Simple guanidinium motif for the selective binding and extraction of sulfate

A simple bidentate anion receptor, shown previously to adopt a rigid pseudobicyclic conformation while binding anions in the solid state, selectively binds sulfate in aqueous solutions with log K₁ and log K₂ values of 3.78 ± 0.12 M-1 and 2.10 ± 0.23 M-1, respectively. This anion receptor has little to no affinity for nitrate and chloride in the same solutions. A lipophilic derivative was synthesized in four steps to yield an extractant that is capable of partitioning sulfate into 1,2 dichloroethane from water in the presence of large excesses of chloride. This extractant demonstrated D values as high as 2.5 with only 30 mM of anion receptor.