Co-reporter:Yun Duan, Jie Li, Xi Yang, Ling Hu, Zhiyong Wang, Yuwen Liu, Cunxin Wang
Journal of Analytical and Applied Pyrolysis 2008 Volume 83(Issue 1) pp:1-6
Publication Date(Web):September 2008
DOI:10.1016/j.jaap.2008.05.001
The thermal decomposition of Zn(AC)2·2H2O has been studied by TG–DTA/DSC at the heating rate of 2, 3, 4, 5, 10 and 20 °C min−1 from ambient temperature to 350 °C in static air and flowing N2, respectively. The TG–DTA/DSC experiments show both the decompositions under the two different atmospheres go through two well-defined steps: release of crystal water and subsequent decomposition of anhydrous zinc acetate into zinc oxide. Kinetic analysis was performed by using an integral composite procedure, which includes an integral isoconversional method and an integral master-plots method. The results of integral isoconversional method at various heating rates suggest that in both atmospheres the dehydration (0.3 < α < 0.9) followed simplex kinetic mechanism which can be described by an Avrami-Erofeev (A1.5) model. The evolved gas of non-isothermal decomposition of Zn(AC)2·2H2O in flowing N2 was measured by TG coupled with Fourier transform infrared spectroscopy (FTIR). During 60–120 °C water was firstly detected. And in the range of 175–390 °C acetic acid, acetone and carbon dioxide were detected.
Co-reporter:Jing-Yan SHI;Jie LI;Zhi-Yong WANG;Yu-Wen LIU;Cun-Xin WANG
Chinese Journal of Chemistry 2008 Volume 26( Issue 2) pp:249-254
Publication Date(Web):
DOI:10.1002/cjoc.200890049
Abstract
The thermokinetic mathematical models for consecutive first-order reactions in titration period and the stopped-titration reaction period were proposed for titration calorimetry, based on which, thermodynamic parameters (reaction enthalpies, ΔrHm1and ΔrHm2) and kinetic parameters (rate constants, k1 and k2) of the consecutive first-order reactions could be obtained by directly simulating the calorimetric curve from a single experiment with the method of nonlinear least squares regression (NLLS). The reliability of the model has been verified by investigating the reaction of the saponification of diethyl succinate in an aqueous ethanol solvent.
Co-reporter:Li Jie, Liu Yuwen, Shi Jingyan, Wang Zhiyong, Hu Ling, Yang Xi, Wang Cunxin
Thermochimica Acta 2008 Volume 467(1–2) pp:20-29
Publication Date(Web):30 January 2008
DOI:10.1016/j.tca.2007.10.014
An online-coupled TG–FTIR evolved gas analysis (EGA) instruments have been used to identify and monitor the evolution of gaseous products during the thermal decomposition of phenylalanine and tyrosine in flowing N2 atmosphere up to 800 °C. The results indicate that the thermolysis processes of these two compounds are similar. For both of them the main primary decomposition steps are two competing paths: the direct decarboxylation and the concerted rupturing of C–C bonds. And the primary decomposition reactions also include deamination and dehydration. The main secondary reaction is the crack of cyclic dipeptide which also presents two competing pathways. The main gaseous products are NH3, H2O, CO2, CO, HNCO, HCN and some organic compounds. However, compared with tyrosine, the decomposition of phenylalanine is more complete and involves less secondary reaction. That is caused by their different thermal stability and decomposition temperature.
Co-reporter:Xiaomin Cao, Jie Li, Xi Yang, Yun Duan, Yuwen Liu, Cunxin Wang
Thermochimica Acta 2008 Volume 467(1–2) pp:99-106
Publication Date(Web):30 January 2008
DOI:10.1016/j.tca.2007.11.009
The effect of protein concentration on bovine serum albumin (BSA) aggregation kinetics at high concentration was studied by differential scanning calorimetry (DSC). The nonisothermal kinetic analysis of this process was carried out using a composite procedure involving the iso-conversional method and the master plots method. The observed aggregation process was characterized by denaturation temperature (Td max), apparent activation energy (E), the apparent order of reaction (n), and pre-exponential factor (A) which all increased with the increase of BSA concentration. The results suggested that the apparent aggregation reaction of BSA approximately conformed to the simple order reaction model. The higher BSA concentration, the higher the apparent order of reaction and the more close to 2 was. The difference intrinsic fluorescence of BSA between before and after the thermal denaturation and aggregation provided the evidences of conformation changes of BSA and the substantial impact of BSA concentration on aggregation. This study showed the combination of iso-conversional method and the master plots method could be used to model the aggregation mechanism of the protein.
