Liu Yuwen

New Temperature Integral Approximate Formula for Non-isothermal Kinetic Analysis

A new approximate formula for temperature integral is proposed. The linear dependence of the new fomula on x has been established. Combining this linear dependence and integration-by-parts, new equation for the evaluation of kinetic parameters has been obtained from the above dependence. The validity of this equation has been tested with data from numerical calculating. And its deviation from the values calculated by Simpsons numerical integrating was discussed. Compared with several published approximate formulae, this new one is much superior to all other approximations and is the most suitable solution for the evaluation of kinetic parameters from TG experiments.

Investigation of thermal decomposition of ascorbic acid by TG-FTIR and thermal kinetics analysis

The thermal behavior of dry solid ascorbic acid in nitrogen atmosphere in the temperature range of 25-800°C was investigated by TG-FTIR. During the thermal decomposition process, five evolved gaseous species, including H2O, CO2, CO, CH4 and HCOOH, were identified and monitored, in which HCOOH was detected for the first time. The results indicated that ascorbic acid began to decompose at 191°C. Its decomposition process consisted of three stages, and dehydration and decarboxylation to form furfural were the possible principal mechanism. The kinetic analysis for the first decomposition stage was also carried out by the isoconversional method and the master plots method. The results indicated that this process can be described by the model of 1st order reaction.

Investigation of thermal behavior of enoxacin and its hydrochloride

The thermal behaviors of enoxacin and its hydrochloride under inert conditions were investigated by TG, FTIR, and TG/DSC-FTIR. The results indicated that the thermal behavior of enoxacin can be divided into three stages, while its hydrochloride consisted of four stages. The main difference lay in the sequence of decarboxylation and decarbonylation. For the enoxacin, the decarboxylation and decarbonylation occurred simultaneously, but for its hydrochloride, the two processes occurred in turn. The reason for this was the existence of hydrochloric acid in enoxacin hydrochloride, which changed its intermolecular force. The thermal analysis kinetic calculations of their first two stages were carried out, respectively. The apparent activation energy, pre-exponential factor, and the most probable model function were obtained using the master plots method. The results indicated that all these stages can be described by the model of nucleation and nucleus growing.

Microcalorimetric study of the metabolism of U-937 cells undergoing apoptosis induced by the combined treatment of hyperthermia and chemotherapy

Hyperthermia is a useful adjunct in cancer therapy, as it can increase the effectiveness and decrease the toxicity of currently available cancer treatments such as chemotherapy and radiation. In this study we determined the power-time curves of U-937 cell line treated by the combination of hyperthermia and Carmofur by using an LKB 2277 Bioactivity Monitor. The maximal thermal power and the heat production were used to evaluate the antitumor effect. Our results show that the combined treatment of hyperthermia and Carmofur had a synergistic antitumor effect, which is consistent with the apoptosis ratio obtained by TUNEL assay. The results also indicate that the metabolic activity of apoptotic cells is lower than that of normal cells. Thus microcalorimetry is a powerful tool in fields of hyperthermia.

Kinetic Studies on Na+/K+-ATPase and Inhibition of Na+/K+-ATPase by ATP

Na+/K+-ATPase (EC 3.6.1.3) is an important membrane-bound enzyme. In this paper, kinetic studies on Na+/K+-ATPase were carried out under mimetic physiological conditions. By using microcalorimeter, a thermokinetic method was employed for the first time. Compared with other methods, it provided accurate measurements of not only thermodynamic data (δrHm) but also the kinetic data (Km and Vmax). At 310.15 K and pH 7.4, the molar reaction enthalpy (δrHm) was measured as -40.514 ± 0.9 kJ mol−1. The Michaelis constant (Km) was determined to be 0.479 ± 0.020 mM and consistent with literature data. The reliability of the thermokinetic method was further confirmed by colorimetric studies. Furthermore, a simple and reliable kinetic procedure was presented for ascertaining the true substrate for Na+/K+-ATPase and determining the effect of free ATP. Results showed that the MgATP complex was the real substrate with a Km value of about 0.5 mM and free ATP was a competitive inhibitor with a Ki value of 0.253 mM.

Analysis of the calibration constant of a heat conduction calorimeter

Abstract The variation of the calibration constant of a heat conduction calorimeter is discussed. Our model was proved by the experimental results. The results illustrated that in order to keep the calibration constant as invariable as possible, the following measures can be taken. Electrical calibration and experimental determinations are done in the same medium; the diameter of the lead and stirrer should be small; the stirrer should be made with a material of low thermal conductivity; the heating coil is submerged completely in the medium; the volume of the medium is kept invariate during electrical calibration and experimental determination. In addition, there is a linear relationship between the calibration constant and the reciprocal of the thermal conductivity. Based on the analysis, thermal conductivity can be determined by using a heat conduction calorimeter.

The difference of energy metabolism between persistent and cytocidal virus infections

Abstract In this study, microcalorimetric measurements were carried out on PK-15 cell line persistently infected by cholera swine fever virus (CSFV) and BHK-21 cell line infected by foot and mouth disease virus (FMDV). The aim of this investigation was to investigate the difference of energy metabolism between the different kinds of virus infections—persistent infection and cytocidal infection. The thermogenesis curves determined by using a LKB 2277 Bioactivity Monitor were significantly different. From these thermogenic curves, the maximum heat production rate P m and total heat output Q are obtained. The results show that energy metabolism is different between persistent infection and cytocidal infection.