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1.
J. Orbán Sz. Halasi G. Papp Szilvia Barkó Beáta Bugyi 《Journal of Thermal Analysis and Calorimetry》2005,82(1):287-290
Summary The thermodynamic properties of the cardiac and skeletal a-actin isoforms were studied to characterize the molecular bases
of the functional differences between them with the method of differential scanning calorimetry (DSC). The thermal properties
of the actin filaments were described in the presence of calcium and magnesium ions as well. Based on the calculated free
energy changes the α-cardiac actin filaments appeared to be more stable in its physiologically more relevant, magnesium saturated
form. The magnesium saturated form of the α-cardiac actin filaments seemed to be more stable compared to the calcium saturated
form of it. The enthalpy and entropy changes could differentiate between the α-cardiac and α-skeletal actin isoforms and between
the calcium and magnesium saturated cardiac actin isoforms as well. Our results can demonstrate that the few differences between
the amino acid sequences of the α-actin isoforms have an influence on the thermal properties and maybe on the function of
these proteins as well. 相似文献
2.
Andrea Vig Réka Dudás Tünde Kupi J. Orbán G. Hild D. Lőrinczy M. Nyitrai 《Journal of Thermal Analysis and Calorimetry》2009,95(3):721-725
The effect of phalloidin on filaments polymerized from ADP-actin monomers of the heart muscle was investigated with differential
scanning calorimetry. Heart muscle contains α-skeletal and α-cardiac actin isoforms. In the absence of phalloidin the melting
temperature was 55°C for the α-cardiac actin isoform and 58°C for the α-skeletal one when the filaments were generated from
ADP-actin monomers. After the binding of phalloidin the melting temperature was isoform independent (85.5°C). We concluded
that phalloidin stabilized the actin filaments of α-skeletal and α-cardiac actin isoforms to the same extent when they were
polymerized from ADP-actin monomers. 相似文献
3.
The thermal decomposition kinetics of nickel ferrite (NiFe2O4) precursor prepared using egg white solution route in dynamical air atmosphere was studied by means of TG with different
heating rates. The activation energy (E
α) values of one reaction process were estimated using the methods of Flynn–Wall–Ozawa (FWO) and Kissinger–Akahira–Sunose (KAS),
which were found to be consistent. The dependent activation energies on extent of conversions of the decomposition reaction
indicate “multi-step” processes. XRD, SEM and FTIR showed that the synthesized NiFe2O4 precursor after calcination at 773 K has a pure spinel phase, having particle sizes of ~54 ± 29 nm. 相似文献
4.
Nopsiri Chaiyo Rangson Muanghlua Surasak Niemcharoen Banjong Boonchom Panpailin Seeharaj Naratip Vittayakorn 《Journal of Thermal Analysis and Calorimetry》2012,107(3):1023-1029
The thermal transformation of Na2C2O4 was studied in N2 atmosphere using thermo gravimetric (TG) analysis and differential thermal analysis (DTA). Na2C2O4 and its decomposed product were characterized using a scanning electron microscope (SEM) and the X-ray diffraction technique
(XRD). The non-isothermal kinetic of the decomposition was studied by the mean of Ozawa and Kissinger–Akahira–Sunose (KAS)
methods. The activation energies (E
α) of Na2C2O4 decomposition were found to be consistent. Decreasing E
α at increased decomposition temperature indicated the multi-step nature of the process. The possible conversion function estimated
through the Liqing–Donghua method was ‘cylindrical symmetry (R2 or F1/2)’ of the phase boundary mechanism. Thermodynamic functions (ΔH*, ΔG* and ΔS*), calculated by the Activated complex theory and kinetic parameters, indicated that the decomposition step is a high energy
pathway and revealed a very hard mechanism. 相似文献
5.
