Dynamic Devices. Shape Switching and Substrate Binding in Ion-Controlled Nanomechanical Molecular Tweezers

As examples of supramolecular devices performing chemical (ionic, molecular) control of binding
events and models of related natural systems, two molecular conformational switches are described, which
display cation-controlled nanomechanical motion coupled to substrate binding and release. The substrate
binding relies on donor/acceptor interactions, provided by intercalation between planar sites located at the
extremities of the switching units, whereas cation complexation is responsible for conformational regulation.
The terpyridine py-py-py-based receptor is activated toward substrate binding upon complexation of a
zinc(II) cation and operates in a two-state process. The replacement of the central pyridine by a 4,6-disubstituted pyridimine as in py-pym-py induces a state reversal and yields a new receptor which binds
a substrate in the absence of cation, and releases it when copper(I) is introduced, following a three-step
process. These systems represent effector-triggered supramolecular switching devices leading toward
multistate nanomechanical chemical systems. These two systems illustrate the use of simple conformational
switches in the binding site and allosteric regulation of substrate affinity.