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Water confined into the interior channels of narrow carbon nanotubes or

transmembrane proteins forms collectively oriented molecular wires held
together by tight hydrogen bonds. Here, I will explore the
thermodynamic stability and dipolar orientation of such one-dimensional
(1D) water chains from nanoscopic to macroscopic dimensions. A simple dipole lattice model accurately recovers key properties of 1D-confined water when compared to atomically detailed simulations. In a major reduction in computational complexity, the dipole model can be
represented in terms of effective Coulombic charges, which allows us to
study pores of macroscopic lengths in equilibrium with a water bath (or
vapor). At ambient conditions, the water chains filling the tube are
essentially continuous up to macroscopic dimensions. The properties of
nanopore water can be probed experimentally with dielectric
spectroscopy. Our computer simulations, carried out for a simplified
water model, demonstrate that the dielectric response of 1d water chains follows Debye behavior. Exploiting that the time evolution of the total dipole moment of a 1D water chain is determined by the diffusive
dynamics of essentially uncorrelated defects, we have derived simple
formulas for the susceptibility and relaxation times as a function of
chain length. These expressions, verified in extensive computer
simulations, permit to extract fundamental molecular information such as the defect energy and their diffusion constant from dielectric
relaxation spectra. The implications of the dipolar order of
nanoconfined 1D water for long-range proton transport are also discussed.

J. Köfinger and C. Dellago, "Orientational Dynamics and Dielectric
Response of Nanopore Water", Physical Review Letters 103, 080601 (2009).

J. Köfinger, G. Hummer, and C. Dellago, "A one-dimensional dipole
lattice model for water in narrow nanopores" Journal of Chemical
Physics 130, 154110 (2009).

J. Köfinger, G. Hummer, and C. Dellago, "Macroscopically Ordered Water
in Nanopores", Proceedings of the National Academy of Sciences 105,
13218 (2008).