Structural dynamics of proteins, scaling behaviour and liquid glass transition

Inelastic neutron scattering was used to study liquid-like motions and the nature of a dynamical transition in myoglobin, a small globular protein. The signature of the transition is a strong enhancement of low-frequency density fluctuations and a corresponding non-linear increase in atomic mean squared displacement above 180 K. The inelastic scattering function displays two power-law regions, whereby the crossover energy decreases with temperature. It is shown that the rescaled spectrum approximates a temperature and wave vector independent master function. Such features have been predicted for simple undercooled liquids in the vicinity of the glass transition by recent mode coupling theories.