Tiny artificial channels that ferry water almost as fast as nature's own, while turning salt away

What is it about?

Living cells move water across their membranes through natural protein pores called aquaporins, which let water through fast while blocking salt. We set out to build much simpler, sturdier stand-ins from small designed molecules. We combined a pyridine-2,6-dicarboxamide core with imidazole arms (borrowed from histamine and histidine) to make U-shaped building blocks. Left to themselves, these blocks stack into channels held together by many weak "hydrogen bonds", the same gentle grip water uses to cling to the inside of aquaporins. The crystal structures show two kinds of channel: wide ones about 9 Å across that cradle little clusters of water, and narrow ones about 3 Å across that thread water in single-file wires. The best of them shuttles water at 1.2 × 10⁷ molecules per second per channel, only about ten times slower than a real aquaporin. The same channels carry protons, and they turn ions away almost completely.

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Photo by Tarik SABOUR on Unsplash

Photo by Tarik SABOUR on Unsplash

Why is it important?

Fresh water is scarce for billions of people, and one route to making more is a membrane that lets water through but stops salt. Natural aquaporins do this beautifully, but they fall apart under the pressure and saltiness of a real desalination plant. A small, robust molecule that assembles itself into an aquaporin-like channel is a much more practical starting point. This work shows that stacking many weak hydrogen bonds around water, rather than relying on one strong grip, is enough to build a fast and salt-rejecting channel from scratch. It also gives a clear design rule: change the shape and crowding of the arms and you switch the channel between cradling water clusters and threading single water wires, which tunes how fast and how selective it is.

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