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1
Wigfield, Donald C., and Douglas M. Goltz. "Kinetics of reconstitution of apotyrosinase by copper." Biochemistry and Cell Biology 68, no. 2 (February 1, 1990): 476–79. http://dx.doi.org/10.1139/o90-067.
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The kinetics of the reconstitution reaction of apotyrosinase with copper (II) ions are reported. The reaction is pseudo first order with respect to apoenzyme and the values of these pseudo first order rate constants are reported as a function of copper (II) concentration. Two copper ions bind to apoenzyme, and if the second one is rate limiting, the kinetically relevant copper concentration is the copper originally added minus the amount used in binding the first copper ion to enzyme. This modified copper concentration is linearly related to the magnitude of the pseudo first order rate constant, up to a copper concentration of 1.25 × 10−4 M (10-fold excess), giving a second order rate constant of 7.67 × 102 ± 0.93 × 102 M−1∙s−1.Key words: apotyrosinase, copper, tyrosinase.
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Ho, Y. S., and G. McKay. "Kinetic Model for Lead(II) Sorption on to Peat." Adsorption Science & Technology 16, no. 4 (April 1998): 243–55. http://dx.doi.org/10.1177/026361749801600401.
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The kinetics of lead sorption on to peat have been investigated. The batch sorption model, based on the assumption of a pseudo-second order mechanism, has been developed to predict the rate constant of sorption, the equilibrium capacity and initial sorption rate with the effect of initial lead(II) concentration, peat particle size and temperature. An equilibrium capacity of sorption has been evaluated with the pseudo-second order rate equation. In addition, an activation energy of sorption has also been determined based on the pseudo-second order rate constants.
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Wigfield, Donald C., and Season Tse. "Oxidation of the mercurous ion by peroxidase." Canadian Journal of Chemistry 64, no. 5 (May 1, 1986): 969–72. http://dx.doi.org/10.1139/v86-162.
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The kinetics of oxidation of the mercurous ion by peroxidase have been measured by following the disappearance of mercurous ion using cold-vapour atomic absorption spectroscopy. Pseudo-first-order kinetics are observed with respect to mercurous ion, and the pseudo-first-order rate constants are linearly related to peroxidase concentration, showing first-order dependence on peroxidase. This behaviour is identical to oxidation of elemental mercury, and the second-order rate constant, 1.44 × 104 M−1 s−1 at 23 °C, is also, within experimental error, the same as that for elemental mercury oxidation. The data are interpreted in terms of peroxidase-induced disproportionation of the mercurous dimer, followed by two-electron oxidation of zero-valent mercury.
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Pe, Justin Alfred, Sung-Phil Mun, and Min Lee. "Fe–Doped TiO2–Carbonized Medium–Density Fiberboard for Photodegradation of Methylene Blue under Visible Light." Materials 14, no. 17 (August 27, 2021): 4888. http://dx.doi.org/10.3390/ma14174888.
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Fe–doped titanium dioxide–carbonized medium–density fiberboard (Fe/TiO2–cMDF) was evaluated for the photodegradation of methylene blue (MB) under a Blue (450 nm) light emitting diode (LED) module (6 W) and commercial LED (450 nm + 570 nm) bulbs (8 W, 12 W). Adsorption under daylight/dark conditions (three cycles each) and photodegradation (five cycles) were separately conducted. Photodegradation under Blue LED followed pseudo-second-order kinetics while photodegradation under commercial LED bulbs followed pseudo-first-order kinetics. Photodegradation rate constants were corrected by subtracting the adsorption rate constant except on the Blue LED experiment due to their difference in kinetics. For 8 W LED, the rate constants remained consistent at ~11.0 × 10−3/h. For 12 W LED, the rate constant for the first cycle was found to have the fastest photodegradation performance at 41.4 × 10−3/h. After the first cycle, the rate constants for the second to fifth cycle remained consistent at ~28.5 × 10−3/h. The energy supplied by Blue LED or commercial LEDs was sufficient for the bandgap energy requirement of Fe/TiO2–cMDF at 2.60 eV. Consequently, Fe/TiO2–cMDF was considered as a potential wood-based composite for the continuous treatment of dye wastewater under visible light.
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Djordjevic, Dragan, Dragan Stojiljkovic, and Miodrag Smelcerovic. "Adsorption Kinetics of Reactive Dyes on Ash from Town Heating Plant." Archives of Environmental Protection 40, no. 3 (December 11, 2014): 123–35. http://dx.doi.org/10.2478/aep-2014-0024.
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Abstract In order to investigate the mechanism of adsorption of reactive dyes from the textile industry on ash from heating plant produced by brown coal combustion, some characteristic sorption constants are determined using Langergren adsorption equations for pseudo-fi rst and pseudo-second order. Combined kinetic models of pseudo-first order and pseudo-second order can provide a simple but satisfactory explanation of the adsorption process for a reactive dye. According to the characteristic diagrams and results of adsorption kinetic parameters of reactive dyes on ashes, for the applied amounts of the adsorbents and different initial dye concentrations, it can be concluded that the rate of sorption is fully functionally described by second order adsorption model. According to the results, the rate constant of pseudo-second order decreases with increasing initial dye concentration and increases with increasing amount of adsorbent – ash.
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Aviram, I., and M. Sharabani. "Kinetic studies of the reduction of neutrophil cytochrome b-558 by dithionite." Biochemical Journal 237, no. 2 (July 15, 1986): 567–72. http://dx.doi.org/10.1042/bj2370567.
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The reduction with dithionite of neutrophil cytochrome b-558, implicated in superoxide generation by activated neutrophils, was investigated by a stopped-flow technique in non-ionic-detergent extracts of the membranes and in crude membrane particles. The dependence of the pseudo-first-order rate constants on the concentration of dithionite was consistent with a mechanism of reduction that involves the dithionite anion monomer SO2.- as the reactive species. The estimated second-order rate constant was 7.8 × 10(6) M-1 × S-1 for Lubrol PX-solubilized cytochrome b-558 and 5.1 × 10(6) M-1 × S-1 for the membrane-bound protein. The similarity of the kinetic constants suggests that solubilization did not introduce gross changes in the reactive site. Imidazole and p-chloromercuribenzoate, known as inhibitors of NADPH oxidase, did not affect significantly cytochrome b-558 reduction rates. The reaction rate of cytochrome b-558 with dithionite exhibited a near-zero activation energy. The first-order rate constant for reduction decreased with increasing ionic strength, indicating a positive effective charge on the reacting protein.
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Filatova, Elena G., and Yury N. Pozhidaev. "Kinetics and Adsorption Ions of Heavy Metal by Modified Alumino-Silicates." Solid State Phenomena 316 (April 2021): 170–74. http://dx.doi.org/10.4028/www.scientific.net/ssp.316.170.
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Adsorption isotherms of Ni (II) and Cu (II) ions by alumino-silicates, modified with N, N'-bis (3-triethoxysilylpropyl) thiocarbamide (BTM-3), and HCl, were obtained. The adsorption kinetics of heavy metal ions is studied, using the kinetic pseudo-first and pseudo-second order models. It is shown that, when alumino-silicates are modified, the rate and energy of adsorption increase. It is established that the kinetics of the adsorption of the studied ions is best described by a pseudo-second order model. The maximum value of the adsorption rate constant of 33.7∙10-5 g/ (mmol min) corresponds to nickel (II) ions for alumino-silicates, modified with HCl. The maximum value of the adsorption rate constant value of 2.91∙10-5 g/ (mmol min) for alumino-silicates, modified with BTM-3, corresponds to Cu (II) ions.
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Galezowski, Wlodzimierz, and Arnold Jarczewski. "Study of the dissociation of the products of some proton transfer reactions in acetonitrile solvent." Canadian Journal of Chemistry 70, no. 3 (March 1, 1992): 935–42. http://dx.doi.org/10.1139/v92-126.
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The conductometric study of the products of the proton transfer reactions of C-acids (nitriles, nitroalkanes, and 2,4,6-trinitrotoluene) with the strong amine bases (1,1,3,3-tetramethylguanidine (TMG), 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), 1,8-bis(dimethylamino)naphthalene (DMAN), and piperidine) in acetonitrile shows their large degree of dissociation into free ions. The dissociation constant values have been estimated at 25 °C to be larger than 1 × 10−4 M. This weakens the formalism commonly accepted in spectrophotometric kinetic studies of these systems of reactions, based on the assumption that the product is an ion pair. Spectrophotometric equilibrium and kinetic measurements provided evidence that reverse reaction is a second-order process (pseudo-first order because cation concentration is controlled by side reactions). The influence of the common cation (TMGH+) on the equilibria of the proton abstraction from 2-methyl-1-(4-nitrophenyl)-1-nitropropane and 4-nitrophenylcyanomethane with TMG base in acetonitrile at 25 °C was examined and was found to be compatible with the assumption of large dissociation of the reaction product for free ions. "Equilibrium constants" estimated by the Benesi and Hildebrand method (which assumes an ion-pair product) decreased with increasing concentration of added TMGH+ cation, but these "equilibrium constants" multiplied by [TMGH+] are constant. The observed pseudo-first-order rate constants of the proton transfer reaction, measured at large excess of the base over C-acid, grow with the cation concentration due to the increase of the backward reaction rate. The concentration of added common cation shows a negligible influence on the observed rate constants of deuteron transfer reaction. Thus, as a result of side reactions, in which extra amounts of cation are formed, some second-order rate constants [Formula: see text] and also kinetic isotope effects (KIEs) [Formula: see text] that have been measured in acetonitrile can be substantially overestimated. Keywords: ion-pair dissociation, proton transfer reactions, kinetic isotope effects.
