Quantitative analysis of the calorimetric parameters associated with the temperature induced aggregation of aqueous solutions of polyoxypropylene

High sensitivity differential scanning calorimetry (HSDSC)—coupled with the application of a previously outlined thermodynamic model [Patterson et al., Langmuir 13 (1997) 2219]—has been used to the obtain thermodynamic parameters that characterise thermal aggregation in aqueous solutions of polyoxypropylene (POP) of molecular mass 1000 g mol⁻¹ over a range of concentrations (2.5–51.5 g dm⁻³). An important aspect of the derived thermodynamic values, which complements previously reported HSDSC data [Armstrong et al., J. Phys. Chem. 99 (1995) 4590], is the elaboration of heat capacity changes which accompany the aggregation transition. The concentration dependence of the POP thermodynamic data, obtained in this investigation, has been established. These observations provide the means for establishing functional relationships between enthalpy and temperature as well as heat capacity and temperature. The parameters describing the quadratic relationship between enthalpy change associated with aggregation and temperature are in close agreement with those describing the linear relationship between heat capacity change and temperature.     

Solid-state reactions from isothermal heat conduction microcalorimetry theoretical approach and evaluation via simulated data

Several recent publications from this laboratory have reported developments in the capacity to calculate thermodynamic and kinetic parameters, such as rate constant, enthalpy, order of reaction, from isothermal micro-calorimetric data. To date these developments have all been associated with the calculation of the desired parameters from solution phase reactions. This paper furthers these developments to a theoretical consideration of solid-state reactions and the calculation of the values for the rate coefficient, k, the fitting parameters m and n, the total number of joules released over the lifetime of reaction, Q, and hence either the specific enthalpy or the molar enthalpy of reaction, H. This revised version was published online in July 2006 with corrections to the Cover Date.     

立方体纳米氧化亚铜反应动力学的理论及实验研究

为了探究纳米多相反应过程的动力学行为,本文通过液相还原法可控合成了粒度为55 nm的立方体氧化亚铜（Cu₂O）。基于纳米与块体Cu₂O的区别,采用原位微量热技术获取Cu₂O体系与HNO₃反应过程的热动力学精细信息,结合热动力学原理及动力学过渡态理论计算得到Cu₂O反应动力学参数,并建立立方体动力学模型讨论并佐证动力学实验结果。结果表明,纳米Cu₂O的反应速率常数大于块体,而表观活化能、指前因子、活化焓、活化熵和活化Gibbs自由能均小于块体;随着温度的升高,纳米Cu₂O的反应速率常数和活化Gibbs自由能均增大。动力学模型表明影响反应动力学参数的主要因素为：偏摩尔表面焓影响表观活化能,偏摩尔表面熵影响指前因子,偏摩尔表面Gibbs自由能影响反应速率常数。本文为纳米材料多相反应动力学参数的获取和分析应用提供了一种普适的理论模型和实验方法。     

Theoretical Considerations on the Possibility of Enhancing the Effect of Temperature upon the Melt Viscosity of Linear Polymers by the Incorporation of Weak Bonds in the Chains. II. Kinetic Factors

On the basis of a realization of thermodynamic requirements as given in part I, simple kinetic considerations are applied to the processes of weak bond fission and block recombination from two distinct bases: (a) independence of rate constants and viscosity (or average molecular weight) of the polymer system; and (b) a diffusion-controlled situation where the rate of block recombination is governed by the viscosity of the medium. On the independent rate constant model, an activation energy for the recombination process of less than 40 kJ [mole (of weak bonds)]^?1 gives an acceptable rate of equilibration at ambient temperatures; this criterion ought to be readily satisfied in practice. However, considerations of diffusion control suggest that equilibration may be too slow to be practicable and this is probably the major limitation on preparing rigid polymers with temperature-varying molecular weights     

Determination of Michaelis-Menten parameters obtained from isothermal flow calorimetric data

Recent papers have reported [Thermochim. Acta 399 (2003) 63; Thermochim. Acta, in press] the results of a preliminary inter/intra laboratory study into the suitability of the base-catalysed hydrolysis of methyl paraben as a test and reference reaction for isothermal flow-through calorimeters. It was shown that this reaction can be used to investigate the flow characteristics of the instrument being used. It has also allowed, for the first time, the calculation of accurate values for the rate constant and for the enthalpy change, ΔH (hereafter H (enthalpy) for simplicity) of reaction directly from the calorimetric data, free from assumption. These findings have been extended to permit the direct determination of Michaelis-Menten based kinetic parameters from calorimetric data again free from assumption (except that the system conforms to Michaelis-Menten kinetic theory). This paper describes the method used for such an analysis and reports the results of a preliminary study on the urea/urease enzymatic system.     

