Spectrophotometric and Calorimetric Studies of Np(V) Complexation with Acetate at Various Temperatures from <Emphasis Type="Italic">T</Emphasis>=283 to 343 K

Spectrophotometric titrations were performed to identify the Np(V)/acetate complex and determine the equilibrium constants at various temperatures (T=283 to 343 K) and at the ionic strength 1.05 mol⋅kg⁻¹. The enthalpies of complexation at the corresponding temperatures were determined by microcalorimetric titrations. Results show that the complexation of Np(V) with acetate is weak but strengthens as the temperature increases. The complexation reaction is endothermic and entropy driven. The enhancement of complexation at higher temperatures is primarily due to the increasingly larger entropy gain when the solvent molecules are released from the highly-ordered solvation spheres of NpO₂⁺\mathrm{NpO}_{2}^{+} and acetate to the bulk solvent where the degree of disorder is higher at higher temperatures.     

Spectrophotometric and calorimetric studies of Np(V) complexation with sulfate at 10–70°c

Sulfate, one of the inorganic constituents in the groundwater of nuclear waste repository, could affect the migration of radioactive materials by forming complexes. Spectrophotometric and microcalorimetric titrations were performed to identify the Np(V)/sulfate complex and determine the equilibrium constants and enthalpy of complexation at 10–70°C. Results show that the complexation of Np(V) with sulfate is weak but slightly enhanced by the increase in temperature. The complexation is endothermic and becomes more endothermic with the increase in temperature. The enhanced complexation at elevated temperatures is due to the increasingly larger entropy of complexation that exceeds the increase in enthalpy, indicating that the complexation of Np(V) with sulfate is entropy-driven.     

Effect of temperature on the complexation of NpO2+ with benzoic acid: Spectrophotometric and calorimetric studies

The equilibrium constants of the 1:1 NpO₂⁺/benzoate complex were determined by spectrophotometric titrations at variable temperatures (T = 283 to 343 K) and the ionic strength of 1.05 mol · kg⁻¹. The enthalpy of complexation at T = 298 K was determined by microcalorimetric titrations. Similar to other monocarboxylates, benzoate forms a weak complex with NpO₂⁺ and the complexation is strengthened as the temperature is increased. The complexation is endothermic and is entropy-driven. The enhancement of the complexation at elevated temperatures is primarily attributed to the increasingly larger entropy gain when the water molecules are released from the highly-ordered solvation spheres of NpO₂⁺ and benzoate to the bulk solvent where the degree of disorder is higher at higher temperatures. The spectroscopic features of the Np(V)/benzoate system, including the effect of temperature on the absorption bands, are discussed in terms of ligand field splitting and a thermal expansion mechanism.     

DHDECMP萃取硝酸铀酰的热力学研究

在288—343 K的温度范围内, 研究了不同浓度的DHDECMP(溶于DEB)自0.25—5摩尔硝酸介质中萃取铀(Ⅵ)的分配比与温度的关系. 据此, 用外推法首次获得了该萃取体系离子强度为零时的萃取热力学参数: K_t(1.15±0.10)×10~3, △H_t~0=27.5 kJ·mol~(-1), △G~0=-17.5 kJ·mol~(-1), △S°=33.5 J·mol~(-1)K~(-1).     

Thermodynamics of neptunium(V) complexes with phosphate at elevated temperatures

The complexation of Np(V) with phosphate at elevated temperatures was studied by a synergistic extraction method. A mixed buffer solution of TRIS and MES was used to maintain an appropriate pH value during the distribution experiments. The distribution ratio of Np(V) between the organic and aqueous phases was found to decrease as the concentrations of phosphate were increased. Stability constants of the 1:1 and 1:2 Np(V)-HPO₄ ²⁻ complexes, dominant in the aqueous phase under the experimental conditions, were calculated from the effect of [HPO₄ ²⁻] on the distribution ratio. The thermodynamic parameters including enthalpy and entropy of complexation between Np(V) and HPO₄ ²⁻ at 25 °C–55 °C were calculated by the temperature coefficient method.     

