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  • kinetics  (70)
  • Springer  (70)
  • American Institute of Physics
  • 2020-2023
  • 2010-2014
  • 1995-1999  (70)
  • 1996  (70)
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  • 2020-2023
  • 2010-2014
  • 1995-1999  (70)
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  • 1
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    Adsorption 2 (1996), S. 265-277 
    ISSN: 1572-8757
    Keywords: frequency response ; diffusion cell ; kinetics ; diffusion ; heat effects
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract This paper deals with frequency response (FR) analysis of a closed diffusion cell system with two resonators, that is both the LHS and RHS volumes are modulated. The analysis is made for a homogeneous particle described by a single effective diffusivity as well as a biporous pellet described by macropore and micropore diffusions. It is shown that if the perturbation of the volume of the reservoir #2 is lagged behind that of the reservoir #1 by 3π/2, the pressure response in reservoir #1 is significantly enhanced with larger amplitude as well as phase angle. When the perturbations of the two reservoirs are out of phase, the heat effect is reduced and can become insignificant when the two perturbations are completely out of phase (ψ = π). Under such a condition, the pressure difference between the two reservoirs could be doubled. In the case of biporous pellets, it is shown that the FR behaviours obtained for micropore diffusion control and macropore diffusion control are well distinguished. In the former case, the FR system reduces to a traditional batch adsorber one while in the latter case, the FR behaviour is the same as for a two resonator system with homogeneous particles. This difference can be used for the discrimination of micropore and macropore diffusion processes.
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  • 2
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    Catalysis letters 37 (1996), S. 167-172 
    ISSN: 1572-879X
    Keywords: dissociation ; kinetics ; Co-Mo sulphide ; H2S
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract In this study, a high surface area 4Co∶6Mo∶100γ-Al2O3 sulphide prepared using precipitation from homogeneous solution (PFHS) has been used for the catalytic splitting of hydrogen sulphide into H2 and elemental sulphur. The activity of this new formulation was significantly better than previously reported recipes. Kinetic data collected over a wide range of H2S partial pressures between 883 and 983 K revealed that, although the decomposition followed a first-order law, a mechanism involving H2S adsorption on co-ordinative unsaturation sites of the Co-Mo sulphide catalyst gave a Langmuir-Hinshelwood rate expression that yielded satisfactory model parameters. In particular, the scission of the surface H-S bond appeared to be the rate determining step.
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  • 3
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    Catalysis letters 37 (1996), S. 173-179 
    ISSN: 1572-879X
    Keywords: ammonia synthesis ; iron catalysts ; potassium promotion ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Measurements were performed of reaction rate in the process of ammonia synthesis (T=370–470°C) on doubly promoted (DP) (Al2O3, CaO) and triply promoted (TP) (K2O, Al2O3, CaO) iron catalysts. The latter were obtained by impregnation of the reduced and subsequently passivated DP precursors with alcoholic solution of KOH. The studies were carried out under high total pressure (10 MPa) in a wide range of ammonia partial pressure in the gas phase: from 0.25 to about 7 bar. The results are shown to be authoritative for the so-called kinetic regime. The effect of the presence of K+ cations in the catalyst was the stronger, as the temperature of the reaction was the lower and, in particular, the ammonia pressure in the gas phase the higher. The obtained results are in good accordance with the results of Somorjai's studies on activity of iron single crystal surfaces both clean and covered with (K+O) adlayer.
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  • 4
    ISSN: 1572-882X
    Keywords: accelerated tests ; aging tests ; cellulose degradation ; durability ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Accelerated aging tests are credible and useful to predict paper permanence only if such tests can be shown to correlate with natural aging. In the first part of this study, a kinetic model was developed based on the accelerated aging results. In this report, we have shown that this kinetic model can indeed predict the natural aging results of lignin-free sheets with a statistical confidence. This is the first quantitative comparison of accelerated aging with natural aging.
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  • 5
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    Cellulose 3 (1996), S. 243-267 
    ISSN: 1572-882X
    Keywords: aging tests ; cellulose degradation ; durability ; kinetics ; paper properties
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract The validity of accelerated aging tests to predict and rank papers on their permanence has been under question, preventing the development of performance-based standards for permanent paper. We conducted a general kinetic analysis to investigate the aging process of paper. A general kinetic model is proposed to describe the depolymerization of cellulose. Experimentally it was shown that in the case of aging, cellulose degradation follows classic first-order kinetics as a special case of our general kinetic model. The Arrhenius equation was critically re-examined for the case of a multiple reaction system. It was shown analytically that the Arrhenius equation is still applicable when certain conditions are met. This was convincingly supported by experimental results. We also analysed the dependence of the degradation rate on the moisture content and hydrogen ion concentration. By conducting systematic experiments on these two factors, a general and quantitative relationship was established to explain the contribution of each factor and their interactions. Finally, based on this kinetic analysis, the effects of storage conditions on the life expectancy of paper were estimated.
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  • 6
    ISSN: 1572-879X
    Keywords: non-uniform surface ; kinetics ; ethanol ; oxidation ; molybdenum oxide
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Temkin's theory of rates of catalytic reactions on non-uniform surfaces is extended to the MoO3-catalyzed oxidation of ethanol to acetaldehyde. Two types of sites are assumed to be present, an oxygen atom site that can be modeled with uniform properties and a metal atom site characterized by non-uniform properties both for ethanol chemisorption to an ethoxide intermediate and the conversion of this intermediate to acetaldehyde. The rate-limiting step is the cleavage of a C-H bond in the absorbed ethoxide intermediate. Non-uniform surface kinetics leads to a kinetic rate expression of the form $$v = kP_{C_2 H_5 OH}^{1 - m} P_{O_2 }^{(1 - m)/4} P_{H_2 O}^{ - (1 - m)/2} $$ . Such a rate expression, withm=0.14, is shown to provide a good fit to kinetic data for the selective oxidation of ethanol on a silica supported molybdenum oxide catalyst.
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  • 7
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    Catalysis letters 36 (1996), S. 31-36 
    ISSN: 1572-879X
    Keywords: ethanol ; kinetics ; oxidation ; oxydehydrogenation ; platinum ; structure sensitivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The effect of the platinum particle size was investigated for the catalytic oxidative dehydrogenation of aqueous ethanol to ethanal at a temperature of 303 K, an ethanol concentration of 260 mol m−3, a partial oxygen pressure 60 kPa, a pH of 9, and an ethanal and ethanoate concentration of 20 mol m−3. A particle size effect on the turnover frequency was observed but only for particle sizes smaller than 2 nm. Hence, the reaction shows a limited structure sensitivity.
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  • 8
    ISSN: 1436-5073
    Keywords: kinetics ; rates ; integrating ratemeter ; optimization ; first-order
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The integrating ratemeter is used in concert with the two-rate parameter to form the integrating ratemeter two-rate parameter. Propagation of error theory is applied to the integrating ratemeter two-rate parameter to yield expressions for the precision of rates calculated from the integrating ratemeter two-rate parameter in terms of the precision of the rates measured with the integrating ratemeter. Simulations and experimental results show that in cases where the standard deviation of the rate is relatively constant, the optimum time to make a rate measurement using the integrating ratemeter is also the optimum time to measure either of the rates in the two-rate parameter. If either of the two rates comprising the two-rate parameter is measured at the optimum time, then the precision and accuracy of concentrations measured with this technique are optimized.
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  • 9
    ISSN: 1572-9729
    Keywords: bioavailability ; builders ; detergents ; kinetics ; mineralization ; sewage sludge ; soil
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Tetradecenyl succinic acid (TSA) is the major component of a detergent builder (C12-C14 alkenyl succinic acid), which is inherently biodegradable. 14C-TSA was dosed as a component of sewage sludge into a soil with a history of sludge amendment at final added concentrations of 1.5 and 30 mg (kg soil)-1. In addition, it was dosed to the soil in an aqueous solution to a final added concentration of 30 mg (kg soil)-1. Dose and form were found to have a pronouced effect on the mineralization kinetics. When dosed in a realistic form and concentration (i.e. 1.5 mg (kg soil)-1 as a component of sludge), TSA was mineralized at its highest rate and to its greatest extent, and the mineralization half-life was 2.4 days. When dosed at 30 mg (kg soil)-1 as a component of sludge, mineralization began immediately, and the half-life was 23 days. In contrast, when dosed at this concentration in aqueous solution, the onset of mineralization was preceded by a 13 day lag period and the mineralization half-life was 69 days. Primary biodegradation and mineralization rates of TSA were very similar. Approximately, half the radioactivity was evolved as 14CO2, while the remaining radioactivity became non-extractable, having presumably been incorporated into biomass or natural soil organic matter (humics). This study demonstrated that TSA is effectively removed from sludge-amended soils as a result of biodegradation. Furthermore, it showed the effect that dose form and concentration have on the biodegradation kinetics and the importance of dosing a chemical not only at a relevant concentration but also in the environmental form in which it enters the soil environment.
