Method For Kinetic Analysis Research Articles

Effect of multiwalled carbon nanotubes on the kinetics of the aniline polymerization: the semi-quantitative OCP approach.

We demonstrate applicability of the open-circuit potential (OCP) method for kinetic analysis of the oxidative chemical polymerization of aniline both in clear solution and in dispersions of multiwalled carbon nanotubes (MWCNT). The characteristic points and the shape of the OCP profile are used to estimate the kinetic parameters of the main stages of the known two-step polymerization mechanism of aniline. We have found that the reciprocal values of the duration of the main polymerization stages namely the induction period, pernigraniline (PN) accumulation and reduction of PN with residual aniline are the linear functions of the weight fraction of MWCNT. To compare the kinetic data of the proposed OCP and known approaches the last two stages have been considered as a single heterogeneous stage of emeraldine (EM) formation. The kEM rate constant calculated by the OCP profiles for this EM stage in the solution and dispersion media is in a very good agreement with the known k2 values.

TG/DTG/DTA data used for determining the kinetic parameters of the thermal degradation process of an immunosuppressive agent: mycophenolate mofetil

Mycophenolate mofetil is a strong immunosuppressive therapeutic agent that was primely licensed to prevent rejection of transplanted organs. The decomposition reactions of pharmaceuticals, alongside other processes that occur, are important ones from both fundamental and practical point of view. The thermal stability of pharmaceuticals is important from both fundamental and clinical point of view. Kinetic analysis is one of the best method for an objective and less speculative determination of the Life Time Prediction. Following the ICTAC 2000 Protocol, the thermal behavior of mycophenolate was recorded at five different heating rates, in air atmosphere. The activation energy for the main degradation process was obtained by using four isoconversional methods of kinetic analysis: Friedman, Flynn–Wall–Ozawa, Kissinger–Akahira–Sunose and modified nonparametric kinetic methods. The obtained values of the activation energy were in a very close range.

Thermogravimetric analysis of the behavior of sub-bituminous coal and cellulosic ethanol residue during co-combustion

The influence of the addition of cellulosic ethanol residue (CER) on the combustion of Indonesian sub-bituminous coal was analyzed by non isothermal thermo-gravimetric analysis (TGA). The effect of blends ratio (5%, 10%, 15% and 20%), interaction mechanism, and heating rate (5°C/min, 10°C/min, 15°C/min, 20°C/min) on the combustion process was studied. The results show that the increase of the blending ratio allows to achieve the increase of the combustibility index from 7.49E−08 to 5.26E−07 at the blending ratio of 20%. Two types of non-isothermal kinetic analysis methods (Ozawa–Flynn–Wall and Vyazovkin) were also applied. Results indicate that the activation energy of the blends decreases with increasing the conversion rate. In particular, the blending ratio of 20% confirms to have the better combustion performance, with the average value of the activation energy equal to 41.10kJ/mol obtained by Ozawa–Flynn–Wall model and 31.17kJ/mol obtained by Vyazovkin model.

Application of model-free kinetic analysis methods to dehydration of a HEU-type zeolite rich tuff from Turkey

AbstractNon-isothermal dehydration kinetics of a heulandite-type zeolite-rich tuff from Turkey was investigated using thermogravimetric data recorded at three different heating rates (5, 10 and 20°C/min) under nitrogen flow. Isoconversional model-free methods gave a constant activation energy over the temperature range 30–200°C suggesting that the dehydration is a single-step process within this temperature range. The apparent activation energy was determined as: 34.54±1.18, 30.99±1.14 and 27.79±1.42 kJ/mol by the Flynn–Wall–Ozawa, the Kissinger–Akahira–Sunose and the Friedman methods, respectively. The activation energy values determined were less than the activation energy for vaporization of bulk water, indicating control of the dehydration rate by diffusion of water within this temperature range.