Stability constants of Np(V) complexes with fluoride and sulfate at variable temperatures

Summary A solvent extraction method was used to determine the stability constants of Np(V) complexes with fluoride and sulfate in 1.0M NaClO₄ from 25 to 60 °C. The distribution ratio of Np(V) between the organic and aqueous phases was found to decrease as the concentrations of fluoride and sulfate were increased. Stability constants of the 1 : 1 Np(V)-fluoride complexes and the 1 : 1 Np(V)-sulfate and 1 : 2 Np(V)-sulfate complexes, dominant in the aqueous phase under the experimental conditions, were calculated from the effect of [F^-] and [SO₄^2-] on the distribution ratio. The enthalpy and entropy of complexation were calculated from the stability constants at different temperatures by using the Van't Hoff equation.     

Excess thermodynamic properties of thin water films confined between hydrophobized gold surfaces

Surface forces between gold surfaces were measured in pure water at temperatures in the range of 10-40 °C using an atomic force microscope (AFM). The surfaces were hydrophobized by self-assembly of alkanethiols (C(n)SH) with n=2 and 16 in ethanol solutions. The data were used to determine the changes in excess free energies (ΔG(f)) of the thin water films per unit area by using the Derjaguin approximation [1]. The free energy data were then used to determine the changes in excess film entropy (ΔS(f)) and the excess film enthalpy (ΔH(f)) per unit area. The results show that both ΔS(f) and ΔH(f) decrease with decreasing film thickness, suggesting that the macroscopic hydrophobic interaction involves building some kind of structures in the intervening thin films of water. It was found that |ΔH(f)|>|TΔS(f)|, which is a necessary condition for an attractive force to appear when the enthalpy and entropy changes are both negative. That macroscopic hydrophobic interaction is enthalpically driven is contrary to the hydrophobic interactions at molecular scale. The results obtained in the present work are used to discuss possible origins for the long-range attractions observed between hydrophobic surfaces.     

Thermodynamics of U(VI) complexation by succinate at variable temperatures

Complexation of U(VI) by succinate has been studied at various temperatures in the range of (298 to 338) K by potentiometry and isothermal titration calorimetry at constant ionic strength (1.0 M). The potentiometric titrations revealed the formation of 1:1 uranyl succinate complex in the pH range of 1.5 to 4.5. The stability constant of uranyl succinate complex was found to increase with temperature. Similar trend was observed in the case of enthalpy of complex formation. However, the increase in entropy with temperature over-compensated the increase in enthalpy, thereby favouring the complexation reaction at higher temperatures. The linear increase of enthalpy of complexation with temperature indicates constancy of the change in heat capacity during complexation. The temperature dependence of stability constant data was well explained with the help of Born equation for electrostatic interaction between the metal ion and the ligand. The data have been compared with those for uranyl complexes with malonate and oxalate to study the effect of ligand size and hydrophobicity on the temperature dependence of thermodynamic quantities.     

锆钴合金氢化反应热力学函数的计算

在有效原子实势近似下,采用Gaussian 98计算程序及B3LYP/SDD密度泛函方法计算得到了ZrCo和ZrCoH分子的结构、力常数、离解能,能量(E)、熵(S)以及ZrCo与氢同位素气体反应的热力学函数.在固态ZrCo、ZrCoH(D、T)的E和S的计算中,近似以气态分子总能量中的振动能EV代替该分子处于固态时的振动能量,以电子运动和振动运动熵SEv代替分子处于固态的熵,在这种近似下,计算了不同温度下ZrCo与H2、D2、T2反应的ΔH、ΔG、ΔS及氢化反应平衡压力,导出了氢化反应温度与平衡压力的依赖关系.计算得出：ZrCoH、ZrCoD、ZrCoT的生成焓(398～598 K）分别为82.81、81.54和80.49 kJ•mol－1,与实验结果有很好的一致性,表明这种近似处理方法是合理的,可以用于一些未知氢化物的热力学函数的近似计算.     

