液-固吸附体系中计量置换吸附模型的热力学研究

研究了液-固吸附体系中溶质计量置换吸附过程中的自由能变,推导出了新的表示溶质种类、溶质浓度和溶剂对Gibbs自由能变贡献的数学表达式,并阐明了该表达式中各种参数的物理意义.将用通常方法测定的自由能变分为与溶质吸附和溶剂解吸附有关的两个独立的自由能变,推导出了液-固吸附体系中溶质计量置换吸附模型的两个线性参数β_a和q/Z对绝对温度倒数的线性关系,又将吸附过程中溶质的焓变和熵变分成两个独立的分量.用文献中的实验数据,对本文推导出的公式进行了检验,理论结果与实验结果一致.     

Determination of the enthalpy of solute-solvent interaction from the enthalpy of solution: aqueous solutions of erythritol and L-threitol

In this work the enthalpy of the solute-solvent interaction of erythritol and L-threitol in aqueous solution was determined from the values obtained for the enthalpy of solvation. The values for this property were calculated from those determined for the enthalpies of solution and sublimation. To determine the values of the enthalpy of solute-solvent interaction, the solvation process is considered as taking place in three steps: opening a cavity in the solvent to hold the solute molecule, changing the solute conformation when it passes from the gas phase into solution, and interaction between the solute and the solvent molecules. The cavity enthalpy was calculated by the scaled particle theory and the conformational enthalpy change was estimated from the value of this function in the gas phase and in solution. Both terms were determined by DFT calculations. The solvent effect on the solute conformation in solution was estimated using the CPCM solvation model. The importance of the cavity and conformational terms in the interpretation of the enthalpy of solvation is noted. While the cavity term has been used by some authors, the conformational term is considered for the first time. The structural features in aqueous solution of erythritol and L-threitol are discussed.     

Mixed implicit/explicit solvation models in quantum mechanical calculations of binding enthalpy for protein–ligand complexes

An approach to quantum mechanical investigation of interactions in protein–ligand complexes has been developed that treats the solvation effect in a mixed scheme combining implicit and explicit solvent models. In this approach, the first solvation shell of the solvent around the solute is modeled with a limited number of hydrogen bonded explicit solvent molecules. The influence of the remaining bulk solvent is treated as a surrounding continuum in the conductor‐like screening model (COSMO). The enthalpy term of the binding free energy for the protein–ligand complexes was calculated using the semiempirical PM3 method implemented in the MOPAC package, applied to a trimmed model of the protein–ligand complex constructed with special rules. The dependence of the accuracy of binding enthalpy calculations on size of the trimmed model and number of optimized parameters was evaluated. Testing of the approach was performed for 12 complexes of different ligands with trypsin, thrombin, and ribonuclease with experimentally known binding enthalpies. The root‐mean‐square deviation (RMSD) of the calculated binding enthalpies from experimental data was found as ～1 kcal/mol over a large range. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006     

Investigation of salt — Mixed solvent systems. XXXVII. Crystallization enthalpy of lithium chloride in mixed solvent systems

The crystallization enthalpy of LiCl at 25°C in LiCl-H₂O-cosolvent systems is determined calorimetrically as a function of the cosolvent content in the mixed solvent. This parameter is used for the investigation of heat phenomena accompanying the solvation of the salt in a saturated solution. The cosolvents employed include methanol, acetone, and N,N-dimethylformamide. The most pronounced change is effected by replacement of water with N,N-dimethylformamide.     

计量置换参数Z值分量的测定(英文)

 以计量置换吸附理论(SDT A)为基础,从理论上推导出计量吸附模型中表征溶质对固定相亲合势大小的参数βa值与流动相中强置换剂浓度的对数呈线性关系。计量置换模型中的参数n和q(n和q分别代表1摩尔溶剂化溶质被吸附时,从吸附剂表面和从溶质分子表面所释放出的溶剂的物质的量)是计量置换参数Z值的分量,是两个非常有用的参数,可以从这个定量关系中直接获得。推导出的方程用苯的衍生物进行了实验验证,获得了较满意的结果。将这种方法计算得到的分量值与SDT A与计量置换保留模型(SDT R)相结合的方法得到的分量值进行了比较。     