Several phenol‐urea‐formaldehyde (PUF) cocondensed resol resins were synthesized by different procedures. The curing kinetics and network properties of these PUF resins were examined by differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA). A kinetic study indicated that the activation energy values of PUF resins are generally higher than those of phenol‐formaldehyde (PF) resins during curing processes, but the curing rates of PUF resins are faster than those of PF resins. The pH values of PUF systems have a significant influence on the rate constants, although they affect the activation energy very slightly. Moreover, the dependence of activation energy on the conversion showed that there are more individual reactions with different activation energies occurring during the curing processes in PUF resins than in PF resins. The decomposition of methylene ether bridges to form methylene bridges probably occurs at high temperature in PUF resins. DMTA data indicated that the network rigidity of PUF resins is slightly lower than that of PF resin. The gel point and Ttan δ2 transition measured by DMTA were consistent with the kinetic results obtained from the DSC data, but they were also related to the physical and mechanical properties of the network, especially with regard to the Ttan δ2 transition. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1929–1938, 2003 相似文献
6.
The thermal decomposition of three new reagent cyclohexylamine-p-tolylglyoxime (L1H2), tertiarybutyl amine-p-tolylglyoxime (L2H2) and secondary butylamine-p-tolylglyoxime (L3H2 and their Co-complexes were studied by both isothermal and nonisothermal methods. As expected, the complex structure of Co-complexes,
different steps with different activation energies were realized in decomposition process. Model-fitting and model-free kinetic
approaches were applied to nonisothermal and isothermal data. The kinetic triplet (f(α), A and E) related to nonisothermal model-fitting method can not be meaningfully compared with values obtained from isothermal method.
The complex nature of the multi-step process of the studied compounds was more easily revealed using a wider temperature range
in nonisothermal isoconversional method. 相似文献
7.
This work presents a study of the thermal
degradation of ultra-high molecular mass polyethylene (UHMWPE) stabilized
with natural (α-tocopherol and carvacrol) and synthetic antioxidants.
Thermogravimetric analysis in dynamic mode was used to determine the apparent
activation energies of different samples. The stabilization of UHMWPE with
low concentrations (around 0.3%) of α-tocopherol is enough to obtain
an efficient thermal performance of the polymer. Carvacrol is also a good
stabilizer for UHMWPE, but at higher concentration than in the case of α-tocopherol.
The comparison of apparent activation energy between samples with natural
and synthetic antioxidants in similar concentration shows that α-tocopherol
is a better stabilizer in terms of their thermal performance. 相似文献
8.
S. M. Sidel F. A. Santos V. O. Gordo E. Idalgo A. A. Monteiro J. C. S. Moraes K. Yukimitu 《Journal of Thermal Analysis and Calorimetry》2011,106(2):613-618
Nucleation process and crystal growth for three samples of the (20-x)Li2O–80TeO2–xWO3 glass system were studied using X-ray diffraction and differential scanning calorimetry techniques. X-ray diffraction data
confirmed the amorphous characteristic of the as-quenched samples and indicated the growth of crystalline phases formed due to the thermal treatment for annealed samples. These results
reveal the presence of three distinct γ-TeO2, α-TeO2 and α-Li2Te2O5 crystalline phases in the TL sample, and two distinct α-TeO2 and γ-TeO2 crystalline phases in the TLW5 and TLW10 samples. The activation energy and the Avrami exponent were determined from DSC
measurements. The activation energy values X-ray diffraction data of the TLW10 glass sample suggest that γ-TeO2 phase occur before the α-TeO2. The results obtained for the Avrami exponent point to that the nucleation process is volumetric and that the crystal growth
is two or three-dimensional. 相似文献
9.
