Single file water transport across peptidic nanopores

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Confinement of water by pore geometry to a one-dimensional file of molecules interacting with the pore alters its physical characteristics. Changes in flow dynamics is partially due to the reduction in number of hydrogen bonds compared to the bulk fluid. Predicting the turnover rate from channel geometry (length and diameter) and from the diffusion coefficient in bulk water, macroscopic models clearly fail to describe the rates of single file water transport, which differ by several orders of magnitude among membrane channels. Desformylation, for example, increases the water permeability of gramicidin-A beyond the diffusion limit. We now aim to investigate both capillary evaporation and icelike structures in nanopores, which are predicted to occur by molecular dynamics simulations. After insertion into planar bilayers, water flow across a variety of new gramicidin derivatives will be measured by scanning microelectrodes. The effect of nanopore geometry and hydrophobicity on water and proton permeation rates is calculated by molecular dynamics simulations to gain insight into the molecular mechanism of single file water transport. This will allow design and synthesis of novel nanopores with optimized permeation characteristics. Since water ordering may modulate proton conductance via a "proton wire" hydrogen-bonding network, possible applications include switchable nanoscale conductors.