Electron-deficient hemicryptophanes for the recognition of anions through anion–π interactions

Abstract

The selective recognition and encapsulation of anions are crucial in many biological and environmental processes. Anion–π interactions, characterized by attractive non-covalent interactions between anions and electron-deficient aromatic surfaces, have gained significant attention for their potential in anion binding. However, due to the weak nature of these interactions, receptors that rely solely on anion–π interactions are scarce. To promote anion binding via electron-deficient surfaces, we constructed a cavity within the hemicryptophane framework using tetrafluoroxylylene arms and a benzene triimide unit, thereby displaying multiple electron-deficient surfaces. Binding studies revealed that the electron-deficient receptor exhibits significantly higher anion binding constants compared to a less electron-deficient hemicryptophane. For example, the affinity for chloride (K_a = 207) is ten times higher for the most electron-deficient hemicryptophane. More impressive is the unique affinity for triiodide (K_a = 416), representing the first example of triiodide recognition by a BTI-based receptor. The enhanced binding properties of this receptor result from the combination of different π-acidic surfaces in a single cage molecule.