Hatzinikolaou DG Mamma D Christakopoulos P Kekos D 《Applied biochemistry and biotechnology》2007,142(1):29-43
Two glucose oxidase (GOX) isoforms where purified to electrophoretic homogeneity from the mycelium extract (GOXI) and the extracellular medium (GOXII) of Aspergillus niger BTL cultures. Both enzymes were found to be homodimers with nonreduced molecular masses of 148 and 159 kDa and pI values
of 3.7 and 3.6 for GOXI and GOXII, respectively. The substrate specificity and the kinetic characteristics of the two GOX forms, as expressed through their
apparent K
m values on glucose, as well as pH and T activity optima, were almost identical. The only structural difference between the
two enzymes was in their degrees of glycosylation, which were determined equal to 14.1 and 20.8% (w/w) of their molecular
masses for GOXI and GOXII, respectively. The above difference in the carbohydrate content between the two enzymes seems to influence their pH and thermal
stabilities. GOXII proved to be more stable than GOXI at pH values 2.5, 3.0, 8.0, and 9.0. Half-lives of GOXI at pH 3.0 and 8.0 were 8.9 and 17.5 h, respectively, whereas the corresponding values for GOXII were 13.5 and 28.1 h. As far as the thermal stability is concerned, GOXII was also more thermostable than GOXI as judged by the deactivation constants determined at various temperatures. More specifically, the half-lives of GOXI and GOXII, at 45°C, were 12 and 49 h, respectively. These results suggest A. niger BTL probably possesses a secondary glycosylation mechanism that increases the stability of the excreted GOX. 相似文献
10.
Iulia Contineanu Loredana Chivu Şt. Perişanu 《Journal of Thermal Analysis and Calorimetry》2005,82(1):3-6
Summary The energies of combustion of crystalline L-α-glutamic and 6-aminohexanoic acids were measured in a static bomb adiabatic calorimeter, in pure oxygen at 3040 kPa. Corrections
were made for the heats due to the ignition of sample and for the nitric acid formation. The derived enthalpies of formation
for L-α -glutamic and 6-aminohexanoic acids are ΔfHcr0= -1002.6±1.1 kJ mol-1and ΔfHcr0= -641.6±1.2 kJ mol-1, respectively. The data of enthalpy of formation are compared with literature values and with estimated values by means of
group additivity, using parameters recommended by Domalski and Hearing. 相似文献
11.
Á. Révész 《Journal of Thermal Analysis and Calorimetry》2008,91(3):879-884
The thermal stability, kinetics and glass forming ability of an Fe77C5B4Al2GaP9Si2 bulk amorphous alloy have been studied by differential scanning calorimetry. The activation energy, frequency factor and
rate constant corresponding to the multiple crystallization steps were determined by the Kissinger method. X-ray diffraction
and transmission electron microscopy studies revealed that the crystallization starts with the primary precipitation of α-Fe
from the amorphous matrix. The kinetics of nucleation of the α-Fe nanoparticles was investigated by two different methods,
i.e. isothermal annealing and continuous heating after partial annealing. 相似文献
12.
Stefano Vecchio Romolo Di Rocco Carla Ferragina 《Journal of Thermal Analysis and Calorimetry》2009,97(3):805-810
The thermal behaviour of the complexes formed in situ between the aromatic diamine 1,10-phenanthroline and the Co(II) and
Ni(II) ions intercalated between the layers of γ-zirconium phosphate was studied by simultaneous TG/DSC techniques. The obtained
materials show similar thermal behaviour: after a multi-step dehydration process they showed an oxidative decomposition in
only one step. The kinetic study of the decomposition process was performed using both the model-free methods of Ozawa-Flynn-Wall
and Kissinger. The former method provides a negligible dependence of activation energy on the degree of reaction α for both
materials. Activation energies derived by the Kissinger method show a good agreement with the mean values derived by the Ozawa-Flynn-Wall
method. The Arrhenius rate constants determined using also the pre-exponential factor values demonstrate that their thermal
stability can be considered comparable, within the experimental uncertainty. Finally, a reliable method was applied to determine
the model function from the best fit between the numerical dependence of the integral function g(α) vs. α and several theoretical model dependencies reported in literature for the most commonly used models. A Mampel first-order
reaction model was selected to describe the thermal decomposition in both the materials studied. 相似文献
13.
