Fig. 1: Compound structures, synthesis and crystal structure.

a Synthesis of macrocycle 1. The SO42– template could be removed by EtOAc/H2O extraction, which, however, led to partial degradation of the macrocycle. The free macrocycle with 80–90% purity was used in 1H NMR titrations in DMSO-d6/0.5% H2O. The pure SO42– complex was used in fluorescence and membrane transport studies in water where the complex completely dissociated at 50 nM due to the competitive aqueous conditions. b Top and side views of the crystal structure of the 1–SO42– complex (CCDC: 2128483) with solvent removed by PLATON SQUEEZE and cation and disorder omitted for clarity. c Reference bis-urea anion receptor 2.