Salt-Excluding Artificial Water Channels Exhibiting Enhanced Dipolar Water and Proton Translocation

Abstract

Aquaporins (AQPs) are biological water channels known for fast water transport (∼10(8)-10(9) molecules/s/channel) with ion exclusion. Few synthetic channels have been designed to mimic this high water permeability, and none reject ions at a significant level. Selective water translocation has previously been shown to depend on water-wires spanning the AQP pore that reverse their orientation, combined with correlated channel motions. No quantitative correlation between the dipolar orientation of the water-wires and their effects on water and proton translocation has been reported. Here, we use complementary X-ray structural data, bilayer transport experiments, and molecular dynamics (MD) simulations to gain key insights and quantify transport. We report artificial imidazole-quartet water channels with 2.6 Å pores, similar to AQP channels, that encapsulate oriented dipolar water-wires in a confined chiral conduit. These channels are able to transport ∼10(6) water molecules/s, which is within 2 orders of magnitude of AQPs' rates, and reject all ions except protons. The proton conductance is high (∼5 H(+)/s/channel) and approximately half that of the M2 proton channel at neutral pH. Chirality is a key feature influencing channel efficiency.

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“…Due to the different arrangement of the conformational enantiomers, W1 and W2 are hence not environmentally identical (Figure d), and the dipole moment direction of W2 is rotated about 38° anticlockwise related to that of W1. The rotated‐reflection relationship between the two congruent triangles defined by the three H‐bonded oxygen atoms around each H 2 O (Figure d) reflects that the host molecules involved in the two linked three‐HB clamps form two cavities with equal sizes, in which the shortest distance between the atoms of host channel molecules is 2.47 Å (Supporting Information, Figure S38), similar to the cavity of aquaporin …”

Biomimetic and bioinspired membranes for water purification: A critical review and future directions

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“…Ideally, artificial channels can be synthesized using simple chemistry and are compatible with various solvents which make them convenient to synthesize. There has been an increase in recent years in studies discussing the design considerations, challenges encountered, and performance of membranes with artificial water channels [132,135,[138][139][140][141][142][143][144][145][146]. There are mainly two types of artificial channel types: self-assembling channels and unimolecular channels [135].…”