Triggered Reversible Reconfiguration of G‑Quadruplex-Bridged “Domino”-Type Origami Dimers: Application of the Systems for Programmed Catalysis

The reversible and switchable reconfiguration of the two-origami-dimer mixture AB plus CD into the dimer mixture DA plus BC and back using the triggered formation of K⁺-ion-stabilized G-quadruplexes and subsequent treatment with 18-crown-6-ether is presented. The reconfiguration processes are followed by atomic force microscopy imaging of the dimer structures that include tiles marked with 0, 1, 2, and 3 4× hairpin labels. By the functionalization of AB and CD dimers with the Mg²⁺-ion-dependent DNAzyme subunits, the AB plus CD mixture leads to the cleavage of the fluorophore- and quencher-modified substrate of the DNAzyme and to the activation of the fluorescence of the fluorophore (fluorescein)-modified fragment product. The K⁺-ion-induced isomerization of the mixture of AB plus CD into the mixture DA plus BC separates the Mg²⁺-ion-dependent DNAzyme subunits and concomitantly reconfigures the K⁺-ion-stabilized G-quadruplex associated with the two dimers. After the binding of hemin to the G-quadruplexes, the hemin/G-quadruplex DNAzyme is generated, leading to the catalyzed oxidation of Amplex Red by H₂O₂ to yield the fluorescent resorufin product. By the cyclic treatment of the AB plus CD mixture with K⁺ ions to yield the DA plus BC mixture and the subsequent recovery of the AB plus CD mixture by subjecting the DA plus BC mixture to 18-crown-6-ether, the fluorescence output signals of the system are switched on and off between the fluorescence of fluorescein and resorufin, respectively.