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Holle, Rizky B., Audy D. Wuntu, and Meiske S. Sangi. "Kinetika Adsorpsi Gas Benzena Pada Karbon Aktif Tempurung Kelapa." Jurnal MIPA 2, no. 2 (July 8, 2013): 100. http://dx.doi.org/10.35799/jm.2.2.2013.2997.
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Telah diteliti kinetika adsorpsi gas benzena pada karbon aktif tempurung kelapa yang diaktivasi dengan NaCl dengan tujuan menentukan model kinetika yang dapat diaplikasikan untuk adsorpsi gas benzena pada karbon aktif tempurung kelapa. Data adsorpsi dianalisis dengan menggunakan empat model persamaan laju adsorpsi yaitu (1) persamaan laju order pertama pseudo Lagergren, (2) persamaan laju order kedua pseudo Ho, (3) persamaan Elovich, dan (4) persamaan Ritchie. Hasil kajian menunjukkan bahwa model kinetika dengan persamaan laju order ke-2 pseudo Ho adalah yang paling sesuai diaplikasikan untuk adsorpsi gas benzena pada karbon aktif tempurung kelapa. Dari model kinetika order ke-2 pseudo Ho diperoleh konstanta adsorpsi benzena sebesar 1,63x10-4 g mg-1 min-1. Nilai energi adsorpsi menunjukkan bahwa benzena teradsorpsi secara fisik pada adsorben.Kinetics of gaseous benzene adsorption on coconut shell NaCl-activated carbon had been studied. The research was aimed to determine the appropriate kinetic model applied to gaseous benzene adsorption on the adsorbent. Adsorption data was analyzed using four kinetic models of adsorption rate equation, which were (1) Lagergren’s pseudo first order rate equation, (2) Ho’s pseudo second order rate equation, (3) Elovich‘s equation, and (4) Ritchie’s equation. The results showed that the Ho’s pseudo second order rate equation was best applied to gaseous benzene adsorption on coconut shell activated carbon. The second order rate constant for benzene adsorption was 1.63x10-4 g mg-1 min-1. The value of adsorption energy showed that benzene was physically adsorbed on the adsorbent.
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João, Jair Juarez, Walter Satiro Júnior, and José Luiz Vieira. "Use of zeolite synthesized from coal ashl from Santa Catarina for removal of iron, manganese and methylene blue dye in water." Ambiente e Agua - An Interdisciplinary Journal of Applied Science 13, no. 4 (July 5, 2018): 1. http://dx.doi.org/10.4136/ambi-agua.2224.
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The fly ash of coal, generated in a thermoelectric plant, was used to synthesize zeolite by hydrothermal treatment with a sodium hydroxide solution. The zeolite synthesized was used as an adsorbent of metals (Fe and Mn) and of the methylene blue dye in water. The characterization of the zeolite showed that silicon oxide is the main compound in its composition, followed by aluminum, iron, sodium and calcium, which together correspond to more than 86% of its composition. These were used to investigate the kinetic parameters of adsorption and the isotherm of the metals and the methylene blue dye in aqueous solutions. Three kinetic models, pseudo-first order, pseudo-second order and intraparticle diffusion were used to predict adsorption rate constants. The adsorption kinetics of the dye and metals followed the pseudo-second order kinetics and reached equilibrium in 15 minutes with a 99% removal rate for metals, independently of the pH. The values of the diffusion constants (K2) for iron in pH 5, 7 and 8 were 1.3158; 1.3881 e 0.6053 mg.g-1.min-1 and for manganese 1.2511; 1.5239 and 1.4336 mg.g-1.min-1, respectively. For methylene blue, the removal rate was 90% and the constant (K2) value was 0.5437 mg.g-1.min-1. The studies showed the existence of different stages in the adsorption of the metals and the methylene blue dye in zeolite.
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Wuntu, Audy D., and Vanda S. Kamu. "KINETICS OF GASEOUS TOLUENE ADSORPTION ON CANDLENUT SHELL ACTIVATED CARBON." JURNAL ILMIAH SAINS 13, no. 1 (June 2, 2013): 33. http://dx.doi.org/10.35799/jis.13.1.2013.1979.
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KINETICS OF GASEOUS TOLUENE ADSORPTION ON CANDLENUT SHELL ACTIVATED CARBON ABSTRACT Adsorption kinetics of gaseous toluene on activated carbon prepared from candlenut shell had been studied. The research was performed by examining adsorption data, which was obtained in previous research, over several rate equations, which were: (1) Lagergren’s pseudo first order rate equation, (2) Ho’s pseudo second order rate equation, (3) Elovich’s equation, and (4) persamaan Ritchie’s equation. The result showed that the data of toluene adsorption on candlenut shell activated carbon fits the Ho’s pseudo second order rate equation and, hence, the model is the most applicable model for the adsorption. Calculation from linear regression of Ho’s pseudo second order rate equation gave the equilibrium adsorption capacity value of 56,069 mg g-1, second order rate constant of 3,54x10–4 g mg-1 min-1, and initial adsorption rate of 1,112 mg g-1 min-1. Keywords: adsorption, candlenut, activated carbon, toluene KINETIKA ADSORPSI GAS TOLUENA PADA KARON AKTIF TEMPURUNG KEMIRI ABSTRAK Studi mengenai aspek kinetika adsorpsi toluena pada arang aktif yang terbuat dari tempurung kemiri telah dilakukan. Penelitian dilakukan dengan menguji data adsorpsi yang telah diperoleh pada penelitian terdahulu menggunakan empat persamaan laju adsorpsi, yaitu (1) persamaan laju pseudo order pertama Lagergren, (2) persamaan laju pseudo order kedua Ho, (3) persamaan Elovich, dan (4) persamaan Ritchie. Hasil kajian menunjukkan bahwa model kinetika dengan persamaan laju pseudo order kedua Ho adalah yang paling sesuai diaplikasikan untuk adsorpsi gas toluena pada arang aktif tempurung kemiri. Dari persamaan linear untuk model kinetika pseudo order kedua Ho diperoleh nilai kapasitas adsorpsi pada kesetimbangan sebesar 56,069 mg g-1, konstanta adsorpsi sebesar 3,54x10–4 g mg-1 menit-1, dan laju adsorpsi awal sebesar 1,112 mg g-1 menit-1. Kata kunci: adsorpsi, kemiri, karbon aktif, toluena
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Hargono, Hargono, Angga Mei Sarah, Feninda Nevrita, and Bakti Jos. "Kinetics and equilibriums adsorption of Cu (II) ion by chitosan and cross-linked chitosan-bentonite." Reaktor 19, no. 3 (October 25, 2019): 117–24. http://dx.doi.org/10.14710/reaktor.19.3.117-124.
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The sorption of Cu (II) particle from aqueous solution onto chitosan and cross-connected chitosan-bentonite (CTS-BTN) as adsorbent were conducted in batch conditions. The impact of different test parameters: starting pH, sorption time was assessed. Equilibrium studies have been completed to decide the limit of chitosan and CTS-BTN for Cu (II) particle. The Langmuir and Freundlich isotherm models were used in the examination of the trial information as linearized conditions. It was discovered that the isotherm information were all around portrayed by the Langmuir isotherm. Chitosan and CTS-BTN showed an adsorption capacity of 125 mg/g and 142.86 mg/g, respectively. The constant of adsorption rate was investigation utilizing a pseudo first order and a pseudo second order model. The pseudo second order model brought about the best fit with test information (R2= 0,991 for CTS and R2= 0,995 for CTS-BTN), additionally giving a constant rate k2, ads= 8.85 x 10-5 g/mg min for CTS and 3.72 x 10-4 g/mg min for CTS-BTN. Recommending that this model could be used in design and applications.Keywords: adsorption; Cu(II) ion; chitosan; cross-linked; isotherm; kinetics
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Nekipelova, T. D. "Phototransformations of non-toxic antioxidants, the derivatives of 1,2-dihydroquinolines, in homogeneous and micellar solutions." International Journal of Photoenergy 1, no. 1 (1999): 31–34. http://dx.doi.org/10.1155/s1110662x99000069.
