The permeation of hydrophobic, cylindrical nanopores by water molecules and ions is investigated under equilibrium and out-of-equilibrium conditions by extensive molecular-dynamics simulations. Neglecting the chemical structure of the confining pore surface, we focus on the effects of pore radius and electric field on permeation. The simulations confirm the intermittent filling of the pore by water, reported earlier under equilibrium conditions for pore radii larger than a critical radius . Below this radius, water can still permeate the pore under the action of a strong electric field generated by an ion concentration imbalance at both ends of the pore embedded in a structureless membrane. The water driven into the channel undergoes considerable electrostriction characterized by a mean density up to twice the bulk density and by a dramatic drop in dielectric permittivity which can be traced back to a considerable distortion of the hydrogen-bond network inside the pore. The free-energy barrier to ion permeation is estimated by a variant of umbrella sampling for , , , and ions, and correlates well with known solvation free energies in bulk water. Starting from an initial imbalance in ion concentration, equilibrium is gradually restored by successive ion passages through the water-filled pore. At each passage the electric field across the pore drops, reducing the initial electrostriction, until the pore, of radius less than , closes to water and hence to ion transport, thus providing a possible mechanism for voltage-dependent gating of hydrophobic pores.
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15 June 2005
Research Article|
June 21 2005
Electric-field-controlled water and ion permeation of a hydrophobic nanopore
J. Dzubiella;
J. Dzubiella
a)
University Chemical Laboratory
, Lensfield Road, Cambridge CB2 1EW, United Kingdom
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J.-P. Hansen
J.-P. Hansen
University Chemical Laboratory
, Lensfield Road, Cambridge CB2 1EW, United Kingdom
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a)
Present address: NSF Center for Theoretical Biological Physics (CTBP), Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, California 92093-0365. Electronic mail: jdzubiella@ucsd.edu
J. Chem. Phys. 122, 234706 (2005)
Article history
Received:
January 10 2005
Accepted:
April 13 2005
Citation
J. Dzubiella, J.-P. Hansen; Electric-field-controlled water and ion permeation of a hydrophobic nanopore. J. Chem. Phys. 15 June 2005; 122 (23): 234706. https://doi.org/10.1063/1.1927514
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