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Abstract  

The kinetics of protein thermal transition is of a significant interest from the standpoint of medical treatment. The effect of sucrose (0–15 mass%) on bovine serum albumin denatured aggregation kinetics at high concentration was studied by the iso-conversional method and the master plots method using differential scanning calorimetry. The observed aggregation was irreversible and conformed to the simple order reaction. The denaturation temperature (T m), the kinetic triplets all increased as the sucrose concentration increased, which indicated the remarkable stabilization effect of sucrose. The study purpose is to provide new opportunities in exploring aggregation kinetics mechanisms in the presence of additive.

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Abstract  

The kinetics of bovine serum albumin (BSA) denaturation in the absence and the presence of urea was studied by the iso-conversional method and the master plots method using differential scanning calorimetry (DSC). The observed denaturation process was irreversible and approximately conformed to the simple order reaction, and the denaturation did not follow rigorously first-order kinetic model or other integral order reaction models. The denaturation temperature (T m), apparent activation energy (E a), approximate order of reaction (n), and pre-exponential factor (A) all distinctly decreased as the 2 mol L−1 urea was added, which indicated that the urea accelerated the denaturation process of BSA and greatly reduced thermal and kinetic stability of BSA. This study also demonstrated that the iso-conversional method, in combination with the master plots method, provides a valuable and useful approach to the study of the kinetic process of protein denaturation.

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Abstract  

The possibility to determine the kinetic parameters for temperature programmed reduction of Cu/Fe3O4 using only one TPR profile is analyzed. The same data are analyzed both by Friedman’s iso-conversional method and another one previously derived and published by the authors. One shows that taking into account the experimental restrictions of Monti and Baiker, the Friedman’s method, although gives values of the activation energy smaller than the real values, indicates a very similar dependence of these on the reduction degree. On the basis of some synthetic data one shows that the errors are very large when these recommendations are neglected, being possible to determine a false dependence on the degree of reduction.

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Abstract  

The non-isothermal kinetics of precipitation of an Al-12.6 mass% Mg alloy for different heating rates were studied using thermal expansion techniques. The structural changes associated with the precipitation of the and b phases were identified. The conversion degree of each phase was associated with the area under the derivative curve of the thermal expansion with respect to temperature. Using the Kissinger relation and an iso-conversional method we calculated the apparent activation energies associated with formation of the precipitated phases. We report an increasing dependence of the activation energy on the conversion degree, the values obtained being within the range reported in the literature.

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Abstract  

The effect of glucose (0–15 mass%) on the kinetics of bovine serum albumin (BSA) denatured aggregation at high concentration in aqueous solution has been studied by differential scanning calorimetry. The observed denatured aggregation process was irreversible and could be characterized by a denaturation temperature (T m), apparent activation energy (E a), the approximate order of reaction, and pre-exponential factor (A). As the glucose concentration increased from 0 to 15 mass%, T m increased, E a also increased from 514.59409±6.61489 to 548.48611±7.81302 kJ mol−1, and A/s−1 increased from 1.24239E79 to 5.59975E83. The stabilization increased with an increasing concentration of glucose, which was attributed to its ability to alter protein denatured aggregation kinetics. The kinetic analysis was carried out using a composite procedure involving the iso-conversional method and the master plots method. The iso-conversional method indicated that denatured aggregation of BSA in the presence and absence of glucose should conform to single reaction model. The master plots method suggested that the simple order reaction model best describe the process. This study shows the combination of iso-conversional method and the master plots method can be used to quantitatively model the denatured aggregation mechanism of the BSA in the presence and absence of glucose.

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Introduction Iso-conversional methods are used for non-isothermal analysis, in which the transformation rate at a constant extent of conversion is only a function of temperature as suggested by Vyazovkin et al. [ 1 – 4 ] and

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known mechanism [ 8 ]. Hence, classical model-dependent kinetic analysis is not suitable to predict cure kinetics for the exact reaction model is usually unknown. For complex processes model-free kinetics or so-called iso-conversional methods have been

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Journal of Thermal Analysis and Calorimetry
Authors: José Geraldo de P. Espínola, Evandro P. S. Martins, Franklin P. Aguiar, Haryane R. M. Silva, M. G. Fonseca, L. N. H. Arakaki, and Ercules E. S. Teotônio

methods of analysis of thermo-gravimetric curves were used, which are based on the Coats–Redfern equation: model fixing [ 11 ], and iso-conversional methods. In general, the rate law of a decomposition reaction in the solid state is expressed as dα/dt = A

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activation energy E 1 . The conventional iso-conversional methods stop the calculation at this step; (ii) using E 1 , calculate a new value of E 2 for the activation energy from the plot of ln[ q / H ( x )] versus 1/ T or ln[ q / h ( x ) T 2 ) versus 1

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Abstract

Kinetic analysis of the thermal processes occurring during water loss for γ-MnO2 was performed using two techniques, namely, the induction period and iso-conversional methods. The modelling and analysis arising from thermogravimetric studies of the material gave rise to the pre-exponential factor and, most importantly, the activation energy for the transition. Analysis using the induction period showed the activation energy to increase linearly with extent of conversion, ranging from 109–250 kJ mol−1, while the iso-conversional method gave values in the range 66–76 kJ mol−1, with higher values for both lower and higher extents of conversion. Comparison of these methods indicates that the iso-conversional method is the preferred technique for determining the kinetic parameters for this process. Overall, this allows for the determination of the optimum heat treatment temperature and time for the γ-MnO2.

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