液-固吸附体系中扩展的Langmuir方程的推导和检验

从气-固吸附体系中推导出的Langmuir方程,近一世纪来只能经验性地描述液相吸附。本研究以液-固界面上的溶质计量置换模型为基础,考虑到液-固吸附体系中各组分之间的相互作用,从理论上推导出了在液-固体系中描述在不同溶剂浓度条件下的溶质吸附的扩展的Langmuir公式,并称其为扩展的Langmuir公式。将Langmuir公式中经验参数与液相色谱中的计量置换平衡中的参相关联,还将其扩展到在不同溶剂浓度条件下的溶质定量吸附的描述,为Langmuir方程在描述不同溶剂浓度条件下的组分吸附奠定了理论基础,扩大了Langmuir公式的应用。以不同溶剂浓度条件下所得到的吸附等温线数据对理论推导出的扩展的Langmuir公式进行了验证,并与计算置平衡中的参数相关联,表现用吸附等温线法计算的计量置换参数Z与用高效液相色谱法得到的Z值符合程度很好。     

A New Equation for Solute Retention in Liquid Chromatography

In consideration of the adsorption of solvent, diluent and solute molecules on the surface of a stationaryphase, a new equation for solute retention in liquid chromatography is presented. This equation includesthree parameters: the displacement equilibrium constant (Ksd) between the solvent and diluent molecules onthe surface of the stationary phase, the total number(N) of the solvent and diluent molecules released fromthe stationary phase after one solute molecule being adsorbed, and the parameter (I) related to the thermody-namic equilibrium constant for the solute adsorption on the stationary phase. Over the whole concentrationrange of the solvent in the mobile phase, the experimental retention data can be well described by this equa-tion, parameters K~, N and I can be obtained by the regression analysis of the experimental retention data,and consequently the number of the solvent and the diluent molecules displaced by one solute molecule fromthe stationary phase can also be derived at different solvent concentrations in the mobile phase,     

毛细管气液色谱保留过程的研究

以ＰＥＧ２０Ｍ为代表研究了石英毛细管柱气液色谱保留过程,提出了利用毛细管柱测定分配和吸附常数的公式,并测定了９个温度下的分配和吸附常数。计算了８０℃和１２０℃下４支不同液膜厚度柱上吸附对保留的贡献。结果表明,在薄液膜的柱子上界面吸附对保留具有重要贡献;温度升高可以降低弱极性化合物（如正构烷烃和饱和醚）吸附对保留的贡献,但对其它化合物影响不明显。验证了正构烷烃、２－酮系列和正构伯醇的吸附常数的碳数规律。     

Solvation enthalpy and the thermodynamics of hydration of trans-cyclohexyl-1,4-diamine and cis-cyclohexyl-1,2-diamine

The enthalpy of solution of trans-cyclohexyl-1,4-diamine and cis-cyclohexyl-1,2-diamine in water was determined by calorimetry. The enthalpy of hydration was determined from this quantity and from the enthalpy of sublimation/vaporization presented in another paper by the authors. Considering the solvation process resulting from cavity creation in the solvent and variation of solute conformation transfer steps, the enthalpy corresponding to solute–solvent interaction was estimated. The entropies of solvation and interaction were calculated from the values given for the enthalpies in the present paper and those available for the Gibbs free energies.     

Effect of temperature on competitive adsorption of the solute and the organic solvent in reversed-phase liquid chromatography

In analysis of the temperature effect on chromatographic separations the influence of the adsorption of organic solvent on the retention properties of solute is generally not taken into account. In fact, adsorption behavior of solutes is strongly affected by competitive adsorption of organic solvents, which is temperature dependent. In this work changes of adsorption equilibrium of an organic solvent as well as a solute with temperature have been analyzed. Data of the excess adsorption of methanol from aqueous solutions on octadecyl-bonded silica have been acquired at different temperature. Experiments have been performed over a relatively narrow temperature range corresponding to typical chromatographic conditions, i.e., 10-50 degrees C. The competitive adsorption equilibria of model solutes (i.e., two homologous compounds: cyclopentanone and cyclohexanone) have been measured at different temperature and composition of the mobile phase. Temperature alterations to the retention properties were found to result from combined effects of changes in adsorption behavior of the organic solvent and of the solute. The influence of temperature on the separation selectivity has been considered.     

