Selective recognition of quaternary ammonium cations

The selective recognition of ammonium cations fundamentally relies on their degree of substitution. In biological systems, proteins can preferentially bind more substituted ammonium cations over less substituted homologs. By contrast, the stronger hydrogen-bond donor ability and enhanced cation-π interactions of less substituted cations would predict the preferential recognition of these species. Here, we show that combining supramolecular recognition with solid-phase abstraction enables the selective abstraction of quaternary ammonium cations across diverse cation scaffolds in the solid crystalline state. Quaternary ammonium cations access a lower-energy solid state than tertiary counterparts through multipoint binding to an adaptive array of isostructural BINOL·counterion networks. The preferential abstraction of quaternary ammonium cations from mixtures of homologous cations proceeds under thermodynamic control with excellent selectivity and remains operative even under aqueous conditions.