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  • 10
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    Biodegradation 7 (1996), S. 73-81 
    ISSN: 1572-9729
    Keywords: diesel oil ; biodegradation ; CSTR ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract In batch culture diesel oil was degraded rapidly, with a maximum growth rate (for a consortium of microorganisms) of 0.55 h-1. The corresponding yield Y SX was 0.1 Cmol/Cmol. In a continuous stirred tank reactor the maximum dilution rate was about 0.25 h-1, with a yield of 0.3 Cmol/Cmol. With a residence time of 1 day 82% of the influent oil was degraded. In the batch reactor, of the mixture of linear and branched alkanes the linear alkanes were degraded fastest and with the highest yield. Only after most of the linear alkanes had disappeared were the branched alkanes consumed. In a CSTR a large part of the branched alkanes was not degraded.
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  • 11
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    Pure and applied geophysics 147 (1996), S. 367-375 
    ISSN: 1420-9136
    Keywords: Induced seismicity ; kinetics ; rock fracture ; rockburst ; earthquake
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Powerful seismic events, such as earthquakes and rockbursts, are caused by the accumulation of energy in rocks and loss of rock mass stability. Usually methods of their forecasting are based on the registration of anomalous behavior of geophysical fields. However an efficiency of this approach is low. The present paper proposes a kinetic approach to the description of rock fracture process, which can be used for the forecasting of seismic events and an investigation of structure and energy distributions in rock. 3-D and 1-D kinetic equations describing a process of cluster formation in rock were obtained. The equations are invariant to deformation conditions and to the scale level of events. They showed a good agreement with the results of field observations and laboratory experiments. It was also shown that these equations well describe the processes of earthquake, rockburst and rock sample failure preparation. Catalogues of rockbursts in mines were analyzed with the use of the kinetic equations to find out evidence of induced seismic events. The proposed approach makes it possible to reveal trends in rock behavior and thus predict the rock failure at different scale levels.
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  • 12
    ISSN: 1432-1041
    Keywords: Key words Diphemanil methylsulphate ; Neonate; antimuscarinic agent ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
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  • 13
    ISSN: 1432-072X
    Keywords: Key words Auxostat ; Batch culture ; Chemostat ; Continuous culture ; Fermentation control ; Inhibition ; kinetics ; Nutristat ; On-line measurement ; Pentachlorophenol ; Pollutant ; Sphingomonas ; Steady-state conditions ; Toxicity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A bacterium degrading pentachlorophenol (PCP) as the only source of carbon and energy was grown in a “nutristat”, i.e., a continuous culture with on-line measurement and control of the substrate concentration. We improved the PCP nutristat by incorporation of a personal computer with a proportional integral derivative (PID) algorithm for controlling the medium feed pump. The controlled value deviated from the average (set-point) value by 1% maximally. In the PCP nutristat (30°C), the steady-state dilution rate, and hence, specific growth rate, showed a maximum value of 0.142 ± 0.004 h–1 at set-point PCP concentrations between 37 and 168 μM. At PCP concentrations above 168 μM, the steady-state growth rate decreased because of inhibition. The growth yield coefficient was not seriously affected by the PCP concentration, suggesting that uncoupling was not the inhibitory mechanism. It was concluded that the PCP nutristat is very useful for establishing steady-state conditions that maintain growth-inhibitory PCP concentrations and high cell concentrations, conditions for which the chemostat is not suitable.
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  • 14
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    Journal of thermal analysis and calorimetry 47 (1996), S. 35-49 
    ISSN: 1572-8943
    Keywords: bone cement ; DSC ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Bone cements are widely used for the fixation of metallic prostheses in orthopaedics and to form replacements for skull defects in neurosurgery. Acrylic bone cements are based on a mixture of methyl methacrylate (MMA) and a fine powder of polymethyl methacrylate (PMMA). The polymerization of the bone cement occurs in contact with the bone and the prosthesis which act as the boundaries of a bulk polymerization reactor. The kinetic behaviour of the bone cement plays a fundamental role for the final performance of the implant. In this paper, the isothermal and non-isothermal polymerization behaviour of a commercial bone cement is described. A simple phenomenological model, accounting for the autoacceleration ffect, for a diffusion controlled termination mechanism and for the reaction between inhibitor and initiator, is proposed. The reaction kinetics is analysed by DSC. DSC data are used for the determination of the rates of polymerization under isothermal and non-isothermal conditions. The experimental data are processed to calculate the parameters of the proposed phenomenological kinetic model. The analytical and numerical details related to the integration of the model are discussed.
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  • 15
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    Journal of thermal analysis and calorimetry 47 (1996), S. 543-557 
    ISSN: 1572-8943
    Keywords: compensation effect ; DSC ; kinetics ; TG
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Four computer programs as well as one demo-version for non-linear evaluation of kinetic data in thermal analysis and calorimetry, were presented. The multi-task program TA-kin meets all mathematical requirements for solving the numerical assignments. It is shown that the so-called compensation effect is due to the mathematical structure of the Arrhenius equation. Several applications of TA-kin to a lot of DSC- and TG-measurements and isoperibolic batch experiments as well as adiabatic semi batch experiments realized by precision calorimetry have been discussed.
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  • 16
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    Journal of thermal analysis and calorimetry 47 (1996), S. 569-575 
    ISSN: 1572-8943
    Keywords: Bi2O3 ; CaCO3 decomposition ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Former studies concerning the formation of the compounds in the pseudobinary systems of Bi2O3-MO type (M =Ca, Sr, Ca+Sr) have shown that the reaction which occurs with the highest rate is that between Bi2O3 and CaO. In the present work CaCO3 was used as CaO source. We carried out an investigation of the thermal decomposition of CaCO3 in the presence of Bi2O3 in comparison with the decomposition of pure CaCO3. The presence of Bi2O3 exerts a complex influence on the CaCO3 decomposition acting on the nucleation as well as on the diffusion of CO2. The decomposition of the samples with low Bi2O3 content follows the mechanism of a contracting sphere. A change from surface nucleation to bulk nucleation is recorded for higher amounts of Bi2O3.
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  • 17
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    Journal of thermal analysis and calorimetry 47 (1996), S. 1437-1450 
    ISSN: 1572-8943
    Keywords: browning ; crystallization ; glass transition ; kinetics ; milk powder ; water
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract An exotherm, observed in differential scanning calorimetry (DSC) scans of amorphous food materials above their glass transition temperature,T g, may occur due to sugar crystallization, nonenzymatic browning, or both. In the present study, this exothermal phenomenon in initially anhydrous skim milk and lactose-hydrolyzed skim milk was considered to occur due to browning during isothermal holding at various temperatures above the initialT g. The nonenzymatic, Maillard browning reaction produces water that in amorphous foods, may plasticize the material and reduceT g. The assumption was that quantification of formation of water from theT g depression, which should not be observed as a result of crystallization under anhydrous conditions, can be used to determine kinetics of the nonenzymatic browning reaction. The formation of water was found to be substantial, and the amount formed could be quantified from theT g measured after isothermal treatment at various temperatures using DSC. The rate of water formation followed zero-order kinetics, and its temperature dependence well aboveT g was Arrhenius-type. Although water plasticization of the material occurred during the reaction, and there was a dynamic change in the temperature differenceT−T g, the browning reaction was probably diffusioncontrolled in anhydrous skim milk in the vicinity of theT g of lactose. This could be observed from a significant increase in activation energy. The kinetics and temperature dependence of the Maillard reaction in skim milk and lactose-hydrolyzed skim milk were of similar type well above the initialT g. The difference in temperature dependence in theT g region of lactose, but above that of lactose-hydrolyzed skim milk, became significant, as the rate in skim milk, but not in lactose-hydrolyzed skim milk, became diffusion-controlled. The results showed that rates of diffusion-controlled reactions may follow the Williams-Landel-Ferry (WLF) equation, as kinetic restrictions become apparent within amorphous materials in reactions exhibiting high rates at the same temperature under non-diffusion-controlled conditions.
