Transient and Regulated Cycles of Chemically Driven Disassembly and Reassembly in Anion-Driven Supramolecular...

Anion-driven supramolecular polymers that are disassembled and then reassembled using trichloroacetic acid (TCAH) in transient pH-responsive cycles are rare. Proton transfer from TCAH drives switching to a transient state until the conjugate base, TCA^-, decarboxylates (-CO₂) and recaptures the proton as CHCl₃, returning the system to the initial state. We report cycles of molecular switching using TCAH to neutralize monotopic phosphate anions originally bound inside cyanostar receptors, thereby generating transient metastable states that subsequently reassemble. Use of ditopic analogs, diphosphonates, produce supramolecular polymers that disassemble and reassemble with switchable solution viscosities and solid-state morphologies. Despite high fidelity switching, use of the anion receptor leads to the unexpected capture and stabilization of the conjugate base, trichloroacetate, inside cyanostar as an acid-anion TCAH···TCA^- complex in the transient state. Thus, and for the first time, we observe large 300-fold elongation of the reassembly time and large variations in kinetics in response to the pool of anions in solution. Reaction times are shortened by the addition of exogenous anions, where Cl^- concentration regulates reaction rates. S-shaped kinetics curves are observed that show positive feedback loops relying on endogenous anions.