Enthalpic and Liquid-Phase Adsorption Study of Toluene–Cyclohexane and Toluene–Hexane Binary Systems on Modified Activated Carbons

The liquid-phase adsorption of toluene in cyclohexane and hexane solutions on modified activated carbons was evaluated; the energy involved in the interaction between these solutions and the solids was determined by immersion enthalpies of pure solvents and their mixtures, and the contribution of the system constituents was calculated by differential enthalpies. The thermal treatment generated modifications that favored adsorption and interaction with the evaluated solutions, since it increased the textural parameters and the basic character of the samples. Cyclohexane could create greater competition with the adsorption sites compared to hexane, but it favored the increase in adsorption capacities (0.416 to 1.026 mmol g⁻¹) and the interactions with the solid evaluated through the immersion enthalpies. The immersion enthalpies of pure solvents (−16.36 to −112.7 J g⁻¹) and mixtures (−25.65 to −104.34 J g⁻¹) had exothermic behaviors that were decreasing due to the possible displacement of solvent molecules when increasing the solute concentration in the mixtures. The differential enthalpies for toluene were negative (−18.63 to −2.14 J), mainly due to the π–π interaction with the solid, while those of the solvent–solid component tended to be positive values (−4.25 to 55.97 J) due to the displacement of the solvent molecules by those of toluene.     

A STOICHIOMETRIC DISPLACEMENT MODEL FOR RETENTION OF SOLUTE IN LIQUID CHROMATOGRAPHY WITH MULTI-COMPONENT SYSTEM

Considering all the kinds of interactions between solute and solvent, solute and stationary phase, solvent and stationary phase molecules as well as the competitional adsorption among various kinds of solvent molecules on the stationary phase, we present a stoichiometric displacement model of solute retention with four sets of parameters in liquid chromatography. This model was tested with data from both literature and experiments done by ourselves. These results show that this model may fit the experimental data for a liquid chromatography system with various kinds of mobile phases consisting of a complete range of multi-components and with different types of stationary phases.     

Computational screening of biomolecular adsorption and self‐assembly on nanoscale surfaces

The quantification of binding properties of ions, surfactants, biopolymers, and other macromolecules to nanometer‐scale surfaces is often difficult experimentally and a recurring challenge in molecular simulation. A simple and computationally efficient method is introduced to compute quantitatively the energy of adsorption of solute molecules on a given surface. Highly accurate summation of Coulomb energies as well as precise control of temperature and pressure is required to extract the small energy differences in complex environments characterized by a large total energy. The method involves the simulation of four systems, the surface‐solute–solvent system, the solute–solvent system, the solvent system, and the surface‐solvent system under consideration of equal molecular volumes of each component under NVT conditions using standard molecular dynamics or Monte Carlo algorithms. Particularly in chemically detailed systems including thousands of explicit solvent molecules and specific concentrations of ions and organic solutes, the method takes into account the effect of complex nonbond interactions and rotational isomeric states on the adsorption behavior on surfaces. As a numerical example, the adsorption of a dodecapeptide on the Au {111} and mica {001} surfaces is described in aqueous solution. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2010     

A generalized scale of free energy of excess adsorption of solute and absolute composition of the interfacial phase

Moles of a surfactant (gamma2(1)) absorbed per unit area of the solid-liquid interface estimated analytically from the difference of the solute molality in the bulk phase before and after adsorption have been quantitatively related to the absolute compositions deltan1 and deltan2 of the solvent and solute forming the inhomogeneous surface phase in contact with the bulk phase of homogeneous composition. By use of isopiestic experiments, negative values of gamma2(1) for the adsorption of inorganic salts onto a solid-liquid interface have been calculated in the same manner. From the linear plot of gamma2(1) versus the ratio of the bulk mole fractions of the solute and solvent, values of deltan1 and deltan2 have been evaluated under a limited range of concentrations. For the adsorption of the surfactant and the inorganic salt respectively onto the fluid interface, gamma2(1) values have been evaluated from the surface tension concentration data using the Gibbs adsorption equation. Gamma2(1) based on the arbitrary placement of the Gibbs dividing plane near the fluid interface is quantitatively related to the composition of the inhomogeneous surface phase. Also, the Gibbs equation for multicomponent solutions has been appropriately expressed in terms of a suitably derived coefficient m. Integrating the Gibbs adsorption equation for a multicomponent system, the standard free energy change, deltaG degrees, per unit of surface area as a result of the maximum adsorption gamma2(m) of the surfactant at fluid interfaces due to the change of the activity alpha2 of the surfactant in the bulk from zero to unity have been calculated. A similar procedure has been followed for the calculation of deltaG degrees for the surfactant adsorption at solid-liquid interfaces using thermodynamically derived equations. deltaG degrees values for surfactant adsorption for all such systems are found to be negative. General expressions of deltaG degrees for negative adsorption of the salt on fluid and solid-liquid interfaces respectively have also been derived on thermodynamic grounds. deltaG degrees for all such systems are positive due to the excess spontaneous hydration of the interfacial phase in the presence of inorganic salt. Negative and positive values of deltaG degree for excess surfactant and salt adsorption respectively have been discussed in light of a generalized scale of free energy of adsorption.     

