pH-Stimulated Reconfiguration and Structural Isomerization of Origami Dimer and Trimer Systems.

Reversible pH-responsive dimer or trimer origami structures are assembled by bridging origami frames with pH-responsive units. The cyclic pH-stimulated separation and reassembly of dimer origami structures is demonstrated using i-motif or Hoogsteen-type (C-G·C+ or T-A·T) interactions. The duplex-bridged dimer T1-T2 is separated by the pH-induced formation of an i-motif structure (pH = 4.5), and the dimer is reassembled at pH = 7.0. The duplex-bridged dimer, T3-T4, is separated at pH = 4.5 through the formation of C-G·C+ triplex structures and is reassembled to the dimer at pH = 7.0. Similarly, the T-A·T triplex-bridged dimer, T5-T6, is separated at pH = 9.5 and is reassembled at neutral pH. Finally, a trimer, T3-T7-T6, that includes C-G·C+ and T-A·T pH-responsive bridges reveals pH-programmed cleavage to selectively yield the dimers T3-T7 or T7-T6, which reassemble to the trimer at pH = 7.0. A linear three-frame origami structure bridged by duplexes including caged i-motif units undergoes pH-stimulated isomerization to a bent structure (pH = 4.5) through the formation of i-motif complex and bridging T-A·T triplex units.