Origin and control of ionic hydration patterns in nanopores

Abstract

In order to permeate a nanopore, an ion must overcome a dehydration energy barrier caused by the redistribution of surrounding water molecules. The redistribution is inhomogeneous, anisotropic and strongly position-dependent, resulting in complex patterns that are routinely observed in molecular dynamics simulations. We now address the questions of the physical origin of these patterns and of how they can be predicted and controlled. We introduce an analytic model able to predict the patterns in terms of experimentally accessible radial distributions functions, yielding results that agree well with molecular dynamics simulations. We show that the patterns are attributable to a complex interplay of ionic hydration shells with water layers adjacent to the membrane and with the hydration cloud of the nanopore rim atoms, and we discuss ways of controlling them. Our findings pave the way to designing required transport properties into nanoionic devices by optimising the structure of the hydration patterns.

Field-Dependent Dehydration and Optimal Ionic Escape Paths for C2N Membranes

“…However, to analyze the asymmetry of hydration shells, the RDF-based methods have to be substantially extended. 57 Therefore, a conventional RDF-based analysis does not provide any additional information as compared with the MD-based approach adopted in this work.…”

Physics of Selective Conduction and Point Mutation in Biological Ion Channels

“…We plan to estimate analytically a multi-ion PMF that includes polarisation. We will do so by extending the results from [68,69], and using the Drude model introduced by Roux [70,71]. In addition polarisation can be included explicitly within the linear response formalism [11] via fluctuations of energy which account for the changes in structure and polarisation.…”