Highly Selective Artificial Lithium Channels

Sustainable mining and recycling of lithium (Li) have the potential to offer a secure and reliable global supply of lithium to meet rapidly growing energy-storage demands. Bioinspired technologies have the potential to increase sustainability and reduce the environmental impacts of lithium purification. In this study, we report the design of a class of bioinspired supramolecular membrane channels that, to the best of our knowledge, achieve one of the highest overall Li+ selectivities reported to date for artificial transmembrane ion channels, with conservative lower-limit selectivity estimates of Li+/Na+ ≥ 94, Li+/K+ ≥ 136, Li+/Mg2+ ≥ 286, and Li+/Ca2+ ≥ 228 under electrochemically driven transport conditions, thereby establishing a new benchmark for Li+-selective membrane channels. The single-channel conductance of this channel for Li+ ions was determined to be 13.35 pS, equating to Li+ ion transport rates of approximately 1.34 × 107 ions/s per channel at -160 mV. These channels were constructed using a central-ring pillar[5]arene appended with alkyl chains ending in diphenylphosphine oxide (DPP) ligands. Molecular dynamics simulations suggest that Li+ selectivity arises from coupled hydration-shell retention, ion-ligand coordination at the DPP-functionalized entrance, and confinement effects within the LAP5n10-DPP channel. At the DPP-functionalized entrance, Li+ retains much of its compact hydration shell while engaging the phosphoryl oxygen through a favorable ligand-exchange interaction, whereas Na+ interacts with the DPP region primarily through a water-separated outer-shell geometry, and K+ interacts more strongly with the adjacent hydrophobic/phenyl-rich region. At the central constriction, all ions experience hydration-shell disruption, but divalent Ca2+ and Mg2+ face the largest dehydration penalties because pore passage would require near-complete dehydration of their strongly bound hydration shells.