Solid-State Conformational Flexibility at Work: Zipping and Unzipping within a Cyclic Peptoid Single Crystal

A peptidomimetic compound undergoes a reversible single‐crystal‐to‐single‐crystal transformation upon guest release/uptake with the transformation involving a drastic conformational change. The extensive and reversible alteration in the solid state is connected to the formation of an unprecedented “CH–π zipper” which can reversibly open and close (through the formation of CH–π interactions), thus allowing for guest sensing. Zip it! A cyclic peptoid undergoes a reversible single‐crystal‐to‐single‐crystal transformation with drastic conformational changes within the structure upon guest release or uptake. As determined by single‐crystal X‐ray analysis, the structural changes are mediated by the formation of a CH–π zipper which can reversibly open and close upon adsorption or desorption of acetonitrile guest molecules (yellow).