Allosterically Controlled Threading of Polymers through Macrocyclic Dimers

As part of an ongoing study to construct a molecular Turing machine in which a polymer chain is encoded via allosteric information transfer between macrocyclic complexes, we describe the thermodynamic and kinetic characterization of a multicomponent self-assembled system based on a zinc porphyrin macrocyclic compound, a bidentate ligand (1,4-diazabicyclo[2.2.2]octane, DABCO), and a viologen-substituted polymer guest. Initial addition of DABCO to the porphyrin macrocycle in chloroform solution leads to the formation of a stable 2:1 (porphyrin:DABCO) dimeric complex, even under dilute conditions, by means of strong cooperative interactions involving hydrogen and metal–ligand bonds. Further titration of the porphyrin-DABCO mixtures with the polymer gives rise to a complex array of species in the solution. The system is analyzed in detail by a combination of spectroscopic measurements and computational modeling. Each association constant in the binding scheme and the fraction of each individual complex that i...