Pohorille A, Pratt L R
Department of Chemistry, University of California, Berkeley 94720, USA.
J Am Chem Soc. 1990;112(13):5066-74. doi: 10.1021/ja00169a011.
Thermal configurational data on neat liquids are used to obtain the work of formation of hard spherical cavities of atomic size in six molecular solvents: n-hexane, n-dodecane, n-undecyl alcohol, chloroform, carbon tetrachloride, and water. These results are used to test a recent suggestion that the differences between nonaqueous solvents and liquid water in solvation of inert gases are not principally due to the hydrogen-bonded structure of liquid water but rather to the comparatively small size of the water molecule. The frequencies of occurrence of cavities in liquid water can be meaningfully distinguished from those in the organic solvents. Liquid water has a larger fractional free volume, but that free volume is distributed in smaller packets. With respect to cavity work, water is compared to a solvent of the same molecular density and composed of hard spheres of the same size as the water molecule. That comparison indicates that the hard-sphere liquid finds more ways to configure its free volume in order to accommodate an atomic solute of substantial size and thus, would be more favorable solvent for inert gases. The scaled particle model of inert gas solubility in liquid water predicts cavity works 20% below the numerical data for TIP4P water at 300 K and 1.0 g/cm3 for cavity radii near 2.0 angstroms. It is argued that the sign of this difference is just the sign that ought to be expected and that the magnitude of this difference measures structural differences between water and the directly comparable hard-sphere liquid. In conjunction with previous data, these results indicate that atomic sized cavities should be considered submacroscopic.
纯净液体的热构型数据被用于获取在六种分子溶剂中形成原子尺寸硬球空腔的生成功，这六种溶剂分别是：正己烷、正十二烷、正十一醇、氯仿、四氯化碳和水。这些结果被用于检验最近的一个观点，即惰性气体在非水溶剂和液态水中溶剂化的差异，主要不是由于液态水的氢键结构，而是由于水分子相对较小的尺寸。液态水中空腔出现的频率可以与有机溶剂中的频率进行有意义的区分。液态水具有更大的自由体积分数，但该自由体积分布在更小的单元中。关于空腔功，将水与具有相同分子密度且由与水分子大小相同的硬球组成的溶剂进行比较。该比较表明，硬球液体有更多方式来配置其自由体积以容纳具有相当尺寸的原子溶质，因此，对于惰性气体而言是更有利的溶剂。惰性气体在液态水中溶解度的标度粒子模型预测，对于半径接近2.0埃的空腔，在300K和1.0g/cm³时，TIP4P水的数值数据下的空腔功低20%。有人认为，这种差异的符号正是应该预期的符号，并且这种差异的大小衡量了水与直接可比的硬球液体之间的结构差异。结合先前的数据，这些结果表明原子尺寸的空腔应被视为亚宏观的。
