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.