Molecular Dynamics Simulation of Aqueous Solutions Using Interaction Energy Components: Application to the Solvation Gibbs Energy

Molecular dynamics simulations of aqueous solutions of the solutes acetamide (AcNH₂), acetic acid (AcOH), and acetaldehyde (AcH) were made using Lennard–Jones 12-6-1 potentials to describe the solute–solvent interactions. The Morokuma decomposition scheme and the ESIE solute atomic charges were used to reproduce the exchange, polarization, and electrostatic components of the solute–water interaction energy. A nonlinear perturbation was incorporated into the “slow-growth” technique in order to improve the results for the solvation Gibbs energy that were found to be in agreement with the available experimental and theoretical values.     

用Pitzer理论预测混合电解质溶液的偏摩尔体积

用Pitzer理论研究了混合电解质溶液的偏摩尔体积,建立了偏摩尔体积的预测方法,并利用所得电解质溶液的表观摩尔体积的Pitzer参数预测了HNO₃-UO₂(NO₃)₂-H₂O、KCl-Na₂SO₄-H₂O、NaCl-Na₂SO₄-H₂O、NaCl-CaCl₂-H₂O、KCl-CaCl₂-H₂O、KCl-MgCl₂-H₂O和KCl-NaBr-H₂O共7个系统4种类型的混合溶液的偏摩尔体积。     

MX—NX2和MX—NX3电解质水溶液的热力学研究

本文用Pitzer方程研究相同阴离子的非对称性混合电解质溶液的热力学性质,讨论了高次静电项(~Eθ_(ij)、~Eθ′_(ij))所产生的效应。引入混合参数(θ_(ij))和离子强度(Ⅰ)的关系式,估算了25℃时MX-NX_2和MX-NX_3电解质水溶液的Pitzer混合参数~Sθ_(ij)~(0)、~Sθ_(ij0~(1)和φ_(ij)k,其计算值和文献值吻合。     

A Conductometric Study of Aqueous Solutions of Some Cyclohexylsulfamates

The electric conductivities of aqueous solutions of the lithium, sodium, potassium and ammonium salts of cyclohexylsulfamic acid were measured from 5 to 35 ^∘C (in steps of 5 ^∘C) in the concentration range 3 × 10⁻⁴ < c/mol-dm⁻³ < 0.01. Data analysis based on a chemical model of electrolyte solutions yielded the limiting molar conductance Λ^∞ and the association constant K_A. Using the known values of the limiting conductances of lithium, sodium and potassium ions, the limiting conductances of the cyclohexylsulfamic ion were evaluated. Total dissociation of the investigated salts in water and negligible hydration of the cyclohexylsulfamate anion are evident.     

Solid-Solute Phase Equilibria in Aqueous Solution. XI. Aqueous Solubility and Standard Gibbs Energy of Cadmium Carbonate

The solubilities of CdCO₃ (otavite) in aqueous NaClO₄ solutions have been investigated as a function of ionic strength (0.15 I/mol-kg^–1 5.35, 25°C) and temperature (25°C T 75°C, I = 1.00 mol-kg^–1). A new Chemsage optimization routine was employed to simultaneously evaluate solubility data from this work and other sources, as well as standard electrode potentials determined at different ionic strengths. With the Pitzer equations the solubility constants, , were extrapolated to infinite dilution resulting in log and the ternary ion-interaction parameters ^S_Na,Cd = 0.19 and at 25°C. In addition, the following set of thermodynamic quantities can be derived from the present solubility data for otavite: _f G = –674.2±0.6 kJ-mol^–1; _f H = –755.3±3.4 kJ-mol^–1; S = 93±10 J-mol^–1K^–1. However, the present solubility data are also consistent with a recent determination of the standard entropy of otavite which leads to a recommended set of thermodynamic quantities [_f G (CdCO₃) = –674.2±0.6; _f H (CdCO₃) = –752.1±0.6; S (CdCO₃) = 103.9±0.2].     

