Fast transport of dissolved ions and molecules from one solution to another is important for many chemical and biological processes.  An example is transport of ions across synthetic membranes for efficient water purification or osmotic power generation.   Another example is ion transport across cellular membranes for electrical signaling.   A fundamental question is whether the nanopores should mimic the hydration properties of specific ions and molecules to facilitate their transfer from solution to the nanopore interior.  A nanopore that provides the same solvation free energy to an ion as liquid water is expected to promote fast ion permeation.  It is less clear whether a nanopore that matches local hydration structure is needed to provide that matching solvation free energy.   To address this question, we first applied ab initio molecular dynamics (MD) simulations to interrogate hydration structure of several metal ions in water.   Our results on local hydration structure agree with scattering experiments and indicate that water hydrates each ion differently.  That result supports the argument that local hydration structure is a differentiating feature of metal ions.  But to explain how two ions with different hydration structures may act as analogues and permeate the same nanopore, a more restrictive definition of local hydration is needed.   Next, we interrogated ion solvation in synthetic nanopores.   A comparison of hydration vs solvation structure in synthetic and biological nanopores suggests that hydration mimicry is not necessarily the best strategy for fast transport.     Sandia National Laboratories is a multiprogram laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under Contract DE-AC04-94AL8500.

Hydration mimicry:  A strategy for fast ion transport through membrane nanopores?

248th National Meeting (2014)

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