Fast fluctuations in protein powders: The role of hydration

An elastic neutron scattering investigation of the molecular dynamics of hydrated lysozyme powders has been undertaken for different water contents h (g water/g Lysozyme). The dry sample exhibits a harmonic behaviour in the whole temperature range, while anharmonic motions arise on hydrated samples at a temperature Td. Both Td and the magnitude of the anharmonic motions are markedly hydration dependent. On increasing water content the crossing barrier entropy change increases, while the enthalpy change keeps constant. The estimated average rigidity of the protein structure decreases abruptly immediately below the onset of the enzymatic activation at around 0.2h.