Anion Recognition by a Bioactive Diureidodecalin Anionophore: Solid-State, Solution, and Computational Studies

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^- , SO₄^2- and AcO^- , supported by computational studies, show how the binding site can adapt to accommodate these anions. ¹ H NMR binding studies revealed exceptionally high affinities for anions in DMSO, decreasing in the order SO₄^2- >H₂ PO₄^- ≈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.