New Physico-Chemical Properties of Extremely Diluted Aqueous Solutions

The extremely diluted solutions are anomalous solutions obtained through the iteration of two processes: a dilution 1:100 in mass and a succussion. The iteration is repeated until extreme dilutions are reached (less than 1·10^-5mol kg^-1) to the point that we may call the resulting solution an extremely diluted solution, namely the composition of the solution is identical to that of the solvent used (e.g. twice distilled water). We conducted thermodynamic and transport measurements of the solutions and of the interaction of those solutions with acids or bases. The purpose of this study is to obtain information about the influence of successive dilutions and succussions on the water structure of the solutions under study. We measured the heats of mixing of acid or basic solutions with such extremely diluted solutions, their electrical conductivity and pH, comparing with the analogous heats of mixing, electrical conductivity and pH of the solvent. We found some relevant exothermic excess heats of mixing, higher electrical conductivity and pH than those of the untreated solvent. The measurements show a good correlation between independent physico-chemical parameters. Care was taken to take into account the effect of chemical impurities deriving from the glass containers. Here we thus show that successive dilutions and succussions can permanently alter the physico-chemical properties of the water solvent. The nature of the phenomena here described still remains unexplained, nevertheless some significant experimental results were obtained. This revised version was published online in August 2006 with corrections to the Cover Date.     

A nonelectrolyte local composition model and its application in the correlation of the mean activity coefficient of aqueous electrolyte solutions

The local composition models have been widely used for the correlation of activity coefficient of nonelectrolyte and electrolyte solutions. A new equation for the excess Gibbs energy function is developed based on the local composition expression of Wilson and the random reference state. This new function, the nonelectrolyte Wilson nonrandom factor (N-Wilson-NRF) model, is presented in the form of a molecular framework so that it can be used for both nonelectrolyte and electrolyte solutions. Without any particular assumptions for ionic solutions, the new function is used to described the short-range contribution of the excess Gibbs energy of electrolyte solutions. The long-range contribution is represented by Pitzer–Debye–Hückel model. With two adjustable parameters per electrolyte, the new model is applied to correlate the mean activity coefficients of more than 150 binary aqueous electrolyte solutions at 25 °C. The results are compared with various local composition models such as the electrolyte-NRTL, electrolyte NRF-Wilson and electrolyte-NRTL-NRF models. The comparison of the results with experiment demonstrates that the new model can correlate the experimental data accurately. Moreover, the model shows high precision of predictability for the osmotic coefficient of binary electrolyte solutions.     

电解质溶液自扩散系数的布朗动力学模拟

采用布朗动力学方法对电解质溶液进行了模拟,在传统布朗动力学的基础上综合考虑了流体力学的影响,并且引入SmartMonteCarlo方法的接受概率,避免了离子不现实的移动和位型重叠,这样不仅可以将模拟过程中的时间步长大幅度提高,而且还可使溶质在相空间的演化过程更接近实际.模拟过程以电解质溶液的原始模型为基础,将溶剂看作连续介质,溶质分子之间的相互作用采用软核加静电的势能函数模型,长程静电力采用Ewald加和的处理方法.模拟得到KCl和NaCl溶液的径向分布函数g+-(r),g++(r)和g--(r),并与文献中HNC计算以及模拟的结果进行比较,使用推广的Green-Kubo公式模拟计算溶液中各种离子的自扩散性质,计算结果与实验数据吻合良好.     

Electrolyte-UNIQUAC-NRF model for the correlation of the mean activity coefficient of electrolyte solutions

The new electrolyte-UNIQUAC-NRF excess Gibbs function is obtained for calculation of the activity coefficient of the binary electrolyte solutions. The excess Gibbs energy of the model consists of the Pitzer–Debye–Hückel equation, describing the long-range electrostatic contribution and the electrolyte-UNIQUAC-NRF model to account for the short-range contributions. With two adjustable parameters per electrolyte, the new model is applied to correlation of the mean activity coefficients of more than 130 binary aqueous electrolyte solutions at 25 °C. Also the binary parameters, obtaining from regression of mean activity data, are used for prediction of osmotic coefficient data for the same electrolytes. The results are compared with various local composition models such as the electrolyte-NRTL, electrolyte NRF-Wilson, electrolyte-NRTL-NRF, N-Wilson-NRF models. The comparison of the results with experiment demonstrates that the new model can correlate the experimental activity coefficient data and predict the osmotic coefficient data of binary electrolytes accurately.     

