Tunable Length of Cyclic Peptide-Polymer Conjugate Self-Assemblies in Water

Abstract

Polymers conjugated to cyclic peptides capable of forming strong hydrogen bonds can self-assemble into supramolecular bottlebrushes even in aqueous solutions. However, controlling the aggregation of these supramolecular assemblies remains an obstacle that is yet to be overcome. By introducing pH-responsive poly(dimethylamino ethyl methacrylate) (pDMAEMA) arms, the repulsive forces were tuned by adjusting the degree of protonation on the polymer arms. Neutron scattering experiments demonstrated that conjugates in an uncharged state will self-assemble into supramolecular bottlebrushes. Reducing the pH in the system led to a decrease in the number of aggregation, which was reversible by addition of base. Potentiometric titration showed a correlation between the number of aggregation and the degree of ionization of the pDMAEMA arms. Hence, a balance between the strength of the hydrogen bonds and the repulsive electrostatic interactions determines the number of aggregation and extent of self-assembly. The presented work demonstrates that conjugate self-association can be controlled by tuning the charge density on the conjugated polymer arms, paving the way for the use of responsive cyclic peptide conjugates in pharmaceutical applications.