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Reactions of transient species photogenerated from 6-R-2,2,4-trimethyl-1,2-dihydroquinolines (TMDQ) are very sensitive to medium variation. In anhydrous organic solvents, aminyl radicals were generated. They decay in the reaction of dimerization with the second-order rate constant decreasing in a row heptane>benzene>2-propanol. When passing from organic solvents to water, methanol, and water-alcohol solutions, the kinetics and the direction of the reaction crucially change. As a result of the photolysis, the product of the addition of a solvent to the double bond of heterocycle, 4-hydroxy- or 4-methoxy-6-R-2,2,4- tetramethyl-1,2,3,4-tetrahydroquinoline is formed in water and methanol, respectively. The transformation is a complex reaction, and the formation of excited transient species is followed by a sequence of first-order and pseudo-first-order reactions. Unlike the photolysis in anhydrous organic solvents, the reaction in water and methanol does not involve aminyl radicals. In aqueous solutions, the first-order rate constants for the decay of transient species are higher in acidic and neutral solutions. At the pH close to pKa of the transient species, it drops, indicating that the neutral form is less reactive. The same product is formed over the whole range of pH. For the anionic surfactant (SDS) in acidic and alkaline solutions, the apparent rate constant in the micellar solutions is lower than that in the aqueous (negative micellar catalysis). At the medium pH, a positive micellar catalysis is observed, and the rate constant of the decay depends linearly on the concentration of TMDQ in the micelles, indicative of the direct reaction between TMDQ and the cationic transient species.
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Bunton, Clifford A., and Angela Cuenca. "Micellar effects upon reactions of the 2,2′,4,4′,4″-pentamethoxytrityl cation with nucleophiles." Canadian Journal of Chemistry 64, no. 6 (June 1, 1986): 1179–83. http://dx.doi.org/10.1139/v86-195.
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Cationic micelles of cetyltrimethylammonium chloride and bromide (CTACl and CTABr) speed attack of water upon the 2,2′,4,4′,4″-pentamethoxytrityl cation by a factor of ca. 5. The first-order rate constant in water is 5.51 s−1 at 25.0 °C. Anionic micelles of sodium dodecyl sulfate (SDS) have little effect on this reaction, but they strongly inhibit attack of OH−. In water, second-order rate constants for attack of OH−, CN−, and N3− are, respectively, 235, 177, and 2.8 × 105 M−1 s−1. Rate constants of reaction in CTACl go through maxima with increasing [surfactant] and analysis of the data shows that second-order rate constants at the micellar surface are similar to those in water.
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Pełech, Robert. "Mass transfer in the bath reactor of the adsorption process of 1,2-dichloropropane from aqueous solution onto the activated carbon." Polish Journal of Chemical Technology 9, no. 2 (January 1, 2007): 30–33. http://dx.doi.org/10.2478/v10026-007-0020-0.
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Mass transfer in the bath reactor of the adsorption process of 1,2-dichloropropane from aqueous solution onto the activated carbon A pseudo-second order rate equation describing the kinetics of the adsorption of 1,2-dichloropropane from aqueous solution onto the activated carbon at different initial concentrations, adsorbent dose, temperature, particle diameter and the rate of stirring have been developed. The rate constant was calculated. The rate constant correlation in a good mixing conditions was described as a function of the temperature.
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Bunting, John W., and P. Philippe Aubin. "Thermodynamic and kinetic acidities of N-(substituted benzyl) 4-phenylacetylpyridinium cations in aqueous solution." Canadian Journal of Chemistry 69, no. 6 (June 1, 1991): 945–48. http://dx.doi.org/10.1139/v91-140.
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The pKa values for the deprotonation of a series of eight 1-(X-benzyl)-4-phenylacetylpyridinium cations (6) have been measured in aqueous solutions of ionic strength 0.1 at 25 °C: pKa = −0.18σ + 8.91. The pseudo-first-order rate constants for deprotonation of these carbon acids have been measured over the range pH = 11–13, and have been found to display kinetic saturation effects that are consistent with the addition of hydroxide ion to the carbonyl group (pKz) as the product of kinetic control upon basification of neutral aqueous solutions of these pyridinium cations, with the subsequent transformation of this anionic hydrate to the thermodynamically more stable enolate conjugate base. Analysis of the pH–rate profiles gives substituent effects upon pKz (ρ = −0.19) and upon the second-order rate constant (kOH (ρ = 0.09)) for deprotonation of 6 by hydroxide ion. Key words: carbon acids, deprotonation, pKa, kinetics, substituent effects.
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Mozaffari, Nastaran, Alireza Haji Seyed Mirzahosseini, Amir Hossein Sari, and Leila Fekri Aval. "Investigation of carbon monoxide gas adsorption on the Al2O3/Pd(NO3)2/zeolite composite film." Journal of Theoretical and Applied Physics 14, no. 1 (December 17, 2019): 65–74. http://dx.doi.org/10.1007/s40094-019-00360-6.
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AbstractIn this study, Al2O3/Pd(NO3)2/zeolite composite films have been fabricated by roll coating method and characterized by X-ray diffraction, energy-dispersive X-ray spectroscopy and field emission scanning electron microscopy. The gas adsorption was tested in an experimental setup by a continuous gas analyzer KIMO KIGAZ 210 at constant temperature and pressure (32 °C and 1.5 bar) and as a function of reaction time (s). The inlet CO gas concentration was 150 mg L−1, and the saturation level of CO gas concentration was 5 mg L−1. The maximum adsorption capacity (qmax) and maximum adsorption efficiency (%) were calculated as 111.16 mg g−1 and 97%, respectively. Pseudo-first-order, pseudo-second-order, and intra-particle diffusion models were investigated to kinetic study of CO adsorption on Al2O3/Pd(NO3)2/zeolite adsorbents. Results indicated that CO adsorption follows the pseudo-second-order model well according to regression coefficient value (R2 = 0.98), and the value of pseudo-second-order rate constant of adsorption was obtained as 2 × 10−5 g mg−1 s−1. According to the intra-particle diffusion model, adsorption is affected by only one process. So, adsorption of CO by Al2O3/Pd(NO3)2/zeolite adsorbent indicated an effective adsorption by obtained results.
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Marasinghe, P. A. B., and L. M. Wirth. "A graphical solution of the second-reaction rate constant of a two-step consecutive first-order reaction." Journal of Chemical Education 69, no. 4 (April 1992): 285. http://dx.doi.org/10.1021/ed069p285.
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Ho, Y. S., and G. McKay. "Application of Kinetic Models to the Sorption of Copper(II) on to Peat." Adsorption Science & Technology 20, no. 8 (October 2002): 797–815. http://dx.doi.org/10.1260/026361702321104282.
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A comparison of the kinetics of the sorption of copper(II) on to peat from aqueous solution at various initial copper(II) concentrations and peat doses was made. The Elovich model and the pseudo-second order model both provided a high degree of correlation with the experimental data for most of the sorption process. There was a small discrepancy at the initial stages of sorption which suggested that film diffusion or wetting of the peat may be involved in the early part of the sorption process. Models evaluated included the fractional power equation, the Elovich equation, the pseudo-first order equation and the pseudo-second order equation. The kinetics of sorption were followed based on the sorption capacity of copper(II) on peat at various time intervals. Results show that chemical sorption processes may be rate-limiting in the sorption of copper(II) on to peat during agitated batch contact time experiments. The rate constant, the equilibrium sorption capacity and the initial sorption rate were calculated. From these parameters, an empirical model for predicting the concentrations of metal ions sorbed was derived.
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Dela Cruz, Michael Leo, Khryslyn Araño, Eden May Dela Pena, and Leslie Joy L. Diaz. "Nanoclay-Supported Zero-Valent Iron as an Efficient Adsorbent Material for Arsenic." Advanced Materials Research 686 (April 2013): 296–304. http://dx.doi.org/10.4028/www.scientific.net/amr.686.296.
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The release of arsenic to aqueous environment imposes threats to human health. Montmorillonite supported zero-valent iron (ZVI-MMT) is a material with capability of immobilizing arsenic from aqueous environment. The arsenic adsorption efficiency of ZVI-MMT was obtained. In addition, adsorption kinetics of arsenic contaminated water on the material was determined. Arsenic and iron content was quantified by an inductively coupled plasma mass spectrometer (ICP-MS), interplanar distance of the adsorbent was measured by x-ray diffractometer (XRD), and the morphology of the adsorbent was obtained from a transmission electron microscope (TEM). Isotherm data were analyzed using the Langmuir and Freundlich isotherms. The data fitted well to Langmuir isotherm with derived adsorption capacity of 20.1 mg/g. Kinetics data were analyzed using intra-particle model, Elovich equation, pseudo first-, and pseudo second-order models. Elovich equation and pseudo second-order equation fitted the experimental data with pseudo second-order rate constant of 61.2 x 10-4 g/mg-min.
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Attwood, P. V., and J. C. Wallace. "The carboxybiotin complex of chicken liver pyruvate carboxylase. A kinetic analysis of the effects of acetyl-CoA, Mg2+ ions and temperature on its stability and on its reaction with 2-oxobutyrate." Biochemical Journal 235, no. 2 (April 15, 1986): 359–64. http://dx.doi.org/10.1042/bj2350359.