Co-reporter:Jie Li, Zhiyong Wang, Xi Yang, Ling Hu, Yuwen Liu, Cunxin Wang
Journal of Analytical and Applied Pyrolysis 2007 Volume 80(Issue 1) pp:247-253
Publication Date(Web):August 2007
DOI:10.1016/j.jaap.2007.03.001
An online-coupled TG–FTIR evolved gas analysis (EGA) instruments has been used to identify and monitor the evolution of gaseous products during thermal decomposition of glycine and its dipeptide in flowing N2 atmosphere up to 800 °C. The first gaseous products of glycine pyrolysis, evolved around 260 °C are NH3, H2O and CO2. The max releasing rates of both NH3 and H2O are reached at 282 °C and that of CO2 is reached at 308 °C. At 400 °C HNCO becomes the main product, accompanied by CO, HCN and some other species. HCN is the main gaseous species released around 700 °C. Compared with glycine, glycylglycine has lower thermal stability, which begins to decompose at 214 °C. However, that the evolution profiles of gaseous products from glycine and glycylglycine are similar, which suggests the decomposition of them may occur through similar pathways. Our results indicate that the primary decomposition steps include deamination and dehydration. CO2 is mainly formed through the secondary reactions. And the crack of cyclic amide, 2,5-diketopiperazine (DKP), is suggested to be the main origin of HNCO and HCN at higher temperature.
Co-reporter:Heng Zhang;Cong-Yi Zheng;Jie Li;Chao-Jiang Gu;Cun-Xin Wang;Yu-Wen Liu
Chinese Journal of Chemistry 2006 Volume 24(Issue 2) pp:
Publication Date(Web):13 FEB 2006
DOI:10.1002/cjoc.200690035
The metabolic thermogenic power data of the HSV-2 infected HeLa cells and the FMDV infected BHK-21 cells were determined by LKB-2277 bioactivity monitor. The aim of the study was to investigate the difference of the cell metabolism under the action of two different viruses and the effects of hyperthermia and drugs on it. The results illustrated that the metabolic thermogenic power of infected cells was larger than the uninfected ones and there was a significant difference between the metabolism heat released by the two types of infected cells. From the maximal thermal power and total metabolism heat, the infection process was observed to be thermosensitive and could be inhibited by interferon. Our experiments also revealed that 6 month storage of FMDV could attenuate its virulence and infectivity. The study shows that microcalorimetry is a potent tool to investigate the metabolism of virus infection process.
Co-reporter:Jie Li, Zhiyong Wang, Xi Yang, Ling Hu, Yuwen Liu, Cunxin Wang
Thermochimica Acta 2006 Volume 447(Issue 2) pp:147-153
Publication Date(Web):15 August 2006
DOI:10.1016/j.tca.2006.05.004
The thermal behavior of l-leucine under inert conditions was investigated by TGA, FTIR and TG–FTIR. The TG results showed that only one mass loss stage of more than 99% happened when l-leucine was under program heating with temperature ranging from 30 to 600 °C. The apparent activation energy, pre-exponential factor and the most probable model function were obtained by using of master plots method. The results of kinetic study showed that the decrease in mass of l-leucine was due to subliming rather than decomposing. And this was proved by the FTIR spectrum analysis and the directly observed subliming phenomenon. The results of TG–FTIR experiments showed that there was only one stage of decomposition process that happened after the subliming of leucine. The gas products were CO2, NH3, CO and some organic compounds such as 3-methyl-1-butanamine, and the main primary decomposition was decarboxylation.
