Tris-ureas as transmembrane anion transporters

Nine tris-urea receptors (L1-L9) have been synthesised and shown to coordinate to a range of anionic guests both by 1H NMR titration techniques and single crystal X-ray structural analysis. The compounds have been shown to be capable of mediating the exchange of chloride and nitrate and also chloride and bicarbonate across POPC or POPC:cholesterol 7:3 vesicle bilayer membranes at low transporter loadings. An interesting dependency of anion transport on the nature of the cation is evidence to suggest that a M+/Cl- cotransport process may also contribute to the release of chloride from the vesicles.