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The enzyme-[14C]carboxybiotin complex of chicken liver pyruvate carboxylase has been isolated and shown to be relatively stable, with a half-life at 0 degree C of 342 min. The kinetic properties of the decay of this complex, in both the presence and the absence of the substrate analogue, 2-oxobutyrate, have been examined. The data for the reaction with 2-oxobutyrate at 0 degree C fitted a biphasic exponential decay curve, enabling the calculation of rate constants for both the fast and slow phases of the reaction at this temperature. The effect of temperature on the observed pseudo-first-order rate constant for the slow phase of the reaction with 2-oxobutyrate, and that for the decay of the enzyme-[14C]carboxybiotin complex alone, have been examined. Arrhenius plots of these data revealed that the processes being studied in each type of experiment were single reactions represented by one rate constant in each case. For the decay of the enzyme-[14C]carboxybiotin complex in the absence of 2-oxobutyrate, the rate-determining process may be the movement of carboxybiotin from the site of the first partial reaction to the site of the second. The calculated thermodynamic activation parameters indicate that this reaction is accompanied by a large change in protein conformation. With 2-oxobutyrate present, the observed process in the slow phase of the reaction was probably the dissociation of the carboxybiotin from the first subsite. Here, the activation parameters suggest that a much smaller change in protein conformation accompanies this reaction. Both sets of experiments were also performed in the presence of acetyl-CoA, but this activator had little effect on the measured thermodynamic activation parameters. However, in both cases the observed pseudo-first-order rate constants in the presence of acetyl-CoA were about 75% of those in its absence. The effects of Mg2+ on the reaction kinetics of the enzyme-[14C]carboxybiotin complex with 2-oxobutyrate were similar to those observed with the sheep enzyme by Goodall, Baldwin, Wallace & Keech [(1981) Biochem. J. 199, 603-609].
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Singh, Tej Pratap, and Majumder Cb. "REMOVAL OF FLUORIDE USING NEEM LEAVES BATCH REACTOR: KINETICS AND EQUILIBRIUM STUDIES." Asian Journal of Pharmaceutical and Clinical Research 11, no. 3 (March 1, 2018): 237. http://dx.doi.org/10.22159/ajpcr.2018.v11i3.14080.
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Objective: The aim of this paper is to study the fluoride removal efficiency of the neem leaves low-cost biosorbent for defluoridation of sewage wastewater.Methods: For finding the best operating condition for maximum removal of fluoride, batchwise experiments were performed at different contact times and keeping other parameters to be constant such as pH, initial fluoride concentration, and adsorbent dose. Various kinetic models such as intraparticle diffusion model, Bangham’s model, and Elovich model had been investigated for determining the suitable adsorption mechanism. The rate of adsorption of fluoride on neem leaves has been determined by pseudo-first-order and pseudo-second-order rate models.Results: The adsorption kinetics rate and mechanism was best described by the pseudo-second-order model and Bangham’s model, respectively. The optimum pH, initial concentration, adsorbent dose, and contact time were found to be 7, 20 mg/L, 10 g/L, and 40 min, respectively, for which there was maximum fluoride removal.Conclusion: The result obtained from the experiments show that the neem leaves have been proved to be a low-cost biosorbent for the defluoridation of the sewage wastewater and have high fluoride removal efficiency.
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Parker, Vernon D. "Is the single transition-state model appropriate for the fundamental reactions of organic chemistry?" Pure and Applied Chemistry 77, no. 11 (January 1, 2005): 1823–33. http://dx.doi.org/10.1351/pac200577111823.
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In recent years, we have reported that a number of organic reactions generally believed to follow simple second-order kinetics actually follow a more complex mechanism. This mechanism, the reversible consecutive second-order mechanism, involves the reversible formation of a kinetically significant reactant complex intermediate followed by irreversible product formation. The mechanism is illustrated for the general reaction between reactant and excess reagent under pseudo-first-order conditions in eq. i where kf' is the pseudo-first-order rate constant equal to kf[Excess Reagent].Reactant + Excess reagent = Reactant complex = Products (i)The mechanisms are determined for the various systems, and the kinetics of the complex mechanisms are resolved by our "non-steady-state kinetic data analysis". The basis for the non-steady-state kinetic method will be presented along with examples. The problems encountered in attempting to identify intermediates formed in low concentration will be discussed.
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Rajamohan, N., and M. Rajasimman. "Parametric, equilibrium and kinetic studies on the removal of mercury using ion exchange resin." Water Practice and Technology 12, no. 2 (June 1, 2017): 305–13. http://dx.doi.org/10.2166/wpt.2017.037.
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This experimental research was an investigation into removal of mercury by using a strong acid cation resin, 001 × 7. Parametric experiments were conducted to determine the optimum pH, resin dosage, agitation speed and the effect of change in concentration in the range of 50–200 mg/L. High resin dosages favoured better removal efficiency but resulted in lower uptakes. Equilibrium experiments were performed and fitted to Langmuir and Freundlich isotherm models. Langmuir model suited well to this study confirming the homogeneity of the resin surface. The Langmuir constants were estimated as qmax = 110.619 mg/g and KL = 0.070 L/g at 308 K. Kinetic experiments were modeled using Pseudo second order model and higher values of R2 (>0.97) were obtained. The Pseudo second order kinetic constants, namely, equilibrium uptake (qe) and rate constant (k2), were evaluated as 59.17 mg/g and 40.2 × 10−4 g mg−1 min−1 at an initial mercury concentration of 100 mg/L and temperature of 308 K.
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Humeres, Eduardo, Maria de Nazaré M. Sanchez, Conceição ML Lobato, Nito A. Debacher, and Eduardo P. de Souza. "The mechanisms of hydrolysis of alkyl N-alkylthioncarbamate esters at 100 °C." Canadian Journal of Chemistry 83, no. 9 (September 1, 2005): 1483–91. http://dx.doi.org/10.1139/v05-165.
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The hydrolysis of ethyl N-ethylthioncarbamate (ETE) at 100 °C was studied in the range of 7 mol/L HCl to 4 mol/L NaOH. The pHrate profile showed that the hydrolysis occurred through specific acid catalysis at pH < 2, spontaneous hydrolysis at pH 26.5, and specific basic catalysis at pH > 6.5. The Hammett acidity plot and the excess acidity plot against X were linear. The BunnettOlsen plot gave a negative slope indicating that the conjugate acid was less hydrated than the neutral substrate. It was concluded that the acid hydrolysis occurred by an A1 mechanism. The neutral species hydrolyzed with general base catalysis shown by the Brønsted plot with β = 0.48 ± 0.04. Water acted as a general base catalyst with (pseudo-)first-order rate constant, kN = 3.06 × 107 s1. At pH > 6.5 the rate constants increased, reaching a plateau at high basicity. The basic hydrolysis rate constant of ethyl N,N-diethylthioncarbamate, which must react by a BAc2 mechanism, increased linearly at 13 mol/L NaOH with a second-order rate constant, k2 = 2.3 × 104 (mol/L)1 s1, which was 10 times slower than that expected for ETE. Experiments of ETE in 0.6 mol/L NaOH with an excess of ethylamine led to the formation of diethyl thiourea, presenting strong evidence that the basic hydrolysis occurred by the E1cb mechanism. In the rate-determining step, the E1cb mechanism involved the elimination of ethoxide ion from the thioncarbamate anion, producing an isothiocyanate intermediate that decomposed rapidly to form ethylamine, ethanol, and COS.Key words: alkylthioncarbamate esters, ethyl N-ethylthioncarbamate, ethyl N,N-diethylthioncarbamate, hydrolysis, mechanism.
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Bandyopadhyay, U., D. K. Bhattacharyya, and R. K. Banerjee. "Mechanism-based inactivation of gastric peroxidase by mercaptomethylimidazole." Biochemical Journal 296, no. 1 (November 15, 1993): 79–84. http://dx.doi.org/10.1042/bj2960079.
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The mechanism of inhibition of gastric peroxidase (GPO) activity by mercaptomethylimidazole (MMI), an inducer of gastric acid secretion, has been investigated. Incubation of purified GPO with MMI in the presence of H2O2 results in irreversible inactivation of the enzyme. No significant inactivation occurs in the absence of H2O2 or MMI, suggesting the involvement of peroxidase-catalysed oxidized MMI (MMIOX.) in the inactivation process. The inactivation follows pseudo-first-order kinetics consistent with a mechanism-based (suicide) mode. The pseudo-first-order kinetic constants at pH 8 are ki = 111 microM, k(inact.) = 0.55 min-1 and t1/2 = 1.25 min, and the second-order rate constant is 0.53 x 10(4) M-1 x min-1. Propylthiouracil also inactivates GPO activity in the same manner but its efficiency (k(inact./ki = 0.46 mM-1 x min-1) is about 10 times lower than that of MMI (k(inact./ki = 5 mM-1 x min-1). The rate of inactivation with MMI shows pH-dependence with an inflection point at 7.3, indicating the involvement in the inactivation process of an ionizable group on the enzyme with a pKa of 7.3. The enzyme is remarkably protected against inactivation by micromolar concentrations of electron donors such as iodide and bromide but not by chloride. Although GPO oxidizes MMI slowly, iodide stimulates it through enzymic generation of I+ which is reduced back to I- by MMI. Although MMIOX. is formed at a much higher rate in the presence of I-, a constant concentration of I- maintained via the reduction of I+ by MMI, protects the active site of the enzyme against inactivation. We suggest that MMI inactivates catalytically active GPO by acting as a suicidal substrate.