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  • 18
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    Journal of thermal analysis and calorimetry 46 (1996), S. 795-808 
    ISSN: 1572-8943
    Keywords: DSC ; kinetics ; liquid crystalline polymer ; optical transmittance ; polycarbosilane ; side-chain mesogen ; transition parameters
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract This paper is concerned with an analysis of the thermodynamics and kinetics of mesophase formation by cooling from the isotropic state of side-chain liquid crystalline polycarbosilanes containing spacers in the range from 3 to 11 CH2-groups. The polymers are characterized by their thermotropic behaviour as far as temperature, enthalpy and entropy of the transitions are concerned. The kinetics was followed by optical and calorimetric methods. Longer spacer length leads to more perfect ordering in the mesophase, higher isotropization temperatures, and lower glass transition temperatures. The Avrami and Ozawa formalism to describe the transition kinetics to the mesophase from the isotropic state cannot be interpreted as the nucleation and growth mechanism known from crystallization.
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  • 19
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    Journal of thermal analysis and calorimetry 47 (1996), S. 1081-1091 
    ISSN: 1572-8943
    Keywords: kinetics ; thermal degradation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The kinetic study of thermal degradation takes into account the validity of the Arrhenius equation. From TG data, the activation energy,E a and pre-exponential factor,A, are evaluated. These results are interpreted by using the ‘kinetic compensation effect’ as basis. A linear correlation between In(A) andE a is obtained in all cases studied. However, in a plot of the logarithm of the rate constant as a function of reciprocal temperature for the same series of reactions, the thermal oxidative degradations of Nylon-6 and PVC display a point of concurrence and one isokinetic temperature, whereas those of HIPS and PC do not. Therefore, in the thermal oxidative degradations of Nylon-6 and PVC a ‘true’ compensation effect occurs, which could be related to the bulk properties of metal oxides, such as different valence states, whereas for other polymers it displays only an ‘apparent’ compensation effect. This means that degradation is largely independent of the bulk properties of oxides, but may be related to the distribution of different kinds of active links in the polymer surface having different activation energies.
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  • 20
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    Journal of thermal analysis and calorimetry 46 (1996), S. 49-54 
    ISSN: 1572-8943
    Keywords: kinetics ; solid-phase reactions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The convexity of localization forms, strictly required by conventional geometric-probabilistic formalism, is not in agreement with many experimental observations concerning solid-phase chemical reactions. In a discussion of the essence of this requirement, it is shown that it may be weakened for non-convex localization forms consistent with the symmetry of a solid reagent and described within the geometric-probabilistic approach in terms of planigons and Wigner-Seitz cells.
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  • 21
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    Journal of thermal analysis and calorimetry 46 (1996), S. 225-236 
    ISSN: 1572-8943
    Keywords: IR ; kinetics ; TG-DTG-DTA ; l,3,5-triamino-2,4,6-trinitrobenzene
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The kinetics of the thermal decomposition of 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) in condensed state has been investigated by high temperature infrared spectroscopy (IR) and thermogravimetry (TG) in conjunction with pyrolysis gas analysis, differential thermal analysis (DTA) and hot stage microscopy. The decomposition proceeds in two main stages under isothermal conditions and the initial stage involving about 24% loss in weight obeys Avrami-Erofe'ev equation (n= 1), and is governed by an activation energy (E) of 150.58 kJ·mol−1 and log(A in s−1) 12.06. The second stage corresponding to 24 to 90% loss in weight gave best fit for Avrami-Erofe'ev equation,n=2, withE=239.56 kJ·mol−1 and log(A in s−1) 19.88 by isothermal TG. The effect of additives, on the initial thermolysis of TATB has also been studied. Evolved gas analysis by IR showed that NH3, CO2, NO2, HCN and H2O are produced in the initial stage of decomposition. The decomposition in KBr matrix in the temperature range 272 to 311.5°C shows relative preferential loss in the -NH2 to -NO2 band intensity which indicates that the rupture of C-NH2 bond, weakened also by the interaction of the NH2 with the neighbouring NO2 group, appears to be the primary step in the thermolysis of TATB.
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  • 22
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    Journal of thermal analysis and calorimetry 46 (1996), S. 285-290 
    ISSN: 1572-8943
    Keywords: kinetics ; system FeSO4·7H2O-MnO2
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Processes which occur during the thermal treatment of system FeSO4·7H2O-MnO2 are of the interest for obtaining MnSO4, which can be easily soluted in water and separated from impurities in manganese slime in zinc metallurgy. Results of the experimental investigations of such processes are given in this paper. Kinetic parameters for the previously defined mechanism were determined using Borchardt and Daniels method.
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  • 23
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    Journal of thermal analysis and calorimetry 46 (1996), S. 377-385 
    ISSN: 1572-8943
    Keywords: crystallization ; drawing ; kinetics ; Kissinger ; Ozawa ; poly(ethylene terephthalate)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The non-isothermal crystallization kinetics of hot drawn poly(ethylene terephthalate) films were studied using the Kissinger and Ozawa equations. The influence of the initial drawing on the crystallization kinetics was investigated. The values of the apparent activation energy and of the Avrami exponent indicates that the nucleation and growth of crystallites depend greatly on the stress submitted to the samples.
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  • 24
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    Journal of thermal analysis and calorimetry 46 (1996), S. 1223-1238 
    ISSN: 1572-8943
    Keywords: dehydroxylation ; goethite ; hematite ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The kinetics of dehydroxylation of synthetic aluminous goethite was studied using isothermal and non-isothermal thermogravimetry. The complete isothermal dehydroxylation can be described by the Johnson-Mehl equation with up to three linear regions in plots of lnln [1/(1−y)]vs. Int Kinetics for the initial stage of dehydroxylation changed from diffusion to first-order through the temperature range 190 to 260°C. The rate of dehydroxylation was reduced by Al-substitution and increased with temperature. Activation energy for dehydroxylation, calculated from the time to achieve a given dehydroxylation extent, varied depending on the extent of dehydroxylation and Al-substitution. Non-stoichiometric OH existed in goethite and some remained in hematite after the complete crystallographic transition.
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  • 25
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    Journal of thermal analysis and calorimetry 46 (1996), S. 1271-1282 
    ISSN: 1572-8943
    Keywords: CrO3 ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The course of the non-isothermal decomposition of CrO3 in air was explored kinetically, by using a number of widely accepted methods. The credibility of the values obtained from a given kinetic parameter (the reaction order, the activation energy and the frequency factor) was justified on the grounds of (i) a multiple correlation coefficient, and (ii) the merits and demerits of the method adopted. The results obtained may help towards a characterization of the non-isothermal conditions under which the encountered decomposition events and products could be resolved. The study was motivated by the results of previous physicochemical characterization studies [1, 2], in which catalytically important intermediates CrOx(3〈x〈6) were structurally identified.
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  • 26
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    Journal of thermal analysis and calorimetry 46 (1996), S. 1313-1324 
    ISSN: 1572-8943
    Keywords: kinetics ; polyester resin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The isothermal and non-isothermal degradation of a typical styrenated phthalic acid-maleic acid-propylene glycol polyester were measured. Non-isothermal and isothermal kinetic analyses were performed on the various degradation steps observed. The values of the non-isothermal and the isothermal kinetic parameters are in good agreement.
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  • 27
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    Journal of thermal analysis and calorimetry 46 (1996), S. 1671-1679 
    ISSN: 1572-8943
    Keywords: kinetics ; polycarbonate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Thermal degradation of poly(2,2′,-propane-bis-4-phenyl carbonate) or bisphenol A polycarbonate (PC) alone and in presence of metal oxide as additives have been discussed. Thermal degradation of PC in presence of metal oxide additives may be surface induced catalytic thermo-oxidative degradation. Some metal oxides retard thermo-oxidative degradation of PC.
