Water-Pore Flow Permeation through Multivalent H-Bonding Pyridine-2,6-dicarboxamide-histamine/Histidine Water Channels

Aquaporins (AQPs) are natural proteins that can selectively transport water across cell membranes. Heterogeneous H-bonding of water with the inner wall of the pores of AQPs is of maximal importance regarding the optimal stabilization of water clusters within channels, leading to selective pore flow water transport against ions. To gain deeper insight into the water permeation mechanisms, simpler artificial water channels (AWCs) have been developed. Several H-bonding motifs (i.e., imidazole, polyhydroxy, etc.) have been reported as distinct and efficient for water-cluster stabilization within AWCs. Herein we combine two pyridine-2,6 dicarboxamide and imidazole to conceive multivalent U-shaped AWCs able to stabilize, like in AQP water clusters via different H-bonding groups. The crystal structures reveal that stable water superstructures are formed in the solid state, one with hydrophilic pores of ∼9 Å diameter, accommodating water clusters, and one with sterically hindered hydrophobic channels of ∼3 Å diameter, stabilizing water wires. As a result, a single-channel permeability of 1.2 × 107 H2O/s/channel has been achieved by the U-channels, which is only 1 order of magnitude lower than that of AQPs. Moreover, U-channels perform proton transport and completely reject anions and potentially can be applied in desalination membranes. Molecular simulation confirmed that U-channels can generate stable supramolecular porous sponges when they are decorated with hydrophobic alkyl chains featuring multivalent water H-bonding units that serve as water-cluster relays within the channel. To the best of our knowledge, this work is a rare biomimetic example of the importance of water-cluster stabilization via multivalent H-bonding and toward selective transport through water channels.