-en-2-ol by iodobenzene catalyzed by palladium acetate in presence of triethylamine in DMF. The reaction leads to a mixture of two ketones. Students use GC analysis to quantify reagents and products of reaction. They control the…

  17. Photosynthetic hydrogen and oxygen production - Kinetic studies

    NASA Astrophysics Data System (ADS)

    Greenbaum, E.

    1982-01-01

    The simultaneous photoproduction of hydrogen and oxygen was measured in a study of the steady-state turnover times of two biological systems, by driving them into the steady state with repetitive, single-turnover flash illumination. The systems were: (1) in vitro, isolated chloroplasts, ferredoxin and hydrogenase; and (2) the anaerobically-adapted green alga Chlamydomonas reinhardtii. It is found that the turnover times for production of both oxygen and hydrogen in photosynthetic water splitting are in milliseconds, and either equal to, or less than, the turnover time for carbon dioxide reduction in intact algal cells. There is therefore mutual compatibility between hydrogen and oxygen turnover times, and partial compatibility with the excitation rate of the photosynthetic reaction centers under solar irradiation conditions.

  18. Experimental kinetic study of the smectite-to-illite transformation

    NASA Astrophysics Data System (ADS)

    Cuadros, J.; Linares, J.

    1996-02-01

    The <20 μm size fraction of a bentonite from the Serrata de Níjar deposit (Almería, southeastern Spain) was hydrothermally treated to study the kinetics of the smectite-to-illite transformation, in order to estimate the performance life of a bentonite barrier in a high level nuclear waste repository. The bentonite studied consisted of randomly interstratified illite/montmorillonite with 15% illite. Minor amounts of other minerals (3% quartz, plagioclase, and cristobalite) were also present. The run conditions of the hydrothermal treatments were combinations of the following variables: KCl concentration 0.025, 0.05, 0.1, 0.3, 0.5, and 1 mol L-1; temperature 60, 120, 175, and 200°C; time 1, 5, 15, 30, 90, and 180 days. The solid:solution ratio was 1:5. Pressures were those corresponding to water vapor. The solid reaction products were analyzed by means of XRD, DTA/TG, FTIR, and NMR. The final solutions were chemically analyzed for Si and exchange cations (K, Ca, Mg, and Na), and pH. XRD detected some transformation (up to 15%), while DTA/TG, FTIR, NMR, and exchange cation analysis did not show any appreciable transformation. This leads to the conclusion that analysis of the amount of illite in illite/smectite, in hydrothermally treated samples, by means of XRD can be inaccurate. Transformation to illite was observed, however, when aqueous silica concentrations were examined. These concentrations yielded the kinetic expression -dS/dt = kK1/4Sn, where S is the fraction of smectite in illite/smectite, t time, k the rate constant, and K potassium concentration in solution. The exact value for n could not be determined, although data from this and other studies suggest n > 1. The activation energy of the process is ˜7 kcal mol-1, suggesting a solid transformation mechanism. Based on these results, smectite seems to offer a safe barrier for nuclear waste.

  19. Study of kinetics of crystallization of Ge7Se75Sb18 chalcogenide glass

    NASA Astrophysics Data System (ADS)

    Tanwar, Naveen; Saraswat, Vibhav K.

    2014-04-01

    Present paper is an attempt to study kinetics of crystallization of Ge7Se75Sb18 chalcogenide glass by Differential Scanning Calorimetery (DSC) under non-isothermal condition. The sample was prepared by melt quenched technique and amorphous nature has been confirmed by XRD. Activation energy of crystallization has been evaluated using Kissinger, Augis-Bennett and Ozawa models.

  20. Active mechanics in living oocytes reveal molecular-scale force kinetics

    NASA Astrophysics Data System (ADS)

    Ahmed, Wylie; Fodor, Etienne; Almonacid, Maria; Bussonnier, Matthias; Verlhac, Marie-Helene; Gov, Nir; Visco, Paolo; van Wijland, Frederic; Betz, Timo

    Unlike traditional materials, living cells actively generate forces at the molecular scale that change their structure and mechanical properties. This nonequilibrium activity is essential for cellular function, and drives processes such as cell division. Single molecule studies have uncovered the detailed force kinetics of isolated motor proteins in-vitro, however their behavior in-vivo has been elusive due to the complex environment inside the cell. Here, we quantify active forces and intracellular mechanics in living oocytes using in-vivo optical trapping and laser interferometry of endogenous vesicles. We integrate an experimental and theoretical framework to connect mesoscopic measurements of nonequilibrium properties to the underlying molecular- scale force kinetics. Our results show that force generation by myosin-V drives the cytoplasmic-skeleton out-of-equilibrium (at frequencies below 300 Hz) and actively softens the environment. In vivo myosin-V activity generates a force of F ~ 0 . 4 pN, with a power-stroke of length Δx ~ 20 nm and duration τ ~ 300 μs, that drives vesicle motion at vv ~ 320 nm/s. This framework is widely applicable to characterize living cells and other soft active materials.

  1. Optimization of the activated sludge anoxic reactor configuration as a means to control nutrient removal kinetically.

    PubMed

    Plósz, Benedek Gy

    2007-04-01

    Factors influencing the determination of optimum reactor configuration for activated sludge denitrification are investigated in this paper. A kinetic optimization method is presented to evaluate optimal pre- and post-denitrification bioreactor stages. Applying the method developed, simulation studies were carried out to investigate the impacts of the ratio of the influent readily biodegradable and slowly biodegradable substrates and the oxygen entering the denitrification zones on the optimal anoxic reactor configuration. In addition, the paper describes the effects of the slowly biodegradable substrate on the denitrification efficiency using external substrate dosing, and it demonstrates kinetic considerations concerning the hydrolysis process. It has been shown that as a function of the biodegradable substrate composition, the stage system design with three optimized reactor compartments can effectively increase reaction rates in the denitrification zones, and can provide flexibility for varying operation conditions. PMID:17321565

  2. Kinetic study of seawater reverse osmosis membrane fouling.

    PubMed

    Khan, Muhammad Tariq; de O Manes, Carmem-Lara; Aubry, Cyril; Gutierrez, Leonardo; Croue, Jean Philippe

    2013-10-01

    Reverse osmosis (RO) membrane fouling is not a static state but a dynamic phenomenon. The investigation of fouling kinetics and dynamics of change in the composition of the foulant mass is essential to elucidate the mechanism of fouling and foulant-foulant interactions. The aim of this work was to study at a lab scale the fouling process with an emphasis on the changes in the relative composition of foulant material as a function of operating time. Fouled membrane samples were collected at 8 h, and 1, 2, and 4 weeks on a lab-scale RO unit operated in recirculation mode. Foulant characterization was performed by CLSM, AFM, ATR-FTIR, pyrolysis GC-MS, and ICP-MS techniques. Moreover, measurement of active biomass and analysis of microbial diversity were performed by ATP analysis and DNA extraction, followed by pyro-sequencing, respectively. A progressive increase in the abundance of almost all the foulant species was observed, but their relative proportion changed over the age of the fouling layer. Microbial population in all the membrane samples was dominated by specific groups/species belonging to Proteobacteria and Actinobacteria phyla; however, similar to abiotic foulant, their relative abundance also changed with the biofilm age. PMID:24032659

  3. Substrate kinetics of the tonoplast h-translocating inorganic pyrophosphatase and its activation by free mg.

    PubMed

    White, P J; Marshall, J; Smith, J A

    1990-07-01

    To clarify the kinetic characteristics and ionic requirements of the tonoplast H(+)-translocating inorganic pyrophosphatase (H(+)-PPiase), PPi hydrolysis and PPi-dependent H(+) transport were studied in tonoplast vesicles isolated from leaf mesophyll tissue of Kalanchoë daigremontiana Hamet et Perrier de la Bâthie. The tonoplast H(+)-PPiase showed an absolute requirement for a monovalent cation and exhibited hyperbolic kinetics with respect to cation concentration. H(+)-PPiase activity was maximal in the presence of K(+) (K(50) approximately 3 millimolar), with PPi-dependent H(+) transport being more selective for K(+) than PPi hydrolysis. When assayed in the presence of 50 millimolar KCl at fixed PPi concentrations, H(+)-PPiase activity showed sigmoidal kinetics with respect to total Mg concentration, reflecting a requirement for a Mg/PPi complex as substrate and free Mg(2+) for activation. At saturating concentrations of free Mg(2+), H(+)-PPiase activity exhibited Michaelis-Menten kinetics towards MgPPi(2-) but not Mg(2)PPi, demonstrating that MgPPi(2-) was the true substrate of the enzyme. The apparent K(m) (MgPPi(2-)) for PPi hydrolysis (17 micromolar) was significantly higher than that for PPi-dependent H(+) transport (7 micromolar). Free Mg(2+) was shown to be an allosteric activator of the H(+)-PPiase, with Hill coefficients of 2.5 for PPi hydrolysis and 2.7 for PPi-dependent H(+) transport. Half-maximal H(+)-PPiase activity occurred at a free Mg(2+) concentration of 1.1 millimolar, which lies within the range of accepted values for cytosolic Mg(2+). In contrast, cytosolic concentrations of K(+) and MgPPi(2-) appear to be saturating for H(+)-PPiase activity. We propose that one function of the H(+)-PPiase may be to act as an ancillary enzyme that maintains the proton-motive force across the vacuolar membrane when the activity of the tonoplast H(+)-ATPase is restricted by substrate availability. As ATP levels decline in the cytosol, free Mg(2+) would be

  4. Colloidal particle adsorption at liquid interfaces: capillary driven dynamics and thermally activated kinetics.

    PubMed

    Rahmani, Amir M; Wang, Anna; Manoharan, Vinothan N; Colosqui, Carlos E

    2016-08-14

    The adsorption of single colloidal microparticles (0.5-1 μm radius) at a water-oil interface has been recently studied experimentally using digital holographic microscopy [Kaz et al., Nat. Mater., 2012, 11, 138-142]. An initially fast adsorption dynamics driven by capillary forces is followed by an unexpectedly slow relaxation to equilibrium that is logarithmic in time and can span hours or days. The slow relaxation kinetics has been attributed to the presence of surface "defects" with nanoscale dimensions (1-5 nm) that induce multiple metastable configurations of the contact line perimeter. A kinetic model considering thermally activated transitions between such metastable configurations has been proposed [Colosqui et al., Phys. Rev. Lett., 2013, 111, 028302] to predict both the relaxation rate and the crossover point to the slow logarithmic regime. However, the adsorption dynamics observed experimentally before the crossover point has remained unstudied. In this work, we propose a Langevin model that is able to describe the entire adsorption process of single colloidal particles by considering metastable states produced by surface defects and thermal motion of the particle and liquid interface. Invoking the fluctuation dissipation theorem, we introduce a drag term that considers significant dissipative forces induced by thermal fluctuations of the liquid interface. Langevin dynamics simulations based on the proposed adsorption model yield close agreement with experimental observations for different microparticles, capturing the crossover from (fast) capillary driven dynamics to (slow) thermally activated kinetics. PMID:27373956

  5. Kinetic study of non-isothermal decomposition of a composite diasporic-boehmitic bauxite

    NASA Astrophysics Data System (ADS)

    Samouhos, M.; Angelopoulos, P.; Pilatos, G.; Taxiarchou, M.; Papageorgiou, S.

    2016-04-01

    In the current study, the kinetic of the thermal decomposition of a composite diasporic-boehmitic bauxite is investigated under non-isothermal heating conditions by means of thermogravimetric analysis. The calculation of activation energy (Ea) has been performed by various methods and the attained values range from 185000 to 190000 J.mol-1 for conversion rate of 0.5. The first-order kinetic model can adequately be used to describe thermal decomposition of bauxite composite, while the pre-exponential factor value was found to be 2.088*1011 min-1. The calculated activation energy value together with pre-exponential factor and the solid state kinetic model factors enable the simulation of the thermal decomposition under various heating conditions by the implementation of an ordinary differential equation. The calculated values are in satisfactory agreement with the experimental ones.

  6. Kinetic and thermodynamic study of the liquid-phase etherification of isoamylenes with methanol

    SciTech Connect

    Piccoli, R.L. ); Lovisi, H.R. )

    1995-02-01

    The kinetics and thermodynamics of liquid-phase etherification of isoamylenes with methanol on ion exchange catalyst (Amberlyst 15) were studied. Thermodynamic properties and rate data were obtained in a batch reactor operating under 1,013 kPa and 323--353 K. The kinetic equation was modeled following the Langmuir-Hinshelwood-Hougen-Watson formalism according to a proposed surface mechanism where the rate-controlling step is the surface reaction. According to the experimental results, methanol adsorbs very strongly on the active sites, covering them completely, and thus the reaction follows an apparent first-order behavior. The isoamylenes, according to the proposed mechanism, adsorb simultaneously on the same single active center already occupied by methanol, migrating through the liquid layer formed by the alcohol around the catalyst to react in the acidic site. From the proposed mechanism a model was suggested and the kinetic and thermodynamic parameters were obtained using nonlinear estimation methods.

  7. COMSOL-based Nuclear Reactor Kinetics Studies at the HFIR

    SciTech Connect

    Chandler, David; Freels, James D; Maldonado, G Ivan; Primm, Trent

    2011-01-01

    The computational ability to accurately predict the dynamic behavior of a nuclear reactor core in response to reactivity-induced perturbations is an important subject in reactor physics. Space-time and point kinetics methodologies were developed for the purpose of studying the transient-induced behavior of the High Flux Isotope Reactor s (HFIR) compact core. The space-time simulations employed the three-energy-group neutron diffusion equations, and transients initiated by control cylinder and hydraulic tube rabbit ejections were studied. The work presented here is the first step towards creating a comprehensive multiphysics methodology for studying the dynamic behavior of the HFIR core during reactivity perturbations. The results of these studies show that point kinetics is adequate for small perturbations in which the power distribution is assumed to be time-independent, but space-time methods must be utilized to determine localized effects.

  8. A study of the Sabatier-methanation reaction kinetics

    NASA Technical Reports Server (NTRS)

    Verostko, C. E.; Forsythe, R. K.

    1974-01-01

    The kinetics of the Sabatier methanation reaction, the reduction of carbon dioxide with hydrogen to methane and water, was investigated for 58 percent nickel on kieselguhr catalyst and 20 percent ruthenium on alumina catalyst. Differential rate data from an experimental program were correlated with a power function rate equation both for forward and reverse reactions. The kinetic parameters of activation energy, frequency rate constant and reaction order were determined for the rate equation. The values of these parameters were obtained from an Arrhenius plot of the experimental differential rate data. Also the carbon monoxide side reaction effect was measured and included in the correlation of parameters. The reaction was found to fit the rate equation experimentally within the temperature range 421 K, where the reaction effectively begins, the 800 K where the reaction rate drops and departs from the rate equation form.

  9. Covalent binding of aniline to humic substances. 1. Kinetic studies

    USGS Publications Warehouse

    Weber, E.J.; Spidle, D.L.; Thorn, K.A.

    1996-01-01

    The reaction kinetics for the covalent binding of aniline with reconstituted IHSS humic and fulvic acids, unfractionated DOM isolated from Suwannee River water, and whole samples of Suwannee River water have been investigated. The reaction kinetics in each of these systems can be adequately described by a simple second-order rate expression. The effect of varying the initial concentration of aniline on reaction kinetics suggested that approximately 10% of the covalent binding sites associated with Suwannee River fulvic acid are highly reactive sites that are quickly saturated. Based on the kinetic parameters determined for the binding of aniline with the Suwannee River fulvic and humic acid isolates, it was estimated that 50% of the aniline concentration decrease in a Suwannee River water sample could be attributed to reaction with the fulvic and humic acid components of the whole water sample. Studies with Suwannee River fulvic acid demonstrated that the rate of binding decreased with decreasing pH, which parallels the decrease in the effective concentration of the neutral form, or reactive nucleophilic species of aniline. The covalent binding of aniline with Suwannee River fulvic acid was inhibited by prior treatment of the fulvic acid with hydrogen sulfide, sodium borohydride, or hydroxylamine. These observations are consistent with a reaction pathway involving nucleophilic addition of aniline to carbonyl moieties present in the fulvic acid.

  10. Structure and thermochemical kinetic studies of coal pyrolysis

    SciTech Connect

    Dodoo, J.N.D.

    1991-01-01

    The overall objectives of this project is an intensive effort on the application of laser to the microscopic structure and thermochemical kinetic studies of coal particles pyrolysis, char combustion and ash transformation at combustion level heat fluxes in a laser beam. Research emphasis in FY91 is placed on setup and calibration of the laser pyrolysis system, preparation and mass loss studies of Beulah lignite and subbituminous coals. The task is therefore divided into three subtasks.

  11. Computational Kinetic Study for the Unimolecular Decomposition Pathways of Cyclohexanone.

    PubMed

    Zaras, Aristotelis M; Dagaut, Philippe; Serinyel, Zeynep

    2015-07-16

    There has been evidence lately that several endophytic fungi can convert lignocellulosic biomass into ketones among other oxygenated compounds. Such compounds could prove useful as biofuels for internal combustion engines. Therefore, their combustion properties are of high interest. Cyclohexanone was identified as an interesting second-generation biofuel ( Boot , M. ; et al. Cyclic Oxygenates: A New Class of Second-Generation Biofuels for Diesel Engines? Energy Fuels 2009 , 23 , 1808 - 1817 ; Klein-Douwel , R. J. H. ; et al. Soot and Chemiluminescence in Diesel Combustion of Bio-Derived, Oxygenated and Reference Fuels . Proc. Combust. Inst. 2009 , 32 , 2817 - 2825 ). However, until recently ( Serinyel , Z. ; et al. Kinetics of Oxidation of Cyclohexanone in a Jet- Stirred Reactor: Experimental and Modeling . Proc. Combust. Inst. 2014 ; DOI: 10.1016/j.proci.2014.06.150 ), no previous studies on the kinetics of oxidation of that fuel could be found in the literature. In this work, we present the first theoretical kinetic study of the unimolecular decomposition pathways of cyclohexanone, a cyclic ketone that could demonstrate important fuel potential. Using the quantum composite G3B3 method, we identified six different decomposition pathways for cyclohexanone and computed the corresponding rate constants. The rate constants were calculated using the G3B3 method coupled with Rice-Ramsperger-Kassel-Marcus theory in the temperature range of 800-2000 K. Our calculations show that the kinetically more favorable channel for thermal decomposition is pathway 2 that produces 1,3-butadien-2-ol, which in turn can isomerize easily to methyl vinyl ketone through a small barrier. The results presented here can be used in a future kinetic combustion mechanism. PMID:25354027

  12. Surface heterogeneity effects of activated carbons on the kinetics of paracetamol removal from aqueous solution

    NASA Astrophysics Data System (ADS)

    Ruiz, B.; Cabrita, I.; Mestre, A. S.; Parra, J. B.; Pires, J.; Carvalho, A. P.; Ania, C. O.

    2010-06-01

    The removal of a compound with therapeutic activity (paracetamol) from aqueous solutions using chemically modified activated carbons has been investigated. The chemical nature of the activated carbon material was modified by wet oxidation, so as to study the effect of the carbon surface chemistry and composition on the removal of paracetamol. The surface heterogeneity of the carbon created upon oxidation was found to be a determinant in the adsorption capability of the modified adsorbents, as well as in the rate of paracetamol removal. The experimental kinetic data were fitted to the pseudo-second order and intraparticle diffusion models. The parameters obtained were linked to the textural and chemical features of the activated carbons. After oxidation the wettability of the carbon is enhanced, which favors the transfer of paracetamol molecules to the carbon pores (smaller boundary layer thickness). At the same time the overall adsorption rate and removal efficiency are reduced in the oxidized carbon due to the competitive effect of water molecules.

  13. A study of the non-isothermal crystallization kinetic of Zn10Se90 glass

    NASA Astrophysics Data System (ADS)

    Abdel-Rahim, M. A.; Hafiz, M. M.; Abdel-Latief, A. Y.; Abd-Elnaiem, Alaa M.; Alwany, A. Elwhab. B.

    2015-06-01

    The glass transition and the crystallization kinetics of Zn10Se90 glass by differential thermal analysis (DTA) technique under non-isothermal conduction were studied. The effective activation energies of the glass transition and the crystallization have been evaluated on the basses of the Kissinger and Matusita et al. approximations. Kinetic parameters of the crystallization process are significantly influenced by the heating rate. We have compared the experimental DTA with the calculated data curves for Zn10Se90 system using the Johanson-Mehl-Avrami (JMA) and Sestak-Berggren SB( M, N) models. Simulation results indicated that the SB( M, N) model is more suitable for describing the crystallization kinetics for the studied composition. Furthermore, the crystalline phases of annealed Zn10Se90 were characterized by X-ray diffraction. The surface morphology of the annealed samples was examined using scanning electron microscopy.

  14. Mechanistic Study of Manganese-Substituted Glycerol Dehydrogenase Using a Kinetic and Thermodynamic Analysis

    PubMed Central

    Fang, Baishan; Niu, Jin; Ren, Hong; Guo, Yingxia; Wang, Shizhen

    2014-01-01

    Mechanistic insights regarding the activity enhancement of dehydrogenase by metal ion substitution were investigated by a simple method using a kinetic and thermodynamic analysis. By profiling the binding energy of both the substrate and product, the metal ion's role in catalysis enhancement was revealed. Glycerol dehydrogenase (GDH) from Klebsiella pneumoniae sp., which demonstrated an improvement in activity by the substitution of a zinc ion with a manganese ion, was used as a model for the mechanistic study of metal ion substitution. A kinetic model based on an ordered Bi-Bi mechanism was proposed considering the noncompetitive product inhibition of dihydroxyacetone (DHA) and the competitive product inhibition of NADH. By obtaining preliminary kinetic parameters of substrate and product inhibition, the number of estimated parameters was reduced from 10 to 4 for a nonlinear regression-based kinetic parameter estimation. The simulated values of time-concentration curves fit the experimental values well, with an average relative error of 11.5% and 12.7% for Mn-GDH and GDH, respectively. A comparison of the binding energy of enzyme ternary complex for Mn-GDH and GDH derived from kinetic parameters indicated that metal ion substitution accelerated the release of dioxyacetone. The metal ion's role in catalysis enhancement was explicated. PMID:24896258

  15. Kinetic study of alkaline protease 894 for the hydrolysis of the pearl oyster Pinctada martensii

    NASA Astrophysics Data System (ADS)

    Chen, Xin; Chen, Hua; Cai, Bingna; Liu, Qingqin; Sun, Huili

    2013-05-01

    A new enzyme (alkaline protease 894) obtained from the marine extremophile Flavobacterium yellowsea (YS-80-122) has exhibited strong substrate-binding and catalytic activity, even at low temperature, but the characteristics of the hydrolysis with this enzyme are still unclear. The pearl oyster Pinctada martensii was used in this study as the raw material to illustrate the kinetic properties of protease 894. After investigating the intrinsic relationship between the degree of hydrolysis and several factors, including initial reaction pH, temperature, substrate concentration, enzyme concentration, and hydrolysis time, the kinetics model was established. This study showed that the optimal conditions for the enzymatic hydrolysis were an initial reaction pH of 5.0, temperature of 30°C, substrate concentration of 10% (w/v), enzyme concentration of 2 500 U/g, and hydrolysis time of 160 min. The kinetic characteristics of the protease for the hydrolysis of P. martensii were obtained. The inactivation constant was found to be 15.16/min, and the average relative error between the derived kinetics model and the actual measurement was only 3.04%, which indicated a high degree of fitness. Therefore, this study provides a basis for the investigation of the concrete kinetic characteristics of the new protease, which has potential applications in the food industry.

  16. Kinetic study of asphaltene dissolution in amphiphile/alkane solutions

    SciTech Connect

    Permsukarome, P.; Chang, C.; Fogler, H.S.

    1997-09-01

    The kinetics of dissolution of pentane-insoluble solid asphaltene precipitates by amphiphile/alkane solutions were investigated using a differential reactor flow system. Two amphiphiles, dodecylbenzenesulfonic acid and nonylphenol, and five alkane solvents, ranging from hexane to hexadecane, were used. Results showed that the rate of asphaltene dissolution in amphiphile/alkane fluids could be approximated with a first-order kinetics with respect to the undissolved asphaltene mass in solution. The specific dissolution rate constant, k, varied with the concentration of amphiphiles, the type of alkane solvents, the temperature, and the fluid flow rate. The rate of asphaltene dissolution displayed a Langmuir-Hinshelwood kinetics with respect to the concentration of amphiphiles. Increasing the temperature of amphiphile/alkane fluids also enhanced the rate of asphaltene dissolution. The apparent activation energy for asphaltene dissolution was approximated to be 4--7 kcal/mol. The rate of asphaltene dissolution was also greater in amphiphile solutions containing lighter alkanes, such as hexane, with lower viscosities. These trends suggest that both surface reaction and mass transfer processes are important to the rate of asphaltene dissolution in amphiphile/alkane fluids.

  17. Kinetic characterization of thermophilic and mesophilic anaerobic digestion for coffee grounds and waste activated sludge.

    PubMed

    Li, Qian; Qiao, Wei; Wang, Xiaochang; Takayanagi, Kazuyuki; Shofie, Mohammad; Li, Yu-You

    2015-02-01

    This study was conducted to characterize the kinetics of an anaerobic process (hydrolysis, acetogenesis, acidogenesis and methanogenesis) under thermophilic (55 °C) and mesophilic (35 °C) conditions with coffee grounds and waste activated sludge (WAS) as the substrates. Special focus was given to the kinetics of propionic acid degradation to elucidate the accumulation of VFAs. Under the thermophilic condition, the methane production rate of all substrates (WAS, ground coffee and raw coffee) was about 1.5 times higher than that under the mesophilic condition. However, the effects on methane production of each substrate under the thermophilic condition differed: WAS increased by 35.8-48.2%, raw coffee decreased by 76.3-64.5% and ground coffee decreased by 74.0-57.9%. Based on the maximum reaction rate (Rmax) of each anaerobic stage obtained from the modified Gompertz model, acetogenesis was found to be the rate-limiting step for coffee grounds and WAS. This can be explained by the kinetics of propionate degradation under thermophilic condition in which a long lag-phase (more than 18 days) was observed, although the propionate concentration was only 500 mg/L. Under the mesophilic condition, acidogenesis and hydrolysis were found to be the rate-limiting step for coffee grounds and WAS, respectively. Even though reducing the particle size accelerated the methane production rate of coffee grounds, but did not change the rate-limiting step: acetogenesis in thermophilic and acidogenesis in mesophilic. PMID:25534040

  18. Linking wheelchair kinetics to glenohumeral joint demand during everyday accessibility activities.

    PubMed

    Holloway, Catherine S; Symonds, Andrew; Suzuki, Tatsuto; Gall, Angela; Smitham, Peter; Taylor, Stephen

    2015-08-01

    The aim of the study was to investigate if push-rim kinetics could be used as markers of glenohumeral joint demand during manual wheelchair accessibility activities; demonstrating a method of biomechanical analysis that could be used away from the laboratory. Propulsion forces, trunk and upper limb kinematics and surface electromyography were recorded during four propulsion tasks (level, 2.5% cross slope, 6.5% incline and 12% incline). Kinetic and kinematic data were applied to an OpenSim musculoskeletal model of the trunk and upper limb, to enable calculation of glenohumeral joint contact force. Results demonstrated a positive correlation between propulsion forces and glenohumeral joint contact forces. Both propulsion forces and joint contact forces increased as the task became more challenging. Participants demonstrated increases in trunk flexion angle as the requirement for force application increased, significantly so in the 12% incline. There were significant increases in both resultant glenohumeral joint contact forces and peak and mean normalized muscle activity levels during the incline tasks. This study demonstrated the high demand placed on the glenohumeral joint during accessibility tasks, especially as the gradient of incline increases. A lightweight instrumented wheelchair wheel has potential to guide the user to minimize upper limb demand during daily activity. PMID:26736796

  19. Controlling enzymatic activity and kinetics in swollen mesophases by physical nano-confinement

    NASA Astrophysics Data System (ADS)

    Sun, Wenjie; Vallooran, Jijo J.; Zabara, Alexandru; Mezzenga, Raffaele

    2014-05-01

    into a highly confined environment. We show that the enzymatic activity of a model enzyme, horseradish peroxidase (HRP), can be accurately controlled by relaxing its confinement within the cubic phases' water channels, when the aqueous channel diameters are systematically swollen with varying amount of hydration-enhancing sugar ester. The in-meso activity and kinetics of HRP are then systematically investigated by UV-vis spectroscopy, as a function of the size of the aqueous mesophase channels. The enzymatic activity of HRP increases with the swelling of the water channels. In swollen mesophases with water channel diameter larger than the HRP size, the enzymatic activity is more than double that measured in standard mesophases, approaching again the enzymatic activity of free HRP in bulk water. We also show that the physically-entrapped enzymes in the mesophases exhibit a restricted-diffusion-induced initial lag period and report the first observation of in-meso enzymatic kinetics significantly deviating from the normal Michaelis-Menten behaviour observed in free solutions, with deviations vanishing when enzyme confinement is released by swelling the mesophase. Electronic supplementary information (ESI) available: Visual appearance of the standard mesophase before and after HRP enzymatic reaction (Fig. S1); SAXS results of four Pn3m phases with increasing amount of SE 0%, 10%, 15% and 20% just below maximum hydration (Fig. S2); calibration curve for determining the partition coefficient of ABTS in lipids (Fig. S3); progress curves of the HRP catalytic reaction in pure water (Fig. S4) and reactions at varying ABTS concentrations for the in-meso enzymatic kinetics studies (Fig. S5); SAXS characterization of the influence of the added H2O2 (Fig. S6) and HRP (Fig. S7) on the hosted mesophases; initial rate as function of H2O2 concentration in 3 varying environments (Fig. S8). See DOI: 10.1039/c4nr01394h

  20. A study of switchgrass pyrolysis: Product variability and reaction kinetics

    NASA Astrophysics Data System (ADS)

    Bovee, Jonathan Matthew

    Samples of the same cultivar of cave-in-rock switchgrass were harvested from plots in Frankenmuth, Roger City, Cass County, and Grand Valley, Michigan. It was determined that variation exists, between locations, among the pyrolytic compounds which can lead to variability in bio-oil and increased processing costs at bio-refineries to make hydrocarbon fuels. Washed and extractives-free switchgrass samples, which contain a lower alkali and alkaline earth metals content than untreated samples, were shown to produce lower amounts of acids, esters, furans, ketones, phenolics, and saccharides and also larger amounts of aldehydes upon pyrolysis. Although the minerals catalyzed pyrolytic reactions, there was no evidence indicating their effect on reducing the production of anhydrosugars, specifically levoglucosan. To further link minerals present in the biomass to a catalytic pathway, mathematic models were employed to determine the kinetic parameters of the switchgrass. While the calculated activation energies of switchgrass, using the FWO and KAS methods, were 227.7 and 217.8 kJ/mol, correspondingly, it was concluded that the activation energies for the switchgrass hemicellulose and cellulose peaks were 115.5 and 158.2 kJ/mol, respectively, using a modified model-fitting method. The minerals that effect the production of small molecules and levoglucosan also have an observable catalytic effect on switchgrass reaction rate, which may be quantifiable through the use of reaction kinetics so as to determine activation energy.

  1. A chemical kinetic modeling study of chlorinated hydrocarbon combustion

    SciTech Connect

    Pitz, W.J.; Westbrook, C.K.

    1990-09-05

    The combustion of chloroethane is modeled as a stirred reactor so that we can study critical emission characteristics of the reactor as a function of residence time. We examine important operating conditions such as pressure, temperature, and equivalence ratio and their influence on destructive efficiency of chloroethane. The model uses a detailed chemical kinetic mechanism that we have developed previously for C{sub 3} hydrocarbons. We have added to this mechanism the chemical kinetic mechanism for C{sub 2} chlorinated hydrocarbons developed by Senkan and coworkers. In the modeling calculations, sensitivity coefficients are determined to find which reaction-rate constants have the largest effect on destructive efficiency. 24 refs., 6 figs., 1 tab.

  2. Kinetic Study of Acid Hydrolysis of Rice Straw

    PubMed Central

    Sarkar, Nibedita; Aikat, Kaustav

    2013-01-01

    Rice straw is a renewable, cheap, and abundant waste in tropical countries. The pentose content of rice straw can be used as a substrate for many types of value-added products such as xylitol and biofuel. Dilute acid hydrolysis mainly releases pentose from rice straw. The objective of the study was to determine the effect of H2SO4 concentration and reaction time on the xylose production. The variation of the main product xylose with the reaction time was described by a kinetic model and kinetic parameters were calculated to describe the variation of the xylose production with time. The optimum yield (19.35 g/L) was obtained at 0.24 mol/L H2SO4 and 30 minutes. PMID:25969789

  3. Kinetic Studies of Biological Interactions By Affinity Chromatography

    PubMed Central

    Schiel, John E.; Hage, David S.

    2009-01-01

    The rates at which biological interactions occur can provide important information on the mechanism and behavior of such processes in living systems. This review will discuss how affinity chromatography can be used as a tool to examine the kinetics of biological interactions. This approach, referred to here as biointeraction chromatography, uses a column with an immobilized binding agent to examine the association or dissociation of this agent with other compounds. The use of HPLC-based affinity columns in kinetic studies has received particular attention in recent years. Advantages of using HPLC with affinity chromatography for this purpose include the ability to reuse the same ligand within a column for a large number of experiments, and the good precision and accuracy of this approach. A number of techniques are available for kinetic studies through the use of affinity columns and biointeraction chromatography. These approaches include plate height measurements, peak profiling, peak fitting, split-peak measurements, and peak decay analysis. The general principles for each of these methods are discussed in this review and some recent applications of these techniques are presented. The advantages and potential limitations of each approach are also considered. PMID:19391173

  4. Kinetic study of aluminum adsorption by aluminosilicate clay minerals

    SciTech Connect

    Walker, W.J.; Cronan, C.S.; Patterson, H.H.

    1988-01-01

    The adsorption kinetics of Al/sup 3 +/ by montmorillonite, kaolinite, and vermiculite were investigated as a function of the initial Al concentration, the surface area of the clay, and H/sup +/ concentration, at 25/sup 0/, 18/sup 0/, and 10/sup 0/C. In order to minimize complicated side reactions the pH range was kept between 3.0 and 4.1. Results showed that the adsorption rate was first order with respect to both the initial Al concentration and the clay surface area. Changes in pH within this narrow range had virtually no effect on adsorption rate. This zero order reaction dependence suggested that the H/sup +/, compared to Al, has a weak affinity for the surface. The rates of adsorption decreased in the order of montmorillonite > kaolinite > vermiculite when compared on the basis of equal surface areas, but changed to kaolinite > montmorillonite > vermiculite when the clays were compared on an equal exchange capacity basis. The calculated apparent activation energies were < 32 kJ mol/sup -1/, indicating that over the temperature range of the study the adsorption process is only marginally temperature sensitive. The mechanism is governed by a simple electrostatic cation exchange involving outer sphere complexes between adsorbed Al and the clay surface. Vermiculite, may have a second reaction step governed by both electrostatic attraction and internal ion diffusion. Equilibrium constants for the formation of an adsorbed Al clay complex were also estimated and are 10/sup 5.34/, 10/sup 5.18/, and 10/sup 4.94/ for kaolinite, montmorillonite, and vermiculite, respectively, suggesting that these clays could play a significant role in controlling soil solutions Al concentrations.

  5. Isopeptidase activity of human transglutaminase 2: disconnection from transamidation and characterization by kinetic parameters.

    PubMed

    Király, Róbert; Thangaraju, Kiruphagaran; Nagy, Zsófia; Collighan, Russell; Nemes, Zoltán; Griffin, Martin; Fésüs, László

    2016-01-01

    Transglutaminase 2 (TG2) is a multifunctional protein with diverse catalytic activities and biological roles. Its best studied function is the Ca(2+)-dependent transamidase activity leading to formation of γ-glutamyl-ε-lysine isopeptide crosslinks between proteins and γ-glutamyl-amine derivatives. TG2 has a poorly studied isopeptidase activity cleaving these bonds. We have developed and characterised TG2 mutants which are significantly deficient in transamidase activity while have normal or increased isopeptidase activity (W332F) and vice versa (W278F). The W332F mutation led to significant changes of both the K m and the V max kinetic parameters of the isopeptidase reaction of TG2 while its calcium and GTP sensitivity was similar to the wild-type enzyme. The W278F mutation resulted in six times elevated amine incorporating transamidase activity demonstrating the regulatory significance of W278 and W332 in TG2 and that mutations can change opposed activities located at the same active site. The further application of our results in cellular systems may help to understand TG2-driven physiological and pathological processes better and lead to novel therapeutic approaches where an increased amount of crosslinked proteins correlates with the manifestation of degenerative disorders. PMID:26250429

  6. Comparison of the growth kinetics and proteolytic activities of Chryseobacterium species and Pseudomonas fluorescens.

    PubMed

    Bekker, A; Steyn, L; Charimba, G; Jooste, P; Hugo, C

    2015-12-01

    The effect of temperature on the growth kinetics and proteolytic activity of Chryseobacterium joostei and Chryseobacterium bovis was determined during this study. The results were compared with the activities of Pseudomonas fluorescens, which is regarded to be a major food spoilage psychrotolerant microorganism. For the growth studies, cultures were incubated in nutrient broth in a temperature gradient incubator (from 9 to 50 °C) and separately at 4 °C, and the optical density was measured at different time intervals. Growth temperature profiles for each organism were constructed. For determination of proteolytic activity, the cultures were incubated in fat-free ultra-high temperature processed milk in the temperature gradient incubator for 72 h (temperature range as above). Cell-free extracts were used to determine the proteolytic activity using the azocasein method. Results of the growth studies showed that C. joostei had the ability to grow over a wider temperature range than C. bovis and P. fluorescens without being affected by changes in the temperature. For the proteolytic activity, C. joostei had significantly (p < 0.001) higher activity per milligram of protein at 15.5 °C, followed by C. bovis and P. fluorescens. The results showed that C. joostei potentially has an even greater spoilage capacity in milk on the basis of growth rate and proteolytic activity than did P. fluorescens. PMID:26451905

  7. Kinetic Activation-Relaxation Technique and Self-Evolving Atomistic Kinetic Monte Carlo: Comparison of on-the-fly kinetic Monte Carlo algorithms

    DOE PAGESBeta

    Beland, Laurent Karim; Osetskiy, Yury N.; Stoller, Roger E.; Xu, Haixuan

    2015-02-07

    Here, we present a comparison of the Kinetic Activation–Relaxation Technique (k-ART) and the Self-Evolving Atomistic Kinetic Monte Carlo (SEAKMC), two off-lattice, on-the-fly Kinetic Monte Carlo (KMC) techniques that were recently used to solve several materials science problems. We show that if the initial displacements are localized the dimer method and the Activation–Relaxation Technique nouveau provide similar performance. We also show that k-ART and SEAKMC, although based on different approximations, are in agreement with each other, as demonstrated by the examples of 50 vacancies in a 1950-atom Fe box and of interstitial loops in 16,000-atom boxes. Generally speaking, k-ART’s treatment ofmore » geometry and flickers is more flexible, e.g. it can handle amorphous systems, and rigorous than SEAKMC’s, while the later’s concept of active volumes permits a significant speedup of simulations for the systems under consideration and therefore allows investigations of processes requiring large systems that are not accessible if not localizing calculations.« less

  8. Kinetic Activation-Relaxation Technique and Self-Evolving Atomistic Kinetic Monte Carlo: Comparison of on-the-fly kinetic Monte Carlo algorithms

    SciTech Connect

    Beland, Laurent Karim; Osetskiy, Yury N.; Stoller, Roger E.; Xu, Haixuan

    2015-02-07

    Here, we present a comparison of the Kinetic Activation–Relaxation Technique (k-ART) and the Self-Evolving Atomistic Kinetic Monte Carlo (SEAKMC), two off-lattice, on-the-fly Kinetic Monte Carlo (KMC) techniques that were recently used to solve several materials science problems. We show that if the initial displacements are localized the dimer method and the Activation–Relaxation Technique nouveau provide similar performance. We also show that k-ART and SEAKMC, although based on different approximations, are in agreement with each other, as demonstrated by the examples of 50 vacancies in a 1950-atom Fe box and of interstitial loops in 16,000-atom boxes. Generally speaking, k-ART’s treatment of geometry and flickers is more flexible, e.g. it can handle amorphous systems, and rigorous than SEAKMC’s, while the later’s concept of active volumes permits a significant speedup of simulations for the systems under consideration and therefore allows investigations of processes requiring large systems that are not accessible if not localizing calculations.

  9. Equilibrium and kinetics studies of arsenate adsorption by FePO(4).

    PubMed

    Hamayun, M; Mahmood, T; Naeem, A; Muska, M; Din, S U; Waseem, M

    2014-03-01

    The present work is focusing on removal of arsenate from aqueous solution using FePO4. The equilibrium study regarding the removal of arsenic by FePO4 was carried out at 298, 308, 318 and 328K. Langmuir parameters were found to increase with the increase in temperature indicating that the adsorption is favorable at high temperature. Kinetic study of arsenate adsorption on FePO4 was also carried out at different temperatures and at pH 6 and 8. Different kinetic models were used to the kinetic data amongst which pseudo second order model was best fitted. The mechanism of the adsorption kinetics was investigated by employing intraparticle diffusion and Richenberg models. The energy of activation (Ea) was found to be 30 and 35.52kJmol(-1) at pH 6 and pH 8, respectively, suggesting chemisorption nature of the adsorption process. The negative entropic values of activation signified the existence of entropy barrier while the positive ΔG(#) values indicated the existence of energy barrier to be crossed over for the occurrence of a chemical reaction. Both the spectroscopic studies and increase in equilibrium pH reveal the anion exchange removal of arsenate from aqueous solution to the solid surface. PMID:24280053

  10. 4-Hydroxy cinnamic acid as mushroom preservation: Anti-tyrosinase activity kinetics and application.

    PubMed

    Hu, Yong-Hua; Chen, Qing-Xi; Cui, Yi; Gao, Huan-Juan; Xu, Lian; Yu, Xin-Yuan; Wang, Ying; Yan, Chong-Ling; Wang, Qin

    2016-05-01

    Tyrosinase is a key enzyme in post-harvest browning of fruit and vegetable. To control and inhibit its activity is the most effective method for delaying the browning and extend the shelf life. In this paper, the inhibitory kinetics of 4-hydroxy cinnamic acid on mushroom tyrosinase was investigated using the kinetics method of substrate reaction. The results showed that the inhibition of tyrosinase by 4-hydroxy cinnamic acid was a slow, reversible reaction with fractional remaining activity. The microscopic rate constants were determined for the reaction on 4-hydroxy cinnamic acid with tyrosinase. Furthermore, the molecular docking was used to simulate 4-hydroxy cinnamic acid dock with tyrosinase. The results showed that 4-hydroxy cinnamic acid interacted with the enzyme active site mainly through the hydroxy competed with the substrate hydroxy group. The cytotoxicity study of 4-hydroxy cinnamic acid indicated that it had no effects on the proliferation of normal liver cells. Moreover, the results of effects of 4-hydroxy cinnamic acid on the preservation of mushroom showed that it could delay the mushroom browning. These results provide a comprehensive underlying the inhibitory mechanisms of 4-hydroxy cinnamic acid and its delaying post-harvest browning, that is beneficial for the application of this compound. PMID:26812105

  11. Stochastic theory of interfacial enzyme kinetics: A kinetic Monte Carlo study

    NASA Astrophysics Data System (ADS)

    Das, Biswajit; Gangopadhyay, Gautam

    2012-01-01

    In the spirit of Gillespie's stochastic approach we have formulated a theory to explore the advancement of the interfacial enzyme kinetics at the single enzyme level which is ultimately utilized to obtain the ensemble average macroscopic feature, lag-burst kinetics. We have provided a theory of the transition from the lag phase to the burst phase kinetics by considering the gradual development of electrostatic interaction among the positively charged enzyme and negatively charged product molecules deposited on the phospholipid surface. It is shown that the different diffusion time scales of the enzyme over the fluid and product regions are responsible for the memory effect in the correlation of successive turnover events of the hopping mode in the single trajectory analysis which again is reflected on the non-Gaussian distribution of turnover times on the macroscopic kinetics in the lag phase unlike the burst phase kinetics.

  12. Kinetic Demonstration.

    ERIC Educational Resources Information Center

    Burgardt, Erik D.; Ryan, Hank

    1996-01-01

    Presents a unit on chemical reaction kinetics that consists of a predemonstration activity, the demonstration, and a set of postdemonstration activities that help students transfer the concepts to actual chemical reactions. Simulates various aspects of chemical reaction kinetics. (JRH)

  13. Inhibition of bovine beta-trypsin by the active site titrant N alpha-(N,N-dimethylcarbamoyl)-alpha-azaornithine p-nitrophenyl ester: a kinetic and X-ray crystallographic study.

    PubMed

    Ascenzi, P; Balliano, G; Milla, P; Ferraccioli, R; Sartori, P; Djinovic-Carugo, K; Bolognesi, M

    1995-12-14

    Kinetics of the bovine beta-trypsin (trypsin) reaction with the active site titrant N alpha-(N,N-dimethylcarbamoyl)- alpha-aza-ornithine p-nitrophenyl ester (Dmc-azaOrn-ONp) was obtained at pH 6.2 and 21.0 degrees C. The results are consistent with the minimum three-step catalytic mechanism of serine proteinases involving a stable acyl.enzyme adduct. Dmc-azaOrn-ONp binds stoichiometrically to trypsin and allows the reliable determination of the active enzyme concentration between 1.0 x 10(-6) M and 3.0 x 10(-4) M. The three-dimensional structure of the trypsin.Dmc-azaOrn acyl.enzyme adduct has been solved by X-ray crystallography at 1.8 A resolution (R = 0.153). The Dmc-azaOrn moiety of the active site titrant is accommodated in the serine proteinase active center, occupying the S1 specificity subsite, and is covalently linked to the OG atom of the Ser195 catalytic residue. PMID:7503719

  14. Exploring Secondary Students' Understanding of Chemical Kinetics through Inquiry-Based Learning Activities

    ERIC Educational Resources Information Center

    Chairam, Sanoe; Klahan, Nutsuda; Coll, Richard K.

    2015-01-01

    This research is trying to evaluate the feedback of Thai secondary school students to inquiry-based teaching and learning methods, exemplified by the study of chemical kinetics. This work used the multiple-choice questions, scientifically practical diagram and questionnaire to assess students' understanding of chemical kinetics. The findings…

  15. DSC and curing kinetics study of epoxy grouting diluted with furfural -acetone slurry

    NASA Astrophysics Data System (ADS)

    Yin, H.; Sun, D. W.; Li, B.; Liu, Y. T.; Ran, Q. P.; Liu, J. P.

    2016-07-01

    The use of furfural-acetone slurry as active diluents of Bisphenol-A epoxy resin (DGEBA) groutings has been studied by dynamic and non-isothermal DSC for the first time. Curing kinetics study was investigated by non-isothermal differential scanning calorimetries at different heating rates. Activation enery (Ea) was calculated based on Kissinger and Ozawa Methods, and the results showed that Ea increased from 58.87 to 71.13KJ/mol after the diluents were added. The furfural-acetone epoxy matrix could cure completely at the theoretical curing temperature of 365.8K and the curing time of 139mins, which were determined by the kinetic model parameters.

  16. On pressure-shear plate impact for studying the kinetics of stress-induced phase transformations

    NASA Astrophysics Data System (ADS)

    Escobar, Joanne C.; Clifton, Rodney J.

    1992-07-01

    Pressure-shear plate impact experiments are proposed for studying the kinetics of stress-induced phase transformations. The purpose of this paper is to determine loading conditions and specimen orientations which can be expected to activate a single habit plane variant parallel to the impact plane, thereby simplifying the study of the kinetics of the transformation through monitoring the wave profiles associated with the propagating phase boundary. The Wechsler Lieberman-Read phenomenological theory was used to determine habit plane indices and directions of shape deformation for a Cu-Al-Ni shape memory alloy which undergoes a martensitic phase transformation under stress. Elastic waves generated by pressure-shear impact were analyzed for wave propagation in the direction of the normal to a habit plane. A critical resolved shear stress criterion was used to predict variants which are expected to be activated for a range of impact velocities and relative magnitudes of the normal and transverse components of the impact velocity.

  17. Harvesting energy from the marine sediment-water interface II. Kinetic activity of anode materials.

    PubMed

    Lowy, Daniel A; Tender, Leonard M; Zeikus, J Gregory; Park, Doo Hyun; Lovley, Derek R

    2006-05-15

    Here, we report a comparative study on the kinetic activity of various anodes of a recently described microbial fuel cell consisting of an anode imbedded in marine sediment and a cathode in overlying seawater. Using plain graphite anodes, it was demonstrated that a significant portion of the anodic current results from oxidation of sediment organic matter catalyzed by microorganisms colonizing the anode and capable of directly reducing the anode without added exogenous electron-transfer mediators. Here, graphite anodes incorporating microbial oxidants are evaluated in the laboratory relative to plain graphite with the goal of increasing power density by increasing current density. Anodes evaluated include graphite modified by adsorption of anthraquinone-1,6-disulfonic acid (AQDS) or 1,4-naphthoquinone (NQ), a graphite-ceramic composite containing Mn2+ and Ni2+, and graphite modified with a graphite paste containing Fe3O4 or Fe3O4 and Ni2+. It was found that these anodes possess between 1.5- and 2.2-fold greater kinetic activity than plain graphite. Fuel cells were deployed in a coastal site near Tuckerton, NJ (USA) that utilized two of these anodes. These fuel cells generated ca. 5-fold greater current density than a previously characterized fuel cell equipped with a plain graphite anode, and operated at the same site. PMID:16574400

  18. Expression and kinetics of induced procoagulant activity in bovine pulmonary alveolar macrophages.

    PubMed

    Car, B D; Slauson, D O; Suyemoto, M M; Doré, M; Neilsen, N R

    1991-01-01

    Leukocytes, especially macrophages, are important cellular mediators of fibrin deposition and removal at tissue sites of inflammation. Pulmonary fibrin deposition is a prominent feature of bovine acute lung injury; therefore, we studied the resting and stimulated procoagulant responses of bovine pulmonary alveolar macrophages (PAM) and peripheral blood neutrophils (PMN). Freshly isolated normal PAM and PMN expressed negligible procoagulant activity. PAM stimulated with endotoxin lipopolysaccharide (LPS), 4 beta-phorbol 12-myristate 13-acetate (PMA) and bovine recombinant interleukin-1 beta (rBIL-1 beta) exhibited protein synthesis- and dose-dependent enhancement of procoagulant activity in 8-h cultures. Bovine recombinant granulocyte macrophage-colony stimulating factor (rBGM-CSF) and recombinant human gamma-interferon (rHIFN-gamma) did not induce procoagulant activity. The kinetics of LPS- and PMA-enhanced PAM procoagulant activity differed: LPS-induced enhancement developed earlier and more rapidly than PMA-induced enhancement. Pasteurella haemolytica LPS was more potent than Escherichia coli LPS in enhancing PAM procoagulant activity, while dexamethasone decreased both baseline and LPS- or PMA-stimulated activity by approximately 50%. PAM procoagulant activity resulted from tissue factor expression. Bovine PMN produced negligible procoagulant activity when stimulated, and are thus unlikely to be major contributors to procoagulant activity in bovine lung. Activity inhibitory to bovine tissue factor was present in both calf and adult sera, and was partly dependent on the presence of factor X for activity. Rapid induction of bovine PAM procoagulant activity by inflammatory mediators, and subsequent resistance to degradation, may thus combine to promote an alveolar microenvironment permissive to fibrin deposition in bovine acute lung injury. PMID:1959504

  19. A kinetic study of jack-bean urease denaturation by a new dithiocarbamate bismuth compound

    NASA Astrophysics Data System (ADS)

    Menezes, D. C.; Borges, E.; Torres, M. F.; Braga, J. P.

    2012-10-01

    A kinetic study concerning enzymatic inhibitory effect of a new bismuth dithiocarbamate complex on jack-bean urease is reported. A neural network approach is used to solve the ill-posed inverse problem arising from numerical treatment of the subject. A reaction mechanism for the urease denaturation process is proposed and the rate constants, relaxation time constants, equilibrium constants, activation Gibbs free energies for each reaction step and Gibbs free energies for the transition species are determined.

  20. Inhibition of yeast hexokinase: a kinetic and phosphorus nuclear magnetic resonance study

    NASA Astrophysics Data System (ADS)

    Willson, Michèle; Perie, Jacques

    1999-04-01

    Glucosamine analogues are inhibitors of yeast hexokinase (HK); kinetic analysis with respect to glucose and ATP suggests a pseudo-substrate behaviour for these compounds. However, a spectroscopy study by 31P NMR indicates that they are not phosphorylated but that, in fact, they enhance the ATPase activity of HK; this result gives a further insight into the phosphorylation or ATP hydrolysis process in HK.

  1. Kinetic studies of the hydroxyl radical reaction with PAHs

    NASA Astrophysics Data System (ADS)

    Ananthula, Rajeshwar

    An existing quartz optical reactor heating system was designed to permit higher temperature kinetic measurements more closely associated with post-combuston conditions (up to 1200 K). A pulsed laser photolysis/pulsed laser-induced fluorescence (PLP/PLIF) technique was then applied with this modified reactor to study the OH radical kinetics with polycyclic aromatic hydrocarbons (PAHs). The kinetics of the reaction of a surrogate three-ring PAH, anthracene (and its deuterated form) with hydroxyl (OH) radicals was investigated over the temperature range of 373 to 1200 K. This study represents the first examination of the OH kinetics for this class of reactions at elevated temperatures (>470 K). The results indicate a complex temperature dependence similar to that observed for simpler aromatic compounds, e.g., benzene. At low temperatures (373-498 K), the rate measurements exhibited Arrhenius behavior (1.82 x 10-11 exp(542.35/T) in units of cm3 molecule -1 s-1) and kinetic isotope effect (KIE) measurements were consistent with an OH addition mechanism. The low temperature results are extrapolated to atmospheric temperatures and compared with previous measurements. Rate measurements between 673 and 923 K exhibited a sharp decrease in the magnitude of the rate coefficients (a factor of 9). KIE measurements under these conditions were still consistent with an OH addition mechanism. The following modified Arrhenius equation is the best fit to our anthracene measurements between 373 and 923 K, 8.17 x 1014 T-8.3 exp(-3171.71/T) (in units of cm3 molecule-1 s-1). For a limited temperature range between 1000 and 1200 K, the rate measurements exhibited an apparent positive temperature dependence with the following Arrhenius equation the best fit to the data, 2.18 x 10-11*exp(-1734.11/T) (in units of cm3molecule-1s -1). KIE measurements above 999 K were slightly larger than unity, but inclusive regarding the mechanism of the reaction. Theoretical calculations of the KIE indicate

  2. A Simple and Fast Kinetic Assay for the Determination of Fructan Exohydrolase Activity in Perennial Ryegrass (Lolium perenne L.)