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  • 28
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    Journal of thermal analysis and calorimetry 46 (1996), S. 1657-1669 
    ISSN: 1572-8943
    Keywords: activation energy ; combustion ; differential scanning calorimetry ; kinetics ; lignite ; oxidation ; thermogravimetric analysis
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Thermal analysis increasingly being used to obtain kinetic data relating to sample decomposition. This work involves a comparative study of several methods used to analyse DSC and TG/DTG data obtained on the oxidation of Beypazari lignite. A general computer program was developed and the methods are compared with regard to their accuracy and the ease of interpretation of the kinetics of thermal decomposition. For this study, the ratio method was regarded as the preferred method, because it permits the estimation of reaction order, activation energy and Arrhenius constant simultaneously from a single experiment.
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  • 29
    ISSN: 1572-8943
    Keywords: kinetics ; thermal decomposition
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    Topics: Chemistry and Pharmacology
    Notes: Abstract The thermal behaviour of some compounds derived from 5-phenylfuran-2,3-dione was studied. The thermoanalytical data relating to the decomposition steps and intermediates were completed with mass spectrometric analysis and infrared spectroscopy results. For some of the investigated reactions, the kinetic and structural data correlated satisfactorily.
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  • 30
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    Journal of thermal analysis and calorimetry 47 (1996), S. 247-258 
    ISSN: 1572-8943
    Keywords: ethylene (vinyl acetate) ; kinetics ; polymer
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Ethylene (vinyl acetate), EVA, is a copolymer which is thermally degraded at high temperatures, with acetic acid release at approximately 620 K. This release can be studied by using thermal methods, and in particular thermogravimetric analysis. The present work was focused on establishing the polymer weight loss with temperature in order to calculate the activation energy of the overall deacetylation process. To obtain the final results, a Mettler TC50 instrument coupled with a Mettler TC11 microprocessor was used. The activation energies of four different industrial EVA formulations were calculated. The results obtained by applying different kinetic methods reported in the literature agreed reasonably well; they were compared in order to select the best method of reporting EVA deacetylation results.
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  • 31
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    Journal of thermal analysis and calorimetry 47 (1996), S. 1041-1062 
    ISSN: 1572-8943
    Keywords: kinetics ; polymerization
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    Topics: Chemistry and Pharmacology
    Notes: Abstract The method of computer experiments can be successfully applied to radical polymerization with the inclusion of initiation, propagation and termination. The convenient PC-program ‘TAkin’ for non-linear estimation of the parameters of calorimetric and thermoanalytical experiments was applied for determination of the activation parameters of chain propagation and termination. The overall evaluation of three or more data sets was preferred. The determination of the kinetic parameters proceeds satisfactorily of the measured curves are strongly different, e.g. with a changed start temperature of modified application of batch and semi-batch technique, including acceptable experimental errors. Eight recommendations for laboratory experts are given.
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  • 32
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    Journal of thermal analysis and calorimetry 47 (1996), S. 1063-1080 
    ISSN: 1572-8943
    Keywords: depolymerization ; kinetics
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    Topics: Chemistry and Pharmacology
    Notes: Abstract The method of computer-experiments can be applied successfully on the radical depolymerization under inclusion of initiation, depropagation and termination. The comfortable PC-program ‘TA-kin’ for the non-linear estimation of parameters for TG- or DSC-experiments was applied to the determination of activation parameters of depropagation and termination. Therefore the overall-evaluation of three or more data sets is a prerequisite. The determination of kinetic parameters runs satisfactory if the measured curves are strongly different, e.g. by varying the heating rate, including acceptable experimental errors. Several recommendations for laboratory experts are given. A great support for a very sufficient estimation is the inclusion of simultaneous analysis of the radical concentration.
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  • 33
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    Journal of thermal analysis and calorimetry 47 (1996), S. 1709-1718 
    ISSN: 1572-8943
    Keywords: kinetics
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Results are presented on the thermal behaviour of [Fe(III)2Cu(C2C4)2(OH)4(H2O)2] precursor of copper ferrite. An investigation of the decomposition steps and intermediates was followed by a non-isothermal kinetic analysis of the processable steps.
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  • 34
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    Journal of thermal analysis and calorimetry 46 (1996), S. 1201-1213 
    ISSN: 1572-8943
    Keywords: calcium aconitate ; DTA ; EGA ; kinetics ; SEM ; TG/DTG ; thermal decomposition
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    Topics: Chemistry and Pharmacology
    Notes: Abstract The thermal decomposition of calcium and dicalcium magnesium aconitate hydrates were studied by TG/DTG, DTA, EGA, SEM and other physico-chemical techniques. The decomposition proceeds in four stages: dehydration; oxidation of the carboxylic acid portion of the salt; complete fragmentation of the hydrocarbon portion; and finally, decarboxylation of the metal carbonate to the oxide. The crystal morphologies of the hydrate and anhydrous salts of each compound are very similar. Tricalcium aconitate consists of well-developed twinned crystals and stellate clusters intergrown with flat platy crystals. On the other hand, dicalcium magnesium aconitate crystals are monoclinic with well-developed pinacoidal faces. The activation energy,E d (43±2 kJ mol−1 water), calculated from Borchardt and Daniels' method, for the dehydration process of calcium aconitate trihydrate is of the same order of magnitude as some simple metal salt hydrates. The rate constant, kd increased from 0.04/min at 238°C to greater than 0.86/min at 295°C. It is concluded that the dehydration process is due to cation bound water.
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  • 35
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    Journal of thermal analysis and calorimetry 47 (1996), S. 445-452 
    ISSN: 1572-8943
    Keywords: catalysts ; catalyst activity ; catalyst deactivation ; DSC ; gas reactions ; kinetics
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Gas reactions, catalyzed by solid catalysts, can be measured by DSC. In the experimental set-up an open sample pan with catalyst (powder or pellet) is placed on the sample side of the DSC sensor. The reactive gas mixture flows through the cell and reacts on the catalyst surface. The heat effect, caused by this reaction, results into a DSC signal. The calibration procedure is described for quantitative evaluation of the DSC measurements. For illustration four different reaction systems are discussed.
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  • 36
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    Journal of thermal analysis and calorimetry 47 (1996), S. 535-542 
    ISSN: 1572-8943
    Keywords: cellulose ; kinetics ; thermogravimetry
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    Topics: Chemistry and Pharmacology
    Notes: Abstract The complexity of the phenomena which arise during the heating of the various substances seldom can be described by a single reaction kinetic equation. As a consequence, sophisticated models with several unknown parameters have to be developed. The determination of the unknown parameters and the validation of the models requires the simultaneous evaluation of whole series of experiments. We can accept a model and its parameters if, and only if we get a reasonable fit to several experiments carried out at different experimental conditions. In the field of the thermal analysis the method of least squares alone seldom can select abest model or abest set of parameter values. Nevertheless, the careful evaluation of the experiments may help in the discerning between various chemical or physical assumptions by the quality of the corresponding fit between the experimental and the simulated date. The problem is illustrated by the thermal de-composition of cellulose under various experimental conditions.
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  • 37
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    Molecular and cellular biochemistry 156 (1996), S. 93-100 
    ISSN: 1573-4919
    Keywords: rat liver nucleus ; oxalate binding protein ; histone III ; purification ; kinetics
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    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract The rat liver nuclear oxalate binding protein was isolated, purified by anion and cation exchange column chromatography using Diethyl Amino Ethyl Sephadex, Carboxy Methyl Cellulose and Carboxy Methyl Sephadex C-50 ion exchangers. The purified oxalate binding protein was found to be H1B of H1 fraction of histories. Kinetic analysis of oxalate binding showed the presence of two affinity sites, one with Kd of 133.5 nM and Bmax of 40 pmoles and another with Kd of 262.5 nM and Bmax of 210 pmoles. The optimal oxalate binding was at pH 4.2 and at 28°C. The oxalate binding was specific and reversible and not due to ionic charge interaction. The IC50 of other dicarboxylates was higher than that of oxalate. EGTA had no effect on oxalate binding but di- and tri-carboxylate carrier inhibitors and thiol modifying agents significantly lowered the binding activity. Oxalate binding to histones was significantly reduced in the presence of DNA or nucleotides, but RNA had no effect. ATP completely inhibited the oxalate binding activity at 1 mM concentration. Different tissues exhibited oxalate binding showing ubiquitous nature. Calf thymus H1 showed maximal binding similar to liver histones.
