Controllable chiral memory in an anion tetrahedral cage

Abstract

The construction of chiral structures, especially through chiral guest induction and subsequent chiral memory, is an important yet challenging task in hydrogen-bonded supramolecular systems. Here, we report the chiral induction of a series of chiral guests (R/S-α-methylcholine, G^1S/1R; R/S-β-methylcholine, G^2S/2R) to an anion-coordination-driven tetrahedral cage 1. Interestingly, the chiral memory effect is observed, where the induced chirality can be retained for a certain period (up to several days) upon replacing the chiral guests with achiral ones (TEA⁺, TMA⁺ or Ch⁺). Low Gibbs energies of activation may contribute to facile chiral induction and retention, while the high binding affinity between cage 1 and TEA⁺ enables the replacement of the trapped chiral guest to obtain chiral memory. Moreover, the controllable retention time of induced chirality could be realized by using different achiral guests. The findings provide a convenient way for “aniono” cages to achieve stereochemical control from achiral building blocks.