KBPh4由水到系列水-醇混合溶剂的迁移自由能

由于四苯硼盐在分析化学、生物学、电化学等各领域中的广泛用途及其大阴离子在研究与计算单个离子迁移热力学函数中所具有的特殊作用,人们对四苯硼盐的溶液热力学性质进行了广泛研究,特别是对四苯硼钠和可作为参考电解质的四苯硼盐进行了深入细致的研究 [1, 2],得到了一些重要的的结论,为溶液理论的研究提供了有力的实验基础 .但是文献中对难溶碱金属四苯硼盐由单一到不同混合溶剂中的迁移热力学性质的系统研究较少 .在前文 [3]对 KBPh4由水到水-异丙醇和由甲醇到甲醇-异丙醇混合溶剂的迁移自由能进行研究的基础上,我们系统地对 KB…     

The Viscosity Properties of Sodium Silicate Solutions

Using a NDJ-1 rotational viscometer and an AR500 rheometer, both static and dynamic viscosities of sodium silicate solutions were measured with changes of concentration, temperature, modulus (molar ratio of SiO₂ to Na₂O), shear rate and chemical additives. Static results show that viscosity increases monotonously with concentration varying from 15 to 55%, decreases with temperature rising from 15 to 70 °C, and has a minimum value at a modulus of about 1.8. Measured data can be fitted quantitatively either by the Krieger-Dougherty expression or the Arrhenius equation with good agreement. This fact suggests that the sodium silicate solutions exhibit the properties of a suspension, in which the silicate anions, mainly constructed of Q ¹ and Q ² groups, act as a binder; the colloidal particles mainly constructed of Q ³ and Q ⁴ groups and small cations, act as effective rigid particles. Dynamic results show a shear thickening property in the high shear-rate regime, and a Newtonian property in the low shear-rate regime.     

Cationic and Anionic Effects on the Glass Transition Temperature for Aqueous Electrolyte Solutions

Glass-forming composition regions of aqueous CH₃COOM (M = Li, Na, K, Rb, Cs, and Tl), CF₃COOM (M = Li, Na, K, Rb, and Cs), and Et₄NX (Et₄ = C₂H₅, X = OH, CH₃COO, Cl, Br, NO₃, and SCN) solutions are reported as a function of water concentration R (R = moles of water per moles of salt). Glass transition temperatures (T _g) were measured by a simple differential thermal analysis (DTA) method with a cooling rate of about 600 K-min^–1. The T _g of all solutions decrease with increasing R (decreasing salt concentration). It is found that T _g at the same R value decrease in the order Na⁺ > Li⁺ > K⁺ > Rb⁺ > Cs⁺ in all glass-forming composition regions of the alkali acetate salt and alkali trifluoroacetate salt solutions. T _g for Et₄NX solutions decrease in the order CH₃COO^– ~OH^– > Cl^– > Br^– > NO ₃ ^– > SCN^–. The effects of the cation and anion on the glass-forming behavior in these aqueous solutions are discussed.     

A Gibbs free energy correlation for automated docking of carbohydrates

Thermodynamic information can be inferred from static atomic configurations. To model the thermodynamics of carbohydrate binding to proteins accurately, a large binding data set has been assembled from the literature. The data set contains information from 262 unique protein-carbohydrate crystal structures for which experimental binding information is known. Hydrogen atoms were added to the structures and training conformations were generated with the automated docking program AutoDock 3.06, resulting in a training set of 225,920 all-atom conformations. In all, 288 formulations of the AutoDock 3.0 free energy model were trained against the data set, testing each of four alternate methods of computing the van der Waals, solvation, and hydrogen-bonding energetic components. The van der Waals parameters from AutoDock 1 produced the lowest errors, and an entropic model derived from statistical mechanics produced the only models with five physically and statistically significant coefficients. Eight models predict the Gibbs free energy of binding with an error of less than 40% of the error of any similar models previously published.     

电解质溶液对聚吡咯电聚合中过氧化行为的影响

分别以硫酸/水和高氯酸锂/乙腈为电解质溶液, 采用循环伏安法在铂基底电极上电聚合制备了聚吡咯, 研究了电解质溶液对聚吡咯电聚合过程中过氧化行为的影响. 与硫酸/水溶液相比, 在高氯酸锂/乙腈溶液中电聚合制备的聚吡咯发生过氧化的峰电位正移了0.42 V. 采用原位傅里叶变换红外(in situ FTIR)光谱技术检测, 结果表明, 电聚合制备的聚吡咯在2种电解质溶液中均发生了过氧化反应, 其β-C经氧化生成C-OH或CO. 在硫酸/水溶液中, 部分聚吡咯发生电氧化降解生成CO₂, 致使其共轭结构被破坏, 电导率迅速下降. 而在高氯酸锂/乙腈溶液中, 在更高的电位范围内, 聚吡咯并没有氧化降解成CO₂.     

