Simple guanidinium motif for the selective binding and extraction of sulfate

<p>It is shown that a simple guanidinium molecule binds sulfate selectively in methanol/water solution, and a synthesized lipophilic analog permits the selective extraction of sulfate from aqueous sodium chloride into 1,2-dichloroethane. This receptor, <i>N</i>,<i>N</i>’-bis(2-pyridyl)guanidinium, features a rigid pseudo-bicyclic conformation in binding anions in the solid state. It selectively binds sulfate in 10% water/90% MeOD-d₄ solutions with stepwise log <i>K</i>₁ and log <i>K</i>₂ values of 3.78 ± 0.12 and 2.10 ± 0.23, respectively. Density functional theory calculations were performed to predict the conformational preferences of guanidinium receptors upon anion coordination in solution.</p