    PubMed Central

    Gasperl, Anna; Morvan-Bertrand, Annette; Prud’homme, Marie-Pascale; Roitsch, Thomas

    2015-01-01

    Despite the fact that fructans are the main constituent of water-soluble carbohydrates in forage grasses and cereal crops of temperate climates, little knowledge is available on the regulation of the enzymes involved in fructan metabolism. The analysis of enzyme activities involved in this process has been hampered by the low affinity of the fructan enzymes for sucrose and fructans used as fructosyl donor. Further, the analysis of fructan composition and enzyme activities is restricted to specialized labs with access to suited HPLC equipment and appropriate fructan standards. The degradation of fructan polymers with high degree of polymerization (DP) by fructan exohydrolases (FEHs) to fructosyloligomers is important to liberate energy in the form of fructan, but also under conditions where the generation of low DP polymers is required. Based on published protocols employing enzyme coupled endpoint reactions in single cuvettes, we developed a simple and fast kinetic 1-FEH assay. This assay can be performed in multi-well plate format using plate readers to determine the activity of 1-FEH against 1-kestotriose, resulting in a significant time reduction. Kinetic assays allow an optimal and more precise determination of enzyme activities compared to endpoint assays, and enable to check the quality of any reaction with respect to linearity of the assay. The enzyme coupled kinetic 1-FEH assay was validated in a case study showing the expected increase in 1-FEH activity during cold treatment. This assay is cost effective and could be performed by any lab with access to a plate reader suited for kinetic measurements and readings at 340 nm, and is highly suited to assess temporal changes and relative differences in 1-FEH activities. Thus, this enzyme coupled kinetic 1-FEH assay is of high importance both to the field of basic fructan research and plant breeding. PMID:26734049

  3. Kinetics of adsorption with granular, powdered, and fibrous activated carbon

    SciTech Connect

    Shmidt, J.L.; Pimenov, A.V.; Lieberman, A.I.; Cheh, H.Y.

    1997-08-01

    The properties of three different types of activated carbon, fibrous, powdered, and granular, were investigated theoretically and experimentally. The adsorption rate of the activated carbon fiber was found to be two orders of magnitude higher than that of the granular activated carbon, and one order of magnitude higher than that of the powdered activated carbon. Diffusion coefficients of methylene blue in the fibrous, powdered, and granular activated carbons were determined experimentally. A new method for estimating the meso- and macropore surface areas in these carbons was proposed.

  4. Kinetics study on biomass pyrolysis for fuel gas production.

    PubMed

    Chen, Guan-Yi; Fang, Meng-Xiang; Andries, J; Luo, Zhong-Yang; Spliethoff, H; Cen, Ke-Fa

    2003-01-01

    Kinetic knowledge is of great importance in achieving good control of the pyrolysis and gasification process and optimising system design. An overall kinetic pyrolysis scheme is therefore addressed here. The kinetic modelling incorporates the following basic steps: the degradation of the virgin biomass materials into primary products (tar, gas and semi-char), the decomposition of primary tar into secondary products and the continuous interaction between primary gas and char. The last step is disregarded completely by models in the literature. Analysis and comparison of predicted results from different kinetic schemes and experimental data on our fixed bed pyrolyser yielded very positive evidence to support our kinetic scheme. PMID:12861621

  5. Antibacterial Activity and Kinetics of Litsea cubeba Oil on Escherichia coli

    PubMed Central

    Li, Wen-Ru; Shi, Qing-Shan; Liang, Qing; Xie, Xiao-Bao; Huang, Xiao-Mo; Chen, Yi-Ben

    2014-01-01

    Litsea cubeba oil is extracted from the fresh fruits of Litsea cubeba by distillation. In this study, its chemical constituents, antibacterial activity, kinetics and effects against Escherichia coli were studied. Its minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were both 0.125% (v/v) by toxic food method. Moreover, the antibacterial kinetic curves indicated 0.0625% (v/v) of litsea cubeba oil was able to prolong the growth lag phase of E. coli cells to approximate 12 hours while 0.125% (v/v) of litsea cubeba oil was able to kill the cells completely. Furthermore, transmission electron microscope (TEM) observation showed most E. coli cells treated with 0.125% (v/v) of litsea cubeba oil were killed or destroyed severely within 2 hours. The litsea cubeba oil might penetrate and destroy the outer and inner membrane of E. coli cells. Thus many holes and gaps were observed on the damaged cells, which led to their death eventually. The antibacterial effects of litsea cubeba oil mainly attributed to the presence of aldehydes, which accounted for approximately 70% in its whole components analyzed by GC/MS. Based on the antimicrobial properties, litsea cubeba oil would have a broad application in the antimicrobial industry. PMID:25372706

  6. Degradation of oxcarbazepine by UV-activated persulfate oxidation: kinetics, mechanisms, and pathways.

    PubMed

    Bu, Lingjun; Zhou, Shiqing; Shi, Zhou; Deng, Lin; Li, Guangchao; Yi, Qihang; Gao, Naiyun

    2016-02-01

    The degradation kinetics and mechanism of the antiepileptic drug oxcarbazepine (OXC) by UV-activated persulfate oxidation were investigated in this study. Results showed that UV/persulfate (UV/PS) process appeared to be more effective in degrading OXC than UV or PS alone. The OXC degradation exhibited a pseudo-first order kinetics pattern and the degradation rate constants (k obs) were affected by initial OXC concentration, PS dosage, initial pH, and humic acid concentration to different degrees. It was found that low initial OXC concentration, high persulfate dosage, and initial pH enhanced the OXC degradation. Additionally, the presence of humic acid in the solution could greatly inhibit the degradation of OXC. Moreover, hydroxyl radical (OH•) and sulfate radical (SO4 (-)••) were identified to be responsible for OXC degradation and SO4 (-)• made the predominant contribution in this study. Finally, major intermediate products were identified and a preliminary degradation pathway was proposed. Results demonstrated that UV/PS system is a potential technology to control the water pollution caused by emerging contaminants such as OXC. PMID:26452660

  7. Blueberry polyphenol oxidase: Characterization and the kinetics of thermal and high pressure activation and inactivation.

    PubMed

    Terefe, Netsanet Shiferaw; Delon, Antoine; Buckow, Roman; Versteeg, Cornelis

    2015-12-01

    Partially purified blueberry polyphenol oxidase (PPO) in Mcllvaine buffer (pH=3.6, typical pH of blueberry juice) was subjected to processing at isothermal-isobaric conditions at temperatures from 30 to 80 °C and pressure from 0.1 to 700 MPa. High pressure processing at 30-50 °C at all pressures studied caused irreversible PPO activity increase with a maximum of 6.1 fold increase at 500 MPa and 30 °C. Treatments at mild pressure-mild temperature conditions (0.1-400 MPa, 60 °C) also caused up to 3 fold PPO activity increase. Initial activity increase followed by a decrease occurred at relatively high pressure-mild temperature (400-600 MPa, 60 °C) and mild pressure-high temperature (0.1-400 MPa, 70-80 °C) combinations. At temperatures higher than 76 °C, monotonic decrease in PPO activity occurred at 0.1 MPa and pressures higher than 500 MPa. The activation/inactivation kinetics of the enzyme was successfully modelled assuming consecutive reactions in series with activation followed by inactivation. PMID:26041182

  8. Immobilization of enzymes using non-ionic colloidal liquid aphrons (CLAs): Activity kinetics, conformation, and energetics.

    PubMed

    Ward, Keeran; Xi, Jingshu; Stuckey, David C

    2016-05-01

    This study seeks to examine the ability of non-ionic/non-polar Colloidial Liquid Aphrons (CLAs) to preserve enzyme functionality upon immobilization and release. CLAs consisting of micron-sized oil droplets surrounded by a thin aqueous layer stabilized by a mixture of surfactants, were formulated by direct addition (pre-manufacture addition) using 1% Tween 80/mineral oil and 1% Tween 20 and the enzymes lipase, aprotinin and α-chymotrypsin. The results of activity assays for both lipase and α-chymotrypsin showed that kinetic activity increased upon immobilization by factors of 7 and 5.5, respectively, while aprotinin retained approximately 85% of its native activity. The conformation of the enzymes released through desorption showed no significant alterations compared to their native state. Changes in pH and temperature showed that optimum conditions did not change after immobilization, while analysis of activation energy for the immobilized enzyme showed an increase in activity at higher temperatures. Furthermore, the effect of bound water within the aphron structure allowed for some degree of enzyme hydration, and this hydration was needed for an active conformation with results showing a decrease in ΔH* for the immobilized system compared to its native counterpart. PMID:26497856

  9. Kinetic analysis of the interaction between plasminogen activator inhibitor-1 and tissue-type plasminogen activator.

    PubMed Central

    Masson, C; Angles-Cano, E

    1988-01-01

    The kinetics of inhibition of tissue-type plasminogen activator (t-PA) by the fast-acting plasminogen activator inhibitor-1 (PAI-1) was investigated in homogeneous (plasma) and heterogeneous (solid-phase fibrin) systems by using radioisotopic and spectrophotometric analysis. It is demonstrated that fibrin-bound t-PA is protected from inhibition by PAI-1, whereas t-PA in soluble phase is rapidly inhibited (K1 = 10(7) M-1.s-1) even in the presence of 2 microM-plasminogen. The inhibitor interferes with the binding of t-PA to fibrin in a competitive manner. As a consequence the Kd of t-PA for fibrin (1.2 +/- 0.4 nM) increases and the maximal velocity of plasminogen activation by fibrin-bound t-PA is not modified. From the plot of the apparent Kd versus the concentration of PAI-1 a Ki value of 1.3 +/- 0.3 nM was calculated. The quasi-similar values for the dissociation constants between fibrin and t-PA (Kd) and between PAI-1 and t-PA (Ki), as well as the competitive type of inhibition observed, indicate that the fibrinolytic activity of human plasma may be the result of an equilibrium distribution of t-PA between both the amount of fibrin generated and the concentration of circulating inhibitor. Images Fig. 2. Fig. 3. PMID:3146972

  10. Experimental and Kinetic Modeling Study of 2-Methyl-2-Butene: Allylic Hydrocarbon Kinetics.

    PubMed

    Westbrook, Charles K; Pitz, William J; Mehl, Marco; Glaude, Pierre-Alexandre; Herbinet, Olivier; Bax, Sarah; Battin-Leclerc, Frederique; Mathieu, Olivier; Petersen, Eric L; Bugler, John; Curran, Henry J

    2015-07-16

    Two experimental studies have been carried out on the oxidation of 2-methyl-2-butene, one measuring ignition delay times behind reflected shock waves in a stainless steel shock tube, and the other measuring fuel, intermediate, and product species mole fractions in a jet-stirred reactor (JSR). The shock tube ignition experiments were carried out at three different pressures, approximately 1.7, 11.2, and 31 atm, and at each pressure, fuel-lean (ϕ = 0.5), stoichiometric (ϕ = 1.0), and fuel-rich (ϕ = 2.0) mixtures were examined, with each fuel/oxygen mixture diluted in 99% Ar, for initial postshock temperatures between 1330 and 1730 K. The JSR experiments were performed at nearly atmospheric pressure (800 Torr), with stoichiometric fuel/oxygen mixtures with 0.01 mole fraction of 2M2B fuel, a residence time in the reactor of 1.5 s, and mole fractions of 36 different chemical species were measured over a temperature range from 600 to 1150 K. These JSR experiments represent the first such study reporting detailed species measurements for an unsaturated, branched hydrocarbon fuel larger than iso-butene. A detailed chemical kinetic reaction mechanism was developed to study the important reaction pathways in these experiments, with particular attention on the role played by allylic C-H bonds and allylic pentenyl radicals. The results show that, at high temperatures, this olefinic fuel reacts rapidly, similar to related alkane fuels, but the pronounced thermal stability of the allylic pentenyl species inhibits low temperature reactivity, so 2M2B does not produce "cool flames" or negative temperature coefficient behavior. The connections between olefin hydrocarbon fuels, resulting allylic fuel radicals, the resulting lack of low-temperature reactivity, and the gasoline engine concept of octane sensitivity are discussed. PMID:25822578

  11. Accelerated hydrolysis of substituted cellulose for potential biofuel production: kinetic study and modeling.

    PubMed

    Mu, Bingnan; Xu, Helan; Yang, Yiqi

    2015-11-01

    In this work, kinetics of substitution accelerated cellulose hydrolysis with multiple reaction stages was investigated to lay foundation for mechanism study and molecular design of substituting compounds. High-efficiency hydrolysis of cellulose is critical for cellulose-based bioethanol production. It is known that, substitution could substantially decrease activation energy and increase reaction rate of acidic hydrolysis of glycosidic bonds in cellulose. However, reaction kinetics and mechanism of the accelerated hydrolysis were not fully revealed. In this research, it was proved that substitution therefore accelerated hydrolysis only occurred in amorphous regions of cellulose fibers, and was a process with multiple reaction stages. With molar ratio of substitution less than 1%, the overall hydrolysis rate could be increased for around 10 times. We also quantified the relationship between the hydrolysis rate of individual reaction stage and its major influences, including molar ratio of substitution, activation energy of acidic hydrolysis, pH and temperature. PMID:26253917

  12. Lipase-catalyzed ethanolysis of borage oil: a kinetic study.

    PubMed

    Torres, Carlos F; Hill, Charles G; Otero, Cristina

    2004-01-01

    Ethanolysis of borage oil catalyzed by two commercial lipases (from Pseudomonas cepacia and Candida antarctica) was studied using two different methodologies. Multiresponse models derived from a generalized Michaelis-Menten mechanism were utilized to describe the rates of formation of ethyl esters of the primary fatty acids present in the precursor oil. The relative rate constants determined for each of the fatty acid residues indicated that both lipases discriminate against release of gamma-linolenic acid residues under the reaction conditions studied. However, both lipases also released some of the residues located at the sn-2 position, indicating that for the experimental conditions studied, both lipases are nonspecific. Moreover, inactivation of Novozym 435 was rapid. Because the half-life of this enzyme (ca. 2.2 h) is comparable to the half-life of the reaction, the intrinsic reaction rate and enzyme deactivation must both be considered in modeling the kinetics. PMID:15176879

  13. Orszag Tang vortex - Kinetic study of a turbulent plasma

    SciTech Connect

    Parashar, T. N.; Servidio, S.; Shay, M. A.; Matthaeus, W. H.; Cassak, P. A.

    2010-03-25

    Kinetic evolution of the Orszag-Tang vortex is studied using collisionless hybrid simulations based on particle in cell ions and fluid electrons. In magnetohydrodynamics (MHD) this configuration leads rapidly to broadband turbulence. An earlier study estimated the dissipation in the system. A comparison of MHD and hybrid simulations showed similar behavior at large scales but substantial differences at small scales. The hybrid magnetic energy spectrum shows a break at the scale where Hall term in the Ohm's law becomes important. The protons heat perpendicularly and most of the energy is dissipated through magnetic interactions. Here, the space time structure of the system is studied using frequency-wavenumber (k-omega) decomposition. No clear resonances appear, ruling out the cyclotron resonances as a likely candidate for the perpendicular heating. The only distinguishable wave modes present, which constitute a small percentage of total energy, are magnetosonic modes.

  14. Size dependence of the thermal decomposition kinetics of nano- CaC2O4: A theoretical and experimental study

    NASA Astrophysics Data System (ADS)

    Fu, Qingshan; Cui, Zixiang; Xue, Yongqiang

    2015-10-01

    In the processes of preparation and application of nanomaterials, the thermal decomposition of nanoparticles is often involved. An improved general theory of thermal decomposition kinetics of nanoparticles, developed over the past 10 years, was presented in this paper where the relations between reaction kinetic parameters and particle size were derived. Experimentally, the thermal decomposition kinetics of nano-sized calcium oxalate (nano- CaC2O4 with different sizes was studied by means of Thermogravimetry Analysis (TGA) at different heating rates. The values of the apparent activation energy and the logarithm of pre-exponential factor were calculated using the equation of Iterative Kissinger-Akahira-Sunose (IKAS) and its deformations. The influence regularities of particle size on the apparent activation energy and the pre-exponential factor were summarized, which are consistent with the thermal decomposition kinetics theory of nanoparticles. Based on the theory, the method of obtaining the surface thermodynamic properties by the determination of kinetic parameters was presented. Theoretical and experimental results show that the particle size, through the effect on the surface thermodynamic properties, has notable effect on the thermal decomposition kinetics. With the particle size decreasing, the partial molar surface enthalpy and the partial molar surface entropy increases, leading to the decrease of the apparent activation energy and the pre-exponential factor, respectively. Furthermore, the apparent activation energy, the pre-exponential factor, the partial molar surface enthalpy and the partial molar surface entropy are linearly related to the reciprocal of particle diameter, respectively.

  15. Activity Level-Dependent Synapse-Specific AMPA Receptor Trafficking Regulates Transmission Kinetics

    PubMed Central

    Zhu, J. Julius

    2009-01-01

    Central glutamatergic synapses may express AMPA-sensitive glutamate receptors (AMPA-Rs) with distinct gating properties and exhibit different transmission dynamics, which are important for computing various synaptic inputs received at different populations of synapses. However, how glutamatergic synapses acquire AMPA-Rs with distinct kinetics to influence synaptic integration remains poorly understood. Here I report synapse-specific trafficking of distinct AMPA-Rs in rat cortical layer 4 stellate and layer 5 pyramidal neurons. The analysis indicates that in single layer 4 stellate neurons thalamocortical synapses generate faster synaptic responses than intracortical synapses. Moreover, GluR1-containing AMPA-Rs traffic selectively into intracortical synapses, and this process requires sensory experience-dependent activity and slows down transmission kinetics. GluR4-containing AMPA-Rs traffic more heavily into thalamocortical synapses than intracortical synapses, and this process requires spontaneous synaptic activity and speeds up transmission kinetics. GluR2-containing AMPA-Rs traffic equally into both thalamocortical and intracortical synapses, and this process requires no synaptic activity and resets transmission kinetics. Notably, synaptic trafficking of distinct AMPA-Rs differentially regulates synaptic integration. Thus, synapse-specific AMPA-R trafficking coarsely sets and synaptic activity finely tunes transmission kinetics and integration properties at different synapses in central neurons. PMID:19439609

  16. Kinetic Study of [2]Pseudorotaxane Formation with an Asymmetrical Thread.

    PubMed

    Quiroga, Miguel; Parajó, Mercedes; Rodríguez-Dafonte, Pedro; García-Río, Luis

    2016-06-28

    Kinetic and thermodynamic studies on cyclodextrin (CD)-based [2]pseudorotaxane formation have been carried out by a combination of NMR and calorimetric techniques using bolaform surfactants as axles. Experimental evidence of the formation of an external complex between the trimethylammonium head groups of the axle and the external hydrogen atoms of α-cyclodextrin (α-CD) is reported. Inclusion of this external complex in the reaction pathway allows us to explain the kinetic behavior as well as the nonlinear dependence of the observed rate constant on CD concentrations. The equilibrium constant for [2]pseudorotaxane formation is strongly affected by the spacer length of the axle. This effect is a consequence of increasing rotaxane stability because the threading rate constant is almost independent of the spacer length, but dethreading strongly decreases on increasing the axle size. Using a nonsymmetrical axle with tripropyl and trimethylammonium cations precludes CD threading by the large head side. CDs will thread this asymmetrical bolaform by both their wide and narrow sides, yielding two isomeric [2]pseudorotaxanes. Threading by the wide side of the CD is 60% more favorable than that by the narrow one, but dethreading rate constants are the same for both isomers. PMID:27232769

  17. Kinetic Batch Soil Adsorption Studies of 2, 4-dinitroanisole (DNAN)

    NASA Astrophysics Data System (ADS)

    Arthur, J.; Mark, N. W.; Taylor, S.; Brusseau, M. L.; Dontsova, K.

    2014-12-01

    Currently the explosive 2, 4, 6- trinitrotoluene (TNT) is used as a main ingredient in munitions; however the compound has failed to meet sensitivity requirements. The replacement compound being tested is 2, 4-dinitroanisole (DNAN). DNAN is less sensitive to shock, high temperatures, and has good detonation characteristics. However, DNAN is more soluble than TNT, which can influence transport and fate behavior and thus bioavailability and exposure potential. DNAN has been shown to have some human and environmental toxicity. The objective of this study was to investigate the environmental fate of DNAN in soil, with a specific focus on sorption processes. Batch experiments were conducted using 11 soils collected from military installations located across the United States. The soils were characterized for pH, specific surface area, electrical conductivity, cation exchange capacity, and organic carbon content. Adsorption kinetic data determined at room temperature were fitted using the first order kinetic equation. Adsorption isotherms were fitted with linear and Freundlich isotherm equations. The magnitudes of the linear adsorption coefficients ranged from 0.6 to 6 cm3/g. Results indicated that the adsorption of DNAN is strongly dependent on the amount of organic carbon present in the soil.

  18. Hydrodynamic shock wave studies within a kinetic Monte Carlo approach

    NASA Astrophysics Data System (ADS)

    Sagert, Irina; Bauer, Wolfgang; Colbry, Dirk; Howell, Jim; Pickett, Rodney; Staber, Alec; Strother, Terrance

    2014-06-01

    We introduce a massively parallelized test-particle based kinetic Monte Carlo code that is capable of modeling the phase space evolution of an arbitrarily sized system that is free to move in and out of the continuum limit. Our code combines advantages of the DSMC and the Point of Closest Approach techniques for solving the collision integral. With that, it achieves high spatial accuracy in simulations of large particle systems while maintaining computational feasibility. Using particle mean free paths which are small with respect to the characteristic length scale of the simulated system, we reproduce hydrodynamic behavior. To demonstrate that our code can retrieve continuum solutions, we perform a test-suite of classic hydrodynamic shock problems consisting of the Sod, the Noh, and the Sedov tests. We find that the results of our simulations which apply millions of test-particles match the analytic solutions well. In addition, we take advantage of the ability of kinetic codes to describe matter out of the continuum regime when applying large particle mean free paths. With that, we study and compare the evolution of shock waves in the hydrodynamic limit and in a regime which is not reachable by hydrodynamic codes.

  19. Kinetics of Bacterial Phospholipase C Activity at Micellar Interfaces: Effect of Substrate Aggregate Microstructure and a Model for the Kinetic Parameters

    PubMed Central

    Singh, Jasmeet; Ranganathan, Radha; Hajdu, Joseph

    2009-01-01

    Activity at micellar interfaces of bacterial phospholipase C from Bacillus cereus on phospholipids solubilized in micelles was investigated with the goal of elucidating the role of the interface microstructure and developing further an existing kinetic model. Enzyme kinetics and physicochemical characterization of model substrate aggregates were combined; thus enabling the interpretation of kinetics in the context of the interface. Substrates were diacylphosphatidylcholine of different acyl chain lengths in the form of mixed micelles with dodecyldimethylammoniopropanesulfonate. An early kinetic model, reformulated to reflect the interfacial nature of the kinetics, was applied to the kinetic data. A better method of data treatment is proposed, use of which makes the presence of microstructure effects quite transparent. Models for enzyme-micelle binding and enzyme-lipid binding are developed and expressions incorporating the microstructural properties are derived for the enzyme-micelle dissociation constant KS and the interface Michaelis-Menten constant, KM. Use of these expressions in the interface kinetic model brings excellent agreement between the kinetic data and the model. Numerical values for the thermodynamic and kinetic parameters are determined. Enzyme-lipid binding is found to be an activated process with an acyl chain length dependent free energy of activation that decreases with micelle lipid molar fraction with a coefficient of about −15 RT and correlates with the tightness of molecular packing in the substrate aggregate. Thus the physical insight obtained includes a model for the kinetic parameters that shows that these parameters depend on the substrate concentration and acyl chain length of the lipid. Enzyme-micelle binding is indicated to be hydrophobic and solvent mediated with a dissociation constant of 1.2 mM. PMID:19367944

  20. Nicotine evokes kinetic tremor by activating the inferior olive via α7 nicotinic acetylcholine receptors.

    PubMed

    Kunisawa, Naofumi; Iha, Higor A; Shimizu, Saki; Tokudome, Kentaro; Mukai, Takahiro; Kinboshi, Masato; Serikawa, Tadao; Ohno, Yukihiro

    2016-11-01

    Nicotinic acetylcholine (nACh) receptors are implicated in the pathogenesis of movement disorders (e.g., tremor) and epilepsy. Here, we performed behavioral and immunohistochemical studies using mice and rats to elucidate the mechanisms underlying nicotine-induced tremor. Treatments of animals with nicotine (0.5-2mg/kg, i.p.) elicited kinetic tremor, which was completely suppressed by the nACh receptor antagonist mecamylamine (MEC). The specific α7 nACh receptor antagonist methyllycaconitine (MLA) also inhibited nicotine-induced tremor, whereas the α4β2 nACh antagonist dihydro-β-erythroidine (DHβE) or the peripheral α3β4 nACh antagonist hexamethonium showed no effects. Mapping analysis of Fos protein expression, a biological marker of neural excitation, revealed that a tremorgenic dose (1mg/kg) of nicotine region-specifically elevated Fos expression in the piriform cortex (PirC), medial habenula, solitary nucleus and inferior olive (IO) among 44 brain regions examined. In addition, similarly to the tremor responses, nicotine-induced Fos expression in the PirC and IO was selectively antagonized by MLA, but not by DHβE. Furthermore, an electrical lesioning of the IO, but not the PirC, significantly suppressed the induction of nicotine tremor. The present results suggest that nicotine elicits kinetic tremor in rodents by activating the IO neurons via α7 nACh receptors. PMID:27506652

  1. Kinetic energy budget during strong jet stream activity over the eastern United States

    NASA Technical Reports Server (NTRS)

    Fuelberg, H. E.; Scoggins, J. R.

    1980-01-01

    Kinetic energy budgets are computed during a cold air outbreak in association with strong jet stream activity over the eastern United States. The period is characterized by large generation of kinetic energy due to cross-contour flow. Horizontal export and dissipation of energy to subgrid scales of motion constitute the important energy sinks. Rawinsonde data at 3 and 6 h intervals during a 36 h period are used in the analysis and reveal that energy fluctuations on a time scale of less than 12 h are generally small even though the overall energy balance does change considerably during the period in conjunction with an upper level trough which moves through the region. An error analysis of the energy budget terms suggests that this major change in the budget is not due to random errors in the input data but is caused by the changing synoptic situation. The study illustrates the need to consider the time and space scales of associated weather phenomena in interpreting energy budgets obtained through use of higher frequency data.

  2. Structural and Kinetic Analyses of Macrophage Migration Inhibitory Factor Active Site Interactions

    SciTech Connect

    Crichlow, G.; Lubetsky, J; Leng, L; Bucala, R; Lolis, E

    2009-01-01

    Macrophage migration inhibitory factor (MIF) is a secreted protein expressed in numerous cell types that counters the antiinflammatory effects of glucocorticoids and has been implicated in sepsis, cancer, and certain autoimmune diseases. Interestingly, the structure of MIF contains a catalytic site resembling the tautomerase/isomerase sites of microbial enzymes. While bona fide physiological substrates remain unknown, model substrates have been identified. Selected compounds that bind in the tautomerase active site also inhibit biological functions of MIF. It had previously been shown that the acetaminophen metabolite, N-acetyl-p-benzoquinone imine (NAPQI), covalently binds to the active site of MIF. In this study, kinetic data indicate that NAPQI inhibits MIF both covalently and noncovalently. The structure of MIF cocrystallized with NAPQI reveals that the NAPQI has undergone a chemical alteration forming an acetaminophen dimer (bi-APAP) and binds noncovalently to MIF at the mouth of the active site. We also find that the commonly used protease inhibitor, phenylmethylsulfonyl fluoride (PMSF), forms a covalent complex with MIF and inhibits the tautomerase activity. Crystallographic analysis reveals the formation of a stable, novel covalent bond for PMSF between the catalytic nitrogen of the N-terminal proline and the sulfur of PMSF with complete, well-defined electron density in all three active sites of the MIF homotrimer. Conclusions are drawn from the structures of these two MIF-inhibitor complexes regarding the design of novel compounds that may provide more potent reversible and irreversible inhibition of MIF.

  3. Biosorption of uranium by melanin: kinetic, equilibrium and thermodynamic studies.

    PubMed

    Saini, Amardeep Singh; Melo, Jose Savio

    2013-12-01

    Limitation of conventional techniques for the removal of heavy metals present at low concentrations, has led to the need for developing alternate technologies like biosorption. In the present study we describe the use of melanin pigment synthesized through green technology, for sorption of uranium from aqueous system. Biosynthesized melanin showed good uptake over a broad pH range. Removal of uranium was rapid and equilibrium was reached within 2h of contact. It was observed that the kinetic data fits well into Lagergren's pseudo-second order equation. A maximum loading capacity of 588.24 mg g(-1) was calculated from Langmuir plot. Thermodynamic studies performed revealed that sorption process was favorable. Binding of uranium on the surface of melanin was confirmed by FT-IR and energy dispersive spectroscopy (EDS). Thus, biosynthesized melanin can be efficiently used as a sorbent for removal of uranium from aqueous solution. PMID:24099972

  4. Radiochemical study of the kinetics of crystal growth in gels

    NASA Astrophysics Data System (ADS)

    Cecal, Alexandru; Palamaru, Mircea; Juverdeanu, Anca; Giosan, Marcel

    1996-01-01

    A kinetic study was performed on nucleation and growth of crystals containing radioactive ions in gelatin and agar gels. The investigated crystals were: 60CoHPO 4, 60CoS, 60Co(OH) 2, 60Co(SCN) 2, 204Tl(OH) 3, and 204Tl[(C 2H 5) 2NCS 2] 3. The study shows that the crystal growth rate depends on the cation size and charge, the nature of anion as well as on the colloidal medium. The crystallisation process in the gel has two distinctive steps: diffusion of reactant ions in the gel followed by a chemical reaction which leads to nucleation of the crystal. Both steps are described quantitatively.

  5. Kinetic Study of the Combustion of Phosphorus Containing Species

    SciTech Connect

    Glaude, P.A.; Curran, H.J.; Pitz, W.J.; Westbrook, C.K.

    1999-10-22

    The combustion of organophosphorus compounds is of great interest for the incineration of chemical warfare agent and their use in flame inhibition as halon replacement. The thermochemical data of these species and the reactions involved at high temperature are not well known, despite some recent experimental studies. With BAC-MP4 ab initio estimations as a basis and semi-empirical estimations for many new compounds, the thermochemistry of organophosphorus compounds is studied. New group additivity values are proposed for enthalpies of formation at 298K, entropies and heat capacities of species involving pentavalent phosphorus bonded to carbon, hydrogen, oxygen, fluorine, nitrogen and sulfur atoms. The kinetic of unimolecular elimination is investigated by modeling pyrolysis experiments of DEMP, TEP and DIMP. A new combustion mechanism is described and applied to the modeling of DMMP reaction in a H{sub 2}/O{sub 2} flame.

  6. Calorimetric Studies of Precipitation and Dissolution Kinetics in Aluminum Alloys 2219 and 7075

    NASA Astrophysics Data System (ADS)

    Papazian, John M.

    1982-05-01

    Differential scanning calorimetry (DSC) was used to study the kinetics of precipitation and dissolution of metastable and stable phases in aluminum alloys 2219 and 7075. A comparison of DSC scans obtained at heating rates of 1, 5, 10, and 20 K per minute showed that, during a DSC scan, the rates of precipitation of θ' and θ in 2219 and η' and η in 7075 were limited by their reaction kinetics. Likewise, the rates of dissolution of GP zones, θ' and η', were found to be dominated by kinetics. In contrast, the dissolution of θ and η was dominated by the thermodynamic equilibrium between these phases and the matrix. Analysis of the kinetically dominated reaction peaks and their dependence on heating rate and particle size showed that the GP zone dissolution reaction could best be described by a three-dimensional volume diffusion limited rate expression with an activation energy equal to that for diffusion. The rate of formation of θ' was best described by an Avrami expression with n = 1.1, indicating that nucleation was not the rate controlling step. A pronounced dependence of the θ' formation rate on prior plastic deformation was observed and ascribed to the influence of the matrix dislocation density on diffusivity.

  7. Alkaline assisted thermal oil recovery: Kinetic and displacement studies

    SciTech Connect

    Saneie, S.; Yortsos, Y.C.

    1993-06-01

    This report deals with two major issues of chemical assisted flooding - the interaction of caustic, one of the proposed additives to steam flood, with the reservoir rock, and the displacement of oil by a chemical flood at elevated temperatures. A mathematical model simulating the kinetics of silica dissolution and hydroxyl ion consumption in a typical alkaline flooding environment is first developed. The model is based on the premise that dissolution occurs via hydrolysis of active sites through the formation of an intermediate complex, which is in equilibrium with the silicic acid in solution. Both static (batch) and dynamic (core flood) processes are simulated to examine the sensitivity of caustic consumption and silica dissolution to process parameters, and to determine rates of propagation of pH values. The model presented provides a quantitative description of the quartz-alkali interaction in terms of pH, salinity, ion exchange properties, temperature and contact time, which are of significant importance in the design of soluble silicate flooding processes. The modeling of an adiabatic hot waterflood assisted by the simultaneous injection of a chemical additive is next presented. The model is also applicable to the hot alkaline flooding under conditions of negligible adsorption of the generated anionic surfactant and of hydroxide adsorption being Langmuirian. The theory of generalized simple waves (coherence ) is used to develop solutions for the temperature, concentration, and oil saturation profiles, as well as the oil recovery curves. It is shown that, for Langmuir adsorption kinetics, the chemical resides in the heated region of the reservoir if its injection concentration is below a critical value, and in the unheated region if its concentration exceeds this critical value. Results for a chemical slug injection in a tertiary recovery process indicate recovery performance is maximized when chemical resides in the heated region of the reservior.

  8. Human alpha-thrombin inhibition by the active site titrant N alpha-(N,N-dimethylcarbamoyl)-alpha-azalysine p-nitrophenyl ester: a comparative kinetic and X-ray crystallographic study.

    PubMed

    Nardini, M; Pesce, A; Rizzi, M; Casale, E; Ferraccioli, R; Balliano, G; Milla, P; Ascenzi, P; Bolognesi, M

    1996-05-24

    Kinetics for the hydrolysis of the chromogenic active site titrant N alpha-(N,N-dimethylcarbamoyl)-alpha-azalysine p-nitrophenyl ester (Dmc-azaLys-ONp) catalyzed by bovine beta-trypsin, bovine alpha-thrombin, human alpha-thrombin, human Lys77-plasmin, human urinary kallikrein, the M(r) 33,000 and M(r) 54,000 species of human urokinase, as well as by porcine pancreatic beta-kallikrein-A and B have been obtained between pH 6.0 and 8.0, at 21.0 degrees C. Moreover, the three dimensional structure of the human alpha-thrombin-(hirugen).Dmc-azaLys acyl.enzyme complex has been analyzed and refined by X-ray crystallography at 2.0 A resolution (R-factor = 0.168). As observed for bovine beta-trypsin, the acylating inhibitor molecule is covalently bound to the Ser195 catalytic residue, filling the human alpha-thrombin S1 primary specificity subsite with its lysyl side-group. However, the carbonyl group of the scissile human alpha-thrombin.Dmc-azaLys acyl bond does not occupy properly the oxyanion binding hole. At variance from the bovine beta-trypsin.Dmc-azaLys acyl.enzyme structure, a second, not covalently bound, inhibitor molecule, partly shielded by the 60-insertion loop of human alpha-thrombin, is contacting the enzyme "aryl-binding site". PMID:8637015

  9. Chronic impact of tetracycline on nitrification kinetics and the activity of enriched nitrifying microbial culture.

    PubMed

    Katipoglu-Yazan, Tugce; Merlin, Christophe; Pons, Marie-Noëlle; Ubay-Cokgor, Emine; Orhon, Derin

    2015-04-01

    This study evaluated the chronic impact of tetracycline on biomass with enriched nitrifying community sustained in a lab-scale activated sludge system. For this purpose, a fill and draw reactor fed with 100 mg COD/L of peptone mixture and 50 mg N/L of ammonia was sustained at a sludge age of 15 days. At steady-state, the reactor operation was continued with a daily tetracycline dosing of 50 mg/L for more than 40 days, with periodic monitoring of the microbial composition, the nitrifying bacteria abundance, as well as the amoA and 16S rRNA gene activity, using molecular techniques. Changes in the kinetics of nitrification were quantified by modelling concentration profiles of major nitrogen fractions and oxygen uptake rate profiles derived from parallel batch experiments. Activated sludge modeling results indicated inhibitory impact of tetracycline on the growth of nitrifiers with a significant increase of the half saturation coefficients in corresponding rate equations. Tetracycline also inactivated biomass components of the enriched culture at a gradually increasing rate with time of exposure, leading to total collapse of nitrification. Molecular analyses revealed significant changes in the composition of the microbial community throughout the observation period. They also showed that continuous exposure to tetracycline inflicted significant reduction in amoA mRNA and 16S rRNA levels directly affecting nitrification. The chronic impact was much more pronounced on the ammonia oxidizing bacteria (AOB) community. These observations explained the basis of numerical changes identified in the growth kinetics of nitrifiers under stress conditions. PMID:25616640

  10. [Study on Chemical Kinetic Effect of Dielectric Barrier Discharge Plasma].

    PubMed

    Zrang, Peng; Hong, Yan-ji; Shen, Shuang-yan; Ding, Xiao-yu; Ma, Di

    2015-03-01

    To reveal the mechanism of plasma (assisted the ignition process of methane/air further, schematic of dielectric barrier discharge plasma system with atmospheric air was designed and set up, the emission spectrum of dielectric barrier discharge plasma with atmospheric air was measured, and the active particles produced by the interaction of dielectric barrier discharge plasma with atmospheric air were analyzed with the spectrum technology, the ignition model and calculation methods of sensitivity analysis and reaction path analysis were given, effects of NO and O3 on the ignition delay time were simulated, and the chemical kinetics mechanism of NO and O3 assisted ignition was revealed via sensitivity analysis and reaction path analysis. The results show that main excited particles of N2 and O3 are generated via effect of plasma on the atmospheric air, which are converted into active particles of NO(ξ) and O3 in the end, the life of which are longer than any other active particles, effects of plasma on the ignition is simplified as effects of NO(ξ) and O3 on the ignition; NO and O3 could reduce the ignition delay time significantly, but the amplitude decrease with increase of the initial temperature, this is because the rate of ignition is decided by the oxidation rate of CH3, the oxidized pathway of CH3 is R155 and R156 for auto-ignition and their rates are slower when temperature is low, so the ignition delay time of methane/air is longer; NO could reduce the ignition delay time significantly because of the oxidized pathway of CH3 is changed to R327 CH3O2 + NO = CH3O + NO2, R328 CH3 + NO2 = CH3O + NO for NO(ξ) (assisted ignition process from R155 and R156 for auto-ignition; and the chemical kinetic effect is the dominating factor of O3 on the ignition and which change the reaction path. PMID:26117883

  11. Kinetic Defects Induced by Melittin in Model Lipid Membranes: A Solution Atomic Force Microscopy Study.

    PubMed

    Pan, Jianjun; Khadka, Nawal K

    2016-05-26

    Quantitative characterization of membrane defects (pores) is important for elucidating the molecular basis of many membrane-active peptides. We study kinetic defects induced by melittin in vesicular and planar lipid bilayers. Fluorescence spectroscopy measurements indicate that melittin induces time-dependent calcein leakage. Solution atomic force microscopy (AFM) is used to visualize melittin-induced membrane defects. After initial equilibration, the most probable defect radius is ∼3.8 nm in 1,2-dilauroyl-sn-glycero-3-phosphocholine (DLPC) bilayers. Unexpectedly, defects become larger with longer incubation, accompanied by substantial shape transformation. The initial defect radius is ∼4.7 nm in 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) bilayers. Addition of 30 mol % cholesterol to DOPC bilayers suppresses defect kinetics, although the inhibitory impact is negated by longer incubation. Overall, the kinetic rate of defect development follows DLPC > DOPC > DOPC/cholesterol. Kinetic defects are also observed when anionic lipids are present. Based on the observation that defects can occupy as large as 40% of the bilayer surface, we propose a kinetic defect growth model. We also study the effect of melittin on the phase behavior of DOPC/egg-sphingomyelin/cholesterol bilayers. We find that melittin initially suppresses or eliminates liquid-ordered (Lo) domains; Lo domains gradually emerge and become the dominant species with longer incubation; and defects in phase-coexisting bilayers have a most probable radius of ∼5 nm and are exclusively localized in the liquid-disordered (Ld) phase. Our experimental data highlight that melittin-induced membrane defects are not static; conversely, spontaneous defect growth is intrinsically associated with membrane permeabilization exerted by melittin. PMID:27167473

  12. Kinetic characterisation and thermal inactivation study of red alga (Mastocarpus stellatus) peroxidase.

    PubMed

    Fortea, M I; López-Miranda, S; Serrano-Martínez, A; Hernández-Sánchez, P; Zafrilla, M P; Martínez-Cachá, A; Núñez-Delicado, E

    2011-08-01

    Peroxidase (POD) was extracted from red alga (Mastocarpus stellatus) using Triton X-114 and characterised by UV-spectrophotometry. Optimum activity using 2,2´-azinobis(3-ethylbenzothiazolinesulphonic acid) (ABTS) as the H-donor was obtained at pH 5.0. In the presence of the anionic detergent, sodium dodecyl sulphate (SDS), however, POD was inactivated at all the pH values studied and totally inactivated at 1mM SDS. When the enzyme was kinetically characterised, the KM and Vm values for ABTS were found to be 13mM and 40μM/min, respectively. In addition, when the H2O2 concentration was increased, at a fixed concentration of ABTS, the activity was inhibited at the highest H2O2 concentrations. In a study of the effect of several reducing agents, l-cysteine was found to be the most active. A thermal inactivation study showed a first-order inactivation kinetic, and the Arrhenius plot yielded a straight line with a slope equivalent to an activation energy of 121.6kJ/mol. Significant inactivation occurred at temperatures of>35°C, with>90% of the relative activity being lost after only 5min of incubation at 48.4°C. PMID:25214100

  13. Kinetic studies of interfacial photocurrents in platinized chloroplasts

    SciTech Connect

    Greenbaum, E.

    1992-12-01

    The present experiments focus on kinetic studies of phototocurrents generated in a photobioelectrochemical cell constructed from platinized chloroplast membranes. These chloroplast membranes although separated from the CO{sub 2}-reducing enzymes of the Calvin-Benson cycle, contain the full complement of photosystem I and II reaction centers along with the electron transport chain linking these two centers. The vectorial model of photosynthesis indicates that the orientation of the reaction centers in the photosynthetic membranes is such that electrons emerge from the membranes into the stroma region of the chloroplasts. Since the flattened saclike vesicles of the thylakoid membranes are topologically equivalent to spheres, it follows that, irrespective of the rotational orientation of the membranes, the photogenerated electrons emerge from the reaction centers in a radial direction away from the intra-thylakoid region.

  14. Kinetic study of lead adsorption to composite biopolymer adsorbent

    SciTech Connect

    Seki, H.; Suzuki, A.

    1999-03-15

    A kinetic study of lead adsorption to composite biopolymer adsorbents was carried out. Spherical and membranous adsorbents containing two biopolymers, humic acid and alginic acid, were used for lead adsorption in dilute acidic solutions. The shrinking core model derived by M.G. Rao and A.K. Gupta was applied to describe the rate process of lead adsorption to spherical adsorbents (average radii of 0.12, 0.15, and 0.16 cm). Furthermore, the shrinking core model was modified and adapted for description of the rate process of lead adsorption to membranous adsorbent (average thickness of 0.0216 cm). The adsorption rate process for both the cases was well described and average apparent lead diffusion coefficients of about 6 {times} 10{sup {minus}6} and 7 {times} 10{sup {minus}6} cm{sup 2}/s were found for the spherical and membranous adsorbents, respectively.

  15. Kinetic Study of Lead Adsorption to Composite Biopolymer Adsorbent.

    PubMed

    Seki; Suzuki

    1999-03-15

    A kinetic study of lead adsorption to composite biopolymer adsorbents was carried out. Spherical and membranous adsorbents containing two biopolymers, humic acid and alginic acid, were used for lead adsorption in dilute acidic solutions. The shrinking core model derived by M. G. Rao and A. K. Gupta (Chem. Eng. J. 24, 181, 1982) was applied to describe the rate process of lead adsorption to spherical adsorbents (average radii of 0.12, 0.15, and 0.16 cm). Furthermore, the shrinking core model was modified and adapted for description of the rate process of lead adsorption to membranous adsorbent (average thickness of 0.0216 cm). The adsorption rate process for the both cases was well described and average apparent lead diffusion coefficients of about 6 x 10(-6) and 7 x 10(-6) cm2 s-1 were found for the spherical and membranous adsorbents, respectively. Copyright 1999 Academic Press. PMID:10049553

  16. An Experimental and Kinetic Modeling Study of Methyl Decanoate Combustion

    SciTech Connect

    Sarathy, S M; Thomson, M J; Pitz, W J; Lu, T

    2010-02-19

    Biodiesel is typically a mixture of long chain fatty acid methyl esters for use in compression ignition engines. Improving biofuel engine performance requires understanding its fundamental combustion properties and the pathways of combustion. This research study presents new combustion data for methyl decanoate in an opposed-flow diffusion flame. An improved detailed chemical kinetic model for methyl decanoate combustion is developed, which serves as the basis for deriving a skeletal mechanism via the direct relation graph method. The novel skeletal mechanism consists of 648 species and 2998 reactions. This mechanism well predicts the methyl decanoate opposed-flow diffusion flame data. The results from the flame simulations indicate that methyl decanoate is consumed via abstraction of hydrogen atoms to produce fuel radicals, which lead to the production of alkenes. The ester moiety in methyl decanoate leads to the formation of low molecular weight oxygenated compounds such as carbon monoxide, formaldehyde, and ketene.

  17. PLK1 regulates spindle formation kinetics and APC/C activation in mouse zygote.

    PubMed

    Baran, Vladimir; Brzakova, Adela; Rehak, Pavol; Kovarikova, Veronika; Solc, Petr

    2016-06-01

    Polo-like kinase 1 (PLK1) is involved in essential events of cell cycle including mitosis in which it participates in centrosomal microtubule nucleation, spindle bipolarity establishment and cytokinesis. Although PLK1 function has been studied in cycling cancer cells, only limited data are known about its role in the first mitosis of mammalian zygotes. During the 1-cell stage of mouse embryo development, the acentriolar spindle is formed and the shift from acentriolar to centrosomal spindle formation progresses gradually throughout the preimplantation stage, thus providing a unique possibility to study acentriolar spindle formation. We have shown previously that PLK1 activity is not essential for entry into first mitosis, but is required for correct spindle formation and anaphase onset in 1-cell mouse embryos. In the present study, we extend this knowledge by employing quantitative confocal live cell imaging to determine spindle formation kinetics in the absence of PLK1 activity and answer the question whether metaphase arrest at PLK1-inhibited embryos is associated with low anaphase-promoting complex/cyclosome (APC/C) activity and consequently high securin level. We have shown that inhibition of PLK1 activity induces a delay in onset of acentriolar spindle formation during first mitosis. Although these PLK1-inhibited 1-cell embryos were finally able to form a bipolar spindle, not all chromosomes were aligned at the metaphase equator. PLK1-inhibited embryos were arrested in metaphase without any sign of APC/C activation with high securin levels. Our results document that PLK1 controls the onset of spindle assembly and spindle formation, and is essential for APC/C activation before anaphase onset in mouse zygotes. PMID:26174739

  18. Cross-metathesis of polynorbornene with polyoctenamer: a kinetic study

    PubMed Central

    Denisova, Yulia I; Gringolts, Maria L; Peregudov, Alexander S; Krentsel, Liya B; Litmanovich, Ekaterina A; Litmanovich, Arkadiy D; Finkelshtein, Eugene Sh

    2015-01-01

    Summary The cross-metathesis of polynorbornene and polyoctenamer in d-chloroform mediated by the 1st generation Grubbs’ catalyst Cl2(PCy3)2Ru=CHPh is studied by monitoring the kinetics of carbene transformation and evolution of the dyad composition of polymer chains with in situ 1H and ex situ 13C NMR spectroscopy. The results are interpreted in terms of a simple kinetic two-stage model. At the first stage of the reaction all Ru-benzylidene carbenes are transformed into Ru-polyoctenamers within an hour, while the polymer molar mass is considerably decreased. The second stage actually including interpolymeric reactions proceeds much slower and takes one day or more to achieve a random copolymer of norbornene and cyclooctene. Its rate is limited by the interaction of polyoctenamer-bound carbenes with polynorbornene units, which is hampered, presumably due to steric reasons. Polynorbornene-bound carbenes are detected in very low concentrations throughout the whole process thus indicating their higher reactivity, as compared with the polyoctenamer-bound ones. Macroscopic homogeneity of the reacting media is proved by dynamic light scattering from solutions containing the polymer mixture and its components. In general, the studied process can be considered as a new way to unsaturated multiblock statistical copolymers. Their structure can be controlled by the amount of catalyst, mixture composition, and reaction time. It is remarkable that this goal can be achieved with a catalyst that is not suitable for ring-opening metathesis copolymerization of norbornene and cis-cyclooctene because of their substantially different monomer reactivities. PMID:26664599

  19. Cross-metathesis of polynorbornene with polyoctenamer: a kinetic study.

    PubMed

    Denisova, Yulia I; Gringolts, Maria L; Peregudov, Alexander S; Krentsel, Liya B; Litmanovich, Ekaterina A; Litmanovich, Arkadiy D; Finkelshtein, Eugene Sh; Kudryavtsev, Yaroslav V

    2015-01-01

    The cross-metathesis of polynorbornene and polyoctenamer in d-chloroform mediated by the 1(st) generation Grubbs' catalyst Cl2(PCy3)2Ru=CHPh is studied by monitoring the kinetics of carbene transformation and evolution of the dyad composition of polymer chains with in situ (1)H and ex situ (13)C NMR spectroscopy. The results are interpreted in terms of a simple kinetic two-stage model. At the first stage of the reaction all Ru-benzylidene carbenes are transformed into Ru-polyoctenamers within an hour, while the polymer molar mass is considerably decreased. The second stage actually including interpolymeric reactions proceeds much slower and takes one day or more to achieve a random copolymer of norbornene and cyclooctene. Its rate is limited by the interaction of polyoctenamer-bound carbenes with polynorbornene units, which is hampered, presumably due to steric reasons. Polynorbornene-bound carbenes are detected in very low concentrations throughout the whole process thus indicating their higher reactivity, as compared with the polyoctenamer-bound ones. Macroscopic homogeneity of the reacting media is proved by dynamic light scattering from solutions containing the polymer mixture and its components. In general, the studied process can be considered as a new way to unsaturated multiblock statistical copolymers. Their structure can be controlled by the amount of catalyst, mixture composition, and reaction time. It is remarkable that this goal can be achieved with a catalyst that is not suitable for ring-opening metathesis copolymerization of norbornene and cis-cyclooctene because of their substantially different monomer reactivities. PMID:26664599

  20. Kinetic study of the inactivation of ascorbate peroxidase by hydrogen peroxide.

    PubMed Central

    Hiner, A N; Rodríguez-López, J N; Arnao, M B; Lloyd Raven, E; García-Cánovas, F; Acosta, M

    2000-01-01

    The activity of ascorbate peroxidase (APX) has been studied with H(2)O(2) and various reducing substrates. The activity decreased in the order pyrogallol>ascorbate>guaiacol>2, 2'-azino-bis-(3-ethylbenzthiazoline-6-sulphonic acid) (ABTS). The inactivation of APX with H(2)O(2) as the sole substrate was studied. The number of H(2)O(2) molecules required for maximal inactivation of the enzyme was determined as approx. 2.5. Enzymic activity of approx. 20% of the original remained at the end of the inactivation process (i.e. approx. 20% resistance) when ascorbate or ABTS was used as the substrate in activity assays. With pyrogallol or guaiacol no resistance was seen. Inactivation by H(2)O(2) followed over time with ascorbate or pyrogallol assays exhibited single-exponential decreases in enzymic activity. Hyperbolic saturation kinetics were observed in both assay systems; a similar dissociation constant (0.8 microM) for H(2)O(2) was obtained in each case. However, the maximum rate constant (lambda(max)) obtained from the plots differed depending on the assay substrate. The presence of reducing substrate in addition to H(2)O(2) partly or completely protected the enzyme from inactivation, depending on how many molar equivalents of reducing substrate were added. An oxygen electrode system has been used to confirm that APX does not exhibit a catalase-like oxygen-releasing reaction. A kinetic model was developed to interpret the experimental results; both the results and the model are compared and contrasted with previously obtained results for horseradish peroxidase C. The kinetic model has led us to the conclusion that the inactivation of APX by H(2)O(2) represents an unusual situation in which no enzyme turnover occurs but there is a partition of the enzyme between two forms, one inactive and the other with activity towards reducing substrates such as ascorbate and ABTS only. The partition ratio is less than 1. PMID:10816425

  1. Inhibitory effect of ebselen on cerebral acetylcholinesterase activity in vitro: kinetics and reversibility of inhibition.

    PubMed

    Martini, Franciele; Bruning, César Augusto; Soares, Suelen Mendonca; Nogueira, Cristina Wayne; Zeni, Gilson

    2015-01-01

    Ebselen is a synthetic organoselenium compound that has been considered a potential pharmacological agent with low toxicity, showing antioxidant, anti-inflammatory and neuroprotective effects. It is bioavailable, blood-brain barrier permeant and safe based on cellular toxicity and Phase I-III clinical trials. There is evidence that ebselen inhibits acetylcholinesterase (AChE) activity, an enzyme that plays a key role in the cholinergic system by hydrolyzing acetylcholine (ACh), in vitro and ex vivo. This system has a well-known relationship with cognitive process, and AChE inhibitors, such as donepezil and galantamine, have been used to treat cognitive deficits, mainly in the Alzheimer's Disease (AD). However, these drugs have poor bioavailability and a number of side effects, including gastrointestinal upsets and hepatotoxicity. In this way, this study aimed to evaluate the effect of ebselen on cerebral AChE activity in vitro and to determine the kinetic profile and the reversibility of inhibition by dialysis. Ebselen inhibited the cerebral AChE activity with an IC50 of 29 µM, similar to IC50 found with pure AChE from electric eel, demonstrating a mixed and reversible inhibition of AChE, since it increased Km and decreased Vmax. The AChE activity was recovered within 60 min of dialysis. Therefore, the use of ebselen as a therapeutic agent for treatment of AD should be considered, although memory behavior tasks are needed to support such hypothesis. PMID:25312723

  2. Activation Kinetics of Skinned Cardiac Muscle by Laser Photolysis of Nitrophenyl-EGTA

    PubMed Central

    Martin, Hunter; Bell, Marcus G.; Ellis-Davies, Graham C. R.; Barsotti, Robert J.