Co-reporter:Haifeng Liu, Zhiyong Wang, Yuwen Liu, Jing Xiao, Cunxin Wang
Thermochimica Acta 2006 Volume 443(Issue 2) pp:173-178
Publication Date(Web):15 April 2006
DOI:10.1016/j.tca.2006.01.005
The hydrogen peroxide-oxidation of o-phenylenediamine (OPD) catalyzed by horseradish peroxidase (HRP) at 37 °C in 50 mM phosphate buffer (pH 7.0) was studied by calorimetry. The apparent molar reaction enthalpy with respect to OPD and hydrogen peroxide were −447 ± 8 kJ mol−1 and −298 ± 9 kJ mol−1, respectively. Oxidation of OPD by H2O2 catalyzed by HRP (1.25 nM) at pH 7.0 and 37 °C follows a ping–pong mechanism. The maximum rate Vmax (0.91 ± 0.05 μM s−1), Michaelis constant for OPD Km,S (51 ± 3 μM), Michaelis constant for hydrogen peroxide Km,H2O2Km,H2O2 (136 ± 8 μM), the catalytic constant kcat (364 ± 18 s−1) and the second-order rate constants k+1 = (2.7 ± 0.3) × 106 M−1 s−1 and k+5 = (7.1 ± 0.8) × 106 M−1 s−1 were obtained by the initial rate method.
Co-reporter:Xiu-Yin Xie, Xia Li, Zhi-Yong Wang, Cun-Xin Wang
Thermochimica Acta 2004 Volume 414(Issue 1) pp:19-23
Publication Date(Web):6 May 2004
DOI:10.1016/j.tca.2003.11.004
The activation of bovine liver arginase, which catalyzes the hydrolysis of l-arginine to l-ornithine and urea, by manganese ions was studied by thermokinetic methods at 37 °C in 40 mM sodium barbiturate–HCl buffer solution (pH 9.4). Full activation of arginase, by incubation with 0.1 mM Mn2+, resulted in increased of Vmax, and a higher sensitivity of the enzyme to product and l-lysine inhibition, with no change in the Km for arginine. Upon addition of 0.1 mM Mn2+ to the reaction, the inhibitory constants of product (KP) and l-lysine (KI) decreased from 1.18 to 0.70 mM and from 5.60 to 3.10 mM, respectively. We suggest that the exogenous manganese ions in reaction recovered the activity of arginase, which was lost in dissolving and dilution, without effecting on the mechanism of the reaction.
Co-reporter:Xia Li;Jie Li;Zhi-Yong Wang;Xiu-Yin Xie;Xi Yang;Cun-Xin Wang
Chinese Journal of Chemistry 2004 Volume 22(Issue 3) pp:
Publication Date(Web):26 AUG 2010
DOI:10.1002/cjoc.20040220307
Na+/K−-ATPasc (EC 3.6.1.3) is an important membrane-bound enzyme. By using microcalorimetry, the thermokinetic method was developed to kinetic studies on Na+/K+-ATPase for the first time. Compared with other ones, the method provided accurate measurements of not only thermodynamic data but also the kinetic data. At 310.15 K and pH=7.4, the molar reaction enthalpy ΔrHm, was measured as (-40.408k 1.9) kJ mol−1. The Michaelis constant Km was determined to be (0.479 0.020) 10−-3 mol L−1 and consistent with literature figure which is about 0.5 10−-3 moi L−1. The maximum velocity Vmax obtained was (0.6810.026) μmol Pi min−1 mg protein−1. All of the data have good repeatability and self-consistency. The reliability of thermokinetic method was verified by the experimental results and further confirmed by colorimetric studies. Moreover. the effect of enzyme pre-dilution on its activities was also investigated.
Co-reporter:Wanjun Tang, Yuwen Liu, Hen Zhang, Cunxin Wang
Thermochimica Acta 2003 Volume 408(1–2) pp:39-43
Publication Date(Web):17 December 2003
DOI:10.1016/S0040-6031(03)00310-1
In this paper a more precise approximate formula for Arrhenius temperature integral, i.e., , is proposed, by using two-step linearly fitting process: (i) the linear dependence of on 1/u and (ii) the linear dependence of () on u. Values of p(u) at different u were directly obtained from numerical integration of temperature integral without derivation from any approximating infinite series, and values of were obtained by numerical differentiating. New equation for the evaluation of non-isothermal kinetic parameters has been obtained from the above dependence, which can be put in the form The validity of this formula was confirmed and its deviation from the values of numerical integrating was discussed. Compared with some previously published approximate formulae, our formula has the best result in the kinetics analysis of non-isothermal process.
