Diffusive dynamics of ordered solutions of apoferritin near the structure factor peak

Aqueous solutions of apoferritin, which consists of 24 proteins assembled into a spherical shell (outer diameter 12 nm), represent highly monodisperse systems. In low-salt solutions, a pronounced peak in the static structure factor S ( q ) indicates intermolecular interactions due to the net negative charge (pH ≈ 5) of apoferritin. We have investigated both the structure and dynamics of ordered solutions for the first time in the vicinity of the S ( q ) peak at q *. Coherent small-angle neutron scattering experiments were performed at the Institute Laue-Langevin (Grenoble) and the dynamics was studied using the high-resolution neutron spin echo spectrometer IN15. The dynamics at q > q * coincides with extrapolated results of previous experiments. For low-salt solutions, the normalized intermediate-scattering function has a shape that qualitatively resembles that of S ( q ) in the vicinity of q *. However, the inverse effective diffusion constant differs quantitatively from S ( q ) below q *.