Berlin 2008 – scientific programme

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SYMP: Symposium Computational Soft matter physics

SYMP 1: Computational soft matter physics

SYMP 1.5: Invited Talk

Thursday, February 28, 2008, 11:15–11:45, H 0105

Proton transport through water-filled narrow pores — •Christoph Dellago — Institute for Experimental Physics, University of Vienna, Boltzmanngasse 5, A-1090 Vienna, Austria

One-dimensional chains of hydrogen bonded water molecules provide excellent conductors for protonic currents through pores across membranes, a process which is fundamental to many biological systems and technological applications. In this talk, I will report on the results of computer simulations of proton transfer along water chains inside the cavity of narrow carbon nanotubes. Free energy and rate constant calculations show that protons move across the membrane diffusively along single-file chains of hydrogen-bonded water molecules. Proton passage through the membrane is opposed by a high barrier in the effective potential, reflecting the large electrostatic penalty for desolvation and reminiscent of charge exclusion in biological water channels. Inside the pore, the proton mobility along the water chain exceeds that in bulk water by a factor of 40, but is reduced if orientational defects are present. Excess protons interact with such hydrogen-bonding defects through long-range electrostatics, resulting in coupled motion of protons and defects. The effective proton-defect interaction as well as the defect-defect interactions can be understood in terms of one-dimensional lattice model, in which water molecules located at regularly spaced lattice sites interact via dipole-dipole interactions. Using canonical and grand canonical Monte Carlo simulations of this simplified model, we have studied the filling behavior of long pores and find that the water chains remain ordered up to nearly macroscopic lengths, carrying implications for long-range proton transfer and the collective behavior of water molecules in carbon nanotube bundles.