Raoult's law revisited: accurately predicting equilibrium relative humidity points for humidity control experiments.
Raoult's law revisited: accurately predicting equilibrium relative humidity points for humidity control experiments.
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DOI：
10.1107/s1600576717003636
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发表时间：
2017-04-01
影响因子：
6.1
通讯作者：
Bowler MW
中科院分区：
文献类型：
--
作者：
Bowler MG;Bowler DR;Bowler MW
用一种新型的湿度控制装置测量了生物大分子结晶过程中常用的几种沉淀剂的平衡相对湿度值。统计力学中的一个简单论证表明，溶剂的平衡蒸气压与其在理想溶液中的摩尔分数成正比（拉乌尔定律）。同样的论点可以推广到溶剂分子和溶质分子大小不同的情况。在科学实验中，样品周围的湿度是一个重要的变量。特别是生物样品不仅需要潮湿的气氛，而且通常需要相对湿度（RH）与稳定溶液平衡，以在测量过程中保持样品处于相同的状态。大分子晶体的可控脱水可使晶体有序度显著提高，从而提高衍射质量。随着实验变得更容易和更可重复性，可以在监测衍射的同时精确控制晶体周围湿度的设备已经导致这种技术被越来越多地采用。将相对湿度与母液相匹配是使晶体稳定安装的第一步。在之前的工作中[Wheeler， Russi, Bowler & Bowler(2012)]。Acta结晶。[68, 111-114]，对大分子晶体学中最常用的沉淀剂浓度范围内的平衡RHs进行了测量，并显示了这些RHs与溶液上方水的平衡蒸气压的拉乌尔定律的关系。然而，测量值与理论预测值之间的差异无法解释。在这里，一个更精确的湿度控制装置被用来确定平衡RH点。新的结果与拉乌尔定律一致。还提出了统计力学中的一个简单的论点，证明了溶剂的平衡蒸气压与其在理想溶液中的摩尔分数成正比：拉乌尔定律。同样的论点可以推广到溶剂分子和溶质分子大小不同的情况，如聚合物的情况。结果为样品周围RH的正确维护提供了一个框架。
The equilibrium relative humidity values for a number of the most commonly used precipitants in biological macromolecule crystallization have been measured using a new humidity control device. A simple argument in statistical mechanics demonstrates that the equilibrium vapour pressure of a solvent is proportional to its mole fraction in an ideal solution (Raoult’s law). The same argument can be extended to the case where the solvent and solute molecules are of different sizes. The humidity surrounding a sample is an important variable in scientific experiments. Biological samples in particular require not just a humid atmosphere but often a relative humidity (RH) that is in equilibrium with a stabilizing solution required to maintain the sample in the same state during measurements. The controlled dehydration of macromolecular crystals can lead to significant increases in crystal order, leading to higher diffraction quality. Devices that can accurately control the humidity surrounding crystals while monitoring diffraction have led to this technique being increasingly adopted, as the experiments become easier and more reproducible. Matching the RH to the mother liquor is the first step in allowing the stable mounting of a crystal. In previous work [Wheeler, Russi, Bowler & Bowler (2012). Acta Cryst. F68, 111–114], the equilibrium RHs were measured for a range of concentrations of the most commonly used precipitants in macromolecular crystallography and it was shown how these related to Raoult’s law for the equilibrium vapour pressure of water above a solution. However, a discrepancy between the measured values and those predicted by theory could not be explained. Here, a more precise humidity control device has been used to determine equilibrium RH points. The new results are in agreement with Raoult’s law. A simple argument in statistical mechanics is also presented, demonstrating that the equilibrium vapour pressure of a solvent is proportional to its mole fraction in an ideal solution: Raoult’s law. The same argument can be extended to the case where the solvent and solute molecules are of different sizes, as is the case with polymers. The results provide a framework for the correct maintenance of the RH surrounding a sample.