A surface site interaction model for the properties of liquids at equilibrium
A surface site interaction model for the properties of liquids at equilibrium
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DOI：
10.1039/c3sc22124e
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发表时间：
2013-01-01
期刊：
影响因子：
8.4
通讯作者：
Hunter, Christopher A.
中科院分区：
文献类型：
--
作者：
Hunter, Christopher A.
为估计溶剂对两种溶质之间形成1：1络合物的溶液相缔合常数的影响而开发的静电溶剂竞争模型已被扩展，以提供对液体状态下分子间相互作用的一般处理。分子与其溶剂化壳层的相互作用由一组表面位相互作用点(SSIP)来描述。SSIP表示分子表面积为9.5埃(2)，体积为5埃(3)，由静电相互作用参数epsilon(I)表征，该参数是从气相中计算的分子静电势面或从实验测定的溶液中的官能团氢键参数获得的。液体被视为SSIP的系综，其相互作用的概率由静电相互作用能和常数范德华项-5.6kJ·mol(-1)之和决定。SSIP接触的物种形成被确定为玻尔兹曼加权的状态总体，这允许计算溶液的各种热力学性质。该模型假定由于液体中存在大量的空穴空间，SSIP有可能处于非束缚状态。这提供了不同相之间直接的热力学联系，因为非束缚态在不同的环境中具有相同的化学势。分子在两个不同的液相之间转移的自由能被计算为结合能和限制能的总和，结合能是分子中所有SSIP与液体的总相互作用的量度，约束能是将分子SSIP限制到该相的熵成本的量度。对于烷烃、醚、醇和水，计算的液-液传递自由能与实验值(+/-1~3kJ mol(-1))相吻合。这些计算提供了疏水效应的分子基础，水和醇中氢键分布差异的根源，以及作为疏水性衡量标准的正辛醇和正十六烷分配系数之间的差异。溶剂对1：1氢键络合物形成的缔合常数的影响也被计算(+/-0.5个对数单位)再现。除了与实验热力学数据进行比较外，该模型还可以利用溶液中不同氢键形态的光谱数据进行验证。
The electrostatic solvent competition model developed to estimate solvent effects on solution phase association constants for formation of 1 : 1 complexes between two solutes has been extended to provide a general treatment of intermolecular interactions in the liquid state. The interactions of a molecule with its solvation shell are described by a set of surface site interaction points (SSIPs). An SSIP represents a molecular surface area of 9.5 angstrom(2), a volume of 5 angstrom(3), and is characterised by an electrostatic interaction parameter, epsilon(i), obtained from the molecular electrostatic potential surface calculated in the gas phase or from functional group H-bond parameters experimentally determined in solution. A liquid is treated as an ensemble of SSIPs that interact with a probability governed by the sum of the electrostatic interaction energy, given by epsilon(i)epsilon(j), and a constant van der Waals term of -5.6 kJ mol(-1). The speciation of SSIP contacts is determined as a Boltzmann-weighted population of states, and this allows calculation of a variety of thermodynamic properties of solutions. The model assumes that unbound states are possible for SSIPs due to the large amount of void space present in a liquid. This provides a straightforward thermodynamic connection between different phases, because unbound states have the same chemical potential in different environments. The free energy of transfer of a molecule between two different liquid phases is calculated as the sum of a binding energy, which is a measure of the total interaction of all SSIPs in the molecule with the liquid, and a confinement energy, which is a measure of the entropic cost of confining the molecular SSIPs to that phase. Calculated liquid-liquid transfer free energies agree with experiment (+/- 1 to 3 kJ mol(-1)) for a collection of alkanes, ethers, alcohols and water. The calculations provide insight into the molecular basis of the hydrophobic effect, the origin of the difference in H-bond populations in water and alcohols, and the differences between 1-octanol and n-hexadecane partition coefficients as measures of hydrophobicity. Solvent effects on association constants for formation of 1 : 1 H-bonded complexes are also reproduced by the calculations (+/- 0.5 log units). In addition to comparison with experimental thermodynamic data, this model can also be validated using spectroscopic data on the speciation of different H-bonded states in solution.