    2004-01-01

    The kinetics of Ca2+-induced contractions of chemically skinned guinea pig trabeculae was studied using laser photolysis of NP-EGTA. The amount of free Ca2+ released was altered by varying the output from a frequency-doubled ruby laser focused on the trabeculae, while maintaining constant total [NP-EGTA] and [Ca2+]. The time courses of the rise in stiffness and tension were biexponential at 23°C, pH 7.1, and 200 mM ionic strength. At full activation (pCa < 5.0), the rates of the rapid phase of the stiffness and tension rise were 56 ± 7 s−1 (n = 7) and 48 ± 6 s−1 (n = 11) while the amplitudes were 21 ± 2 and 23 ± 3%, respectively. These rates had similar dependencies on final [Ca2+] achieved by photolysis: 43 and 50 s−1 per pCa unit, respectively, over a range of [Ca2+] producing from 15% to 90% of maximal isometric tension. At all [Ca2+], the rise in stiffness initially was faster than that of tension. The maximal rates for the slower components of the rise in stiffness and tension were 4.1 ± 0.8 and 6.2 ± 1.0 s−1. The rate of this slower phase exhibited significantly less Ca2+ sensitivity, 1 and 4 s−1 per pCa unit for stiffness and tension, respectively. These data, along with previous studies indicating that the force-generating step in the cross-bridge cycle of cardiac muscle is marginally sensitive to [Ca2+], suggest a mechanism of regulation in which Ca2+ controls the attachment step in the cross-bridge cycle via a rapid equilibrium with the thin filament activation state. Myosin kinetics sets the time course for the rise in stiffness and force generation with the biexponential nature of the mechanical responses to steps in [Ca2+] arising from a shift to slower cross-bridge kinetics as the number of strongly bound cross-bridges increases. PMID:14747333

  3. Kinetic studies on the regulation of rabbit liver pyruvate kinase

    PubMed Central

    Irving, M. G.; Williams, J. F.

    1973-01-01

    Two kinetically distinct forms of pyruvate kinase (EC 2.7.1.40) were isolated from rabbit liver by using differential ammonium sulphate fractionation. The L or liver form, which is allosterically activated by fructose 1,6-diphosphate, was partially purified by DEAE-cellulose chromatography to give a maximum specific activity of 20 units/mg. The L form was allosterically activated by K+ and optimum activity was recorded with 30mm-K+, 4mm-MgADP−, with a MgADP−/ADP2− ratio of 50:1, but inhibition occurred with K+ concentrations in excess of 60mm. No inhibition occurred with either ATP or GTP when excess of Mg2+ was added to counteract chelation by these ligands. Alanine (2.5mm) caused 50% inhibition at low concentrations of phosphoenolpyruvate (0.15mm). The homotropic effector, phosphoenolpyruvate, exhibited a complex allosteric pattern (nH=2.5), and negative co-operative interactions were observed in the presence of low concentrations of this substrate. The degree of this co-operative interaction was pH-dependent, with the Hill coefficient increasing from 1.1 to 3.2 as the pH was raised from 6.5 to 8.0. Fructose 1,6-diphosphate interfered with the activation by univalent ions, markedly decreased the apparent Km for phosphoenolpyruvate from 1.2mm to 0.2mm, and transformed the phosphoenolpyruvate saturation curve into a hyperbola. Concentrations of fructose 1,6-diphosphate in excess of 0.5mm inhibited this stimulated reaction. The M or muscle-type form of the enzyme was not activated by fructose 1,6-diphosphate and gave a maximum specific activity of 0.3 unit/mg. A Michaelis–Menten response was obtained when phosphoenolpyruvate was the variable substrate (Km=0.125mm), and this form was inhibited by ATP, as well as alanine, even in the presence of excess of Mg2+. PMID:4722439

  4. Role of plasma activation in the kinetics of CNT growth in PECVD process

    NASA Astrophysics Data System (ADS)

    Lebedeva, Irina; Gavrikov, Alexey; Baranov, Alexey; Belov, Maxim; Knizhnik, Andrey; Potapkin, Boris; Sommerer, Timothy

    2009-10-01

    The work presents kinetic modeling of the effect of acceleration for the growth kinetics of carbon nanotubes by hydrocarbon gas mixture modification with plasma discharge. The plasma activation creates active species in hydrocarbon gas mixture, which can easily adsorb and dissociate on the catalyst surface. So plasma treatment of the gas mixture in the CVD process allows to increase the carbon supply rate by a few orders of magnitude compared to that in thermal CVD process. On the other hand, plasma can also provide etching of carbon species from the catalyst surface. To correctly reproduce both of these effects of plasma, the kinetic model of growth of carbon nanotubes is developed based on first-principles analysis of heterogeneous processes on the catalyst surface and detailed kinetics of gas phase chemistry. The model is used to compare the growth rates of carbon nanotubes in thermal and plasma-enhanced CVD processes and to determine critical gas pressures, at which CNT growth kinetics switches from the adsorption limitation to the limitation by reaction and diffusion on the catalyst.

  5. Reduction of Carbon Dioxide by a Molybdenum-Containing Formate Dehydrogenase: A Kinetic and Mechanistic Study.

    PubMed

    Maia, Luisa B; Fonseca, Luis; Moura, Isabel; Moura, José J G

    2016-07-20

    Carbon dioxide accumulation is a major concern for the ecosystems, but its abundance and low cost make it an interesting source for the production of chemical feedstocks and fuels. However, the thermodynamic and kinetic stability of the carbon dioxide molecule makes its activation a challenging task. Studying the chemistry used by nature to functionalize carbon dioxide should be helpful for the development of new efficient (bio)catalysts for atmospheric carbon dioxide utilization. In this work, the ability of Desulfovibrio desulfuricans formate dehydrogenase (Dd FDH) to reduce carbon dioxide was kinetically and mechanistically characterized. The Dd FDH is suggested to be purified in an inactive form that has to be activated through a reduction-dependent mechanism. A kinetic model of a hysteretic enzyme is proposed to interpret and predict the progress curves of the Dd FDH-catalyzed reactions (initial lag phase and subsequent faster phase). Once activated, Dd FDH is able to efficiently catalyze, not only the formate oxidation (kcat of 543 s(-1), Km of 57.1 μM), but also the carbon dioxide reduction (kcat of 46.6 s(-1), Km of 15.7 μM), in an overall reaction that is thermodynamically and kinetically reversible. Noteworthy, both Dd FDH-catalyzed formate oxidation and carbon dioxide reduction are completely inactivated by cyanide. Current FDH reaction mechanistic proposals are discussed and a different mechanism is here suggested: formate oxidation and carbon dioxide reduction are proposed to proceed through hydride transfer and the sulfo group of the oxidized and reduced molybdenum center, Mo(6+)═S and Mo(4+)-SH, are suggested to be the direct hydride acceptor and donor, respectively. PMID:27348246

  6. Thermodynamic and kinetic study of phenol degradation by a non-catalytic wet air oxidation process.

    PubMed

    Lefèvre, Sébastien; Boutin, Olivier; Ferrasse, Jean-Henry; Malleret, Laure; Faucherand, Rémy; Viand, Alain

    2011-08-01

    This work is dedicated to an accurate evaluation of thermodynamic and kinetics aspects of phenol degradation using wet air oxidation process. Phenol is a well known polluting molecule and therefore it is important having data of its behaviour during this process. A view cell is used for the experimental study, with an internal volume of 150 mL, able to reach pressures up to 30 MPa and temperatures up to 350°C. Concerning the thermodynamic phase equilibria, experimental and modelling results are obtained for different binary systems (water/nitrogen, water/air) and ternary system (water/nitrogen/phenol). The best model is the Predictive Soave Redlich Kwong one. This information is necessary to predict the composition of the gas phase during the process. It is also important for an implementation in a process simulation. The second part is dedicated to kinetics evaluation of the degradation of phenol. Different compounds have been detected using GC coupled with a MS. A kinetic scheme is deduced, taking into account the evolution of phenol, hydroquinones, catechol, resorcinol and acetic acid. The kinetic parameters are calculated for this scheme. These data are important to evaluate the evolution of the concentration of the different polluting molecules during the process. A simplified kinetic scheme, which can be easily implemented in a process simulation, is also determined for the direct degradation of phenol into H(2)O and CO(2). The Arrhenius law data obtained for the phenol disappearance are the following: k=1.8×10(6)±3.9×10(5)M(-1)s(-1) (pre-exponential factor) and E(a)=77±8 kJ mol(-1) (activation energy). PMID:21700312

  7. CCN Activity, Hygroscopicity, and Droplet Activation Kinetics of Secondary Organic Aerosol Resulting from the 2010 Gulf Oil Spill

    NASA Astrophysics Data System (ADS)

    Moore, R.; Lathem, T. L.; Cerully, K.; Bahreini, R.; Brock, C. A.; Langridge, J. M.; Middlebrook, A. M.; Nenes, A.; Calnex Science Team

    2010-12-01

    We present an analysis of the hygroscopicity and droplet activation kinetics of cloud condensation nuclei (CCN) sampled onboard the National Oceanic and Atmospheric Administration WP-3D aircraft downwind of the Deepwater Horizon oil spill site on June 8th and 10th, 2010. This set of measurements provides a unique case study for assessing in-situ the impact of fresh, hydrocarbonlike aerosols, which are expected to be formed via gas-to-particle conversion of the semi-volatile vapors released from oil evaporation. Similar hydrocarbon-rich aerosols constitute an important local emissions source in urban areas, but often coexist as an external/partially-internal mixture with more-oxidized, aged organic and sulfate aerosol. The DWH site provides the means to study the hygroscopic properties of these less-oxidized organic aerosols above a cleaner environmental background typical of marine environments in order to better discern their contribution to CCN activity and droplet growth. Measurements were performed with a Droplet Measurement Technologies Streamwise, Thermal-Gradient CCN counter, operating both as a counter (s=0.3%) and as a spectrometer (s=0.2-0.6%) using the newly-developed Scanning Flow CCN Analysis (SFCA) technique [1]. The instrument measures both the number concentration of particles able to nucleate droplets and also their resulting droplet sizes. The measured size information combined with a comprehensive computational fluid dynamics instrument model enables us to determine the rate of water uptake onto the particles and parameterize it in terms of an effective mass transfer coefficient [2], a key parameter needed to predict the number of activated droplets in ambient clouds. Non-refractory aerosol chemical composition was measured with an Aerodyne compact time-of-flight aerosol mass spectrometer. It was observed that the aerosols sampled downwind of the site on both days were composed predominantly of organics with a low degree of oxidation and low

  8. Equilibrium and kinetic modeling of contaminant immobilization by activated carbon amended to sediments in the field.

    PubMed

    Rakowska, Magdalena I; Kupryianchyk, Darya; Koelmans, Albert A; Grotenhuis, Tim; Rijnaarts, Huub H M

    2014-12-15

    Addition of activated carbons (AC) to polluted sediments and soils is an attractive remediation technique aiming at reducing pore water concentrations of hydrophobic organic contaminants (HOCs). In this study, we present (pseudo-)equilibrium as well as kinetic parameters for sorption of a series of PAHs and PCBs to powdered and granular activated carbons (AC) after three different sediment treatments: sediment mixed with powdered AC (PAC), sediment mixed with granular AC (GAC), and addition of GAC followed by 2 d mixing and subsequent removal ('sediment stripping'). Remediation efficiency was assessed by quantifying fluxes of PAHs towards SPME passive samplers inserted in the sediment top layer, which showed that the efficiency decreased in the order of PAC > GAC stripping > GAC addition. Sorption was very strong to PAC, with Log KAC (L/kg) values up to 10.5. Log KAC values for GAC ranged from 6.3-7.1 and 4.8-6.2 for PAHs and PCBs, respectively. Log KAC values for GAC in the stripped sediment were 7.4-8.6 and 5.8-7.7 for PAH and PCB. Apparent first order adsorption rate constants for GAC (kGAC) in the stripping scenario were calculated with a first-order kinetic model and ranged from 1.6 × 10(-2) (PHE) to 1.7 × 10(-5) d(-1) (InP). Sorption affinity parameters did not change within 9 months post treatment, confirming the longer term effectiveness of AC in field applications for PAC and GAC. PMID:25262554

  9. Stoichiometric and kinetic studies of phenolic antioxidants from Andean purple corn and red-fleshed sweetpotato.

    PubMed

    Cevallos-Casals, Bolívar A; Cisneros-Zevallos, Luis

    2003-05-21

    Stoichiometric and kinetic values of phenolics against DPPH (2,2-diphenyl-1-picrylhydrazyl) were determined for Andean purple corn (Zea mays L.) and red sweetpotato (Ipomoea batatas). Both crops had higher antioxidant capacity and antiradical kinetics than blueberries and higher or similar anthocyanin and phenolic contents. The second-order rate constant (k(2)) was 1.56, 1.12, 0.57, and 0.26 (mg antiradical/mL)(-1) s(-1) for red sweetpotato, Trolox, purple corn, and blueberry, respectively. On the molar basis of active hydroxyl groups, k(2)' showed the same order as for k(2). Corn cob and sweetpotato endodermis contributed the most in phenolic compounds and antioxidant capacity. Both crops studied can be considered as excellent novel sources of natural antioxidants for the functional food and dietary supplement markets. PMID:12744660

  10. Kinetics of Methane Hydrate Decomposition Studied via in Situ Low Temperature X-ray Powder Diffraction

    SciTech Connect

    Everett, Susan M; Rawn, Claudia J; Keffer, David J.; Mull, Derek L; Payzant, E Andrew; Phelps, Tommy Joe

    2013-01-01

    Gas hydrates are known to have a slowed decomposition rate at ambient pressure and temperatures below the melting point of ice termed self-preservation or anomalous preservation. As hydrate exothermically decomposes, gas is released and water of the clathrate cages transforms into ice. Two regions of slowed decomposition for methane hydrate, 180 200 K and 230 260 K, were observed, and the kinetics were studied by in situ low temperature x-ray powder diffraction. The kinetic constants for ice formation from methane hydrate were determined by the Avrami model within each region and activation energies, Ea, were determined by the Arrhenius plot. Ea determined from the data for 180 200 K was 42 kJ/mol and for 230 260 K was 22 kJ/mol. The higher Ea in the colder temperature range was attributed to a difference in the microstructure of ice between the two regions.

  11. Negative activation enthalpies in the kinetics of protein folding.

    PubMed

    Oliveberg, M; Tan, Y J; Fersht, A R

    1995-09-12

    Although the rates of chemical reactions become faster with increasing temperature, the converse may be observed with protein-folding reactions. The rate constant for folding initially increases with temperature, goes through a maximum, and then decreases. The activation enthalpy is thus highly temperature dependent because of a large change in specific heat (delta Cp). Such a delta Cp term is usually presumed to be a consequence of a large decrease in exposure of hydrophobic surfaces to water as the reaction proceeds from the denatured state to the transition state for folding: the hydrophobic side chains are surrounded by "icebergs" of water that melt with increasing temperature, thus making a large contribution to the Cp of the denatured state and a smaller one to the more compact transition state. The rate could also be affected by temperature-induced changes in the conformational population of the ground state: the heat required for the progressive melting of residual structure in the denatured state will contribute to delta Cp. By examining two proteins with different refolding mechanisms, we are able to find both of these two processes; barley chymotrypsin inhibitor 2, which refolds from a highly unfolded state, fits well to a hydrophobic interaction model with a constant delta Cp of activation, whereas barnase, which refolds from a more structured denatured state, deviates from this ideal behavior. PMID:7568045

  12. Employing Magnetic Levitation to Monitor Reaction Kinetics and Measure Activation Energy

    ERIC Educational Resources Information Center

    Benz, Lauren; Cesafsky, Karen E.; Le, Tran; Park, Aileen; Malicky, David

    2012-01-01

    This article describes a simple and inexpensive undergraduate-level kinetics experiment that uses magnetic levitation to monitor the progress and determine the activation energy of a condensation reaction on a polymeric solid support. The method employs a cuvette filled with a paramagnetic solution positioned between two strong magnets. The…

  13. A kinetic study of the polymorphic transformation of nimodipine and indomethacin during high shear granulation.

    PubMed

    Guo, Zhen; Ma, Mingxin; Wang, Tianyi; Chang, Di; Jiang, Tongying; Wang, Siling

    2011-06-01

    The objective of the present study was to investigate the mechanism, kinetics, and factors affecting the polymorphic transformation of nimodipine (NMD) and indomethacin (IMC) during high shear granulation. Granules containing active pharmaceutical ingredient, microcrystalline cellulose, and low-substituted hydroxypropylcellulose were prepared with ethanolic hydroxypropylcellulose solution, and the effects of independent process variables including impeller speed and granulating temperature were taken into consideration. Two polymorphs of the model drugs and granules were characterized by X-ray powder diffraction analysis and quantitatively determined by differential scanning calorimetry. A theoretical kinetic method of ten kinetic models was applied to analyze the polymorphic transformation of model drugs. The results obtained revealed that both the transformation of modification I to modification II of NMD and the transformation of the α form to the γ form of IMC followed a two-dimensional nuclei growth mechanism. The activation energy of transformation was calculated to be 7.933 and 56.09 kJ·mol(-1) from Arrhenius plot, respectively. Both the granulating temperature and the impeller speed affected the transformation rate of the drugs and, in particular, the high shear stress significantly accelerated the transformation process. By analyzing the growth mechanisms of granules in high-shear mixer, it was concluded that the polymorphic transformation of NMD and IMC took place in accordance with granule growth in a high-shear mixer. PMID:21553164

  14. Denitrification kinetics in anoxic/aerobic activated sludge systems

    SciTech Connect

    Horne, G.M.

    1998-12-11

    Nitrogen removal needs at municipal wastewater treatment plants (WWTPs) have increased due to greater concerns about eutrophication and increased interest in reuse of treated municipal effluents. Biological processes are the most cost-effective method for nitrogen removal. Biological nitrogen removal is accomplished in two distinctly different processes by the conversion of nitrogen in the wastewater from organic nitrogen and ammonia to nitrate, followed by reduction of the nitrate to nitrogen gas. Nitrate production occurs in an aerobic activated sludge treatment zone during a process called nitrification. The nitrate is then converted through a series of intermediate steps to nitrogen gas in an anoxic zone (an anaerobic condition with nitrate present) during a process called denitrification, effectively removing the nitrogen from the wastewater. Many different WWTP designs have been developed to incorporate these two conditions for nitrogen removal.

  15. The kinetics of ulvoespinel reduction - Synthetic study and applications to lunar rocks.

    NASA Technical Reports Server (NTRS)

    Mccallister, R. H.; Taylor, L. A.

    1973-01-01

    The kinetics of Fe2TiO4 reduction to FeTiO3 + Fe were studied using CO-CO2 gas mixtures with fO2 measured by a solid ceramic (calcia-zirconia) oxygen electrolyte cell. Isothermal rate studies at 900 C suggest that the mechanism of Fe2TiO4 reduction is one of nucleation and growth, where the growth stage may be controlled by the diffusion of the reactant through the product layer or volume diffusion. The activation energy for the growth stage of the process was determined to be 46 plus or minus 4 kcal/mole.

  16. Analysing properties of proteasome inhibitors using kinetic and X-ray crystallographic studies.

    PubMed

    Gallastegui, Nerea; Groll, Michael

    2012-01-01

    The combination of X-ray crystallography and kinetic studies of proteasome:ligand complexes has proven to be an important tool in inhibitor analysis of this crucial protein degradation machinery. Here, we describe in detail the purification protocols, proteolytic activity assays, crystallisation methods, and structure determination for the yeast 20S proteasome (CP) in complex with its inhibitors. The fusion of these advanced techniques offers the opportunity to further optimise drugs which are already tested in different clinical phase studies, as well as to design new promising proteasome lead structures which might be suitable for their application in medicine, plant protection, and antibiotics. PMID:22350899

  17. Penicillin V acylase from Pectobacterium atrosepticum exhibits high specific activity and unique kinetics.

    PubMed

    Avinash, V S; Ramasamy, Sureshkumar; Suresh, C G; Pundle, Archana

    2015-08-01

    Penicillin V acylases (PVAs, E.C.3.5.11) belong to the Ntn hydrolase super family of enzymes that catalyze the deacylation of the side chain from phenoxymethyl penicillin (penicillin V). Penicillin acylases find use in the pharmaceutical industry for the production of semi-synthetic antibiotics. PVAs employ the N-terminal cysteine residue as catalytic nucleophile and are structurally and evolutionarily related to bile salt hydrolases (BSHs). Here, we report the cloning and characterization of a PVA enzyme from the Gram-negative plant pathogen, Pectobacterium atrosepticum (PaPVA). The enzyme was cloned and expressed in Escherichia coli attaining a very high yield (250 mg/l) and a comparatively high specific activity (430 IU/mg). The enzyme showed marginally better pH and thermo-stability over PVAs characterized from Gram-positive bacteria. The enzyme also showed enhanced activity in presence of organic solvents and detergents. The enzyme kinetics turned out to be significantly different from that of previously reported PVAs, displaying positive cooperativity and substrate inhibition. The presence of bile salts had a modulating effect on PaPVA activity. Sequence analysis and characterization reveal the distinctive nature of these enzymes and underscore the need to study PVAs from Gram-negative bacteria. PMID:25931393

  18. Kinetics of exercise-induced neural activation; interpretive dilemma of altered cerebral perfusion.

    PubMed

    Miyazawa, Taiki; Horiuchi, Masahiro; Ichikawa, Daisuke; Sato, Kohei; Tanaka, Naoki; Bailey, Damian M; Ogoh, Shigehiko

    2012-02-01

    Neural activation decreases cerebral deoxyhaemoglobin (HHb(C)) and increases oxyhaemoglobin concentration (O(2)Hb(C)). In contrast, patients who present with restricted cerebral blood flow, such as those suffering from cerebral ischaemia or Alzheimer's disease, and during the course of ageing the converse occurs, in that HHb(C) increases and O(2)Hb(C) decreases during neural activation. In the present study, we examined the interpretive implications of altered exercise-induced cerebral blood flow for cortical oxygenation in healthy subjects. Both O(2)Hb(C) and HHb(C) (prefrontal cortex) were determined in 11 healthy men using near-infrared spectroscopy (NIRS). Middle cerebral artery mean blood velocity (MCA V(mean)) was determined via transcranial Doppler ultrasonography. Measurements were performed during contralateral hand-grip exercise during suprasystolic bilateral thigh-cuff occlusion (Cuff+) and within 2 s of cuff release (Cuff-) for the acute manipulation of cerebral perfusion. During Cuff+, both MCA V(mean) and O(2)Hb(C) increased during exercise, whereas HHb(C) decreased. In contrast, the opposite occurred during the Cuff- manipulation. These findings highlight the inverse relationship between cerebral blood flow and cerebral oxygenation as determined by NIRS, which has interpretive implications for the kinetics underlying exercise-induced neural activation. PMID:22041980

  19. Kinetic modeling and docking study of immobilized lipase catalyzed synthesis of furfuryl acetate.

    PubMed

    Mathpati, Ashwini C; Badgujar, Kirtikumar C; Bhanage, Bhalchandra M

    2016-03-01

    The present work deals with the kinetic modeling and docking study for the furfuryl acetate synthesis using immobilized Burkholderia cepacia (BCL) lipase. Initially various lipases were immobilized on hydroxypropyl methyl cellulose (HPMC) and poly vinyl alcohol (PVA) base hybrid polymer matrix. After screening of various immobilized biocatalysts, HPMC:PVA:BCL was found to be a robust biocatalyst. Various reaction conditions were optimized using response surface methodology (RSM) based on a four-factor-three-level Box-Behnken design. The optimal conditions were obtained at molar ratio of 1:2 of furfuryl alcohol to acyl donor, temperature 50°C with catalyst loading of 30mg in 3mL of non-aqueous media toluene. Under these conditions 99.98% yield was obtained in 3h. The Arrhenius plot showed that the activation energy for furfuryl acetate synthesis was 10.68kcal/mol. The kinetics of reaction was studied close to optimized conditions which obey order bi-bi model. Molecular docking study was carried out to understand the active site of BCL which is responsible for the reaction. It was observed that the reaction proceeds via acylation of the active serine of BCL and demonstrating strong hydrogen bond between the substrate and histidine site. The catalyst recyclability study was carried up to five cycles. PMID:26827768

  20. An improved pyrite pretreatment protocol for kinetic and isotopic studies

    NASA Astrophysics Data System (ADS)

    Mirzoyan, Natella; Kamyshny, Alexey; Halevy, Itay

    2014-05-01

    An improved pyrite pretreatment protocol for kinetic and isotopic studies Natella Mirzoyan1, Alexey Kamyshny Jr.2, Itay Halevy1 1Earth and Planetary Sciences, Weizmann Institute of Science, Rehovot 76100, Israel 2Geological and Environmental Sciences, Ben-Gurion University of the Negev, Beer Sheva 84105, Israel Pyrite is one of the most abundant and widespread of the sulfide minerals with a central role in biogeochemical cycles of iron and sulfur. Due to its diverse roles in the natural and anthropogenic sulfur cycle, pyrite has been extensively studied in various experimental investigations of the kinetics of its dissolution and oxidation, the isotopic fractionations associated with these reactions, and the microbiological processes involved. Pretreatment of pyrite for removal of oxidation impurities to prevent experimental artifacts and inaccuracies is often practiced. While numerous pyrite-cleaning methods have been used in experiments, a common pyrite pretreatment method, often used to investigate pyrite chemistry by the isotopic fractionations associated with it, includes several rinses by HCl, acetone and deionized water. Elemental sulfur (S0) is a common product of incomplete pyrite oxidation. Removal of S0 is desirable to avoid experimental biases associated with its participation in pyrite transformations, but is more complicated than the removal of sulfate. Although rinsing with an organic solvent is in part aimed at removing S0, to the best of our knowledge, the extraction efficiency of S0 in existing protocols has not been assessed. We have developed and tested a new protocol for elemental sulfur removal from the surface of pyrite by ultrasonication with warm acetone. Our data demonstrate the presence of large fractions of S0 on untreated pyrite particle surfaces, of which only approximately 60% was removed by the commonly used pretreatment method. The new protocol described here was found to be more efficient at S0 removal than the commonly used method

  1. Effect of heating rate and kinetic model selection on activation energy of nonisothermal crystallization of amorphous felodipine.

    PubMed

    Chattoraj, Sayantan; Bhugra, Chandan; Li, Zheng Jane; Sun, Changquan Calvin

    2014-12-01

    The nonisothermal crystallization kinetics of amorphous materials is routinely analyzed by statistically fitting the crystallization data to kinetic models. In this work, we systematically evaluate how the model-dependent crystallization kinetics is impacted by variations in the heating rate and the selection of the kinetic model, two key factors that can lead to significant differences in the crystallization activation energy (Ea ) of an amorphous material. Using amorphous felodipine, we show that the Ea decreases with increase in the heating rate, irrespective of the kinetic model evaluated in this work. The model that best describes the crystallization phenomenon cannot be identified readily through the statistical fitting approach because several kinetic models yield comparable R(2) . Here, we propose an alternate paired model-fitting model-free (PMFMF) approach for identifying the most suitable kinetic model, where Ea obtained from model-dependent kinetics is compared with those obtained from model-free kinetics. The most suitable kinetic model is identified as the one that yields Ea values comparable with the model-free kinetics. Through this PMFMF approach, nucleation and growth is identified as the main mechanism that controls the crystallization kinetics of felodipine. Using this PMFMF approach, we further demonstrate that crystallization mechanism from amorphous phase varies with heating rate. PMID:25351553

  2. Effect of electric current frequency on the activation kinetics of raw charcoal

    SciTech Connect

    Shevchenko, A.O.; Ivakhnyuk, G.K.; Fedorov, N.F.

    1993-12-10

    The effect of electric current frequency on the kinetics of raw charcoal activation with water vapor has been investigated. It was established that under the effect of alternating current the rate constant increases under otherwise equal conditions. A dependence of the reaction rate on the current frequency was found. It was discovered that under the effect of alternating current the activation energy of interaction with water vapor diminishes.

  3. A Validity Study of the Kinetic School Drawing Technique.

    ERIC Educational Resources Information Center

    Prout, H. Thompson; Celmer, David S.

    1984-01-01

    Examined the relationship between Kinetic School Drawing responses and academic achievement in 100 normal fifth-grade students. Significant correlations were found for a number of measures, generally supporting the validity of the technique. (JAC)

  4. Kinetic Study to Predict Sigma Phase Formation in Duplex Stainless Steels

    NASA Astrophysics Data System (ADS)

    dos Santos, Daniella Caluscio; Magnabosco, Rodrigo

    2016-04-01

    This work presents an improved kinetic study of sigma phase formation during isothermal aging between 973 K and 1223 K (700 °C and 950 °C), based on Kolmogorov-Johnson-Mehl-Avrami (K-J-M-A) model, established from volume fraction of sigma phase determined in backscattered electron images over polished surfaces of aged samples. The kinetic study shows a change in the main mechanism of sigma formation between 973 K and 1173 K (700 °C and 900 °C), from a nucleation-governed stage to a diffusion-controlled growth-coarsening stage, confirmed by a double inclination in K-J-M-A plots and microstructural observations. A single inclination in K-J-M-A plots was observed for the 1223 K (950 °C) aging temperature, showing that kinetic behavior in this temperature is only related to diffusion-controlled growth of sigma phase. The estimated activation energies for the nucleation of sigma phase are close to the molybdenum diffusion in ferrite, probably the controlling mechanism of sigma phase nucleation. The proposed time-temperature-transformation (TTT) diagram shows a "double c curve" configuration, probably associated to the presence of chi-phase formed between 973 K and 1073 K (700 °C and 800 °C), which acts as heterogeneous nuclei for sigma phase formation in low aging temperatures.

  5. Combustion Research Program: Flame studies, laser diagnostics, and chemical kinetics

    SciTech Connect

    Crosley, D.R.

    1992-09-01

    This project has comprised laser flame diagnostic experiments, chemical kinetics measurements, and low pressure flame studies. Collisional quenching has been investigated for several systems: the OH radical, by H{sub 2}0 in low pressure flames; the rotational level dependence for NH, including measurements to J=24; and of NH{sub 2} at room temperature. Transition probability measurements for bands involving v{prime} = 2 and 3 of the A-X system of OH were measured in a flame. Laser-induced fluorescence of vinyl radicals was unsuccessfully attempted. RRKM and transition state theory calculations were performed on the OH + C{sub 2}H{sub 4} reaction, on the t-butyl radical + HX; and transition state theory has been applied to a series of bond scission reactions. OH concentrations were measured quantitatively in low pressure H{sub 2}/N{sub 2}O and H{sub 2}/O{sub 2} flames, and the ability to determine spatially precise flame temperatures accurately using OH laser-induced fluorescence was studied.

  6. Structural and Kinetic Studies of Formate Dehydrogenase from Candida boidinii.

    PubMed

    Guo, Qi; Gakhar, Lokesh; Wickersham, Kyle; Francis, Kevin; Vardi-Kilshtain, Alexandra; Major, Dan T; Cheatum, Christopher M; Kohen, Amnon

    2016-05-17

    The structure of formate dehydrogenase from Candida boidinii (CbFDH) is of both academic and practical interests. First, this enzyme represents a unique model system for studies on the role of protein dynamics in catalysis, but so far these studies have been limited by the availability of structural information. Second, CbFDH and its mutants can be used in various industrial applications (e.g., CO2 fixation or nicotinamide recycling systems), and the lack of structural information has been a limiting factor in commercial development. Here, we report the crystallization and structural determination of both holo- and apo-CbFDH. The free-energy barrier for the catalyzed reaction was computed and indicates that this structure indeed represents a catalytically competent form of the enzyme. Complementing kinetic examinations demonstrate that the recombinant CbFDH has a well-organized reactive state. Finally, a fortuitous observation has been made: the apoenzyme crystal was obtained under cocrystallization conditions with a saturating concentration of both the cofactor (NAD(+)) and inhibitor (azide), which has a nanomolar dissociation constant. It was found that the fraction of the apoenzyme present in the solution is less than 1.7 × 10(-7) (i.e., the solution is 99.9999% holoenzyme). This is an extreme case where the crystal structure represents an insignificant fraction of the enzyme in solution, and a mechanism rationalizing this phenomenon is presented. PMID:27100912

  7. Dusty Plasmas - Kinetic Studies of Strong Coupling Phenomena

    NASA Astrophysics Data System (ADS)

    Morfill, Gregor

    2011-10-01

    ``Dusty plasmas'' can be found almost everywhere - in the interstellar medium, in star and planet formation, in the solar system in the Earth's atmosphere and in the laboratory. In astrophysical plasmas the dust component accounts for only about 1% of the mass, nevertheless this component has a profound influence on the thermodynamics, the chemistry and the dynamics. Important physical processes are charging, sputtering, cooling, light absorption and radiation pressure, connecting electromagnetic forces to gravity. Surface chemistry is another important aspect. In the laboratory there is great interest in industrial processes (e.g. etching, vapor deposition) and at the fundamental physics level - the main topic here - the study of strong coupling phenomena. Here the dust (or microparticles) are the dominant component of the multi-species plasma. The particles can be observed in real time and pace, individually resolved at all relevant length and time scales. This provides an unprecedented means for studying self-organisation processes in many particle systems including the onset of cooperative phenomena. Due to the comparatively large mass of the microparticles (10-12 to 10-9 g) precision experiments are performed on the ISS. The following topics will be discussed: Phase transitions, phase separation, electrorheology, flow phenomena including the onset of turbulence at the kinetic level.

  8. Determination of Phosphate-activated Glutaminase Activity and Its Kinetics in Mouse Tissues using Metabolic Mapping (Quantitative Enzyme Histochemistry)

    PubMed Central

    Botman, Dennis; Tigchelaar, Wikky

    2014-01-01

    Phosphate-activated glutaminase (PAG) converts glutamine to glutamate as part of the glutaminolysis pathway in mitochondria. Two genes, GLS1 and GLS2, which encode for kidney-type PAG and liver-type PAG, respectively, differ in their tissue-specific activities and kinetics. Tissue-specific PAG activity and its kinetics were determined by metabolic mapping using a tetrazolium salt and glutamate dehydrogenase as an auxiliary enzyme in the presence of various glutamine concentrations. In kidney and brain, PAG showed Michaelis-Menten kinetics with a Km of 0.6 mM glutamine and a Vmax of 1.1 µmol/mL/min when using 5 mM glutamine. PAG activity was high in the kidney cortex and inner medulla but low in the outer medulla, papillary tip, glomeruli and the lis of Henle. In brain tissue sections, PAG was active in the grey matter and inactive in myelin-rich regions. Liver PAG showed allosteric regulation with a Km of 11.6 mM glutamine and a Vmax of 0.5 µmol/mL/min when using 20 mM glutamine. The specificity of the method was shown after incubation of brain tissue sections with the PAG inhibitor 6-diazo-5-oxo-L-norleucine. PAG activity was decreased to 22% in the presence of 2 mM 6-diazo-5-oxo-L-norleucine. At low glutamine concentrations, PAG activity was higher in periportal regions, indicating a lower Km for periportal PAG. When compared with liver, kidney and brain, other tissues showed 3-fold to 6-fold less PAG activity. In conclusion, PAG is mainly active in mouse kidney, brain and liver, and shows different kinetics depending on which type of PAG is expressed. PMID:25163927

  9. Educational activities of CAREER: Crystallization Kinetics in Volcanology

    NASA Astrophysics Data System (ADS)

    Hammer, J. E.

    2011-12-01

    Professional development of teachers is recognized as critical for improving student learning outcomes. The major outreach initiative of my CAREER award was to develop a teacher professional development program for middle school (grades 6-8) teachers that would improve teacher's mastery of geoscience and basic science skills and practices and expose them to an authentic research environment. The explicit objectives of the Research Experience for Teachers in Volcano-Petrology (RET/V-P) were for teachers to (1) master technical skills for safe and productive laboratory work, (2) deepen understanding of science content, (3) develop scientific "habits of the mind" as outlined in the National Science Standards, and (4) hone science communication skills. Six teachers, one undergraduate, and two graduate students participated in the teacher professional development program during the summers of the CAREER award period. A subsequent EAR award now supports the program, and summer 2011 saw the participation of five additional teachers. The teachers span a wide range of educational backgrounds, prior exposure to geoscience, and teaching assignments at public and private schools. Each year, the program was modified using formative and summative evaluation tools to better serve the scheduling needs and content preferences. In general, the program has evolved from an emphasis on research exposure to an emphasis on imparting basic geoscience concepts. A myriad of approaches including field trips to local outcrops, lecture tutorials and lecture-based active engagement exercises (such as iclicker delivery of Geoscience Concept Inventory questions), with a taste of laboratory work (crystal growth experiments, optics primer), has emerged as the most successful means of achieving objectives 1-4, above. The first summer I advertised the RET/V-P, no teachers applied. (This challenge was overcome in subsequent years by targeting the solicitation using teacher list serves, the Hawaii

  10. Kinetics of the Vacuolar H-Pyrophosphatase : The Roles of Magnesium, Pyrophosphate, and their Complexes as Substrates, Activators, and Inhibitors.

    PubMed

    Leigh, R A; Pope, A J; Jennings, I R; Sanders, D

    1992-12-01

    The responses of the vacuolar membrane (tonoplast) proton-pumping inorganic pyrophosphatase (H(+)-PPase) from oat (Avena sativa L.) roots to changes in Mg(2+) and pyrophosphate (PPi) concentrations have been characterized. The kinetics were complex, and reaction kinetic models were used to determine which of the various PPi complexes were responsible for the observed responses. The results indicate that the substrate for the oat root vacuolar H(+)-PPase is Mg(2)PPi and that this complex is also a non-competitive inhibitor. In addition, the enzyme is activated by free Mg(2+) and competitively inhibited by free PPi. This conclusion differs from that reached in previous studies, in which it was proposed that MgPPi is the substrate for plant vacuolar H(+)-PPases. However, models incorporating MgPPi as a substrate were unable to describe the kinetics of the oat H(+)-PPase. It is demonstrated that models incorporating Mg(2)PPi as the substrate can describe some of the published kinetics of the Kalanchoë daigremontiana vacuolar H(+)-PPase. Calculations of the likely concentrations of Mg(2)PPi in plant cytoplasm suggest that the substrate binding site of the oat vacuolar H(+)-PPase would be about 70% saturated in vivo. PMID:16653186

  11. Integrated Analysis of Contractile Kinetics, Force Generation, and Electrical Activity in Single Human Stem Cell-Derived Cardiomyocytes.

    PubMed

    Kijlstra, Jan David; Hu, Dongjian; Mittal, Nikhil; Kausel, Eduardo; van der Meer, Peter; Garakani, Arman; Domian, Ibrahim J

    2015-12-01

    The quantitative analysis of cardiomyocyte function is essential for stem cell-based approaches for the in vitro study of human cardiac physiology and pathophysiology. We present a method to comprehensively assess the function of single human pluripotent stem cell-derived cardiomyocyte (hPSC-CMs) through simultaneous quantitative analysis of contraction kinetics, force generation, and electrical activity. We demonstrate that statistical analysis of movies of contracting hPSC-CMs can be used to quantify changes in cellular morphology over time and compute contractile kinetics. Using a biomechanical model that incorporates substrate stiffness, we calculate cardiomyocyte force generation at single-cell resolution and validate this approach with conventional traction force microscopy. The addition of fluorescent calcium indicators or membrane potential dyes allows the simultaneous analysis of contractility and calcium handling or action potential morphology. Accordingly, our approach has the potential for broad application in the study of cardiac disease, drug discovery, and cardiotoxicity screening. PMID:26626178

  12. Integrated Analysis of Contractile Kinetics, Force Generation, and Electrical Activity in Single Human Stem Cell-Derived Cardiomyocytes

    PubMed Central

    Kijlstra, Jan David; Hu, Dongjian; Mittal, Nikhil; Kausel, Eduardo; van der Meer, Peter; Garakani, Arman; Domian, Ibrahim J.

    2015-01-01

    Summary The quantitative analysis of cardiomyocyte function is essential for stem cell-based approaches for the in vitro study of human cardiac physiology and pathophysiology. We present a method to comprehensively assess the function of single human pluripotent stem cell-derived cardiomyocyte (hPSC-CMs) through simultaneous quantitative analysis of contraction kinetics, force generation, and electrical activity. We demonstrate that statistical analysis of movies of contracting hPSC-CMs can be used to quantify changes in cellular morphology over time and compute contractile kinetics. Using a biomechanical model that incorporates substrate stiffness, we calculate cardiomyocyte force generation at single-cell resolution and validate this approach with conventional traction force microscopy. The addition of fluorescent calcium indicators or membrane potential dyes allows the simultaneous analysis of contractility and calcium handling or action potential morphology. Accordingly, our approach has the potential for broad application in the study of cardiac disease, drug discovery, and cardiotoxicity screening. PMID:26626178

  13. Comparisons of kinetics, thermodynamics and regeneration of tetramethylammonium hydroxide adsorption in aqueous solution with graphene oxide, zeolite and activated carbon

    NASA Astrophysics Data System (ADS)

    Chang, Shenteng; Lu, Chungsying; Lin, Kun-Yi Andrew

    2015-01-01

    Graphene oxide (GO), sodium Y-type zeolite (NaY) and granular activated carbon (GAC) are selected as adsorbents to study their kinetics, thermodynamics and regeneration of tetramethylammonium hydroxide (TMAH) adsorption from water. The adsorption kinetics follows the pseudo-second-order rate law while the adsorption thermodynamics shows an exothermic reaction with GO and GAC but displays an endothermic reaction with NaY. The adsorbed TMAH can be readily desorbed from the surface of GO and NaY by 0.05 M NaCl solution. A comparative study on the cyclic TMAH adsorption with GO, NaY and GAC is also conducted and the results reveal that GO exhibits the greatest TMAH adsorption capacity as well as superior reversibility of TMAH adsorption over 10 cycles of adsorption and desorption process. These features indicate that GO is a promising and efficient adsorbent for TMAH removal in wastewater treatment.

  14. Biological conversion of synthesis gas. Mass transfer/kinetic studies

    SciTech Connect

    Klasson, K.T.; Basu, R.; Johnson, E.R.; Clausen, E.C.; Gaddy, J.L.

    1992-03-01

    Mass transfer and kinetic studies were carried out for the Rhodospirillum rubrum and Chlorobium thiosulfatophilum bacterial systems. R. rubrum is a photosynthetic anaerobic bacterium which catalyzes the biological water gas shift reaction: CO + H{sub 2}0 {yields} CO{sub 2} + H{sub 2}. C. thiosulfatophilum is also a H{sub 2}S and COS to elemental sulfur. The growth of R. rubrum may be satisfactorily carried out at 25{degree} and 30{degree}C, while CO uptake and thus the conversion of CO best occurs at temperatures of either 30{degree}, 32{degree} or 34{degree}C. The rate of conversion of COs and H{sub 2}O to CO{sub 2} and H{sub 2}S may be modeled by a first order rate expression. The rate constant at 30{degree}C was found to be 0.243 h{sup {minus}1}. The growth of C. thiosulfatophilum may be modeled in terms of incoming light intensity using a Monod equation: {mu} = {sub 351} + I{sub o}/{sup 0.152}I{sub o}. Comparisons of the growth of R. rubrum and C. thiosulfatophilum shows that the specific growth rate of C. thiosulfatophilum is much higher at a given light intensity.

  15. Photodegradation of the acaricide abamectin: a kinetic study.

    PubMed

    Escalada, Juan Pablo; Gianotti, José; Pajares, Adriana; Massad, Walter A; Amat-Guerri, Francisco; García, Norman A

    2008-08-27

    The acaricide abamectin is a mixture of two colorless homologues in a molar ratio of at least 4:1 with the same structure of macrocyclic lactone. The kinetics of its degradation under direct (254 nm) and dye-sensitized (>400 nm) photoirradiation in methanol solution has been studied by UV-vis spectrophotometry, potentiometric detection of dissolved oxygen, stationary fluorescence, laser flash photolysis, and time-resolved detection of singlet molecular oxygen (O2((1)Delta(g))) phosphorescence. The results indicate that the degradation is very efficient under direct irradiation with UV light (254 nm), with a quantum yield of 0.23. On the contrary, under visible-light irradiation, using the natural pigment riboflavin or the synthetic dye rose bengal as sensitizers, the degradation is very inefficient and proceeds through a O2((1)Delta(g))-mediated mechanism, with a bimolecular rate constant for the overall O2((1)Delta(g)) quenching (the sum of physical and chemical quenching) of 5.5 x 10(5) M(-1) s(-1). This value is similar to those reported for the rate constants of the reactions of O2((1)Delta(g)) with isolated double bonds or conjugated dienes and points to similar processes in the case of abamectin. PMID:18642837

  16. Aqueous chlorination of diclofenac: kinetic study and transformation products identification.

    PubMed

    Soufan, M; Deborde, M; Legube, B

    2012-06-15

    Diclofenac reactivity and fate during water chlorination was investigated in this work. In the first step, chlorination kinetic of diclofenac (DCF) was studied in the pH range of 4-10 at 20 ± 2 °C and in the presence of an excess of total chlorine. A second-order reaction (first-order relative to DCF concentration and first-order relative to free chlorine concentration) was shown with rate constant about 3.89 ± 1.17 M(-1) s(-1) at pH 7. The elementary reactions (i.e. reactions of hypochlorous acid (HOCl) with neutral and ionized forms of DCF, and acid-catalysed reaction of HOCl with neutral and ionized forms of DCF) were proposed to explain the pH-dependence of the rate constants and intrinsic constant of each of them were calculated. In the second step, several degradation products formed during chlorination of DCF were identified. These compounds could come from an initial chlorine electrophilic attack on aromatic ring or amine function of DCF. Some of these chlorinated derivatives seem to accumulate in solution in the presence of an excess of chlorine. PMID:22525458

  17. Complex (dusty) plasmas-kinetic studies of strong coupling phenomena

    SciTech Connect

    Morfill, Gregor E.; Ivlev, Alexei V.; Thomas, Hubertus M.

    2012-05-15

    'Dusty plasmas' can be found almost everywhere-in the interstellar medium, in star and planet formation, in the solar system in the Earth's atmosphere, and in the laboratory. In astrophysical plasmas, the dust component accounts for only about 1% of the mass, nevertheless this component has a profound influence on the thermodynamics, the chemistry, and the dynamics. Important physical processes are charging, sputtering, cooling, light absorption, and radiation pressure, connecting electromagnetic forces to gravity. Surface chemistry is another important aspect. In the laboratory, there is great interest in industrial processes (e.g., etching, vapor deposition) and-at the fundamental level-in the physics of strong coupling phenomena. Here, the dust (or microparticles) are the dominant component of the multi-species plasma. The particles can be observed in real time and space, individually resolved at all relevant length and time scales. This provides an unprecedented means for studying self-organisation processes in many-particle systems, including the onset of cooperative phenomena. Due to the comparatively large mass of the microparticles (10{sup -12}to10{sup -9}g), precision experiments are performed on the ISS. The following topics will be discussed: Phase transitions, phase separation, electrorheology, flow phenomena including the onset of turbulence at the kinetic level.

  18. Kinetic studies of cascade reactions in high-throughput systems.

    PubMed

    Iron, David; Boelens, Hans F M; Westerhuis, Johan A; Rothenberg, Gadi

    2003-12-01

    The application of robotic systems to the study of complex reaction kinetics is considered, using the cascade reaction A --> B --> C as a working example. Practical problems in calculating the rate constants k1 and k2 for the reactions A --> B and B --> C from concentration measurements of CA, CB, or CC are discussed in the light of the symmetry and invertability of the rate equations. A D-optimal analysis is used to determine the points in time and the species that will give the best (i.e., most accurate) results. When exact data are used, the most robust solution results from measuring the pair of concentrations (CA, CC). The system's information function is computed using numeric methods. This function is then used to estimate the amount of information obtainable from a given cascade reaction at any given time. The theoretical findings are compared with experimental results from a set of two-stage cascade experiments monitored using UV-visible spectroscopy. Finally, the pros and cons of using a single reaction sample to estimate both k1 and k2 are discussed. PMID:16465720

  19. Complex (dusty) plasmas—kinetic studies of strong coupling phenomenaa)

    NASA Astrophysics Data System (ADS)

    Morfill, Gregor E.; Ivlev, Alexei V.; Thomas, Hubertus M.

    2012-05-01

    "Dusty plasmas" can be found almost everywhere—in the interstellar medium, in star and planet formation, in the solar system in the Earth's atmosphere, and in the laboratory. In astrophysical plasmas, the dust component accounts for only about 1% of the mass, nevertheless this component has a profound influence on the thermodynamics, the chemistry, and the dynamics. Important physical processes are charging, sputtering, cooling, light absorption, and radiation pressure, connecting electromagnetic forces to gravity. Surface chemistry is another important aspect. In the laboratory, there is great interest in industrial processes (e.g., etching, vapor deposition) and—at the fundamental level—in the physics of strong coupling phenomena. Here, the dust (or microparticles) are the dominant component of the multi-species plasma. The particles can be observed in real time and space, individually resolved at all relevant length and time scales. This provides an unprecedented means for studying self-organisation processes in many-particle systems, including the onset of cooperative phenomena. Due to the comparatively large mass of the microparticles (10-12to10-9g), precision experiments are performed on the ISS. The following topics will be discussed: Phase transitions, phase separation, electrorheology, flow phenomena including the onset of turbulence at the kinetic level.

  20. Aqueous photodegradation of antibiotic florfenicol: kinetics and degradation pathway studies.

    PubMed

    Zhang, Ya; Li, Jianhua; Zhou, Lei; Wang, Guoqing; Feng, Yanhong; Wang, Zunyao; Yang, Xi

    2016-04-01

    The occurrence of antibacterial agents in natural environment was of scientific concern in recent years. As endocrine disrupting chemicals, they had potential risk on ecology system and human beings. In the present study, the photodegradation kinetics and pathways of florfenicol were investigated under solar and xenon lamp irradiation in aquatic systems. Direct photolysis half-lives of florfenicol were determined as 187.29 h under solar irradiation and 22.43 h under xenon lamp irradiation, respectively. Reactive oxygen species (ROS), such as hydroxyl radical (·OH) and singlet oxygen ((1)O2) were found to play an important role in indirect photolysis process. The presence of nitrate and dissolved organic matters (DOMs) could affect photolysis of florfenicol in solutions through light screening effect, quenching effect, and photoinduced oxidization process. Photoproducts of florfenicol in DOMs solutions were identified by solid phase extraction-liquid chromatography-mass spectrometry (SPE-LC-MS) analysis techniques, and degradation pathways were proposed, including photoinduced hydrolysis, oxidation by (1)O2 and ·OH, dechlorination, and cleavage of the side chain. PMID:26705756

  1. Kinetic and Structural Studies of Interactions between Glycosaminoglycans and Langerin.

    PubMed

    Zhao, Jing; Liu, Xinyue; Kao, Chelsea; Zhang, Emily; Li, Quanhong; Zhang, Fuming; Linhardt, Robert J

    2016-08-16

    Langerin, a C-type lectin, is expressed in Langerhans cells. It was reported that langerin binds sulfated glycans, which is an important initial step for its role in blocking human immunodeficiency virus (HIV) transmission by capturing HIV pathogens and mediating their internalization into Birbeck granules for their elimination. It is fundamentally important to understand these interactions at the molecular level for the design of new highly specific therapeutic agents for HIV. Surface plasmon resonance (SPR), which allows for the real-time, direct, quantitative analysis of the label-free molecular interactions, has been used successfully for biophysical characterization of glycosaminoglycan (GAG)-protein interactions. In this study, we report kinetics, structural analysis, and the effects of physiological conditions (e.g., pH, salt concentration, and Ca(2+) and Zn(2+)concentrations) on the interactions between GAGs and langerin using SPR. SPR results revealed that langerin binds to heparin with high affinity (KD ∼ 2.4 nM) and the oligosaccharide length required for the interactions is larger than a tetrasaccharide. This heparin/heparan sulfate-binding protein also interacts with other GAGs, including dermatan sulfate, chondroitin sulfates C-E and KS. In addition, liquid chromatography-mass spectrometry analysis was used to characterize the structure of sulfated glycans that bound to langerin. PMID:27447199

  2. Thiolate alkylation in tripod zinc complexes: a comparative kinetic study.

    PubMed

    Rombach, Michael; Seebacher, Jan; Ji, Mian; Zhang, Guofang; He, Guosen; Ibrahim, Mohamed M; Benkmil, Boumahdi; Vahrenkamp, Heinrich

    2006-05-29

    The biologically relevant alkylations of the thiolate ligands in tripod zinc thiolates by methyl iodide were studied kinetically. Five tripod ligands of the pyrazolyl/thioimidazolyl borate type were employed, offering N3, N2S, NS2, and S3 donor sets. For each of them, the ethyl-, benzyl-, phenyl-, and p-nitrophenylthiolate zinc complexes were investigated, yielding a total of 20 second-order rate constants. The comparison of these rate constants shows three effects: (1) the electronic effect among the thiolates, i.e., the ethanethiolates react about 3 orders of magnitude faster than the p-nitrophenylthiolates; (2) the steric effect among the pyrazolylborates, i.e., the phenyl-substituted ones react about 2 orders of magnitude faster than the tert-butyl-substituted ones; and (3) the strong acceleration by the sulfur donors in the tripods, reaching 4 orders of magnitude between the reaction times of the (N3)Zn-SR and (S3)Zn-SR complexes. PMID:16711708

  3. Detailed kinetic modeling study of n-pentanol oxidation

    DOE PAGESBeta

    Heufer, K. Alexander; Sarathy, S. Mani; Curran, Henry J.; Davis, Alexander C.; Westbrook, Charles K.; Pitz, William J.

    2012-09-28

    To help overcome the world’s dependence upon fossil fuels, suitable biofuels are promising alternatives that can be used in the transportation sector. Recent research on internal combustion engines shows that short alcoholic fuels (e.g., ethanol or n-butanol) have reduced pollutant emissions and increased knock resistance compared to fossil fuels. Although higher molecular weight alcohols (e.g., n-pentanol and n-hexanol) exhibit higher reactivity that lowers their knock resistance, they are suitable for diesel engines or advanced engine concepts, such as homogeneous charge compression ignition (HCCI), where higher reactivity at lower temperatures is necessary for engine operation. The present study presents a detailedmore » kinetic model for n-pentanol based on modeling rules previously presented for n-butanol. This approach was initially validated using quantum chemistry calculations to verify the most stable n-pentanol conformation and to obtain C–H and C–C bond dissociation energies. In addition, the proposed model has been validated against ignition delay time data, speciation data from a jet-stirred reactor, and laminar flame velocity measurements. Overall, the model shows good agreement with the experiments and permits a detailed discussion of the differences between alcohols and alkanes.« less

  4. Impact of Assay conditions on activity estimate and kinetics comparison of Aspergillus niger PhyA and Escherichia coli AppA2 phytases

    Technology Transfer Automated Retrieval System (TEKTRAN)

    This study was to compare three phytase activity assays and kinetics of Aspergillus niger PhyA and Escherichia coli AppA2 phytases expressed in Pichia pastoris at the observed stomach pH of 3.5. In Experiment 1, equivalent phytase activities in the crude preparations of PhyA and AppA2 were tested ...

