Dipole Oriented Water Wires Confined in Artificial Chiral Membrane Channels

Aquaporins (AQPs) are known for their highly selective water transport through cell membranes. Oriented water-wires spanning the AQPs pore is of considerable importance for the selective translocation of water over ions. We recently discovered that water translocation through artificial I-quartets (self-assembled imidazole structures) increases when water molecules display dipolar orientation. Here, we show that water confined inside self-assembled I-quartets integrated into supported lipid bilayers (SLB) form oriented water-wires exhibiting a chiral super-structure, as visualized with static solid state X-ray single-crystal structures and sum-frequency generation (SFG) spectroscopy. The integration and assembly of I-quartets into SLB were also monitored with a Quartz Crystal Microbalance with Dissipation (QCM-D) and modeled with molecular simulations in order to provide physical insight into dipolar water orientation within artificial I-quartet channels. This study provides the first experimental proof of dipole orientated water wires within artificial water channels inserted in bilayer membranes and the characterization of their hydrogen-bond connectivity and chiral alignment. Uncovering the interplay between the hydrogen-bonded water structure and water transport through the self-assembled i-quartets is critical to understanding the function of natural membrane channels and will guide the design principles for developing artificial water channels for water purification.