纳米硫化钴与明胶蛋白质的原位键合作用研究

利用紫外-可见吸收光谱(UV-Vis)和傅里叶变换红外光谱(FT-IR),研究了pH值11.00时,不同温度下CoS纳米粒子与明胶蛋白质的键合作用.根据吸光度与CoS浓度的关系,由Lineweave-Burk方程计算了不同温度下CoS纳米粒子与明胶蛋白作用的键合常数K(温度为293 K时键合常数K为3.01×10³L/mol;温度为301 K时键合常数K为2.12×10³L/mol;温度为313 K时键合常数K为1.85×10³L/mol)以及对应温度下反应的热力学参数(ΔrH_m=-17.93 kJ/mol;ΔrS_m=4.93 J/(K.mol);ΔrG_m=-19.37/-19.41/-19.47kJ/mol).CoS纳米粒子与明胶蛋白之间主要靠静电力结合.研究结果为初步探索纳米颗粒与纤维状蛋白质之间相互作用的化学机制提供了必要的信息.     

Cation-cation interactions between NpO2(+) and UO2(2+) at different temperatures and ionic strengths

Cation-cation interactions between NpO(2)(+) and UO(2)(2+) were studied at different temperatures (283.15 K to 358.15 K) and different ionic strengths (3-4.5 mol dm(-3)) by spectrophotometry and microcalorimetry. The cation-cation complex between NpO(2)(+) and UO(2)(2+) was weak and became stronger as the temperature was increased from 283.15 K to 358.15 K. The molar enthalpy of complexation was directly determined for the first time by microcalorimetry to be (4.2 ± 1.6) kJ mol(-1) at 298.15 K, in good agreement with the trend in the stability constant at different temperatures. The small and positive enthalpy and entropy of complexation support the argument that the cation-cation complex between NpO(2)(+) and UO(2)(2+) is of inner-sphere type. At each temperature, the stability constants of the cation-cation complex were found to increase as the ionic strength was increased. The specific ion interaction theory (SIT) was used to obtain the stability constants at infinite dilution and variable temperatures.     

含酯基Gemini表面活性剂在有机醇-水体系中的胶束热力学及聚集行为

采用电导法研究了不同温度下含酯基Gemini表面活性剂在纯水和在质量分数为10%的甲醇-水(MAWR),乙二醇-水(EG-WR),丙三醇-水(GL-WR)四种体系中的集聚行为和胶束热力学;聚集行为参数包括临界胶束浓度(cmc)和抗衡离子的解离程度(α)以及胶束的热力学参数,包括标准吉布斯自由能(ΔG_m~o)、吉布斯迁移自由能(ΔG_(trans)~o)、吉布斯烷基链胶束化自由能(ΔG_(tail)~o)、标准焓变(ΔH_m~o)和标准熵变(ΔS_m~o),均被计算和讨论。研究表明在所有的研究体系中,cmc值随着疏水链的增加而减小,随着加入的醇结构中羟基数目的增加而增大,随温度的升高先变小,后变大呈U字形;胶束化过程都是自发进行的,并且在293.15 K下,胶束化过程是吸热的,在293.15 K上,胶束化过程是放热的;通过稳态荧光光谱法研究了表面活性剂在纯水、有机醇-水混合溶液中的微极性,结果表明,在相同溶剂中,随着烷基链长度的增加,溶液微环境的疏水性越强;对于相同的Gemini表面活性剂,随着加入含羟基数目越多的醇,其微环境的疏水性越强。并研究了Gemini表面活性剂在混合体系中形成胶束过程的焓-熵补偿曲线。     

Thermal stability and degradation kinetic study of white and colored cotton fibers by thermogravimetric analysis

Complexation of neptunium(V) with fluoride in aqueous solutions at elevated temperatures was studied by spectrophotometry and microcalorimetry. Two successive complexes, NpO₂F(aq) and NpO₂F₂⁻, were identified by spectrophotometry in the temperature range of 10–70°C. Thermodynamic parameters, including the equilibrium constants and enthalpy of complexation between Np(V) and fluoride at 10–70°C were determined. Results show that the complexation of Np(V) with fluoride is endothermic and that the complexation is enhanced by the increase in temperature — a two-fold increase in the stability constants of NpO₂F(aq) and more than five-fold increase in the stability constants of NpO₂F₂⁻ as the temperature is increased from 10 to 70°C.     

