Selective Nitrate Transmembrane Transport Through Adaptive Weak C─H Bonding Cyanostilbene Water Channels

Transmembrane water transport strongly depends on how dynamic, translocating water clusters are stabilized within hydrogen-bonding (HB) channels. Both structural order and short-lived disorder of transient channels play important roles in ion and water translocation. Strong HB can result in tight water binding and reduced mobility. We hypothesize that weaker HB binding sites reduce water friction, thereby enhancing water permeation while suppressing ion transport due to their unmet dehydration requirements within membrane. Herein, we show that weak HB CH donor cyanostilbenes promote water transport through adaptive, less-ordered water channels within the lipid bilayer, with water translocation efficiency depending in part, on the strength of the CH donor sites. Fine-tuning both CH donor strength and binding geometry enables modulation of anion transport selectivity, ranging from moderate NO₃ ^- over Cl^- selectivity to highly NO₃ ^--selective transport and ultimately to exclusive water transport. For instance, we achieved over 200-fold selectivity for NO₃ ^- over Cl^- and ∼100-fold selectivity for NO₃ ^- over Br^-, while some systems showed no detectable Cl^- or Br^- transport yet retaining strong NO₃ ^- transport activity. This work represents a step toward adaptive transmembrane water channels and highlights the potential of HB CH donor channels for water translocation and for increased NO₃ ^-/ Cl^- selectivity.