Mechatronic DNA devices driven by a G-quadruplex-binding platinum ligand

Contractile duplexes are DNA double helices that incorporate two strategically placed patches of guanine–guanine (G·G) base mismatches. Such duplexes are cation-driven mechatronic devices, able to toggle between states with distinct mechanical and charge conduction properties. In aqueous lithium chloride solution contractile duplexes have an extended (E) and poorly conductive conformation; however, potassium ions drive them to a relatively conductive and structurally contracted (C) conformation, via intramolecular G-quadruplex formation. Here, we report that even in the absence of K+ ions, a known G-quadruplex binding ligand, Pt-PIP [phenylphenanthroimidazole ethylenediamine platinum(II)] efficiently promotes the E→C transition, while a poor binder, Pt-bpy [bipyridine ethylenediamine platinum(II)], does not promote this transition. An examination of E→C transitions within two different designs for DNA contractile helices found an unexpected complexity: the formation of distinct C states, both electrically conductive, but possessing dissimilar DNA topologies. Ligand-driven DNA mechatronic devices such as these may constitute prototypes for electronic biosensors that identify G-quadruplex binding ligands.