Piezoresistive microcantilever aptasensor for ricin detection and kinetic analysis

Up to now, there has been no report on target molecules detection by a piezoresistive microcantilever aptasensor. In order to evaluate the test performance and investigate the response dynamic characteristics of a piezoresistive microcantilever aptasensor, a novel method for ricin detection and kinetic analysis based on a piezoresistive microcantilever aptasensor was proposed, where ricin aptamer was immobilised on the microcantilever surface by biotin-avidin binding system. Results showed that the detection limit of ricin was 0.04μg L−1 (S/N ≥ 3). A linear relationship between the response voltage and the concentration of ricin in the range of 0.2μg L−1-40μg L−1 was obtained, with the linear regression equation of ΔUe = 0.904C + 5.852 (n = 5, R = 0.991, p < 0.001). The sensor showed no response for abrin, BSA, and could overcome the influence of complex environmental disruptors, indicating high specificity and good selectivity. Recovery and reproducibility in the result of simulated samples (simulated water, soil, and flour sample) determination met the analysis requirements, which was 90.5∼95.5% and 7.85%∼9.39%, respectively. On this basis, a reaction kinetic model based on ligand-receptor binding and the relationship with response voltage was established. The model could well reflect the dynamic response of the sensor. The correlation coefficient (R) was greater than or equal to 0.9456 (p < 0.001). Response voltage (ΔUe) and response time (t0) obtained from the fitting equation on different concentrations of ricin fitted well with the measured values.

Molecular mechanism of Mg-ATPase activity.

Mg-ATPase is very important in living organisms. To better understand the molecular mechanism of Mg-ATPase activity, we applied the method of kinetic analysis of multi-sited enzyme systems; this is a suitable approach used for kinetic investigation of multi-sited enzyme systems. The study of Mg-ATPase has demonstrated: (1) It is a multi-sited enzyme system whose functional unit is minimum a dimmer; (2) Its substrate is MgATP, while free ATP and Mg(2+) appear to be the enzyme modifiers with a dual effect; (3) The enzyme system for MgATP has at least three sites: i.e., the essential activator, full inhibitor, and partial effect modifiers sites; (4) Mg-ATPase carries out Mg(2+) transport through the 1Mg(2+):1ATP stochiometry. Based on the results of these analyses, the kinetic scheme for Mg-ATPase has been developed.

Kinetic analysis of the main glow peak of α-Al2O3:C exposed to high irradiation dose

This paper reports kinetic analysis of the main thermoluminescent peak in α-Al2O3:C for irradiation doses as high as 120 Gy and at various heating rates going as low as 0.01 K/s. The dependence of the various methods of kinetic analysis on irradiation dose and/or heating rate has been assessed with respect to the main peak. The dose response of the peak to high beta irradiation has also been presented.

A novel method for kinetics analysis of pyrolysis of hemicellulose, cellulose, and lignin in TGA and macro-TGA

A novel peak analysis-least square method to analyze the kinetics is developed. The accuracy of this method is very good.

ICONE23-1618 Fission Probability Density Functions for Super Prompt Criticality Accident Analysis in Weakly Coupled Systems by Integral Kinetic Model

Kinetic analysis in criticality accident is necessary for the estimation of the integral power and the dose. The analysis must be performed even for the geometry of several regions which are weakly coupled, i.e. each region is apart from other regions or/and moderating material exists between the regions. A kinetic analysis method for weakly coupled systems has been developed to analyze the first pulse in super prompt criticality accidents. In the method, time dependent fission probability density functions after a fission in each region are calculated by Monte Carlo method from the time between the collisions. By using the fission probability density functions, kinetic behavior of each region can be calculated. The difference of the functions between the different systems is discussed based on the difference of compositions and geometry of the systems.

An incremental isoconversional method for kinetic analysis based on the orthogonal distance regression.

The parameters obtained from a kinetic analysis of thermoanalytical data often exhibit a conversion-dependent behavior. A novel incremental isoconversional method able to deal with this phenomenon is proposed. The kinetic model is directly fitted to the experimental data using nonlinear orthogonal least squares procedure. The data are processed without transformations, so their error distribution is preserved. As the objective function is based on a maximum likelihood approach, reliable uncertainties of the parameters can be estimated. In contrast to other methods, the activation energy and the pre-exponential factor are treated as equally important kinetic parameters and are estimated simultaneously. Validity of the method is verified on simulated data, including a dataset with local nonlinearity in the temperature variation. A practical application on the nonisothermal cold crystallization of polyethylene terephthalate is presented.