  5. Single-Channel Kinetic Analysis for Activation and Desensitization of Homomeric 5-HT3A Receptors

    PubMed Central

    Corradi, Jeremías; Gumilar, Fernanda; Bouzat, Cecilia

    2009-01-01

    Abstract The 5-HT3A receptor is a member of the Cys-loop family of ligand-gated ion channels. To perform kinetic analysis, we mutated the 5-HT3A subunit to obtain a high-conductance form so that single-channel currents can be detected. At all 5-HT concentrations (>0.1 μM), channel activity appears as openings in quick succession that form bursts, which coalesce into clusters. By combining single-channel and macroscopic data, we generated a kinetic model that perfectly describes activation, deactivation, and desensitization. The model shows that full activation arises from receptors with three molecules of agonist bound. It reveals an earlier conformational change of the fully liganded receptor that occurs while the channel is still closed. From this pre-open closed state, the receptor enters into an open-closed cycle involving three open states, which form the cluster whose duration parallels the time constant of desensitization. A similar model lacking the pre-open closed state can describe the data only if the opening rates are fixed to account for the slow activation rate. The application of the model to M4 mutant receptors shows that position 10′ contributes to channel opening and closing rates. Thus, our kinetic model provides a foundation for understanding structural bases of activation and drug action. PMID:19720021

  6. Brain lactate kinetics: Modeling evidence for neuronal lactate uptake upon activation.

    PubMed

    Aubert, Agnès; Costalat, Robert; Magistretti, Pierre J; Pellerin, Luc

    2005-11-01

    A critical issue in brain energy metabolism is whether lactate produced within the brain by astrocytes is taken up and metabolized by neurons upon activation. Although there is ample evidence that neurons can efficiently use lactate as an energy substrate, at least in vitro, few experimental data exist to indicate that it is indeed the case in vivo. To address this question, we used a modeling approach to determine which mechanisms are necessary to explain typical brain lactate kinetics observed upon activation. On the basis of a previously validated model that takes into account the compartmentalization of energy metabolism, we developed a mathematical model of brain lactate kinetics, which was applied to published data describing the changes in extracellular lactate levels upon activation. Results show that the initial dip in the extracellular lactate concentration observed at the onset of stimulation can only be satisfactorily explained by a rapid uptake within an intraparenchymal cellular compartment. In contrast, neither blood flow increase, nor extracellular pH variation can be major causes of the lactate initial dip, whereas tissue lactate diffusion only tends to reduce its amplitude. The kinetic properties of monocarboxylate transporter isoforms strongly suggest that neurons represent the most likely compartment for activation-induced lactate uptake and that neuronal lactate utilization occurring early after activation onset is responsible for the initial dip in brain lactate levels observed in both animals and humans. PMID:16260743

  7. Substrate uptake tests and quantitative FISH show differences in kinetic growth of bulking and non-bulking activated sludge.

    PubMed

    Lou, Inchio; de Los Reyes, Francis L

    2005-12-20

    The competition between filaments and floc formers in activated sludge has been historically described using kinetic selection. However, recent studies have suggested that bacterial storage may also be an important factor in microbial selection, since the dynamic nature of substrate flows into wastewater treatment plants elicit transient responses from microorganisms. Respirometry-based kinetic selection should thus be reevaluated by considering cell storage, and a more reliable method should be developed to include bacterial storage in the analysis of growth of filaments and floc formers in activated sludge. In this study, we applied substrate uptake tests combined with metabolic modeling to determine the growth rates, yields and maintenance coefficients of bulking and non-bulking activated sludge developed in lab scale reactors under feast and famine conditions. The results of quantitative fluorescence in situ hybridization (FISH) showed that the filaments Eikelboom Type 1851, Type 021N, and Thiothrix nivea were dominant in bulking sludge, comprising 42.0 % of mixed liquor volatile suspended solids (MLVSS), with 61.6% of the total filament length extending from flocs into bulk solution. Only low levels of Type 1851 filament length (4.9% of MLVSS) occurred in non-bulking sludge, 83.0% of which grew inside the flocs. The kinetic parameters determined from the substrate uptake tests were consistent with those from respirometry and showed that filamentous bulking sludge had lower growth rates and maintenance coefficients than non-bulking sludge. These results provide support for growth kinetic differences in explaining the competitive strategy of filamentous bacteria. PMID:16155949

  8. Formation of distinct soluble microbial products by activated sludge: kinetic analysis and quantitative determination.

    PubMed

    Ni, Bing-Jie; Fang, Fang; Xie, Wen-Ming; Xu, Juan; Yu, Han-Qing

    2012-02-01

    Soluble microbial products (SMP) released by microorganisms in bioreactors are classified into two distinct groups according to their different chemical and degradation kinetics: utilization-associated products (UAP) and biomass-associated products (BAP). SMP are responsible for effluent chemical oxygen demand or for membrane fouling of membrane bioreactor. Here an effective and convenient approach, other than the complicated chemical methods or complex models, is developed to quantify the formation of UAP and BAP together with their kinetics in activated sludge process. In this approach, an integrated substrate utilization equation is developed and used to determine UAP and their production kinetics. On the basis of total SMP measurements, BAP formation is determined with an integrated BAP formation equation. The fraction of substrate electrons diverted to UAP, and the content of BAP derived from biomass can then be calculated. Dynamic quantification data are obtained for UAP and BAP separately and conveniently. The obtained kinetic parameters are found to be reasonable as they are generally bounded and comparable to the literature values. The validity of this approach is confirmed by independent SMP production tests in six different activated sludge systems, which demonstrates its applicability in a wide range of engineered system regarding SMP production. This work provides a widely applied approach to determine the formation of UAP and BAP conveniently, which may offer engineers with basis to optimize bioreactor operation to avoid a high effluent soluble organics from SMP or SMP-based membrane fouling in membrane bioreactors. PMID:22185635

  9. A study of transglucosylation kinetic in an enzymatic synthesis of benzyl alcohol glucoside by α-glucosidase from S. cerevisiae

    NASA Astrophysics Data System (ADS)

    Pavlović, M.; Dimitrijević, A.; Trbojević, J.; Milosavić, N.; Gavrović-Jankulović, M.; Bezbradica, D.; Veličković, D.

    2013-12-01

    α-1,4-Glucosidase from Saccharomyces cerevisiae is an enzyme which is widely used in synthesis of different drugs. Glucosidase inhibitors are studied as potential drugs for prevention of HIV and diabetes. For understanding of these processes it is very important to have insights in the transglucosylation activity of this enzyme. In this paper the kinetics of transglucosylation reaction catalyzed by this enzyme in the synthesis of benzyl alcohol glucoside was studied and all relevant kinetic constants for this system are found. It was shown one additional property of transglycosylation reactions catalyzed by glycosidases—inhibition by both, glucose acceptor and glucose donor, and mechanisms for these inhibitions were proposed.

  10. Long-term correlation in single calcium-activated potassium channel kinetics

    NASA Astrophysics Data System (ADS)

    Campos de Oliveira, R. A.; Barbosa, C. T. F.; Consoni, L. H. A.; Rodrigues, A. R. A.; Varanda, W. A.; Nogueira, R. A.

    2006-05-01

    Ion channels are protein molecules found in biological membranes, which can assume distinct open and closed conformational states, a phenomenon called ion channel kinetics. The transitions from one state to another are dependent on the potential energy barrier that separates them and can be controlled by the electrical field, ions and/or drugs. Both Markovian and fractal models have been used for modeling the ion channel kinetics. Ion single channel records are characterized by successive openings and closings, which are correlated in time. Here the rescaled range analysis ( R/S Hurst analysis) is used to test for the occurrence of long-term correlation in the kinetics of a calcium-activated potassium channel of Leydig cells. A Hurst coefficient H=0.640±0.064 ( n=5) was found for the single calcium-activated potassium channel clamped at -80 mV and exposed to a free Ca 2+ concentration equal to 10 nM. This numerical value indicates the presence of long-term correlation (memory) in this kinetic process. However, when the R/ S analysis was applied to ion channel data simulated using Markovian and fractal models, it could not account for the long-term correlation previously found in the experimental data. In summary, in this work we show that: (i) opening and closing dwell times for the single calcium-activated potassium channel of Leydig cells present long-term correlation and (ii) Markovian and fractal models, which describe well the dwell time distributions, are not adequate to describe the memory found in the kinetics of this channel.

  11. Elution kinetics, antimicrobial activity, and mechanical properties of 11 different antibiotic loaded acrylic bone cement.

    PubMed

    Gálvez-López, Ruben; Peña-Monje, Alejandro; Antelo-Lorenzo, Ramón; Guardia-Olmedo, Juan; Moliz, Juan; Hernández-Quero, José; Parra-Ruiz, Jorge

    2014-01-01

    Antibiotic-loaded acrylic bone cements (ALABC) spacers are routinely used in the treatment of prosthetic joint infections. The objectives of our study were to evaluate different ALABC for elution kinetics, thermal stability, and mechanical properties. A 10 or 20% mixture (w/w) beads of medium viscosity bone cement (DePuy, Inc) and vancomycin (VAN), gentamycin (GM), daptomycin (DAP), moxifloxacin (MOX), rifampicin (RIF), cefotaxime (CTX), cefepime (FEP), amoxicillin clavulanate (AmC), ampicillin (AMP), meropenem (MER), and ertapenem (ERT) were formed and placed into wells filled with phosphate-buffered saline. Antibiotic concentrations were determined using high-performance liquid chromatography. Antimicrobial activity was tested against Micrococcus luteus ATCC 9341 or Escherichia coli ATCC 25922. AmC, AMP, and FEP concentration rapidly decreased after day 2, being almost undetectable at day 4. Sustained and high elution rates were observed with VAN, GM, MOX, and RIF for the 30-day duration of the experiment. DAP, MER, ERT, and CTX elution rates constantly decreased from day 4. All antibiotics tested retained antimicrobial activity proving thermal stability. Mechanical properties of ALABC were maintained except when RIF was used. PMID:24231380

  12. A two-dimensional adsorption kinetic model for thermal hysteresis activity in antifreeze proteins.

    PubMed

    Li, Q Z; Yeh, Y; Liu, J J; Feeney, R E; Krishnan, V V

    2006-05-28

    Antifreeze proteins (AFPs) and antifreeze glycoproteins (AFGPs), collectively abbreviated as AF(G)Ps, are synthesized by various organisms to enable their cells to survive in subzero environments. Although the AF(G)Ps are markedly diverse in structure, they all function by adsorbing to the surface of embryonic ice crystals to inhibit their growth. This adsorption results in a freezing temperature depression without an appreciable change in the melting temperature. The difference between the melting and freezing temperatures, termed thermal hysteresis (TH), is used to detect and quantify the antifreeze activity. Insights from crystallographic structures of a number of AFPs have led to a good understanding of the ice-protein interaction features. Computational studies have focused either on verifying a specific model of AFP-ice interaction or on understanding the protein-induced changes in the ice crystal morphology. In order to explain the origin of TH, we propose a novel two-dimensional adsorption kinetic model between AFPs and ice crystal surfaces. The validity of the model has been demonstrated by reproducing the TH curve on two different beta-helical AFPs upon increasing the protein concentration. In particular, this model is able to accommodate the change in the TH behavior observed experimentally when the size of the AFPs is increased systematically. Our results suggest that in addition to the specificity of the AFPs for the ice, the coverage of the AFPs on the ice surface is an equally necessary condition for their TH activity. PMID:16774359

  13. Kinetic and mechanistic investigations of the degradation of sulfamethazine in heat-activated persulfate oxidation process.

    PubMed

    Fan, Yan; Ji, Yuefei; Kong, Deyang; Lu, Junhe; Zhou, Quansuo

    2015-12-30

    Sulfamethazine (SMZ) is widely used in livestock feeding and aquaculture as an antibiotic agent and growth promoter. Widespread occurrence of SMZ in surface water, groundwater, soil and sediment has been reported. In this study, degradation of SMZ by heat-activated persulfate (PS) oxidation was investigated in aqueous solution. Experimental results demonstrated that SMZ degradation followed pseudo-first-order reaction kinetics. The pseudo-first-order rate constant (kobs) was increased markedly with increasing concentration of PS and temperature. Radical scavenging tests revealed that the predominant oxidizing species was SO4·(-) with HO playing a less important role. Aniline moiety in SMZ molecule was confirmed to be the reactive site for SO4·(-) attack by comparison with substructural analogs. Nontarget natural water constituents affected SMZ removal significantly, e.g., Cl(-) and HCO3(-) improved the degradation while fulvic acid reduced it. Reaction products were enriched by solid phase extraction (SPE) and analyzed by liquid chromatography-electrospray ionization-triple quadrupole mass spectrometry (LC-ESI-MS/MS). 6 products derived from sulfonamide S--N bond cleavage, aniline moiety oxidation and Smiles-type rearrangement were identified, and transformation pathways of SMZ oxidation were proposed. Results reveal that heat-activated PS oxidation could be an efficient approach for remediation of water contaminated by SMZ and related sulfonamides. PMID:26151383

  14. Oxidative dehydrogenation dimerization of propylene over bismuth oxide: kinetic and mechanistic studies

    SciTech Connect

    White, M.G.; Hightower, J.W.

    1983-07-01

    Classical kinetic experiments together with pulse microreactor studies involving deuterium and carbon-13-labeled isotopic tracers were used to investigate the oxidative dehydrogenation dimerization (OXDD) of propylene to 1,5-hexadiene and benzene over bismuth oxide between 748 and 898/sup 0/K. The kinetic data, which indicated that the OXDD reaction is of variable order with respect to oxygen and propylene concentrations, could be fit to rate equations based on either the Langmuir-Hinshelwood model or the Mars-van Krevelen model, although the former gave more linear Arrhenius plots. A significant kinetic isotope effect (k/sub H//k/sub D/ = 1.7 at 873/sup 0/K) shows that the rate-limiting step for the OXDD reaction involves C-H cleavage, and there is only a small amount of H/D scrambling among reactant and product molecules. Analysis of liquid products by infrared spectroscopy indicated that both 1,5-hexadiene and 1,3-cyclohexadiene are stable reaction intermediates; microreactor results involving unlabeled propylene, 1,5-hexadiene, 1,3-cyclohexadiene, and 1,4-cyclohexadiene as reactants confirmed the infrared findings. Pulse microreactor experiments with /sup 13/C-labeled propylene clearly showed that deep oxidation (complete combustion) occurs via a consecutive-parallel network involving the partially oxidized intermediates as well as the starting propylene. Changes in the particle size do not alter the overall activity, although larger particles have lower selectivities for C/sub 6/ products than do smaller particles.

  15. Kinetic study on the isothermal and nonisothermal crystallization of monoglyceride organogels.

    PubMed

    Meng, Zong; Yang, Lijun; Geng, Wenxin; Yao, Yubo; Wang, Xingguo; Liu, Yuanfa

    2014-01-01

    The isothermal and nonisothermal crystallization kinetics of monoglyceride (MAG) organogels were studied by pulsed nuclear magnetic resonance (pNMR) and differential scanning calorimetry (DSC), respectively. The Avrami equation was used to describe the isothermal crystallization kinetics and experimental data fitted the equation fairly well. Results showed that the crystal growth of MAG organogels was a rod-like growth of instantaneous nuclei at higher degrees of supercooling and a plate-like form with high nucleation rate at lower degrees of supercooling. The exothermic peak in nonisothermal DSC curves for the MAG organogels became wider and shifted to lower temperature when the cooling rate increased, and nonisothermal crystallization was analyzed by Mo equation. Results indicated that at the same crystallization time, to get a higher degree of relative crystallinity, a higher cooling rate was necessary. The activation energy of nonisothermal crystallization was calculated as 739.59 kJ/mol according to the Kissinger method. Therefore, as the results of the isothermal and nonisothermal crystallization kinetics for the MAG organogels obtained, the crystallization rate, crystal nucleation, and growth during the crystallization process could be preliminarily monitored through temperature and cooling rate regulation, which laid the foundation for the real industrial manufacture and application of the MAG organogels. PMID:24701138

  16. Kinetic Study on the Isothermal and Nonisothermal Crystallization of Monoglyceride Organogels

    PubMed Central

    Meng, Zong; Yang, Lijun; Geng, Wenxin; Yao, Yubo; Wang, Xingguo; Liu, Yuanfa

    2014-01-01

    The isothermal and nonisothermal crystallization kinetics of monoglyceride (MAG) organogels were studied by pulsed nuclear magnetic resonance (pNMR) and differential scanning calorimetry (DSC), respectively. The Avrami equation was used to describe the isothermal crystallization kinetics and experimental data fitted the equation fairly well. Results showed that the crystal growth of MAG organogels was a rod-like growth of instantaneous nuclei at higher degrees of supercooling and a plate-like form with high nucleation rate at lower degrees of supercooling. The exothermic peak in nonisothermal DSC curves for the MAG organogels became wider and shifted to lower temperature when the cooling rate increased, and nonisothermal crystallization was analyzed by Mo equation. Results indicated that at the same crystallization time, to get a higher degree of relative crystallinity, a higher cooling rate was necessary. The activation energy of nonisothermal crystallization was calculated as 739.59 kJ/mol according to the Kissinger method. Therefore, as the results of the isothermal and nonisothermal crystallization kinetics for the MAG organogels obtained, the crystallization rate, crystal nucleation, and growth during the crystallization process could be preliminarily monitored through temperature and cooling rate regulation, which laid the foundation for the real industrial manufacture and application of the MAG organogels. PMID:24701138

  17. A Kinetic Study of Indium Leaching from Indium-Bearing Zinc Ferrite Under Microwave Heating

    NASA Astrophysics Data System (ADS)

    Zhang, Linye; Mo, Jiamei; Li, Xuanhai; Pan, Liuping; Liang, Xinyuan; Wei, Guangtao

    2013-12-01

    To obtain information about leaching reaction and kinetics of indium from indium-bearing materials under microwave heating (MH), leaching of indium from indium-bearing zinc ferrite (IBZF) has been investigated. IBZF samples under MH and under conventional heating (CH) were studied by X-ray diffraction and specific surface area. Compared with that of CH, the effect of MH and the effects of various control parameters on indium leaching were studied. The results showed that compared with CH, MH enhanced the indium leaching from IBZF and increased the leaching rate. The leaching behavior of indium from IBZF was analyzed by unreacted shrinking core model, and the regression of kinetic equations showed that leaching of indium from IBZF obeyed the model very well. The activation energies under MH and under CH were 77.374 kJ/mol and 53.555 kJ/mol, respectively; the ratio of frequency factor K 0(MH)/ K 0(CH) was 10,818.36. The activation mechanism involved in leaching of indium under MH was mainly the increase of reactant energy and effective collision, which caused by the thermal and nonthermal microwave effect. Compared with the activation energy, the effective collision played a more important role in the acceleration of leaching of indium.

  18. The Study of a Simple Redox Reaction as an Experimental Approach to Chemical Kinetics.

    ERIC Educational Resources Information Center

    Elias, Horst; Zipp, Arden P.

    1988-01-01

    Recommends using iodide ions and peroxodisulfate ions for studying rate laws instead of the standard iodine clock for kinetic study. Presents the methodology and a discussion of the kinetics involved for a laboratory experiment for a high school or introductory college course. (ML)

  19. Kinetic and structural evaluation of selected active site mutants of the Aspergillus fumigatus KDNase (sialidase).

    PubMed

    Yeung, Juliana H F; Telford, Judith C; Shidmoossavee, Fahimeh S; Bennet, Andrew J; Taylor, Garry L; Moore, Margo M

    2013-12-23

    Aspergillus fumigatus is an airborne fungal pathogen. We previously cloned and characterized an exo-sialidase from A. fumigatus and showed that it preferred 2-keto-3-deoxynononic acid (KDN) as a substrate to N-acetylneuraminic acid (Neu5Ac). The purpose of this study was to investigate the structure-function relationships of critical catalytic site residues. Site-directed mutagenesis was used to create three mutant recombinant enzymes: the catalytic nucleophile (Y358H), the general acid/base catalyst (D84A), and an enlargement of the binding pocket to attempt to accommodate the N-acetyl group of Neu5Ac (R171L). Crystal structures for all enzymes were determined. The D84A mutation had an effect in decreasing the activity of AfKDNase that was stronger than that of the same mutation in the structurally similar sialidase from the bacterium Micromonospora viridifaciens. These data suggest that the catalytic acid is more important in the reaction of AfKDNase and that catalysis is less dependent on nucleophilic or electrostatic stabilization of the developing positive charge at the transition state for hydrolysis. Removal of the catalytic nucleophile (Y358H) significantly lowered the activity of the enzyme, but this mutant remained a retaining glycosidase as demonstrated by nuclear magnetic resonance spectroscopic analysis. This is a novel finding that has not been shown with other sialidases. Kinetic activity measured at pH 5.2 revealed that R171L had higher activity on a Neu5Ac-based substrate than wild-type KDNase; hence, leucine in place of arginine in the binding pocket improved catalysis toward Neu5Ac substrates. Hence, whether a sialidase is primarily a KDNase or a neuraminidase is due in part to the presence of an amino acid that creates a steric clash with the N-acetyl group. PMID:24295366

  20. Early kinetic window of target T cell susceptibility to CD25+ regulatory T cell activity.

    PubMed

    Sojka, Dorothy K; Hughson, Angela; Sukiennicki, Teresa L; Fowell, Deborah J

    2005-12-01

    Peripheral tolerance is maintained in part by thymically derived CD25+CD4+ T cells (regulatory T cells (Tregs)). Their mechanism of action has not been well characterized. Therefore, to get a better understanding of Treg action, we investigated the kinetics of murine Treg activity in vitro. Tregs were suppressive within a surprisingly narrow kinetic window: necessary and sufficient only in the first 6-10 h of culture. Visualization of this time frame, using a sensitive single-cell assay for IL-2, revealed the early elaboration of target cell IL-2 producers in the first 6 h despite the presence of CD25+CD4+ Tregs. However, after 6 h, a rapid rise in the number of IL-2 producers in the absence of Tregs was dramatically abrogated by the presence of Tregs. Importantly, the timing of suppression was dictated by the kinetics of target T cell activation suggesting that early target T cell signals may alter susceptibility to suppression. Modulating target T cell activation signals with provision of CD28, IL-2, or high Ag dose all abrogated suppression of proliferation late in culture. However, only CD28 signals enabled target T cells to resist the early Treg-induced down-regulation of IL-2. Therefore the quality of early target T cell activation signals, in particular engagement of CD28, represents an important control point in the balance between vulnerability and resistance to Treg suppression. PMID:16301632

  1. Mechanistic studies with solubilized rat liver steroid 5 alpha-reductase: Elucidation of the kinetic mechanism

    SciTech Connect

    Levy, M.A.; Brandt, M.; Greway, A.T. )

    1990-03-20

    A solubilized preparation of steroid 5 alpha-reductase from rat liver has been used in studies focused toward an understanding of the kinetic mechanism associated with enzyme catalysis. From the results of analyses with product and dead-end inhibitors, a preferentially ordered binding of substrates and release of products from the surface of the enzyme is proposed. The observations from these experiments were identical with those using the steroid 5 alpha-reductase activity associated with rat liver microsomes. The primary isotope effects on steady-state kinetic parameters when (4S-2H)NADPH was used also were consistent with an ordered kinetic mechanism. Normal isotope effects were observed for all three kinetic parameters (Vm/Km for both testosterone and NADPH and Vm) at all substrate concentrations used experimentally. Upon extrapolation to infinite concentration of testosterone, the isotope effect on Vm/Km for NADPH approached unity, indicating that the nicotinamide dinucleotide phosphate is the first substrate binding to and the second product released from the enzyme. The isotope effects on Vm/Km for testosterone at infinite concentration of cofactor and on Vm were 3.8 +/- 0.5 and 3.3 +/- 0.4, respectively. Data from the pH profiles of these three steady-state parameters and the inhibition constants (1/Ki) of competitive inhibitors versus both substrates indicate that the binding of nicotinamide dinucleotide phosphate involves coordination of its anionic 2'-phosphate to a protonated enzyme-associated base with an apparent pK near 8.0. From these results, relative limits have been placed on several of the internal rate constants used to describe the ordered mechanism of the rat liver steroid 5 alpha-reductase.

  2. Fundamental studies on kinetic isotope effect (KIE) of hydrogen isotope fractionation in natural gas systems

    NASA Astrophysics Data System (ADS)

    Ni, Yunyan; Ma, Qisheng; Ellis, Geoffrey S.; Dai, Jinxing; Katz, Barry; Zhang, Shuichang; Tang, Yongchun

    2011-05-01

    Based on quantum chemistry calculations for normal octane homolytic cracking, a kinetic hydrogen isotope fractionation model for methane, ethane, and propane formation is proposed. The activation energy differences between D-substitute and non-substituted methane, ethane, and propane are 318.6, 281.7, and 280.2 cal/mol, respectively. In order to determine the effect of the entropy contribution for hydrogen isotopic substitution, a transition state for ethane bond rupture was determined based on density function theory (DFT) calculations. The kinetic isotope effect (KIE) associated with bond rupture in D and H substituted ethane results in a frequency factor ratio of 1.07. Based on the proposed mathematical model of hydrogen isotope fractionation, one can potentially quantify natural gas thermal maturity from measured hydrogen isotope values. Calculated gas maturity values determined by the proposed mathematical model using δD values in ethane from several basins in the world are in close agreement with similar predictions based on the δ 13C composition of ethane. However, gas maturity values calculated from field data of methane and propane using both hydrogen and carbon kinetic isotopic models do not agree as closely. It is possible that δD values in methane may be affected by microbial mixing and that propane values might be more susceptible to hydrogen exchange with water or to analytical errors. Although the model used in this study is quite preliminary, the results demonstrate that kinetic isotope fractionation effects in hydrogen may be useful in quantitative models of natural gas generation, and that δD values in ethane might be more suitable for modeling than comparable values in methane and propane.

  3. Fundamental studies on kinetic isotope effect (KIE) of hydrogen isotope fractionation in natural gas systems

    USGS Publications Warehouse

    Ni, Y.; Ma, Q.; Ellis, G.S.; Dai, J.; Katz, B.; Zhang, S.; Tang, Y.

    2011-01-01

    Based on quantum chemistry calculations for normal octane homolytic cracking, a kinetic hydrogen isotope fractionation model for methane, ethane, and propane formation is proposed. The activation energy differences between D-substitute and non-substituted methane, ethane, and propane are 318.6, 281.7, and 280.2cal/mol, respectively. In order to determine the effect of the entropy contribution for hydrogen isotopic substitution, a transition state for ethane bond rupture was determined based on density function theory (DFT) calculations. The kinetic isotope effect (KIE) associated with bond rupture in D and H substituted ethane results in a frequency factor ratio of 1.07. Based on the proposed mathematical model of hydrogen isotope fractionation, one can potentially quantify natural gas thermal maturity from measured hydrogen isotope values. Calculated gas maturity values determined by the proposed mathematical model using ??D values in ethane from several basins in the world are in close agreement with similar predictions based on the ??13C composition of ethane. However, gas maturity values calculated from field data of methane and propane using both hydrogen and carbon kinetic isotopic models do not agree as closely. It is possible that ??D values in methane may be affected by microbial mixing and that propane values might be more susceptible to hydrogen exchange with water or to analytical errors. Although the model used in this study is quite preliminary, the results demonstrate that kinetic isotope fractionation effects in hydrogen may be useful in quantitative models of natural gas generation, and that ??D values in ethane might be more suitable for modeling than comparable values in methane and propane. ?? 2011 Elsevier Ltd.

  4. Kinetic and isotherm studies of adsorption and biosorption processes in the removal of phenolic compounds from aqueous solutions: comparative study

    PubMed Central

    2013-01-01

    The phenolic compounds are known by their carcinogenicity and high toxicity as well as creating unpleasant taste and odor in water resources. The present study develops a cost-effective technology for the treatment of water contaminated with phenolic compounds, including Phenol (Ph), 2-chlorophenol (2-CP), and 4-chlorophenol (4-CP). So, two sorbents, rice bran ash (RBA) and biomass of brown algae, Cystoseiraindica, were used and results were compared with the commercially granular activated carbon (GAC). The phenolic compounds were determined using a high performance liquid chromatography (HPLC) under batch equilibrium conditions. The effects of contact time, pH, initial adsorbate concentration, and adsorbent dosages on the removal efficiency were studied. The adsorption data were simulated by isotherm and kinetic models. Results indicated that RBA and GAC had the lowest efficiency for the removal of 2-CP, while the order of removal efficiency for C. indica biomass was as follows: 2-CP > 4-CP > phenol. The efficiency of GAC was higher than those of other adsorbents for all of the phenolic compounds. Furthermore, the adsorption capacity of RBA was found to be higher than that of C. indica biomass. The optimal initial pH for the removal of phenol, 2-CP and 4-CP was determined to be 5, 7, and 7 for RBA, GAC, and algal biomass, respectively. Kinetic studies suggested that the pseudo-second order best fitted the kinetic data. PMID:24355013

  5. Substrate Kinetics of the Tonoplast H+-Translocating Inorganic Pyrophosphatase and Its Activation by Free Mg2+1

    PubMed Central

    White, Philip J.; Marshall, Jacqueline; Smith, J. Andrew C.

    1990-01-01

    To clarify the kinetic characteristics and ionic requirements of the tonoplast H+-translocating inorganic pyrophosphatase (H+-PPiase), PPi hydrolysis and PPi-dependent H+ transport were studied in tonoplast vesicles isolated from leaf mesophyll tissue of Kalanchoë daigremontiana Hamet et Perrier de la Bâthie. The tonoplast H+-PPiase showed an absolute requirement for a monovalent cation and exhibited hyperbolic kinetics with respect to cation concentration. H+-PPiase activity was maximal in the presence of K+ (K50 approximately 3 millimolar), with PPi-dependent H+ transport being more selective for K+ than PPi hydrolysis. When assayed in the presence of 50 millimolar KCl at fixed PPi concentrations, H+-PPiase activity showed sigmoidal kinetics with respect to total Mg concentration, reflecting a requirement for a Mg/PPi complex as substrate and free Mg2+ for activation. At saturating concentrations of free Mg2+, H+-PPiase activity exhibited Michaelis-Menten kinetics towards MgPPi2− but not Mg2PPi, demonstrating that MgPPi2− was the true substrate of the enzyme. The apparent Km (MgPPi2−) for PPi hydrolysis (17 micromolar) was significantly higher than that for PPi-dependent H+ transport (7 micromolar). Free Mg2+ was shown to be an allosteric activator of the H+-PPiase, with Hill coefficients of 2.5 for PPi hydrolysis and 2.7 for PPi-dependent H+ transport. Half-maximal H+-PPiase activity occurred at a free Mg2+ concentration of 1.1 millimolar, which lies within the range of accepted values for cytosolic Mg2+. In contrast, cytosolic concentrations of K+ and MgPPi2− appear to be saturating for H+-PPiase activity. We propose that one function of the H+-PPiase may be to act as an ancillary enzyme that maintains the proton-motive force across the vacuolar membrane when the activity of the tonoplast H+-ATPase is restricted by substrate availability. As ATP levels decline in the cytosol, free Mg2+ would be released from the MgATP2− complex, thereby activating

  6. Aqueous chlorination of carbamazepine: kinetic study and transformation product identification.

    PubMed

    Soufan, M; Deborde, M; Delmont, A; Legube, B

    2013-09-15

    Carbamazepine reactivity and fate during chlorination was investigated in this study. From a kinetic standpoint, a third-order reaction (first-order relative to the CBZ concentration and second-order relative to the free chlorine concentration) was observed at neutral and slightly acidic pH, whereas a second-order reaction (first order relative to the CBZ concentration and first order relative to the free chlorine concentration) was noted under alkaline conditions. In order to gain insight into the observed pH-dependence of the reaction order, elementary reactions (i.e. reactions of Cl2, Cl2O, HOCl with CBZ and of ClO(-) with CBZ or of HOCl with the ionized form of CBZ) were highlighted and second order rate constants of each of them were calculated. Close correlations between the experimental and modeled values were obtained under these conditions. Cl2 and Cl2O were the main chlorination agents at neutral and acidic pH. These results indicate that, for a 1 mg/L free chlorine concentration and 1-10 mg/L chloride concentration at pH 7, halflives about 52-69 days can be expected. A low reactivity of chlorine with CBZ could thus occur under the chlorination steps used during water treatment. From a mechanistic viewpoint, several transformation products were observed during carbamazepine chlorination. As previously described for the chlorination of polynuclear aromatic or unsaturated compounds, we proposed monohydroxylated, epoxide, diols or chlorinated alcohol derivatives of CBZ for the chemical structures of these degradation products. Most of these compounds seem to accumulate in solution in the presence of excess chlorine. PMID:23891541

  7. Kinetic studies of the sucrose adsorption onto an alumina interface

    NASA Astrophysics Data System (ADS)

    Singh, Kaman; Mohan, Sudhanshu

    2004-01-01

    An account is given of an experimental kinetic study of adsorption of analar reagent sucrose (ARS) onto an alumina interface spectrometrically ( λmax=570 nm) at pH 8.0 and at room temperature. The adsorption isotherm is a typical Langmuirian isotherm (S-type) and adsorption parameters have been deduced according to the Langmuir's model. The adsorption coefficient evaluated from the Langmuir's equation was found to be 2.52×10 2 l mol -1. Adsorption mechanism has been interpreted on the basis of metal-saccharide interaction as found in organometallic compounds and interaction due to negatively charged ends on the disaccharide molecules and positively charge groups on the surface on alumina which depends on the pH value. The effects of variation in experimental conditions of the adsorption system have also been investigated. The adsorption exhibited a typical response to the pH effect and on going towards the PZC the net charge decreases and any reaction making dependence on charge and maximum adsorption (amount) was found near the isoelectric point of alumina (pH 9.0). The presence of ions like Cl -, SO 42- and PO 43- affect the adsorbed amount quantitatively and it seems that these anions compete with sucrose for the positively charged surface sites. The addition of similar concentration of cations was found to reduce the adsorbed amount. The temperature was found to have an inverse effect on adsorption. The additions of catonic and anionic detergents influence both the adsorbed amount and the adsorption rate. The thermodynamics of the titled adsorption model indicates the spontaneous and exothermic nature. The negative value of entropy is an indication of probability of favorable and complex nature of the adsorption.

  8. A two-parameter kinetic model based on a time-dependent activity coefficient accurately describes enzymatic cellulose digestion

    PubMed Central

    Kostylev, Maxim; Wilson, David

    2014-01-01

    Lignocellulosic biomass is a potential source of renewable, low-carbon-footprint liquid fuels. Biomass recalcitrance and enzyme cost are key challenges associated with the large-scale production of cellulosic fuel. Kinetic modeling of enzymatic cellulose digestion has been complicated by the heterogeneous nature of the substrate and by the fact that a true steady state cannot be attained. We present a two-parameter kinetic model based on the Michaelis-Menten scheme (Michaelis L and Menten ML. (1913) Biochem Z 49:333–369), but with a time-dependent activity coefficient analogous to fractal-like kinetics formulated by Kopelman (Kopelman R. (1988) Science 241:1620–1626). We provide a mathematical derivation and experimental support to show that one of the parameters is a total activity coefficient and the other is an intrinsic constant that reflects the ability of the cellulases to overcome substrate recalcitrance. The model is applicable to individual cellulases and their mixtures at low-to-medium enzyme loads. Using biomass degrading enzymes from a cellulolytic bacterium Thermobifida fusca we show that the model can be used for mechanistic studies of enzymatic cellulose digestion. We also demonstrate that it applies to the crude supernatant of the widely studied cellulolytic fungus Trichoderma reesei and can thus be used to compare cellulases from different organisms. The two parameters may serve a similar role to Vmax, KM, and kcat in classical kinetics. A similar approach may be applicable to other enzymes with heterogeneous substrates and where a steady state is not achievable. PMID:23837567

  9. Comparison of the activation kinetics of the M3 acetylcholine receptor and a constitutively active mutant receptor in living cells.

    PubMed

    Hoffmann, Carsten; Nuber, Susanne; Zabel, Ulrike; Ziegler, Nicole; Winkler, Christiane; Hein, Peter; Berlot, Catherine H; Bünemann, Moritz; Lohse, Martin J

    2012-08-01

    Activation of G-protein-coupled receptors is the first step of the signaling cascade triggered by binding of an agonist. Here we compare the activation kinetics of the G(q)-coupled M(3) acetylcholine receptor (M(3)-AChR) with that of a constitutively active mutant receptor (M(3)-AChR-N514Y) using M(3)-AChR constructs that report receptor activation by changes in the fluorescence resonance energy transfer (FRET) signal. We observed a leftward shift in the concentration-dependent FRET response for acetylcholine and carbachol with M(3)-AChR-N514Y. Consistent with this result, at submaximal agonist concentrations, the activation kinetics of M(3)-AChR-N514Y were significantly faster, whereas at maximal agonist concentrations the kinetics of receptor activation were identical. Receptor deactivation was significantly faster with carbachol than with acetylcholine and was significantly delayed by the N514Y mutation. Receptor-G-protein interaction was measured by FRET between M(3)-AChR-yellow fluorescent protein (YFP) and cyan fluorescent protein (CFP)-Gγ(2). Agonist-induced receptor-G-protein coupling was of a time scale similar to that of receptor activation. As observed for receptor deactivation, receptor-G-protein dissociation was slower for acetylcholine than that for carbachol. Acetylcholine-stimulated increases in receptor-G-protein coupling of M(3)-AChR-N514Y reached only 12% of that of M(3)-AChR and thus cannot be kinetically analyzed. G-protein activation was measured using YFP-tagged Gα(q) and CFP-tagged Gγ(2). Activation of G(q) was significantly slower than receptor activation and indistinguishable for the two agonists. However, G(q) deactivation was significantly prolonged for acetylcholine compared with that for carbachol. Consistent with decreased agonist-stimulated coupling to G(q), agonist-stimulated G(q) activation by M(3)-AChR-N514Y was not detected. Taken together, these results indicate that the N514Y mutation produces constitutive activation of M(3

  10. A Case Study in Chemical Kinetics: The OH + CO Reaction.

    ERIC Educational Resources Information Center

    Weston, Ralph E., Jr.

    1988-01-01

    Reviews some important properties of the bimolecular reaction between the hydroxyl radical and carbon monoxide. Investigates the kinetics of the reaction, the temperature and pressure dependence of the rate constant, the state-to-state dynamics of the reaction, and the reverse reaction. (MVL)

  11. Penicillin Hydrolysis: A Kinetic Study of a Multistep, Multiproduct Reaction.

    ERIC Educational Resources Information Center

    McCarrick, Thomas A.; McLafferty, Fred W.

    1984-01-01

    Background, procedures used, and typical results are provided for an experiment in which students carry out the necessary measurements on the acid-catalysis of penicillin in two hours. By applying kinetic theory to the data obtained, the reaction pathways for the hydrolysis of potassium benzyl penicillin are elucidated. (JN)

  12. An Undergraduate Laboratory Exercise for Studying Kinetics of Batch Crystallization

    ERIC Educational Resources Information Center

    Louhi­-Kultanen, Marjatta; Han, Bing; Nurkka, Annikka; Hatakka, Henry

    2015-01-01

    The present work describes an undergraduate laboratory exercise for improving understanding of fundamental phenomena in cooling crystallization. The exercise of nucleation and crystal growth kinetics supports learning of theories and models presented in lectures and calculation exercises. The teaching methodology incorporates precepts the…

  13. Antibacterial activities and release kinetics of a newly developed recoverable controlled agent-release system.

    PubMed

    Ehara, A; Torii, M; Imazato, S; Ebisu, S

    2000-03-01

    We attempted to develop a resin with a recoverable antibacterial activity based on the desorption/adsorption of a cationic bactericide by the ion-exchange mechanism. The aims of this study were to investigate the release kinetics of the agent and the antibacterial activity of this newly designed resin system. An experimental resin was prepared by the addition of methacrylic acid as a cation-exchanger and a cationic antibacterial agent, cetylpyridinium chloride (CPC), to triethyleneglycol dimethacrylate. The amount of CPC desorbed from the experimental resin into buffer solutions at pH 4-8 was measured. The adsorption of CPC to control resin and re-adsorption of CPC to the experimental resin, which had once desorbed the agent, were also determined. The antibacterial activity of experimental resin against Streptococcus mutans was evaluated, and the relationship between bacterial acid production and antibacterial effect was assessed. The experimental resin desorbed CPC at pH < or = 6, and the amount of agent desorbed increased with increasing acidity. The control resin adsorbed CPC when immersed in CPC aqueous solution at a rate determined by the concentration of the agent and immersion time. The experimental resin, once desorbed CPC, could re-adsorb the bactericide by being exposed to a solution of the agent. Less plaque formed on the experimental resin, and the growth and survival of S. mutans was inhibited in the condition in which acid was produced. These results demonstrate that the resin system proposed was able to desorb and re-adsorb the cationic bactericide by an ion-exchange mechanism and could show an inhibitory effect on S. mutans growth and plaque formation. PMID:10765955

  14. Kinetics studies with fruit bromelain (Ananas comosus) in the presence of cysteine and divalent ions.

    PubMed

    Kaur, Tajwinder; Kaur, Amandeep; Grewal, Ravneet K

    2015-09-01

    The kinetics of cysteine and divalent ion modulation viz. Ca(2+), Cu(2+), Hg(2+) of fruit bromelain (EC 3.4.22.33) have been investigated in the present study. Kinetic studies revealed that at pH 4.5, cysteine induced V-type activation of bromelain catalyzed gelatin hydrolysis. At pH 3.5, Ca(2+) inhibited the enzyme noncompetitively, whereas, both K-and V-type activations of bromelain were observed in the presence of 0.5 mM Ca(2+) at pH 4.5 and 7.5. Bromelain was inhibited competitively at 0.6 mM Cu(2+) ions at pH 3.5, which changed to an uncompetitive inhibition at pH 4.5 and 7.5. An un-competitive inhibition of bromelain catalyzed gelatin hydrolysis was observed in the presence of 0.6 mM Hg(2+) at pH 3.5 and 4.5. These findings suggest that divalent ions modulation of fruit bromelain is pH dependent. PMID:26345013

  15. Kinetic study of hydrated lime reaction with HCl.

    PubMed

    Yan, Rong; Chin, Terence; Liang, David Tee; Laursen, Karin; Ong, Wan Yean; Yao, Kaiwen; Tay, Joo Hwa

    2003-06-01

    Hydrochloride (HCl) is an acidic pollutant present in the flue gas of most municipal or hazardous waste incinerators. Hydrated lime (Ca(OH)2) is often used as a dry sorbent for injection in a spray reactor to remove HCI. However, due to the short residence time encountered, this control method has generally been found to have low conversion efficiencies which results in the high lime usage and generates large amount of fly ash as solid wastes. A fundamental study was carried outto investigate the kinetics of HCl-lime reaction under simulated flue gas conditions in order to better understand the process thereby providing a basis for an optimized lime usage and reduced fly ash production. The initial reaction rate and conversion of three limes were studied using a thermogravimetric analyzer by varying the gas flow rate, temperature (170-400 degrees C), and HCI concentrations (600-1200 mg/m3) as well as the associated particle size and surface area of the limes. The initial lime conversions were found to rely mostly on the residence time, while the ultimate lime conversions were strongly influenced by temperature and the reaction products. CaOHCI was found to be the primary product in most cases, while for one specific lime, CaCl2 was the ultimate conversion product after an extended time period. The true utilization of lime in flue gas cleanup is thus higher when CaOHCl is considered as the final product than those based on CaCl2 as the final product, which has been commonly used in previous studies. The initial reaction was controlled by diffusion of HCl in gas phase and the subsequent reaction by gaseous diffusion through the developing product layer. Increasing the HCI concentration raised the initial rate as well as conversion. However, overloading the lime with excessive HCI caused clogging at its surface and a drop in the ultimate conversion. Limes with smaller particle diameters and higher surface areas were found to be more reactive. The effect of gas

  16. Palladium nanoparticles anchored on graphene nanosheets: Methanol, ethanol oxidation reactions and their kinetic studies

    SciTech Connect

    Nagaraju, D.H.; Devaraj, S.; Balaya, P.

    2014-12-15

    Highlights: • Palladium nanoparticles decorated graphene is synthesized in a single step. • Electro-catalytic activity of Gra/Pd toward alcohol oxidation is evaluated. • 1:1 Gra/Pd exhibits good electro-catalytic activity and efficient electron transfer. - Abstract: Palladium nanoparticles decorated graphene (Gra/Pd nanocomposite) was synthesized by simultaneous chemical reduction of graphene oxide and palladium salt in a single step. The negatively charged graphene oxide (GO) facilitates uniform distribution of Pd{sup 2+} ions onto its surface. The subsequent reduction by hydrazine hydrate provides well dispersed Pd nanoparticles decorated graphene. Different amount of Pd nanoparticles on graphene was synthesized by changing the volume to weight ratio of GO to PdCl{sub 2}. X-ray diffraction studies showed FCC lattice of Pd with predominant (1 1 1) plane. SEM and TEM studies revealed that thin graphene nanosheets are decorated by Pd nanoparticles. Raman spectroscopic studies revealed the presence of graphene nanosheets. The electro-catalytic activity of Gra/Pd nanocomposites toward methanol and ethanol oxidation in alkaline medium was evaluated by cyclic voltammetric studies. 1:1 Gra/Pd nanocomposite exhibited good electro-catalytic activity and efficient electron transfer. The kinetics of electron transfer was studied using chronoamperometry. Improved electro-catalytic activity of 1:1 Gra/Pd nanocomposite toward alcohol oxidation makes it as a potential anode for the alcohol fuel cells.

  17. KINETIC STUDIES OF THE REDUCTION OF AROMATIC AZO COMPOUNDS IN ANAEROBIC SEDIMENT/WATER SYSTEMS

    EPA Science Inventory

    The reductive transformation of azobenzene and selected derivatives was investigated in anaerobic sediment/water systems. The azo compounds exhibited pseudo-first-order disappearance kinetics through at least three half-lives. The reduction kinetics of these compounds was studied...

  18. In situ hydrogen consumption kinetics as an indicator of subsurface microbial activity.

    PubMed

    Harris, Steve H; Smith, Richard L; Suflita, Joseph M

    2007-05-01

    There are few methods available for broadly assessing microbial community metabolism directly within a groundwater environment. In this study, hydrogen consumption rates were estimated from in situ injection/withdrawal tests conducted in two geochemically varying, contaminated aquifers as an approach towards developing such a method. The hydrogen consumption first-order rates varied from 0.002 nM h(-1) for an uncontaminated, aerobic site to 2.5 nM h(-1) for a contaminated site where sulfate reduction was a predominant process. The method could accommodate the over three orders of magnitude range in rates that existed between subsurface sites. In a denitrifying zone, the hydrogen consumption rate (0.02 nM h(-1)) was immediately abolished in the presence of air or an antibiotic mixture, suggesting that such measurements may also be sensitive to the effects of environmental perturbations on field microbial activities. Comparable laboratory determinations with sediment slurries exhibited hydrogen consumption kinetics that differed substantially from the field estimates. Because anaerobic degradation of organic matter relies on the rapid consumption of hydrogen and subsequent maintenance at low levels, such in situ measures of hydrogen turnover can serve as a key indicator of the functioning of microbial food webs and may be more reliable than laboratory determinations. PMID:17439588

  19. Antifungal activity, kinetics and molecular mechanism of action of garlic oil against Candida albicans.

    PubMed

    Li, Wen-Ru; Shi, Qing-Shan; Dai, Huan-Qin; Liang, Qing; Xie, Xiao-Bao; Huang, Xiao-Mo; Zhao, Guang-Ze; Zhang, Li-Xin

    2016-01-01

    The antifungal activity, kinetics, and molecular mechanism of action of garlic oil against Candida albicans were investigated in this study using multiple methods. Using the poisoned food technique, we determined that the minimum inhibitory concentration of garlic oil was 0.35 μg/mL. Observation by transmission electron microscopy indicated that garlic oil could penetrate the cellular membrane of C. albicans as well as the membranes of organelles such as the mitochondria, resulting in organelle destruction and ultimately cell death. RNA sequencing analysis showed that garlic oil induced differential expression of critical genes including those involved in oxidation-reduction processes, pathogenesis, and cellular response to drugs and starvation. Moreover, the differentially expressed genes were mainly clustered in 19 KEGG pathways, representing vital cellular processes such as oxidative phosphorylation, the spliceosome, the cell cycle, and protein processing in the endoplasmic reticulum. In addition, four upregulated proteins selected after two-dimensional fluorescence difference in gel electrophoresis (2D-DIGE) analysis were identified with high probability by mass spectrometry as putative cytoplasmic adenylate kinase, pyruvate decarboxylase, hexokinase, and heat shock proteins. This is suggestive of a C. albicans stress responses to garlic oil treatment. On the other hand, a large number of proteins were downregulated, leading to significant disruption of the normal metabolism and physical functions of C. albicans. PMID:26948845

  20. In situ hydrogen consumption kinetics as an indicator of subsurface microbial activity

    USGS Publications Warehouse

    Harris, S.H.; Smith, R.L.; Suflita, J.M.

    2007-01-01

    There are few methods available for broadly assessing microbial community metabolism directly within a groundwater environment. In this study, hydrogen consumption rates were estimated from in situ injection/withdrawal tests conducted in two geochemically varying, contaminated aquifers as an approach towards developing such a method. The hydrogen consumption first-order rates varied from 0.002 nM h-1 for an uncontaminated, aerobic site to 2.5 nM h-1 for a contaminated site where sulfate reduction was a predominant process. The method could accommodate the over three orders of magnitude range in rates that existed between subsurface sites. In a denitrifying zone, the hydrogen consumption rate (0.02 nM h-1) was immediately abolished in the presence of air or an antibiotic mixture, suggesting that such measurements may also be sensitive to the effects of environmental perturbations on field microbial activities. Comparable laboratory determinations with sediment slurries exhibited hydrogen consumption kinetics that differed substantially from the field estimates. Because anaerobic degradation of organic matter relies on the rapid consumption of hydrogen and subsequent maintenance at low levels, such in situ measures of hydrogen turnover can serve as a key indicator of the functioning of microbial food webs and may be more reliable than laboratory determinations. ?? 2007 Federation of European Microbiological Societies.

  1. Antifungal activity, kinetics and molecular mechanism of action of garlic oil against Candida albicans

    PubMed Central

    Li, Wen-Ru; Shi, Qing-Shan; Dai, Huan-Qin; Liang, Qing; Xie, Xiao-Bao; Huang, Xiao-Mo; Zhao, Guang-Ze; Zhang, Li-Xin

    2016-01-01

    The antifungal activity, kinetics, and molecular mechanism of action of garlic oil against Candida albicans were investigated in this study using multiple methods. Using the poisoned food technique, we determined that the minimum inhibitory concentration of garlic oil was 0.35 μg/mL. Observation by transmission electron microscopy indicated that garlic oil could penetrate the cellular membrane of C. albicans as well as the membranes of organelles such as the mitochondria, resulting in organelle destruction and ultimately cell death. RNA sequencing analysis showed that garlic oil induced differential expression of critical genes including those involved in oxidation-reduction processes, pathogenesis, and cellular response to drugs and starvation. Moreover, the differentially expressed genes were mainly clustered in 19 KEGG pathways, representing vital cellular processes such as oxidative phosphorylation, the spliceosome, the cell cycle, and protein processing in the endoplasmic reticulum. In addition, four upregulated proteins selected after two-dimensional fluorescence difference in gel electrophoresis (2D-DIGE) analysis were identified with high probability by mass spectrometry as putative cytoplasmic adenylate kinase, pyruvate decarboxylase, hexokinase, and heat shock proteins. This is suggestive of a C. albicans stress responses to garlic oil treatment. On the other hand, a large number of proteins were downregulated, leading to significant disruption of the normal metabolism and physical functions of C. albicans. PMID:26948845

  2. Natural History, Growth Kinetics and Outcomes of Untreated Clinically Localized Renal Tumors Under Active Surveillance

    PubMed Central

    Crispen, Paul L.; Viterbo, Rosalia; Boorjian, Stephen A.; Greenberg, Richard E.; Chen, David Y.T.; Uzzo, Robert G.

    2010-01-01

    Background The growth kinetics of untreated solid organ malignancies are not defined. Radiographic active surveillance (AS) of renal tumors in patient unfit or unwilling to undergo intervention provides an opportunity to quantitate the natural history of untreated localized tumors. Here we report the radiographic growth kinetics of renal neoplasms during a period of surveillance. Methods We identified patients with enhancing renal masses who were radiographically observed for at least 12 months. Clinical and pathological records were reviewed to determine tumor growth kinetics and clinical outcomes. Tumor growth kinetics were expressed in terms of absolute and relative linear and volumetric growth. Results We identified 172 renal tumors in 154 patients under AS. Median tumor diameter and volume on presentation was 2.0 cm (mean 2.5, range 0.4 - 12.0) and 4.18 cm3 (mean 20.0, range 0.0033 – 904). Median duration of follow-up was 24 months (mean 31, range 12 – 156). A significant association between presenting tumor size and proportional growth was noted, with smaller tumors growing faster than larger tumors. 39% (68/173) of tumors underwent delayed intervention and 84% (57/68) were pathologically malignant. Progression to metastatic disease was noted in 1.3% (2/154) of patients. Conclusions We demonstrate the association between a tumor’s volume and subsequent growth with smaller tumors exhibiting significantly faster volumetric growth than larger tumors, consistent with Gompertzian kinetics. Surveillance of localized renal tumors is associated with a low rate of disease progression in the intermediate term and suggests potential over-treatment biases in select patients. PMID:19402168

  3. [Kinetic studies of protein kinase A in rat liver during late sepsis].

    PubMed

    Jin, Y W; Yang, S L; Hsu, H K; Wu, S N; Liu, M S

    1992-09-01

    The covalent modification of receptor proteins via phosphorylation and dephosphorylation is one of the principal mechanisms controlling carbohydrate metabolism and is known to be regulated by various protein kinases. Recent studies indicated that many hormones may exert their effects on cellular metabolism by regulating intracellular c-AMP levels and by activating a c-AMP dependent protein kinase, i.e., protein kinase A. The metabolic disturbances during sepsis are characterized by an initial hyperglycemia followed by a progressive hypoglycemia and a depletion of hepatic glycogen content. The latter is coupled with a slowdown in glycogenesis, an accelerated glycogenolysis, and a depression in gluconeogenesis in the liver. Since the liver is the major organ that regulates the homeostatic level of blood glucose, it is conceivable that the sepsis-induced glucose dyshomeostasis might be mediated by changes in protein kinase activity and the kinetic characteristics of enzymes. The present experiment was designed to study the correlation between protein kinase A and the pathophysiology of hepatic glucose dyshomeostasis during sepsis. Sepsis was induced in rats by cecal ligation and puncture (CLP). Late sepsis occurred 18 hours after CLP. Protein kinase A was extracted from the rat livers by acid precipitation and ammonium sulfate fractionation, and then partially purified by DEAE-cellulose. The results show that in the late sepsis, type-I protein kinase A (eluted at low ionic strength) activity was significantly decreased by 34-52% (P < 0.01). The kinetic parameters such as Vmax's for ATP, histone, and c-AMP were also significantly decreased from the control values of 6.1 +/- 0.9, 5.4 +/- 0.8, and 5.1 +/- 1.9 nmoles/mg.min. to 3.6 +/- 0.5, 2.8 +/- 0.3, and 2.5 +/- 0.5 nmoles/mg.min., respectively. Analysis using Hill's equation indicates that the S0.5 and n (Hill coefficient) values of the various substrates and activators for type-I protein kinase A remained unchanged

  4. A kinetic model based on experimental study of structural evolution of natural carbonaceous material to graphite

    NASA Astrophysics Data System (ADS)

    Nakamura, Y.; Yoshino, T.; Satish-Kumar, M.

