"Molecular Shakers" as Transmembrane Single-Molecule Channels Toward 1:1 Cl^-/K⁺ Cotransport

Cation-chloride cotransporters (CCCs) are an important family of chloride channel proteins that mediate electroneutral transport of Cl^- with Na⁺ and/or K⁺. In this study, we introduced ultracycles (molecular shakers-so named for their cocktail-shaker-like shape) designed to mimic the binding sites and functions of KCC1. These ultracycles incorporate both anion (S_Cl1, S_Cl2) and cation (S_K) binding sites within the single-molecular backbone. The synthesis was achieved through dynamic nucleophilic aromatic substitution, starting from a rigid-flexible macrocyclic precursor and diphenol derivatives. Planar lipid bilayer measurements demonstrated that the molecular shakers function as single-molecule channels, mediating ion transport. By varying the structural features of the lower and larger rims of the macrocycle, as well as the glycol chains and the pH of the bulk solution, we achieved a permeability ratio up to P_Cl ^-/P_K ⁺ = 0.83.