Nonstationary diffusion of polystyrenes through a cellophane membrane

Diffusion of five polystyrene fractions at various concentrations in toluene through cellophane membranes has been observed. The results have been used to calculate friction coefficients between solvent and solute, and between solute and membrane. The calculation requires measurement of the diffusion coefficient and the reflection coefficient of the solute, of the permeability for the solvent, of the pore volume of the membrane, and of the partition coefficient of the solute between membrane and solvent. By comparing the friction coefficient between solvent and solute in the membrane with this coefficient in free solution, the tortuosity factor and the pore diameter of the membrane can be estimated. The dependence of the friction coefficients on molecular weight M₂ of the solute is determined. For large values of M₂, the friction between solute and solvent is the determining factor. The friction coefficient between solute and solvent increases more strongly with M₂ in the membrane than in free solution owing to an entrance effect for the permeating solute at the interface.     

A new model to describe the sorption of surfactants on solids in non-aqueous media

A new phenomenological model is developed to describe the sorption of surfactants on solids in non-aqueous media. This is based on the use of interaction parameters (delta) among solid, solute and solvent to assess the degree of the various interactions and computing an effective interaction parameter for the entire system represented by delta eff = abs{A|delta solid - delta solvent| + B|delta solute - delta solvent| - C|delta solid - delta solute|}. The effective interaction parameter determines the extent of adsorption that can occur in a given system. Interaction parameters typically account for dispersive interactions between the different components. This new model is used to describe the sorption behavior of a number of surfactant/solvent/solid systems.     

Investigations of salt — Mixed solvent systems XXXVIII. Crystallization enthalpy of magnesium chloride in mixed solvent systems

The crystallization enthalpies of MgCl₂ in MgCl₂–H₂O-cosolvent systems at 25°C were determined calorimetrically as a function of the cosolvent content in the mixed solvent. Methanol, acetone, and N,N-dimethylformamide were employed as cosolvents. The results show the individual cosolvents to have very differently influences on the energy state of the salt in the saturated solution. The most pronounced changes are effected by an increase of the DMF content in the mixed solvent. The intensity of Mg²⁺-DMF interaction at a higher DMF content in the saturated solution considerably exceeds the Li⁺-DMF interaction in LiCl solutions.     

Thermochemical investigations of nearly idela binary solvents. II. Standard heats of solution in systems of nonspecific interactions

Standard heats of solution at 25°C are reported for squalane in mixtures ofn-heptane + iso-octane and in binary mixtures of chloroform, carbon tetrachloride, and cyclohexane; for cyclohexane in chloroform + carbon tetrachloride; and for chloroform in carbon tetrachloride + cyclohexane. General equations based on simple mixing models are developed for the excess thermodynamic properties of a solute at infinite dilution in a binary solvent. For the systems studied, mixing equations based on volume fractions give better agreement than those based on mole fractions, and the agreement is further improved by the use of weighting factors based on the properties of the solute + solvent binary systems.     

Evaluation of the contribution to hydration of nonelectrolytes from the hydrophobic effect

A new method was suggested for estimating the hydrophobic effect of contributions to the Gibbs energies and enthalpies of hydration of hydrocarbons, inorganic gases and rare gases. In accordance with this method the hydrophobic effect contribution to the Gibbs energy was evaluated from the difference between the hydration Gibbs energy of a solute and the non hydrophobic contribution. To estimate the latter value, the known dependence connecting the Gibbs energies of solvation of a solute in a number of aprotic solvents to the Hildebrand solubility parameter for these solvents was used. The non hydrophobic contribution to the Gibbs energy of hydration was calculated for various solutes from such dependences extended to water as solvent. The Hildebrand solubility parameter for water used in the calculation was corrected for the effect of association through hydrogen bonding. This correction was made by subtraction of the water self-association enthalpy from the enthalpy of vaporization of water. The evaluated Gibbs energies of the hydrophobic effect are positive for saturated hydrocarbons, inorganic gases and rare gases and linearly depend on the solute molecular refraction. The hydrophobic contribution to the hydration enthalpies of the solutes was calculated in the same manner as was made to calculate the hydrophobic contribution to Gibbs energies of hydration. Enthalpies of the hydrophobic effect for the solutes under study are negative.