Conductometric and 1H NMR studies of thermodynamics of complexation of Zn2+, Cd2+ and Pb2+ ions with tetrathia-12-crown-4 in dimethylsulfoxide-nitrobenzene mixtures

The complex formation between Zn²⁺, Cd²⁺ and Pb²⁺ ions with macrocyclic ligand, tetrathia12-crown-4 (12S4) was studied in dimethylsulfoxide (DMSO)–nitrobenzene binary mixtures at different temperatures using conductometric and ¹H NMR methods. In all cases, 12S4 found to form 1:1 complexes with these cations. The formation constants of the resulting 1:1 complexes in different solvent mixtures were determined by computer fitting of the resulting molar conductance- and chemical shift-mole ratio data. There is an inverse relationship between the complex stability and the amount of DMSO in the solvent mixtures. The stability of the resulting M²⁺-12S4 complexes found to decrease in the order Pb²⁺ > Cd²⁺ > Zn²⁺. The values of ?H°, ?S° and ?G° for complexation reactions were evaluated from the temperature dependence of formation constants via van’t Hoff method. The obtained results revealed that, in all cases, the complexes are enthalpy stabilized, but entropy destabilized and the values of ?H° and ?S° are strongly depend on the nature of medium. There is also a linear relationship between all ΔH° and TΔS° values indicating the existence of entropy–enthalpy compensation in complexation of the three cations and ligand in the solvent systems studied.     

Changes in thermodynamic quantities upon contact of two solutes in solvent under isochoric and isobaric conditions

The changes in excess thermodynamic quantities upon the contact of two solutes immersed in a solvent are analyzed using the radial-symmetric and three-dimensional versions of the integral equation theory. A simple model mimicking a solute in water is employed. The solute-solute interaction energy is not included in the calculations. Under the isochoric condition, the solute contact always leads to a positive entropy change irrespective of the solute solvophobicity or solvophilicity. The energy change is negative for solvophobic solutes while it is positive for solvophilic ones. Under the isobaric condition, the contact of solvophobic solutes results in system-volume compression but that of solvophilic ones gives rise to expansion. Effects of the compression and expansion on the changes in enthalpy and entropy are enlarged with rising temperature. When the solute solvophobicity is sufficiently high, the entropy change (multiplied by the absolute temperature) can become negative due to the compression, except at low temperatures with the result of an even larger, negative enthalpy change. The expansion in the case of solvophilic solutes leads to a large, positive entropy change accompanied by an even larger, positive enthalpy change. The changes in enthalpy and entropy are strongly dependent on the temperature. However, the changes in enthalpy and entropy are largely cancelled out and the temperature dependency of the free-energy change is much weaker. The authors also discuss possible relevance to the enthalpy-entropy compensation experimentally known for a variety of physicochemical processes in aqueous solution such as protein folding.     

柠檬酸镧催化双基推进剂的非等温热分解反应动力学

采用TG-DTG和DSC技术研究了含二缩三乙二醇二硝酸酯(TEGDN)和硝化甘油(NG)的混合酯、硝化棉(NC)和用作燃烧催化剂的柠檬酸镧组成的双基推进剂在常压和流动态氮气气氛下的非等温热分解反应动力学. 结果表明, 该双基推进剂的热分解过程存在2个失重阶段: 第I失重阶段为混合酯的挥发分解过程; 第II失重阶段为主放热分解反应, 机理服从三级化学反应, 减速型α-t曲线, 动力学参数: Ea=231.14 kJ·mol-1, A=10^23.29 s-1, 动力学方程为dα/dt=10^22.99(1-α)³ e^-2.78×104/T. 由外推起始点温度(Te)和峰顶温度(Tp)计算得出该双基推进剂的热爆炸临界温度值分别为Tbe=463.62 K, Tbp=477.88 K. 反应的活化熵(⊿S^≠)、活化焓(⊿H^≠)和活化能(⊿G^≠)分别为219.75 J·mol-1·K-1, 239.23 kJ·mol-1和135.96 kJ·mol-1.     