S. -X. Wang Z. -C. Tan Y. -S. Li L. -X. Sun Y. Li 《Journal of Thermal Analysis and Calorimetry》2008,92(2):483-487
Synthesis, characterization and thermal analysis of polyaniline (PANI)/ZrO2 composite and PANI was reported in our early work. In this present, the kinetic analysis of decomposition process for these
two materials was performed under non-isothermal conditions. The activation energies were calculated through Friedman and
Ozawa-Flynn-Wall methods, and the possible kinetic model functions have been estimated through the multiple linear regression
method. The results show that the kinetic models for the decomposition process of PANI/ZrO2 composite and PANI are all D3, and the corresponding function is ƒ(α)=1.5(1−α)2/3[1−(1-α)1/3]−1. The correlated kinetic parameters are E
a=112.7±9.2 kJ mol−1, lnA=13.9 and E
a=81.8±5.6 kJ mol−1, lnA=8.8 for PANI/ZrO2 composite and PANI, respectively. 相似文献
14.
Rodrigo Casasnovas David Fernández Joaquín Ortega-Castro Juan Frau Josefa Donoso Francisco Muñoz 《Theoretical chemistry accounts》2011,130(1):1-13
CBS-QB3, two simplified and less computationally demanding versions of CBS-QB3, DFT-B3LYP, and HF quantum chemistry methods
have been used in conjunction with the CPCM continuum solvent model to calculate the free energies of proton exchange reactions
in water solution following an isodesmic reaction approach. According to our results, the precision of the predicted pK
a values when compared to experiment is equivalent to that of the thermodynamic cycles that combine gas-phase and solution-phase
calculations. However, in the aqueous isodesmic reaction schema, the accuracy of the results is less sensitive to the presence
of explicit water molecules and to the global charges of the involved species since the free energies of solvation are not
required. In addition, this procedure makes easier the prediction of pK
a values for molecules that undergo large conformational changes in solvation process and makes possible the pK
a prediction of unstable species in gas-phase such as some zwitterionic tautomers. The successive pK
a values of few amino acids corresponding to the ionization of the α-carboxylic acid and α-amine groups, which is one of the
problematic cases for thermodynamic cycles, were successfully calculated by employing the aqueous isodesmic reaction yielding
mean absolute deviations of 0.22 and 0.19 pK
a units for the first and second ionization processes, respectively. 相似文献
15.
16.
A. L. F. S. d’Almeida D. W. Barreto V. Calado J. R. M. d’Almeida 《Journal of Thermal Analysis and Calorimetry》2008,91(2):405-408
The thermal behavior of four unusual lignocellulose fibers — namely Caroa, Curaua, Piassava and Sponge gourd — is described.
Caroa and Curaua fibers showed a more homogeneous thermal degradation, with a single peak dominating in the DTG curve. Piassava
and Sponge gourd showed two separated peaks, revealing the more pronounced amounts of hemicellulose present at these fibers.
All four fibers are, however, thermally stable up to temperatures of around 200°C. The activation energies for the thermal
degradation of the fibers were similar, except for the Caroa fiber. The lower activation energy associated to this fiber was
attributed to its higher hemicellulose to cellulose ratio. 相似文献
17.
Pontes F. M. L. Oliveira S. F. Espínola J. G. P. Arakaki L. N. H. Fonseca M. G. Airoldi C. 《Journal of Thermal Analysis and Calorimetry》2004,75(3):975-988
Solid adducts SbX3·L-pic (X=Cl, I and L=α-, β- and γ-picolines) were synthesized and characterized by elemental analysis, 1H and 13C NMR, IR spectroscopy and thermal analysis. The infrared spectroscopy and the magnetic resonance for 1H and 13C nuclei of these compounds suggest that the ligands coordinate through nitrogen atom. Kinetic studies were accomplished by
means of thermogravimetric data, through isothermal and non-isothermal techniques. The best adjusting models for adducts thermal
decomposition were R1 for isothermal and R1 and R2 for the non-isothermal methods. The energy of activation values obtained by isothermal method indicate the following orders
of thermal stability for adducts: i) SbCl3·α-pic>SbCl3·β-pic>SbCl3·γ-pic and ii) SbI3·β-pic>SbI3·γ-pic>SbI3·α-pic. The activation energy values obtained by non-isothermal were higher than those from isothermal methods, showing the
order of stability:iii) SbCl3·α-pic<SbCl3·β-pic<SbCl3·γ-pic and iv) SbI3·β-pic>SbI3·α-pic=SbI3··γ-pic. These obtained data through R1 model presented the kinetic compensation effect for trichloride adducts, which could be associated to both isothermal and
non-isothermal processes.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
18.
