热动力学的滴定量热法研究2: 考虑热滞后的一级 反应精确热动力学

建立了滴定热量计滴定期一级反应热动力学的精确数学模型,并在此基础上探讨了热滞后对此模型的影响。经过改进的模型大大提高了利用滴定热量计获取动力学数据的准确度,且扩大了滴定热量计研究的一级反应体系的范围,使其适用反应的半衰期可以小至十几秒。本文采用此模型,研究了去离子水溶剂中乙酸乙酯皂化反应的热动力学,实验结果验证了该模型研究一级反应热动力学的适用性。     

乙酸乙酯皂化反应的热动力学实验

介绍基于量热法的热动力学原理。利用该方法测定了乙酸乙酯皂化反应的速率常数,并比较了该方法与电导法的优缺点。     

热动力学的滴定量热法研究2: 单底物酶促反应的热动力学

用滴定量热法分别建立了滴定期和停滴反应期单底物酶促反应热动力学的数学模型。根据这两种模型,可由一次实验的滴定量热曲线同时解析出单底物酶促反应的热力学参数(Δ~rH~m)和动力学参数(K~m和k~2)。用滴定量热法研究了一个经典的单底物酶促反应---过氧化氢酶催化分解过氧化氢反应的热动力学,由滴定期和停滴反应期热动力学模型解析出在298.15K和pH=7.0时该反应的米氏常数K~m分别为(5.41±0.24)×10^-^3和(5.43±0.21)×10^-^3mol.L^-^1,酶转换数k~2分别为(3.58±0.33)×10^3和(3.60±0.41)×10^3s^-^1,摩尔反应焓为(-86.75±0.88)kJ.mol^-^1,实验结果验证了上述热动力学模型的正确性。     

热动力学的滴定量热法研究2: 单底物酶促反应的热动力学

用滴定量热法分别建立了滴定期和停滴反应期单底物酶促反应热动力学的数学模型。根据这两种模型,可由一次实验的滴定量热曲线同时解析出单底物酶促反应的热力学参数(Δ~rH~m)和动力学参数(K~m和k~2)。用滴定量热法研究了一个经典的单底物酶促反应---过氧化氢酶催化分解过氧化氢反应的热动力学,由滴定期和停滴反应期热动力学模型解析出在298.15K和pH=7.0时该反应的米氏常数K~m分别为(5.41±0.24)×10^-^3和(5.43±0.21)×10^-^3mol.L^-^1,酶转换数k~2分别为(3.58±0.33)×10^3和(3.60±0.41)×10^3s^-^1,摩尔反应焓为(-86.75±0.88)kJ.mol^-^1,实验结果验证了上述热动力学模型的正确性。     

较快反应的热动力学天空

根据热导式热量计的工作原理,提出了热导式热量计的界面模型,建立了感温滞后条件下热量计的理论方程,从而提出了一种较快反应的热动力学研究法---失真热谱曲线修正法,并利用该法成功地研究了几个较快的准一级和等浓度二级反应的热动力学。     

较快反应的热动力学天空

根据热导式热量计的工作原理,提出了热导式热量计的界面模型,建立了感温滞后条件下热量计的理论方程,从而提出了一种较快反应的热动力学研究法---失真热谱曲线修正法,并利用该法成功地研究了几个较快的准一级和等浓度二级反应的热动力学。     

较快一级化学反应的热动力学研究法: 热弛豫法

分析了非稳态传热情况下热导式热量计的动态性能,通过对输出信号的剖析,建立了热导式热量计冷却常数的经验动态模型。通过对热弛豫现象的分析,建立了可用于研究快速化学反应的热动力学研究法-热弛豫法,应用此种量热研究法可用于研究速率常数小于5s^-^1的一级化学反应。研究了25℃下乙酸甲酯、甲酸乙酯和甲酸甲酯在水溶液中的皂化反应,其计算结果与文献值相吻合,从而验证了热弛豫法的正确性。     

自函数回归法: 连续一级反应的热动力学研究

根据热动力学基本原理,推导出了连续一级反应热动力学自函数递推方程,从而建立了一种新的连续一级反应的热动力学研究法---自函数回归法.应用该法分别研究了丁二酸二乙酯和邻苯二甲酸二乙酯皂化反应的热动力学。     

热动力学的滴定量热法研究 Ⅰ.一级反应的热动力学

用滴定量热法分别建立了满定期和停满反应期一级反应热动力学的数学模型．根据这两种模型，均可由一次实验的滴定量热曲线同时解析出一级反应的速率常数（k1）和摩尔反应治（△rHm）．用液定量热法研究了去离子水溶剂中乙酸乙酯皂化反应的热动力学，实验结果验证了本文用滴定量热法研究一级反应热动力学的运用性．     

