SQUEEZING water through carbon nanotubes could shed light on how it moves with such ease across cell membranes in our body.
Water channels in cell membranes can selectively transport water molecules while blocking ions and other solutes. But it is difficult to study these channels, as removing them from the membrane can destroy them. Now, Alexander Kolesnikov of the Argonne National Laboratory in Illinois and colleagues say carbon nanotubes can serve as models for these channels.
Water molecules measure a few tenths of a nanometre and are usually tightly bound by hydrogen bonds, which could impede their flow through narrow channels. To study what happened to water inside nanotubes, the team fired a beam of neutrons at water-filled nanotubes with an average 鈥渂ore鈥� of about 1.4 nanometres. The way the neutrons bounced off the atoms of the water molecules revealed that the molecules were bound less tightly, allowing them to flow freely inside the tight confines of the nanotube.
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By combining computer models and their experimental data, the group worked out that an ice-like sheet forms on the inner walls of the nanotube, while a chain of water molecules moves in single file through the middle (Physical Review Letters, vol 93, p 035503). The team suggests the water molecules behave similarly in channels in cell membranes, which are narrower than the nanotubes.