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  • 38
    ISSN: 1573-4919
    Keywords: acetylcholinesterase ; kinetics ; inhibition ; methotrexate ; anticancer drugs ; human erythrocyte
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    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract This work addresses the kinetic analysis of the interaction of methotrexate (MTX) with human erythrocyte membrane-bound acetylcholinesterase (AChE, EC 3.1. 1.7). It was found that the MTX effect was independent of time of incubation with AChE before the addition of substrate which proves its reversible action. The IC50 was determined, by three methods, to be 0.73 mM. The Michaelis-Menten constant (Ks) for the hydrolysis of acetylthiocholine iodide (ASCh) by AChE was 0.13 mM in the control system, a value decreased by 30–61% in the MTX treated systems. The Vmax was 1.27μtmole/min/mg protein for the control system while it was decreased by 44–77% in the MTX treated systems. The Linexveaver-Buck plot, Dixon plot, and their secondary replots indicated that the nature of the inhibition was of the linear mixed type, i.e. uncompetitive and noncompetitive. The values of Ki(slope) and KI(tntecept) were estimated as 1.67 and 0.34 mM, respectively.
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  • 39
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    Journal of fluorescence 6 (1996), S. 165-168 
    ISSN: 1573-4994
    Keywords: Cation binding ; fluorescence decay ; kinetics ; binding constants ; Na,K-ATPase ; eosin Y
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    Topics: Physics
    Notes: Abstract Time-resolved fluorescence and binding studies have been carried out on Na,K-ATPase in the presence of the fluorescent dye eosin Y to obtain thermodynamic and kinetic parameters for the interaction of the enzyme with different cations. Eosin Y binding is indicated by a 3 ns fluorescence decay process and is observed only in the presence of mono- and divalent cations. This type of cation binding is interpreted as a nonselective electrostatic interaction, with negatively charged groups of the enzyme providing a high-affinity eosin Y binding site. Eosin Y binding is observed only under conditions where the enzyme exists in the conformational state F1. The kinetic parameters of eosin Y binding have been determined employing stopped-flow fluorometry.
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  • 40
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    The protein journal 15 (1996), S. 631-637 
    ISSN: 1573-4943
    Keywords: Aminocyclase ; denaturation ; inactivation ; conformation ; kinetics
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    Topics: Chemistry and Pharmacology
    Notes: Abstract The inactivation and unfolding of aminoacyclase (EC 3.5.1.14) during denaturation by different concentrations of trifluoroethanol (TFE) have been studied. A marked decrease in enzyme activity was observed at low TFE concentrations. The kinetic theory of the substrate reaction during irreversible inhibition of enzyme activity described previously by Tsou [Tsou (1988),Adv. Enzymol. Related Areas Mol. Biol. 61, 381–436] was applied to study the kinetics of the inactivation course of aminoacyclase during denaturation by TFE. The inactivation rate constants for the free enzyme and substrate-enzyme complex were determined by Tsou's method. The inactivation reaction was a monophasic first-order reaction. The kinetics of the unfolding course were a biphasic process consisting of two first-order reactions. At 2% TFE concentration, the inactivation rate of the enzyme was much faster than the unfolding rate. At a higher concentration of TFE (10%), the inactivation rate was too fast to be determined by conventional methods, whereas the unfolding course remained as a biphasic process with fast and slow reactions occurring at measurable rates. The results suggest that the aminoacyclase active site containing Zn2+ ions is situated in a limited and flexible region of the enzyme molecule that is more fragile to the denaturant than the protein as a whole.
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  • 41
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    Russian chemical bulletin 45 (1996), S. 2760-2762 
    ISSN: 1573-9171
    Keywords: chemiluminescence ; kinetics ; xenon trioxide ; europium(II,III) ions
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Chemiluminescence has been observed in the reduction of perchloric aqueous solutions of XeO3 with Eu2+ ions, Fast (several seconds) consumption of EuII occurs when the ratio of the initial concentrations of the reactants (Eu2+]0 : [XeO3]0 〈 6; however, the chemiluminescence remains sufficiently bright and prolonged (up to −10 min after nearly complete oxidation of EuII to EuIII). The assumption was made that intermediates in the reduction of XeO3 participate in the chemiluminescent stages of the process.
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  • 42
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    Russian chemical bulletin 45 (1996), S. 328-334 
    ISSN: 1573-9171
    Keywords: vapor nitration ; cellulose ; nitric anhydride ; kinetics ; diffusion constant
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    Topics: Chemistry and Pharmacology
    Notes: Abstract The kinetics of vapor nitration of cellulose with nitric anhydride at various pressures was studied under conditions of natural convection in the absence of air, using the nonisothermal kinetic method. The process rate was found to be proportional to the N2O5 pressure. The nitration is described by a law of the dη/dt =k 1/(1+βν) type, wherek 1 = 103.82±0.5 exp[-(36000±(RT)]p N 2O5 s−1. β = 10−7.33±1.4exp[(41300±8000)/(RT)] s−1, s−1, within the extents of conversion from 0.04 to 0.4. At high levels of conversion, the nitration occurs with autoacceleration caused by the accumulation of the HNO3 formed. The diffusion mechanism of vapor nitration of cellulose was suggested and discussed. The values of the effective diffusion constant for N2O5 in cellulose and the corresponding activation energy (38.4±2.8 kJ mol−1) have been estimated.
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  • 43
    ISSN: 1573-9171
    Keywords: complex formation ; kinetics ; sodium dodecyl sulfate ; copper(II) ; 2-dimethylaminomethylphenol
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    Topics: Chemistry and Pharmacology
    Notes: Abstract The effects of the anionic surfactant sodium dodecyl sulfate on complex formation of 2-dimethylaminomethylphenol (1) with copper(u) in aqueous solutions and on the kinetics of the reactions of copper(n) complexes of 1 with 4-nitrophenylbis(chloromethyl)phosphinate (2) were studied. The reactivities of the complexes in these reactions are higher than that of 1 at all concentrations of SDS studied (0.010–0.200 mol L−1 with pH 7–9.
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  • 44
    ISSN: 1573-9171
    Keywords: unsaturated nitroxyl radicals ; secondary amines ; addition ; kinetics ; mechanism
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Routes for the reaction of a conjugated methylene group of nitroxyl radicals (NR) with secondary amines were suggested and analyzed. Kinetic parameters of the limiting step of this reaction for the NR-amine and diamagnetic analog of NR-amine systems were estimated. The effect of the medium on these reactions was examined. The specific behavior of polyethyleneimine in the reaction with activated methylene groups of 2,2,6,6-tetra methyl-3, 5-dimethylene-4-oxopiperidine-i-oxyl was demonstrated.
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  • 45
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    Russian chemical bulletin 45 (1996), S. 871-874 
    ISSN: 1573-9171
    Keywords: Kharash reaction ; catalysis ; iron pentacarbonyl ; kinetics ; thermal stability ; thermal reaction with CCl3X (X = Br, Cl) ; effect of olefin and DMF
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Fe(CO)5 is sufficiently stable at 80 °C in benzene solution and its thermal decomposition is not accelerated in the presence of phenyl cinnamate or/and DMF. The decomposition is accelerated by CCl3Br (drastically) and by CCl4 (to a lesser extent). DMF accelerates the reaction of Fe(CO)5 with CCl4. The (FeCl(DMF)5]2+[Cl3FeOFeCl3]2− complex has been isolated as a product; its composition and structure have been determined by X-ray analysis. The obtained data indicate the absence of coordination of DMF or/and an olefin with Fe0 species at the stage preceding oxidation. The mechanisms of the generation of CCl3 radicals in thermal and photochemical Kharash reactions in the presence of Fe(CO)5 are basically different. The probable pathways of the effect of DMF on the rate of the oxidative decomposition of Fe(CO)5 are discussed.
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  • 46
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    Russian chemical bulletin 45 (1996), S. 1875-1878 
    ISSN: 1573-9171
    Keywords: 2,4,6-trinitrotoluene ; thermal decomposition ; solvent effect ; chain mechanism ; dissociation energy of C-H bond ; kinetics
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    Topics: Chemistry and Pharmacology
    Notes: Abstract The rate constants for the thermal decomposition of 2,4,6-trinitrotoluene have been measured in toluene and other hydrocarbon solvents. The initial, observed rate constant (k i) increases with dilution with toluene. The concentration dependence is described by the chain decomposition scheme with the transfer of the free valence to a solvent molecule. The activation energy and logk i were found to linearly correlate with the dissociation energy of the C-H bond of the solvent.
