Dynamics of single-file water chains inside nanoscale channels: physics, biological significance and applications

Transportation of water across nanochannels is of great importance for biological activities as well as for designing novel molecular devices/machines/sensors, which has wide applications in nanotechnology. With the development of experimental and computational facilities and technologies, it becomes possible to study the water dynamics inside and across the nanoscale channels by both experiments and numerical simulations. When the radius of a nanochannel is appropriate, the water molecules inside the channel form a single-file structure. Water confined in these nanoscale channels usually exhibits different dynamics not seen in the bulk system, including the wet-dry transition due to confinement, concerted hydrogen-bond orientations and flipping, concerted motion of water molecules and wavelike density distribution pattern. The permeation of water across the channels also shows unique behaviours, such as extra-high permeability, excellent on-off gating behaviour with response to the external mechanical and electrical signals and noises, reduction and enhancement by charge distributions on the channel walls, as well as directional transportation by a combination of charges close to a channel. In this review, we examine some of the recent advances in the dynamics of these single-file water molecules inside very narrow nanochannels.