Kinetic and thermodynamic assessments of the mediator-template assembly of nanoparticles

The understanding of kinetic and thermodynamic factors governing the assembly of nanoparticles is important for the design and control of functional nanostructures. This paper describes a study of the kinetic and thermodynamic factors governing the mediator-template assembly of gold nanoparticles into spherical assemblies in solutions. The study is based on spectrophotometric measurements of the surface plasmon (SP) resonance optical property. Gold nanoparticle cores ( approximately 5 nm) encapsulated with tetraoctylammonium bromide shells were studied as a model system. The mediator-template assembly involves a thioether-based multidentate ligand (e.g., MeSi(CH2SMe)3) which functions as a mediator, whereas the tetraoctylammonium bromide capping molecules function as template agents. On the basis of the temperature dependence of the SP optical property in the mediator-template assembly process, the kinetic and thermodynamic parameters such as the reaction rate constant and reaction enthalpy have been determined. The results led to two important findings. First, the mediator-template assembly of nanoparticles is an enthalpy-driven process. Second, the enthalpy change (-1.3 kcal/mol) is close to the magnitude of the van der Waals interaction energy for alkyl chains and the condensation energy of hydrocarbons. Implications of the findings to the understanding of the interparticle interactions have also been discussed.     

表面活性剂分子间弱相互作用的直接能量表征——高灵敏等温滴定量热法

分子间弱相互作用热力学研究的直接实验方法就是利用量热手段测定相互作用的能量参数. 本文对TAM III-ITC 纳焦级量热计进行了电标定实验和标准反应热测量, 结果显示本量热计的精密度为±0.09%; 量热用基准物质三羟甲基氨基甲烷(Tris)与盐酸的反应热((-47.48±0.12) kJ·mol^-1)与文献值一致. 采用此量热计,对典型的头-尾链型阳离子表面活性剂十二烷基三甲基溴化铵(DTAB)测量得到了与文献报导值很好吻合的临界胶束浓度(cmc)和胶束化焓, 而且对具有亲水-疏水面式刚性结构的生物表面活性剂胆酸钠(NaC)也获得了可靠的结果. 进一步地, 对于相反电荷的混合表面活性剂体系(DTAB/NaC), 分别研究了在富NaC区和富DTAB区体系混合胶束的形成. 结果说明DTAB/NaC混合表面活性剂体系在富NaC区有较强的协同效应, 而在富DTAB区的协同效应较弱. 本文结合电导率测定结果, 对DTAB/NaC混合体系在水溶液中的分子自组装热力学行为进行了有价值的讨论.     

硫酸锌与组氨酸固液反应的热动力学研究

用微热量计对硫酸锌与组氨酸在水中的固液反应进行了热动力学研究。通过实验和计算得出了该反应的热动力学参数（活化焓,活化熵及活化自由能）,速率常数和动力学参数（活化能,指前因子及反应级数）,并对温度改变对该反应的影响及配合物的合成条件进行了讨论。     

Identification of micro-scale calorimetric devicesIV. Descriptive models in 3-D

The experimental analysis of conventional conduction calorimeters shows excellent reproducibility and relevant systematic errors in comparison with thermodynamic values established via adiabatic calorimeters. Two examples: a DSC and a liquid flow device are schematically analyzed. When an increased accuracy will be obtained the positional effects on the experimental set-up and on the measurement process need to be modelled. From experimental measurements realized on the Xensor liquid nano-calorimeter representative models can be built. To evaluate the reliability of measurement routines, established from experimental basis, several different dissipation structures inside the working space can be simulated. Two experimental configurations related to drop to drop reaction and to continuous mixing are modelled via RC approach. The RC formalism is extended to evaluate the carried energy effect produced by the continuous inflow/outflow of reactants in the mixing enthalpy chamber. This revised version was published online in July 2006 with corrections to the Cover Date.     

