Logarithmic decay in single-particle relaxations of hydrated lysozyme powder

We present the self-dynamics of protein amino acids of hydrated lysozyme powder around the physiological temperature by means of molecular dynamics (MD) simulations. The self-intermediate scattering functions (SISF) of the amino acid residue center-of-mass and of the protein hydrogen atoms display a logarithmic decay over 3 decades of time, from 2 picoseconds to 2 nanoseconds, followed by an exponential alpha-relaxation. This kind of slow dynamics resembles the relaxation scenario within the beta-relaxation time range predicted by the mode coupling theory (MCT) in the vicinity of higher-order singularities. These results suggest a strong analogy between the single-particle dynamics of the protein and the dynamics of colloidal, polymeric and molecular glass-forming liquids.