Ln(III) Selectivity in Biomimetic Ligand-appended Channels

Modern lanthanide separations through solvent-solvent processes are a major source of waste and come at large thermodynamic cost while sporting relatively low selectivities. With exponential demand for lanthanide resources in energy efficient lighting, permanent magnets, and electronics, the virtually identical set of 14 f-block elements is a necessary front in energy efficient membrane separations. While dawning applications for biological water channels in forward water and resource recovery processes fall short due to thermal instabilities, the synthetic pillar[n]ene template provides a wide parameter space for design based on chemistry, ligand length, bilayer composition, and sequence to mimic the biologically optimized conductivities and selectivities found in AQP (O(10⁹) H₂O/channel/s, 10⁹ H₂O:Na⁺) and KcsA (10⁷ ions/channel/s, 10⁴ K⁺:Na⁺). In this work, we offer a mechanistic insight into lanthanide-lanthanide separations in angstrom scale, transmembrane channels through molecular dynamics simulations and potential mean force calculations. The resulting conductivity measurements, energetic profiles, and coordination structures provide insight into pillar[n]ene monovalent/divalent rejection, trivalent selectivity, and water conductivity.