    2015-12-01

    We report here new experimental kinetic data on the structural evolution of carbonaceous materials (CM) to graphite in a wide range of temperature conditions (1000 and 1450 °C) and treatment time (10 min to 115 hrs) under a pressure condition of 1GPa. The morphologies and crystallinities of natural CM, extracted from sediments in the Shimanto accretionary complex and Hidaka metamorphic belt, transformed to fully ordered graphite with increasing temperature and annealing duration. The time-temperature relations of each crystal parameter obtained using XRD analysis and micro-Raman spectroscopy demonstrated sigmoidal transformations from amorphous to graphitic structure, suggesting the complexity of chemical reactions undergoing during graphitization. To assess these kinetic processes, the results were analyzed using a superposition method in which the crystal parameters were superposed to reference temperature with non-linear regression curves. The master curves fitted by sigmoidal and power functions exhibited very good correlation coefficients of 0.940 to 0.991, suggesting the Arrhenian relation between temperature and time. On the basis of master curves and shift values, we obtained the effective activation energies of 274 +/- 9 kJmol-1 and 339 +/- 6 kJmol-1 for two different natural CM. When compared with the previous studies, our data gave remarkably low activation energies for natural graphitization, which can be represented in a time-temperature relation. In addition, the sigmoidal functions obtained from time-temperature relations can be extrapolated for low temperature condition at 1GPa. Our kinetic model predicts that if the CM underwent metamorphism for about one million years, it begins to crystallize at ≈ 420 °C and transform to fully ordered graphite at over ≈ 510 °C. Thus, natural graphitization could be discussed by the laboratory experiments using natural precursor materials under realistic pressure condition and time span in the Earth's crust.

  5. Crystallographic, kinetic, and spectroscopic study of the first ligninolytic peroxidase presenting a catalytic tyrosine.

    PubMed

    Miki, Yuta; Calviño, Fabiola R; Pogni, Rebecca; Giansanti, Stefania; Ruiz-Dueñas, Francisco J; Martínez, María Jesús; Basosi, Riccardo; Romero, Antonio; Martínez, Angel T

    2011-04-29

    Trametes cervina lignin peroxidase (LiP) is a unique enzyme lacking the catalytic tryptophan strictly conserved in all other LiPs and versatile peroxidases (more than 30 sequences available). Recombinant T. cervina LiP and site-directed variants were investigated by crystallographic, kinetic, and spectroscopic techniques. The crystal structure shows three substrate oxidation site candidates involving His-170, Asp-146, and Tyr-181. Steady-state kinetics for oxidation of veratryl alcohol (the typical LiP substrate) by variants at the above three residues reveals a crucial role of Tyr-181 in LiP activity. Moreover, assays with ferrocytochrome c show that its ability to oxidize large molecules (a requisite property for oxidation of the lignin polymer) originates in Tyr-181. This residue is also involved in the oxidation of 1,4-dimethoxybenzene, a reaction initiated by the one-electron abstraction with formation of substrate cation radical, as described for the well known Phanerochaete chrysosporium LiP. Detailed spectroscopic and kinetic investigations, including low temperature EPR, show that the porphyrin radical in the two-electron activated T. cervina LiP is unstable and rapidly receives one electron from Tyr-181, forming a catalytic protein radical, which is identified as an H-bonded neutral tyrosyl radical. The crystal structure reveals a partially exposed location of Tyr-181, compatible with its catalytic role, and several neighbor residues probably contributing to catalysis: (i) by enabling substrate recognition by aromatic interactions; (ii) by acting as proton acceptor/donor from Tyr-181 or H-bonding the radical form; and (iii) by providing the acidic environment that would facilitate oxidation. This is the first structure-function study of the only ligninolytic peroxidase described to date that has a catalytic tyrosine. PMID:21367853

  6. Polymer conformations of gas-hydrate kinetic inhibitors: A small-angle neutron scattering study

    NASA Astrophysics Data System (ADS)

    King, H. E.; Hutter, Jeffrey L.; Lin, Min Y.; Sun, Thomas

    2000-02-01

    We have used small-angle neutron scattering to characterize the polymer conformations of four nonionic water soluble polymers: poly(ethylene oxide), poly(N-vinyl-2-pyrollidone), poly(N-vinyl-2-caprolactam), and an N-methyl, N-vinylacetamide/N-vinyl-2-caprolactam copolymer. The last three of these are able to kinetically suppress hydrate crystallization, and their inhibitor activity ranges from moderate to very effective. This attribute is of significant commercial importance to the oil and gas industry, but the mechanism of the activity is unknown. The dilute-solution polymer conformation in a hydrate-forming tetrahydrofuran/water fluid shows little difference among the four polymers: the majority of the scattering is that expected for a polymer in a good solvent. Each solution also exhibits some additional low-q scattering which we attribute to aggregates. In the presence of a hydrate-crystal/liquid slurry, the three inhibitor polymers significantly change their conformation. Utilizing results from our previous contrast variation study, we show that this arises from polymer adsorbed to the hydrate-crystal surface. Furthermore, we find a strong correlation between the scattering intensity at low q values and the effectiveness of the inhibitor polymer. We suggest this is an indication that as surface adsorption increases, the inhibitor's blocking of growth sites increases. Also measured for one of the kinetic-inhibitor polymers was the dilute-solution polymer conformation in a hydrate-forming propane/water fluid (hydrate crystal free). This system shows additional low-q scattering, possibly indicating a polymer-propane interaction prior to crystal formation. This may affect hydrate nucleation behavior and offer a second mechanism for kinetic hydrate inhibition.

  7. Inhibition kinetics of cabbage butterfly (Pieris rapae L.) larvae phenoloxidase activity by 3-hydroxy-4-methoxybenzaldehyde thiosemicarbazone.

    PubMed

    Xue, Chao-Bin; Luo, Wan-Chun; Jiang, Lin; Xie, Xian-Ye; Xiao, Ting; Yan, Lei

    2007-11-01

    Phenoloxidase (PO) is a key enzyme in insect development, responsible for catalyzing the hydroxylation of tyrosine into o-diphenols and the oxidation of o-diphenols into o-quinones. In the present study, the kinetic assay in air-saturated solutions and the kinetic behavior of PO from Pieris rapae (Lepidoptera) larvae in the oxidation of L-tyrosine (a monophenol) and L-DOPA (l-3, 4-dihydroxyphenylalanine) (a diphenol) was studied. The inhibitory effects of 3-hydroxy-4-methoxybenzaldehyde thiosemicarbazone (3-H-4-MBT) on the monophenolase and diphenolase activities of PO were also studied. The results show that 3-H-4-MBT can inhibit both the monophenolase and diphenolase activities of PO. The lag period of L-tyrosine oxidation catalyzed by the enzyme was obviously lengthened and the steady-state activities of the enzyme sharply decreased. The inhibitor was found to be noncompetitively reversible with a K I (K I = K IS) of 0.30 micromol/L and an estimated IC50 of 0.14 +/- 0.02 micromol/L for monophenolase and 0.26 +/- 0.04 micromol/L for diphenolase. In the time course of the oxidation of L-DOPA catalyzed by the enzyme in the presence of different concentrations of 3-H-4-MBT, the rate decreased with increasing time until a straight line was approached. The microscopic rate constants for the reaction of 3-H-4-MBT with the enzyme were determined. PMID:18025600

  8. Evidence for the kinetic partitioning of polymerase activity on G-quadruplex DNA

    PubMed Central

    Eddy, Sarah; Maddukuri, Leena; Ketkar, Amit; Zafar, Maroof K.; Henninger, Erin E.; Pursell, Zachary F.; Eoff, Robert L.

    2015-01-01

    We have investigated the action of the human DNA polymerase epsilon (hpol ε) and eta (hpol η) catalytic cores on G-quadruplex (G4) DNA substrates derived from the promoter of the c-MYC proto-oncogene. The translesion enzyme hpol η exhibits a 6.2-fold preference for binding to G4 DNA relative to non-G4 DNA, while hpol ε binds both G4 and non-G4 substrates with near equal affinity. Kinetic analysis of single-nucleotide insertion by hpol η reveals that it is able to maintain greater than 25% activity on G4 substrates compared to non-G4 DNA substrates, even when the primer template junction is positioned directly adjacent to G22 (the first tetrad-associated guanine in the c-MYC G4 motif). Surprisingly, hpol η fidelity increases ~15-fold when copying G22. By way of comparison, hpol ε retains ~4% activity and has a 33-fold decrease in fidelity when copying G22. The fidelity of hpol η is ~100-fold more accurate than hpol ε when comparing the mis-insertion frequencies of the two enzymes opposite a tetrad-associated guanine. The kinetic differences observed for the B- and Y-family pols on G4 DNA support a model where a simple kinetic switch between replicative and TLS pols could help govern fork progress during G4 DNA replication. PMID:25903680

  9. Hydroxylamine nitrate self-catalytic kinetics study with adiabatic calorimetry.

    PubMed

    Liu, Lijun; Wei, Chunyang; Guo, Yuyan; Rogers, William J; Sam Mannan, M

    2009-03-15

    Hydroxylamine nitrate (HAN) is an important member of the hydroxylamine compound family with applications that include equipment decontamination in the nuclear industry and aqueous or solid propellants. Due to its instability and autocatalytic behavior, HAN has been involved in several incidents at the Hanford and Savannah River Site (SRS) [Technical Report on Hydroxylamine Nitrate, US Department of Energy, 1998]. Much research has been conducted on HAN in different areas, such as combustion mechanism, decomposition mechanism, and runaway behavior. However, the autocatalytic decomposition behavior of HAN at runaway stage has not been fully addressed due to its highly exothermic and rapid decomposition behavior. This work is focused on extracting HAN autocatalytic kinetics and analyzing HAN critical behavior from adiabatic calorimetry measurements. A lumped autocatalytic kinetic model for HAN and associated model parameters are determined. Also the storage and handling critical conditions of diluted HAN solution without metal presence are quantified. PMID:18639378

  10. A Kinetic Degradation Study of Curcumin in Its Free Form and Loaded in Polymeric Micelles.

    PubMed

    Naksuriya, Ornchuma; van Steenbergen, Mies J; Torano, Javier S; Okonogi, Siriporn; Hennink, Wim E

    2016-05-01

    Curcumin, a phenolic compound, possesses many pharmacological activities and is under clinical evaluation to treat different diseases. However, conflicting data about its stability have been reported. In this study, the kinetic degradation of curcumin from a natural curcuminoid mixture under various conditions (pH, temperature, and dielectric constant of the medium) was investigated. Moreover, the degradation of pure curcumin at some selected conditions was also determined. To fully solubilize curcumin and to prevent precipitation of curcumin that occurs when low concentrations of co-solvent are present, a 50:50 (v/v) aqueous buffer/methanol mixture was used as standard medium to study its degradation kinetics. The results showed that degradation of curcumin both as pure compound and present in the curcuminoid mixture followed first order kinetic reaction. It was further shown that an increasing pH, temperature, and dielectric constant of the medium resulted in an increase in the degradation rate. Curcumin showed rapid degradation due to autoxidation in aqueous buffer pH = 8.0 with a rate constant of 280 × 10(-3) h(-1), corresponding with a half-life (t1/2) of 2.5 h. Dioxygenated bicyclopentadione was identified as the final degradation product. Importantly, curcumin loaded as curcuminoid mixture in ω-methoxy poly (ethylene glycol)-b-(N-(2-benzoyloxypropyl) methacrylamide) (mPEG-HPMA-Bz) polymeric micelles and in Triton X-100 micelles was about 300-500 times more stable than in aqueous buffer. Therefore, loading of curcumin into polymeric micelles is a promising approach to stabilize this compound and develop formulations suitable for further pharmaceutical and clinical studies. PMID:27038456

  11. Catalyst Screening and Kinetic Studies Using Microchannel Reactors

    SciTech Connect

    Cao, Chunshe; Palo, Daniel R.; Tonkovich, Annalee Y.; Wang, Yong

    2007-07-15

    A multi-parallel microchannel reactor system is described, as related to catalyst screening and discovery for heat-intensive heterogeneous catalytic reactions. Example systems are detailed, in which the rapid heat transfer of the screening device is utilized to maintain isothermal operation in multiple channels for catalyst screening as well as kinetic investigations. The advantages of the system and pertinent results are discussed, specifically for Fischer-Tropsch synthesis, methanol oxidation to formaldehyde, and methanol steam reforming.

  12. Crystallization kinetics study of cerium titanate CeTi2O6

    NASA Astrophysics Data System (ADS)

    Valeš, Václav; Matějová, Lenka; Matěj, Zdeněk; Brunátová, Tereza; Holý, Václav

    2014-02-01

    Cerium titanate CeTi2O6 has been investigated recently for its photocatalytic activity and as a safe analogue to actinide-containing brannerite-like titanates (UTi2O6, PuTi2O6, e.g.) which are intensively studied because of their use for storing nuclear waste. In this paper we report on the monoclinic phase CeTi2O6 obtained from the Ti-Ce oxide mixture prepared by a reverse micelles directed sol-gel method and subsequently annealed. The kinetics of the isothermal crystallization process is investigated by means of Johnson-Mehl-Avrami-Kolmogorov equation. The effective activation energy of the formation of CeTi2O6 particles, which is an important parameter for its synthesis, is estimated.

  13. Highly Active Titanocene Catalysts for Epoxide Hydrosilylation: Synthesis, Theory, Kinetics, EPR Spectroscopy.

    PubMed

    Henriques, Dina Schwarz G; Zimmer, Katharina; Klare, Sven; Meyer, Andreas; Rojo-Wiechel, Elena; Bauer, Mirko; Sure, Rebecca; Grimme, Stefan; Schiemann, Olav; Flowers, Robert A; Gansäuer, Andreas

    2016-06-27

    A catalytic system for titanocene-catalyzed epoxide hydrosilylation is described. It features a straightforward preparation of titanocene hydrides that leads to a reaction with low catalyst loading, high yields, and high selectivity of radical reduction. The mechanism was studied by a suite of methods, including kinetic studies, EPR spectroscopy, and computational methods. An unusual resting state leads to the observation of an inverse rate order with respect to the epoxide. PMID:27125466

  14. Active matter beyond mean-field: Ring-kinetic theory for self-propelled particles

    NASA Astrophysics Data System (ADS)

    Chou, Yen-Liang; Ihle, Thomas

    2015-02-01

    Recently, Hanke et al. [Phys. Rev. E 88, 052309 (2013), 10.1103/PhysRevE.88.052309] showed that mean-field kinetic theory fails to describe collective motion in soft active colloids and that correlations must not be neglected. Correlation effects are also expected to be essential in systems of biofilaments driven by molecular motors and in swarms of midges. To obtain correlations in an active matter system from first principles, we derive a ring-kinetic theory for Vicsek-style models of self-propelled agents from the exact N -particle evolution equation in phase space. The theory goes beyond mean-field and does not rely on Boltzmann's approximation of molecular chaos. It can handle precollisional correlations and cluster formation, which are both important to understand the phase transition to collective motion. We propose a diagrammatic technique to perform a small-density expansion of the collision operator and derive the first two equations of the Bogoliubov-Born-Green-Kirkwood-Yvon (BBGKY) hierarchy. An algorithm is presented that numerically solves the evolution equation for the two-particle correlations on a lattice. Agent-based simulations are performed and informative quantities such as orientational and density correlation functions are compared with those obtained by ring-kinetic theory. Excellent quantitative agreement between simulations and theory is found at not-too-small noises and mean free paths. This shows that there are parameter ranges in Vicsek-like models where the correlated closure of the BBGKY hierarchy gives correct and nontrivial results. We calculate the dependence of the orientational correlations on distance in the disordered phase and find that it seems to be consistent with a power law with an exponent around -1.8 , followed by an exponential decay. General limitations of the kinetic theory and its numerical solution are discussed.

  15. Kinetic Monte Carlo simulations of thermally activated magnetization reversal in dual-layer Exchange Coupled Composite recording media

    NASA Astrophysics Data System (ADS)

    Plumer, M. L.; Almudallal, A. M.; Mercer, J. I.; Whitehead, J. P.; Fal, T. J.

    The kinetic Monte Carlo (KMC) method developed for thermally activated magnetic reversal processes in single-layer recording media has been extended to study dual-layer Exchange Coupled Composition (ECC) media used in current and next generations of disc drives. The attempt frequency is derived from the Langer formalism with the saddle point determined using a variant of Bellman Ford algorithm. Complication (such as stagnation) arising from coupled grains having metastable states are addressed. MH-hysteresis loops are calculated over a wide range of anisotropy ratios, sweep rates and inter-layer coupling parameter. Results are compared with standard micromagnetics at fast sweep rates and experimental results at slow sweep rates.

  16. Aerobic composting of waste activated sludge: Kinetic analysis for microbiological reaction and oxygen consumption

    SciTech Connect

    Yamada, Y.; Kawase, Y. . E-mail: bckawase@mail.eng.toyo.ac.jp

    2006-07-01

    In order to examine the optimal design and operating parameters, kinetics for microbiological reaction and oxygen consumption in composting of waste activated sludge were quantitatively examined. A series of experiments was conducted to discuss the optimal operating parameters for aerobic composting of waste activated sludge obtained from Kawagoe City Wastewater Treatment Plant (Saitama, Japan) using 4 and 20 L laboratory scale bioreactors. Aeration rate, compositions of compost mixture and height of compost pile were investigated as main design and operating parameters. The optimal aerobic composting of waste activated sludge was found at the aeration rate of 2.0 L/min/kg (initial composting mixture dry weight). A compost pile up to 0.5 m could be operated effectively. A simple model for composting of waste activated sludge in a composting reactor was developed by assuming that a solid phase of compost mixture is well mixed and the kinetics for microbiological reaction is represented by a Monod-type equation. The model predictions could fit the experimental data for decomposition of waste activated sludge with an average deviation of 2.14%. Oxygen consumption during composting was also examined using a simplified model in which the oxygen consumption was represented by a Monod-type equation and the axial distribution of oxygen concentration in the composting pile was described by a plug-flow model. The predictions could satisfactorily simulate the experiment results for the average maximum oxygen consumption rate during aerobic composting with an average deviation of 7.4%.

  17. Long-time atomistic evolution of grain boundary in nickel using the kinetic activation-relaxation technique

    NASA Astrophysics Data System (ADS)

    Mahmoud, Sami; Trochet, Mickaël; Restrepo, Oscar; Mousseau, Normand

    The microscopic mechanisms associated with the evolution of metallic materials are still a matter of debate as both experimental and numerical approaches fail to provide a detailed atomic picture of their time evolution. Here, we use the kinetic activation-relaxation technique (k-ART), an unbiased off-lattice kinetic Monte Carlo method with on-the-fly catalog building to overcome these limitations and follow the atomistic evolution of a 10.000-atom grain boundary Ni system over macroscopic time scales. We first characterize the kinetic properties of four different empirical potentials, the embedded atom method (EAM), the first and second modified embedded atom method (MEAM1NN and MEAM2NN respectively) and the Reax force field (ReaxFF) potentials. Comparing the energetics, the elastic effects and the diffusion mechanisms for systems with one to three vacancies and one to three self-interstitials in nickel simulated over second time scale, we conclude that ReaxFF and EAM potentials are closest to experimental values. We then proceed to study the long-time evolution of a grain boundary with the Reax forcefield and to offer a detailed description of its energy landscape, including the exact description of short and long-range effects on self-diffusion along the interface

  18. Adsorption behavior of direct red 80 and congo red onto activated carbon/surfactant: Process optimization, kinetics and equilibrium

    NASA Astrophysics Data System (ADS)

    Cheng, Zhengjun; Zhang, Lei; Guo, Xiao; Jiang, Xiaohui; Li, Tian

    2015-02-01

    Adsorptions of congo red and direct red 80 onto activated carbon/surfactant from aqueous solution were optimized. The Box-Behnken design (BBD) has been employed to analyze the effects of concentration of surfactant, temperature, pH, and initial concentration of the dye in the adsorption capacity. Their corresponding experimental data could be evaluated excellently by second order polynomial regression models and the two models were also examined based on the analysis of variance and t test statistics, respectively. The optimum conditions were obtained as follows: Cs = 34.10 μM, T = 50 °C, pH = 3.5, and CCR = 160 mg/L for the congo red system, and Cs = 34.10 μM, T = 50 °C, pH = 6.1, and CDR80 = 110 mg/L for the direct red 80 system. And in these conditions, the measured experimental maximum adsorption capacities for the congo red and direct red 80 removals were 769.48 mg/g and 519.90 mg/g, which were consistent with their corresponding predicted values, with small relative errors of -2.81% and -0.67%, respectively. The adsorption equilibrium and kinetics for the two dye adsorptions onto AC/DDAC were also investigated. The experimental data were fitted by four isotherm models, and Langmuir model presented the best fit. The kinetic studies indicated that the kinetic data followed the pseudo-second-order model.

  19. Kinetics of Ion Transport in Perovskite Active Layers and Its Implications for Active Layer Stability.

    PubMed

    Bag, Monojit; Renna, Lawrence A; Adhikari, Ramesh Y; Karak, Supravat; Liu, Feng; Lahti, Paul M; Russell, Thomas P; Tuominen, Mark T; Venkataraman, D

    2015-10-14

    Solar cells fabricated using alkyl ammonium metal halides as light absorbers have the right combination of high power conversion efficiency and ease of fabrication to realize inexpensive but efficient thin film solar cells. However, they degrade under prolonged exposure to sunlight. Herein, we show that this degradation is quasi-reversible, and that it can be greatly lessened by simple modifications of the solar cell operating conditions. We studied perovskite devices using electrochemical impedance spectroscopy (EIS) with methylammonium (MA)-, formamidinium (FA)-, and MA(x)FA(1-x) lead triiodide as active layers. From variable temperature EIS studies, we found that the diffusion coefficient using MA ions was greater than when using FA ions. Structural studies using powder X-ray diffraction (PXRD) show that for MAPbI3 a structural change and lattice expansion occurs at device operating temperatures. On the basis of EIS and PXRD studies, we postulate that in MAPbI3 the predominant mechanism of accelerated device degradation under sunlight involves thermally activated fast ion transport coupled with a lattice-expanding phase transition, both of which are facilitated by absorption of the infrared component of the solar spectrum. Using these findings, we show that the devices show greatly improved operation lifetimes and stability under white-light emitting diodes, or under a solar simulator with an infrared cutoff filter or with cooling. PMID:26414066

  20. Monte-Carlo modelling of nano-material photocatalysis: bridging photocatalytic activity and microscopic charge kinetics.

    PubMed

    Liu, Baoshun

    2016-04-20

    In photocatalysis, it is known that light intensity, organic concentration, and temperature affect the photocatalytic activity by changing the microscopic kinetics of holes and electrons. However, how the microscopic kinetics of holes and electrons relates to the photocatalytic activity was not well known. In the present research, we developed a Monte-Carlo random walking model that involved all of the charge kinetics, including the photo-generation, the recombination, the transport, and the interfacial transfer of holes and electrons, to simulate the overall photocatalytic reaction, which we called a "computer experiment" of photocatalysis. By using this model, we simulated the effect of light intensity, temperature, and organic surface coverage on the photocatalytic activity and the density of the free electrons that accumulate in the simulated system. It was seen that the increase of light intensity increases the electron density and its mobility, which increases the probability for a hole/electron to find an electron/hole for recombination, and consequently led to an apparent kinetics that the quantum yield (QY) decreases with the increase of light intensity. It was also seen that the increase of organic surface coverage could increase the rate of hole interfacial transfer and result in the decrease of the probability for an electron to recombine with a hole. Moreover, the increase of organic coverage on the nano-material surface can also increase the accumulation of electrons, which enhances the mobility for electrons to undergo interfacial transfer, and finally leads to the increase of photocatalytic activity. The simulation showed that the temperature had a more complicated effect, as it can simultaneously change the activation of electrons, the interfacial transfer of holes, and the interfacial transfer of electrons. It was shown that the interfacial transfer of holes might play a main role at low temperature, with the temperature-dependence of QY

  1. Structure-activity relationships (SAR) and structure-kinetic relationships (SKR) of pyrrolopiperidinone acetic acids as CRTh2 antagonists.

    PubMed

    Andrés, Miriam; Buil, Maria Antonia; Calbet, Marta; Casado, Oscar; Castro, Jordi; Eastwood, Paul R; Eichhorn, Peter; Ferrer, Manel; Forns, Pilar; Moreno, Imma; Petit, Silvia; Roberts, Richard S

    2014-11-01

    Pyrrolopiperidinone acetic acids (PPAs) were identified as highly potent CRTh2 receptor antagonists. In addition, many of these compounds displayed slow-dissociation kinetics from the receptor. Structure-kinetic relationship (SKR) studies allowed optimisation of the kinetics to give potent analogues with long receptor residence half-lives of up to 23 h. Low permeability was a general feature of this series, however oral bioavailability could be achieved through the use of ester prodrugs. PMID:25437503

  2. Kinetic studies of nitrate removal from aqueous solution using granular chitosan-Fe(III) complex.

    PubMed

    Hu, Qili; Chen, Nan; Feng, Chuanping; Zhang, Jing; Hu, Weiwu; Lv, Long

    2016-01-01

    In the present study, a granular chitosan-Fe(III) complex was prepared as a feasible adsorbent for the removal of nitrate from an aqueous solution. There was no significant change in terms of nitrate removal efficiency over a wide pH range of 3-11. Nitrate adsorption on the chitosan-Fe(III) complex followed the Langmuir-Freundlich isotherm model. In order to more accurately reflect adsorption and desorption behaviors at the solid/solution interface, kinetic model I and kinetic model II were proposed to simulate the interfacial process in a batch system. Nitrate adsorption on the chitosan-Fe(III) complex followed the pseudo-first-order kinetic model and kinetic model I. The proposed half-time could provide useful information for optimizing process design. Adsorption and desorption rate constants obtained from kinetic model I and kinetic model II were beneficial to understanding the interfacial process and the extent of adsorption reaction. Kinetic model I and kinetic model II implied that nitrate uptake exponentially approaches a limiting value. PMID:26942545

  3. A Novel Approach to Experimental Studies of Mineral Dissolution Kinetics

    SciTech Connect

    Chen Zhu; William E. Seyfried

    2005-01-01

    Currently, DOE is conducting pilot CO{sub 2} injection tests to evaluate the concept of geological sequestration. One strategy that potentially enhances CO{sub 2} solubility and reduces the risk of CO{sub 2} leak back to the surface is dissolution of indigenous minerals in the geological formation and precipitation of secondary carbonate phases, which increases the brine pH and immobilizes CO{sub 2}. Clearly, the rates at which these dissolution and precipitation reactions occur directly determine the efficiency of this strategy. However, one of the fundamental problems in modern geochemistry is the persistent two to five orders of magnitude discrepancy between laboratory-measured and field derived feldspar dissolution rates. To date, there is no real guidance as to how to predict silicate reaction rates for use in quantitative models. Current models for assessment of geological carbon sequestration have generally opted to use laboratory rates, in spite of the dearth of such data for compositionally complex systems, and the persistent disconnect between lab and field applications. Therefore, a firm scientific basis for predicting silicate reaction kinetics in CO{sub 2} injected geological formations is urgently needed to assure the reliability of the geochemical models used for the assessments of carbon sequestration strategies. The funded experimental and theoretical study attempts to resolve this outstanding scientific issue by novel experimental design and theoretical interpretation to measure silicate dissolution rates and iron carbonate precipitation rates at conditions pertinent to geological carbon sequestration. In the first year of the project, we have successfully developed a sample preparation method and completed three batch feldspar dissolution experiments at 200 C and 300 bars. The changes of solution chemistry as dissolution experiments progressed were monitored with on-line sampling of the aqueous phase at the constant temperature and pressure

  4. Real-time kinetic method to monitor isopeptidase activity of transglutaminase 2 on protein substrate.

    PubMed

    Thangaraju, Kiruphagaran; Biri, Beáta; Schlosser, Gitta; Kiss, Bence; Nyitray, László; Fésüs, László; Király, Róbert

    2016-07-15

    Transglutaminase 2 (TG2) is a ubiquitously expressed multifunctional protein with Ca(2+)-dependent transamidase activity forming protease-resistant N(ε)-(γ-glutamyl) lysine crosslinks between proteins. It can also function as an isopeptidase cleaving the previously formed crosslinks. The biological significance of this activity has not been revealed yet, mainly because of the lack of a protein-based method for its characterization. Here we report the development of a novel kinetic method for measuring isopeptidase activity of human TG2 by monitoring decrease in the fluorescence polarization of a protein substrate previously formed by crosslinking fluorescently labeled glutamine donor FLpepT26 to S100A4 at a specific lysine residue. The developed method could be applied to test mutant enzymes and compounds that influence isopeptidase activity of TG2. PMID:27131890

  5. Study of the Reaction Stages and Kinetics of the Europium Oxide Carbochlorination

    NASA Astrophysics Data System (ADS)

    Pomiro, Federico J.; Fouga, Gastón G.; Gaviría, Juan P.; Bohé, Ana E.

    2015-02-01

    The europium oxide (Eu2O3(s)) chlorination reaction with sucrose carbon was studied by thermogravimetry between room temperature and 1223 K (950 °C). The nonisothermal thermogravimetry showed that the reaction consists of three stages, and their stoichiometries were studied. The product of the first stage was europium oxychloride, and it showed independence of the reaction kinetics with the carbon content. Subsequently, in the second stage, the EuOCl(s) was carbochlorinated with formation of EuCl3(l) and its evaporation is observed in the third stage. The analysis by Fourier transform infrared spectroscopy of gaseous species showed that the reaction at second stage occurs with the formation of CO2(g) and CO(g). Both reactants and products were analyzed by X-ray diffraction, scanning electron microscopy and wavelength-dispersive X-ray fluorescence spectroscopy. The influence of carbon content, total flow rate, sample initial mass, chlorine partial pressure, and temperature were evaluated. The second stage kinetics was analyzed, which showed an anomalous behavior caused by generation of chlorine radicals during interaction of Cl2(g) and carbon. It was found that the reaction rate at 933 K (660 °C) was proportional to a potential function of the chlorine partial pressure whose exponent is 0.56. The conversion curves were analyzed with the Avrami-Erofeev model and it was obtained an activation energy of 154 ± 5 kJ mol-1.

  6. Optimization and kinetic studies on algal oil extraction from marine macroalgae Ulva lactuca.

    PubMed

    Suganya, Tamilarasan; Renganathan, Sahadevan

    2012-03-01

    In this present investigation, kinetic studies on oil extraction were performed in marine macroalgae Ulva lactuca. The algal biomass was characterized by scanning electron microscopy and Fourier Transform-Infra Red Spectroscopy. Six different pre-treatment methods were carried out to evaluate the best method for maximum oil extraction. Optimization of extraction parameters were performed and high oil yield was obtained at 5% moisture content, 0.12 mm particle size, 500 rpm stirrer speed, 55°C temperature, 140 min time and solvent-to-solid ratio as 6:1 with 1% diethyl-ether and 10% methylene chloride in n-hexane solvent mixture. After optimization, 10.88% (g/g) of oil extraction yield was achieved from 30 g of algal biomass. The rate constant was obtained for the first order kinetic study by differential method. The activation energy (Ea) was calculated as 63.031 kJ/mol. From the results obtained in the investigation, U. lactuca biomass was proved to be a suitable source for the biodiesel production. PMID:22209436

  7. Adsorption kinetics of phosphate and arsenate on goethite. A comparative study.

    PubMed

    Luengo, Carina; Brigante, Maximiliano; Avena, Marcelo

    2007-07-15

    The adsorption kinetics of phosphate and arsenate on goethite is studied and compared. Batch adsorption experiments were performed at different adsorbate concentrations, pH, temperatures and stirring rates. For both oxoanions the adsorption rate increases by increasing adsorbate concentration, decreasing pH and increasing temperature. It does not change by changing stirring rate. The adsorption takes place in two processes: a fast one that takes place in less than 5 min and a slow one that takes place in several hours or more. The rate of the slow process does not depend directly on the concentration of phosphate or arsenate in solution, but depends linearly on the amount of phosphate or arsenate that was adsorbed during the fast process. Apparent activation energies and absence of stirring rate effects suggest that the slow process is controlled by diffusion into pores, although the evidence is not conclusive. The similarities in the adsorption kinetics of phosphate and arsenate are quantitatively shown by using a three-parameters equation that takes into account both the fast and the slow processes. These similarities are in line with the similar reactivity that phosphate and arsenate have in general and may be important for theoretical and experimental studies of the fate of these oxoanions in the environment. PMID:17448491

  8. Quantum dot based enzyme activity sensors present deviations from Michaelis-Menten kinetic model

    NASA Astrophysics Data System (ADS)

    Díaz, Sebastián. A.; Brown, Carl W.; Malanoski, Anthony P.; Oh, Eunkeu; Susumu, Kimihiro; Medintz, Igor L.

    2016-03-01

    Nanosensors employing quantum dots (QDs) and enzyme substrates with fluorescent moieties offer tremendous promise for disease surveillance/diagnostics and as high-throughput co-factor assays. Advantages of QDs over other nanoscaffolds include their small size and inherent photochemical properties such as size tunable fluorescence, ease in attaching functional moieties, and resistance to photobleaching. These properties make QDs excellent Förster Resonance Energy Transfer (FRET) donors; well-suited for rapid, optical measurement applications. We report enzyme sensors designed with a single FRET donor, the QD donor acting as a scaffold to multiple substrates or acceptors. The QD-sensor follows the concrete activity of the enzyme, as compared to the most common methodologies that quantify the enzyme amount or its mRNA precursor. As the sensor reports on the enzyme activity in real-time we can actively follow the kinetics of the enzyme. Though classic Michaelis-Menten (MM) parameters can be obtained to describe the activity. In the course of these experiments deviations, both decreasing and increasing the kinetics, from the common MM model were observed upon close examinations. From these observations additional experiments were undertaken to understand the varying mechanisms. Different enzymes can present different deviations depending on the chosen target, e.g. trypsin appears to present a positive hopping mechanism while collagenase demonstrates a QD caused reversible inhibition.

  9. Molten carbonate fuel cell (MCFC) porous electrode and kinetic studies

    SciTech Connect

    Selman, J.R. )

    1992-10-01

    This report sumarizes a research project undertaken to improve the performance and understand the limitations of porous electrodes for molten carbonate fuel cells (MCFCs). Using a novel MCFC rotating-disk'' electrode, the electrode kinetic and mass transfer properties of commonly used electrode materials were determined, and a practical performance model for MCFC electrodes was developed. The report also outlines a general strategy for designing a high-performance MCFC electrode, assesses the current understanding of porous electrode operation, and discusses some of the unresolved questions of the field. An appendix gives a complete list of the many theses, journal articles, and symposium contributions based on this research.

  10. Kinetic study of ion-acoustic plasma vortices

    SciTech Connect

    Khan, S. A.; Aman-ur-Rehman; Mendonca, J. T.

    2014-09-15

    The kinetic theory of electron plasma waves with finite orbital angular momentum has recently been introduced by Mendonca. This model shows possibility of new kind of plasma waves and instabilities. We have extended the theory to ion-acoustic plasma vortices carrying orbital angular momentum. The dispersion equation is derived under paraxial approximation which exhibits a kind of linear vortices and their Landau damping. The numerical solutions are obtained and compared with analytical results which are in good agreement. The physical interpretation of the ion-acoustic plasma vortices and their Landau resonance conditions are given for typical case of Maxwellian plasmas.

  11. Amide-Modified Prenylcysteine based Icmt Inhibitors: Structure Activity Relationships, Kinetic Analysis and Cellular Characterization

    PubMed Central

    Majmudar, Jaimeen D.; Hodges-Loaiza, Heather B.; Hahne, Kalub; Donelson, James L.; Song, Jiao; Shrestha, Liza; Harrison, Marietta L.; Hrycyna, Christine A.; Gibbs, Richard A.

    2012-01-01

    Human protein isoprenylcysteine carboxyl methyltransferase (hIcmt) is the enzyme responsible for the α-carboxyl methylation of the C-termimal isoprenylated cysteine of CaaX proteins, including Ras proteins. This specific posttranslational methylation event has been shown to be important for cellular transformation by oncogenic Ras isoforms. This finding led to interest in hIcmt inhibitors as potential anti-cancer agents. Previous analog studies based on N-acetyl-S-farnesylcysteine identified two prenylcysteine-based low micromolar inhibitors (1a and 1b) of hIcmt, each bearing a phenoxyphenyl amide modification. In this study, a focused library of analogs of 1a and 1b was synthesized and screened versus hIcmt, delineating structural features important for inhibition. Kinetic characterization of the most potent analogs 1a and 1b established that both inhibitors exhibited mixed-mode inhibition and that the competitive component predominated. Using the Cheng – Prusoff method, the Ki values were determined from the IC50 values. Analog 1a has a KIC of 1.4 ± 0.2 μM and a KIU of 4.8 ± 0.5 μM while 1b has a KIC of 0.5 ± 0.07 μM and a KIU of 1.9 ± 0.2 μM. Cellular evaluation of 1b revealed that it alters the subcellular localization of GFP-KRas, and also inhibits both Ras activation and Erk phosphorylation in Jurkat cells. PMID:22142613

  12. Study of Electron Acceleration and Multiple Dipolarization Fronts in 3D kinetic models

    NASA Astrophysics Data System (ADS)

    Lapenta, Giovanni; Ashour-Abdalla, Maha; Walker, Raymond; El-Alaoui, Mostafa

    2014-05-01

    The THEMIS mission encountered a depolarization front (DF) during a magnetotail crossing in the interval 035600 - 035900 UT on February 15, 2008 [1]. We present the results of an innovative investigative approach: we combine a global MHD model of the full Earth environment with a local PIC simulation. The global MHD view is provided on the UCLA model applied to the conditions for the interval of interest on Feb 15, 2008. At the specific time of 034800UT, a reconnection site first appear at about x=-15RE, y=4RE. We then use this specific MHD state as the initial setup for a fully kinetic PIC simulation, performed with the iPic3D code [2]. We consider a one way coupling where the MHD state is used as initial state and boundary conditions for the kinetic study [3]. In the present case, the time span of the kinetic simulation is short form the perspective of the global MHD simulation and does not require a full coupling where the MHD then process the information received back from the kinetic run [4]. The fields and particles are advanced self-consistently from the MHD state using a completely kinetic treatment. Many features missed by the MHD model emerge. Most notably a fast reconnection pattern develops and an unsteady reconnection process develops. The typical signatures of fast kinetic reconnection (Hall field) are observed and particle acceleration is obtained self consistently in the fields generated by the PIC simulation. The focus of the presentation will be the mechanisms of unsteady reconnection leading to multiple DFs. We observe intense wave activity propagating off the separatrices. We conduct a spectral analysis to isolate the different wave components in the lower hybrid and whistler regime. The unsteady reconnection and multiple DFs are also analysed in their impact on the energy transfer. We track the conversion of magnetic energy to particle energy and Poynting flux. The processes observed in the simulation are then compared with in situ THEMIS data

  13. Kinetics and equilibrium of cadmium complexation with heterogeneous complexants: A stopped-flow study at Na-illite

    SciTech Connect

    Pohlmeier, A.; Ruetzel, H.

    1996-07-15

    Rapid kinetics and equilibrium of the ion exchange of Na{sup +} by Cd{sup 2+} at illite are studied by the stopped-flow technique and DPASV, respectively, as an example for reactions at heterogeneous surfaces. For the first time both kinetics and equilibrium are analyzed for the same system by kinetic- and affinity-spectra, taking into consideration the heterogeneity of binding sites. It is possible to calculate model independent kinetic spectra by means of the CONTIN program; the isotherm is evaluated by Sips` distribution function. Monomodal distribution functions are found, characterized by mean values and half widths at half height in the range between 0.2 and 0.3 log (k/s{sup {minus}1}) for the kinetics and 0.16 log (K/L/mol) for the affinity. From both analyses the mean ion exchange coefficient is determined as 2.2 {+-} 0.4 mol/liter and 1.5 {+-} 0.4 mol/liter, respectively. The kinetics are rapid; only one process is observed that is assigned to the binding of Cd{sup 2+} at the outer surface. The high activation-enthalpy of 35 kJ/mol proves that the exchange reaction of 2 Na{sup +} by cd{sup 2+} at the binding site is the rate-determining step and not the diffusion to the surface. The large negative activation-entropy of {minus}105 J/mol K indicates that this rate-determining step is of associative nature.

  14. Structural basis for selective inhibition of purine nucleoside phosphorylase from Schistosoma mansoni: kinetic and structural studies.

    PubMed

    Castilho, Marcelo S; Postigo, Matheus P; Pereira, Humberto M; Oliva, Glaucius; Andricopulo, Adriano D

    2010-02-15

    Selectivity plays a crucial role in the design of enzyme inhibitors as novel antiparasitic agents, particularly in cases where the target enzyme is also present in the human host. Purine nucleoside phosphorylase from Schistosoma mansoni (SmPNP) is an attractive target for the discovery of potential antischistosomal agents. In the present work, kinetic studies were carried out in order to determine the inhibitory potency, mode of action and enzyme selectivity of a series of inhibitors of SmPNP. In addition, crystallographic studies provided important structural insights for rational inhibitor design, revealing consistent structural differences in the binding mode of the inhibitors in the active sites of the SmPNP and human PNP (HsPNP) structures. The molecular information gathered in this work should be useful for future medicinal chemistry efforts in the design of new inhibitors of SmPNP having increased affinity and selectivity. PMID:20129792

  15. A Novel Approach to Experimental Studies of Mineral Dissolution Kinetics

    SciTech Connect

    Chen Zhu

    2006-08-31

    Currently, DOE is conducting pilot CO{sub 2} injection tests to evaluate the concept of geological sequestration. One strategy that potentially enhances CO{sub 2} solubility and reduces the risk of CO{sub 2} leak back to the surface is dissolution of indigenous minerals in the geological formation and precipitation of secondary carbonate phases, which increases the brine pH and immobilizes CO{sub 2}. Clearly, the rates at which these dissolution and precipitation reactions occur directly determine the efficiency of this strategy. However, one of the fundamental problems in modern geochemistry is the persistent two to five orders of magnitude discrepancy between laboratory measured and field derived feldspar dissolution rates. To date, there is no real guidance as to how to predict silicate reaction rates for use in quantitative models. Current models for assessment of geological carbon sequestration have generally opted to use laboratory rates, in spite of the dearth of such data for compositionally complex systems, and the persistent disconnect between laboratory and field applications. Therefore, a firm scientific basis for predicting silicate reaction kinetics in CO2 injected geological formations is urgently needed to assure the reliability of the geochemical models used for the assessments of carbon sequestration strategies. The funded experimental and theoretical study attempts to resolve this outstanding scientific issue by novel experimental design and theoretical interpretation to measure silicate dissolution rates and iron carbonate precipitation rates at conditions pertinent to geological carbon sequestration. In the second year of the project, we completed CO{sub 2}-Navajo sandstone interaction batch and flow-through experiments and a Navajo sandstone dissolution experiment without the presence of CO{sub 2} at 200 C and 250-300 bars, and initiated dawsonite dissolution and solubility experiments. We also performed additional 5-day experiments at the

  16. A Simulation Game for the Study of Enzyme Kinetics and Inhibition.

    ERIC Educational Resources Information Center

    Chayoth, Reuben; Cohen, Annette

    1996-01-01

    Presents a simulation game that facilitates understanding of the concepts of enzyme kinetics and inhibition. The first part of the game deals with the relationship between enzyme activity and substrate concentration while the second part deals with characterization of competitive and noncompetitive inhibition of enzyme activity. (JRH)

  17. Advances in Studies of Electrode Kinetics and Mass Transport in AMTEC Cells (abstract)

    NASA Technical Reports Server (NTRS)

    Williams, R. M.; Jeffries-Nakamura, B.; Ryan, M. A.; Underwood, M. L.; Kisor, A.; O'Connor, D.; Kikkert, S.

    1993-01-01

    Previous work reported from JPL has included characterization of electrode kinetics and alkali atom transport from electrodes including Mo, W, WRh(sub x), WPt(sub x)(Mn), in sodium AMTEC cells and vapor exposure cells, and Mo in potassium vapor exposure cells. These studies were generally performed in cells with small area electrodes (about 1 to 5 cm(sup 2)), and device geometry had little effect on transport. Alkali diffusion coefficients through these electrodes have been characterized, and approximate surface diffusion coefficients derived in cases of activated transport. A basic model of electrode kinetic at the alkali metal vapor/porous metal electrode/alkali beta'-alumina solid electrolyte three phase boundary has been proposed which accounts for electrochemical reaction rates with a collision frequency near the three phase boundary and tunneling from the porous electrode partially covered with adsorbed alkali metal atoms. The small electrode effect in AMTEC cells has been discussed in several papers, but quantitative investigations have described only the overall effect and the important contribution of electrolyte resistance. The quantitative characterization of transport losses in cells with large area electrodes has been limited to simulations of large area electrode effects, or characterization of transport losses from large area electrodes with significant longitudinal temperature gradients. This paper describes new investigations of electrochemical kinetics and transport, particularily with WPt(sub 3.5) electrodes, including the influence of electrode size on the mass transport loss in the AMTEC cell. These electrodes possess excellent sodium transport properties making verification of device limitations on transport much more readily attained.

  18. Oxygen uptake on-kinetics in dog gastrocnemius in situ following activation of pyruvate dehydrogenase by dichloroacetate.

    PubMed

    Grassi, Bruno; Hogan, Michael C; Greenhaff, Paul L; Hamann, Jason J; Kelley, Kevin M; Aschenbach, William G; Constantin-Teodosiu, Dumitru; Gladden, L Bruce

    2002-01-01

    The aim of the present study was to determine whether the activation of the pyruvate dehydrogenase complex (PDC) by dichloroacetate (DCA) is associated with faster O(2) uptake (V(O2)) on-kinetics. V(O2) on-kinetics was determined in isolated canine gastrocnemius muscles in situ (n = 6) during the transition from rest to 4 min of electrically stimulated isometric tetanic contractions, corresponding to approximately 60-70 % of peak V(O2). Two conditions were compared: (1) control (saline infusion, C); and (2) DCA infusion (300 mg (kg body mass)(-1), 45 min before contraction). Muscle blood flow (Q) was measured continuously in the popliteal vein; arterial and popliteal vein O(2) contents were measured at rest and at 5-7 s intervals during the transition. Muscle V(O2) was calculated as Q multiplied by the arteriovenous O(2) content difference. Muscle biopsies were taken before and at the end of contraction for determination of muscle metabolite concentrations. DCA activated PDC at rest, as shown by the 9-fold higher acetylcarnitine concentration in DCA (vs. C; P < 0.0001). Phosphocreatine degradation and muscle lactate accumulation were not significantly different between C and DCA. DCA was associated with significantly less muscle fatigue. Resting and steady-state V(O2) values during contraction were not significantly different between C and DCA. The time to reach 63 % of the V(O2) difference between the resting baseline and the steady-state V(O2) values during contraction was 22.3 +/- 0.5 s in C and 24.5 +/- 1.4 s in DCA (n.s.). In this experimental model, activation of PDC by DCA resulted in a stockpiling of acetyl groups at rest and less muscle fatigue, but it did not affect 'anaerobic' energy provision and V(O2) on-kinetics. PMID:11773328

  19. A kinetic study of hydrolysis of polyester elastomer in magnetic tape

    NASA Technical Reports Server (NTRS)

    Yamamoto, K.; Watanabe, H.

    1994-01-01

    A useful method for kinetic study of the hydrolysis of polyester elastomer is established which uses the number-average molecular weight. The reasonableness of this method is confirmed and the effect of magnetic particles on hydrolysis is considered.

  20. Studies on cultivation kinetics for elastase production by Bacillus sp. EL31410.

    PubMed

    Chen, Qi-He; He, Guo-Qing; Schwarz, Paul

    2004-06-01

    It was the first time to study elastase batch cultivation kinetics. This paper discusses the growth kinetics, elastase production, and substrate consumption kinetics model of Bacillus sp. EL31410 in batch cultivation. A simple model was proposed using a logistic equation for growth, the Luedeking-Piret equation for elastase production, and the Luedeking-Piret-like equation for glucose consumption. The model appeared to provide a reasonable description for each parameter during the growth phase. This study could provide some support for studying elastase fermentation kinetics, especially for studying its singular growth phenomenon. However, the model for elastase production is not good for explaining the real process and is still up to research. PMID:15161197

  1. Study of the kinetics of catalytic decomposition of hydrazine vapors on palladium

    NASA Technical Reports Server (NTRS)

    Khomenko, A. A.; Apelbaum, L. O.

    1987-01-01

    The decomposition rates of N2H4 on a palladium surface are studied. Experiments were conducted in a circulating unit at atmosphere pressure. The experimental method is described. The laws found for the reaction kinetics are explained by equations.

  2. A Study in Enzyme Kinetics Using an Ion-Specific Electrode.

    ERIC Educational Resources Information Center

    Turchi, Sandra; And Others

    1989-01-01

    Describes an undergraduate biochemistry laboratory experiment on enzyme kinetics using the D-amino acid oxidase system and an ammonia electrode. Preparation of an ammonia standard curve, a sample preparation, and inhibition studies are discussed. (YP)

  3. A kinetic study of the antihistaminic effect of terfenadine.

    PubMed

    Cheng, H C; Woodward, J K

    1982-01-01

    Kinetics of the antihistaminic effect of alpha-[4-(1,1-dimethylethyl)phenyl]-4-(hydroxydiphenylmethyl)-1- piperidinebutanol (terfenadine, RMI 9918, Triludan, Teldane, resp.) were examined in the isolated guinea pig ileum and spirally cut tracheal strip preparations. In the isolated guinea pig ileum, terfenadine produced a parallel or competitive shift (3.16 X 10(-8) and 10(-7) mol/l) as well as a nonparallel or unsurmountable shift (3.16 X 10(-7) and 10(-6) mol/l) of the histamine dose response curves. Using the dose ratio test, it was concluded that terfenadine competes at the same receptors as chlorpheniramine, namely, the histamine H1-receptors. The antihistaminic effects of terfenadine, both the competitive and unsurmountable effects, were difficult to reverse by washout techniques whereas the nonspecific effects (against acetylcholine and barium chloride) could be readily washed out. The unsurmountable antagonism of histamine by terfenadine may result from a slow dissociation of terfenadine from the histamine H1-receptor. When terfenadine (2 mg/kg) or chlorpheniramine (2 mg/kg) was administered systemically, either orally or intraperitoneally, to guinea pigs and the antihistaminic effect assessed in vitro (isolated ileal strips and tracheal strips) terfenadine consistently produced a longer duration of action than chlorpheniramine. It is concluded that terfenadine is a potent, selective histamine H1-receptor antagonist; the kinetics of association/dissociation of terfenadine with histamine H1-receptors may account for the long-lasting antihistaminic effect in various animal models. PMID:6129862

  4. Stable isotope studies of nicotine kinetics and bioavailability

    SciTech Connect

    Benowitz, N.L.; Jacob, P. 3d.; Denaro, C.; Jenkins, R. )

    1991-03-01

    The stable isotope-labeled compound 3',3'-dideuteronicotine was used to investigate the disposition kinetics of nicotine in smokers, the systemic absorption of nicotine from cigarette smoke, and the bioavailability of nicotine ingested as oral capsules. Blood levels of labeled nicotine could be measured for 9 hours after a 30-minute intravenous infusion. Analysis of disposition kinetics in 10 healthy men revealed a multiexponential decline after the end of an infusion, with an elimination half-life averaging 203 minutes. This half-life was longer than that previously reported, indicating the presence of a shallow elimination phase. Plasma clearance averaged 14.6 ml/min/kg. The average intake of nicotine per cigarette was 2.29 mg. A cigarette smoke-monitoring system that directly measured particulate matter in smoke was evaluated in these subjects. Total particulate matter, number of puffs on the cigarette, total puff volume, and time of puffing correlated with the intake of nicotine from smoking. The oral bioavailability of nicotine averaged 44%. This bioavailability is higher than expected based on the systemic clearance of nicotine and suggests that there may be significant extrahepatic metabolism of nicotine.

  5. Computational Study and Kinetic Analysis of the Aminolysis of Thiolactones.

    PubMed

    Desmet, Gilles B; D'hooge, Dagmar R; Sabbe, Maarten K; Marin, Guy B; Du Prez, Filip E; Espeel, Pieter; Reyniers, Marie-Françoise

    2015-09-01

    The aminolysis of three differently α-substituted γ-thiolactones (C4H5OSX, X = H, NH2, and NH(CO)CH3) is modeled based on CBS-QB3 calculated free energies corrected for solvation using COSMO-RS. For the first time, quantitative kinetic and thermodynamic data are provided for the concerted path and the stepwise path over a neutral tetrahedral intermediate. These paths can take place via an unassisted, an amine-assisted, or a thiol-assisted mechanism. Amine assistance lowers the free energy barriers along both paths, while thiol assistance only lowers the formation of the neutral tetrahedral intermediate. Based on the ab initio calculated rate coefficients, a kinetic model is constructed that is able to reliably describe experimental observations for the aminolysis of N-acetyl-dl-homocysteine thiolactone with n-butylamine in THF and CHCl3. Reaction path analysis shows that for all conditions relevant for applications in polymer synthesis and postpolymer modification, an assisted stepwise mechanism is operative in which the formation of the neutral tetrahedral intermediate is rate-determining and which is mainly amine-assisted at low conversions and thiol-assisted at high conversions. PMID:26280542

  6. A study of the kinetics of isothermal nicotine desorption from silicon dioxide

    NASA Astrophysics Data System (ADS)

    Adnadjevic, Borivoj; Lazarevic, Natasa; Jovanovic, Jelena

    2010-12-01

    The isothermal kinetics of nicotine desorption from silicon dioxide (SiO 2) was investigated. The isothermal thermogravimetric curves of nicotine at temperatures of 115 °C, 130 °C and 152 °C were recorded. The kinetic parameters ( Ea, ln A) of desorption of nicotine were calculated using various methods (stationary point, model constants and differential isoconversion method). By applying the "model-fitting" method, it was found that the kinetic model of nicotine desorption from silicon dioxide was a phase boundary controlled reaction (contracting volume). The values of the kinetic parameters, Ea,α and ln Aα, complexly change with changing degree of desorption and a compensation effect exists. A new mechanism of activation for the desorption of the absorbed molecules of nicotine was suggested in agreement with model of selective energy transfer.