滴定量热法研究连串一级反应热动力学

本文用滴定量热法分别建立了滴定期和停滴反应期1-1级连串反应热动力学的数学模型。根据这两种模型,由非线性最小二乘法原理直接拟合单次实验结果可同时求得1-1级连串反应的速率常数（ k ₁和 k ₂）和摩尔反应焓。并用滴定量热法研究了丁二酸二乙酯皂化反应的热动力学,实验结果验证了两种数学模型的正确性。     

A study on the thermodynamic properties of polyimide BTDA-ODA by adiabatic calorimetry and thermal analysis

Polyimide BTDA-ODA sample was prepared by polycondensation or step-growth polymerization method. Its low temperature heat capacities were measured by an adiabatic calorimeter in the temperature range between 80 and 400 K. No thermal anomaly was found in this temperature range. A DSC experiment was conducted in the temperature region from 373 to 673 K. There was not phase change or decomposition phenomena in this temperature range. However two glass transitions were found at 420.16 and 564.38 K. Corresponding heat capacity increments were 0.068 and 0.824 J g^–1 K^–1, respectively. To study the decomposition characteristics of BTDA-ODA, a TG experiment was carried out and it was found that this polyimide started to decompose at ca 673 K.This revised version was published online in November 2005 with corrections to the Cover Date.     

Analysis of the interactions between human serum albumin/amphiphilic penicillin in different aqueous media: an isothermal titration calorimetry and dynamic light scattering study

The complexation process of the amphiphilic penicillins sodium cloxacillin and sodium dicloxacillin with the protein human serum albumin (HSA) in aqueous buffered solutions of pH 4.5 and 7.4 at 25 °C was investigated through isothermal titration calorimetry (ITC) and dynamic light scattering. ITC experiments were carried out in the very dilute regime and showed that although hydrophobic interactions are the leading forces for complexation, electrostatic interactions also play an important role. The possibility of the formation of hydrogen bonds is also deduced from experimental data. The thermodynamic quantities of the binding mechanism, i.e, the enthalpy, , entropy, , Gibbs energy, , binding constant, and the number of binding sites, n_i, were obtained. The binding was saturable and is characterised by Langmuir adsorption isotherms. From ITC data and following a theoretical model, the number of bound and free penicillin molecules was calculated. From Scatchard plots, and n_i were obtained and compared with those from ITC data. The interaction potential between the HSA–penicillin complexes and their stability were determined at pH 7.4 from the dependence of the diffusion coefficients on protein concentration by application of the DLVO colloidal stability theory. The results indicate decreasing stability of the colloidal dispersion of the drug–protein complexes with increase in the concentration of added drug.     

A thermometric titration study of the interaction of Al3+, Co2+, Ni2+ and Zr4+ with xylenol orange

A thermometric titrimetry study of the interaction in aqueous solution of A1³⁺, Co²⁺, Ni²⁺ and Zr⁴⁺ with xylenol orange has revealed in each case a linear reaction heat/[Mⁿ⁺] relationship at a specified pH, thereby suggesting the potential of metallochromic indicators for the analytical determination of these metals in water. The effect of pH on the reaction heat is investigated and is interpreted in terms of the ability of these metal cations to complex with the known xylenol orange species existing at the various pH studied. An interference study, involving transition and non-transition metal ions, is also reported and the interference effect, as measured by the deviation ofQ/Q from unity (Q andQ are the relevant reaction heats in the presence and absence of interfering ion), is partially explained in terms of the coordination numbers, relative sizes and crystal field stabilization energies of the cations studied and the known behaviour of xylenol orange in aqueous solution.     

A potentiometric titration study on the dissociation of bile acids related to the mode of interaction between different head groups of nonionic surfactants with free bile salts upon mixed micelle formation in water

By constructing an elaborate set of potentiometric titration together with data analysis system, apparent acid dissociation indices (pK _a ^app ) for two bile acids were determined in the mixed surfactant system of bile salts (Sodium Deoxycholate, NaDC, and Sodium Chenodeoxycholate, NaCDC) with nonionic surfactants (Hexaethyleneglycol monon-dodecylether, C₁₂E₆, Decanoyl-N-methylglucamide, MEGA-10) in aqueous solution at ionic strength 1.5 as a function of mole fraction in the surfactant mixture. It was found that with increasing the bile salt concentration, pK _a ^app as well as pH showed an abrupt rise at a certain concentration of the bile salt being regardable as a critical micellization concentration (CMC) and reached a constant value at the range sufficiently higher than CMC for each pure bile salt system, meaning that the dissociation degree of carboxyl group in micelle is smaller than that in bulk. In the mixed systems of free bile salts with nonionic surfactants, the dissociation state of carboxyl groups in mixed micelles depends on the species of hydrophilic group of nonionic surfactants as well as on mole fraction in the surfactant mixture.     

