Wang Cunxin

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.

Microcalorimetric studies of the toxic action of La3+ in mitochondria isolated from Star-cross 288 chicken heart tissue cells.

The thermogenic curves of the metabolism of mitochondria isolated from the heart of chicken Star-cross 288 and the effect of La3+ on it were studied by using an LKB-2277 BioActivity Monitor, ampoule method, at 37 degrees C. After isolation from the chicken heart tissue, mitochondria still have metabolic activity and can live for a long time by using the stored nutrients. From the thermogenic curves, we obtained the thermokinetic equations under different conditions. The kinetics show that La3+ has changed the metabolism completely.

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.

Microcalorimetric Studies of Rhus vernicifera LaccaseCatalytic Oxidation Reactions

The oxidation of substrates with various function groups (i.e., ortho-diphenol, ortho-aminophenol, p-aminophenol, ortho-phenylene diamine and p-phenylene diamine) catalyzed by Laccase have been studied using of LKB-2107 batch microcalorimetry system. The overall reaction enthalpy ΔrHm, Michaelis constant Km, pseudo-first-order rate constant k2 of the reactions and binding energy ΔG0 of Laccase-substrate complex for each substrate have been determined at 298.15 K, pH 7.4. The binding enthalpy ΔH0 and binding entropy ΔS0 of LS complex, when the substrate is Gallic acid and 2,3-dicyan hydroquinone respectively, have been also determined. The rate constants of the reaction between Laccase and these substrates are essentially identical because the rate of Laccase-catalytic reaction is limited by the step of electron transfer from the type 2 Cu(II)-bound substrate to the less exposed type 1 copper site, and the intra-complex electron transfer rate mainly dependents on the amino residues conformational changes. But the rate of the reaction between Laccase and substrates with group -OH is slower than group -NH2, because of the higher energy of bounding electron. The stability of LS complex depends on ΔS0, since ΔH0>0, substrate distinguished by Laccase depends on the value of allosteric entropy of the amino acid residues induced by substrate. The relationship between Laccase and its substrates cannot be regarded as a simple relationship of lock and key, but an induce-fit relationship.

A microcalorimetric study of the effect of La3+ on mitochondria isolated from Star-Cross 288 chicken liver tissue cells.

The thermogenic curves of the metabolism of mitochondria isolated from the liver of chicken Star-Cross 288 and the effect of La3+ on it were studied by using an LKB-2277 BioActivity Monitor, ampoule method, at 37 degrees C. After isolation from the chicken liver tissue, mitochondria still have metabolic activity and can live for a long time by using the stored nutrients. From the thermogenic curves, we obtained the thermokinetic equations under different condition. The kinetic study shows that La3+ has changed the metabolism completely.The thermogenic curves of the metabolism of mitochondria isolated from the liver of chicken Star-Cross 288 and the effect of La3+ on it were studied by using an LKB-2277 BioActivity Monitor, ampoule method, at 37°C. After isolation from the chicken liver tissue, mitochondria still have metabolic activity and can live for a long time by using the stored nutrients. From the thermogenic curves, we obtained the thermokinetic equations under different condition. The kinetic study shows that La3+ has changed the metabolism completely.

Insights Into The Working Mechanism and Unfolding Property of Arthrobacter chlorophenolicus Amylosucrase

Amylosucrase (AS) is a kind of glucosyltransferase (B.C. 2.4.1.4) belonging to the glycoside hydrolase (GH) family 13. In the presence of an activator polymer, in vitro, AS is able to catalyze the synthesis of an amylose-like polysaccharide composed of only alpha-1,4-linkages using sucrose as the only energy source. Unlike AS, other enzymes responsible for the synthesis of such amylose-like polymers require the addition of expensive nucleotide-activated sugars. These properties make AS an interesting enzyme for industrial applications. In spite of the great application potential, industrial applications of AS were largely hampered by its low stability. In this work, the structure of Arthrobacter chlorophenolicus amylosucrase (AcAS) was modeled according to crystal structures of Neisseria polysaccharea amylosucrase (NpAS) and Deinococcus geothermalis amylosucrase (DgAS). The structural difference of the three AS were investigated for the sake of exploring the working mechanism of AcAS. The dynamics and functional motions of AcAS were also investigated by the Gaussian network model (GNM). Based on GNM, it was found that AcAS can be divided into two regions with different moving directions. Finally, the unfolding property of AcAS was studied by the iterative GNM, and several kinetically weak regions were identified on the basis of the predicted unfolding pathway. These discoveries may be helpful to the industrial development of AS.

Synthesis, characterization and calorimetry of Ni(C4H8N2O3)2Cl2

A coordination complex was synthesized from NiCl2 and dipeptide glycylglycine(GG). It was characterized by element analysis, NMR and TG methods, and then was determined to be Ni(C4H8N2O3)2Cl2. Using an isoperibolic reaction calorimeter, the standard molar enthalpy of formation of Ni(GG)2Cl2(solid) has been determined to be −(1 674.66±2.02) kJ · mol−1 at 298.15 K.