  7. mRNA Noise Reveals that Activators Induce a Biphasic Response in the Promoter Kinetics of Highly Regulated Genes

    NASA Astrophysics Data System (ADS)

    Quinn, Katie; To, Tsz-Leung; Maheshri, Narendra

    2012-02-01

    A dominant source of fluctuations in gene expression is thought to be the process of transcription. The statistics of these fluctuations arise from the kinetics of transcription. Multiple studies suggest the bulk of fluctuations can be understood by a simple process where genes are inactive for exponentially distributed times punctuated by geometric bursts of mRNA. Yet it's largely unknown how cis and trans factors affect the two lumped kinetic parameters, burst size and burst frequency, that describe this process. Importantly, how these parameters are regulated in a single gene can qualitatively affect the dynamical behavior of the network it is embedded within. Here, we ask whether transcriptional activators increase gene expression by increasing the burst size or burst frequency. We do so by deducing these parameters from steady-state mRNA distributions measured in individual yeast cells using single molecule mRNA FISH. We find that for both a synthetic and natural promoter, activators appear to first increase burst size, then burst frequency. We suggest this biphasic response may be common to all highly regulated genes and was previously unappreciated because of measurement techniques. Furthermore, its origins appear to relate to cis events at the promoter, and may arise from combinations of basal and activator-dependent bursts. Our measurements shed new light on transcriptional mechanisms and should assist in building synthetic promoters with tunable statistics.

  8. Effects of PEF and heat pasteurization on PME activity in orange juice with regard to a new inactivation kinetic model.

    PubMed

    Agcam, E; Akyıldız, A; Evrendilek, G Akdemir

    2014-12-15

    The inactivation kinetics of pectin methyl esterase (PME) during the shelf life (4°C-180 days) of freshly squeezed orange juice samples processed by both pulsed electric fields (PEF) and heat pasteurization (HP) was evaluated in the study. The PME inactivation level after the PEF (25.26 kV/cm-1206.2 μs) and HP (90°C-20s) treatments were 93.8% and 95.2%, respectively. The PME activity of PEF-processed samples decreased or did not change, while that of HP samples increased during storage (p<0.01). A kinetic model was developed expressing PME inactivation as a function of the PEF treatment conditions, and this enabled the estimation of the reaction rate constant (587.8-2375.4s(-1)), and the time required for a 90% reduction (De, 3917.7-969.5s). Quantification of the increase in PEF energy to ensure a ten-fold reduction in De (ze, 63.7 J), activation electric fields (-921.2 kV cm(-1)mol(-1)), and electrical activation energy (12.9 kJ mol(-1)) was also carried out. Consequently, PEF processing was very effective for the inactivation of PME and for providing stability of orange juice during storage. PMID:25038650

  9. Predictive Framework and Experimental Tests of the Kinetic Isotope Effect at Redox-Active Interfaces

    NASA Astrophysics Data System (ADS)

    Kavner, A.; John, S.; Black, J. R.

    2013-12-01

    Electrochemical reactions provide a compelling framework to study kinetic isotope effects because redox-related processes are important for a wide variety of geological and environmental processes. In the laboratory, electrochemical reaction rates can be electronically controlled and measured in the laboratory using a potentiostat. This enables variation of redox reactions rates independent of changes in chemistry and, and the resulting isotope compositions of reactants and products can be separated and analyzed. In the past years, a series of experimental studies have demonstrated a large, light, and tunable kinetic isotope effect during electrodeposition of metal Fe, Zn, Li, Cu, and Mo from a variety of solutions (e.g. Black et al., 2009, 2010, 2011). A theoretical framework based on Marcus kinetic theory predicts a voltage-dependent kinetic isotope effect (Kavner et al., 2005, 2008), however while this framework was able to predict the tunable nature of the effect, it was not able to simultaneously predict absolute reaction rates and relative isotope rates. Here we present a more complete development of a statistical mechanical framework for simple interfacial redox reactions, which includes isotopic behavior. The framework is able to predict a kinetic isotope effect as a function of temperature and reaction rate, starting with three input parameters: a single reorganization energy which describes the overall kinetics of the electron transfer reaction, and the equilibrium reduced partition function ratios for heavy and light isotopes in the product and reactant phases. We show the framework, elucidate some of the predictions, and show direct comparisons against isotope fractionation data obtained during laboratory and natural environment redox processes. A. Kavner, A. Shahar, F. Bonet, J. Simon and E. Young (2005) Geochim. Cosmochim. Acta, 69(12), 2971-2979. A. Kavner, S. G. John, S. Sass, and E. A. Boyle (2008), Geochim. Cosmochim. Acta, vol 72, pp. 1731

  10. Comparative Kinetic Study and Microwaves Non-Thermal Effects on the Formation of Poly(amic acid) 4,4′-(Hexafluoroisopropylidene)diphthalic Anhydride (6FDA) and 4,4′-(Hexafluoroisopropylidene)bis(p-phenyleneoxy)dianiline (BAPHF). Reaction Activated by Microwave, Ultrasound and Conventional Heating

    PubMed Central

    Tellez, Hugo Mendoza; Alquisira, Joaquín Palacios; Alonso, Carlos Rius; Cortés, José Guadalupe López; Toledano, Cecilio Alvarez

    2011-01-01

    Green chemistry is the design of chemical processes that reduce or eliminate negative environmental impacts. The use and production of chemicals involve the reduction of waste products, non-toxic components, and improved efficiency. Green chemistry applies innovative scientific solutions in the use of new reagents, catalysts and non-classical modes of activation such as ultrasounds or microwaves. Kinetic behavior and non-thermal effect of poly(amic acid) synthesized from (6FDA) dianhydride and (BAPHF) diamine in a low microwave absorbing p-dioxane solvent at low temperature of 30, 50, 70 °C were studied, under conventional heating (CH), microwave (MW) and ultrasound irradiation (US). Results show that the polycondensation rate decreases (MW > US > CH) and that the increased rates observed with US and MW are due to decreased activation energies of the Arrhenius equation. Rate constant for a chemical process activated by conventional heating declines proportionally as the induction time increases, however, this behavior is not observed under microwave and ultrasound activation. We can say that in addition to the thermal microwave effect, a non-thermal microwave effect is present in the system. PMID:22072913

  11. Oxidation of chlorinated ethenes by heat-activated persulfate: kinetics and products.

    PubMed

    Waldemer, Rachel H; Tratnyek, Paul G; Johnson, Richard L; Nurmi, James T

    2007-02-01

    In situ chemical oxidation (ISCO) and in situ thermal remediation (ISTR) are applicable to treatment of groundwater contaminated with chlorinated ethenes. ISCO with persulfate (S2O8(2-)) requires activation, and this can be achieved with the heat from ISTR, so there may be advantages to combining these technologies. To explore this possibility, we determined the kinetics and products of chlorinated ethene oxidation with heat-activated persulfate and compared them to the temperature dependence of other degradation pathways. The kinetics of chlorinated ethene disappearance were pseudo-first-order for 1-2 half-lives, and the resulting rate constants-measured from 30 to 70 degrees C--fit the Arrhenius equation, yielding apparent activation energies of 101 +/- 4 kJ mol(-1) for tetrachloroethene (PCE), 108 +/- 3 kJ mol(-1) for trichloroethene (TCE), 144 +/- 5 kJ mol(-1) for cis-1,2-dichloroethene (cis-DCE), and 141 +/- 2 kJ mol(-1) for trans-1,2-dichloroethene (trans-DCE). Chlorinated byproducts were observed, but most of the parent material was completely dechlorinated. Arrhenius parameters for hydrolysis and oxidation by persulfate or permanganate were used to calculate rates of chlorinated ethene degradation by these processes over the range of temperatures relevant to ISTR and the range of oxidant concentrations and pH relevant to ISCO. PMID:17328217

  12. Kinetic Modeling of the Arabidopsis Cryptochrome Photocycle: FADHo Accumulation Correlates with Biological Activity

    PubMed Central

    Procopio, Maria; Link, Justin; Engle, Dorothy; Witczak, Jacques; Ritz, Thorsten; Ahmad, Margaret

    2016-01-01

    Cryptochromes are flavoprotein photoreceptors with multiple signaling roles during plant de-etiolation and development. Arabidopsis cryptochromes (cry1 and cry2) absorb light through an oxidized flavin (FADox) cofactor which undergoes reduction to both FADH° and FADH− redox states. Since the FADH° redox state has been linked to biological activity, it is important to estimate its concentration formed upon illumination in vivo. Here we model the photocycle of isolated cry1 and cry2 proteins with a three-state kinetic model. Our model fits the experimental data for flavin photoconversion in vitro for both cry1 and cry2, providing calculated quantum yields which are significantly lower in cry1 than for cry2. The model was applied to the cryptochrome photocycle in vivo using biological activity in plants as a readout for FADH° concentration. The fit to the in vivo data provided quantum yields for cry1 and cry2 flavin reduction similar to those obtained in vitro, with decreased cry1 quantum yield as compared to cry2. These results validate our assumption that FADH° concentration correlates with biological activity. This is the first reported attempt at kinetic modeling of the cryptochrome photocycle in relation to macroscopic signaling events in vivo, and thereby provides a theoretical framework to the components of the photocycle that are necessary for cryptochrome response to environmental signals. PMID:27446119

  13. Kinetic Modeling of the Arabidopsis Cryptochrome Photocycle: FADH(o) Accumulation Correlates with Biological Activity.

    PubMed

    Procopio, Maria; Link, Justin; Engle, Dorothy; Witczak, Jacques; Ritz, Thorsten; Ahmad, Margaret

    2016-01-01

    Cryptochromes are flavoprotein photoreceptors with multiple signaling roles during plant de-etiolation and development. Arabidopsis cryptochromes (cry1 and cry2) absorb light through an oxidized flavin (FADox) cofactor which undergoes reduction to both FADH° and FADH(-) redox states. Since the FADH° redox state has been linked to biological activity, it is important to estimate its concentration formed upon illumination in vivo. Here we model the photocycle of isolated cry1 and cry2 proteins with a three-state kinetic model. Our model fits the experimental data for flavin photoconversion in vitro for both cry1 and cry2, providing calculated quantum yields which are significantly lower in cry1 than for cry2. The model was applied to the cryptochrome photocycle in vivo using biological activity in plants as a readout for FADH° concentration. The fit to the in vivo data provided quantum yields for cry1 and cry2 flavin reduction similar to those obtained in vitro, with decreased cry1 quantum yield as compared to cry2. These results validate our assumption that FADH° concentration correlates with biological activity. This is the first reported attempt at kinetic modeling of the cryptochrome photocycle in relation to macroscopic signaling events in vivo, and thereby provides a theoretical framework to the components of the photocycle that are necessary for cryptochrome response to environmental signals. PMID:27446119

  14. Kinetics of methane hydrate decomposition studied via in situ low temperature X-ray powder diffraction.

    PubMed

    Everett, S Michelle; Rawn, Claudia J; Keffer, David J; Mull, Derek L; Payzant, E Andrew; Phelps, Tommy J

    2013-05-01

    Gas hydrate is known to have a slowed decomposition rate at ambient pressure and temperatures below the melting point of ice. As hydrate exothermically decomposes, gas is released and water of the clathrate cages transforms into ice. Based on results from the decomposition of three nominally similar methane hydrate samples, the kinetics of two regions, 180-200 and 230-260 K, within the overall decomposition range 140-260 K, were studied by in situ low temperature X-ray powder diffraction. The kinetic rate constants, k(a), and the reaction mechanisms, n, for ice formation from methane hydrate were determined by the Avrami model within each region, and activation energies, E(a), were determined by the Arrhenius plot. E(a) determined from the data for 180-200 K was 42 kJ/mol and for 230-260 K was 22 kJ/mol. The higher E(a) in the colder temperature range was attributed to a difference in the microstructure of ice between the two regions. PMID:23557375

  15. Clinical study of quantitative diagnosis of early cervical cancer based on the classification of acetowhitening kinetics

    NASA Astrophysics Data System (ADS)

    Wu, Tao; Cheung, Tak-Hong; Yim, So-Fan; Qu, Jianan Y.

    2010-03-01

    A quantitative colposcopic imaging system for the diagnosis of early cervical cancer is evaluated in a clinical study. This imaging technology based on 3-D active stereo vision and motion tracking extracts diagnostic information from the kinetics of acetowhitening process measured from the cervix of human subjects in vivo. Acetowhitening kinetics measured from 137 cervical sites of 57 subjects are analyzed and classified using multivariate statistical algorithms. Cross-validation methods are used to evaluate the performance of the diagnostic algorithms. The results show that an algorithm for screening precancer produced 95% sensitivity (SE) and 96% specificity (SP) for discriminating normal and human papillomavirus (HPV)-infected tissues from cervical intraepithelial neoplasia (CIN) lesions. For a diagnostic algorithm, 91% SE and 90% SP are achieved for discriminating normal tissue, HPV infected tissue, and low-grade CIN lesions from high-grade CIN lesions. The results demonstrate that the quantitative colposcopic imaging system could provide objective screening and diagnostic information for early detection of cervical cancer.

  16. Thermoluminescence of kunzite: A study of kinetic processes and dosimetry characteristics

    NASA Astrophysics Data System (ADS)

    Ogundare, F. O.; Alatishe, M. A.; Chithambo, M. L.; Costin, G.

    2016-04-01

    Since the use of natural minerals for dating and dose reconstruction using luminescence techniques is well-established and always of interest, we present thermoluminescence characteristics of kunzite, a gem variety of spodumene. The chemical composition of the sample was determined using an Electron Probe MicroAnalyzer to be (Li0.996Na0.009Mn0.006)∑ = 1.016(Al0.981Cr0.003Fe2+0.001)∑ = 0.995[(Si1.993Al0.008)∑ = 2.000O6]. Thermoluminescence glow curves measured at 0.5 K/s after laboratory irradiation consist of three prominent peaks at 338 K (labelled as peak I), 454 K (peak II) and 681 K (peak III). The dose response of these three peaks is linear in the range 20-308 Gy studied. The position of each of the peaks is independent of dose, an archetypical feature of first order behaviour. However, detailed kinetic analyses showed that in fact, the peaks are not subject to first order kinetics. Each of the three peaks is affected by thermal quenching with an associated activation energy of thermal quenching estimated to be 0.70, 1.35 and 0.54 eV for peaks I, II and III respectively. In terms of dosimetry use, only peak III was found to be reliable for possible use in luminescence dating and dose reconstruction.

  17. Kinetic Study and Mathematical Model of Hemimorphite Dissolution in Low Sulfuric Acid Solution at High Temperature

    NASA Astrophysics Data System (ADS)

    Xu, Hongsheng; Wei, Chang; Li, Cunxiong; Deng, Zhigan; Li, Minting; Li, Xingbin

    2014-10-01

    The dissolution kinetics of hemimorphite with low sulfuric acid solution was investigated at high temperature. The dissolution rate of zinc was obtained as a function of dissolution time under the experimental conditions where the effects of sulfuric acid concentration, temperature, and particle size were studied. The results showed that zinc extraction increased with an increase in temperature and sulfuric acid concentration and with a decrease in particle size. A mathematical model able to describe the process kinetics was developed from the shrinking core model, considering the change of the sulfuric acid concentration during dissolution. It was found that the dissolution process followed a shrinking core model with "ash" layer diffusion as the main rate-controlling step. This finding was supported with a linear relationship between the apparent rate constant and the reciprocal of squared particle radius. The reaction order with respect to sulfuric acid concentration was determined to be 0.7993. The apparent activation energy for the dissolution process was determined to be 44.9 kJ/mol in the temperature range of 373 K to 413 K (100 °C to 140 °C). Based on the shrinking core model, the following equation was established:

  18. Kinetic and theoretical study of the reaction of Cl atoms with a series of linear thiols

    SciTech Connect

    Garzon, Andres; Albaladejo, Jose

    2008-11-21

    The reactions of Cl with a series of linear thiols: 1-propanethiol (k{sub 1}), 1-butanethiol (k{sub 2}), and 1-pentanethiol (k{sub 3}) were investigated as a function of temperature (in the range of 268-379 K) and pressure (in the range of 50-200 Torr) by laser photolysis-resonance fluorescence. Only 1-propanethiol has previously been studied, but at 1 Torr of total pressure. The derived Arrhenius expressions obtained using our kinetic data were as follows: k{sub 1}=(3.97{+-}0.44)x10{sup -11} exp[(410{+-}36)/T], k{sub 2}=(1.01{+-}0.16)x10{sup -10} exp[(146{+-}23)/T], and k{sub 3}=(1.28{+-}0.10)x10{sup -10} exp[(129{+-}25)/T] (in units of cm{sup 3} molecule{sup -1} s{sup -1}). Moreover, a theoretical insight into mechanisms of these reactions has also been pursued through ab initio Moeller-Plesset second-order perturbation treatment calculations with 6-311G** basis set. Optimized geometries have been obtained for transition states and molecular complexes appearing along the different reaction pathways. Furthermore, molecular energies have been calculated at QCISD(T) level in order to get an estimation of the activation energies. Finally, the nature of the molecular complexes and transitions states is analyzed by using kinetic-potential and natural bond orbital total energy decomposition schemes.

  19. Kinetic Reaction Mechanism of Sinapic Acid Scavenging NO2 and OH Radicals: A Theoretical Study.

    PubMed

    Lu, Yang; Wang, AiHua; Shi, Peng; Zhang, Hui; Li, ZeSheng

    2016-01-01

    The mechanism and kinetics underlying reactions between the naturally-occurring antioxidant sinapic acid (SA) and the very damaging ·NO2 and ·OH were investigated through the density functional theory (DFT). Two most possible reaction mechanisms were studied: hydrogen atom transfer (HAT) and radical adduct formation (RAF). Different reaction channels of neutral and anionic sinapic acid (SA-) scavenging radicals in both atmosphere and water medium were traced independently, and the thermodynamic and kinetic parameters were calculated. We find the most active site of SA/SA- scavenging ·NO2 and ·OH is the -OH group in benzene ring by HAT mechanism, while the RAF mechanism for SA/SA- scavenging ·NO2 seems thermodynamically unfavorable. In water phase, at 298 K, the total rate constants of SA eliminating ·NO2 and ·OH are 1.30×108 and 9.20×109 M-1 S-1 respectively, indicating that sinapic acid is an efficient scavenger for both ·NO2 and ·OH. PMID:27622460

  20. Calcium current activation kinetics in isolated pyramidal neurones of the Ca1 region of the mature guinea-pig hippocampus.

    PubMed

    Kay, A R; Wong, R K

    1987-11-01

    1. Neurones were isolated from the CA1 region of the guinea-pig hippocampus and subjected to the whole-cell mode of voltage clamping, to determine the kinetics of voltage-gated Ca2+ channel activation. 2. Isolated neurones had an abbreviated morphology, having lost most of the distal dendritic tree during the isolation procedure. The electrical compactness of the cells facilitates voltage clamp analysis. 3. Block of sodium and potassium currents revealed a persistent current activated on depolarization above -40 mV, which inactivated slowly when the intracellular medium contained EGTA. The current was blocked by Co2+ and Cd2+, augmented by increases in Ca2+ and could be carried by Ba2+, suggesting that the current is borne by Ca2+. 4. Steady-state activation of the Ca2+ current was found to be well described by the Boltzman equation raised to the second power. 5. The open channel's current-voltage (I-V) relationship rectified in the inward direction and was consistent with the constant-field equation. 6. The kinetics of Ca2+ current onset followed m2 kinetics throughout the range of its activation. Tail current kinetics were in accord with this model. A detailed Hodgkin-Huxley model was derived, defining the activation of this current. 7. The kinetics of the currents observed in this regionally and morphologically defined class of neurones were consistent with the existence of a single kinetic class of channels. PMID:2451732

  1. An optogenetic gene expression system with rapid activation and deactivation kinetics

    PubMed Central

    Motta-Mena, Laura B.; Reade, Anna; Mallory, Michael J.; Glantz, Spencer; Weiner, Orion D.; Lynch, Kristen W.; Gardner, Kevin H.

    2013-01-01

    Optogenetic gene expression systems can control transcription with spatial and temporal detail unequaled with traditional inducible promoter systems. However, current eukaryotic light-gated transcription systems are limited by toxicity, dynamic range, or slow activation/deactivation. Here we present an optogenetic gene expression system that addresses these shortcomings and demonstrate its broad utility. Our approach utilizes an engineered version of EL222, a bacterial Light-Oxygen-Voltage (LOV) protein that binds DNA when illuminated with blue light. The system has a large (>100-fold) dynamic range of protein expression, rapid activation (< 10 s) and deactivation kinetics (< 50 s), and a highly linear response to light. With this system, we achieve light-gated transcription in several mammalian cell lines and intact zebrafish embryos with minimal basal gene activation and toxicity. Our approach provides a powerful new tool for optogenetic control of gene expression in space and time. PMID:24413462

  2. Dry (CO2) reforming of methane over Pt catalysts studied by DFT and kinetic modeling

    NASA Astrophysics Data System (ADS)

    Niu, Juntian; Du, Xuesen; Ran, Jingyu; Wang, Ruirui

    2016-07-01

    Dry reforming of methane (DRM) is a well-studied reaction that is of both scientific and industrial importance. In order to design catalysts that minimize the deactivation and improve the selectivity and activity for a high H2/CO yield, it is necessary to understand the elementary reaction steps involved in activation and conversion of CO2 and CH4. In our present work, a microkinetic model based on density functional theory (DFT) calculations is applied to explore the reaction mechanism for methane dry reforming on Pt catalysts. The adsorption energies of the reactants, intermediates and products, and the activation barriers for the elementary reactions involved in the DRM process are calculated over the Pt(1 1 1) surface. In the process of CH4 direct dissociation, the kinetic results show that CH dissociative adsorption on Pt(1 1 1) surface is the rate-determining step. CH appears to be the most abundant species on the Pt(1 1 1) surface, suggesting that carbon deposition is not easy to form in CH4 dehydrogenation on Pt(1 1 1) surface. In the process of CO2 activation, three possible reaction pathways are considered to contribute to the CO2 decomposition: (I) CO2* + * → CO* + O*; (II) CO2* + H* → COOH* + * → CO* + OH*; (III) CO2* + H* → mono-HCOO* + * → bi-HCOO* + * [CO2* + H* → bi-HCOO* + *] → CHO* + O*. Path I requires process to overcome the activation barrier of 1.809 eV and the forward reaction is calculated to be strongly endothermic by 1.430 eV. In addition, the kinetic results also indicate this process is not easy to proceed on Pt(1 1 1) surface. While the CO2 activation by H adsorbed over the catalyst surface to form COOH intermediate (Path II) is much easier to be carried out with the lower activation barrier of 0.746 eV. The Csbnd O bond scission is the rate-determining step along this pathway and the process needs to overcome the activation barrier of 1.522 eV. Path III reveals the CO2 activation through H adsorbed over the catalyst

  3. A kinetic study on the reduction of CO2 by frustrated Lewis pairs: from understanding to rational design.

    PubMed

    Liu, Lei; Vankova, Nina; Heine, Thomas

    2016-02-01

    Carbon dioxide (CO2) is known as one of the major reasons for global warming. On the other hand, CO2 is considered as an abundant carbon source. Therefore, transformation of CO2 into target chemicals nowadays is of great interest. Recently, a concept of so-called "frustrated Lewis pairs" (FLPs) has been proposed. Such FLPs show unusual reactivity, such as hydrogen activation and the reduction of CO2. In this study, by means of density functional theory (DFT) and ab initio calculations, we conduct a kinetic survey on the reduction of CO2 by a series of FLPs. We investigate the relationship between the electronic structures and kinetic properties. The kinetic properties include: (1) reaction energy barriers, (2) the structural properties of the associated transition states (TSs), and (3) the natural charge population in these TSs. Our results indicate that there is a systematic relationship between the electronic structures and the kinetic properties, and, as a rule of thumb, similar activation barriers for both individual reactions are needed for best performance. The derived relationship can be used not only to rationalize the published experimental results, but also to assist the future design of more efficient Lewis acid-base pairs as metal-free catalysts for the reduction of CO2. PMID:26751729

  4. Dechlorination of polychlorinated biphenyls: A kinetic study of removal of PCBs from mineral oils

    SciTech Connect

    Filippis, P. de; Scarsella, M.; Pochetti, F.

    1999-02-01

    A kinetic study was done of the dechlorination of polychlorinated biphenyls (PCBs) eliminated from contaminated dielectric oils by using the potassium poly(ethylene glycolate) (KPEG) process. Experimental runs at laboratory scale showed that the kinetics of the removal reaction was first-order for each PCB present and first-order with respect to the KPEG concentration. The PCB elimination grade was also affected by the KOH/PEG ratio. An exponential correlation was found between the kinetic constant for each congener and its respective gas chromatographic relative retention time.

  5. Study of Aspect Ratio Effects on Kinetic MHD Instabilities in NSTX and DIII-D

    SciTech Connect

    E.D. Fredrickson; W.W. Heidbrink; C.Z. Cheng; N.N. Gorelenkov; E. Belova; A.W. Hyatt; G.J. Kramer; J. Manickam; J. Menard; R. Nazikian; T.L. Rhodes; E. Ruskov

    2004-10-21

    We report general observations of kinetic instabilities on the low aspect-ratio National Spherical Torus Experiment (NSTX) and describe explicit aspect ratio scaling studies of kinetic instabilities using both the NSTX and the DIII-D tokamak. The NSTX and the DIII-D tokamak are nearly ideal for such experiments, having a factor of two difference in major radius but otherwise similar parameters. We also introduce new theoretical work on the physics of kinetic ballooning modes (KBM), toroidal Alfven eigenmodes (TAE), and compressional Alfven eigenmodes (CAE) with applications to NSTX.

  6. Autoignition chemistry of the hexane isomers: An experimental and kinetic modeling study

    SciTech Connect

    Curran, H.J.; Gaffuri, P.; Pitz, W.J.; Westbrook, C.K.; Leppard, W.R.

    1995-06-01

    Autoignition of the five distinct isomers of hexane is studied experimentally under motored engine conditions and computationally using a detailed chemical kinetic reaction mechanism. Computed and experimental results are compared and used to help understand the chemical factors leading to engine knock in spark-ignited engines and the molecular structure factors contributing to octane rating for hydrocarbon fuels. The kinetic model reproduces observed variations in critical compression ratio with fuel structure, and it also provides intermediate and final product species concentrations in very dose agreement with observed results. In addition, the computed results provide insights into the kinetic origins of fuel octane sensitive.

  7. Atmospheric chemistry: Laboratory studies of kinetics of important reactions

    NASA Astrophysics Data System (ADS)

    Smith, S. J.

    Experiments to measure the rate constants for some reactions of the atmospherically important nitrate radical (NO3) are described using the discharge-flow technique. The nitrate radical was monitored by optical absorption at lambda = 662 nm. The reactions of NO3 with some stable organic and inorganic substrates are reported. The temperature dependences of some of the rate constants were also determined (298 less than T less than 523 K). In most cases, computer simulation was used to extract the rate constant for the primary process because the time-dependent behavior of (NO3) was affected by secondary reactions of NO3 with products of the primary interaction. The Arrhenius parameter for the reactions of NO3 with CH3CH3, CH2CH2, CH3OH, CHCl3, and HCl were determined. The activation energies for the reactions studied between NO3 and some alkynes are presented along with the corresponding pre-exponential factors. Some reactions were studied at room temperature (298 plus or minus 2 K) only and the rate constants found (in units of cubic cm/molecule sec) are: buta-1,3-diene (1.8 x 10 (exp -13), isobutene (2.8 x 10 (exp -13), HBr (1.3 x 10 (exp -15) and hex-2-yne (3.0 x 10 (exp -14). Non-Arrhenius behavior was found in the reactions of NO3 with n-butane, isobutane and propene. The empirical variation of these rate constants with temperature is presented. The curvature of the Arrhenius plots is discussed in terms of (1) a temperature-dependent pre-exponential factor, and (2) the possibility that two competing channels, possessing differing activation energies, exist for each reaction. The atmospheric implications of these reactions are discussed with reference to the nighttime production of nitric acid and the importance of the these reactions as loss processes for NO3.

  8. Fabrication and kinetics study of nano-Al/NiO thermite film by electrophoretic deposition.

    PubMed

    Zhang, Daixiong; Li, Xueming

    2015-05-21

    Nano-Al/NiO thermites were successfully prepared as film by electrophoretic deposition (EPD). For the key issue of this EPD, a mixture solvent of ethanol-acetylacetone (1:1 in volume) containing 0.00025 M nitric acid was proved to be a suitable dispersion system for EPD. The kinetics of electrophoretic deposition for both nano-Al and nano-NiO were investigated; the linear relation between deposition weight and deposition time in short time and parabolic relation in prolonged time were observed in both EPDs. The critical transition time between linear deposition kinetics and parabolic deposition kinetics for nano-Al and nano-NiO were 20 and 10 min, respectively. The theoretical calculation of the kinetics of electrophoretic deposition revealed that the equivalence ratio of nano-Al/NiO thermites film would be affected by the behavior of electrophoretic deposition for nano-Al and nano-NiO. The equivalence ratio remained steady when the linear deposition kinetics dominated for both nano-Al and nano-NiO. The equivalence ratio would change with deposition time when deposition kinetics for nano-NiO changed into parabolic kinetics dominated after 10 min. Therefore, the rule was suggested to be suitable for other EPD of bicomposites. We also studied thermodynamic properties of electrophoretic nano-Al/NiO thermites film as well as combustion performance. PMID:25950271

  9. Thermal oxidation of single-crystal silicon carbide - Kinetic, electrical, and chemical studies

    NASA Technical Reports Server (NTRS)

    Petit, J. B.; Neudeck, P. G.; Matus, L. G.; Powell, J. A.

    1992-01-01

    This paper presents kinetic data from oxidation studies of the polar faces for 3C and 6H SiC in wet and dry oxidizing ambients. Values for the linear and parabolic rate constants were obtained, as well as preliminary results for the activation energies of the rate constants. Examples are presented describing how thermal oxidation can be used to map polytypes and characterize defects in epitaxial layers grown on low tilt angle 6H SiC substrates. Interface widths were measured using Auger electron spectroscopy (AES) with Ar ion beam depth profiling and variable angle spectroscopic ellipsometry (VASE) with effective medium approximation (EMA) models. Preliminary electrical measurements of MOS capacitors are also presented.

  10. Kinetic study of antibiotic ciprofloxacin ozonation by MWCNT/MnO2 using Monte Carlo simulation.

    PubMed

    Jalali, Hamed Moradmand

    2016-02-01

    Kinetic Monte Carlo simulation was used to investigate kinetics of antibiotic ciprofloxacin degradation by direct and heterogeneous catalytic (MnO2 and carbon nano-tube loaded with MnO2) ozonation. The reaction kinetic mechanisms of each system have been obtained. The rate constant values for the each step of the reaction mechanisms were attained as adjustable parameters by kinetic Monte Carlo simulation. The carbon nano-tube loaded with MnO2 plays important role as catalyst in the ciprofloxacin ozonation by increasing reactivity of ozone and ciprofloxacin drug on the surface of carbon nano-tube. Optimized amount of ozone and catalysts were obtained via studying the effect of inlet ozone concentration and initial amount of catalyst on the rate of ciprofloxacin degradation using Monte Carlo simulation. The simulation results of this study have reasonably agreement with the present experimental data for the ozonation of ciprofloxacin drug. PMID:26652449

  11. Flow-Based Systems for Rapid and High-Precision Enzyme Kinetics Studies

    PubMed Central

    Hartwell, Supaporn Kradtap; Grudpan, Kate

    2012-01-01

    Enzyme kinetics studies normally focus on the initial rate of enzymatic reaction. However, the manual operation of steps of the conventional enzyme kinetics method has some drawbacks. Errors can result from the imprecise time control and time necessary for manual changing the reaction cuvettes into and out of the detector. By using the automatic flow-based analytical systems, enzyme kinetics studies can be carried out at real-time initial rate avoiding the potential errors inherent in manual operation. Flow-based systems have been developed to provide rapid, low-volume, and high-precision analyses that effectively replace the many tedious and high volume requirements of conventional wet chemistry analyses. This article presents various arrangements of flow-based techniques and their potential use in future enzyme kinetics applications. PMID:22577614

  12. Phosphotyrosine-mediated LAT assembly on membranes drives kinetic bifurcation in recruitment dynamics of the Ras activator SOS.

    PubMed

    Huang, William Y C; Yan, Qingrong; Lin, Wan-Chen; Chung, Jean K; Hansen, Scott D; Christensen, Sune M; Tu, Hsiung-Lin; Kuriyan, John; Groves, Jay T

    2016-07-19

    The assembly of cell surface receptors with downstream signaling molecules is a commonly occurring theme in multiple signaling systems. However, little is known about how these assemblies modulate reaction kinetics and the ultimate propagation of signals. Here, we reconstitute phosphotyrosine-mediated assembly of extended linker for the activation of T cells (LAT):growth factor receptor-bound protein 2 (Grb2):Son of Sevenless (SOS) networks, derived from the T-cell receptor signaling system, on supported membranes. Single-molecule dwell time distributions reveal two, well-differentiated kinetic species for both Grb2 and SOS on the LAT assemblies. The majority fraction of membrane-recruited Grb2 and SOS both exhibit fast kinetics and single exponential dwell time distributions, with average dwell times of hundreds of milliseconds. The minor fraction exhibits much slower kinetics, extending the dwell times to tens of seconds. Considering this result in the context of the multistep process by which the Ras GEF (guanine nucleotide exchange factor) activity of SOS is activated indicates that kinetic stabilization from the LAT assembly may be important. This kinetic proofreading effect would additionally serve as a stochastic noise filter by reducing the relative probability of spontaneous SOS activation in the absence of receptor triggering. The generality of receptor-mediated assembly suggests that such effects may play a role in multiple receptor proximal signaling processes. PMID:27370798

  13. Kinetic studies of porphyrin distribution in suspensions of tumor cells

    NASA Astrophysics Data System (ADS)

    Zorin, Vladimir P.; Mel'nov, Sergey B.; Savitsky, Valery P.; Zorina, Tatyana E.

    1996-12-01

    Using a fluorescence activated cell sorting, we investigated the dynamics of porphyrins in suspensions of tumor cells. In addition to direct studies of the incorporation and output of several porphyrins (hematoporphyrin, hematoporphyrin dimethyl ester, chlorin e6 and its mono-, di-, trimethyl esters) from cells, their transfer between cells was investigated. It was shown that the rate of pigment accumulation by cells correlated with the rate of porphyrin penetration across the plasma membrane. As a result, apolar chlorins and HpDME displayed enhanced staining capacity which was independent on the integrity of plasma membrane of cells. To estimate the rate of pigment redistribution between cells, the suspension of tumor cells loaded with porphyrin had been mixed with unloaded cells and the distribution of all cells according to porphyrin fluorescence was determined in different intervals of time. It was obtained that the highest rate of the pigment transfer between cells was exhibited in the case of moderately apolar pigment. Porphyrins with dominantly hydrophobic and hydrophilic properties had a decreased capacity to intercellular migration. The results of this study indicate that, depending on the photosensitizer used, the processes of its distribution in the bulk of tumor tissue mediated by intercellular exchange may occur with a different rate.

  14. Pulsed laser kinetic studies of liquids under high pressure

    NASA Astrophysics Data System (ADS)

    Eyring, E. M.

    1993-06-01

    Experiments have been developed for measuring the rates of chemical reactions liquids and in supercritical CO2. A pulsed (Q-switch) Nd:YAG laser at 355 nm was the pump beam for laser flash photolysis studies of molybdenum and tungsten hexacarbonyls undergoing ligand displacement reactions by bidentate chelating agents such as 2,2'-bipyridine in toluene. Experiments were carried out at 0.1 to 150 MPa. In the case of molybdenum complexes, the reaction mechanism for thermal ring closure is found from activation volumes to change from associative interchange to dissociative interchange as substituents on the 2,2'-bipyridine ligands become bulkier. In a similar study of more rigid, substituted phenanthroline bidentate ligands it was found that substituent bulkiness had little effect on the thermal ring closure mechanism. Similar high pressure flash photolysis experiments with tungsten hexacarbonyl have also been completed. The concentration dependence of the fluorescence and nonradiative decay quantum yields for cresyl violet in several solvents has been reported as well as stability constants for the complexation of lithium ion by four different crown ethers dissolved in a room temperature molten salt.

  15. Pulsed laser kinetic studies of liquids under high pressure

    SciTech Connect

    Eyring, E.M.

    1993-06-21

    Experiments have been developed for measuring the rates of chemical reactions liquids and in supercritical Co[sub 2]. A pulsed (Q-switch) Nd:YAG laser at 355 nm was the pump beam for laser flash photolysis studies of molybdenum and tungsten hexacarbonyls undergoing ligand displacement reactions by bidentate chelating agents such as 2,2[prime]-bipyridine in toluene. Experiments were carried out at 0.1 to 150 MPa. In the case of molybdenum complexes, the reaction mechanism for thermal ring closure is found from activation volumes to change from associative interchange to dissociative interchange as substituents on the 2,2[prime]-bipyridine ligands become bulkier. In a similar study of more rigid, substituted phenanthroline bidentate ligands it was found that substituent bulkiness had little effect on the thermal ring closure mechanism. Similar high pressure flash photolysis experiments with tungsten hexacarbonyl have also been completed. The concentration dependence of the fluorescence and nonradiative decay quantum yields for cresyl violet in several solvent have been reported as well as stability constants for the complexation of lithium ion by four different crown ethers dissolved in a room temperature molten salt.

  16. Photocatalytic activity enhancement of anatase-graphene nanocomposite for methylene removal: Degradation and kinetics.

    PubMed

    Rezaei, Mostafa; Salem, Shiva

    2016-10-01

    In the present research, the TiO2-graphene nanocomposite was synthesized by an eco-friendly method. The blackberry juice was introduced to graphene oxide (GO) as a reducing agent to produce the graphene nano-sheets. The nanocomposite of anatase-graphene was developed as a photocatalyst for the degradation of methylene blue, owing to the larger specific surface area and synergistic effect of reduced graphene oxide (RGO). The UV spectroscopy measurements showed that the prepared nanocomposite exhibited an excellent photocatalytic activity toward the methylene blue degradation. The rate of electron transfer of redox sheets is much higher than that observed on GO, indicating the applicability of proposed method for the production of anatase-RGO nanocomposite for treatment of water contaminated by cationic dye. The prepared materials were characterized with Fourier transform infrared spectroscopy, X-ray diffraction, Brunauer-Emmett-Teller surface area measurement, scanning electron microscopy and transmission electron microscopy. A facile and rapid route was applied for the uniform deposition of anatase nanoparticles on the sheets. The resulting nanocomposite contained nanoparticles with a mean diameter of 10nm. A mechanism for the photocatalytic activity of nanocomposite was suggested and the degradation reaction obeyed the second-order kinetics. It was concluded that the degradation kinetics is changed due to the reduction of GO in the presence of blackberry juice. PMID:27236206

  17. Sonochemical assisted hydrothermal synthesis of ZnO: Cr nanoparticles loaded activated carbon for simultaneous ultrasound-assisted adsorption of ternary toxic organic dye: Derivative spectrophotometric, optimization, kinetic and isotherm study.

    PubMed

    Jamshidi, M; Ghaedi, M; Dashtian, K; Hajati, S; Bazrafshan, A A

    2016-09-01

    Chromium doped zinc oxide nanoparticles (ZnO: Cr-NPs) was synthesized by ultrasonically assisted hydrothermal method and characterized by FE-SEM, XRD and TEM analysis. Subsequently, this composite ultrasonically assisted was deposited on activated carbon (ZnO: Cr-NPs-AC) and used for simultaneous ultrasound-assisted removal of three toxic organic dye namely of malachite green (MG), eosin yellow (EY) and Auramine O (AO). Dyes spectra overlap in mixture (major problem for simultaneous investigation) of this systems was extensively resolved by derivative spectrophotometric method. The magnitude of variables like initial dyes concentration, adsorbent mass and sonication time influence on dyes removal was optimized using small central composite design (CCD) combined with desirability function (DF) approach, while pH was studied by one-a-time approach. The maximized removal percentages at desirability of 0.9740 was set as follow: pH 6.0, 0.019g ZnO: Cr-NPs-AC, 3.9min sonication at 4.5, 4.8 and 4.7mgL(-1) of MG, EY and AO, respectively. Above optimized points lead to achievement of removal percentage of 98.36%, 97.24%, and 99.26% correspond to MG, EY and AO, respectively. ANOVA for each dyes based p-value less than (<0.0001) suggest highly efficiency of CCD model for prediction of data concern to simultaneous removal of these dyes within 95% confidence interval, while their F-value for MG, EY and AO is 935, 800.2, and 551.3, respectively, that confirm low participation of this them in signal. The value of multiple correlation coefficient R(2), adjusted and predicted R(2) for simultaneous removal of MG is 0.9982, 0.9972 and 0.9940, EY is 0.9979, 0.9967 and 0.9930 and for AO is 0.9970, 0.9952 and 0.9939. The adsorption rate well fitted by pseudo second-order and Langmuir model via high, economic and profitable adsorption capacity of 214.0, 189.7 and 211.6mgg(-1) for MG, EY and AO, respectively. PMID:27150752

  18. Kinetic evidence that methionine sulfoxide reductase A can reveal its oxidase activity in the presence of thioredoxin.

    PubMed

    Kriznik, Alexandre; Boschi-Muller, Sandrine; Branlant, Guy

    2014-04-15

    The mouse methionine sulfoxide reductase A (MsrA) belongs to the subclass of MsrAs with one catalytic and two recycling Cys corresponding to Cys51, Cys198 and Cys206 in Escherichia coli MsrA, respectively. It was previously shown that in the absence of thioredoxin, the mouse and the E. coli MsrAs, which reduce two mol of methionine-O substrate per mol of enzyme, displays an in vitro S-stereospecific methionine oxidase activity. In the present study carried out with E. coli MsrA, kinetic evidence are presented which show that formation of the second mol of Ac-L-Met-NHMe is rate-limiting in the absence of thioredoxin. In the presence of thioredoxin, the overall rate-limiting step is associated with the thioredoxin-recycling process. Kinetic arguments are presented which support the accumulation of the E. coli MsrA under Cys51 sulfenic acid state in the presence of Trx. Thus, the methionine oxidase activity could be operative in vivo without the action of a regulatory protein in order to block the action of Trx as previously proposed. PMID:24632144

  19. Thermogravimetric and Kinetic Analysis of Melon (Citrullus colocynthis L.) Seed Husk Using the Distributed Activation Energy Model

    NASA Astrophysics Data System (ADS)

    Nyakuma, Bemgba Bevan

    2015-12-01

    This study seeks to characterize the thermochemical fuel properties of melon seed husk (MSH) as a potential biomass feedstock for clean energy and power generation. It examined the ultimate analysis, proximate analysis, FTIR spectroscopy and thermal decomposition of MSH. Thermogravimetric (TG) analysis was examined at 5, 10, 20 °C/min from 30-800 °C under nitrogen atmosphere. Subsequently, the Distributed Activation Energy Model (DAEM) was applied to determine the activation energy, E, and frequency factor, A. The results revealed that thermal decomposition of MSH occurs in three (3) stages; drying (30-150 °C), devolatization (150-400 °C) and char degradation (400-800 °C). Kinetic analysis revealed that the E values fluctuated from 145.44-300 kJ/mol (Average E = 193 kJ/mol) while A ranged from 2.64 × 1010 to 9.18 × 1020 min-1 (Average E = 9.18 × 1019 min-1) highlighting the complexity of MSH pyrolysis. The fuel characterization and kinetics of MSH showed it is an environmentally friendly solid biofuel for future thermal biomass conversion.

  20. Activation of oxygen-mediating pathway using copper ions: fine-tuning of growth kinetics in gold nanorod overgrowth.

    PubMed

    Liu, Wenqi; Zhang, Hui; Wen, Tao; Yan, Jiao; Hou, Shuai; Shi, Xiaowei; Hu, Zhijian; Ji, Yinglu; Wu, Xiaochun

    2014-10-21

    Growth kinetics plays an important role in the shape control of nanocrystals (NCs). Herein, we presented a unique way to fine-tune the growth kinetics via oxidative etching activated by copper ions. For the overgrowth of gold nanorods (Au NRs), competitive adsorption of dissolved oxygen on rod surface was found to slow down the overgrowth rate. Copper ions were able to remove the adsorbed oxygen species from the Au surface via oxidative etching, thus exposing more reaction sites for Au deposition. In this way, copper ions facilitated the overgrowth process. Furthermore, Cu(2+) rather than Cu(+) acted as the catalyst for the oxidative etching. Comparative study with Ag(+) indicated that Cu(2+) cannot regulate NC shapes via an underpotential deposition mechanism. In contrast, Ag(+) led to the formation of Au tetrahexahedra (THH) and a slight decrease of the growth rate at similar growth conditions. Combining the distinct roles of the two ions enabled elongated THH to be produced. Copper ions activating the O2 pathway suggested that dissolved oxygen has a strong affinity for the Au surface. Moreover, the results of NC-sensitized singlet oxygen ((1)O2) indicated that the absorbed oxygen species on the surface of Au NCs bounded with low-index facets mainly existed in the form of molecular O2. PMID:25244407

  1. A laboratory study of the nucleation kinetics of nitric acid hydrates under stratospheric conditions

    NASA Astrophysics Data System (ADS)

    James, Alexander D.; Murray, Benjamin J.; Plane, John M. C.

    2016-04-01

    Measurements of the kinetics of crystallisation of ternary H2O-H2SO4-HNO3 mixtures to produce nitric acid hydrate phases, as occurs in the lower stratosphere, have been a long-standing challenge for investigators in the laboratory. Understanding polar stratospheric chlorine chemistry and thereby ozone depletion is increasingly limited by descriptions of nucleation processes. Meteoric smoke particles have been considered in the past as heterogeneous nuclei, however recent studies suggest that these particles will largely dissolve, leaving mainly silica and alumina as solid inclusions. In this study the nucleation kinetics of nitric acid hydrate phases have been measured in microliter droplets at polar stratospheric cloud (PSC) temperatures, using a droplet freezing assay. A clear heterogeneous effect was observed when silica particles were added. A parameterisation based on the number of droplets activated per nuclei surface area (ns) has been developed and compared to global model data. Nucleation experiments on identical droplets have been performed in an X-Ray Diffractometer (XRD) to determine the nature of the phase which formed. β-Nitric Acid Trihydrate (NAT) was observed alongside a mixture of Nitric Acid Dihydrate (NAD) phases. It is not possible to determine whether NAT nucleates directly or is formed by a phase transition from NAD (likely requiring the presence of a mediating liquid phase). Regardless, these results demonstrate the possibility of forming NAT on laboratory timescales. In the polar stratosphere, sulfuric acid (present at several weight percent of the liquid under equilibrium conditions) could provide such a liquid phase. This study therefor provides insight into previous discrepancies between phases formed in the laboratory and those observed in the atmosphere. It also provides a basis for future studies into atmospheric nucleation of solid PSCs.

  2. The kinetics of the oxidation of pyrite by ferric ions and dissolved oxygen: An electrochemical study

    SciTech Connect

    Holmes, P.R.; Crundwell, F.K.

    2000-01-01

    The dissolution of pyrite is important in the geochemical cycling of iron and sulphur, in the formation of acid mine drainage, and in the extraction of metals by bacterial leaching. Many researchers have studied the kinetics of dissolution, and the rate of dissolution has often been found to be half-order in ferric ions or oxygen. Previous work has not adequately explained the kinetics of dissolution of pyrite. The dissolution of pyrite is an oxidation-reduction reaction. The kinetics of the oxidation and reduction half-reactions was studied independently using electrochemical techniques of voltammetry. The kinetics of the overall reaction was studied by the electrochemical technique of potentiometry, which consisted of measuring the mixed potential of a sample of corroding pyrite in solutions of different compositions. The kinetics of the half reactions are related to the kinetics of the overall dissolution reaction by the condition that there is no accumulation of charge. This principle is used to derive expressions for the mixed potential and the rate of dissolution, which successfully describe the mixed potential measurements and the kinetics of dissolution reported in the literature. It is shown that the observations of half-order kinetics and that the oxygen in the sulphate product arises from water are both a direct consequence of the electrochemical mechanism. Thus it is concluded that the electrochemical reaction steps occurring at the mineral-solution interface control the rate of dissolution. Raman spectroscopy was used to analyze reaction products formed on the pyrite surface. The results indicated that small amounts of polysulphides form on the surface of the pyrite. However, it was also found that the mixed (corrosion) potential does not change over a 14-day leaching period. This indicates that even though polysulphide material is present on the surface, it does not influence the rate of the reactions occurring at the surface. Measurement of the

  3. SMX degradation by ozonation and UV radiation: a kinetic study.

    PubMed

    Liu, Xiaowei; Garoma, Temesgen; Chen, Zhonglin; Wang, Lili; Wu, Youxian

    2012-06-01

    The rate constants of sulfamethoxazole (SMX) degradation by ozonation and UV(254) radiation were investigated under various parameters including influent ozone gas concentration, initial SMX concentration, UV light intensity, ionic strength, water quality in terms of varying anions (bicarbonate, sulfate and nitrate), humic acid (HA) and pH. The results indicated that the removal of SMX by ozonation and UV(254) radiation fitted well to a pseudo first-order kinetic model and the rate constants were in the range of (0.9-9.8)×10(-3) and (1.7-18.9)×10(-3) s(-1), respectively. The second-order rate constants of SMX with ozone (ko(3)), under varying operational parameters, were also determined and varied in the range of (0.60-3.38)±0.13×10(5)M(-1) s(-1). In addition, SMX degradation through UV pretreatment followed by ozonation in the presence of HA was proved to be an effective method which can remove SMX with a low ozone dose. The results suggested that ozonation of SMX was more affected by concentration of influent ozone gas, alkalinity, and HA, while incident UV light intensity, pH, and HA were the dominant factors influencing UV degradation of SMX. PMID:22386457

  4. Kinetic studies of microinstabilities in toroidal plasmas: Simulation and theory

    SciTech Connect

    Lee, W.W.; Haham, T.S.; Parker, S.E.; Perkins, F.W.; Rath, S.; Rewoldt, G.; Reynders, J.V.W.; Santoro, R.A.; Tang, W.M.

    1992-12-01

    A comprehensive program for the development and use of particle simulation techniques for solving the gyrokinetic Vlasov-Maxwell equations on massively parallel computers has been carried out at Princeton Plasma Physics Laboratory. This is a key element of our ongoing theoretical efforts to systematically investigate physics issues vital to understanding tokamak plasmas. In this paper, our focus is on spatial-gradient-driven microinstabilities. Their importance is supported by the recent progress in achieving a physics-based understanding of anomalous transport in toroidal systems which has been based on the proposition that these drift-type electrostatic modes dependent on ion temperature gradient (ITG) and trapped particle effects are dominant in the bulk ( confinement'') region. Although their presence is consistent with a number of significant confinement trends, results from high temperature tokamaks such as TFTR have highlighted the need for better insight into the nonlinear properties of such instabilities in long-mean-free-path plasmas. In addressing this general issue, we report important new results including (i) the first fully toroidal 3D gyrokinetic simulation of ITG modes and (ii) realistic toroidal eigenmode calculations demonstrating the unique capability to deal with large scale kinetic behavior extending over many rational surfaces. The effects of ITG modes (iii) on the inward pinch of impurities in 3D slab geometry and (iv) on the existence of microtearing modes in 2D slab are also discussed. Finally, (v) sheared toroidal flow effects on trapped-particle modes are presented.

  5. Kinetic studies of microinstabilities in toroidal plasmas: Simulation and theory

    SciTech Connect

    Lee, W.W.; Haham, T.S.; Parker, S.E.; Perkins, F.W.; Rath, S.; Rewoldt, G.; Reynders, J.V.W.; Santoro, R.A.; Tang, W.M.

    1992-12-01

    A comprehensive program for the development and use of particle simulation techniques for solving the gyrokinetic Vlasov-Maxwell equations on massively parallel computers has been carried out at Princeton Plasma Physics Laboratory. This is a key element of our ongoing theoretical efforts to systematically investigate physics issues vital to understanding tokamak plasmas. In this paper, our focus is on spatial-gradient-driven microinstabilities. Their importance is supported by the recent progress in achieving a physics-based understanding of anomalous transport in toroidal systems which has been based on the proposition that these drift-type electrostatic modes dependent on ion temperature gradient (ITG) and trapped particle effects are dominant in the bulk (``confinement``) region. Although their presence is consistent with a number of significant confinement trends, results from high temperature tokamaks such as TFTR have highlighted the need for better insight into the nonlinear properties of such instabilities in long-mean-free-path plasmas. In addressing this general issue, we report important new results including (i) the first fully toroidal 3D gyrokinetic simulation of ITG modes and (ii) realistic toroidal eigenmode calculations demonstrating the unique capability to deal with large scale kinetic behavior extending over many rational surfaces. The effects of ITG modes (iii) on the inward pinch of impurities in 3D slab geometry and (iv) on the existence of microtearing modes in 2D slab are also discussed. Finally, (v) sheared toroidal flow effects on trapped-particle modes are presented.

  6. Kinetic studies of amylase and biomass production by Calvatia gigantea

    SciTech Connect

    Kekos, D.; Macris, B.J.

    1987-01-01

    Production of alpha-amylase (alpha-4, glucan 4-glucanohydrolase, EC 3.2.1.1) by microorganisms has been practiced for many years in small and large scale operations and the literature on this enzyme is voluminous. Aspergillus niger and Aspergillus oryzae have been reported as the main fungal species used for commercial production of the enzyme. On the other hand, large volumes of low-cost agricultural products such as acorn (the perisperm-free dry seed contains approximately 60% starch) are wasted in many countries and provide a challenge to biotechnology to efficiently utilize these rich sources of starch for the production of high added value products like enzymes. C. gigantea is an edible puffball excreting high levels of alpha-amylase when cultivated on different sources of starch containing elevated quantities of toxic tannic compounds. This fungus has been employed for the production of microbial protein from wastes and acorns containing high levels of toxic tannic compounds. The same fungus was also reported to grow on both hydrolyzable and condensed tannins as sole carbon sources. The present work was undertaken to investigate certain kinetic characteristics of alpha-amylase and biomass production by C. gigantea grown on soluble and acorn starch in a lab fermenter. (Refs. 18).

  7. Active galactic nucleus feedback in an isolated elliptical galaxy: The effect of strong radiative feedback in the kinetic mode

    SciTech Connect

    Gan, Zhaoming; Yuan, Feng; Ostriker, Jeremiah P.; Ciotti, Luca; Novak, Gregory S.