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  • 47
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    Russian chemical bulletin 45 (1996), S. 1879-1882 
    ISSN: 1573-9171
    Keywords: cellulose ; nitration ; nitric acid ; kinetics ; diffusion coefficient
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    Topics: Chemistry and Pharmacology
    Notes: Abstract The regularities of vapor-phase nitration of cellulose with HNO3 under conditions of natural convection and hindered heat removal in the absence of air were studied using the nonisothermal kinetic method. It was established that the nitration rate at the depth of conversion of 0.08 to 0.7 is described by the kinetic law dη/dt =k 1 p/(1+βη), wherek 1 = 104.49±0.6 exp(−A/RT) s−1 atm−1, β = 10−35.5±15.7exp(B/RT),A = 36.6±3.8 kl mol−1, andB = 203±88 kJ mol−1. The diffusion mechanism of vapor-phase nitration of cellulose, which explains the high value of activation energies, is discussed. The effective diffusion coefficient of HNO3 in cellulose at 25 °3.7 · 10−7 cm2 s−1) and the activation energy of diffusion (38.3±4.2 kJ mol−1) were estimated.
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    Russian chemical bulletin 45 (1996), S. 1883-1888 
    ISSN: 1573-9171
    Keywords: decane ; nitric acid ; nitrogen dioxide ; oxidation ; kinetics ; mechanism
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    Topics: Chemistry and Pharmacology
    Notes: Abstract The kinetics of the reaction of decane with nitric acid (25.07–75.53 %) at 57.8 to 119 °C in an acid-decane-gas triphasic system was studied. The main contribution to the rate of heat release is made by the oxidation of decane with nitrogen dioxide in the organic phase proceedingvia the mechanism of a degenerate branched-chain reaction. Nitration plays the role of a chain termination reaction. The acid phase is the source of NO2, whose content increases with oxidation. The equilibrium of the nitrogen dioxide distribution in the triphasic system was analyzed. The kinetic law of the reaction, the dependences of the reaction constants of the initial and catalytic stages on temperature and the acid phase composition were determined. The results allow one to calculate the rate of heat release in the decane-HNO3 system under any conditions of the process.
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  • 49
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    Acta mechanica Sinica 12 (1996), S. 144-157 
    ISSN: 1614-3116
    Keywords: microstructural evolution ; energetics ; kinetics ; dynamic system
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract An evolving material structure is in a non-equilibrium state, with free energy expressed by the generalized coordinates. A global approach leads to robust computations for the generalized thermodynamic forces. Those forces drive various kinetic processes, causing dissipation at spots, along curves, surfaces and interfaces, and within volumetric regions. The actual evolution path, and therefore the final equilibrium state, is determined by the energetics and kinetics. A virtual work principle links the free energy landscape and the kinetic processes, and assigns a viscous environment to every point on the landscape. The approach leads to a dynamical system that governs the evolution of generalized coordinates. The microstructural evolution is globally characterized by a basin map in the coordinate space; and by a diversity map and a variety map in the parameter space. The control of basin boundaries raises the issue of energetic and kinetic bifurcations. The variation of basin boundaries under different sets of controlling parameters provides an analytical way to plot the diversity maps of structural evolution.
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  • 50
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    Hyperfine interactions 101-102 (1996), S. 155-162 
    ISSN: 1572-9540
    Keywords: muon ; muonic hydrogen ; muonic molecule ; deuterium ; tritium ; fusion ; solid target ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The emission of µd and µt atoms from multilayer solid targets consisting of the mixtures of hydrogen isotopes has been investigated with a kinetics model. The methods to study the elastic scattering of muonic atoms, muon transfer, and molecular formation reactions with µ-atomic beams are discussed.
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    Hyperfine interactions 101-102 (1996), S. 163-167 
    ISSN: 1572-9540
    Keywords: muon ; muonic hydrogen ; energy distribution ; kinetics
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    Topics: Physics
    Notes: Abstract The kinetics of muonic atoms of hydrogen isotopes in an axially symmetric trap is studied. The problem of the determination of the initial kinetic energy distribution of µp and µd atoms from time-of-flight spectra is discussed. The effects of the scattering of muonic atoms from gas and of the stopping distribution are evaluated. When the collision length is much larger than the target radius, the moments of the kinetic energy distribution are shown to be determined by the time-of-flight spectrum in a model-independent way.
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  • 52
    ISSN: 1573-0778
    Keywords: hybridomas ; serum-free medium ; monoclonal antibodies ; reactor series ; kinetics ; modeling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Hybridomas were cultured under steady-state conditions in a series of two continuous stirred-tank reactors (CSTRs), using a serum-free medium. The substrate not completely converted in the first CSTR, was transported with the cells to the second one and very low growth rates, high death rates, and lysis of viable cells were observed in this second CSTR. These conditions are hardly accessible in a single vessel, because such experiments would be extremely time-consuming and unstable due to a low viability. In contrast to what is often observed in literature, kinetic parameters could thus be derived without the neccessity for extrapolation to lower growth rates. Good agreement with literature averages for other hybridomas was found. Furthermore, showing that the reactor series is a valuable research tool for kinetic studies under extreme conditions, the possibility to observe cell death under stable and defined steady-state conditions offers interesting opportunities to investigate apoptosis and necrosis. Additionally, a model was developed that describes hybridoma growth and monoclonal antibody production in the bioreactor cascade on the basis of glutamine metabolism. Good agreement between the model and the experiments was found.
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  • 53
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    Journal of pharmacokinetics and pharmacodynamics 24 (1996), S. 19-44 
    ISSN: 1573-8744
    Keywords: indocyanine green ; hepatic removal ; liver function test ; organic anions ; kinetics ; protein binding ; physiologically based pharmacokinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Indocyanine green (ICG) is used in cardiology and hepatology for the estimation of cardiac output, liver function, and splanchnic blood flow. ICG is bound to plasma proteins and ultimately excreted by the liver. We studied the whole body kinetics of ICG during constant infusion in pigs weighing 30–40 kg. The conventional kinetic model (backflux model) assumes that deviations from one-compartmental linear kinetics is caused by backflux from a liver storage to plasma, and that no extravascular, extrahepatic distribution takes place. This model was tested against an alternative (redistribution) model postulating that temporary redistribution of ICG into an extrahepatic extravascular storage was responsible for the deviations while the hepatic uptake was a one-way first-order process. A mathematical analysis of the two models showed that they predicted different time courses of the hepatic extraction fraction of ICG. Thus, with blood sampling from both a peripheral artery and a hepatic vein, a discriminative model-testing experiment was possible. This test required a first-order steady-state hepatic removal of ICG which was confirmed in 7 experiments with infusion rates varied in a stepwise fashion (0.133±0.003, 0.269±0.010, 0.547±0.020 and 0.130±0.003 μmol·min1). In the model-testing experiments (n=10) ICG was infused at a constant rate of 0.135±0.007 μmol·min1. The mean concentration in peripheral artery (μM) was well fitted by the biexponential functionC(t)=0.476·(1–0.632·e0.216–1−0.368·e0.0172–1). The time course of the observed hepatic extraction fraction was significantly different (p=0.004) from that predicted from the backflux model but in agreement (p=0.98) with the new model assuming hepatic removal to be a one-way process and implying temporary ICG redistribution into an extrahepatic, extravascular storage with an apparent volume of 0.144±0.023 L·Kg1. Accordingly, extravascular ICG was demonstrated in a number of different tissues after 4-hr infusion (n=3). If ICG is used to estimate hepatic blood flow according to Fick's principle, the use of a backflux model to correct for non-steady-state conditions will lead to an overestimation of hepatic blood flow of 28% after 25-min infusion, 16% after 50 min, and 6% after 100 min. The study indicated that distribution of ICG between plasma and tissues is not instantaneous, and that the time course of the redistribution itself significantly influences whole body kinetics. Comparison with a previously published study by Ott, Keiding, and Bass of ICG kinetics after bolus injection suggested that a two-compartment model was insufficient and that the kinetics for the exchange of ICG between plasma and the redistribution space may be nonlinear. The study demonstrates how blood sampling on both sides of the eliminating organ can expose the influence of redistribution. The discriminative model test for constant infusion experiments is novel and may be useful with other ligands.