锆氢化反应热力学函数的计算

用B3LYP/SDD密度泛函方法计算了ZrH的微观性质,气态ZrH(D,T)的能量(E),熵(S)以及 Zr与氢同位素气体反应的热力学函数.在ZrH(s)、ZrD(s)和ZrT(s)的E和S的计算中,近似以分 子总能量中的振动能Ev代替固态能量,以电子和振动熵SEv代替固态熵.在这种近似下,计算了 不同温度下Zr与H2、D2、T2反应的ΔH、ΔG、ΔS及氢化反应平衡压力,导出了与温度 的依赖关系.计算结果表明,ZrH(s)的生成热为161.34 kJ穖ol-1,与实验值(173.5 kJ穖ol -1)接近,表明这种近似处理方法是合理的,可以用于研究贮氢材料氢化反应的热力学.     

Arsenic(III) sorption on nanostructured cerium incorporated manganese oxide (NCMO): a physical insight into the mechanistic pathway

Arsenic(III) sorption was investigated with nanostructured cerium incorporated manganese oxide (NCMO). The pH between 6.0 and 8.0 was optimized for the arsenic(III) sorption. Kinetics and equilibrium data (pH=7.0±0.2, T=303±1.6 K, and I=0.01 M) of arsenic(III) sorption by NCMO described, respectively, the pseudo-second order and the Freundlich isotherm equations well. The sorption process was somewhat complicated in nature and divided into two different segments, initially very fast sorption followed by slow intraparticle diffusion process. Sorption reaction of arsenic(III) on NCMO was endothermic (ΔH°=+13.46 kJ mol(-1)) and spontaneous (ΔG°=-24.75 to -30.15 kJ mol(-1) at T=283-323 K), which took place with increasing entropy (ΔS°=+0.14 kJ mol(-1)K(-1)) at solid-liquid interface. Energy of arsenic(III) sorption estimated by analyzing the equilibrium data using the D-R isotherm model was 15.4 kJ mol(-1), indicating the ion-exchange type mechanism. Raman, FT-IR, pH effect, desorption, etc. studies indicated that arsenic(III) was oxidized to arsenic(V) during the sorption process.     

Conductance Study and Thermodynamics of Some Substituted Ammonium Salts with Crown Ethers in Aqueous Solution

A conductance study of the interaction between substituted ammonium ions with three crown ethers in aqueous solution has been carried out at different temperatures. The formation constants of the 1 : 1 complexes at various temperatures were determined from the molar conductance-mole ratio data and found to vary in the order 18C6 > 15C5 > 12C4 for the same salt and with the same crown, the formation constants vary in the order (C2H5)3NHCl > (C2H5)4NBr > (CH3)3NPhI.The enthalpy and entropy of complexation were determined from the temperature dependence of the formation constants. The results indicate that the complexation process is enthalpy unfavored and entropy favored. The influence on the thermodynamic data for different parameters such as cavity size of crown ethers and nature of salt are discussed.     

Proton NMR study of the stoichiometry, stability and thermodynamics of complexation of Rb+ ion with 18-crown-6 in binary dimethylsulfoxide–nitrobenzene mixtures

Proton NMR was used to study the complexation reaction of Rb⁺ ion with 18-crown-6 (18C6) in a number of binary dimethylsulfoxide (DMSO)–nitrobenzene (NB) mixtures at different temperatures. In all cases, the exchange between free and complexed 18C6 was fast on the NMR time scale and only a single population average ¹H signal was observed. The formation constants of the resulting 1:1 complexes in different solvent mixtures were determined by computer fitting of the chemical shift mole ratio data. There is an inverse relationship between the complex stability and the amount of DMSO in the solvent mixtures. The enthalpy and entropy values for the complexation reaction were evaluated from the temperature dependence of formation constants. In all solvent mixtures studied, the resulting complex is enthalpy stabilized but entropy destabilized. The ?H° versus T?S° plot of all thermodynamic data obtained shows a fairly good linear correlation indicating the existence of enthalpy–entropy compensation in the complexation reaction.