Multidentate Anion Receptors for Binding Glyphosate Dianion: Structure and Affinity

For the first time, the relationships between anion receptor structures and their glyphosate dianion (Gly(2-)) binding affinity have been investigated. For this purpose, 12 multidentate bis-indolocarbazole, bis-urea and bis-carbazole based synthetic receptors were synthesized and their binding affinities towards Gly(2-) were measured in H2O/DMSO media (0.5 % to 20 % of H2O). Computational geometries, as well as 1D and 2D NMR experiments were used to elucidate the structures of the complexes formed on binding of Gly(2-). As expected, binding affinity depends strongly on the spatial position of the binding moieties, which, in turn, depend on the spacer length and rigidity. However, the relationships are not straightforward and, in some cases, are counterintuitive. Evidence is presented that, for several receptors, binding occurs through the phosphonate moiety only. One of the receptors described here has, to our knowledge, the strongest affinity towards Gly(2-) ever reported.