Tetraureas versus triureas in sulfate binding.

By mimicking the scaffolds of oligopyridine-based ligands, triurea and tetraurea receptors have been developed for sulfate binding. The triureas (L(1), L(2)) show stronger binding of sulfate than tetraureas (L(3), L(4)) in DMSO because of their better conformational complementarity with sulfate, while the tetraureas display better "water tolerance" benefiting from the chelate effect and hydrophobic effect.