Mechanism and rate constants of the CH2 + CH2CO reactions in triplet and singlet states: A theoretical study

Ab initio and density functional CCSD(T)-F12/cc-pVQZ-f12//B2PLYPD3/6-311G** calculations have been performed to unravel the reaction mechanism of triplet and singlet methylene CH₂ with ketene CH₂CO. The computed potential energy diagrams and molecular properties have been then utilized in Rice–Ramsperger–Kassel–Marcus-Master Equation (RRKM-ME) calculations of the reaction rate constants and product branching ratios combined with the use of nonadiabatic transition state theory for spin-forbidden triplet-singlet isomerization. The results indicate that the most important channels of the reaction of ketene with triplet methylene lead to the formation of the HCCO + CH₃ and C₂H₄ + CO products, where the former channel is preferable at higher temperatures from 1000 K and above. In the C₂H₄ + CO product pair, the ethylene molecule can be formed either adiabatically in the triplet electronic state or via triplet-singlet intersystem crossing in the singlet electronic state occurring in the vicinity of the CH₂COCH₂ intermediate or along the pathway of CO elimination from the initial CH₂CH₂CO complex. The predominant products of the reaction of ketene with singlet methylene have been shown to be C₂H₄ + CO. The formation of these products mostly proceeds via a well-skipping mechanism but at high pressures may to some extent involve collisional stabilization of the CH₃CHCO and cyclic CH₂COCH₂ intermediates followed by their thermal unimolecular decomposition. The calculated rate constants at different pressures from 0.01 to 100 atm have been fitted by the modified Arrhenius expressions in the temperature range of 300–3000 K, which are proposed for kinetic modeling of ketene reactions in combustion. © 2018 Wiley Periodicals, Inc.     

A two transition state model for radical-molecule reactions: a case study of the addition of OH to C2H4

A two transition state model is applied to the study of the addition of hydroxyl radical to ethylene. This reaction serves as a prototypical example of a radical-molecule reaction with a negative activation energy in the high-pressure limit. The model incorporates variational treatments of both inner and outer transition states. The outer transition state is treated with a recently derived long-range transition state theory approach focusing on the longest-ranged term in the potential. High-level quantum chemical estimates are incorporated in a variational transition state theory treatment of the inner transition state. Anharmonic effects in the inner transition state region are explored with direct phase space integration. A two-dimensional master equation is employed in treating the pressure dependence of the addition process. An accurate treatment of the two separate transition state regions at the energy and angular momentum resolved level is essential to the prediction of the temperature dependence of the addition rate. The transition from a dominant outer transition state to a dominant inner transition state is predicted to occur at about 130 K, with significant effects from both transition states over the 10 to 400 K temperature range. Modest adjustment in the ab initio predicted inner saddle point energy yields theoretical predictions which are in quantitative agreement with the available experimental observations. The theoretically predicted capture rate is reproduced to within 10% by the expression [4.93 x 10(-12) (T/298)(-2.488) exp(-107.9/RT) + 3.33 x 10(-12) (T/298)(0.451) exp(117.6/RT); with R = 1.987 and T in K] cm3 molecules(-1) s(-1) over the 10-600 K range.     

A comparative study on the single-scan and multiple-scan techniques in differential scanning calorimetry: Application to the crystallization of the semiconducting Ge0.13Sb0.23Se0.64 alloy

A method has been developed for analysing the evolution with time of the volume fraction transformed and for calculating the kinetic parameters at non-isothermal reactions in materials involving formation and growth of nuclei. By considering the assumptions of extended volume and random nucleation, a general expression of the fraction transformed as a function of time has been obtained in isothermal crystallization processes. Considering the mutual interference of regions growing from separate nuclei the Johnson–Mehl–Avrami equation has been deduced as a particular case. The application of the transformation rate equation to the non-isothermal processes has been carried out under the restriction of a nucleation which takes place early in the transformation and the nucleation frequency is zero thereafter. Under these conditions, the kinetic parameters have been deduced by using the techniques of data analysis of single-scan and multiple-scan. The theoretical method developed has been applied to the glass-crystal transformation kinetics of the semiconducting Ge_0.13Sb_0.23Se_0.64 alloy. The kinetic parameters obtained according to both techniques differ by only about 2.5%, which confirms the reliability and accuracy of the single-scan technique when calculating the above-mentioned parameters in non-isothermal transformation processes. The phases at which the above-mentioned semiconducting glass crystallizes after the thermal process have been identified by X-ray diffraction. The diffractogram of the transformed material shows that microcrystallites of Sb₂Se₃ and GeSe are associated with the crystallization process, remaining a residual amorphous matrix.