    2014-07-10

    Based on two-dimensional high-resolution hydrodynamic numerical simulation, we study the mechanical and radiative feedback effects from the central active galactic nucleus (AGN) on the cosmological evolution of an isolated elliptical galaxy. The inner boundary of the simulation domain is carefully chosen so that the fiducial Bondi radius is resolved and the accretion rate of the black hole is determined self-consistently. It is well known that when the accretion rates are high and low, the central AGNs will be in cold and hot accretion modes, which correspond to the radiative and kinetic feedback modes, respectively. The emitted spectrum from the hot accretion flows is harder than that from the cold accretion flows, which could result in a higher Compton temperature accompanied by a more efficient radiative heating, according to previous theoretical works. Such a difference of the Compton temperature between the two feedback modes, the focus of this study, has been neglected in previous works. Significant differences in the kinetic feedback mode are found as a result of the stronger Compton heating. More importantly, if we constrain models to correctly predict black hole growth and AGN duty cycle after cosmological evolution, we find that the favored model parameters are constrained: mechanical feedback efficiency diminishes with decreasing luminosity (the maximum efficiency being ≅ 10{sup –3.5}), and X-ray Compton temperature increases with decreasing luminosity, although models with fixed mechanical efficiency and Compton temperature can be found that are satisfactory as well. We conclude that radiative feedback in the kinetic mode is much more important than previously thought.

  8. Kinetic Studies with Ion Selective Electrodes: Determination of Creatinine in Urine with a Picrate Ion Selective Electrode: A Laboratory Experiment.

    ERIC Educational Resources Information Center

    Diamandis, E. P.; And Others

    1983-01-01

    The kinetic of the Jaffe reaction with picrate ion selective electrode (ISE) and a kinetic method for determining creatinine in urine is presented. The experiment could be used to familarize students with the application of ISE in kinetic studies and chemical analysis. (Author/JN)

  9. Kinetic studies of phosphoester hydrolysis promoted by a dimeric tetrazirconium(iv) Wells-Dawson polyoxometalate.

    PubMed

    Luong, Thi Kim Nga; Shestakova, Pavletta; Parac-Vogt, Tatjana N

    2016-07-26

    The catalytic hydrolysis of a phosphoester bond in the DNA-model substrate 4-nitrophenyl phosphate (NPP) promoted by Zr(iv)-substituted Wells-Dawson Na14[Zr4(P2W16O59)2(μ3-O)2(OH)2(H2O)4]·57H2O polyoxometalate (ZrWD 4 : 2) was followed by means of (1)H and (31)P NMR spectroscopy. The hydrolytic reaction proceeded with a rate constant of 8.44 (±0.36) × 10(-5) s(-1) at pD 6.4 and 50 °C, representing a 300-fold rate enhancement in comparison with the spontaneous hydrolysis of NPP (kobs = 2.81 (±0.25) × 10(-7) s(-1)) under the same reaction conditions. The ZrWD 4 : 2 was also active towards hydrolysis of bis(4-nitrophenyl) phosphate (BNPP) and the RNA model substrate 2-hydroxypropyl-4-nitrophenyl phosphate (HPNP). The pD dependence of kobs shows that the rate constants for NPP hydrolysis decrease significantly when the pD values of the reaction mixtures increase. The formation constant (Kf = 190 M(-1)) and catalytic rate constant (kc = 6.40 × 10(-4) s(-1)) for the NPP-ZrWD 4 : 2 complex, activation energy (Ea) of 110.15 ± 7.06 kJ mol(-1), enthalpy of activation (ΔH(‡)) of 109.03 ± 6.86 kJ mol(-1), entropy of activation (ΔS(‡)) of 15.20 ± 2.49 J mol(-1) K(-1), and Gibbs activation energy (ΔG(‡)) of 104.32 ± 6.09 kJ mol(-1) at 37 °C were calculated from kinetic studies. The recyclability of ZrWD 4 : 2 was examined by adding an extra amount (5.0 mM) of NPP twice to a fully hydrolyzed mixture of 5.0 mM NPP and 1.0 mM ZrWD 4 : 2. The interaction between ZrWD 4 : 2 and the P-O bond of NPP was evidenced by a change in the (31)P chemical shift of the (31)P atom in NPP upon addition of ZrWD 4 : 2. Based on (31)P NMR experiments and the kinetic studies, a mechanism for NPP hydrolysis promoted by ZrWD 4 : 2 has been proposed. PMID:27406623

  10. Microbial degradation of Paclitaxel using Citrobacter amalonaticus Rashtia isolated from pharmaceutical wastewater: kinetic and thermodynamic study.

    PubMed

    Zamani, Hojjatolah; Grakoee, Seyed Reza; Rakhshaee, Roohan

    2016-08-01

    Paclitaxel is a highly toxic anticancer agent which is used in a wide range against ovarian, breast, lung, and prostate cancers. Paclitaxel is manufactured recently in the north of Iran which may lead to the introduction of the drug into the environment via pharmaceutical wastewater. To our knowledge, Paclitaxel degradation is currently performed using physicochemical methods and biological degradation of Paclitaxel has not been reported. In this study, a Paclitaxel degrading bacterium was isolated from pharmaceutical wastewater for the first time. The bacterium was identified using biochemical and molecular assays and its Paclitaxel degradation potential was evaluated using High Performance Liquid Chromatography (HPLC). In addition, kinetic and thermodynamic study of Paclitaxel degradation at different experimental conditions was performed. A Citrobacter species named as C. amalonaticus Rashtia able to degrade and utilize Paclitaxel as the sole carbon source was isolated. The isolated strain tolerated high level concentration of Paclitaxel (0.4 mg/mL) in liquid culture media and was able to degrade spillage-level concentrations of the drug (0.01-0.1 mg/mL) with 87-93 % efficacy under aerobic condition. Kinetic and thermodynamic study at different pHs (4.0, 7.0 and 10.0) and temperatures (285, 295 and 310 K) revealed that Paclitaxel degradation is a non-spontaneous process and the highest rate constant was observed in the basic condition and at the highest temperature. The ΔG values at 285, 295 and 310 K were determined 103.3, 105.9 and 109.9 kJ/mol, respectively. In addition, The ΔH and activation energy (Ea) of the process were determined +28.7 kJ/mol and +30.87 kJ/mol, respectively. PMID:27339310

  11. Kinetic Study of Adsorption Processes in Solution: An Undergraduate Physical Chemistry Experiment.

    ERIC Educational Resources Information Center

    Casado, Julio; And Others

    1985-01-01

    Background information, apparatus needed, procedures used, and results obtained are provided for a simple kinetic method for the monitoring of adsorption processes. The method, which involved adsorption of crystal violet onto activated carbon, is suitable for classroom and/or research purposes. (JN)

  12. Effects of lead and natriuretic hormone on kinetics of sodium-potassium-activated adenosine triphosphatase: possible relevance to hypertension.

    PubMed Central

    Weiler, E; Khalil-Manesh, F; Gonick, H

    1988-01-01

    Inhibition of vascular smooth muscle sodium-potassium-activated adenosine triphosphatase (Na-K-ATPase) has been postulated as a central mechanism in enhancing vascular contractility. In the present study, kinetics of inhibition of Na-K-ATPase by lead, ouabain, and natriuretic hormone (NH) was studied in a purified hog cerebral cortex enzyme preparation. Determination of I50 values for lead, ouabain, and NH revealed that NH is the most potent inhibitor of the enzyme system (0.8 x 10(-6) M ouabain equivalents). Kinetic analyses indicated that lead and NH exhibited different inhibitory mechanisms. The inhibition by lead was noncompetitive with respect to potassium and competitive with respect to sodium and MgATP. Natriuretic hormone was noncompetitive with respect to potassium, uncompetitive with respect to MgATP, and exhibited no inhibitory effect with respect to sodium. Synergism between lead and NH in the inhibition of Na-K-ATPase raises the possibility that lead may be a contributory factor in hypertension via this mechanism. PMID:2849538

  13. Atmospheric Chemistry: Laboratory Studies of Kinetics of Important Reactions.

    NASA Astrophysics Data System (ADS)

    Smith, S. J.

    Available from UMI in association with The British Library. Requires signed TDF. This thesis describes the experiments to measure the rate constants for some reactions of the atmospherically important nitrate radical (NO_3) using the discharge-flow technique. The nitrate radical was monitored by optical absorption at lambda = 662 nm. The reactions of NO_3 with some stable organic and inorganic substrates are reported. The temperature dependences of some of the rate constants have also been determined (298 < T < 523 K). In most cases, computer simulation was used to extract the rate constant for the primary process because the time-dependent behaviour of (NO_3) was affected by secondary reactions of NO_3 with products of the primary interaction. The Arrhenius parameter in parentheses (E _{rm a}/kJ mol^ {-1}, A/cm^3 molecule ^{-1}s^ {-1} respectively) for the following reactions have been determined: ethane (37, 6.7 times 10^{-12}), ethylene (25.8, 6.3 times 10^ {-12}), CH_3OH (21.3, 1.2 times 10^ {-12}), CHCiota_3 (23.4, 8.6 times 10 ^{-13}) and HCl (27.7, 4 times 10^{-12}). The activation energies for the reactions studied between NO_3 and some alkynes are represented well by the value 25 +/- 3 kJ mol^{-1} and the corresponding pre-exponential factors (expressed as ln(10 ^{13}A/cm^3 molecule^{-1}s ^{-1}) are as follows: C_2H_2 (1.6 +/- 1.4), C_3H _4 (5.0 +/- 1.4), 1-C_4H_6 (5.8 +/- 1.0), 1-C_5 H_8 (5.7 +/- 0.6) and 1-C_6H _{10} (4.5 +/- 0.4). Some reactions were studied at room temperature _3(298 +/- 2 K) only and the rate constants found (in units of cm ^3 molecule^{ -1}s^{-1}) are: buta-1,3-diene (1.8 times 10 ^{-13}), isobutene (2.8 times 10^{-13 }), HBr (1.3 times 10 ^{-15}) and hex-2-yne (3.0 times 10^{-14 }). Non-Arrhenius behaviour was found in the reactions of NO_3 with n-butane, isobutane and propene. The empirical variation of these rate constants with temperature is well represented by the three parameter expressions:. k(T) = 1.2 times 10 ^{-46}T^{11

  14. Fundamentals of the Plasma Sail Concept: MHD and Kinetic Studies

    NASA Technical Reports Server (NTRS)

    Khazanov, G.; Delamere, P.; Kabin, K.; Linde, T. J.; Krivorutsky, E.

    2003-01-01

    The Mini-Magnetospheric Plasma Propulsion (M2P2), originally proposed by Winglee et al. [2000] predicts that a 15-km standoff distance (or 20-km cross-sectional dimension) of the magnetic bubble will provide for sufficient momentum transfer from the solar wind to accelerate a spacecraft to the unprecedented speeds of 50-80 km/s after an acceleration period of about three months. Such velocities will enable travel out of the solar system in period of about seven years-almost an order of magnitude improvement over present chemical based propulsion systems. However, for the parameters of the simulation of Winglee et al. [2000], a fluid model for the interaction of M2P2 with the solar wind is not valid. It is assumed in the MHD fluid model, normally applied to planetary magnetospheres, that the characteristic scale-size is much greater than the Larmor radius and ion skin depth of the solar wind. In the case of M2P2, the size of the magnetic bubble is actually less than or, comparable to, the scale of these characteristic parameters. Therefore, a kinetic approach, which addresses the small-scale physical mechanisms, must be used. We have adopted a two-component approach to determining a preliminary estimate of the momentum transfer to the plasma sail. The first component is a self-consistent MHD simulation of the small-scale expansion phase of the magnetic bubble. The fluid treatment is valid to roughly 5 km from the source and the steady-state MHD solution at the 5 km boundary was then used as initial conditions for the hybrid simulation. The hybrid simulations showed that the momentum transfer to the innermost regions of the plasma sail is negligible.

  15. Kinetic study of acetaminophen degradation by visible light photocatalysis.

    PubMed

    Gotostos, Mary Jane N; Su, Chia-Chi; De Luna, Mark Daniel G; Lu, Ming-Chun

    2014-01-01

    In this work, a novel photocatalyst K3[Fe(CN)6]/TiO2 synthesized via a simple sol-gel method was utilized to degrade acetaminophen (ACT) under visible light with the use of blue and green LED lights. Parameters (medium pH, initial concentration of reactant, catalyst concentration, temperature, and number of blue LED lights) affecting photocatalytic degradation of ACT were also investigated. The experimental result showed that compared to commercially available Degussa P-25 (DP-25) photocatalyst, K3[Fe(CN)6]/TiO2 gave higher degradation efficiency and rate constant (kapp) of ACT. The degradation efficiency or kapp decreased with increasing initial ACT concentration and temperature, but increased with increased number of blue LED lamps. Additionally, kapp increased as initial pH was increased from 5.6 to 6.9, but decreased at a high alkaline condition (pH 8.3). Furthermore, the degradation efficiency and kapp of ACT increased as K3[Fe(CN)6]/TiO2 loading was increased to 1 g L(-1) but decreased and eventually leveled off at photocatalyst loading above this value. Photocatalytic degradation of ACT in K3[Fe(CN)6]/TiO2 catalyst system follows a pseudo-first-order kinetics. The Langmuir-Hinshelwood equation was also satisfactorily used to model the degradation of ACT in K3[Fe(CN)6]/TiO2 catalyst system indicated by a satisfactory linear correlation between 1/kapp and Co, with kini = 6.54 × 10(-4) mM/min and KACT = 17.27 mM(-1). PMID:24766590

  16. A comparative study of chemical kinetics models for HMX in mesoscale simulations of shock initiation due to void collapse

    NASA Astrophysics Data System (ADS)

    Rai, Nirmal; Schweigert, Igor; Udaykumar, H. S.

    2015-06-01

    The development of chemical kinetics schemes for use in modeling the reactive mechanics of energetic materials such as HMX has been an active area of research. Decomposition, deflagration and detonation models need to predict time to ignition and locations of onset of chemical reaction in energetic materials when used in meso- and macro-scale simulations. Modeling the chemical processes and development of appropriate kinetic law is challenging work because of lack of experimental data. However, significant work has been done in this area. Multistep kinetic models by Tarver and Tran, Henson and Smilowitz have provided plausible chemical kinetic rate laws for HMX. These models vary in the way they model the details of the decomposition process. Hence, a comparative study of different models will provide an understanding of the uncertainties involved in predicting ignition in HMX. In the current work, hot-spot ignition due to void collapse in shock compressed HMX has been analyzed using several reaction rate models, including the Tarver-Tran 4-equation model, the Henson-Smilowitz 7-equation model, and a new rate model that combines the condensed-phase decomposition rates measured by Brill et al and the detailed mechanism of nitramine flame chemistry due to Yetter et al. The chemical models have been incorporated in a massively parallel Eulerian code SCIMITAR3D. The variations in the predicted thresholds due to differences in the rate models will be discussed.

  17. Kinetic and thermodynamic studies of Hg(II) adsorption onto MCM-41 modified by ZnCl2

    NASA Astrophysics Data System (ADS)

    Raji, Foad; Pakizeh, Majid

    2014-05-01

    Kinetics and thermodynamics of mercury ions sorption onto ZnCl2-MCM-41 sorbent were studied. Several rate models in the form of two main classes of mathematic kinetic models (adsorption reaction models and adsorption diffusion models) were investigated. Pseudo-first-order, pseudo-second-order, Elovich, film and intraparticle diffusion models were used to analyze the kinetic data. Results showed that the pseudo-second order model can well describe the adsorption kinetic data. The thermodynamic parameters, such as Gibb's free energy change (ΔG°), standard enthalpy change (ΔH°) and standard entropy change (ΔS°) were also evaluated. Negative value of free energy at temperature range of 20-55 °C, indicates the spontaneous nature of Hg(II) sorption by ZnCl2-MCM-41 sorbent. The adsorption capacity which was found to decrease with temperature showed the exothermic nature of the mercury sorption process (ΔH° = -49.4 kJ mol-1). The negative ΔS° value (-148.9 J mol-1 K-1) revealed a decrease in the randomness at the solid/solution interface and also indicated the fast adsorption of the Hg(II) onto active sites.

  18. Hydrolytic Activation Kinetics of the Herbicide Benzobicyclon in Simulated Aquatic Systems.

    PubMed

    Williams, Katryn L; Tjeerdema, Ronald S

    2016-06-22

    Herbicide resistance is a growing concern for weeds in California rice fields. Benzobicyclon (BZB; 3-(2-chloro-4-(methylsulfonyl)benzoyl)-2-phenylthiobicyclo[3.2.1]oct-2-en-4-one) has proven successful against resistant rice field weeds in Asia. A pro-herbicide, BZB forms the active agent, benzobicyclon hydrolysate (BH), in water; however, the transformation kinetics are not understood for aquatic systems, particularly flooded California rice fields. A quantitative experiment was performed to assess the primary mechanism and kinetics of BZB hydrolysis to BH. Complete conversion to BH was observed for all treatments. Basic conditions (pH 9) enhanced the reaction, with half-lives ranging from 5 to 28 h. Dissolved organic carbon (DOC) hindered transformation, which is consistent with other base-catalyzed hydrolysis reactions. BH was relatively hydrolytically stable, with 18% maximum loss after 5 days. Results indicate BZB is an efficient pro-herbicide under aqueous conditions such as those of a California rice field, although application may be best suited for fields with recirculating tailwater systems. PMID:27248841

  19. Chaotic model and memory in single calcium-activated potassium channel kinetics

    NASA Astrophysics Data System (ADS)

    Bandeira, Heliovânio T.; Barbosa, Catão T. F.; Campos De Oliveira, Regina A.; Aguiar, José F.; Nogueira, Romildo A.

    2008-09-01

    Ion channels are pores formed by proteins and responsible for carrying ion fluxes through cellular membranes. The ion channels can assume conformational states thereby controlling ion flow. Physically, the conformational transitions from one state to another are associated with energy barriers between them and are dependent on stimulus, such as, electrical field, ligands, second messengers, etc. Several models have been proposed to describe the kinetics of ion channels. The classical Markovian model assumes that a future transition is independent of the time that the ion channel stayed in a previous state. Others models as the fractal and the chaotic assume that the rate of transitions between the states depend on the time that the ionic channel stayed in a previous state. For the calcium activated potassium channels of Leydig cells the R/S Hurst analysis has indicated that the channels are long-term correlated with a Hurst coefficient H around 0.7, showing a persistent memory in this kinetic. Here, we applied the R /S analysis to the opening and closing dwell time series obtained from simulated data from a chaotic model proposed by L. Liebovitch and T. Tóth [J. Theor. Biol. 148, 243 (1991)] and we show that this chaotic model or any model that treats the set of channel openings and closings as independent events is inadequate to describe the long-term correlation (memory) already described for the experimental data.

  20. Kinetics of Hydrogen Atom Abstraction from Substrate by an Active Site Thiyl Radical in Ribonucleotide Reductase

    PubMed Central

    2015-01-01

    Ribonucleotide reductases (RNRs) catalyze the conversion of nucleotides to deoxynucleotides in all organisms. Active E. coli class Ia RNR is an α2β2 complex that undergoes reversible, long-range proton-coupled electron transfer (PCET) over a pathway of redox active amino acids (β-Y122 → [β-W48] → β-Y356 → α-Y731 → α-Y730 → α-C439) that spans ∼35 Å. To unmask PCET kinetics from rate-limiting conformational changes, we prepared a photochemical RNR containing a [ReI] photooxidant site-specifically incorporated at position 355 ([Re]-β2), adjacent to PCET pathway residue Y356 in β. [Re]-β2 was further modified by replacing Y356 with 2,3,5-trifluorotyrosine to enable photochemical generation and spectroscopic observation of chemically competent tyrosyl radical(s). Using transient absorption spectroscopy, we compare the kinetics of Y· decay in the presence of substrate and wt-α2, Y731F-α2 ,or C439S-α2, as well as with 3′-[2H]-substrate and wt-α2. We find that only in the presence of wt-α2 and the unlabeled substrate do we observe an enhanced rate of radical decay indicative of forward radical propagation. This observation reveals that cleavage of the 3′-C–H bond of substrate by the transiently formed C439· thiyl radical is rate-limiting in forward PCET through α and has allowed calculation of a lower bound for the rate constant associated with this step of (1.4 ± 0.4) × 104 s–1. Prompting radical propagation with light has enabled observation of PCET events heretofore inaccessible, revealing active site chemistry at the heart of RNR catalysis. PMID:25353063

  1. Kinetic and thermodynamic characterization of a novel low-temperature-active xylanase from Arthrobacter sp. GN16 isolated from the feces of Grus nigricollis

    PubMed Central

    Zhou, Junpei; Liu, Yu; Shen, Jidong; Zhang, Rui; Tang, Xianghua; Li, Junjun; Wang, Yiyan; Huang, Zunxi

    2015-01-01

    We previously presented the cloning, heterologous expression, and characterization of a novel multidomain endoxylanase from Arthrobacter sp. GN16 isolated from the feces of Grus nigricollis. Molecular and biochemical characterization studies indicate that the glycoside hydrolase (GH) family 10 domain at the N-terminus of the multidomain xylanase (rXynAGN16L) is a low-temperature-active endoxylanase. Many low-temperature-active enzymes contain regions of high local flexibility related to their kinetic and thermodynamic properties compared with mesophilic and thermophilic enzymes. However, the thermodynamic property of low-temperature-active xylanases, including rXynAGN16L, has rarely been reported. In this study, the kinetic and thermodynamic properties of rXynAGN16L were determined using different substrates and temperature conditions to completely characterize its activity properties. The kinetic property of rXynAGN16L is similar to some low-temperature-active GH 10 endoxylanases. Moreover, the thermodynamic property indicates that rXynAGN16L is typically characterized as a low-temperature-active enzyme. PMID:25587940

  2. Kinetics and mechanistic study of competitive inhibition of thymidine phosphorylase by 5-fluoruracil derivatives.

    PubMed

    Petaccia, Manuela; Gentili, Patrizia; Bešker, Neva; D'Abramo, Marco; Giansanti, Luisa; Leonelli, Francesca; La Bella, Angela; Gradella Villalva, Denise; Mancini, Giovanna

    2016-04-01

    In a previous investigation, cationic liposomes formulated with new 5-FU derivatives, differing for the length of the polyoxyethylenic spacer that links the N(3) position of 5-FU to an alkyl chain of 12 carbon atoms, showed a higher cytotoxicity compared to free 5-FU, the cytotoxic effect being directly related to the length of the spacer. To better understand the correlation of the spacer length with toxicity, we carried out initial rate studies to determine inhibition, equilibrium and kinetic constants (KI, KM, kcat), and get inside inhibition activity of the 5-FU derivatives and their mechanism of action, a crucial information to design structural variations for improving the anticancer activity. The experimental investigation was supported by docking simulations based on the X-ray structure of thymidine phosphorylase (TP) from Escherichia coli complexed with 3'-azido-2'-fluoro-dideoxyuridin. Theoretical and experimental results showed that all the derivatives exert the same inhibition activity of 5-FU either as monomer and when embedded in lipid bilayer. PMID:26752208

  3. A kinetic and thermodynamic study of seratrodast polymorphic transition by isothermal microcalorimetry.

    PubMed

    Urakami, Koji; Beezer, Anthony E

    2003-05-12

    The development of isothermal microcalorimetry to a study of the kinetic and thermodynamics of polymorphic transitions in seratrodast ((+/-)-7-(3,5,6-trimethyl-1,4-benzoquinon-2-yl)-7-phenylheptanoic acid) Form II is reported. Sieved samples of Form II were allowed to convert to Form I, in a reaction vessel of an isothermal microcalorimeter, under 13, 31, 63 and 93% relative humidity (RH) between 48 and 65 degrees C. The power (Phi, in Watts) versus time curves from the microcalorimeter were integrated into the heat output (q, in Joules) versus time curves to yield fractional extent of Form I converted versus time curves. The change in enthalpy (-5.70 kJmol(-1)) agreed very closely with that obtained by differential scanning calorimetry and solution calorimetry, which indicated that the power measured by the microcalorimeter was due only to the Form II-to-Form I transition. Application of the theoretical kinetic method [J. Am. Ceram. Soc. 55 (1972) 74] revealed that the transition took place via a two-dimensional growth of nuclei mechanism at all the studied relative humidities and temperatures. The rate constant increased with increasing RH and temperature, and with decreasing the particle size of sample. The activation energies obtained from Arrhenius plots were 292, 290, 280 and 284 kJmol(-1), and the extrapolated rate constants at 25 degrees C were also 3.01 x 10(-10), 3.11 x 10(-10), 9.65 x 10(-10) and 3.84 x 10(-9)s(-1) for 13, 31, 63 and 93% RH, respectively. PMID:12711181

  4. Matrix rigidity regulates spatiotemporal dynamics of Cdc42 activity and vacuole formation kinetics of endothelial colony forming cells

    PubMed Central

    Kim, Seung Joon; Wan, Qiaoqiao; Cho, Eunhye; Han, Bumsoo; Yoder, Mervin C.; Voytik-Harbin, Sherry L.; Na, Sungsoo

    2014-01-01

    Recent evidence has shown that endothelial colony forming cells (ECFCs) may serve as a cell therapy for improving blood vessel formation in subjects with vascular injury, largely due to their robust vasculogenic potential. The Rho family GTPase Cdc42 is known to play a primary role in this vasculogenesis process, but little is known about how extracellular matrix (ECM) rigidity affects Cdc42 activity during the process. In this study, we addressed two questions: Does matrix rigidity affect Cdc42 activity in ECFC undergoing early vacuole formation? How is the spatiotemporal activation of Cdc42 related to ECFC vacuole formation? A fluorescence resonance energy transfer (FRET)-based Cdc42 biosensor was used to examine the effects of the rigidity of three-dimensional (3D) collagen matrices on spatiotemporal activity of Cdc42 in ECFCs. Collagen matrix stiffness was modulated by varying the collagen concentration and therefore fibril density. The results showed that soft (150 Pa) matrices induced an increased level of Cdc42 activity compared to stiff (1 kPa) matrices. Time-course imaging and colocalization analysis of Cdc42 activity and vacuole formation revealed that Cdc42 activity was colocalized to the periphery of cytoplasmic vacuoles. Moreover, soft matrices generated faster and larger vacuoles than stiff matrices. The matrix-driven vacuole formation was enhanced by a constitutively active Cdc42 mutant, but significantly inhibited by a dominant-negative Cdc42 mutant. Collectively, the results suggest that matrix rigidity is a strong regulator of Cdc42 activity and vacuole formation kinetics, and that enhanced activity of Cdc42 is an important step in early vacuole formation in ECFCs. PMID:24393843

  5. Hydride Transfer in DHFR by Transition Path Sampling, Kinetic Isotope Effects, and Heavy Enzyme Studies.

    PubMed

    Wang, Zhen; Antoniou, Dimitri; Schwartz, Steven D; Schramm, Vern L

    2016-01-12

    Escherichia coli dihydrofolate reductase (ecDHFR) is used to study fundamental principles of enzyme catalysis. It remains controversial whether fast protein motions are coupled to the hydride transfer catalyzed by ecDHFR. Previous studies with heavy ecDHFR proteins labeled with (13)C, (15)N, and nonexchangeable (2)H reported enzyme mass-dependent hydride transfer kinetics for ecDHFR. Here, we report refined experimental and computational studies to establish that hydride transfer is independent of protein mass. Instead, we found the rate constant for substrate dissociation to be faster for heavy DHFR. Previously reported kinetic differences between light and heavy DHFRs likely arise from kinetic steps other than the chemical step. This study confirms that fast (femtosecond to picosecond) protein motions in ecDHFR are not coupled to hydride transfer and provides an integrative computational and experimental approach to resolve fast dynamics coupled to chemical steps in enzyme catalysis. PMID:26652185

  6. Kinetics of Indigenous Nitrate Reducing Sulfide Oxidizing Activity in Microaerophilic Wastewater Biofilms

    PubMed Central

    Villahermosa, Desirée; Corzo, Alfonso; Garcia-Robledo, Emilio; González, Juan M.; Papaspyrou, Sokratis

    2016-01-01

    Nitrate decreases sulfide release in wastewater treatment plants (WWTP), but little is known on how it affects the microzonation and kinetics of related microbial processes within the biofilm. The effect of nitrate addition on these properties for sulfate reduction, sulfide oxidation, and oxygen respiration were studied with the use of microelectrodes in microaerophilic wastewater biofilms. Mass balance calaculations and community composition analysis were also performed. At basal WWTP conditions, the biofilm presented a double-layer system. The upper microaerophilic layer (~300 μm) showed low sulfide production (0.31 μmol cm-3 h-1) and oxygen consumption rates (0.01 μmol cm-3 h-1). The anoxic lower layer showed high sulfide production (2.7 μmol cm-3 h-1). Nitrate addition decreased net sulfide production rates, caused by an increase in sulfide oxidation rates (SOR) in the upper layer, rather than an inhibition of sulfate reducing bacteria (SRB). This suggests that the indigenous nitrate reducing-sulfide oxidizing bacteria (NR-SOB) were immediately activated by nitrate. The functional vertical structure of the biofilm changed to a triple-layer system, where the previously upper sulfide-producing layer in the absence of nitrate split into two new layers: 1) an upper sulfide-consuming layer, whose thickness is probably determined by the nitrate penetration depth within the biofilm, and 2) a middle layer producing sulfide at an even higher rate than in the absence of nitrate in some cases. Below these layers, the lower net sulfide-producing layer remained unaffected. Net SOR varied from 0.05 to 0.72 μmol cm-3 h-1 depending on nitrate and sulfate availability. Addition of low nitrate concentrations likely increased sulfate availability within the biofilm and resulted in an increase of both net sulfate reduction and net sulfide oxidation by overcoming sulfate diffusional limitation from the water phase and the strong coupling between SRB and NR-SOB syntrophic

  7. Molecular Beam and Surface Science Studies of Heterogeneous Reaction Kinetics Including Combustion Dynamics. Final Technical Report.

    SciTech Connect

    Sibener, S. J.

    2006-06-23

    This research program examined the heterogeneous reaction kinetics and reaction dynamics of surface chemical processes which are of direct relevance to efficient energy production, condensed phase reactions, and mateials growth including nanoscience objectives. We have had several notable scientific and technical successes. Illustrative highlights include: (1) a thorough study of how one can efficiently produce synthesis gas (SynGas) at relatively low Rh(111) catalyst temperatures via the reaction CH{sub4}+1/2 O{sub2} {r_arrow} CO+2H{sub2}. In these studies methane activation is accomplished utilizing high-kinetic energy reagents generated via supersonic molecular beams, (2) experiments which have incisively probed the partial oxidation chemistry of adsorbed 1- and 2- butene on Rh and ice, as well as partial oxidation of propene on Au; (3) investigation of structural changes which occur to the reconstructed (23x{radical}3)-Au(111) surface upon exposure to atomic oxygen, (4) a combined experimental and theoretical examination of the fundamental atomic-level rules which govern defect minimization during the formation of self-organizing stepped nanostructures, (5) the use of these relatively defect-free nanotemplates for growing silicon nanowires having atomically-dimensioned widths, (6) a combined scanning probe and atomic beam scattering study of how the presence of self-assembling organic overlayers interact with metallic supports substrates - this work hs led to revision of the currently held view of how such adsorbates reconfigure surface structure at the atomic level, (7) an inelastic He atom scattering study in which we examined the effect of chain length on the low-energy vibrations of alkanethiol striped phase self-assembled monolayers on Au(111), yielding information on the forces that govern interfacial self-assembly, (8) a study of the vibrational properties of disordered films of SF{sub6} adsorbed on Au(111), and (9) a study of the activated chemistry and

  8. Amyloid-β probes: Review of structure–activity and brain-kinetics relationships

    PubMed Central

    Eckroat, Todd J; Mayhoub, Abdelrahman S

    2013-01-01

    Summary The number of people suffering from Alzheimer’s disease (AD) is expected to increase dramatically in the coming years, placing a huge burden on society. Current treatments for AD leave much to be desired, and numerous research efforts around the globe are focused on developing improved therapeutics. In addition, current diagnostic tools for AD rely largely on subjective cognitive assessment rather than on identification of pathophysiological changes associated with disease onset and progression. These facts have led to numerous efforts to develop chemical probes to detect pathophysiological hallmarks of AD, such as amyloid-β plaques, for diagnosis and monitoring of therapeutic efficacy. This review provides a survey of chemical probes developed to date for AD with emphasis on synthetic methodologies and structure–activity relationships with regards to affinity for target and brain kinetics. Several probes discussed herein show particularly promising results and will be of immense value moving forward in the fight against AD. PMID:23766818

  9. Activated desorption at heterogeneous interfaces and long-time kinetics of hydrocarbon recovery from nanoporous media.

    PubMed

    Lee, Thomas; Bocquet, Lydéric; Coasne, Benoit

    2016-01-01

    Hydrocarbon recovery from unconventional reservoirs (shale gas) is debated due to its environmental impact and uncertainties on its predictability. But a lack of scientific knowledge impedes the proposal of reliable alternatives. The requirement of hydrofracking, fast recovery decay and ultra-low permeability-inherent to their nanoporosity-are specificities of these reservoirs, which challenge existing frameworks. Here we use molecular simulation and statistical models to show that recovery is hampered by interfacial effects at the wet kerogen surface. Recovery is shown to be thermally activated with an energy barrier modelled from the interface wetting properties. We build a statistical model of the recovery kinetics with a two-regime decline that is consistent with published data: a short time decay, consistent with Darcy description, followed by a fast algebraic decay resulting from increasingly unreachable energy barriers. Replacing water by CO2 or propane eliminates the barriers, therefore raising hopes for clean/efficient recovery. PMID:27327254

  10. Activated desorption at heterogeneous interfaces and long-time kinetics of hydrocarbon recovery from nanoporous media

    NASA Astrophysics Data System (ADS)

    Lee, Thomas; Bocquet, Lydéric; Coasne, Benoit

    2016-06-01

    Hydrocarbon recovery from unconventional reservoirs (shale gas) is debated due to its environmental impact and uncertainties on its predictability. But a lack of scientific knowledge impedes the proposal of reliable alternatives. The requirement of hydrofracking, fast recovery decay and ultra-low permeability--inherent to their nanoporosity--are specificities of these reservoirs, which challenge existing frameworks. Here we use molecular simulation and statistical models to show that recovery is hampered by interfacial effects at the wet kerogen surface. Recovery is shown to be thermally activated with an energy barrier modelled from the interface wetting properties. We build a statistical model of the recovery kinetics with a two-regime decline that is consistent with published data: a short time decay, consistent with Darcy description, followed by a fast algebraic decay resulting from increasingly unreachable energy barriers. Replacing water by CO2 or propane eliminates the barriers, therefore raising hopes for clean/efficient recovery.

  11. [Automated kinetic assay of plasmatic L-asparaginase activity undergoing therapy for acute lymphoblastic leukemia].

    PubMed

    Orsonneau, J-L; Brassart, E A; Lecame, M; Thomare, P; Delaroche, O; Dudouet, D

    2004-01-01

    The L-asparaginase is a critical drug for the treatment of acute lymphoblastic leukaemia, that achieves blood L-asparagin depletion. However, such a therapy is associated with a high rate of negative side effects, particularly antibody synthesis against L-asparaginase. This therefore decreases therapy efficiency requiring the monitoring of L-asparaginase activity since L-asparagin determination is not easy. We compared here the results obtained with an automated kinetic enzymatic method to those obtained with the most commonly used Nessler reagent method. The correlation coefficient, r = 0,992, obtained was very good, and the allometric regression line was y = 1,038x - 0,37 microkat/L. We also showed that the specificity and the precision were better with the enzymatic method than the Nessler one. Moreover, the enzymatic method was easier and required less time to perform. Finally, the method appears able to perform real time monitoring of the therapy. PMID:15355807

  12. Amyloid-β probes: Review of structure-activity and brain-kinetics relationships.

    PubMed

    Eckroat, Todd J; Mayhoub, Abdelrahman S; Garneau-Tsodikova, Sylvie

    2013-01-01

    The number of people suffering from Alzheimer's disease (AD) is expected to increase dramatically in the coming years, placing a huge burden on society. Current treatments for AD leave much to be desired, and numerous research efforts around the globe are focused on developing improved therapeutics. In addition, current diagnostic tools for AD rely largely on subjective cognitive assessment rather than on identification of pathophysiological changes associated with disease onset and progression. These facts have led to numerous efforts to develop chemical probes to detect pathophysiological hallmarks of AD, such as amyloid-β plaques, for diagnosis and monitoring of therapeutic efficacy. This review provides a survey of chemical probes developed to date for AD with emphasis on synthetic methodologies and structure-activity relationships with regards to affinity for target and brain kinetics. Several probes discussed herein show particularly promising results and will be of immense value moving forward in the fight against AD. PMID:23766818

  13. Activated desorption at heterogeneous interfaces and long-time kinetics of hydrocarbon recovery from nanoporous media

    PubMed Central

    Lee, Thomas; Bocquet, Lydéric; Coasne, Benoit

    2016-01-01

    Hydrocarbon recovery from unconventional reservoirs (shale gas) is debated due to its environmental impact and uncertainties on its predictability. But a lack of scientific knowledge impedes the proposal of reliable alternatives. The requirement of hydrofracking, fast recovery decay and ultra-low permeability—inherent to their nanoporosity—are specificities of these reservoirs, which challenge existing frameworks. Here we use molecular simulation and statistical models to show that recovery is hampered by interfacial effects at the wet kerogen surface. Recovery is shown to be thermally activated with an energy barrier modelled from the interface wetting properties. We build a statistical model of the recovery kinetics with a two-regime decline that is consistent with published data: a short time decay, consistent with Darcy description, followed by a fast algebraic decay resulting from increasingly unreachable energy barriers. Replacing water by CO2 or propane eliminates the barriers, therefore raising hopes for clean/efficient recovery. PMID:27327254

  14. Melanoidin Removal Mechanism in An Aqueous Adsorption System: An Equilibrium, Kinetic and Thermodynamic Study.

    PubMed

    Nunes, Diego L; Oliveira, Leandro S; Franca, Adriana S

    2015-01-01

    Melanoidins are colored products that can be found in food and drinks, formed by Maillard reactions. Sometimes these compounds are considered undesirable in certain food products, because they impart a brownish color and must be removed. An overview of recent patents related to melanoidin removal indicates that it can be performed by chemical/biological degradation or by adsorption processes. Therefore, in the present study, the adsorption mechanism for synthetic melanoidin removal from aqueous solutions was studied using different Raphanus sativus press-cake sorbents, with the precursor material being carbonized in a microwave oven, either with direct heating or after a chemical activation process with phosphoric acid, nitric acid or potassium hydroxide. Physical and chemical modifications were evaluated by FTIR, pHPZC, thermogravimetry and BET. The adsorption kinetics was better described by a pseudo-second order model for all activated carbons (ACs). Evaluation of the diffusion process showed dependence on the initial melanoidin concentration due to the wide range of sizes of the adsorbed molecules. The equilibrium data were best fitted by the Langmuir model for the acid-treated AC and by the Freundlich model for the base-treated and non-chemically treated ACs. Melanoidin adsorption was characterized as a spontaneous, favorable and endothermic process involving hydrogen bonds and π-π interactions between the adsorbents surfaces and the adsorbed molecules. PMID:26013772

  15. Kinetic mechanism for formation of the active, dimeric UvrD helicase-DNA complex.

    PubMed

    Maluf, Nasib K; Ali, Janid A; Lohman, Timothy M

    2003-08-22

    Escherichia coli UvrD protein is a 3' to 5' SF1 helicase required for DNA repair as well as DNA replication of certain plasmids. We have shown previously that UvrD can self-associate to form dimers and tetramers in the absence of DNA, but that a UvrD dimer is required to form an active helicase-DNA complex in vitro. Here we have used pre-steady state, chemical quenched flow methods to examine the kinetic mechanism for formation of the active, dimeric helicase-DNA complex. Experiments were designed to examine the steps leading to formation of the active complex, separate from the subsequent DNA unwinding steps. The results show that the active dimeric complex can form via two pathways. The first, faster path involves direct binding to the DNA substrate of a pre-assembled UvrD dimer (dimer path), whereas the second, slower path proceeds via sequential binding to the DNA substrate of two UvrD monomers (monomer path), which then assemble on the DNA to form the dimeric helicase. The rate-limiting step within the monomer pathway involves dimer assembly on the DNA. These results show that UvrD dimers that pre-assemble in the absence of DNA are intermediates along the pathway to formation of the functional dimeric UvrD helicase. PMID:12788954

  16. Human telomeric G-quadruplex: thermodynamic and kinetic studies of telomeric quadruplex stability

    PubMed Central

    Chaires, Jonathan B.

    2010-01-01

    Summary Thermodynamic and kinetic studies complement high-resolution structures of G-quadruplexes. Such studies are essential for a thorough understanding of the mechanisms that govern quadruplex folding and conformational changes in quadruplexes. This perspective article reviews representative thermodynamic and kinetic studies of the folding of human telomeric quadruplex structures. Published thermodynamic data vary widely and are inconsistent. Possible reasons for these inconsistencies are discussed. The key issue of whether or not such folding reactions are a simple two-state process is examined. A tentative energy balance for the folding of telomeric quadruplexes in Na+ and K+ solution, and for conformational transition between these forms will be presented. PMID:19951355

  17. Degradation kinetics and mechanism of trace nitrobenzene by granular activated carbon enhanced microwave/hydrogen peroxide system.

    PubMed

    Tan, Dina; Zeng, Honghu; Liu, Jie; Yu, Xiaozhang; Liang, Yanpeng; Lu, Lanjing

    2013-07-01

    The kinetics of the degradation of trace nitrobenzene (NB) by a granular activated carbon (GAC) enhanced microwave (MW)/hydrogen peroxide (H202) system was studied. Effects of pH, NB initial concentration and tert-butyl alcohol on the removal efficiency were examined. It was found that the reaction rate fits well to first-order reaction kinetics in the MW/GAC/H202 process. Moreover, GAC greatly enhanced the degradation rate of NB in water. Under a given condition (MW power 300 W, H202 dosage 10 mg/L, pH 6.85 and temperature (60 +/- 5)degrees C), the degradation rate of NB was 0.05214 min-1when 4 g/L GAC was added. In general, alkaline pH was better for NB degradation; however, the optimum pH was 8.0 in the tested pH value range of 4.0-12.0. At H202 dosage of 10 mg/L and GAC dosage of 4 g/L, the removal of NB was decreased with increasing initial concentrations of NB, indicating that a low initial concentration was beneficial for the degradation of NB. These results indicated that the MW/GAC/H202 process was effective for trace NB degradation in water. Gas chromatography-mass spectrometry analysis indicated that a hydroxyl radical addition reaction and dehydrogenation reaction enhanced NB degradation. PMID:24218864

  18. In vitro dissolution kinetic study of theophylline from hydrophilic and hydrophobic matrices.

    PubMed

    Maswadeh, Hamzah M; Semreen, Mohammad H; Abdulhalim, Abdulatif A

    2006-01-01

    Oral dosage forms containing 300 mg theophylline in matrix type tablets, were prepared by direct compression method using two kinds of matrices, glycerylbehenate (hydrophobic), and (hydroxypropyl)methyl cellulose (hydrophilic). The in vitro release kinetics of these formulations were studied at pH 6.8 using the USP dissolution apparatus with the paddle assemble. The kinetics of the dissolution process were studied by analyzing the dissolution data using four kinetic equations, the zero-order equation, the first-order equation, the Higuchi square root equation and the Hixson-Crowell cube root law. The analysis of the dissolution kinetic data for the theophylline preparations in this study shows that it follows the first order kinetics and the release process involves erosion / diffusion and an alteration in the surface area and diameter of the matrix system, as well as in the diffusion path length from the matrix drug load during the dissolution process. This relation is best described by the use of both the first-order equation and the Hixson-Crowell cube root law. PMID:17515331

  19. Detailed kinetic and chemometric study of the cellulose thermal breakdown in artificially aged and non aged commercial paper. Different methods for computing activation energy as an assessment model in archaeometric applications

    PubMed Central

    2012-01-01

    Background The thermal oxidative degradation of aged and non aged cellulose samples of commercial paper was studied using thermogravimetry and derivative thermogravimetry under a forced air flow up to 800°C. Results TG and DTG data were processed using two non-isothermal-based model-fitting methods and one based on linear least squares to calculate Ea trend values, measured as a function of artificially induced sample age. The Ea trends thus obtained were compared in order to assess their potential for yielding archaeometric curves. As the trends of first two methods show an inversion of the direction between non aged cellulose samples and artificially aged samples, while the third method does not, an in-depth study was carried out using a multilinearity assumption. Conclusions The results are discussed and the outcomes indicate that the above cited inversion is real and not linked to the method. Additionally, it was evidenced that the number of points used for the estimation of linear least squares model parameters is of capital importance. PMID:22594442

  20. Gas-kinetic numerical studies of three-dimensional complex flows on spacecraft re-entry

    NASA Astrophysics Data System (ADS)

    Li, Zhi-Hui; Zhang, Han-Xin

    2009-03-01

    The gas-kinetic numerical algorithm solving the Boltzmann model equation is extended and developed to study the three-dimensional hypersonic flows of spacecraft re-entry into the atmosphere in perfect gas. In this study, the simplified velocity distribution function equation for various flow regimes is presented on the basis of the kinetic Boltzmann-Shakhov model. The discrete velocity ordinate technique and numerical quadrature methods, such as the Gauss quadrature formulas with the weight function 2/ π1/2exp(- V2) and the Gauss-Legendre numerical quadrature rule, are studied to resolve the barrier in simulating complex flows from low Mach numbers to hypersonic problems. Specially, the gas-kinetic finite-difference scheme is constructed for the computation of three-dimensional flow problems, which directly captures the time evolution of the molecular velocity distribution function. The gas-kinetic boundary conditions and numerical procedures are studied and implemented by directly acting on the velocity distribution function. The HPF (high performance fortran) parallel implementation technique for the gas-kinetic numerical method is developed and applied to study the hypersonic flows around three-dimensional complex bodies. The main purpose of the current research is to provide a way to extend the gas-kinetic numerical algorithm to the flow computation of three-dimensional complex hypersonic problems with high Mach numbers. To verify the current method and simulate gas transport phenomena covering various flow regimes, the three-dimensional hypersonic flows around sphere and spacecraft shape with different Knudsen numbers and Mach numbers are studied by HPF parallel computing. Excellent results have been obtained for all examples computed.

  1. Kinetic Studies and Bioactivity of Potential Manzamine Prodrugs

    PubMed Central

    Shilabin, Abbas Gholipour; Kasanah, Noer; Tekwani, Babu L.; Hamann, Mark T.

    2016-01-01

    The manzamines represent a class of marine natural products that show considerable promise in the control of malaria but generate GI distress in rodents when administered orally in high doses. In an effort to generate manzamine prodrugs with improved antimalarial activity and reduced GI toxicity, we prepared acetylated 8-hydroxymanzamine A analogues including 8-acetoxymanzamine A (3) and 8,12-diacetoxymanzamine A (4), and 8-methoxymanzamine A (5) beginning with 8-hydroxymanzamine A (2). The semisynthetic analogues were assayed for antimalarial and antimicrobial activities, cytotoxicity, and biological and chemical stability. Due to gradual hydrolysis of the ester group, application of monoacetate 3 as an antimalarial prodrug was investigated. The in vitro and in vivo bioassays show that acetylated analogues exhibit significant antimalarial activity (IC50(3) 9.6–30 ng/mL), which are comparable to the parent molecule; however the monoaceate 3 was shown to actually produce higher toxicity at 30 mg/kg when administered orally. PMID:18598080

  2. Effect of a catalyst on the kinetics of reduction of celestite (SrSO{sub 4}) by active charcoal

    SciTech Connect

    Sonawane, R.S.; Kale, B.B.; Apte, S.K.; Dongare, M.K.

    2000-02-01

    Reduction of celestite (SrSO{sub 4}) powder with particles of active charcoal has been studied extensively in the absence and presence of catalysts. The optimum temperature at the charging zone has been optimized to get a maximum water-soluble strontium sulfide value. The strontium value has been analyzed using a chemical method, which was verified by the instrumental method using an inductively coupled plasma-optical emission spectrophotometer (ICP-OES). The conversion-time data have been analyzed by using a modified volume-reaction (MVR) model, and the effect of the catalyst on kinetic parameters has been elucidated. It was found that potassium carbonate, potassium dichromate, sodium carbonate, and sodium dichromate catalysts were found to enhance the reaction rate quite satisfactorily in the reduction of the celestite (SrSO{sub 4}).

  3. Kinetic Fractionation of Carbon Isotopes During Carbonate Weathering in Glaciated Catchments: Implications for the Detection of Subglacial Microbial Activity

    NASA Astrophysics Data System (ADS)

    Skidmore, M.; Sharp, M.; Tranter, M.; Bottrell, S.

    2003-12-01

    Microbes are abundant at the water-rock-ice interface beneath valley glaciers at Haut Glacier d'Arolla, Switzerland (HGA) and at John Evans Glacier, Ellesmere Island Nunavut, Canada (JEG). However, the importance of in-situ microbial activity in driving subglacial weathering reactions remains unknown. This is a key question when considering the potential role of microbes in mediating subglacial weathering and carbon cycling on a continental scale beneath the Pleistocene mid-latitude ice sheets. This study measured the chemical composition of meltwaters, including δ {13}C-DIC at the two glaciers to quantify microbial CO2 inputs to the DIC budget using isotope mass balance techniques. However, PCO2 data indicates that most of the glacial meltwaters are far from equilibrium with respect to atmospheric CO2 and thus kinetic processes are important in determining the water chemistry. Consequently, conventional equilibrium isotope mass balance techniques were inappropriate in this case. Hence, laboratory experiments were conducted with calcium carbonate and carbonate rich glacial sediments from JEG under simulated subglacial conditions (< 63 micron size fraction, sediment concentrations 0.01 to 5 g/l, 5° C) to investigate potential kinetic isotopic effects and aid in interpretation of the field data (δ {13}C-DIC values ranging from -2.4 to -15.7 ‰ ). The laboratory experiments demonstrate previously unreported kinetic fractionation of carbon isotopes during the initial hydrolysis (closed system conditions) and early stages of carbonate dissolution driven by atmospheric CO2 (open system conditions). Preferential dissolution of Ca12CO3, results in δ {13}C-DIC values that are significantly isotopically lighter than the bulk carbonate. This kinetic isotopic effect (KIE) is more pronounced at higher sediment concentrations and can be up to -17.4 ‰ for glacial sediments under closed system conditions and sediment concentrations of 5g/l. The KIE is also significant

  4. Revealing the activation pathway for TMEM16A chloride channels from macroscopic currents and kinetic models.

    PubMed

    Contreras-Vite, Juan A; Cruz-Rangel, Silvia; De Jesús-Pérez, José J; Figueroa, Iván A Aréchiga; Rodríguez-Menchaca, Aldo A; Pérez-Cornejo, Patricia; Hartzell, H Criss; Arreola, Jorge

    2016-07-01

    TMEM16A (ANO1), the pore-forming subunit of calcium-activated chloride channels, regulates several physiological and pathophysiological processes such as smooth muscle contraction, cardiac and neuronal excitability, salivary secretion, tumour growth and cancer progression. Gating of TMEM16A is complex because it involves the interplay between increases in intracellular calcium concentration ([Ca(2+)]i), membrane depolarization, extracellular Cl(-) or permeant anions and intracellular protons. Our goal here was to understand how these variables regulate TMEM16A gating and to explain four observations. (a) TMEM16A is activated by voltage in the absence of intracellular Ca(2+). (b) The Cl(-) conductance is decreased after reducing extracellular Cl(-) concentration ([Cl(-)]o). (c) ICl is regulated by physiological concentrations of [Cl(-)]o. (d) In cells dialyzed with 0.2 μM [Ca(2+)]i, Cl(-) has a bimodal effect: at [Cl(-)]o <30 mM TMEM16A current activates with a monoexponential time course, but above 30 mM, [Cl(-)]o ICl activation displays fast and slow kinetics. To explain the contribution of Vm, Ca(2+) and Cl(-) to gating, we developed a 12-state Markov chain model. This model explains TMEM16A activation as a sequential, direct, and Vm-dependent binding of two Ca(2+) ions coupled to a Vm-dependent binding of an external Cl(-) ion, with Vm-dependent transitions between states. Our model predicts that extracellular Cl(-) does not alter the apparent Ca(2+) affinity of TMEM16A, which we corroborated experimentally. Rather, extracellular Cl(-) acts by stabilizing the open configuration induced by Ca(2+) and by contributing to the Vm dependence of activation. PMID:27138167

  5. Electro-Hydrodynamics and Kinetic Modeling of Dry and Humid Air Flows Activated by Corona Discharges

    NASA Astrophysics Data System (ADS)

    P. Sarrette, J.; Eichwald, O.; Marchal, F.; Ducasse, O.; Yousfi, M.

    2016-05-01

    The present work is devoted to the 2D simulation of a point-to-plane Atmospheric Corona Discharge Reactor (ACDR) powered by a DC high voltage supply. The corona reactor is periodically crossed by thin mono filamentary streamers with a natural repetition frequency of some tens of kHz. The study compares the results obtained in dry air and in air mixed with a small amount of water vapour (humid air). The simulation involves the electro-dynamics, chemical kinetics and neutral gas hydrodynamics phenomena that influence the kinetics of the chemical species transformation. Each discharge lasts about one hundred of a nanosecond while the post-discharge occurring between two successive discharges lasts one hundred of a microsecond. The ACDR is crossed by a lateral dry or humid air flow initially polluted with 400 ppm of NO. After 5 ms, the time corresponding to the occurrence of 50 successive discharge/post-discharge phases, a higher NO removal rate and a lower ozone production rate are found in humid air. This change is due to the presence of the HO2 species formed from the H primary radical in the discharge zone.

  6. A kinetic study of lipase-catalyzed alcoholysis of palm kernel oil.

    PubMed

    de Oliveira, D; Alves, T L

    2000-01-01

    The use of lipases as biocatalysts in interesterification reactions has been the object of growing interest, owing to the importance of esters as emulsifiers, intermediates to produce oleochemicals, and fuel alternatives. We consider in this article a kinetic study of lipase-catalyzed alcoholysis of palm kernel oil, using n-hexane as the solvent. In a first step the ester production was maximized by using a Taguchi design, and then an empirical model was built to determine the influence of the process variables. Taking into account the results obtained in the first step, we performed a kinetic study and developed a simple model for this system. PMID:10849779

  7. Application of controlled interfacial pore structures to kinetic studies in alumina

    SciTech Connect

    Roedel, J.; Glaeser, A.M.

    1988-04-01

    The application of controlled-geometry interfacial pore structures to fundamental kinetic studies in alumina is described. Results from studies of the morphological stability of high aspect ratio pore channels, crack healing, pore coarsening and pore elimination in sapphire are presented.

  8. PHYTO-REMOVAL OF TRINITROTOLUENE FROM WATER WITH BATCH KINETIC STUDIES

    EPA Science Inventory

    A series of batch reactor studies were conducted to obtain kinetic data for optimizing phyto-treatment of water contaminated with trinitrotoluene (TNT). A plant screening study indicated that stonewort and parrotfeather were the most effective among the plants tested; parrotfeath...

