Highly permeable artificial water channels that can self-assemble into two-dimensional arrays

Significance This study focuses on the design of highly permeable artificial water channels for the use in membrane-based separation materials. A platform was developed for the systematic characterization of the single-channel water conduction of artificial channels, which is based on permeability measurement by stopped-flow light-scattering experiments and single-molecule counting by fluorescence correlation spectroscopy. With this platform the water conduction of the redesigned peptide-appended pillar[5]arene channels was found to be similar to that of aquaporins, natural water channel proteins, and their synthetic analogs, carbon nanotubes, which is an order of magnitude higher than that of first-generation artificial water channels. The channel can also self-assemble into arrays in membranes, opening the possibility for materials that can be used in engineering applications such as liquid and gas separations. Bioinspired artificial water channels aim to combine the high permeability and selectivity of biological aquaporin (AQP) water channels with chemical stability. Here, we carefully characterized a class of artificial water channels, peptide-appended pillar[5]arenes (PAPs). The average single-channel osmotic water permeability for PAPs is 1.0(±0.3) × 10−14 cm3/s or 3.5(±1.0) × 108 water molecules per s, which is in the range of AQPs (3.4∼40.3 × 108 water molecules per s) and their current synthetic analogs, carbon nanotubes (CNTs, 9.0 × 108 water molecules per s). This permeability is an order of magnitude higher than first-generation artificial water channels (20 to ∼107 water molecules per s). Furthermore, within lipid bilayers, PAP channels can self-assemble into 2D arrays. Relevant to permeable membrane design, the pore density of PAP channel arrays (∼2.6 × 105 pores per μm2) is two orders of magnitude higher than that of CNT membranes (0.1∼2.5 × 103 pores per μm2). PAP channels thus combine the advantages of biological channels and CNTs and improve upon them through their relatively simple synthesis, chemical stability, and propensity to form arrays.

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