Detailed Study of Potassium Solvation Using Molecular Dynamics Techniques

Abstract

Molecular dynamics simulations are carried out to examine the solvation properties and the ion-solvation shell exchange process of the K+ ion in liquid water, chloroform, and carbon tetrachloride. The solvent molecules are found to form well-defined solvation shells around the K+ ion and show a preferred orientational order toward the ion. The induced dipole moment distribution of K+ becomes broader and shifts to a larger average value from chloroform to carbon tetrachloride to water. It is observed that the K+ ion diffuses more rapidly in the aqueous phase than in liquid chloroform and carbon tetrachloride. We have also evaluated both ion and first solvent shell velocity autocorrelation functions and the residence time autocorrelation functions for the ion in water, chloroform, and carbon tetrachloride. The residence time is found to be 9.4 ps for water and about 30 ps for both chloroform and carbon tetrachloride. By use of a constrained molecular dynamics technique, the first solvation shell exchange process is investigated. It is found that an estimate using equilibrium solvation and classical transition-state theory overestimates the dissociation rate of the K+ ion. Including the dynamical effects using Grote−Hynes theory yields more accurate dissociation rates.

Diffusion coefficient of ionic solvation shell molecules

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] Generally, their motion is found to be substantially slowed down with respect to bulk solvent molecules but still somewhat faster than that of the ion. This conclusion is usually founded on the computation of the diffusion coefficient for the subset of first solvation shell molecules: its value is larger than that of the ion and lower than that of the bulk.…”

Diffusion constant of K+ inside Gramicidin A: A comparative study of four computational methods

“…Therefore, one must rely on simulations to predict diffusion constants, and, indeed, several theoretical methods have been developed for this purpose. They are widely used for calculating diffusion properties of ions and molecules in bulk phases [20][21][22], but the applicability of some of these methods to narrow ion channels (e.g., Gramicidin A) is questionable. Currently, there is no consensus in the biophysics literature about the magnitude of diffusion constants of ions inside narrow channels [6,[23][24][25][26][27][28].…”

On the coupling between molecular diffusion and solvation shell exchange

“…We believe that in this scenario the effect of the solvation shell exchange is not fully understood. Actually, not even the exchange process by itself can be regarded as a solved issue: although the exchange times for ions in solution have been the subject of study for quite some time 6,[9][10][11][12] ͑by means of molecular dynamics simulations͒, the mechanisms and stereochemistry of the exchange process are just starting to be scrutinized, [13][14][15][16] usually motivated by its key role in other important processes such as ion reactivity. To evidence some unclear aspects of the influence of ex-change on diffusion with an example, an issue such as a characterization of the quantitative speed-up in diffusion induced by exchanges remains unaddressed.…”