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  • 54
    ISSN: 1573-904X
    Keywords: hIGF-I ; oxidation ; methionine ; HPLC ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Purpose. The aim of this work was to study the kinetics of oxidation of methionine in human Insulin-like Growth Factor I (hIGF-I)1 in aqueous solution and in the solid state by the aid of quantification of oxygen. Methods. The oxidized form of hIGF-I was characterized by tryptic peptide analysis, RP-HPLC and FAB-MS and quantified by RP-HPLC. The oxygen content was quantified polarographically by a Clark-type electrode. Results. Second-order kinetics with respect to amount of protein and dissolved oxygen was found to be appropriate for the oxidation of methionine in hIGF-I. The rate constants ranged from 1 to 280 M−1 month−l and had an activation energy of 95 (+/−4) kJ/mole. Light exposure, storage temperature and oxygen content were found to have a considerable impact on the oxidation rates. No significant difference in reaction rates was found for the oxidation of hIGF-I in aqueous solution or in the solid state. A method for decreasing the oxygen content in aqueous solution without purging is described. Conclusions. Polarographic quantification of dissolved oxygen makes it possible to establish the kinetics for oxidation of proteins. The oxidation of methionine in hIGF-I appears to follow second-order kinetics.
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    Plant and soil 181 (1996), S. 169-173 
    ISSN: 1573-5036
    Keywords: kinetics ; microbial biomass ; model
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Many models that describe the turnover of the microbial biomass in soil use either first order kinetics where the rate of turnover is directly proportional to the microbial mass, or a variant of the Michaelis-Menten law that describes enzyme kinetics. To account for the different rates of microbial turnover observed at different times after the addition of substrate, some authors have suggested the existence of more than one pool of biomass. Each pool obeys the same kinetic law but with a different rate. In other experiments a disproportionately large increase in the turnover of native organisms has been observed relative to the amount of fresh substrate added. A change in the kinetic law describing the turnover of organisms can account for these observations and yet retain the simplicity of a single pool of micro-organisms. However where multiple pools of organisms are justified a mixed kinetic law with both first and second order terms may be more appropriate; in other words one pool of micro-organisms but two rate constants. The advantage of retaining a single pool of microbial biomass is that models may more readily be constructed in relation to the routine measurements of total microbial mass.
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    Photosynthesis research 48 (1996), S. 411-417 
    ISSN: 1573-5079
    Keywords: chlorophyll a fluorescence ; kinetics ; Photosystem II ; quinone acceptors ; S-states of oxygen-evolving complex
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The flash-induced kinetics of various characteristics of Photosystem II (PS II) in the thylakoids of oxygenic plants are modulated by a period of two, due to the function of a two-electron gate in the electron acceptor side, and by a period of four, due to the changes in the state of the oxygen-evolving complex. In the absence of inhibitors of PS II, the assignment of measured signal to the oxygen-evolving complex or to quinone acceptor side has frequently been done on the basis of the periodicity of its flash-induced oscillations, i.e. four or two. However, in some circumstances, the period four oscillatory processes of the donor side of PS II can generate period two oscillations. It is shown here that in the Kok model of oxygen evolution (equal misses and equal double hits), the sum of the concentrations of the S 0 and S 2 states (as well as the sum of concentrations of S 1 and S 3 states) oscillates with period of two: S 0+S 2→S 1+S 3→S 0+S 2→S 1+S 3. Moreover, in the generalized Kok model (with specific miss factors and double hits for each S-state) there always exist such ε0, ε1, ε2, ε3 that the sum ε0[S0] + ε1[S1] + ε2[S2] + ε3[S3] oscillates with period of two as a function of flash number. Any other coefficients which are linearly connected with these coefficients, % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGak0dh9WrFfpC0xh9vqqj-hEeeu0xXdbba9frFj0-OqFf% ea0dXdd9vqaq-JfrVkFHe9pgea0dXdar-Jb9hs0dXdbPYxe9vr0-vr% 0-vqpWqaaeaabiGaciaacaqabeaadaqaaqaaaOqaaiqbew7aLzaaja% aaaa!3917!\[\hat \varepsilon \]i = c1εi + c2, also generate binary oscillations of this sum. Therefore, the decomposition of the flash-induced oscillations of some measured parameters into binary oscillations, depending only on the acceptor side of PS II, and quaternary oscillations, depending only on the donor side of PS II, becomes practically impossible when measured with techniques (such as fluorescence of chlorophyll a, delayed fluorescence, electrochromic shift, transmembrane electrical potential, changes of pH and others) that could not spectrally distinguish the donor and acceptor sides. This property of the Kok cycle puts limits on the simultaneous analysis of the donor and acceptor sides of the RC of PS II in vivo and suggests that binary oscillations are no longer a certain indicator of the origin of a signal in the acceptor side of PS II.
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    Journal of atmospheric chemistry 24 (1996), S. 23-37 
    ISSN: 1573-0662
    Keywords: hydroxyl radical ; dimethylsulfoxide ; kinetics ; sulfur cycle
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract We have employed a pulsed laser photolysis-pulsed laser induced fluorescence technique to study the kinetics and mechanism of the reaction of OH with dimethylsulfoxide and its deuterated analogue. A rate coefficient of (1.0±0.3)×10-10 cm3 molecule-1 s-1 was obtained ar room temperature. The rate coefficient was independent of pressure over the range 25–700 Torr, showed no dependence on the nature of the buffer gas and showed no kinetic isotope effect. A limited study of the temperature dependence indicated that the reaction displays a negative activation energy. The gas phase ultraviolet absorption spectrum was obtained at room temperature and showed a strong absorption feature in the far ultraviolet. The absolute absorption cross-section at 205 nm, the absorption peak, is (1.0±0.3)×10-17 cm2, where the large uncertainty results from experimental difficulties associated with the low vapor pressure and ‘stickiness’ of DMSO.
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  • 58
    ISSN: 1573-5036
    Keywords: high-affinity ; kinetics ; low-affinity ; potassium ; regulation ; transport
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Over the last five years, the cloning and characterization of K+ transport genes corresponding to K+ channels (KAT1, AKT1, KST1, AKT2), associated subunits (KAB1) and a high-affinity transporter (HKT1) has opened up important new avenues for research on plant K+ nutrition. With the abundance of molecular data now available it seems timely to link this information with the wealth of data previously accumulated on the physiology of plant K+ acquisition. The ultimate goal of all this research is to gain a better understanding of K+ transport and nutrition in the intact plant. Thus it is important to begin to integrate the molecular research with results from biochemical and physiological research conducted at the cellular, root and whole plant levels. This article will focus on describing the features of the cloned K+ transporters and their possible roles in mediating high- and low-affinity K+ uptake from the soil, as well as how K+ acquisition may be regulated.
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    Photosynthesis research 49 (1996), S. 37-48 
    ISSN: 1573-5079
    Keywords: cytochrome f ; kinetics ; midpoint potential ; plastocyanin ; P700 ; Rieske centre
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Effects of three inhibitors of quinol oxidation in the chloroplast cytochrome bf complex (stigmatellin, tridecylstigmatellin and dibromothymoquinone) were studied in an isolated system comprising Photosystem I (PS I) particles, plastocyanin (PC) and cytochrome bf complex, in the absence of quinol or quinone. Addition of these inhibitors increased the extent of cytochrome f oxidation after a laser flash created oxidised PS I reaction centre (P700) and PC, and decreased somewhat the extent of PC oxidation. The re-reduction of oxidised P700 was more complete than when inhibitor was absent. The data were simulated with reactions which included the putative reduction of cytochrome f by the Rieske centre (FeS) and different rate-coefficients according as to whether inhibitor was bound to the bf complex or not. It was concluded that under the conditions studied the Rieske centre donated electrons to oxidised cytochrome f and plastocyanin with an average rate coefficient of 35 s−1. This electron transfer was prevented by any of the three inhibitors, which also increased the equilibrium coefficient for the cytochrome f/PC reaction by a maximum factor of two. This increase corresponded to a decrease in the back reaction coefficient and an increase in the forward rate. The equilibrium coefficient for the reduction of oxidised P700 by PC was about 2 in the absence of inhibitor but increased to about 20 in their presence, but only if cytochrome bf complex was additionally present. This was attributed to the transient formation of complexes between P700 with bound plastocyanin, and bf complex. The operative mid-point potential of FeS, if that of cytochrome f is 370 mV, was 390 mV. Deviations in midpoint potentials (P700/plastocyanin) from solution values were attributed to the bound state of the reactants. Estimates were made of the binding coefficient of each of the three inhibitors to p-sites in the cytochrome bf complex in the absence of competing quinol. A stoichiometry of two inhibitors per bf dimer was necessary to cause the above changes in reduction potential of cyt f and PC. A result of one inhibitor per dimer was statistically unlikely, particularly in the case of tridecylstigmatellin.