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Suratman, Adhitasari, Alifa Zahra Adhyana, and Dwi Siswanta. "The Effect of CTAB on Bentonite for Slow Release Fertilizer." Key Engineering Materials 884 (May 2021): 226–33. http://dx.doi.org/10.4028/www.scientific.net/kem.884.226.
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Effect of CTAB (Cetyltrimethylammonium Bromide) surfactant concentration on synthesized CTAB modified bentonite and release of NPK has been studied. Besides, the release kinetic model was also determined. Characterizations of the modified bentonite were done using FTIR (Fourier Transform Infra-Red), XRD (X-Ray Diffraction), and SEM (Scanning Electron Microscope). The amount of released NPK was analyzed using Spectrophotometer UV-Visible and AAS (Atomic Absorption Spectrometer). The release kinetics of NPK were determined using zeroth, first, second, pseudo-first, pseudo-second order, and Korsmeyer-Peppas kinetics models. The result of the study showed that CTAB modified bentonite has been successfully synthesized for NPK slow-release fertilizer. The CTAB concentration in CTAB modified bentonite affects the amount of NPK released out of bentonite and also could reduce the release of NPK. Among modified bentonite synthesized, CMB-3 (bentonite modified by CTAB 2 times CEC of bentonite) could reduce NPK release rate in water very well. The release kinetic of NPK followed the pseudo-second order kinetics model, with the release rate constant (k) of N, P, and K were 0.0027, 0.0540, and 0.0169 g mg−1 day−1, respectively.
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Buncel, Erwin, Helen A. Joly, and Diane C. Yee. "Metal ion – biomolecule interactions. Part 14. Methylmercury and hydrogen ion catalysis of C(2)-H isotopic exchange in 1-methylhistidine." Canadian Journal of Chemistry 67, no. 9 (September 1, 1989): 1426–39. http://dx.doi.org/10.1139/v89-219.
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The rate constants for detritiation from the C(2) position of 1-methyl[2-3H]histidine have been determined in a series of aqueous buffers at 85 °C. The resulting sigmoidal rate–pH profile was indicative of a mechanism involving hydroxide ion attack on the N(3)-protonated (4) and the amino-protonated (5) forms of 1-methylhistidine, and dissection of the kinetic data allowed the extraction of the second-order rate constants for the two pathways, k and k′. The unusually large value of k′ for a species not protonated at N(3) of the imidazole ring suggested the involvement of a kinetically equivalent zwitterionic form of the substrate (7). Comparison of the rate constant k with values determined previously for closely related substrates, such as histidine, 1-methylimidazole, and imidazole, led to the use of FMO theory to explain the effect of the various structural changes, e.g., the effect of methylation and a positively charged side chain on k and k′. The addition of MeHgNO3 resulted in a decrease in the pseudo-first-order rate constant for detritiation. The rate retardation was discussed in terms of two mechanisms (Schemes 2 and 3). Analysis of the data in terms of the various metal-ion-coordinated species present under the experimental conditions showed that the reactivity of the protonated substrate greatly exceeds that of the metal-coordinated species. The difference in the catalytic ability of H+ vs. MeHg+ is discussed in terms of the extent of positive charge developed on the ligating heteroatom in the ylide (carbenoid) reaction intermediate. Keywords: methylmercury, 1-methylhistidine, isotopic exchange, proton transfer, metal ion catalysis.
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McClelland, Robert A., and Claude Moreau. "Reversible ring opening in the hydrolysis of spiro ortho esters." Canadian Journal of Chemistry 63, no. 10 (October 1, 1985): 2673–78. http://dx.doi.org/10.1139/v85-444.
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Hydrolysis kinetics are reported for four spiro ortho esters: 3,4-dihydro-6-methoxy-1H-2-benzopyran-1-spiro-2′-1′,3′-dioxolane (13), its 1′,3′-dioxane analog (14), and the 6-unsubstituted versions of each (11 and 12). For comparison, also included are the diethoxy analogs: 1,1-diethoxy-3,4-dihydro-6-methoxy-1H-2-benzopyran (10) and the 6-unsubstituted compound (9). Product analysis implicates an initial opening of the dioxolane or dioxane ring in the spiro ortho esters, as expected on the basis of stereoelectronic considerations. The intermediate dialkoxycarbocations can be observed in HCl solutions. A detailed analysis has been carried out for the 6-methoxy systems to provide the rate constants k1, the second-order rate constant for H+-catalyzed formation of the cation from the ortho ester, k2, the first-order rate constant for water addition to the cation, and k−1, the first-order rate constant for ring closing of the cation to reform the ortho ester. The two spiro ortho esters are shown in this analysis to undergo reversible ring opening in their hydrolysis, in that values of k−1, are greater than k2. The differences, however, are not large, k−1/k2 being 1.2 (dioxolane, 13) and 3.8 (dioxane, 14). Comparison with the diethoxy ortho ester also reveals that the ring opening process (k1, rate constants) is inherently more difficult with the dioxolane, although not with the dioxane. An argument involving lone pair orientation is advanced to explain this.
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Salahshour, Roya, Mehdi Shanbedi, and Hossein Esmaeili. "Methylene Blue Dye Removal from Aqueous Media Using Activated Carbon Prepared by Lotus Leaves: Kinetic, Equilibrium and Thermodynamic Study." Acta Chimica Slovenica 68, no. 2 (June 15, 2021): 363–73. http://dx.doi.org/10.17344/acsi.2020.6311.
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In the present work, methylene blue was eliminated from aqueous solution using activated carbon prepared by lotus leaves. To perform the experiments, batch method was applied. Also, several analyses such as SEM, FTIR, EDAX and BET were done to determine the surface properties of the activated carbon. The results showed that the maximum sorption efficiency of 97.59% was obtained in initial dye concentration of 10 mg/L, pH of 9, adsorbent dosage of 4 g/L, temperature of 25 °C, contact time of 60 min and mixture speed of 400 rpm. Furthermore, the maximum adsorption capacity was determined 80 mg/g, which was a significant value. The experimental data was analyzed using pseudo-first order, pseudo-second order and intra-particle diffusion kinetic models, which the results showed that the pseudo-second order kinetic model could better describe the kinetic behavior of the sorption process. Also, the constant rate of the pseudo-second order kinetic model was obtained in the range of 0.0218–0.0345 g/mg.min. Moreover, the adsorption equilibrium was well described using Freundlich isotherm model. Furthermore, the thermodynamic studies indicated that the sorption process of methylene blue dye using the activated carbon was spontaneous and exothermic.
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Ghuysen, J. M., J. M. Frère, M. Leyh-Bouille, M. Nguyen-Distèche, and J. Coyette. "Active-site-serine d-alanyl-d-alanine-cleaving-peptidase-catalysed acyl-transfer reactions. Procedures for studying the penicillin-binding proteins of bacterial plasma membranes." Biochemical Journal 235, no. 1 (April 1, 1986): 159–65. http://dx.doi.org/10.1042/bj2350159.
Full textAbstract:
Under certain conditions, the values of the parameters that govern the interactions between the active-site-serine D-alanyl-D-alanine-cleaving peptidases and both carbonyl-donor substrates and beta-lactam suicide substrates can be determined on the basis of the amounts of (serine ester-linked) acyl-protein formed during the reactions. Expressing the ‘affinity’ of a beta-lactam compound for a DD-peptidase in terms of second-order rate constant of enzyme acylation and first-order rate constant of acyl-enzyme breakdown rests upon specific features of the interaction (at a given temperature) and permits study of structure-activity relationships, analysis of the mechanism of intrinsic resistance and use of a ‘specificity index’ to define the capacity of a beta-lactam compound of discriminating between various sensitive enzymes. From knowledge of the first-order rate constant of acyl-enzyme breakdown and the given time of incubation, the beta-lactam compound concentrations that are necessary to achieve given extents of DD-peptidase inactivation can be converted into the second-order rate constant of enzyme acylation. The principles thus developed can be applied to the study of the multiple penicillin-binding proteins that occur in the plasma membranes of bacteria.
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Yusuf Ibrahim, Yusuf Usman Jibrin, Zaharaddeen Muhammad, and Mujahid Abubakar. "PHOTOCATALYTIC OPTIMIZATION OF MR DYE BY K-ZnO AND ZnO CATALYSTS UNDER VISIBLE IRRADIATION." FUDMA JOURNAL OF SCIENCES 4, no. 4 (June 12, 2021): 67–76. http://dx.doi.org/10.33003/fjs-2020-0404-408.
