Highly Permeable Artificial Water Channels that Self-Assemble into Two-Dimensional Arrays

Abstract

Artificial nanoscale water channels are the future of cheap, low-power water filtration and desalinization. Biological water channels such as the aquaporin membrane protein selectively pass water across the cell membranes of living creatures, but are prohibitively difficult to incorporate into large-scale technological applications. In response to these challenges, many artificial channels have been designed to imitate the function of aquaporins, including a new single-molecule water channel we introduce here, peptide-appended pillar[5]arene (PAP). PAP is comprised of a single benzyl ring decorated by hydrophobic phenylalanine amino acid arms. Stopped-flow light scattering measurements combined with fluorescence correlation spectroscopy accurately characterized single channel PAP permeability as near to that of aquaporin itself, orders of magnitude better than first-generation artificial water channels. Molecular dynamics simulation supported this assessment and further predicted wetting-dewetting transitions to occur in individual PAP channels on the nanosecond timescale. Molecular dynamics simulation also predicted PAP self-assembly into two-dimentional arrays of lattice size 21 Å, driven by hydrogen bonds among the channel's peptide arms. Aggregation and lattice size were verified to within 1 Å by cryo-electron microscopy. The self-assembly of individual, highly permeable water channels into densely packed two-dimensional arrays can be potentially utilized to design a new generation of high-flux water filtration membranes. Furthermore, as the phenylalanine arms of PAP can be switched out for other amino acids, the individual channels and their self-assembly can be programmed to enable selective transmembrane transport.