The electrostatic origins of specific ion effects: quantifying the Hofmeister series for anions. Issue 45 (10th November 2021)

• Record Type: Journal Article
• Authors: Gregory, Kasimir P.; Wanless, Erica J.; Webber, Grant B.; Craig, Vincent S. J.; Page, Alister J.
• Is Part Of: Chemical science. Volume 12:Issue 45(2021)
• Page Start: 15007
• Page End: 15015
• Publication Date: 2021-11-10
• Subjects: Chemistry -- Periodicals; 540.5
• DOI: 10.1039/d1sc03568a
• Languages: English
• ISSNs: 2041-6520

Abstract

Abstract : Analysis of ions' radial charge densities reveals they correlate with many specific ion effects, and provides a new basis to explain and quantify the 130-year-old Hofmeister series for anions. Abstract : Life as we know it is dependent upon water, or more specifically salty water. Without dissolved ions, the interactions between biological molecules are insufficiently complex to support life. This complexity is intimately tied to the variation in properties induced by the presence of different ions. These specific ion effects, widely known as Hofmeister effects, have been known for more than 100 years. They are ubiquitous throughout the chemical, biological and physical sciences. The origin of these effects and their relative strengths is still hotly debated. Here we reconsider the origins of specific ion effects through the lens of Coulomb interactions and establish a foundation for anion effects in aqueous and non-aqueous environments. We show that, for anions, the Hofmeister series can be explained and quantified by consideration of site-specific electrostatic interactions. This can simply be approximated by the radial charge density of the anion, which we have calculated for commonly reported ions. This broadly quantifies previously unpredictable specific ion effects, including those known to influence solution properties, virus activities and reaction rates. Furthermore, in non-aqueous solvents, the relative magnitude of the anion series is dependent on the Lewis acidity of the solvent, as measured by the Gutmann Acceptor Number. Analogous SIEs for cations bear limited correlation with their radial charge density, highlighting a fundamental asymmetry in the origins of specific ion effects for anions and cations, due to competing non-Coulombic phenomena.