Song Jinsuk, Kang Tae Hui, Kim Mahn Won, Han Songi
Department of Chemistry and Biochemistry, University of California, Santa Barbara, Santa Barbara, CA 93106, USA.
Phys Chem Chem Phys. 2015 Apr 7;17(13):8306-22. doi: 10.1039/c4cp05992a. Epub 2015 Mar 11.
Ion-specific effects in aqueous solution, known as the Hofmeister effect, are prevalent in diverse systems ranging from pure ionic to complex protein solutions. The objective of this paper is to explicitly demonstrate how complex ion-ion and ion-water interactions manifest themselves in the Hofmeister effect based on a series of recent experimental observations. These effects are not considered in the classical descriptions of ion effects, such as the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, and therefore they fail to describe the origin of the phenomenological Hofmeister effect. However, given that models considering the basic forces of electrostatic and van der Waals interactions can offer rationalization for the core experimental observations, a universal interaction model stands a chance of being developed. In this perspective, we separately derive the contribution from ion-ion electrostatic interactions and ion-water interactions from second harmonic generation (SHG) data at the air-ion solution interface, which yields an estimate of the ion-water interactions in solution. The Hofmeister ion effect observed for biological solutes in solution should be similarly influenced by contributions from ion-ion and ion-water interactions, where the same ion-water interaction parameters derived from SHG data at the air-ion solution interface could be applicable. A key experimental data set available from solution systems to probe ion-water interactions is the modulation of water diffusion dynamics near ions in a bulk ion solution, as well as near biological liposome surfaces. This is obtained from Overhauser dynamic nuclear polarization (ODNP), a nuclear magnetic resonance (NMR) relaxometry technique. The surface water diffusivity is influenced by the contribution from ion-water interactions, both from localized surface charges and adsorbed ions, although the relative contribution of the former is larger on liposome surfaces. In this perspective, ion-water interaction energy values derived from experimental data for various ions are compared with theoretical values in the literature. Ultimately, quantifying ion-induced changes in the surface energy for the purpose of developing valid theoretical models for ion-water interactions will be critical to rationalizing the Hofmeister effect.
水溶液中的离子特异性效应，即霍夫迈斯特效应，在从纯离子溶液到复杂蛋白质溶液等各种体系中普遍存在。本文的目的是基于一系列近期的实验观察结果，明确展示复杂的离子 - 离子和离子 - 水相互作用如何在霍夫迈斯特效应中表现出来。这些效应在离子效应的经典描述中未被考虑，例如德亚金 - 朗道 - 韦弗 - 奥弗贝克（DLVO）理论，因此它们无法描述现象学霍夫迈斯特效应的起源。然而，鉴于考虑静电和范德华相互作用基本力的模型能够为核心实验观察结果提供合理化解释，一个通用的相互作用模型有机会被开发出来。从这个角度来看，我们分别从空气 - 离子溶液界面的二次谐波产生（SHG）数据中推导离子 - 离子静电相互作用和离子 - 水相互作用的贡献，从而得出溶液中离子 - 水相互作用的估计值。溶液中生物溶质所观察到的霍夫迈斯特离子效应应该同样受到离子 - 离子和离子 - 水相互作用贡献的影响，其中从空气 - 离子溶液界面的SHG数据得出的相同离子 - 水相互作用参数可能适用。从溶液体系中获取用于探测离子 - 水相互作用的一个关键实验数据集是本体离子溶液中以及生物脂质体表面附近离子周围水扩散动力学的调制情况。这是通过奥弗豪泽动态核极化（ODNP）获得的，它是一种核磁共振（NMR）弛豫测量技术。表面水扩散率受到离子 - 水相互作用贡献的影响，这包括局部表面电荷和吸附离子的贡献，尽管前者在脂质体表面的相对贡献更大。从这个角度来看，将从各种离子的实验数据中得出的离子 - 水相互作用能值与文献中的理论值进行比较。最终，为了开发有效的离子 - 水相互作用理论模型而量化离子诱导的表面能变化对于合理化霍夫迈斯特效应至关重要。