电解质水溶液结构研究进展及前景*

叙述盐湖中主要离子Li⁺ 、Na⁺ 、K⁺ 、Mg²⁺ 、Ca²⁺ 、Cl^- 、SO^2-₄ 、NO^-₃ 的水溶液和纯水的结构, 简单介绍了主要的研究方法, 分析讨论了溶液结构研究的现状和发展前景。     

A model for the Gibbs energy of aqueous solutions of polyelectrolytes

A new model for the excess Gibbs energy of aqueous solutions of polyelectrolytes is presented and applied for the correlation of the activity of water in aqueous solutions of polyelectrolytes without as well as with an added (single) salt. The model considers the phenomenon of counterion condensation, i.e., the partial dissociation of highly charged polyelectrolytes in water. Three parameters (a binary interaction parameter between polymer segments, the equilibrium constant of the dissociation reaction and a parameter which accounts for the polymer configuration) were fitted to the experimental results. The model allows for a reliable correlation of experimental results for the osmotic coefficient of aqueous solutions of a single polyelectrolyte (without as well as with an added salt).     

四苯硼钾由单-到不同混合溶剂的迁移自由能

KBPh4作为一种典型的大阴离子电解质 ,在研究与计算大分子电解质的迁移热力学性质中起着重要的作用 .讨论大分子电解质与不同溶剂间的作用 ,还可以为萃取、色谱及表面活性剂的研究提供理论依据 .一些文献及我们前文曾对四苯硼盐由水到一些纯溶剂 [1,2]及从水到某些水-有机混合溶剂中的标准迁移自由能进行了研究 [3],但对四苯硼盐在有机-有机混合溶剂中的研究报导极少 .本文对 KBPh4由水到水-异丙醇和由甲醇到甲醇-异丙醇混合溶剂的标准迁移自由能进行了研究和探讨 .1实验部分 1.1实验仪器及方法 　　用 CS501型超级恒温槽恒温 ;用 WF…     

An extension of the Pitzer equation for the excess Gibbs energy of aqueous electrolyte systems to aqueous polyelectrolyte solutions

Pitzer's equation for the excess Gibbs energy of aqueous solutions of low-molecular electrolytes is extended to aqueous solutions of polyelectrolytes. The model retains the original form of Pitzer's model (combining a long-range term, based on the Debye–Hückel equation, with a short-range term similar to the virial equation where the second osmotic virial coefficient depends on the ionic strength). The extension consists of two parts: at first, it is assumed that a constant fraction of the monomer units of the polyelectrolyte is dissociated, i.e., that fraction does not depend on the concentration of the polyelectrolyte, and at second, a modified expression for the ionic strength (wherein each charged monomer group is taken into account individually) is introduced. This modification is to account for the presence of charged polyelectrolyte chains, which cannot be regarded as punctual charges. The resulting equation was used to correlate osmotic coefficient data of aqueous solutions of a single polyelectrolyte as well as of binary mixtures of a single polyelectrolyte and a salt with low-molecular weight. It was additionally applied to correlate liquid–liquid equilibrium data of some aqueous two-phase systems that might form when a polyelectrolyte and another hydrophilic but neutral polymer are simultaneously dissolved in water. A good agreement between the experimental data and the correlation result is observed for all investigated systems.     

水溶液纳米簇模型对水溶液性质的理解探讨

针对大学化学中的水溶液平衡问题,在宏观热力学分析的基础上结合现代科学发展对水溶液纳米簇进行了结构研究和模型的科学验证,引入微观结构分析,增强学生在原子、分子层面上对水溶液的性质的理解,保证教学的先进性。     

在电解质溶液中测定非电解质溶解度的新方法

提出了一种可以同时测定电解质溶液中非电解质的溶解度和饱和溶液水活度的新方法。该法把等压平衡与传统化学分析统一起来,其优点是：（1）将多元饱和溶液中非电解质溶解度的测定转变为共存离子的溶度测定,避开了对非电解质难于进行精确化学分析的难题;（2）可以同时确定所测饱和体系的水活度。用该法测定了NaCl和KCl溶液中甘露醇的溶解度并与文献值进行了比较,结果表明二者符合得很好。