The effect of crowder charge in a model polymer-colloid system for macromolecular crowding: Polymer structure and dynamics.

We have examined the effect of crowder particle charge on macromolecular structure, studied via small-angle neutron scattering, and translational dynamics, studied via pulsed-field gradient NMR, in addition to bulk viscosity measurements, in a polymer macromolecule (polyethylene glycol)-nanoparticle crowder (polysucrose, Ficoll70) model system, in the case where polymer size and crowder size are comparable. While there are modest effects of crowder charge on polymer dynamics at relatively low packing fractions, there is only a tiny effect at the high packing fractions that represent the limit of molecular crowding. We find, via different measures of macromolecular mobility, that the mobility of the flexible polymer in the crowding limit is 10-100 times larger than that of the compact, spherical crowder in spite of their similar size, implying that the flexible polymer chain is able to squeeze through crowder interstices.