Full textAbstract:
The lucubration on the visible light methyl red (MR) degradation using K-ZnO and undoped ZnO photo catalyst was investigated. The successive formation of K-ZnO was ascertained by several techniques such as scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FT-IR), and UV-Visible spectrophotometer and solid state UV-Vis band gap energy determination by comparing the Kubelka-Monk equation with Tauc equation and the energy band gap was calculated to be 3.28ev. The influence of reaction variables such as MR concentration, reaction pH, catalyst loadings and temperature have been investigated for both process. The kinetics model was developed for both doped and undoped ZnO photocatalyst using pseudo first and second order kinetics, the result indicated that both doped and undoped ZnO followed pseudo first order kinetics due to higher correlation coefficient (R2) value of 0.985 and 0.922 with rate constant (k) of 0.026 min-1 and 0.062 min-1, respectively. Based on the rate constant value (k) obtained at different reaction temperatures, the Arrhenius expression was derived. The derived activation energy (Ea) for the degradation of MR by K-ZnO photocatalysis was 32.109x103JK-1. The optimum condition for K-ZnO showed nearly complete degradation (95%) of the dye molecules with slightly higher degradation efficiency compares to ZnO (91%).
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Balagurov, Anatoly M., Nataliya Yu Samoylova, Ivan A. Bobrikov, Sergey V. Sumnikov, and Igor S. Golovin. "The first- and second-order isothermal phase transitions in Fe3Ga-type compounds." Acta Crystallographica Section B Structural Science, Crystal Engineering and Materials 75, no. 6 (November 9, 2019): 1024–33. http://dx.doi.org/10.1107/s2052520619013106.
Full textAbstract:
Structural features and kinetics of the transition between ordered metastable b.c.c.-derived D03 and equilibrium f.c.c.-derived L12 phases of Fe–xGa alloys (x = 27.2% and 28.0%) have been analyzed by in situ real-time neutron diffraction during isothermal annealing in the temperature range 405–470°C. It has been revealed that the transition proceeds with alternation of the first- and second-order phase transformations according to a D03 → A2 → A1 → L12 scheme, where A2 and A1 are disordered b.c.c. and f.c.c. structures. Deformations of the crystal lattice that arise due to these transitions are determined. The kinetics of the L12 phase nucleation and growth were analyzed in the frame of the Johnson–Mehl–Avrami–Kolmogorov (JMAK) model; however, only the early stage of the D03 → L12 transition is well described by the JMAK equation. The value of the Avrami exponent corresponds to the constant growth rate of the new L12 phase and decreasing nucleation rate in the Fe–27.2Ga alloy and indicates the presence of pre-existing nucleation centres of the L12 phase in the Fe–28.0Ga alloy.
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Wang, Zhi Feng, Si Dong Li, and Xiao Dong She. "Vulcanization Kinetics of Natural Rubber Coagulated by Microorganisms with Use of a Vulcameter." Advanced Materials Research 160-162 (November 2010): 1181–86. http://dx.doi.org/10.4028/www.scientific.net/amr.160-162.1181.
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Kinetics of vulcanization of natural rubber coagulated by microorganisms (NR-m) was studied with the use of a vulcameter. In the induction period of vulcanization, the time t0 of NR-m is shorter than that of natural rubber coagulated by acid (NR-a), and the rate constant k1/a of NR-m are greater than that of NR-a. Both the curing periods of NR-m and NR-a consist of two stages. The first stage follows first-order reaction. The rate constants k2 of NR-m in the first stage are greater than that of NR-a at the same temperature, and so are the activation energy E2. The second stage (end stage of the curing period) does not follow first-order reaction, and the calculated reaction order n of NR-m is in the range of 0.82-0.85, and that of NR-a is in the range of 0.64-0.72. The rate constants k3 of the second stage for NR -m are greater than that of NR-a at the same temperature, and so is the activation energy E3.
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Sivakuma, Venkatasubramanian. "Influence of Ultrasound on the Adsorption, Diffusion and Kinetics of Leather Dyeing Process: Mechanistic Insight." Journal of the American Leather Chemists Association 115, no. 7 (June 30, 2020): 239–47. http://dx.doi.org/10.34314/jalca.v115i7.3834.
Full textAbstract:
Leather is a natural porous material, which is composed of a three-dimensional weave of tanned collagen fibre bundles. This paper studies the influence of power ultrasound on the adsorption and kinetics of leather dyeing process. Dyeing experiments have been carried out using ultrasound (150 W, 33 kHz) and compared with that of static control dyeing process. The data of dye uptake in leather have been analysed using Freundlich and Langmuir adsorption isotherms. Intra Particle diffusion model has been employed to calculate Intra particle diffusion rate constant and Boundary Layer effect. Diffusion coefficient (D) of dye through leather matrix has also been calculated. Kinetics of leather dyeing process has been studied through pseudo first and second order rate equation. The Freundlich constant (Kf), Langmuir parameter (Qm), Intra Particle diffusion rate constant (Kd) Apparent Diffusion coefficient (D) and Pseudo First order kinetic constant, K1 have been calculated to be 18.67 mg/g, 50 mg/g, 0.006 min-1, 1.89 * 10-6 cm2/s and 1.7 mg/g min0.5 respectively for ultrasound assisted leather dyeing as compared to that of 0.1 mg/g, 26.67 mg/g, 0.733 min-1, 0.19 * 10-6 cm2/s and 0.003 mg/g min0.5 respectively for control process. The results indicate that significant enhancement in adsorption capacity with more favorable dye adsorption as well as about 10- fold increase in Apparent Diffusion coefficient with significant reduction in boundary layer effect, improved kinetic parameters due to the use of ultrasound in leather dyeing as compared to control. Mechanisms for enhancement in Adsorption and Kinetic Parameters in leather dyeing due to the use of ultrasound have been presented and corroborate well with better dye penetration, color value and fastness properties. Therefore, the present study demonstrates that the use of ultrasound in leather dyeing helps both in adsorption of dyes as well as diffusion process through the leather matrix.
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Marczewska, Barbara, Andrzej Persona, and Marek Przegaliński. "Faradaic Impedance Study of Mn(II) Reduction Mechanism in NaClO4 and NaCl Solutions on Mercury Electrode." Collection of Czechoslovak Chemical Communications 67, no. 11 (2002): 1589–95. http://dx.doi.org/10.1135/cccc20021589.
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The electrochemical reaction of the Mn(II)/Mn(Hg) system on mercury electrode was studied in 1 M NaClO4 and 1 M NaCl as supporting electrolytes of different complexing and adsorptive properties. The impedance measurements confirmed the two-stage electroreduction of the Mn(II) in investigated solutions. Both the apparent and the true rate constants of the second electron transfer in both supporting electrolytes are lower by one order of magnitude than the rate constant of the first electron transfer. Similar values of corrected rate constants in both electrolytes suggest the similarity in mechanism of the Mn(II) electroreduction.
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Rajamohan, N., R. Rajesh Kannan, and M. Rajasimman. "Kinetic Modeling and Effect of Process Parameters on Selenium Removal Using Strong Acid Resin." Engineering, Technology & Applied Science Research 6, no. 4 (August 26, 2016): 1045–49. http://dx.doi.org/10.48084/etasr.635.
Full textAbstract:
Heavy metal pollution due to the contamination of Selenium above the tolerable limit in the natural environment is a challenging issue that environmental scientists face. This study is aimed at identifying ion exchange technology as a feasible solution to remove selenium ions using 001x7 resin. Parametric experiments were conducted to identify the optimal pH, sorbent dose and speed of agitation. Selenium removal efficiency of 85% was attained at pH 5.0 with 100 mg/L selenium concentration. The increase in resin dose was found to increase removal efficiency. However, metal uptake decreased. The experiments on the effect of concentration proved the negative effect of higher concentrations of selenium on removal efficiency. The ion exchange process was proved to be optimal at an agitation speed of 200 rpm and a temperature of 35 °C. Pseudo second order model was found to fit the kinetic data very well compared to the pseudo-first order model and the pseudo second order rate constant was estimated as 8.725x10-5 g mg-1 min-1 with a solution containing 100 mg/L selenium.
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Heraldy, Eddy, Fitria Rahmawati, Dwi Ardiyanti, and Ika Nurmawanti. "FABRICATION OF Mg-Zn-Al HYDROTALCITE AND ITS APPLICATION FOR Pb2+ REMOVAL." Acta Polytechnica 59, no. 3 (July 1, 2019): 260–71. http://dx.doi.org/10.14311/ap.2019.59.0260.
Full textAbstract:
The fabrication of Mg-Zn-Al Hydrotalcite (HT) was carried out by the co-precipitation method at various molar ratios. The Mg-Zn-Al HT compound at the optimum molar ratio was then calcined to determine the effect of calcination on the Pb2+ adsorption. The kinetics of the adsorption type was determined by applying pseudo first order and pseudo second order kinetics models. Meanwhile, to investigate the adsorption process, the Freundlich and Langmuir equations were applied to determine the adsorption isotherm. The results showed that the optimum Mg-Zn-Al HT was at a molar ratio of 3 : 1 : 1 with an adsorption efficiency of 73.16 %, while Mg-Zn-Al HT oxide increased the adsorption efficiency to 98.12 %. The optimum condition of Pb2+ removal using Mg-Zn-Al HT oxide was reached at pH 5 and a contact time of 30 minutes. The adsorption kinetics follows the pseudo second order kinetics model with a rate constant of 0.544 g/mg·min. The isotherm adsorption follows the Langmuir isotherm model with a maximum capacity of 3.916 mg/g and adsorption energy of 28.756 kJ/mol.
