Schiff碱药物对产气杆菌代谢抑制的热力学研究

用微量热法测定产气杆菌在不同温度条件下受到Schiff碱药物抑制的热谱曲线, 根据其指数生长期的热谱信息, 确定它在不同温度条件下的生长速率常数和反应活化能, 找出了该细菌的最佳生长温度。同时借用化学反应中的过渡态理论, 得到一系列热力学参数, 对细菌在受到抑制时的生长代谢进行了热力学分析。     

Thermal stability of cellulose acetate urethanes

The thermal degradation of isocyanate modified cellulose acetate has been studied by dynamic thermogravimetric analysis in air. The activation energy of decomposition of these modified polymers has also been determined from differential thermal analysis thermograms. The data indicate that the cellulose acetate urethane polymers are thermally stable.     

厌氧菌生长代谢的微量量热学研究

本世纪七十年代厌氧细菌学的崛起，是近代微生物学的重要进展山．它揭示了一个前所未知或知之不多的微生物世界．在人的皮肤和粘膜表面寄生着几百种、数以亿万计的细菌，它们中绝大多数在有氧的条件下不能生长繁殖，故称为厌氧菌．厌氧细菌学的出现，引起了医务工作者的高度重视．十多年来，积累了大量资料，为医学中的微生物学、免疫学、传染病学、流行病学甚至许多临床学科，增添了新的知识，对厌氧菌的感染，用目前医院的常规细菌培养方法不能检出，用常用的抗生素治疗，也常无效．它是临床上许多疑难杂症迁延不愈和反复发作的重要原因之…     

Glass transition activation energy of CdS/PMMA nano-composite and its dependence on composition of CdS nano-particles

CdS/PMMA nano-composites at different weight percent of CdS (0, 2, 4, 6, and 8) have been prepared using solution casting method. The obtained nano-composites are characterized through the transmission electron microscope (TEM). The differential scanning calorimetry (DSC) measurements have been done on the nano-composites at different heating rates. The peak glass transition temperature is determined using the DSC thermograms. It is found that the glass transition temperature increases with the increase of CdS content up to 6 wt% and then decreases for higher weight percent (8). It is explained on the basis of molecular motion of PMMA, which is restricted when CdS is added into PMMA. An effort is also made to study the activation energy of glass transition in the case of nano-composites of different weight percent of CdS. Variation of activation energy with CdS nano-particle concentration has also been theoretically predicted by using an empirical relation. Thermal stability of these nano-composites has been explained with the help of activation energy in the glassy region.     

Thermal decomposition kinetics of melt-mixed ethylene-co-vinyl acetate – based bio-composites

Bio-composites of ethylene-co-vinyl acetate (EVA) with chitosan (CS) and chitosan-g-PANi (CS-PANi) have been developed by using a melt-mixing process by varying the composition of fillers. Investigations on the degradation mechanism of thermoplastics lead to insights of their performance at high temperatures. The decomposition kinetics of the bio-composites was determined by plotting thermograms at different heating rates. The model-free Flynn-Wall-Ozawa and Kissinger method has been used to estimate the energy of activation (E_a) of the developed composites. The activation energies of EVA/CS composites lie between 162 and 209 kJ/mol and EVA/chitosan-g-PANi composites within the range of 145–256 kJ/mol. The variation in activation energy across the extent of conversion levels denotes multistep kinetics of degradation. The calculated E_a has been found to be in good agreement with the literature reports.     

A study of absorption currents in polystyrene and polystyrene-chloranil complex

The absorption currents in polystyrene (PS) and its donor-acceptor complex with chloranil (PS-CA) have been analysed in the temperature range 323–413 K. Low frequency (10-s-10-3 Hz) dielectric loss has been computed utilizing Haman's Fourier conversion of the absorption currents. A relaxation peak has been observed in the isochronal current and dielectric loss thermograms and identified with the a relaxation process of these polymers. The activation energy of the relaxation process has been evaluated from the Arrhenius shift of the relaxation peak. The effects of complex formation on absorption currents and the relaxation process have been discussed.     

Étude de la cinétique de la dégradation thermique du polypropylene et du polystyrène par analyse thermogravimétrique

Kinetic studies on the thermal degradation of polypropylene and polystyrene have been carried out using the thermogravimetric technique. Experimental thermograms have been interpreted by means of a simulation model which takes into account several simultaneous or consecutive reactions. In nitrogen, polypropylene degradation involves two reactions. The activation energy calculated for the second reaction, which corresponds to the main part of the weight loss curve, agrees with values obtained by means of calculation methods based on only one overall reaction. In air, a third reaction is added. Its activation energy is also in agreement with published values. However, for the two studied materials, orders of reaction are different.     

