Mason P E, Dempsey C E, Neilson G W, Brady J W
Department of Food Science, Stocking Hall, Cornell University, Ithaca, New York 14853, USA.
J Phys Chem B. 2005 Dec 22;109(50):24185-96. doi: 10.1021/jp052799c.
Neutron diffraction experiments and molecular dynamics simulations are used to study the structure of aqueous solutions of two electrolytes: guanidinium sulfate (a mild protein conformation stabilizer) and guanidinium thiocyanate (a powerful denaturant). The MD simulations find the unexpected result that in the Gdm2SO4 solution the ions aggregated into mesoscopic (nanometer-scale) clusters, while no such aggregation is found in the GdmSCN solution. The neutron diffraction studies, the most direct experimental probe of solution structure, provide corroborating evidence that the predicted very strong ion pairing does occur in solutions of 1.5 m Gdm2SO4 but not in 3 m solutions of GdmSCN. A mechanism is proposed as to how this mesoscopic solution structure affects solution denaturant properties and suggests an explanation for the Hofmeister ordering of these solutions in terms of this ion pairing and the ability of sulfate to reverse the denaturant power of guanidinium.
硫酸胍（一种温和的蛋白质构象稳定剂）和硫氰酸胍（一种强大的变性剂）。分子动力学模拟得出了意想不到的结果：在硫酸胍溶液中，离子聚集成介观（纳米级）簇，而在硫氰酸胍溶液中未发现这种聚集现象。中子衍射研究是溶液结构最直接的实验探针，它提供了确凿的证据，表明在1.5 m硫酸胍溶液中确实发生了预测的非常强的离子配对，而在3 m硫氰酸胍溶液中则没有。本文提出了一种关于这种介观溶液结构如何影响溶液变性性质的机制，并根据这种离子配对以及硫酸根逆转胍变性能力的能力，对这些溶液的霍夫迈斯特排序给出了解释。