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Wei, Wen Hui, Mei Na Liang, Zong Qiang Zhu, Hong Dong Qin, and Yi Nian Zhu. "Study on Kinetics and Thermodynamic in Bamboo Charcoal Adsorb Ammonia Nitrogen in Wastewater." Advanced Materials Research 356-360 (October 2011): 355–59. http://dx.doi.org/10.4028/www.scientific.net/amr.356-360.355.
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The Kinetics and thermodynamic was studied in ammonia nitrogen adsorption experiment using bamboo charcoal. The results showed that the dynamical data fit well with the pseudo-second-order kinetic model. The positive value of ΔH° (42.065 kJ/mol) and the apparent activation energy of the reaction of adsorption (20.67 kJ/mol) indicated that adsorption apparent rate constant increased with increasing temperature.
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Borowicz, Paweł, and Bernhard Nickel. "The Kinetics of Joined Action of Triplet-Triplet Annihilation and First-Order Decay of Molecules in the State in the Case of Nondominant First-Order Process." ISRN Spectroscopy 2012 (August 8, 2012): 1–13. http://dx.doi.org/10.5402/2012/316037.
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This paper presents the description of triplet-triplet annihilation in the case of nondominant first-order decay of molecules in the triplet state. The kinetics of the statistical system is influenced by joined action of two processes: the first- and second-order decies. This kinetics can be described with analytical function if the rate parameter of second-order reaction is constant. The approach presented here combines the well-known Smoluchowski formula with the previously published intuitive and non-Fickian models of diffusion-controlled triplet-triplet annihilation. The kinetics of the delayed fluorescence of anthracene is used as a practical example of applicability of the model proposed. The advantages and limits of the proposed model are discussed.
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Song, Changying, Lei Chen, and Jinhuan Shan. "Kinetics and Mechanism of Oxidation of Leucine and Alanine by Ag(III) Complex in Alkaline Medium." Research Letters in Inorganic Chemistry 2008 (October 14, 2008): 1–4. http://dx.doi.org/10.1155/2008/786857.
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Kinetics and mechanism of oxidation of leucine and alanine by Ag(III) complex were studied spectrophotometrically in alkaline medium at constant ion strength. The reaction was in first order with respect to Ag(III) complex and amino acids (leucine, alanine). The second-order rate constant, k−, decreased with the increasing in [OH−] and [IO4−]. A plausible mechanism was proposed from the kinetics study, and the rate equations derived from mechanism can explain all experimental phenomena. The activation parameters were calculated at 298.2 K.
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Pieters, J., T. Lindhout, and G. Willems. "Heparin-stimulated inhibition of factor IXa generation and factor IXa neutralization in plasma." Blood 76, no. 3 (August 1, 1990): 549–54. http://dx.doi.org/10.1182/blood.v76.3.549.549.
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Abstract Generation and inhibition of activated factor IXa was studied in factor XIa-activated plasma containing 4 mmol/L free calcium ions and 20 mumol/L phospholipid (25 mol% phosphatidylserine/75 mol% phosphatidylcholine). Interference of other (activated) clotting factors with the factor IXa activity measurements could be avoided by using a highly specific and sensitive bioassay. Factor IXa generation curves were analyzed according to a model that assumed Michaelis-Menten kinetics of factor XIa-catalyzed factor IXa formation and pseudo first order kinetics of inhibition of factor XIa and factor IXa. In the absence of heparin, factor IXa activity in plasma reached final levels that were found to increase with increasing amounts of factor XIa used to activate the plasma. When the model was fitted to this set of factor IXa generation curves, the analysis yielded a rate constant of inhibition of factor XIa of 0.7 +/- 0.1 min-1 and a kcat/Km ratio of 0.29 +/- 0.01 (nmol/L)-1 min-1. No neutralization of factor IXa activity was observed (the estimated rate constant of inhibition of factor IXa was 0). Thus, in the absence of heparin, the final level of factor IXa in plasma is only dependent on the initial factor XIa concentration. While neutralization of in situ generated factor IXa in normal plasma was negligible, unfractionated heparin dramatically enhanced the rate of inactivation of factor IXa (apparent second order rate constant of inhibition of 5.2 min-1/per microgram heparin/mL). The synthetic pentasaccharide heparin, the smallest heparin chain capable of binding antithrombin III, stimulated the inhibition of in situ generated factor IXa, but sevenfold less than unfractionated heparin (k = 0.76 min-1 per microgram pentasaccharide/mL). We found that free calcium ions were absolutely required to observe an unfractionated heparin and pentasaccharide-stimulated neutralization of factor IXa activity. Factor XIa inhibition (psuedo first order rate constant of 0.7 min-1) was not affected by unfractionated heparin or pentasaccharide in the range of heparin concentrations studied.
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Pieters, J., T. Lindhout, and G. Willems. "Heparin-stimulated inhibition of factor IXa generation and factor IXa neutralization in plasma." Blood 76, no. 3 (August 1, 1990): 549–54. http://dx.doi.org/10.1182/blood.v76.3.549.bloodjournal763549.
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Generation and inhibition of activated factor IXa was studied in factor XIa-activated plasma containing 4 mmol/L free calcium ions and 20 mumol/L phospholipid (25 mol% phosphatidylserine/75 mol% phosphatidylcholine). Interference of other (activated) clotting factors with the factor IXa activity measurements could be avoided by using a highly specific and sensitive bioassay. Factor IXa generation curves were analyzed according to a model that assumed Michaelis-Menten kinetics of factor XIa-catalyzed factor IXa formation and pseudo first order kinetics of inhibition of factor XIa and factor IXa. In the absence of heparin, factor IXa activity in plasma reached final levels that were found to increase with increasing amounts of factor XIa used to activate the plasma. When the model was fitted to this set of factor IXa generation curves, the analysis yielded a rate constant of inhibition of factor XIa of 0.7 +/- 0.1 min-1 and a kcat/Km ratio of 0.29 +/- 0.01 (nmol/L)-1 min-1. No neutralization of factor IXa activity was observed (the estimated rate constant of inhibition of factor IXa was 0). Thus, in the absence of heparin, the final level of factor IXa in plasma is only dependent on the initial factor XIa concentration. While neutralization of in situ generated factor IXa in normal plasma was negligible, unfractionated heparin dramatically enhanced the rate of inactivation of factor IXa (apparent second order rate constant of inhibition of 5.2 min-1/per microgram heparin/mL). The synthetic pentasaccharide heparin, the smallest heparin chain capable of binding antithrombin III, stimulated the inhibition of in situ generated factor IXa, but sevenfold less than unfractionated heparin (k = 0.76 min-1 per microgram pentasaccharide/mL). We found that free calcium ions were absolutely required to observe an unfractionated heparin and pentasaccharide-stimulated neutralization of factor IXa activity. Factor XIa inhibition (psuedo first order rate constant of 0.7 min-1) was not affected by unfractionated heparin or pentasaccharide in the range of heparin concentrations studied.
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Sangjan, Suntree, and Wadchara Thongsamer. "Application of Photocatalytic and Adsorption Process for Residue Organic Degradation Using Doped ZnO Composites Hydrogel Beads." Key Engineering Materials 858 (August 2020): 109–15. http://dx.doi.org/10.4028/www.scientific.net/kem.858.109.
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This research aimes to synthesize photocatalyst-sodium alginate composite hydrogel beads which apply for coupled adsorption and photocatalytic degradation of organic residue. Fe3O4, graphitic carbon nitride (g-C3N4), grapheme oxide (GO) and AgNO3 doped ZnO photocatalyst composites hydrogel beads were synthesized and characterized using Fourier-transform infrared spectroscopy (FT-IR), X-ray Diffraction (XRD), and Transmission Electron Microscopy (TEM). Photocatalytic and adsorption activity are studied by Methylene blue (MB) degradation under sunshine irradiation. The effect of different parameter as photocatalyst types and reaction time were studied upon the efficiency of organic residue degradation. The coupled photocatalytic and adsorption processes were evaluated through various kinetic models such as pseudo-first-order/ pseudo-second-order in Langmuir-Hinshelwood model model, the Elovich model and the intra particle diffusion model. Kinetics studies showed that the coupled photocatalytic and adsorption processes in photodegradation of all sample was well described by the pseudo-second-order model because R2 of all sample were close to 1 which compared with another model. For photodegradation efficiency, the best choice in this condition was g-C3N4 doped ZnO composite hydrogel bead. Photodegradation efficiency and the pseudo second order rate constant of photocatalyst ZnO+gC3N4/SA composite hydrogel bead were 83.80%(for 180 min and up to 96% for 7 hr) and 5.05×10-3 g.mg-1 min-1, respectively.
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Um, Ik-Hwan, Ji-Sun Kang, and Julian M. Dust. "Alkali metal ion catalysis and inhibition in alkaline ethanolysis of O-Y-substituted-phenyl O-phenyl thionocarbonates: contrasting M+ ion effects upon changing electrophilic centre from C=O to C=S." Canadian Journal of Chemistry 95, no. 1 (January 2017): 45–50. http://dx.doi.org/10.1139/cjc-2016-0378.