The matrix influence on the determination of low uranium concentrations by laser induced fluorescence method

A measurement technique enabling the determination of low uranium concentration utilizing system used for time resolved laser induced fluorescence spectroscopy (TRLFS), based on a commercially available kinetic phosphorescence analysis method has been developed. The effect of the matrix, complexing agent, and the level of acidification on the fluorescence spectra and integral intensity was studied. The method is highly influenced by the sample matrix; particularly if different starting uranium salts are in the calibration solutions and in the samples. In the initial study of these effects, TRLFS measurements have been used in order to clarify this behavior.

Effect of Eye Drops Containing Disulfiram and Low-Substituted Methylcellulose in Reducing Intraocular Pressure in Rabbit Models

Purpose: We attempted to develop anti-glaucoma eye drops using 0.5% disulfiram (DSF), 5% 2-hydroxypropyl-β-cyclodextrin, 0.1% hydroxypropylmethylcellulose, and 2% methylcellulose (MC) (DSF eye drops with MC), and tested the ability of a DSF eye drops with MC to reduce intraocular pressure (IOP) in rabbit models.Methods: Elevated IOP was induced by the rapid infusion of 5% glucose solution (15 ml/kg of body weight) through the marginal ear vein or by keeping rabbits in the dark for 5 h. IOP and the nitric oxide (NO) level in the aqueous humor were measured with an electronic tonometer and by a microdialysis method, respectively. ΔIOP and ΔNO values were analyzed as the differences in IOP and NO in rabbits instilled with saline or eye drops, respectively.Results: Increased IOP in rabbit models was reduced by the instillation of DSF eye drops with or without MC, and a close relationship was observed between IOP and NO levels in rabbit receiving a rapid infusion of isotonic glucose. We present kinetic parameters [secondary AUC (prolonged drug effect) and secondary MRT (prolonged effective time)] analyzed as the area under the curve (AUC) of ΔIOP or ΔNO versus time using rabbits instilled with eye drops 10, 50, or 90 min prior to the infusion of the isotonic glucose solution. The elevations in IOP and NO level were reduced by the instillation of DSF eye drops with or without MC; the addition of MC increased the secondary AUC and MRT of DSF eye drops.Conclusions: The present study demonstrates that 0.5% DSF eye drops suppress increased IOP in rabbit models, probably by inhibiting the elevation in NO levels. In addition, we propose a kinetic analysis method to predict drug effects and effective time. These findings suggest that a low-substituted MC-based drug delivery system promotes drug effectiveness and effective time.

Comparative analysis of Mg-dependent and Mg-independent HCO3(-) ATPases.

The comparative analysis between two enzymes, Mg-dependent and Mg-independent HCO3(-) ATPases, were studied in synaptosomal and microsomal membrane fractions of albino rat brain, using the method of kinetic analysis of the multi-sited enzyme systems. Therefore, it can be inferred that Mg-dependent HCO3(-) ATPase belongs to the group of "P-type" transporting ATPases. Mg-independent HCO3(-) ATPase with its kinetic properties may be attributed to the group of "Ecto" ATPases.

Study of the Hydrodesulphurization Process of Hydrogenate of Shubarkol Coal

This is a research on the hydrodesulphurization process of hydrogenate from the coal of Shubarkolsky deposit (Republic of Kazakhstan) in the presence of pyrite and natural zeolite. The rate constants for hydrodesulphurization process of the liquid products and Gibbs energy were calculated by the method of equilibrium kinetic analysis, which was necessary for improving the technological parameters for the hydrotreatment of liquid hydrogenation products. It is shown that the optimal time of the hydrodesulphurization process is 15-25 minutes. The sulfur content in the fraction up to 2000С is 0.043 %, and in a fraction of 200-3000С - 0.065 %, which indicates a high degree of hydrotreatment of the hydrogenate in the presence of the above mentioned catalyst.

