Structure and dynamics of polymeric hybrid physical-covalent assemblies of computationally designed peptidic bundlemers

The nanostructure and dynamics of supramolecular polymers of computationally designed peptidic bundlemers is presented using a combination of Small-Angle Neutron Scattering (SANS), Neutron Spin Echo (NSE) and high-resolution Transmission Electron Microscopy (TEM). The bundlemers are oligomers of four identical alpha-helical peptides that are packed in an antiparallel fashion to form a robust cylindrical building block. Via a hybrid physical-covalent pathway and by employing linkers of different length and geometry, the bundlemers are linked into ultra-rigid rod-like polybundlemers or semi-rigid worm-like chains of polybundlemers. The two polymer systems show distinct scattering signatures in SANS and the differences in rigidity are also readily viewable in TEM micrographs. NSE indicates that the inter-bundlemer dynamics is impacted by the linker type. A dynamical decay rate, Γ ~ Q ² (Q is the scattering vector) is recorded for the rigid rod-like polymers for the entire probed Q-regime. In contrast, semi-rigid chains show a Q-dependent dynamic signature, with a Γ ~ Q ² dependence at high-Q which deviates to a Γ ~ Q ^8/3 dependence in intermediate-Q regime. This indicates Zilman-Granek bending modes are at play at inter-bundlemer length scales in the semi-rigid polybundlemer system.