Microscopic protein diffusion at high concentration by neutron spin-echo spectroscopy

Molecular transport and reactions in biological cells are strongly affected by the presence of macromolecules at high concentration. We studied the intermolecular structure and diffusion of oxygen carriers myoglobin and hemoglobin in concentrated solutions using neutron diffraction and spin-echo spectroscopy. The self-diffusion coefficient measured by NSE spectroscopy is compatible with theoretical prediction for long-time self-diffusion coefficient for colloids. We measured I(q, t) for q ≃ 1 Å−1 trying to observe the short-time diffusion coefficient. A signal which can be attributed to the protein is observed but which origin can neither be attributed to translational nor rotational diffusion.