Kinetic analysis of the complex process of poly(vinyl alcohol) pyrolysis using a new coupled peak deconvolution method

A peak deconvolution procedure used for the analysis of data corresponding to simultaneous overlapping processes begins with separation of individual processes using functions such as Gaussian, Lorentzian, Weibull, and Fraser–Suzuki (FS) followed by application of kinetic analysis methods to the separated peaks. We propose a coupled peak deconvolution procedure to link the parameters of the FS functions of similar peaks in two DTG curves obtained at different linear heating rates, so that the coordinates of each peak can be obtained in a constrained manner. The proposed technique is a kinetic deconvolution method rather than a pure mathematical deconvolution technique. To analyze individual peaks in our study, the non-parametric kinetic and Freidman’s isoconversional methods have been applied to determine kinetic triplet of each process. This technique has been tested with both simulated and experimental data. Using this technique, the effects of molecular weight and degree of hydrolysis of polyvinyl alcohol (PVA) samples on reaction mechanism and activation energy of thermal degradation were studied. The presence of acetate group in the PVA samples causes thermal stability, decreases the rate of main reactions, and increases the activation energy. The results of this study may help tailor heat-resistant materials with proper choice of polymer characteristics.

Kinetics and intermediates of the reaction of fully reduced Escherichia coli bo₃ ubiquinol oxidase with O₂.

Cytochrome bo₃ ubiquinol oxidase from Escherichia coli catalyzes the reduction of O₂ to water by ubiquinol. The reaction mechanism and the role of ubiquinol continue to be a subject of discussion. In this study, we report a detailed kinetic scheme of the reaction of cytochrome bo₃ with O₂ with steps specific to ubiquinol. The reaction was investigated using the CO flow-flash method, and time-resolved optical absorption difference spectra were collected from 1 μs to 20 ms after photolysis. Singular value decomposition-based global exponential fitting resolved five apparent lifetimes, 22 μs, 30 μs, 42 μs, 470 μs, and 2.0 ms. The reaction mechanism was derived by an algebraic kinetic analysis method using frequency-shifted spectra of known bovine states to identify the bo3 intermediates. It shows 42 μs O₂ binding (3.8 × 10(7) M(-1) s(-1)), producing compound A, followed by faster (22 μs) heme b oxidation, yielding a mixture of PR and F, and rapid heme b rereduction by ubiquinol (30 μs), producing the F intermediate and semiquinone. In the 470 μs step, the o₃ F state is converted into the o₃(3+) oxidized state, presumably by semiquinone/ubiquinol, without the concomitant oxidation of heme b. The final 2 ms step shows heme b reoxidation and the partial rereduction of the binuclear center and, following O₂ binding, the formation of a mixture of P and F during a second turnover cycle. The results show that ubiquinol/semiquinone plays a complex role in the mechanism of O₂ reduction by bo₃, displaying kinetic steps that have no analogy in the CuA-containing heme-copper oxidases.

Thermal analysis kinetics of thermal decomposition of nickel–viscose composite fiber

In this study, the thermal decompositions of nickel composite fibers (NCF) under different atmospheres of flowing nitrogen and air were investigated by XRD, SEM–EDS, and TG–DTG techniques. Non-isothermal studies indicated that only one mass loss stage occurred over the temperature regions of 298–1,073 K in nitrogen. The mass loss was from the decomposition. But after this decomposition, nickel was oxidized in air, when the temperature was high enough. In nitrogen media, the model-free kinetic analysis method was applied to calculate the apparent activation energy (E a) and pre-exponential factor (A). The method combining Satava–Sestak equation with one TG curve was used to select the suitable mechanism functions from 30 typical kinetic models. Furthermore, the Coats–Redfern method was used to study the NCF decomposition kinetics. The study results showed that the decomposition of NCF in nitrogen media was controlled by three-dimension diffusion; mechanism function was the anti-Jander equation, the apparent activation energy (E a) and the pre-exponential factor (A) were 172.3 kJ mol−1 and 2.16 × 109 s−1, respectively. The kinetic equation could be expressed as following: $$ \frac{{{\text{d}}\alpha }}{{{\text{d}}T}} = \frac{{ 2. 1 6\times 1 0^{ 9} }}{\beta }{ \exp }\left( {\frac{ - 2 0 7 2 4. 1}{T}} \right)\left\{ {\frac{ 3}{ 2}(1 + \alpha )^{2/3} [(1 + \alpha )^{1/3} - 1]^{ - 1} } \right\}. $$