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    Water, air & soil pollution 90 (1996), S. 295-300 
    ISSN: 1573-2932
    Keywords: dechlorination ; coulometry ; sulfite ; water ; rate ; chloramine ; residual ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract The kinetics of dechlorination show that chlorinated organic amines are not completely dechlorinated during typical contact times. Analytical techniques for measuring residual sulfite must maintain pH neutrality in order to represent the actual extent of dechlorination and must allow for rapid and convenient operation near the sampling site in order to minimize errors due to air oxidation during the procedure. A portable, analog circuitry-based instrument using constant current coulometry with amperometric end point detection was developed and evaluated. laboratory and field operation of the instrument showed an analytical range of 0.015-to-25.0 mg sulfite/l. Relative standard deviation was typically 1–2%.
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  • 61
    ISSN: 1573-5168
    Keywords: temperature ; malate dehydrogenase ; acclimation ; adaptation ; grass carp ; Ctenopharyngodon idella ; teleost fish ; thermostability ; isozyme ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Malate dehydrogenase isozymes of grass carp,Ctenopharyngodon idella, were identified by mitochondrial preparation and thermal denaturation. The structural and kinetic characteristics of chromatographically separated thermostable and thermolabile cMDHs were different in (1) half-life at 42°C, 10 min and 24 h, respectively, (2) optimal substrate, oxaloacetate and malate, concentrations, and (3) the apparent Michaelis-Menten constants of NADH and oxaloacetate. Total MDH activity in white muscle of 11°C-acclimated fish was about twice that of the 30°C-acclimated group. In addition, the ratio of the thermostable to thermolabile cMDH activity in white muscle of 30°C-acclimated fish was significantly higher than that of 11°C-acclimated fish. These results suggest that temperature acclimation can induce temperature compensation in MDH activity and differential expression of thermostable and thermolabile cMDH isozymes in freshwater fish.
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    Reaction kinetics and catalysis letters 58 (1996), S. 97-103 
    ISSN: 1588-2837
    Keywords: Phthalimide ; methylamine ; aminolysis ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract In aqueous methylamine buffers of pH 10.21–11.25 nucleophilic cleavage of ionized (S−) phthalimide and general base-catalyzed cleavage of nonionized (SH) phthalimide is observed.
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    Reaction kinetics and catalysis letters 57 (1996), S. 21-27 
    ISSN: 1588-2837
    Keywords: Phenol ; alkylation ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A kinetic study of phenol alkylation with methanol in the presence of γ-Al2O3 has been carried out. A mechanism involving the reaction of phenol and methanol adsorbed on acid-base pair sites is proposed.
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    Reaction kinetics and catalysis letters 59 (1996), S. 75-86 
    ISSN: 1588-2837
    Keywords: Pt carbonyl clusters ; CO+NO reaction ; NaY ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract [Pt12(CO)24]2−/NaY and [Pt9(CO)18]2−/NaY exhibited much higher activities in the CO+NO reaction at 473 K compared with Pt/Al2O3. Kinetic study andin-situ FTIR results suggest that NO adsorption is the rate-limiting step in the CO+NO reaction on intrazeolite Pt carbonyl clusters.
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    World journal of microbiology and biotechnology 12 (1996), S. 549-556 
    ISSN: 1573-0972
    Keywords: Bacteria inactivation ; chlorine decay ; combined chlorine ; drinking water ; free chlorine ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract The decay of free chlorine (Cl2) and combined chlorine (mostly monochloramine: NH2Cl) and the inactivation of bacteria was examined in Dar es Salaam, Tanzania. Batch experiments, pilot-scale pipe experiments and full-scale pipe experiments were carried out to establish the kinetics for both decay and inactivation, and to compare the two disinfectants for use under tropical conditions. The decay of both disinfectants closely followed first order kinetics, with respect to the concentration of both disinfectant and disinfectant-consuming substances. Bacterial densities exhibited a kinetic pattern consisting of first order inactivation with respect to the density of the bacteria and the concentration of the disinfectant, and first order growth with respect to the bacterial density. The disinfection kinetic model takes the decaying concentration of the disinfectant into account. The decay rate constant for free chlorine was 114 lg-1h-1, while the decay rate constant for combined chlorine was 1.84 lg-1h-1 (1.6% of the decay rate for free chlorine). The average concentration of disinfectant consuming substances in the water phase was 2.6 mg Cl2/l for free chlorine and 5.6 mg NH2Cl/l for combined chlorine. The decay rate constant and the concentration of disinfectant consuming substances when water was pumped through pipes, depended on whether or not chlorination was continuous. Combined chlorine especially could clean the pipes of disinfectant consuming substances. The inactivation rate constant λ, was estimated at 3.06×104 lg-1h-1. Based on the inactivation rate constant, and a growth rate constant determined in a previous study, the critical concentration of free chlorine was found to be 0.08 mg Cl2/l. The critical concentration is a value below which growth rates dominate over inactivation.
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    Journal of inclusion phenomena and macrocyclic chemistry 26 (1996), S. 311-319 
    ISSN: 1573-1111
    Keywords: Intercalation ; X-ray powder diffraction ; thermomechanical analysis ; volumetry ; vanadyl ; phosphate ; ethanol ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The course of intercalation of ethanol into VOPO4 has been studied by X-ray diffraction, thermomechanical analysis and a volumetric method. In all cases the kinetic curves were observed to have a sigmoidal shape. A model, based on the Avrami equation, has been proposed for description of the kinetic behavior. The activation energy of intercalation based on this model has been determined. The existence of the advancing phase boundary in the system during intercalation has been confirmed.
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    Interface science 3 (1996), S. 241-267 
    ISSN: 1573-2746
    Keywords: grain boundary segregation ; grain boundary cohesion ; fracture ; kinetics ; equilibrium ; anisotropy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract This feature article summarizes the present art and science of grain boundary segregation from the viewpoint of the authors activities in this field. In the part on equilibrium segregation, fundamental effects on grain boundary segregation are discussed such as the nature of the solute/matrix binary system, presence of additional elements, temperature, grain boundary orientation and type of interface. In addition, the predictive capabilities of grain boundary segregation diagrams are outlined. The present models of segregation kinetics are reviewed and discussed in connection with recent experiments. The last part of the paper is focussed on the most important consequences of grain boundary segregation, i.e., grain boundary cohesion and fracture.
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    Journal of elasticity 44 (1996), S. 271-284 
    ISSN: 1573-2681
    Keywords: martensite ; kinetics ; driving traction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract A purely mechanical, sharp interface model is developed to consider curved interfaces that have been observed between martensite phase variants. The approach is based on a theory of small strains as distinct from small displacement gradients. It admits a realistic characterization of each phase with standard elasticity tensors and allows for inhomogeneous states of strain within each phase including inhomogeneous, finite rotations. The model indicates that any signficant interface curvature must be due to material rotation because interfaces cannot be finitely curved with respect to the material lattice. It is also found that the interface driving traction is not influenced by local lattice rotations unless inertia affects the reaction.
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    Bulletin of experimental biology and medicine 121 (1996), S. 329-330 
    ISSN: 1573-8221
    Keywords: erythropoiesis ; kinetics ; cell death
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The fundamental patterns of influence of the localization of erythroid cell death on cell kinetics are defined with the aid of mathematical modeling. It is established that the kinetic picture is mainly dictated by the region where the death is localized.
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    Russian chemical bulletin 45 (1996), S. 60-63 
    ISSN: 1573-9171
    Keywords: C-iodotetrazole, thermolysis ; kinetics ; mass spectrometry ; IR spectroscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Thermal decomposition of 1-substitutedC-iodotetrazoles in melt and solutions has been investigated. Thermal stabilities, kinetic and activation parameters, and compositions of products of thermolysis ofC-iodotetrazolcs depend on the substituent nature. The scheme of thermolysis ofC-iodotetrazoles has been suggested.
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