Kinetic studies on saponification of ethyl acetate using an innovative conductivity‐monitoring instrument with a pulsating sensor

An innovative conductometric measurement technique using a nonconventional but high‐performance (high‐precision, high‐resolution, rapid response features for online graphic display) in house–built pulsating conductivity monitoring instrument has been deployed to study the kinetic behavior during the reaction of ethyl acetate and NaOH. A laboratory‐made constant temperature reaction bath with the facility of continuous stirring of solution for homogeneous mixing was used to carry out experiments at desired solution temperatures. Rate constants of the saponification reaction in the temperature range at various temperatures (30–55°C) were determined, and the results were compared with the reported values. Although the reported data exhibit wide scatter, our data are in agreement with some of the literature data. From these data, thermodynamic parameters such as activation energy, activation enthalpy, activation entropy, and activation free energy have been evaluated. With the introduction of this novel conductometric measurement technique, the determination of rate constants at various solution temperatures becomes much simpler and faster. © 2011 Wiley Periodicals, Inc. Int J Chem Kinet 43: 648–656, 2011     

A Thermochemical Study on Complex Nickel(Ⅱ) L-α-Histidine

IntroductionNickel is an essential trace biological element.L-α- Amino acids are the structural units of pro-teins.L- α- Histidine is one of the eight species ofamino acids which have to be absorbed from foodbecause they are not synthesized by organism.Thus,the investigation on the complexation ofnickel and L -α- histidine is of considerable practicaland fundamental importance.For the nickel com-plexes of amino acids,more extensive work hasbeen carried out[1— 3 ] . However,the thermochem…     

Thermodynamic study of ion exchange reaction to predict ionic selectivity using ion exchange resin Indion-850

The thermodynamic study was carried out to predict the selectivity behaviour of ion exchange resin Indion-850 towaed various inorganic anions like chloride, iodide, sulfate, and oxalate. The equilibrium constant K _std values for the ion exchange reactions were calculated at different temperatures from which the enthalpy values where obtained. The K _std values were observed to increase with the rise in temperature, indicating endothermic ion exchange reactions. The thermodynamic data obtained here reveal that iodide ions were more strongly retained on the resin surface compared to chloride ions. Also the low enthalpy and high equilibrium constant values for oxalate ions indicate the greater selectivity of ion exchange resin for oxalate ions as compared to sulfate ions.     

A Thermochemical Study on Complex Nickel（Ⅲ）L—α—Histidine

The formation enthalpy ofcomplex nickel(Ⅱ）-histidine(His)in water was determined by means of microcalorimetry in the temperature range of 298.15-323.15K.The standard enthalpy of the formation of Ni(His)2^2 (aq) was calculated.On the basis of the experimental and the calculated results,three thermodynamic parameters(the activation enthaly,the activation entropy and the activation free energy),the rate constants,three kinetic parameters(the apparent activation energy,the pre-exponential constant and the reaction order)of the formation reaction of the title complex were obtained.     

Charge recombination fluorescence in photosystem I reaction centers from Chlamydomonas reinhardtii

The fluorescence kinetics of photosystem I core particles from Chlamydomonas reinhardtii have been measured with picosecond resolution in order to test a previous hypothesis suggesting a charge recombination mechanism for the early electron-transfer steps and the fluorescence kinetics (Müller et al. Biophys. J. 2003, 85, 3899-3922). Performing global target analyses for various kinetic models on the original fluorescence data confirms the "charge recombination" model as the only acceptable one of the models tested while all of the other models can be excluded. The analysis allowed a precise determination of (i) the effective charge separation rate constant from the equilibrated reaction center excited state (438 ns(-1)) confirming our previous assignment based on transient absorption data (Müller et al. Biophys. J. 2003, 85, 3899-3922), (ii) the effective charge recombination rate constant back to the excited state (52 ns(-1)), and (iii) the intrinsic secondary electron-transfer rate constant (80 ns(-1)). The average energy equilibration lifetime core antenna/RC is about 1 ps in the "charge recombination" model, in agreement with previous transient absorption data, vs the 18-20 ps energy transfer lifetime from antenna to RC within "transfer-to-the-trap-limited" models. The apparent charge separation lifetime in the recombination model is about three times faster than in the "transfer-to-the-trap-limited" model. We conclude that the charge separation kinetics is trap-limited in PS I cores devoid of red antenna states such as in C. reinhardtii.     

