“Glass Transition” in Peptides. Temperature and Pressure Effects

摘要

The internal dynamics of proteins and other biopolymers at different time and length scales are essential for their function. For example, the dynamic arrest at a temperature known as the glass transition temperature (T_g), is an essential feature of protein dynamics that can inhibit biological function. Such a dynamic arrest has been observed in the temperature dependence of the atomic mean-squared displacements obtained by inelastic neutron scattering and X-ray crystallography, Mossbauer spectroscopy , infrared spectroscopy and molecular dynamics simulations. Although there is consensus about the presence of a dynamic arrest at T_g, its origin is not well understood. For example, the very broad distribution of relaxation times (Cole-Davidson exponent of β_(CD) ～0.25) suggested the freezing of the collective protein dynamics whereas in some cases the reduced solvent mobility was thought to be the dominant factor in determining the atomic fluctuations. Similarly, synthetic polymers and glass-forming liquids display a strong non-Arrhenius behavior of relaxation times, τ(T), that practically freeze at the respective T_g.