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Pseudo-first-order rate constants (kobsd) were measured for nucleophilic substitution reactions of O-Y-substituted-phenyl O-phenyl thionocarbonates (4a–4h) with alkali metal ethoxides (EtOM, M = Li, Na, or K) in anhydrous ethanol at 25.0 ± 0.1 °C. Plots of kobsd vs. [EtOM] exhibited upward curvature for the reaction of O-4-nitrophenyl O-phenyl thionocarbonate (4a) with EtOK in the presence of 18-crown-6-ether (18C6), but showed downward curvature for the reaction with EtOLi, indicating that the reaction is catalyzed by the 18C6-crowned K+ ion, but is inhibited by Li+ ion. The kobsd values were dissected into kEtO− and kEtOM, the second-order rate constant for the reaction with dissociated EtO− and ion-paired EtOM, respectively. The reactivity of EtOM toward 4a increases in the order EtOLi < EtONa < EtO− < EtOK < EtOK/18C6, which is in contrast to that reported previously for the corresponding reaction of 4-nitrophenyl phenyl carbonate (a C=O analogue of 4a), e.g., EtO− ≈ EtOK/18C6 < EtOLi < EtONa < EtOK. The reaction mechanism, including the transition-state model and the origin of the contrasting reactivity patterns found for the reactions of the C=O and C=S compounds, are discussed.
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Sundaram, E. J. Saravana, and P. Dharmalingam. "Synthesis and Characterization of PMMA Polymer/Clay Nanocomposites for Removal of Dyes." Asian Journal of Chemistry 31, no. 11 (September 28, 2019): 2589–95. http://dx.doi.org/10.14233/ajchem.2019.22131.
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The adsorbent polymer/clay nanocomposites were prepared by in situ emulsion polymerization method. The prepared adsorbent was characterized using FT-IR, XRD, TGA and the surface morphology was analyzed using FE-SEM. The prepared polymer/clay nano-composite was used for the removal of malachite green and amido black 10B. The effects of initial pH, adsorbent dosage, initial metal ion concentration, contact time and thermodynamic studies on the malachite green and amido black 10B adsorption were studied. The adsorption isotherm parameters of the adsorption process were determined by using Langmuir, Freundlich and Temkin adsorption isotherm equations. The kinetic parameters were predicted with Lagergren’s pseudo-first order and pseudo-second order equations. The effect of temperature of the adsorption process was demonstrated by using the thermodynamic parameters. The maximum adsorption capacity of malachite green and amido black 10B onto polymer/clay nanocomposites was found at pH 7 and 2. Adsorption of malachite green and amido black 10B onto polymer/clay nanocomposites followed the Langmuir adsorption isotherm and it follows pseudo-second order rate constant equation The thermodynamic parameters, such as ΔHº, ΔSº and ΔGº were also determined which suggested that the studied adsorption process was an endothermic reaction.
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Xia, Yanqing, Hongwu Tian, Yanlei Li, Xinru Yang, Jinming Liu, Chunli Liu, Li Zhou, Lincai Zhang, Tiejian Li, and Tiesheng Shi. "Kinetic Analysis of the Reduction Processes of a Cisplatin Pt(IV) Prodrug by Mesna, Thioglycolic Acid, and Thiolactic Acid." Journal of Chemistry 2020 (November 11, 2020): 1–12. http://dx.doi.org/10.1155/2020/5868174.
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Although Mesna is an FDA-approved chemotherapeutic adjuvant and an antioxidant based largely on its antioxidative properties, kinetic and mechanistic studies of its redox reactions are limited. A kinetic analysis of the reduction processes of cis-diamminetetrachloroplatinum(IV) (cis-[Pt(NH3)2Cl4], a cisplatin Pt(IV) prodrug) by thiol-containing compounds Mesna, thioglycolic acid (TGA), and DL-thiolactic acid (TLA) was carried out in this work at 25.0°C and 1.0 M ionic strength. The reduction processes were followed under pseudo-first-order conditions and were found to strictly obey overall second-order kinetics; the observed second-order rate constant k′ versus pH profiles were established in a wide pH range. A general reaction stoichiometry of Δ[Pt(IV)] : Δ[Thiol]tot = 1 : 2 was revealed for all the thiols; the thiols were oxidized to their corresponding disulfides which were identified by mass spectrometry. Reaction mechanisms are proposed which involves all the prololytic species of the thiols attacking the Pt(IV) prodrug in parallel, designating as the rate-determining steps. Transient species chlorothiol and/or chlorothiolate are formed in these steps; for each particular thiol, these transient species can be trapped rapidly by another thiol molecule which is in excess in the reaction mixture, giving rise to a disulfide as the oxidation product. The rate constants of the rate-determining steps were elucidated, revealing reactivity enhancements of (1.4–8.9) × 105 times when the thiols become thiolates. The species versus pH and reactivity of species versus pH distribution diagrams were constructed, demonstrating that the species ‒SCH2CH2SO3‒ of Mesna largely governs the total reactivity when pH > 5; in contrast, the form of Mesna per se (mainly as HSCH2CH2SO3‒) makes a negligible contribution. In addition, a well-determined dissociation constant for the Mesna thiol group (pKa2 = 8.85 ± 0.05 at 25.0°C and μ = 1.0 M) is offered in this work, which was determined by both kinetic approach and spectrophotometic titration method.
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Hawkins, H. C., and R. B. Freedman. "The reactivities and ionization properties of the active-site dithiol groups of mammalian protein disulphide-isomerase." Biochemical Journal 275, no. 2 (April 15, 1991): 335–39. http://dx.doi.org/10.1042/bj2750335.
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1. The number of reactive thiol groups in mammalian liver protein disulphide-isomerase (PDI) in various conditions was investigated by alkylation with iodo[14C]acetate. 2. Both the native enzyme, as isolated, and the urea-denatured enzyme contained negligible reactive thiol groups; the enzyme reduced with dithiothreitol contained two groups reactive towards iodoacetic acid at pH 7.5, and up to five reactive groups were detectable in the reduced denatured enzyme. 3. Modification of the two reactive groups in the reduced native enzyme led to complete inactivation, and the relationship between the loss of activity and the extent of modification was approximately linear. 4. Inactivation of PDI by alkylation of the reduced enzyme followed pseudo-first-order kinetics; a plot of the pH-dependence of the second-order rate constant for inactivation indicated that the essential reactive groups had a pK of 6.7 and a limiting second-order rate constant at high pH of 11 M-1.s-1. 5. Since sequence data on PDI show the presence within the polypeptide of two regions closely similar to thioredoxin, the data strongly indicate that these regions are chemically and functionally equivalent to thioredoxin. 6. The activity of PDI in thiol/disulphide interchange derives from the presence of vicinal dithiol groups in which one thiol group of each pair has an unusually low pK and high nucleophilic reactivity at physiological pH.
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Senapati, Sadhana, S. P. Das, and A. K. Patnaik. "Kinetics and Mechanism of Oxidation of L-Ascorbic Acid by Pt(IV)(aq) in Aqueous Hydrochloric Acid Medium." Advances in Physical Chemistry 2012 (November 20, 2012): 1–5. http://dx.doi.org/10.1155/2012/143734.
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Reduction of [PtCl6]2− by L-ascorbic acid (H2ASc) in 0.1 M aqueous acid medium has been investigated spectrophotometrically under pseudo-first order condition at [PtCl6]2− = 0.005–0.007 mol dm−3, 0.05 ≤ [H2ASc]/mol dm−3 ≤ 0.3, 298 K ≤ T ≤ 308 K, [H+] = 0.14 mol dm−3, I=0.5 mol dm−3. The redox reaction follows the rate law: d[Pt(IV)]/dt = k[H2ASc][Pt(IV)], where k is the second-order rate constant and [H2ASc] is the total concentration of ascorbic acid. Electron transfer from [H2ASc] to Pt(IV) center leading to the release of two halide ions and formation of the reaction products, square planner Pt(II) halide complex, and dehydrated ascorbic acid is suggested. This redox reaction follows an outersphere mechanism as Pt(IV) complex is substituted inert. Activation parameters were calculated corresponding to rate of electron transfer reaction k. Activation parameters favor the electron transfer reaction.
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Ledakowicz, S., R. Maciejewska, J. Perkowski, and A. Bin. "Ozonation of Reactive Blue 81 in the bubble column." Water Science and Technology 44, no. 5 (September 1, 2001): 47–52. http://dx.doi.org/10.2166/wst.2001.0248.
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The decolourisation process of the Reactive Blue 81 was carried out in a laboratory bubble column reactor with inner diameter 110 mm and working height 550 mm, equipped with a porous glass ozone diffuser (diameter 50 mm). A model of ozone absorption with the chemical reaction in the liquid phase was employed. It was found that the decolourisation proceeds in the fast pseudo first-order regime. The average value of the enhancement factor was calculated from the experimental results and compared with those calculated according to the theory of mass transfer with a second-order chemical reaction. In order to determine the intrinsic kinetics of ozonation, a stopped-flow technique was employed. The rate constant of the dyestuff reaction with ozone was determined as equal to 4.5 × 107 mol/(dm3.s).