Metal and Proton Relay-Controlled Hierarchical Multistep Switching Cascade.

Transition metals play an important role in many biological processes including cellular regulation and signal transduction. Emulating such processes on the molecular level, while challenging, can help us learn how to manipulate intermolecular communication, an important requirement for the development of solution-based molecular machines. In this work, we demonstrate a transition metal-based artificial multistep switching cascade that exhibits intrinsic hierarchical level control. The process starts with Zn(II), which initiates a transition metal relay by displacing a macrocycle-encapsulated Pd(II). The latter then binds to a hydrazone switch leading to coordination-coupled deprotonation (CCD). Finally, the proton generated through CCD activates the E / Z isomerization of a second noncoordinating pH-sensitive hydrazone switch. This whole multistep process can be reset to the original state by removing the Pd(II) from the system.