Leberman R, Soper A K
European Molecular Biology Laboratory, Grenoble Outstation, BP 156, 38042 Grenoble Cedex, France.
Nature. 1995 Nov 23;378(6555):364-6. doi: 10.1038/378364a0.
The characteristic tetrahedral structure of water is known to be disrupted by changes in pressure and temperature. It has been suggested that ions in solution may have a similar perturbing effect. Here we use neutron diffraction to compare the effects of applied pressure and high salt concentrations on the hydrogen-bonded network of water. We find that the ions induce a change in structure equivalent to the application of high pressures, and that the size of the effect is ion-specific. Ionic concentrations of a few moles per litre have equivalent pressures that can exceed a thousand atmospheres. We propose that these changes may be understood in terms of the partial molar volume of the ions, relative to those of water molecules. The equivalent induced pressure of a particular ion species is correlated with its efficacy in precipitating, or salting-out, proteins from solution.
众所周知，水的特征四面体结构会因压力和温度的变化而被破坏。有人提出，溶液中的离子可能具有类似的扰动作用。在这里，我们使用中子衍射来比较外加压力和高盐浓度对水的氢键网络的影响。我们发现，离子会引起与施加高压相当的结构变化，而且这种效应的大小具有离子特异性。每升几摩尔的离子浓度所产生的等效压力可能超过一千个大气压。我们认为，这些变化可以根据离子相对于水分子的偏摩尔体积来理解。特定离子种类的等效诱导压力与其从溶液中沉淀或盐析蛋白质的效力相关。
