Benzene-based tripodal isothiouronium compounds as sulfate ion receptors

Novel benzene-based tripodal isothiouronium receptors are synthesized for the selective recognition of tetrahedral oxoanions. The binding study by isothermal titration calorimetry indicates that the cationic receptors bind sulfate ions preferably in a tripodal mode. while they show a mixed binding mode toward phosphate ion. The tripodal isothiouronium receptors show large DeltaG(0) values toward sulfate ions in methanol, which are entropy driven. The results demonstrate that a subtle structural constraint can lead to different binding modes toward structurally similar anions. (C) 2003 Elsevier Ltd. All rights reserved.