Thermal degradation behavior of cellulose fibers partially esterified with some long chain organic acids

The thermal degradation behavior of cellulose fibers and some fibrous cellulose esters with partial degree of substitution has been studied by thermogravimetry analysis (TG) and differential scanning calorimetry (DSC). Cellulose esters were prepared by heterogeneous esterification in Py/TsCl with unsaturated or saturated long chain organic acids [undecylenic (C₁₁), undecanoic (C₁₁), oleic (C₁₈) and stearic (C₁₈)]. The thermal degradation of cellulose fibers follows a one-step process. The thermal stability of cellulose esters is inferior to that of unmodified cellulose fibers and the thermograms show a two-step degradation process, probably controlled by crosslinking reactions, which occur during thermal decomposition. Exothermic peaks in the DSC thermograms are also an indication of such reactions. Kinetic parameters such as the activation energy E, order of decomposition n, and frequency factor Z were obtained following the Friedman method. The cellulose sample followed first order of decomposition, however for cellulose esters higher orders were observed.     

Studies on Thermal Polymerization of Acrylamide

Thermal polymerization of acrylamide has been followed by the DSC technique, and the activation energy (E) values at different stages of the fraction polymerized (a) have been determined from the exotherm of the thermograms obtained. The trend of variation of E with α shows that E remains constant up to α = 0.5 and decreases with a further increase in α. A close look at the composite nature of the exotherms, α-t, and α-T curves shows that the polymerization of acrylamide involves two processes. The first process is the formation of linear polyacrylamide and the second is the simultaneous cross-linking of the linear chains together with the formation of linear polyacrylamide. Experiments such as NH₃ detection by differential thermal analysis techniques and annealing studies have been made to shed further light on the polymerization process.     

Degradation of Phosphorylated Poly(N-Vinylcarbazole) by Thermogravimetry ‡

Abstract

The thermal degradation of phosphorylated poly(N-vinylcarbazole) was studied by thermogravimetry. The onset degradation temperature decreases with respect to that of unmodified poly(N-vinylcarbazole), indicating a lower thermal stability for the phosphorylated sample. The activation energy values for the degradation process were calculated from the thermograms by treating it as a kinetic analysis; these values are smaller than those for unmodified samples and depend on molecular weight, phosphorous contents, and heating rate.     

Mechanism of thermal degradation of poly(vinyl chloride)

The mechanism of thermal degradation of poly(vinyl chloride) has been studied by pyrolysis up to 400°C in a thermobalance under four kinds of dynamic atmospheres: helium, oxygen, air, and hydrogen chloride. The gaseous product from the thermobalance was analyzed for hydrogen chloride by the argentometric determination of chloride ions by using Mohr's method. An attempt was made to analyze for other gases in the product stream by chromatography with the use of a glass column, but failed due to the accumulation irreversibly of hydrogen chloride on the column. The molecular weights of the samples were determined by measurements of viscosities at 25°C in cyclohexanone; their molecular weight distributions were studied by fractionation and gelpermeation chromatography (GPC). From the thermograms, the mechanism of degradation in different heating atmospheres, the rate, the heat effect, the energy of activation, and the order of decomposition were deduced.     

Study of kinetics of thermal degradation and to determine the activation energies of polyamides based on s-triazine

A series of ten polyamides was prepared by the high-temperature polycondensation of 4,6-bis(N-(4-(benzoylchloride)amino))-2-(N-phenyl- piperazin-1-yl)-1,3,5-triazine with different aromatic and aliphatic diamines. The synthesized polyamides were analyzed by physico-chemical properties such as solubility, density, viscosity etc. The structure of prepared polyamides was evaluated by ¹H NMR and FTIR spectrum. Thermogravimetric analysis used to study the kinetics of thermal degradation of some synthesized polyamides. Broido, Horowitz & Metzger, Coats Redfern and Chan et al. models were applied to respective thermograms to determine the activation energy (E_a). Activation energy data shows that the polyamides obtained from aromatic diamine has greater stability than the polyamides obtained from aliphatic amine.     

A thermal study of some Schiff bases derivative of α-napthylamine

Thermal analyses of some Schiff bases, derivative of α-napthylamine, were performed by the DSC, TG and DTA techniques. The thermograms were used to determine various kinetic parameters, such as the order of degradation (n), energy of activation (E), frequency factor (A), and entropy change (ΔS), by the Freeman-Carroll method. The text was submitted by the authors in English.     

Influence of heating and cooling rates on the glass transition temperature and the fragility parameter of sorbitol and fructose as measured by DSC

The glass transition temperatures of sorbitol and fructose were characterized by four points determined on DSC heating thermograms (onset, mid-point, peak and end-point), plus the limit fictive temperature. The variations of these temperature values, observed as functions of cooling and heating rates, were used to determine the fragility parameter, as defined by Angell [1] to characterize the temperature dependence of the dynamic behavior of glass-forming liquids in the temperature range above the glass transition. The apparent activation energy values, determined for the different temperatures studied, were similar for fructose and sorbitol. These values were compared to data obtained from other techniques, such as mechanical spectroscopy. The variations of the apparent activation values, observed in experiments involving cooling and heating at the same rate, slow cooling followed by rate-heating, or rate-cooling followed by fast heating, were explained by aging effects occurring during the heating step.     