Co-reporter:You-Ying Di, Song-Sheng Qu, Yi Liu, De-Cai Wen, Hou-Kuan Tang, Lin-Wei Li
Thermochimica Acta 2002 Volume 387(Issue 2) pp:115-119
Publication Date(Web):23 May 2002
DOI:10.1016/S0040-6031(01)00831-0
The two solid-state coordination reactionsequation(1)equation(2)have been studied by solution calorimetry. The molar dissolution enthalpies of the reactants and the products in some solvents (such as 2 mol l−1 HCl or its solutions) of these solid–solid coordination reactions have been measured by an isoperibol solution calorimeter. The standard molar formation enthalpies of [trans-Cu(Ala)2(s), 298.15 K] and [trans-Cu(Gly)2(s), 298.15 K] have been determined to be −1015.42 ± 0.06 and 1252.36 ± 0.05 kJ mol−1, respectively, from the results of the molar dissolution enthalpies and other auxiliary thermodynamic data.
Co-reporter:You-Ying Di, Xiao-Hong Sun, Zhi-Cheng Tan, Yuan-Fa Liu, Shuang-He Meng, Sheng-Li Gao, Song-Sheng Qu
Thermochimica Acta 2001 Volume 369(1–2) pp:25-30
Publication Date(Web):22 March 2001
DOI:10.1016/S0040-6031(00)00746-2
The low temperature heat capacities of ethyl carbazate (C3H8N2O2) were precisely determined with an adiabatic calorimeter over the temperature range from 78 to 371 K. The sample was observed to melt at 318.92±0.02 K. The molar enthalpy and entropy of the melting as well as the chemical purity of the substance were determined to be 20019±11 J mol−1, 62.77±0.03 J mol−1 K−1 and 99.35±0.01 mol%, respectively. The extrapolated melting temperature for the absolutely pure compound obtained from fractional melting experiments was 319.181±0.005 K.
Co-reporter:You-Ying Di, Zheng-Ning Li, Shuang-He Meng, Zhi-Cheng Tan, Song-Sheng Qu
Thermochimica Acta 2001 Volume 373(Issue 1) pp:31-36
Publication Date(Web):1 June 2001
DOI:10.1016/S0040-6031(01)00469-5
The low-temperature heat capacity of 3,6-dichloro-2-methoxy-benzoic acid was precisely determined with an automated adiabatic calorimeter over the temperature range from 78 to 402 K. The sample was observed to melt at 388.15±0.03 K. The molar enthalpy and entropy of melting as well as the chemical purity of the substance were determined to be 22244±35 J mol−1, 57.31±0.09 J mol−1 K−1 and 99.31±0.02 mol%, respectively. The extrapolated melting temperature for the absolutely pure compound obtained from fractional melting experiments was 388.52±0.08 K.
Co-reporter:Liu Yuwen, Liu Yi, Wang Cunxin, Qu Songsheng, Deng Fengjiao
Thermochimica Acta 2000 Volume 351(1–2) pp:51-54
Publication Date(Web):1 June 2000
DOI:10.1016/S0040-6031(00)00415-9
The metabolic thermogenic curves of mitochondria isolated from fish liver tissue have been determined by an LKB 2277 Bioactivity Monitor. The metabolism activity of mitochondria inhibited by sodium azide has also been studied. The thermogenic curves can be divided into four parts: the lag phase, active recovery phase, stationary phase, and decline phase. From these thermogenic curves, the recovery rate constant k1, decline rate constant k2, the maximum heat production rate Pm, heat output Q are obtained. The metabolic heat released, time of each phase, rate constants, and shape of the thermogenic can be significantly influenced by sodium azide added. These results suggest that sodium azide inhibits the metabolism of mitochondria, and the inhibition is incomplete. The inhibitory effect reaches the maximal value with the exactly sodium azide concentration of 2μg mol−1.