  9. Kinetic attractor phase diagrams of active nematic suspensions: the dilute regime.

    PubMed

    Forest, M Gregory; Wang, Qi; Zhou, Ruhai

    2015-08-28

    Large-scale simulations by the authors of the kinetic-hydrodynamic equations for active polar nematics revealed a variety of spatio-temporal attractors, including steady and unsteady, banded (1d) and cellular (2d) spatial patterns. These particle scale activation-induced attractors arise at dilute nanorod volume fractions where the passive equilibrium phase is isotropic, whereas all previous model simulations have focused on the semi-dilute, nematic equilibrium regime and mostly on low-moment orientation tensor and polarity vector models. Here we extend our previous results to complete attractor phase diagrams for active nematics, with and without an explicit polar potential, to map out novel spatial and dynamic transitions, and to identify some new attractors, over the parameter space of dilute nanorod volume fraction and nanorod activation strength. The particle-scale activation parameter corresponds experimentally to a tunable force dipole strength (so-called pushers with propulsion from the rod tail) generated by active rod macromolecules, e.g., catalysis with the solvent phase, ATP-induced propulsion, or light-activated propulsion. The simulations allow 2d spatial variations in all flow and orientational variables and full spherical orientational degrees of freedom; the attractors correspond to numerical integration of a coupled system of 125 nonlinear PDEs in 2d plus time. The phase diagrams with and without the polar interaction potential are remarkably similar, implying that polar interactions among the rodlike particles are not essential to long-range spatial and temporal correlations in flow, polarity, and nematic order. As a general rule, above a threshold, low volume fractions induce 1d banded patterns, whereas higher yet still dilute volume fractions yield 2d patterns. Again as a general rule, varying activation strength at fixed volume fraction induces novel dynamic transitions. First, stationary patterns saturate the instability of the isotropic

  10. Stoichiometry and kinetics of poly-{beta}-hydroxybutyrate metabolism in aerobic, slow growing, activated sludge cultures

    SciTech Connect

    Beun, J.J.; Paletta, F.; Loosdrecht, M.C.M. Van; Heijnen, J.J.

    2000-02-20

    This paper discusses the poly-{beta}-hydroxybutyrate (PHB) metabolism in aerobic, slow growing, activated sludge cultures, based on experimental data and on a metabolic model. The dynamic conditions which occur in activated sludge processes were simulated in a 2-L sequencing batch reactor (SBR) by subjecting a mixed microbial population to successive periods of external substrate availability (feast period) and no external substrate availability (famine period). Under these conditions intracellular storage and consumption of PHB was observed. It appeared that in the feast period, 66% to almost 100% of the substrate consumed is used for storage of PHB, the remainder is used for growth and maintenance processes. Furthermore, it appeared that at high sludge retention time (SRT) the growth rate in the feast and famine periods was the same. With decreasing SRT the growth rate in the feast period increased relative to the growth rate in the famine period. Acetate consumption and PHB production in the feast period both proceeded with a zero-order rate in acetate and PHB concentration respectively. PHB consumption in the famine period could best be described kinetically with a nth order degradation equation in PHB concentration. The obtained results are discussed in the context of the general activated sludge models.

  11. Removal Rate of Organic Matter Using Natural Cellulose via Adsorption Isotherm and Kinetic Studies.

    PubMed

    Din, Mohd Fadhil Md; Ponraj, Mohanadoss; Low, Wen-Pei; Fulazzaky, Mohamad Ali; Iwao, Kenzo; Songip, Ahmad Rahman; Chelliapan, Shreeshivadasan; Ismail, Zulhilmi; Jamal, Mohamad Hidayat

    2016-02-01

    In this study, the removal of natural organic matter (NOM) using coconut fiber (CF) and palm oil fiber (POF) was investigated. Preliminary analysis was performed using a jar test for the selection of optimal medium before the fabricated column model experiment. The equilibrium studies on isotherms and kinetic models for NOM adsorption were analyzed using linearized correlation coefficient. Results showed that the equilibrium data were fitted to Langmuir isotherm model for both CF and POF. The most suitable adsorption model was the pseudo-first-order kinetic model for POF and pseudo-second-order kinetic model for CF. The adsorption capacities achieved by the CF and POF were 15.67 and 30.8 mg/g respectively. Based on this investigation, it can be concluded that the POF is the most suitable material for the removal of NOM in semi polluted river water. PMID:26803100

  12. Single-molecule enzymology of steroid transforming enzymes: Transient kinetic studies and what they tell us.

    PubMed

    Penning, Trevor M

    2016-07-01

    Structure-function studies on steroid transforming enzymes often use site-directed mutagenesis to inform mechanisms of catalysis and effects on steroid binding, and data are reported in terms of changes in steady state kinetic parameters kcat, Km and kcat/Km. However, this dissection of function is limited since kcat is governed by the rate-determining step and Km is a complex macroscopic kinetic constant. Often site-directed mutagenesis can lead to a change in the rate-determining step which cannot be revealed by just reporting a decrease in kcat alone. These issues are made more complex when it is considered that many steroid transforming enzymes have more than one substrate and product. We present the case for using transient-kinetics performed with stopped-flow spectrometry to assign rate constants to discrete steps in these multi-substrate reactions and their use to interpret enzyme mechanism and the effects of disease and engineered mutations. We demonstrate that fluorescence kinetic transients can be used to measure ligand binding that may be accompanied by isomerization steps, revealing the existence of new enzyme intermediates. We also demonstrate that single-turnover reactions can provide a klim for the chemical step and Ks for steroid-substrate binding and that when coupled with kinetic isotope effect measurements can provide information on transition state intermediates. We also demonstrate how multiple turnover experiments can provide evidence for either "burst-phase" kinetics, which can reveal a slow product release step, or linear-phase kinetics, in which the chemical step can be rate-determining. With these assignments it becomes more straightforward to analyze the effects of mutations. We use examples from the hydroxysteroid dehydrogenases (AKR1Cs) and human steroid 5β-reductase (AKR1D1) to illustrate the utility of the approach, which are members of the aldo-keto reductase (AKR) superfamily. PMID:26596239

  13. Kinetics and thermodynamics of glycans and glycoproteins binding to Holothuria scabra lectin: a fluorescence and surface plasmon resonance spectroscopic study.

    PubMed

    Gowda, Nagaraj M; Gaikwad, Sushama M; Khan, M Islam

    2013-11-01

    Holothuria scabra produces a monomeric lectin (HSL) of 182 kDa. HSL showed strong antibacterial activity and induced bacterial agglutination under in vitro conditions, indicating its role in animals' innate immune responses. Very few lectins have been reported from echinoderms and none of these lectins have been explored in detail for their sugar-binding kinetics. Affinity, kinetics and thermodynamic analysis of glycans and glycoproteins binding to HSL were studied by fluorescence and surface plasmon resonance spectroscopy. Lectin binds with higher affinity to O-linked than N-linked asialo glycans, and the affinities were relatively higher than that for sialated glycans and glycoproteins. T-antigen α-methyl glycoside was the most potent ligand having the highest affinity (Ka 8.32 ×10(7) M(-1)). Thermodynamic and kinetic analysis indicated that the binding of galactosyl Tn-antigen and asialo glycans is accompanied by an enthalpic contribution in addition to higher association rate coupled by low activation energy for the association process. Presence of sialic acid or protein matrix inhibits binding. Higher affinity of HSL for O-glycans than N-glycans had biological implications; since HSL specifically recognizes bacteria, which have mucin or O-glycan cognate on their cell surfaces and play a major role in animal innate immunity. Since, HSL had higher affinity to T-antigen, makes it a useful tool for cancer diagnostic purpose. PMID:23736907

  14. Permeabilization activated reduction in fluorescence: A novel method to measure kinetics of protein interactions with intracellular structures.

    PubMed

    Singh, Pali P; Hawthorne, Jenci L; Davis, Christie A; Quintero, Omar A

    2016-06-01

    Understanding kinetic information is fundamental in understanding biological function. Advanced imaging technologies have fostered the development of kinetic analyses in cells. We have developed Permeabilization Activated Reduction in Fluorescence (PARF) analysis for determination of apparent t1/2 and immobile fraction, describing the dissociation of a protein of interest from intracellular structures. To create conditions where dissociation events are observable, cells expressing a fluorescently-tagged protein are permeabilized with digitonin, diluting the unbound protein into the extracellular media. As the media volume is much larger than the cytosolic volume, the concentration of the unbound pool decreases drastically, shifting the system out of equilibrium, favoring dissociation events. Loss of bound protein is observed as loss of fluorescence from intracellular structures and can be fit to an exponential decay. We compared PARF dissociation kinetics with previously published equilibrium kinetics as determined by FRAP. PARF dissociation rates agreed with the equilibrium-based FRAP analysis predictions of the magnitude of those rates. When used to investigate binding kinetics of a panel of cytoskeletal proteins, PARF analysis revealed that filament stabilization resulted in slower fluorescence loss. Additionally, commonly used "general" F-actin labels display differences in kinetic properties, suggesting that not all fluorescently-tagged actin labels interact with the actin network in the same way. We also observed differential dissociation kinetics for GFP-VASP depending on which cellular structure was being labeled. These results demonstrate that PARF analysis of non-equilibrium systems reveals kinetic information without the infrastructure investment required for other quantitative approaches such as FRAP, photoactivation, or in vitro reconstitution assays. © 2016 Wiley Periodicals, Inc. PMID:27126922

  15. Synthesis of ¹⁸O-labeled RNA for application to kinetic studies and imaging.

    PubMed

    Hamasaki, Tomohiro; Matsumoto, Takahiro; Sakamoto, Naoya; Shimahara, Akiko; Kato, Shiori; Yoshitake, Ayumi; Utsunomiya, Ayumi; Yurimoto, Hisayoshi; Gabazza, Esteban C; Ohgi, Tadaaki

    2013-07-01

    Radioisotopes and fluorescent compounds are frequently used for RNA labeling but are unsuitable for clinical studies of RNA drugs because of the risk from radiation exposure or the nonequivalence arising from covalently attached fluorophores. Here, we report a practical phosphoramidite solid-phase synthesis of (18)O-labeled RNA that avoids these disadvantages, and we demonstrate its application to quantification and imaging. The synthesis involves the introduction of a nonbridging (18)O atom into the phosphate group during the oxidation step of the synthetic cycle by using (18)O water as the oxygen donor. The (18)O label in the RNA was stable at pH 3-8.5, while the physicochemical and biological properties of labeled and unlabeled short interfering RNA were indistinguishable by circular dichroism, melting temperature and RNA-interference activity. The (18)O/(16)O ratio as measured by isotope ratio mass spectrometry increased linearly with the concentration of (18)O-labeled RNA, and this technique was used to determine the blood concentration of (18)O-labeled RNA after administration to mice. (18)O-labeled RNA transfected into human A549 cells was visualized by isotope microscopy. The RNA was observed in foci in the cytoplasm around the nucleus, presumably corresponding to endosomes. These methodologies may be useful for kinetic and cellular-localization studies of RNA in basic and pharmaceutical studies. PMID:23632164

  16. Mechanisms and kinetics study on the trihalomethanes formation with carbon nanoparticle precursors.

    PubMed

    Du, Tingting; Wang, Yingying; Yang, Xin; Wang, Wei; Guo, Haonan; Xiong, Xinyu; Gao, Rui; Wuli, Xiati; Adeleye, Adeyemi S; Li, Yao

    2016-07-01

    With lots of carbon nanoparticles (CNPs) applied in the industry, the possibilities of their environmental release have received much attention. As the CNPs may enter drinking water systems, and persist in water and wastewater treatment systems, their possible reaction with disinfectants should be studied. In this study, the formation of trihalomethanes (THMs) with 5 types of carbon nanotubes (CNTs), graphene oxide (GO) and reduced graphene oxide (rGO) was investigated. All CNPs could act as precursors of THMs in aqueous phase. Total concentrations of THMs formed with CNPs varied from 0.24 to 0.95 μM, much lower than that formed from chlorinated Suwannee River Natural Organic Matter (SRNOM) (approximately 9 μM). The kinetics of THMs formation with GO was 0.0814 M(-1) s(-1), which is higher than most of the chlorinated humic acid obtained from different natural waters. The study indicates that during chlorination, C-Cl bond could be formed on the surface of CNPs. However, carbon atoms at the middle of two meta-positioned OH groups on the benzene ring are more active and may prefer to form THMs with chlorine oxidation. The influences of pH and reactant doses on the formation of THMs were also discussed. PMID:27077535

  17. Enzymatic Synthesis of Furfuryl Alcohol Ester with Oleic Acid by Candida antarctica Lipase B and Its Kinetic Study

    NASA Astrophysics Data System (ADS)

    Sengupta, Avery; Dey, Tanmoy; Ghosh, Mahua; Ghosh, Jaydip; Ghosh, Santinath

    2012-08-01

    This study investigated the successful enzymatic production of furfuryl oleate and its detailed kinetic study by Michaelis-Menten model. Esterification of oleic acid and furfuryl alcohol by Candida antarctica lipase B (Novozym 435 preparation) in a solvent free system was studied in the present work at 1:1 molar ratio of furfuryl alcohol and oleic acid. About 99 % conversion (on the basis of oleic acid) has been achieved within 6 h at 5 % enzyme concentration. Ping-pong bi-bi mechanism (inhibition phenomenon taken into account) was applied to describe the ratios as a complex kinetic model. The kinetic parameters were determined using MATLAB language programme. The two initial rate constants KA and KB respectively were found out by different progress curves plotted with the help of MATLAB language programme. It was concluded from the results that furfuryl alcohol considerably inhibited the enzymatic reaction while oleic acid had negligible inhibitory effect. It was clearly seen that the initial rate was increased with the increase in the furfuryl alcohol concentration until 2 M/L after which there was a drop in the initial rate depicting the inhibitory effect of furfuryl alcohol. Surprisingly, it has been observed that addition of 0.1 mol of product activated the esterification reaction. Finally, the model was found to be statistically fitting well with the experimental data.

  18. Production of ACE inhibitory peptides from sweet sorghum grain protein using alcalase: Hydrolysis kinetic, purification and molecular docking study.

    PubMed

    Wu, Qiongying; Du, Jinjuan; Jia, Junqiang; Kuang, Cong

    2016-05-15

    In this study, sweet sorghum grain protein (SSGP) was hydrolyzed using alcalase yielding ACE inhibitory peptides. A kinetic model was proposed to describe the enzymolysis process of SSGP. The kinetic parameters, a and b, were determined according to experimental data. It was found that the model was reliable to describe the kinetic behaviour for SSGP hydrolysis by alcalase. After hydrolysis, the SSGP hydrolysate with DH of 19% exhibited the strongest ACE inhibitory activity and the hydrolysate was then used to isolate ACE inhibitory peptides. A novel ACE inhibitory peptide was successfully purified from this hydrolysate by ultrafiltration, ion exchange chromatography, gel filtration chromatography, and reversed-phased high performance liquid chromatography (RP-HPLC). The amino acid sequence of the purified peptide was identified as Thr-Leu-Ser (IC50=102.1 μM). The molecular docking studies revealed that the ACE inhibition of the tripeptide was mainly attributed to its C-terminal Ser, which can effectively interact with the S1 and S2 pockets of ACE. Our studies suggest that the tripeptide from the SSGP hydrolysate can be utilized to develop functional food ingredients or pharmaceuticals for prevention of hypertension. PMID:26775955

  19. Start-up of membrane bioreactor and hybrid moving bed biofilm reactor-membrane bioreactor: kinetic study.

    PubMed

    Leyva-Díaz, J C; Poyatos, J M

    2015-01-01

    A hybrid moving bed biofilm reactor-membrane bioreactor (hybrid MBBR-MBR) system was studied as an alternative solution to conventional activated sludge processes and membrane bioreactors. This paper shows the results obtained from three laboratory-scale wastewater treatment plants working in parallel in the start-up and steady states. The first wastewater treatment plant was a MBR, the second one was a hybrid MBBR-MBR system containing carriers both in anoxic and aerobic zones of the bioreactor (hybrid MBBR-MBRa), and the last one was a hybrid MBBR-MBR system which contained carriers only in the aerobic zone (hybrid MBBR-MBRb). The reactors operated with a hydraulic retention time of 30.40 h. A kinetic study for characterizing heterotrophic biomass was carried out and organic matter and nutrients removals were evaluated. The heterotrophic biomass of the hybrid MBBR-MBRb showed the best kinetic performance in the steady state, with yield coefficient for heterotrophic biomass=0.30246 mg volatile suspended solids per mg chemical oxygen demand, maximum specific growth rate for heterotrophic biomass=0.00308 h(-1) and half-saturation coefficient for organic matter=3.54908 mg O2 L(-1). The removal of organic matter was supported by the kinetic study of heterotrophic biomass. PMID:26606088

  20. Kinetic isotope effects for RNA cleavage by 2'-O- transphosphorylation: Nucleophilic activation by specific base

    PubMed Central

    Harris, Michael E; Dai, Qing; Gu, Hong; Kellerman, Dan; Piccirilli, Joseph A; Anderson, Vernon E

    2010-01-01

    To better understand the interactions between catalysts and transition states during RNA strand cleavage, primary 18O kinetic isotope effects and solvent D2O isotope effects were measured to probe the mechanism of base-catalyzed 2'-O-transphosphorylation of the RNA dinucleotide 5'-UpG-3'. The observed 18O KIEs for the nucleophilic 2'-O and in the 5'-O leaving group at pH 14 are both large relative to reactions of phosphodiesters with good leaving groups, indicating that the reaction catalyzed by hydroxide has a transition state (TS) with advanced phosphorus-oxygen bond fission to the leaving group (18kLG = 1.034 ± 0.004) and phosphorous-nucleophile bond formation (18kNUC = 0.984 ± 0.004). A breakpoint in the pH dependence of the 2'-O-transphosphorylation rate to a pH independent phase above pH 13 has been attributed to the pKa of the 2'-OH nucleophile. A smaller nucleophile KIE is observed at pH 12 (18kNUC = 0.995 ± 0.004) that is interpreted as the combined effect of the equilibrium isotope effect (~1.02) on deprotonation of the 2′-hydroxyl nucleophile and the intrinsic KIE on the nucleophilic addition step (ca. 0.981). An alternative mechanism in which the hydroxide ion acts as a general base is considered unlikely given the lack of a solvent deuterium isotope effect above the breakpoint in the pH versus rate profile. These results represent the first direct analysis of the transition state for RNA strand cleavage. The primary 18O KIE results and the lack of a kinetic solvent deuterium isotope effect together provide strong evidence for a late transition state and 2'-O nucleophile activation by specific base catalysis. PMID:20669950

  1. Studies of Reaction Kinetics of Methane Hydrate Dissocation in Porous Media

    SciTech Connect

    Moridis, George J.; Seol, Yongkoo; Kneafsey, Timothy J.

    2005-03-10

    The objective of this study is the description of the kinetic dissociation of CH4-hydrates in porous media, and the determination of the corresponding kinetic parameters. Knowledge of the kinetic dissociation behavior of hydrates can play a critical role in the evaluation of gas production potential of gas hydrate accumulations in geologic media. We analyzed data from a sequence of tests of CH4-hydrate dissociation by means of thermal stimulation. These tests had been conducted on sand cores partially saturated with water, hydrate and CH4 gas, and contained in an x-ray-transparent aluminum pressure vessel. The pressure, volume of released gas, and temperature (at several locations within the cores) were measured. To avoid misinterpreting local changes as global processes, x-ray computed tomography scans provided accurate images of the location and movement of the reaction interface during the course of the experiments. Analysis of the data by means of inverse modeling (history matching ) provided estimates of the thermal properties and of the kinetic parameters of the hydration reaction in porous media. Comparison of the results from the hydrate-bearing porous media cores to those from pure CH4-hydrate samples provided a measure of the effect of the porous medium on the kinetic reaction. A tentative model of composite thermal conductivity of hydrate-bearing media was also developed.

  2. Structure-activity relationships (SAR) and structure-kinetic relationships (SKR) of bicyclic heteroaromatic acetic acids as potent CRTh2 antagonists II: lead optimization.

    PubMed

    Alonso, Juan Antonio; Andrés, Miriam; Bravo, Mónica; Calbet, Marta; Eastwood, Paul R; Eichhorn, Peter; Esteve, Cristina; Ferrer, Manel; Gómez, Elena; González, Jacob; Mir, Marta; Moreno, Imma; Petit, Silvia; Roberts, Richard S; Sevilla, Sara; Vidal, Bernat; Vidal, Laura; Vilaseca, Pere; Zanuy, Miriam

    2014-11-01

    Extensive structure-activity relationship (SAR) and structure-kinetic relationship (SKR) studies in the bicyclic heteroaromatic series of CRTh2 antagonists led to the identification of several molecules that possessed both excellent binding and cellular potencies along with long receptor residence times. A small substituent in the bicyclic core provided an order of magnitude jump in dissociation half-lives. Selected optimized compounds demonstrated suitable pharmacokinetic profiles. PMID:25437505

  3. Submaximal oxygen uptake kinetics, functional mobility, and physical activity in older adults with heart failure and reduced ejection fraction

    PubMed Central

    Hummel, Scott L; Herald, John; Alpert, Craig; Gretebeck, Kimberlee A; Champoux, Wendy S; Dengel, Donald R; Vaitkevicius, Peter V; Alexander, Neil B

    2016-01-01

    Background Submaximal oxygen uptake measures are more feasible and may better predict clinical cardiac outcomes than maximal tests in older adults with heart failure (HF). We examined relationships between maximal oxygen uptake, submaximal oxygen kinetics, functional mobility, and physical activity in older adults with HF and reduced ejection fraction. Methods Older adults with HF and reduced ejection fraction (n = 25, age 75 ± 7 years) were compared to 25 healthy age- and gender-matched controls. Assessments included a maximal treadmill test for peak oxygen uptake (VO2peak), oxygen uptake kinetics at onset of and on recovery from a submaximal treadmill test, functional mobility testing [Get Up and Go (GUG), Comfortable Gait Speed (CGS), Unipedal Stance (US)], and self-reported physical activity (PA). Results Compared to controls, HF had worse performance on GUG, CGS, and US, greater delays in submaximal oxygen uptake kinetics, and lower PA. In controls, VO2peak was more strongly associated with functional mobility and PA than submaximal oxygen uptake kinetics. In HF patients, submaximal oxygen uptake kinetics were similarly associated with GUG and CGS as VO2peak, but weakly associated with PA. Conclusions Based on their mobility performance, older HF patients with reduced ejection fraction are at risk for adverse functional outcomes. In this population, submaximal oxygen uptake measures may be equivalent to VO2 peak in predicting functional mobility, and in addition to being more feasible, may provide better insight into how aerobic function relates to mobility in older adults with HF. PMID:27594875

  4. A Novel Study of Methane-Rich Gas Reforming to Syngas and Its Kinetics over Semicoke Catalyst

    PubMed Central

    Zhang, Guojie; Su, Aiting; Qu, Jiangwen; Du, Yannian

    2014-01-01

    A small-size gasification unit is improved through process optimization to simulate industrial United Gas Improvement Company gasification. It finds that the reaction temperature has important impacts on semicoke catalyzed methane gas mixture. The addition of water vapor can enhance the catalytic activity of reforming, which is due to the fact that addition of water vapor not only removes carbon deposit produced in the reforming and gasification reaction processes, but also participates in gasification reaction with semicoke to generate some active oxygen-containing functional groups. The active oxygen-containing functional groups provide active sites for carbon dioxide reforming of methane, promoting the reforming reaction. It also finds that the addition of different proportions of methane-rich gas can yield synthesis gas with different H2/CO ratio. The kinetics study shows that the semicoke can reduce the activation energy of the reforming reaction and promote the occurrence of the reforming reaction. The kinetics model of methane reforming under the conditions of steam gasification over semicoke is as follows: k-=5.02×103·pCH40.71·pH20.26·exp(−74200/RT). PMID:24959620

  5. A novel study of methane-rich gas reforming to syngas and its kinetics over semicoke catalyst.

    PubMed

    Zhang, Guojie; Su, Aiting; Qu, Jiangwen; Du, Yannian

    2014-01-01

    A small-size gasification unit is improved through process optimization to simulate industrial United Gas Improvement Company gasification. It finds that the reaction temperature has important impacts on semicoke catalyzed methane gas mixture. The addition of water vapor can enhance the catalytic activity of reforming, which is due to the fact that addition of water vapor not only removes carbon deposit produced in the reforming and gasification reaction processes, but also participates in gasification reaction with semicoke to generate some active oxygen-containing functional groups. The active oxygen-containing functional groups provide active sites for carbon dioxide reforming of methane, promoting the reforming reaction. It also finds that the addition of different proportions of methane-rich gas can yield synthesis gas with different H2/CO ratio. The kinetics study shows that the semicoke can reduce the activation energy of the reforming reaction and promote the occurrence of the reforming reaction. The kinetics model of methane reforming under the conditions of steam gasification over semicoke is as follows: [Formula in text]. PMID:24959620

  6. Theoretical Studies in Chemical Kinetics - Annual Report, 1970.

    DOE R&D Accomplishments Database

    Karplus, Martin

    1970-10-01

    The research performed includes (a) Alkali-Halide, Alkali-Halide (MX, M’X’) Exchange Reactions; (b) Inversion Problem; (c) Quantum Mechanics of Scattering Processes, (d) Transition State Analysis of Classical Trajectories, (e) Differential Cross Sections from Classical Trajectories; and (f) Other Studies.

  7. A kinetic study of Trichoderma reesei Cel7B catalyzed cellulose hydrolysis.

    PubMed

    Song, Xiangfei; Zhang, Shujun; Wang, Yefei; Li, Jingwen; He, Chunyan; Yao, Lishan

    2016-06-01

    One prominent feature of Trichoderma reesei (Tr) endoglucanases catalyzed cellulose hydrolysis is that the reaction slows down quickly after it starts (within minutes). But the mechanism of the slowdown is not well understood. A structural model of Tr- Cel7B catalytic domain bound to cellulose was built computationally and the potentially important binding residues were identified and tested experimentally. The 13 tested mutants show different binding properties in the adsorption to phosphoric acid swollen cellulose and filter paper. Though the partitioning parameter to filter paper is about 10 times smaller than that to phosphoric acid swollen cellulose, a positive correlation is shown for two substrates. The kinetic studies show that the reactions slow down quickly for both substrates. This slowdown is not correlated to the binding constant but anticorrelated to the enzyme initial activity. The amount of reducing sugars released after 24h by Cel7B in phosphoric acid swollen cellulose, Avicel and filter paper cellulose hydrolysis is correlated with the enzyme activity against a soluble substrate p-nitrophenyl lactoside. Six of the 13 tested mutants, including N47A, N52D, S99A, N323D, S324A, and S346A, yield ∼15-35% more reducing sugars than the wild type (WT) Cel7B in phosphoric acid swollen cellulose and filter paper hydrolysis. This study reveals that the slowdown of the reaction is not due to the binding of the enzyme to cellulose. The activity of Tr- Cel7B against the insoluble substrate cellulose is determined by the enzyme's capability in hydrolyzing the soluble substrate. PMID:27178789

  8. Synthesis, thermal behavior, and dehydrogenation kinetics study of lithiated ethylenediamine.

    PubMed

    Chen, Juner; Wu, Guotao; Xiong, Zhitao; Wu, Hui; Chua, Yong Shen; Zhou, Wei; Liu, Bin; Ju, Xiaohua; Chen, Ping

    2014-10-13

    The lithiation of ethylenediamine by LiH is a stepwise process to form the partially lithiated intermediates LiN(H)CH2 CH2 NH2 and [LiN(H)CH2 CH2 NH2 ][LiN(H)CH2 CH2 N(H)Li]2 prior to the formation of dilithiated ethylenediamine LiN(H)CH2 CH2 N(H)Li. A reversible phase transformation between the partial and dilithiated species was observed. One dimensional {Lin Nn } ladders and three-dimensional network structures were found in the crystal structures of LiN(H)CH2 CH2 NH2 and LiN(H)CH2 CH2 N(H)Li, respectively. LiN(H)CH2 CH2 N(H)Li undergoes dehydrogenation with an activation energy of 181±8 kJ mol(-1) , whereas the partially lithiated ethylenediamine compounds were polymerized and released ammonia at elevated temperatures. The dynamical dehydrogenation mechanism of the dilithiated ethylenediamine compounds was investigated by using the Johnson-Mehl-Avrami equation. PMID:25164593

  9. A study of spin isomer conversion kinetics in supercritical fluid hydrogen for cyrogenic fuel storage technologies

    NASA Astrophysics Data System (ADS)

    Matthews, Manyalibo J.; Petitpas, Guillaume; Aceves, Salvador M.

    2011-08-01

    A detailed kinetic study of para-ortho hydrogen conversion under supercritical conditions using rotational Raman scattering is presented. Isochoric measurements of initially low ortho concentrations over temperatures 32 < T < 280 K and densities 0.014 < ρ < 0.060 g/cm3 were used to derive kinetic rate constants k(ρ, T) by solving an autocatalytic kinetic rate equation. At low ortho concentrations and T < 100 K, k is found to be ˜2× higher than previous results based on thermal conductivity measurements, decreasing weakly with temperature, similar to Wigner's original paramagnetic theory. Accurate modeling of k(ρ, T) is critical in predicting cryogenic hydrogen fuel tank dormancy performance for hydrogen-power vehicles.

  10. Kinetic Study of Acetone-Butanol-Ethanol Fermentation in Continuous Culture

    PubMed Central

    Buehler, Edward A.; Mesbah, Ali

    2016-01-01

    Acetone-butanol-ethanol (ABE) fermentation by clostridia has shown promise for industrial-scale production of biobutanol. However, the continuous ABE fermentation suffers from low product yield, titer, and productivity. Systems analysis of the continuous ABE fermentation will offer insights into its metabolic pathway as well as into optimal fermentation design and operation. For the ABE fermentation in continuous Clostridium acetobutylicum culture, this paper presents a kinetic model that includes the effects of key metabolic intermediates and enzymes as well as culture pH, product inhibition, and glucose inhibition. The kinetic model is used for elucidating the behavior of the ABE fermentation under the conditions that are most relevant to continuous cultures. To this end, dynamic sensitivity analysis is performed to systematically investigate the effects of culture conditions, reaction kinetics, and enzymes on the dynamics of the ABE production pathway. The analysis provides guidance for future metabolic engineering and fermentation optimization studies. PMID:27486663

  11. Kinetic Study of Acetone-Butanol-Ethanol Fermentation in Continuous Culture.

    PubMed

    Buehler, Edward A; Mesbah, Ali

    2016-01-01

    Acetone-butanol-ethanol (ABE) fermentation by clostridia has shown promise for industrial-scale production of biobutanol. However, the continuous ABE fermentation suffers from low product yield, titer, and productivity. Systems analysis of the continuous ABE fermentation will offer insights into its metabolic pathway as well as into optimal fermentation design and operation. For the ABE fermentation in continuous Clostridium acetobutylicum culture, this paper presents a kinetic model that includes the effects of key metabolic intermediates and enzymes as well as culture pH, product inhibition, and glucose inhibition. The kinetic model is used for elucidating the behavior of the ABE fermentation under the conditions that are most relevant to continuous cultures. To this end, dynamic sensitivity analysis is performed to systematically investigate the effects of culture conditions, reaction kinetics, and enzymes on the dynamics of the ABE production pathway. The analysis provides guidance for future metabolic engineering and fermentation optimization studies. PMID:27486663

  12. A kinetic study of textile dyeing wastewater degradation by Penicillium chrysogenum.

    PubMed

    Durruty, Ignacio; Fasce, Diana; González, Jorge Froilán; Wolski, Erika Alejandra

    2015-06-01

    The potential of Penicillium chrysogenum to decolorize azo dyes and a real industrial textile wastewater was studied. P. chrysogenum was able to decolorize and degrade three azo dyes (200 mg L(-1)), either independently or in a mixture of them, using glucose as a carbon source. A kinetic model for degradation was developed and it allowed predicting the degradation kinetics of the mixture of the three azo dyes. In addition, P. chrysogenum was able to decolorize real industrial wastewater. The kinetic model proposed was also able to predict the decolorization of the real wastewater. The calibration of the proposed model makes it a useful tool for future wastewater facilities' design and for practical applications. PMID:25555702

  13. Herpes Simplex Virus: Genome Size and Redundancy Studied by Renaturation Kinetics

    PubMed Central

    Frenkel, Niza; Roizman, Bernard

    1971-01-01

    Herpes simplex virus subtype 1 deoxyribonucleic acid (DNA) was sheared in a French press to uniform fragments, denatured by heating, then allowed to reassociate. The renaturation reaction followed second-order kinetics with a single rate constant indicating that at least 95% of the genome was unique and that repetitive sequences, if present, were not detectable by this technique. The kinetic complexity of the herpes simplex genome was determined by DNA renaturation kinetics to be (95 ± 1) × 106 daltons. Since this value is in excellent agreement with the molecular weight of viral DNA [(99 ± 5) × 106 daltons] obtained from velocity sedimentation studies, it is concluded that virions contain only one species of double-stranded DNA molecules 95 × 106 to 99 × 106 daltons in molecular weight. PMID:4331657

  14. A Frustrated Phosphane-Borane Lewis Pair and Hydrogen: A Kinetics Study.

    PubMed

    Özgün, Thomas; Bergander, Klaus; Liu, Lei; Daniliuc, Constantin G; Grimme, Stefan; Kehr, Gerald; Erker, Gerhard

    2016-08-16

    The energy profile of a frustrated Lewis pair (FLP) dihydrogen splitting system was determined by a combined experimental kinetic and DFT study. A trimethylene-bridged phosphane-borane FLP was converted into its endothermic H2 -cleavage product by sequential H(+) /H(-) addition. The system could be handled at low temperature, and the kinetics of the H2 elimination were determined to give a rate constant of kHH,exp (299 K)=(2.87±0.1)×10(-4)  s(-1) in solution. The primary kinetic isotope effects were determined; for example, (kHH /kDD )exp =3.19. The system was accurately analyzed by DFT calculations. PMID:27355568

  15. Kinetic and product composition study on the cellulose liquefaction in polyhydric alcohols.

    PubMed

    Shi, Yan; Li, Jingdan; Wang, Jing; Zhao, Tiantian; Yang, Hongmin; Jiang, Jianchun; Jiang, Xiaoxiang

    2016-08-01

    The liquefaction process of cellulose in polyhydric alcohols (PEG 400 and glycerol) was studied by TG-FTIR. Three stages were observed during the solvolysis process and the main liquefaction stage could be further divided into two zones. The differences of liquefaction behavior of cellulose in the two solvents were compared, and the functional groups of volatiles produced by solvolysis were also evaluated. A step-wise procedure based on iso-conversional and Master-plots methods was used for the kinetic and mechanism analysis of the main liquefaction stage. The calculation results based on the kinetic model were in agreement with the experimental data of the conversion rate. The kinetic parameters and mechanism functions between cellulose liquefaction in PEG400 and in glycerol were quite different, which verified that solvolysis behavior and reaction process were seriously influenced by solvent species. Finally, the detailed types of volatiles and product distribution were measured by Py-GC-MS. PMID:27155797

  16. Single-filament kinetic studies provide novel insights into regulation of actin-based motility

    PubMed Central

    Shekhar, Shashank; Carlier, Marie-France

    2016-01-01

    Polarized assembly of actin filaments forms the basis of actin-based motility and is regulated both spatially and temporally. Cells use a variety of mechanisms by which intrinsically slower processes are accelerated, and faster ones decelerated, to match rates observed in vivo. Here we discuss how kinetic studies of individual reactions and cycles that drive actin remodeling have provided a mechanistic and quantitative understanding of such processes. We specifically consider key barbed-end regulators such as capping protein and formins as illustrative examples. We compare and contrast different kinetic approaches, such as the traditional pyrene-polymerization bulk assays, as well as more recently developed single-filament and single-molecule imaging approaches. Recent development of novel biophysical methods for sensing and applying forces will in future allow us to address the very important relationship between mechanical stimulus and kinetics of actin-based motility. PMID:26715420

  17. Crystallization kinetics in a multiply saturated basalt magma - An experimental study of Luna 24 ferrobasalt

    NASA Technical Reports Server (NTRS)

    Grove, T. L.; Bence, A. E.

    1979-01-01

    The paper deals with the effects of kinetics on mineral/melt partitioning and on fractional crystallization for a Luna-24 ferrobasalt. The composition is nearly multiply saturated under lunar surface conditions, making it possible to study the response of several mineral phases to kinetic factors during cooling. The differential suppression of the temperature of appearance of olivine, clinopyroxene, and plagioclase causes changes in the liquid line of descent. The course of liquid line of descent is mapped as a function of the cooling rate, and the partitioning of elements between pyroxene/liquid and olivine/liquid is examined.

  18. Kinetics of Oxygen Reduction in Aprotic Li-O2 Cells: A Model-Based Study.

    PubMed

    Safari, M; Adams, B D; Nazar, L F

    2014-10-16

    A comprehensive and general kinetic model is developed for the oxygen reduction reaction in aprotic Li-O2 cells. The model is based on the competitive uptake of lithium superoxide by the surface and solution. A demonstrative kinetic study is provided to demystify the origin of curvature in Tafel plots as well as the current dependency and aberrant diversity of the nature and morphology of discharge products in these systems. Our results are general and extend to any system where solubilization of superoxide is favored, such as where phase-transfer catalysts play an important role. PMID:26278597

  19. A multiscale numerical study into the cascade of kinetic energy leading to severe local storms

    NASA Technical Reports Server (NTRS)

    Paine, D. A.; Kaplan, M. L.

    1977-01-01

    The cascade of kinetic energy from macro- through mesoscales is studied on the basis of a nested grid system used to solve a set of nonlinear differential equations. The kinetic energy cascade and the concentration of vorticity through the hydrodynamic spectrum provide a means for predicting the location and intensity of severe weather from large-scale data sets. A mechanism described by the surface pressure tendency equation proves to be important in explaining how initial middle-tropospheric mass-momentum imbalances alter the low-level pressure field.

  20. Acetone reactions over the surfaces of polycrystalline UO2: a kinetic and spectroscopic study.

    PubMed

    King, Richard; Idriss, Hicham

    2009-04-21

    The reaction of acetone is studied on the surfaces of polycrystalline UO2, prepared by hydrogen reduction of U3O8 at 770 K. The study is conducted by in situ Fourier transform infrared (FTIR) and temperature-programmed desorption (TPD). Acetone adsorption does not fit the simple Langmuir model, and adsorbate-adsorbate interactions are found to be significant. Acetone adsorbs molecularly on UO2 as evidenced by the nuCO of the eta1(O) mode at 1686 cm(-1). Part of acetone is reduced to the isopropoxide species ((CH3)2HC-O-U4+) upon heating (nu(CC), rho(CH3) at 1167 cm(-1) and nu(CO), rho(CH3) at 980 cm(-1)), and upon further heating, acetates (CH3COO(a), (a) for adsorbed) are observed. Detailed TPD studies indicated that the main reaction of acetone on UO2 is the deoxygenation to propene, driven by the oxophilic nature of UO2. Other reactions were also observed to a lesser extent, and these included reductive coupling to 2,3-dimethylbutene and condensation to mesityl oxide. An attempt to extract kinetic parameters from TPD data was conducted. Three models were studied: variation of heating rate, leading edge analysis (Habenschaden-Kuppers method), and complete analysis. The complete analysis provided the most plausible results, in particular, at low coverage. With this method, at nearly zero coverage the activation energy, Ed, for desorption was found to be close to 140 kJ/mol with a prefactor of 10(13) s(-1). Ed dropped sharply with increasing coverage, theta, to ca. 35 kJ/mol at theta=0.15 with a prefactor of 10(11) s(-1). The activation energy for the desorption of acetone on UO2(111) single crystals, at saturation coverage, was previously found to be equal to 65 kJ/mol using the leading edge analysis. PMID:19366223

  1. Studies on the kinetics of killing and the proposed mechanism of action of microemulsions against fungi.

    PubMed

    Al-Adham, Ibrahim S I; Ashour, Hana; Al-Kaissi, Elham; Khalil, Enam; Kierans, Martin; Collier, Phillip J

    2013-09-15

    Microemulsions are physically stable oil/water clear dispersions, spontaneously formed and thermodynamically stable. They are composed in most cases of water, oil, surfactant and cosurfactant. Microemulsions are stable, self-preserving antimicrobial agents in their own right. The observed levels of antimicrobial activity associated with microemulsions may be due to the direct effect of the microemulsions themselves on the bacterial cytoplasmic membrane. The aim of this work is to study the growth behaviour of different microbes in presence of certain prepared physically stable microemulsion formulae over extended periods of time. An experiment was designed to study the kinetics of killing of a microemulsion preparation (17.3% Tween-80, 8.5% n-pentanol, 5% isopropyl myristate and 69.2% sterile distilled water) against selected test microorganisms (Candida albicans, Aspergillus niger, Schizosaccharomyces pombe and Rhodotorula spp.). Secondly, an experiment was designed to study the effects of the microemulsion preparation on the cytoplasmic membrane structure and function of selected fungal species by observation of 260 nm component leakage. Finally, the effects of the microemulsion on the fungal membrane structure and function using S. pombe were studied using transmission electron microscopy. The results showed that the prepared microemulsions are stable, effective antimicrobial systems with effective killing rates against C. albicans, A. niger, S. pombe and Rhodotorula spp. The results indicate a proposed mechanism of action of significant anti-membrane activity, resulting in the gross disturbance and dysfunction of the cytoplasmic membrane structure which is followed by cell wall modifications, cytoplasmic coagulation, disruption of intracellular metabolism and cell death. PMID:23830945

  2. Kinetics of photo-activated charge carriers in Sn:CdS

    NASA Astrophysics Data System (ADS)

    Patidar, Manju Mishra; Panda, Richa; Gorli, V. R.; Gangrade, Mohan; Nath, R.; Ganesan, V.

    2016-05-01

    Kinetics of the photo-activated charge carriers has been investigated in Tin substituted Cadmium Sulphide, Cd1-xSnxS (x=0, 0.05, 0.10 and 0.15), thin films prepared by spray pyrolysis. X-Ray Diffraction shows an increase in strain that resulted in the decreased crystallite size upon Sn substitution. At the first sight, the photo current characteristics show a quenching effect on Sn substitution. However, survival of persistent photocurrents is seen even up to 15% of Sn substitution. Transient photo current decay could be explained with a 2τ relaxation model. CdS normally has an n-type character and the Sn doping expected to inject hole carriers. The two fold increase in τ1, increase in activation energy and the decrease in photocurrents upon Sn substitution point towards a band gap cleaning scenario that include compensation and associated carrier injection dynamics. In addition Atomic Force Microscopy shows a drastic change in microstructure that modulates the carrier dynamics as a whole.

  3. Inhibition of α-amylase activity by cellulose: Kinetic analysis and nutritional implications.

    PubMed

    Dhital, Sushil; Gidley, Michael J; Warren, Frederick J

    2015-06-01

    We report on inhibition of α-amylase activity by cellulose based on in vitro experiments. The presence of cellulose in the hydrolysing medium reduced the initial velocity of starch hydrolysis in a concentration dependent manner. α-Amylase adsorption to cellulose was reversible, attaining equilibrium within 30min of incubation, and showed a higher affinity at 37°C compared to 20 and 0°C. The adsorption was almost unchanged in the presence of maltose (2.5-20mM) but was hindered in the presence of excess protein, suggesting non-specific adsorption of α-amylase to cellulose. Kinetic analyses of α-amylase hydrolysis of maize starch in the presence of cellulose showed that the inhibition is of a mixed type. The dissociation constant (Kic) of the EI complex was found to be ca. 3mg/mL. The observed inhibition of α-amylase activity suggests that cellulose in the diet can potentially attenuate starch hydrolysis. PMID:25843863

  4. Kinetic Study on the Effect of Chromium Addition to Ni-Based Catalysts for the Steam-CO2 Reforming of Methane.

    PubMed

    Park, Yoon-Hwa; Li, Peng; Moon, Dong-Ju; Park, Nam-Cook; Kim, Young-Chul

    2016-02-01

    In the present work, the kinetic effects of Ni-based catalysts containing various amounts of Cr on the steam-CO2 reforming (SCR) of methane were studied. Kinetic expressions for the SCR of methane over the Ni-based catalysts have been proposed using the power-law rate expression, based on the kinetic data obtained. In addition, the Arrhenius equation was used for calculating the activation energy. Analysis of the data revealed four simple results. Firstly, the partial pressure of CH4 exerts a major influence on the CH4 conversion rates. Secondly, the CH4 conversion rate is inversely proportional to the partial pressure of CO2. Thirdly, the partial pressure of steam has a very slight effect on the reaction rates. Finally, all the catalysts studied have similar apparent activation energies. PMID:27433614

  5. Combustion Research Program: Flame studies, laser diagnostics, and chemical kinetics

    SciTech Connect

    Crosley, D.R.

    1991-01-22

    We have made a detailed study of the care that must be taken to correctly measure OH radical concentrations in flames. A large part of these studies has concerned collisional quenching of hydride radical species (OH, NH, and NH{sub 2}), in particular the dependence upon rotational level and collision velocity (temperature). The results on OH and NH have shown unique and interesting behavior from the viewpoint of fundamental molecular dynamics, pointing to quenching often governed by collisions on an anisotropic, attractive surface, whereas NH{sub 2} quenching appears to depend on state-mixing considerations, not dynamic control. This state-specific behavior of these small, theoretically tractable hydrides has direct ramifications for quantitative flame diagnostics. Our other effort in the diagnostic area has been repeated but unsuccessful searches for laser induced fluorescence in the vinyl radical.

  6. PIXE study of the kinetics of biomaterials ossification

    NASA Astrophysics Data System (ADS)

    Weber, G.; Robaye, G.; Braye, F.; Oudadesse, H.; Irigaray, J. L.

    1994-05-01

    Biomaterials are frequently implanted in bones. This implantation is followed by a phenomenon of ossification. The purpose of this work was to study the time evolution of the gradient of characteristic atomic element's concentrations in the bone, the implant and the bone-implant interface. We have studied two types of neutral biomaterials: pure synthetic hydroxyapatite and porite's asteroid coral. The animal implantations have been made on sheep of the same age and sex having received the same basic diet. The implantations have been made in the cortical femur. On both sides of the implant, at the same distance, two screws were placed to allow further determination of the position of the implant. The PIXE method is particularly suitable here because of the possibility to analyze directly the samples without any preparation and to choose easily the dimensions of beam used for the gradient study. The X-rays have been detected with an ultra LEGe instead of the usual Si(Li) device to avoid the Si escape peak associated with the K α X-ray of calcium, the major constituent of bone. This peak is particularly disturbing here because its energy corresponds to the K α line of phosphorus, an important constituent of bone. The results of these determinations are presented and discussed.

  7. Kinetic study of the formation of oxygen vacancy on lanthanum manganite electrodes

    SciTech Connect

    Jiang, Y.; Wang, S.; Zhang, Y.; Yan, J.; Li, W.

    1998-02-01

    Strontium doped lanthanum manganite (LSM) has been considered one of the most promising cathode materials for solid oxide fuel cells (SOFC). The electrochemical reduction of oxygen on lanthanum manganite (LSM) electrodes has been investigated by cyclic voltammetry, alternating current (ac) impedance, and, in particular, potential step. An emphasis was given to the study of the kinetics of the formation of oxygen vacancy, which is shown to be the main cause for the reversed hysteresis in cyclic voltammograms and for the increase in the electrochemical activity of oxygen reduction on the cathodically polarized LSM electrode observed in both ac impedance and in potential step experiments. The potential step experiments show that the oxygen vacancy concentration increases exponentially with time when the LSM is under a cathodic polarization. In the present study, the rate controlling step for the formation of oxygen vacancies is the oxygen vacancy generation step. The cathodic current rising from the reaction on oxygen vacancies can make a significant contribution to the total reduction current.

  8. Kinetic model of ethopropazine interaction with horse serum butyrylcholinesterase and its docking into the active site.

    PubMed

    Golicnik, Marko; Sinko, Goran; Simeon-Rudolf, Vera; Grubic, Zoran; Stojan, Jure

    2002-02-01

    The action of a potent tricyclic cholinesterase inhibitor ethopropazine on the hydrolysis of acetylthiocholine and butyrylthiocholine by purified horse serum butyrylcholinesterase (EC 3.1.1.8) was investigated at 25 and 37 degrees C. The enzyme activities were measured on a stopped-flow apparatus and the analysis of experimental data was done by applying a six-parameter model for substrate hydrolysis. The model, which was introduced to explain the kinetics of Drosophila melanogaster acetylcholinesterase [Stojan et al. (1998) FEBS Lett. 440, 85-88], is defined with two dissociation constants and four rate constants and can describe both cooperative phenomena, apparent activation at low substrate concentrations and substrate inhibition by excess of substrate. For the analysis of the data in the presence of ethopropazine at two temperatures, we have enlarged the reaction scheme to allow primarily its competition with the substrate at the peripheral site, but the competition at the acylation site was not excluded. The proposed reaction scheme revealed, upon analysis, competitive effects of ethopropazine at both sites; at 25 degrees C, three enzyme-inhibitor dissociation constants could be evaluated; at 37 degrees C, only two constants could be evaluated. Although the model considers both cooperative phenomena, it appears that decreased enzyme sensitivity at higher temperature, predominantly for the ligands at the peripheral binding site, makes the determination of some expected enzyme substrate and/or inhibitor complexes technically impossible. The same reason might also account for one of the paradoxes in cholinesterases: activities at 25 degrees C at low substrate concentrations are higher than at 37 degrees C. Positioning of ethopropazine in the active-site gorge by molecular dynamics simulations shows that A328, W82, D70, and Y332 amino acid residues stabilize binding of the inhibitor. PMID:11811945

  9. Sorption of basic dyes onto granulated pillared clays: thermodynamic and kinetic studies.

    PubMed

    Cheknane, B; Zermane, F; Baudu, M; Bouras, O; Basly, J P

    2012-09-01

    Effect of the granulation process onto the thermodynamic and kinetic sorption parameters of two basic dyes (Basic Yellow 28-BY 28 and Basic Green 4-BG 4) was evaluated in the present work. The charge surface properties of the surfactant-modified aluminium-pillared clay (CTAB-Al-Mont-PILC) particles were not modified, and the isoelectric point remains constant after high shear wet granulation. The Gibbs free energy of both BY 28 and BG 4 sorption was negative and decreased with the granulation; the endothermic nature of the sorption process was confirmed by the positive values of ΔH°. Adsorption kinetics of the two dyes, studied at pH 6 and 150 mg L(-1), follow the pseudo-first order kinetic model with observed rate constants of 2.5-4.2×10(-2) min(-1). The intraparticle diffusion model, proposed by Weber and Morris, was applied, and the intraparticle plots revealed three distinct sections representing external mass transfer, intraparticle diffusion and adsorption/desorption equilibrium. Diffusion coefficients, calculated from the Boyd kinetic equation, increased with the granulation and the particle size. Pseudo-first order kinetic constants, intraparticle diffusion rate constants and diffusion coefficients were determined for two other initial concentrations (50 and 100 mg L(-1)) and include in a statistical study to evaluate the impact of granulation and initial concentration on the kinetic parameters. Kruskal-Wallis tests, Spearman's rank order correlation and factor analysis revealed a correlation between (i) the diffusion coefficients and granulation, and between (ii) the intraparticle diffusion rate constants and initial concentration. PMID:22721789

  10. Kinetics and {sup 13}C NMR study of oxygen incorporation into PVC- and pitch-derived materials

    SciTech Connect

    Gisele F. Altoe; Jair C.C. Freitas; Alfredo G. Cunha; Francisco G. Emmerich; Mark E. Smith

    2009-03-15

    The kinetics of oxygen incorporation into a PVC-derived material with pitch-like characteristics was studied by isothermal thermogravimetric analysis at temperatures ranging from 200 to 270{sup o}C. Activation energy, E{sub a}, pre-exponential factor, A, and rate constants, kT, were obtained from the weight-gain curves recorded during reactions of the material with molecular oxygen, which were analyzed following a kinetic first-order model. The numerical values obtained were E{sub a} = 100.5 kJ/mol and A = 1.6 x 1010 h{sup -1}. The extent of the oxidation at a fixed temperature was monitored by elemental analysis, and the chemical changes in the materials were followed by solid-state {sup 13}C NMR. The study was next extended to the chars obtained from three coal tar pitches with different softening points (55, 85, and 110{sup o}C). Comparisons were then established between the determined kinetic parameters and the chemical/structural aspects and compositions of each analyzed material. 23 refs., 7 figs., 3 tabs,

  11. Equilibrium and kinetic adsorption study of Basic Yellow 28 and Basic Red 46 by a boron industry waste.

    PubMed

    Olgun, Asim; Atar, Necip

    2009-01-15

    In this study, the adsorption characteristics of Basic Yellow 28 (BY 28) and Basic Red 46 (BR 46) onto boron waste (BW), a waste produced from boron processing plant were investigated. The equilibrium adsorption isotherms and kinetics were investigated. The adsorption equilibrium data were analyzed by using various adsorption isotherm models and the results have shown that adsorption behavior of two dyes could be described reasonably well by a generalized isotherm. Kinetic studies indicated that the kinetics of the adsorption of BY 28 and BR 46 onto BW follows a pseudo-second-order model. The result showed that the BW exhibited high-adsorption capacity for basic dyes and the capacity slightly decreased with increasing temperature. The maximum adsorption capacities of BY 28 and BR 46 are reported at 75.00 and 74.73mgg(-1), respectively. The dye adsorption depended on the initial pH of the solution with maximum uptake occurring at about pH 9 and electrokinetic behavior of BW. Activation energy of 15.23kJ/mol for BY 28 and 18.15kJ/mol for BR 46 were determined confirming the nature of the physisorption onto BW. These results indicate that BW could be employed as low-cost material for the removal of the textile dyes from effluents. PMID:18434000

  12. Influence of Posture on Pulmonary O2 Uptake Kinetics, Muscle Deoxygenation and Myolectrical Activity During Heavy-Intensity Exercise

    PubMed Central

    Denis, Romain; Perrey, Stéphane

    2006-01-01

    The aim of the present study was to test the hypothesis that compared to upright posture, slower oxygen uptake (VO2) kinetics resulting from exercise at the same relative metabolic load in the supine posture will be associated with increased muscle de-oxygenation and greater myoelectrical activity. Nine subjects completed one 12-min heavy-intensity constant-load exercises in each of the supine and upright postures on an electronically braked cycle ergometer at a same gain in metabolism per unit increase in work intensity (10.8 ± 1.3 vs. 11.8 ± 1.1 mlO2·min-1·W-1 in upright and supine, respectively) on separate days. Breath-by-breath VO2 kinetics were analyzed with a double exponential model to characterize the primary and slow component phases. Myoelectrical activity (RMS) of the vastus lateralis (VL), rectus femoris, and biceps femoris muscles was recorded at different epochs of the exercise. Oxygenation of the VL muscle was recorded continuously by near-infrared spectroscopy. In supine compared with upright cycling, the primary time constant of VO2 kinetics was significantly increased (32.7 ± 10.7 s vs. 23.5 ± 6.7 s, respectively) while the absolute magnitude of VO2 slow component was decreased (p < 0.05) but not the relative amplitude. VL de-oxygenation was higher (p < 0.05) in supine cycling throughout the exercising period whereas RMS values for all muscles did not change appreciably over time. Our findings suggest that lowered oxygen supply induced by supine heavy exercise, alters oxidative metabolism dynamics and increases muscle de-oxygenation. However, cycling supine d