Structure and Dynamics of Irreversible Single-Chain Nanoparticles in Dilute Solution. A Neutron Scattering Investigation

We present a small-angle neutron scattering (SANS) and neutron spin echo investigation on the structure and dynamics of irreversible single-chain nanoparticles (SCNPs) in dilute solution. SCNPs are ultra-small soft nano-objects obtained by intramolecular folding/collapse of individual linear polymer chains (precursors). SANS has demonstrated the compaction of macromolecules upon creation of internal cross-links, although their conformation is far from a globular topology. To describe the dynamic structure factor of the SCNPs in solution, we have taken into account their dual polymer/nanoparticle character and applied theoretical approximations based on the Zimm model. The study reveals relaxation of internal degrees of freedom but clearly slowed down with respect to the precursor counterparts. This effect is attributed to the internal friction associated to the compartmentation in domains within the macromolecule. We discuss the structural and dynamical similarities of SCNPs with disordered proteins, in particular with intrinsically disordered proteins. The high internal friction in both cases seems to be associated to the existence of internal domains.