Single molecule transport characterization of a high permeable artificial water channel

Bioinspired artificial channels can combine high stability with the high permeability and selectivity found in biological channels. They have potential applications in next-generation energy-efficient and stable aqueous separation applications. This study is focused on a new architecture of artificial water channels-peptide-appended pillar[5]arenes. This study combined stopped-flow measurement with a newly developed fluorescence correlation spectroscopy technique to, for the first time, successfully determined the single channel water permeability of artificial channels. The peptide-appended pillar[5]arene channel permeability was determined to be (2.81±0.11)×10^-17 cm³/s per channel or (9.68±0.38)×10⁵ H₂O molecules/s per channel. This permeability value is only 2 magnitudes lower than that of natural water channel-aquaporins, when the low cross-sectional area (0.65 nm²) is compared to larger cross sectional area biological water channels (∼10 nm²). This is an orders of magnitude improvement over the first-generation of the artificial water channels reported before and is the fastest one reported so far. This channel was found to have a pore size of approximately 450 Da and showed ion selectivity in the order of NH₄ ⁺ < Cs⁺ < Rb⁺ < K⁺ < Na⁺ < Li⁺ < Cl^- as determined by patch clamp studies. The ability to further chemically modify the versatile chemical architecture of the pillar[5]arene channels shows promise for further improving water permeability and selectivity.