种子萌发生长的微量热及非平衡热力学研究

生命系统中发生的许多过程都有放热和吸热现象.人们对于生命过程的热现象进行了很多研究.对于植物生长的能量效应研究也做了一些工作[1—4].种子萌发生长的热释出是植物产热的一个很好例子,在种子萌发生长过程中伴随着物质和能量的转化,用微量热法测定种子萌发生长热谱并解析这些热谱,将有助于我们认识种子萌发生长机理及其影响因素.Ｐｒａｔ等人曾对小麦、玉米及一些蔬菜种子的萌发生长进行过较为系统的研究[1,2].他们的工作为用量热法研究植物产热开辟了道路.但由于当时测量技术与仪器设计的限制,其研究结果是粗糙的,且与种子萌发的实际情…     

Electrical and thermal studies on some acetylacetoneand benzoylacetone-arylhydrazones

The electrical and thermal properties of some acetylacetone-(I) and benzoylacetone-(II) arylhydrazone derivatives have been investigated. The results obtained show semiconductor behavior as evident from the positive temperature coefficient of electrical conductivity (dG/dT). Values of activation energy (ΔE) have been calculated in each case. The electrical conductivity increases with the introduction of either electron-donating or electron-withdrawing substituents to the phenyl ring. Differential thermal analysis curves showed sharp well-defined peaks at the melting point of the investigated compounds. The latent heats of fusion were calculated from these thermograms.     

Differential Thermal Analysis of Rapid High Pressure Decompositions

Abstract

A simple sample handling technique for recording differential thermograms of volatile and/or high pressure producing compounds is described. The calculation of activation energies for several hydrazines and explosives is reported.     

Characterization of methyl methacrylate grafting onto preirradiated biodegradable lignocellulose fiber by gamma-radiation

Gamma-radiation-induced graft copolymerization of methyl methacrylate onto natural lignocellulose (jute) fiber was carried out by the preirradiation method in an aqueous medium by using octylphenoxy-polyethoxyethanol as an emulsifier. The different factors that influenced the graft copolymer reaction process were investigated. In the case of radiation-dose-dependent grafting, samples irradiated in the presence of air produced up to 73% graft weight compared to 53% obtained in the case of irradiation in a nitrogen environment. By assuming Arrhenius reaction kinetics, the activation energy (E(a)) of the grafting reaction process was evaluated for different reaction temperatures. Moreover, the graft copolymer reaction was controlled by incorporating a homopolymer-inhibiting agent and three different chain-transfer agents in the reaction medium. The mechanical and thermal properties of jute fiber 'as received' and jute-graft-poly(methyl methacrylate) were also investigated. The results showed that the percentage of grafting with jute fiber has a significant effect on the properties. The kinetic parameters were evaluated from TGA thermograms by using Broido's method in the temperature range 240-350 degrees C. Scanning electron micrographs show that the structural changes on the surface of jute fibers were induced by graft copolymerization of methyl methacrylate monomer. Fiber-fiber surface friction was measured in terms of the average maximum load and the kinetic friction. SEM of jute-graft-poly(methyl methacrylate).     

A differential scanning calorimetric study of the radical polymerization of N-vinylpyrrolidone in dimethylformamide

Polymerization of N-vinylpyrrolidone (NVP) in dimethylformamide was studied by differential scanning calorimetry (DSC). The concentration of NVP was 0.75 M, that of the radical initiator (azobisisobutyronitrile) 0.01 or 0.02 M. For proper evaluation of scanning thermograms, it was necessary to correct for incomplete monomer conversion due to premature initiator exhaustion and to consider the instantaneous initiator concentration. If these points were allowed for in the computations, activation parameters agree well with those obtained from isothermal thermograms. The values for the overall activation energy were E_a = 82 and 84 kJ/mol, and those for the pre-exponential factor $\text{Z = 6 × 10}{}^{\mathrm{?9}}\text{and}\text{13 × 10}{}^{\mathrm{?9}}\text{(}\text{mol/l}\text{)}{}^{\mathrm{<mtext>?1</mtext><mtext>2</mtext>}}\text{.}\text{sec}{}^{\mathrm{?1}}$, obtained from the scanning (dynamic) and the isothermal method, respectively.     

Effect of the soil uses on their thermal stability

Differential scanning calorimetry was applied to assess on seasonally soil organic matter changes. Soils were collected in two sites located in Viveiro (Galicia, Spain). One of them has been used as arable land and the other one was under pinewood. Soil samples were seasonally collected during a year. The heat of combustion and the ignition temperature of the soil organic matter were calculated by analyzing the thermograms obtained by differential scanning calorimetry. The shape and the maximum and end temperatures of the two exothermic peaks observed in the thermograms, yielded information about the relations between the labile and recalcitrant pools, and hence information about carbon stabilization degree in both soils.