Hydration entropy change from the hard sphere model
Hydration entropy change from the hard sphere model
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DOI：
10.1016/s0301-4622(02)00199-0
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发表时间：
2002-12-10
影响因子：
3.8
通讯作者：
Lee, B
中科院分区：
文献类型：
--
作者：
Graziano, G;Lee, B
纯非极性液体的气液传递熵变可以用遵守Camahan-Starling状态方程的硬球模型相当精确地计算。相同的程序不能产生氢键液体如水、甲醇和乙醇的合理值。然而，当氢键被关闭以产生硬球系统时，分子的尺寸增加，并且体积堆积密度上升。我们在这里表明，具有这种增加的堆积密度的硬球系统相当好地再现了实验转移熵值。对于小的非极性烃的气-水传递熵值也不能通过硬球模型再现，无论对于水使用正常（2.8埃直径）还是增加的（3.2埃）尺寸。具有2.8埃尺寸水的硬球模型产生太小熵变的至少部分原因是水的尺寸对于没有氢键的系统来说太小。3.2埃模型也产生太小的熵值的原因是这是一个过度拥挤的系统，并且通过添加溶质分子在系统中引入的自由体积对这种拥挤产生了太多的缓解。一个硬球模型，其中的自由体积的增加是有限的，要求溶质和水分子之间的平均表面到表面的距离是相同的大小增加的水分子之间的，近似重现实验的水化熵值。(C)2002 Elsevier Science B. V.保留所有权利。
The gas to liquid transfer entropy change for a pure non-polar liquid can be calculated quite accurately using a hard sphere model that obeys the Camahan-Starling equation of state. The same procedure fails to produce a reasonable value for hydrogen bonding liquids such as water, methanol and ethanol. However, the size of the molecules increases when the hydrogen bonds are turned off to produce the hard sphere system and the volume packing density rises. We show here that the hard sphere system that has this increased packing density reproduces the experimental transfer entropy values rather well. The gas to water transfer entropy values for small non-polar hydrocarbons is also not reproduced by a hard sphere model, whether one uses the normal (2.8 Angstrom diameter) or the increased (3.2 Angstrom) size for water. At least part of the reason that the hard sphere model with 2.8 Angstrom size water produces too small entropy change is that the size of water is too small for a system without hydrogen bonds. The reason that the 3.2 Angstrom model also produces too small entropy values is that this is an overly crowded system and that the free volume introduced in the system by the addition of a solute molecule produces too much of a relief to this crowding. A hard sphere model, in which the free volume increase is limited by requiring that the average surface-to-surface distance between the solute and water molecules is the same as that between the increased-size water molecules, does approximately reproduce the experimental hydration entropy values. (C) 2002 Elsevier Science B.V. All rights reserved.