Graziano Giuseppe
Dipartimento di Scienze Biologiche ed Ambientali, Università del Sannio, Via Port'Arsa 11-82100 Benevento, Italy.
J Chem Phys. 2008 Aug 28;129(8):084506. doi: 10.1063/1.2972979.
The salting out of methane by adding NaCl to water at 25 degrees C and 1 atm is investigated by calculating the work of cavity creation by means of scaled particle theory and the methane-solvent energy of attraction. The latter quantity changes to little extent on passing from pure water to an aqueous 4M NaCl solution, whereas the magnitude of the work of cavity creation increases significantly, accounting for the salting out effect. There is quantitative agreement between the experimental values of the hydration Gibbs energy and the calculated ones. The behavior of the work of cavity creation is due to the increase in the volume packing density of NaCl solutions, since the average effective molecular diameter does not change, being always 2.80 A. The same approach allows the rationalization of the difference in methane salting out along the alkali chloride series. These results indicate that, fixed the aqueous solution density, the solubility of nonpolar species is mainly determined by the effective diameter of solvent molecules and the corresponding volume packing density. There is no need to take into account the H-bond rearrangement because it is characterized by an almost complete enthalpy-entropy compensation.
通过利用定标粒子理论计算空穴形成功以及甲烷 - 溶剂吸引能，研究了在25℃和1个大气压下向水中添加氯化钠使甲烷盐析的情况。从纯水转变为4M氯化钠水溶液时，后一量值变化很小，而空穴形成功的大小显著增加，这就解释了盐析效应。水合吉布斯自由能的实验值与计算值之间存在定量一致性。空穴形成功的行为归因于氯化钠溶液体积堆积密度的增加，因为平均有效分子直径不变，始终为2.80埃。相同的方法能够合理解释沿碱金属氯化物系列甲烷盐析的差异。这些结果表明，在水溶液密度固定的情况下，非极性物质的溶解度主要由溶剂分子的有效直径和相应的体积堆积密度决定。无需考虑氢键重排，因为它具有几乎完全的焓 - 熵补偿特征。