Study on release kinetics for gel of Aconitum brachypodum based on nonlinear mixed effect model

To establish the analytical method for the release kinetic (RK) of Aconitum Brachypodum gel based on the nonlinear mixed effect model (NLMEM), in order to rationally evaluate the drug release process and explain the release mechanism. The zero-order kinetic model containing for non-corroded drug system with the random effect was taken as the base model. The fixed effect and random effect factors impacting the drug release were analyzed by PROC NLMIXED of SAS to establish the final typical model. Subsequently, 10 training subsets were randomly extracted from the primary data to respectively their RK models, calculate the corresponding predicted root-mean-square error and average relative error, and evaluate the model stability and prediction accuracy. The burst effect F0 had a very significant effect on the RK model. Among the component factors, carbopol 940 showed an obvious effect on the inherence release speed constant k0 and the concentration gradient change constant a, with different variations on the basis of dosage range. The random effect factors of k0 and a had a significant impact. The final RK model was proved to be stable, effective and reliable in the cross validation. The drug release kinetic analysis method could be used to rationally evaluate the drug release process and explain the release mechanisms.

Determination of the oxidative stability of hazelnut oils by PDSC and Rancimat methods

The present study was conducted to determine the oxidative stability of hazelnut oil and compare it with more common and previously tested olive oil and rapeseed oil. The oxidative stability was determined by means of two independent methods, pressure differential scanning calorimetry (PDSC), and oxidative stability index (OSI) using TA Instruments DSC and Metrohm Rancimat equipment, respectively. Both the PDSC and Rancimat devices were set at five different isothermal temperatures in the range of 100–140 °C. The times to reach peak maximum (τ max) obtained from PDSC exotherms were statistically related with the Rancimat induction times (τ on) to obtain correlation coefficient >0.99 within linear relation. Based on the Arrhenius equation and activated complex theory, activation energies (E a), pre-exponential factors (Z), and specific rate constants (k) for studied oils oxidations were calculated. To the best of our knowledge, this is the first study dealing with oxidative stability of hazelnut oil using PDSC technique. According to the results obtained, PDSC seems to be useful and quick method for kinetic analysis of lipid oxidation in hazelnut oil.

Kinetic method for the large-scale analysis of the binding mechanism of histone deacetylase inhibitors

Performing kinetic studies on protein ligand interactions provides important information on complex formation and dissociation. Beside kinetic parameters such as association rates and residence times, kinetic experiments also reveal insights into reaction mechanisms. Exploiting intrinsic tryptophan fluorescence a parallelized high-throughput Förster resonance energy transfer (FRET)-based reporter displacement assay with very low protein consumption was developed to enable the large-scale kinetic characterization of the binding of ligands to recombinant human histone deacetylases (HDACs) and a bacterial histone deacetylase-like amidohydrolase (HDAH) from Bordetella/Alcaligenes. For the binding of trichostatin A (TSA), suberoylanilide hydroxamic acid (SAHA), and two other SAHA derivatives to HDAH, two different modes of action, simple one-step binding and a two-step mechanism comprising initial binding and induced fit, were verified. In contrast to HDAH, all compounds bound to human HDAC1, HDAC6, and HDAC8 through a two-step mechanism. A quantitative view on the inhibitor-HDAC systems revealed two types of interaction, fast binding and slow dissociation. We provide arguments for the thesis that the relationship between quantitative kinetic and mechanistic information and chemical structures of compounds will serve as a valuable tool for drug optimization.