Highly selective synthetic ion/proton channels

A hallmark of protein channels is their high selectivity in transporting related species across cellular membranes via evolutionarily selected transmembrane pathways. Some notable examples include aquaporins that are super permeable to water molecules (10⁹ molecules per second) but strictly prevent the passage of ions and even protons, the K⁺- channel KcsA that displays a K⁺/Na⁺ selectivity of 10⁴, and the M2 proton channel that is at least 10⁵-fold more selective for protons over other monovalent cations. While these extraordinarily high transport selectivities are crucial for proper cellular functions, including maintaining an ion concentration gradient and regulating membrane potential, they are extremely difficult to replicate in artificially developed species-transporting channels. Over the past few years, we have developed some synthetic versions, enabling highly selective transport of  K⁺ (J. Am. Chem. Soc. 2017, 139, 12338; Angew. Chem. Int. Ed. 2020, 59, 1440), Cl^- (J. Am. Chem. Soc. 2018, 140, 8817) and I^- (Angew. Chem. Int. Ed. 2020, 59, 4806) ions as well as protons (Angew. Chem. Int. Ed. 2022, 61, e202200259). These are the areas that continue to capture our attention.