Separation Science and Technology, Vol.53, No.12, 1864-1873, 2018
Simple guanidinium motif for the selective binding and extraction of sulfate
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, N,N'-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-d(4) solutions with stepwise log K-1 and log K-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.