Abstract

Recent work has identified a bis‐(p‐nitrophenyl)ureidodecalin anion carrier as a promising candidate for biomedical applications, showing good activity for chloride transport in cells yet almost no cytotoxicity. To underpin further development of this and related compounds, a detailed structural and binding investigation is reported. Crystal structures of the transporter as five solvates confirm the diaxial positioning of urea groups while revealing a degree of conformational flexibility. Structures of complexes with Cl⁻, Br⁻, NO₃⁻, SO₄²⁻ and AcO⁻, supported by computational studies, show how the binding site can adapt to accommodate these anions. ¹H NMR binding studies revealed exceptionally high affinities for anions in DMSO, decreasing in the order SO₄²⁻>H₂PO₄⁻≈HCO₃⁻≈AcO⁻≫HSO₄⁻>Cl⁻>Br⁻>NO₃⁻>I⁻. Analysis of the binding results suggests that selectivity is determined mainly by the H‐bond acceptor strength of different anions, but is also modulated by receptor geometry.