DNA mechatronic devices switched by K⁺ and by Sr²⁺ are structurally, topologically, and electronically distinct

DNAs and RNAs that fold via the formation of guanine quartets form G-quadruplexes that are often highly diverse in terms of architecture and topology. G-quadruplexes are specifically stabilized by metal cations such as K(+) and Sr(2+), but not Li(+). DNA duplexes that incorporate two separated clusters of G•G mismatches ("P-duplexes") can function as electronic switches, capable of toggling reversibly from a poorly conductive conformer (E) with only Li(+) in the solution to a G-quadruplex incorporating conformer of higher conductivity (C) in the presence of K(+). Herein, we report results from fluorescence energy transfer, circular dichroism, charge conduction, and chemical footprinting experiments, which cumulatively demonstrate that P-duplex E↔C transitions are genuinely mechatronic, with causally coupled mechanical and electronic states. We show, further, that the K(+) - and the Sr(2+)-fuelled E↔C switching of a given P-duplex are structurally, topologically, and electronically distinct from each other. A single DNA P-duplex can thus exist in at least three distinguishable mechatronic states in aqueous solution.