Dynamical Dimension to the Hofmeister Series: Insights from First-Principles Simulations

A systematic characterization of the competing kosmotropic and chaotropic effects of a series of divalent salts on the aqueous H-bonding structure by means of first-principles molecular dynamics simulations is presented. The structural properties are quantified by means of experimental and computed (1) H NMR chemical shifts, whereby the local environments of cations and anions can be discriminated. Complementary to the well-established structural features, a dynamical aspect is added to the concept of kosmotropes and chaotropes. The H-bond dynamics, quantified in terms of the H-bonding autocorrelation functions, shows a good correlation with the structural kosmotropic and chaotropic modifications, which are commonly referred to as the Hofmeister series. The considerably enhanced (reduced) fluctuations of the H-bonding network in the hydration shells around the anions (cations) are a complementary dynamical dimension to the concept of kosmotropic/chaotropic behavior of solvated ions.