4,4'-Bipyridine as a unidirectional switching unit for a molecular pushing motor.

A chirality switch in which the intrinsic chirality of a 4,4'-bipyridine is combined with a metal-ion-induced switching principle is described. In the uncomplexed state the 4,4'-bipyridine unit, which is linked to an S,S,S,S-configured cyclic imidazole peptide, is P-configured. The addition of zinc ions leads to a rotation around the C-C bond axis of the 4,4'-bipyridine and the M isomer of the metal complex is formed. By addition of a stronger complexing agent the metal ions are removed and the switch returns to its initial position. The combination of the chirality switch with a second switching unit allows the construction of a molecular pushing motor, which is driven chemically and by light.

An azobenzene unit embedded in a cyclopeptide as a type-specific and spatially directed switch.

By embedding an azobenzene unit into a chiral scaffold, switching of azobenzene from the trans-(P) isomer to the cis-(P) isomer and back was achieved (black arrows in picture). The embedding leads to a flipping process in which the phenyl rings can only move directly towards one another in the switching process.