Antioxidant activity of o-bisphenols: the role of intramolecular hydrogen bonding

A kinetic and thermodynamic investigation on the antioxidant activity of 2,2'-methylenebis(6-tert-butyl-4-methylphenol) (2), 2,2'-ethylidenebis(4,6-di-tert-butylphenol) (3), and 4,4'-methylenebis(2,6-di-tert-butylphenol) (4) are reported. EPR studies of the equilibration between 3 or 4 and a reference phenol, and the corresponding phenoxyl radicals, allowed us to determine the O-H bond dissociation enthalpy (BDE) of the O-H bond as 81.2 and 81.1 kcal/mol in 3 and 4, respectively. Despite this similarity, the absolute rate constants for the reaction with peroxyl radicals, determined by autoxidation studies under controlled conditions, indicate that the o-bisphenols 2 and 3 behave as excellent antioxidants while the p-bisphenol 4 is less effective by a factor of 64 and 22, respectively. FT-IR spectroscopy and product studies suggest that the very good antioxidant activity of the o-bisphenols largely arises from both the reduced steric crowding about the hydroxyl group and the stabilization of the aroxyl radical due to the formation of an intramolecular hydrogen bond between the residual OH and the oxygen radical center.     

Rapid mixing of sub-microlitre drops by magnetic micro-stirring

We demonstrate rapid mixing of sub-microlitre droplets (250 nl) using miniaturized magnetic stir bars (400 μm × 200 μm × 15 μm). The stir bars are fabricated using laser micromachining and placed on the substrate on which the drops are manipulated. They are activated by an externally applied magnetic field and used in combination with on-demand drop merging in enthalpy arrays. This technique results in a 10-fold increase in mixing rate, and a mixing time constant of about 2 s. Drop mixing times are measured by F?rster resonance energy transfer (FRET) and verified by thermodynamic measurements of binding and enzymatic reactions.     

Investigation into the effects of temperature and stirring rate on the solid-phase extraction of diuron from water using a C18 extraction disk

A novel experimental method for determining the equilibrium constant, Keq, and the uptake rate constant, kup, for the solid-phase extraction (SPE) of diuron from water using a C18 Empore extraction disk is reported. Log Keq and log kup are determined at 7.0, 11.0, 18.0 and 23.0 degrees C and for stirring rates of 100, 200 and 400 rpm. From a Van 't Hoff plot of log Keq versus T-1 the enthalpy of sorption, delta H0, is shown to be negative which indicates that the thermodynamic process of uptake is exothermic. The rate of stirring has no effect on log Keq over the temperature range 7.0-23.0 degrees C. The enthalpy of activation, delta H0, calculated from Arrhenius plots of log kup versus T-1 at 100, 200 and 400 rpm show that the kinetic process of uptake is endothermic. At 100 rpm the rate of uptake is limited by the aqueous diffusion of diuron. At 200 rpm or greater the aqueous diffusion layer around the disk is sufficiently small to prevent diffusion from being a limiting factor. The method described in this paper is limited to the analysis of analytes that contain a significant UV chromophore and are relatively soluble in water, but it can also be used to investigate pH and salinity effects on the SPE of diuron from water.     

Thermochemical Study of Coordination of Holmium Chloride Hydrate with Diethylammonium Diethyldithiocarbamate

The complex of holmium chloride hydrate with diethylammonium diethyldithiocarbamate (D-DDC) was synthesized via mixing their solutions in absolute alcohol under a dry N2 atmosphere. The elemental and chemical analyses show that the complex has the general formula Et2NH2[Ho(S2CNEt2)4]. It was also characterized by IR spectroscopy. The enthalpies of the dissolution of holmium chloride hydrate and D-DDC in absolute alcohol at 298.15 K o and the enthalpy changes of liquid-phase reactions of the formation of Et2NH2[Ho(S2CNEt2)4] at different temperatures were determined by microcalorimetry. On the basis of experimental and calculated results, three thermodynamic parameters (the activation enthalpy, the activation entropy and the activation free energy), the rate constant and three kinetic parameters (the apparent activation energy, the pre-exponential constant and the reaction order) of the liquid-phase reaction of the complex formation were obtained, The enthalpy change of the solid-phase complex formation reaction at 298.15 K was calculated by means of a thermochemical cycle.     

水合氯化镧与二乙氨基荒酸二乙铵配合行为的热化学

在干燥氮气气氛下，以无水乙醇为溶剂，制备了低水合氯化镧与二乙氨基荒酸 二乙铵（D-DDC）的配合物，确定其组成为Et_2NH_2[La(S_2CNEt_2)_4]。用微量热 法测定了298.15 K下水合氯化镧和D-DDC在无水乙醇中的溶解焓和不同温度下二乙 氨基荒酸镧液相生成反应的焓变。在实验和计算基础上，得到了液相生成反应的热 力学参数（活化焓、活化熵和活化自由能）、速率常数和动力学参数（表现活化能 、频率因子和反应基数），通过合理的热化学循环，求得了标题固相反应的焓变。