In the case of a single-electron reaction with account for slow diffusion of reagents, equations for actual (experimentally
determined) activation energies of two types were derived and analyzed: real energy A f, i.e., the energy measured at a constant electrode polarization value η = const) and formal energy (Ωf, i.e., the value measured at a constant value of potential vs. an ambiguously chosen reference electrode E = const). It is found that under the conditions of a sufficiently significant deviation from equilibrium, the actual activation
energy A
f is the weighted arithmetic mean of the diffusion activation energy and the sum of A
0 + αFη (where A
0 is the real activation energy of the discharge stage at polarization of η = 0); herewith, the weighting coefficients are
the corresponding values of the current of the discharge stage and the limiting diffusion current. A similar relationship
is also obtained for Ωf. It is found that the A
f, η- and Ωf, E-curves can in a number of cases feature regions with the negative A
f and Ωf values in the mixed kinetics range. 相似文献
19.
The electronic and geometric structures of formyl, acetyl, and benzoyl azides were studied and fragments of the potential
surfaces for the thermal Curtius rearrangement of these azides into the corresponding isocyanates were calculated by density
functional theory at the PBE/TZ2P level. Acyl azides adopt two stable, conformations syn and anti, with respect to the C-N bond. The syn conformers are more stable than their anti analogs. The activation energies of the syn-anti isomerization in the series under study are 9.4, 7.0, and 9.2 kcal mol−1, respectively, and the activation energies of the reverse reaction are 8.5, 6.1, and 2.5 kcal mol−1. The rearrangement of syn-acyl azides is a one-step process, in which elimination of N2 occurs synchronously with the rearrangement of atoms and bonds to form isocyanates. The activation energies of the rearrangements
of syn-HC(O)N3, syn-MeC(O)N3, and syn-PhC(O)N3 are 28.0, 32.9, and 34.5 kcal mol−1, respectively. The rearrangement of the anti conformers of the above-mentioned azides involves the formation of singlet acylnitrene. The activation energies of the latter
process are 34.6, 32.9, and 32.3 kcal mol−1, respectively. The activation energies of the rearrangement of acylnitrenes into isocyanates are 20.9, 18.9, and 13.6 kcal
mol−1, respectively. The energy characteristics of the process and the structural data for the starting compounds, final products,
and transition states provide evidence that the thermal Curtius rearrangement occurs predominantly by a concerted mechanism.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2200–2209, October, 2005. 相似文献
20.
C. Păcurariu R. I. Lazău I. Lazău D. Tiţa 《Journal of Thermal Analysis and Calorimetry》2007,88(3):647-652
The crystallization kinetics of some glass-ceramics obtained from Romanian (Şanoviţa) basalt has been studied in non-isothermal
conditions using DTA technique. The activation energies of the crystallization processes were calculated using the isoconversional
methods Kissinger-Akahira-Sunose and Ozawa-Flynn-Wall. The results obtained show a dependence of the activation energy (E
α) on the crystallized fraction (α) that proves the complex mechanism of the glass-ceramics crystallization process. It has
been proved that the Johnson-Mehl-Avrami model cannot be applied for the studied glass-ceramics crystallization process. The
effect of 2% TiO2 as nucleating agent upon the crystallization kinetics and upon the microstructure of the studied glass-ceramics was analyzed. 相似文献