Cation-Induced Molecular Switching Based on Reversible Modulation of Peptoid Conformational States.

Peptoids are oligomers of N-substituted glycines with predictable folding and strong potentials as guest-binding receptor molecules. In this contribution, we investigate the structural features of a series of designed symmetric cyclic octamer peptoids (with methoxyethyl/propargyl side chains) as free hosts and reveal their morphologic changes in the presence of sodium and alkylammonium guests as tetrakis[3,5-bis(trifluoromethyl)phenyl]borate salts, reporting the first case of reversible adaptive switching between defined conformational states induced by cationic guests (Na+ and benzylammonium ion) in the peptoid field. The reported results are based on 1H NMR data, theoretical models, and single-crystal X-ray diffraction analysis. They represent initial steps toward deciphering the unique conformational states of cyclic octamer peptoids as supramolecular hosts with the aim to fully disclose their functional and dynamic properties.