Protein functions require conformational motions. We show here that the dominant conformational motions are slaved by the hydration shell and the bulk solvent. The protein contributes the structure necessary for function. We formulate a model that is based on experiments, insights from the physics of glass-forming liquids, and the concepts of a hierarchically organized energy landscape. To explore the effect of external fluctuations on protein dynamics, we measure the fluctuations in the bulk solvent and the hydration shell with broadband dielectric spectroscopy and compare them with internal fluctuations measured with the Mössbauer effect and neutron scattering. The result is clear. Large-scale protein motions are slaved to the fluctuations in the bulk solvent. They are controlled by the solvent viscosity, and are absent in a solid environment. Internal protein motions are slaved to the beta fluctuations of the hydration shell, are controlled by hydration, and are absent in a dehydrated protein. The model quantitatively predicts the rapid increase of the mean-square displacement above ≈200 K, shows that the external beta fluctuations determine the temperature- and time-dependence of the passage of carbon monoxide through myoglobin, and explains the nonexponential time dependence of the protein relaxation after photodissociation.

We show that the viscosity-related main ($\alpha$) relaxation of confined water vanishes at a temperature where the volume required for the cooperative $\alpha$ relaxation becomes larger than the size of the geometrically confined water cluster. This occurs typically around 200 K, implying that above this temperature we observe a merged $\alpha \mathrm{\text{−}}\beta$ relaxation, whereas below it only a local ($\beta$) relaxation remains. This also means that such confined supercooled water does not exhibit any true glass transition, in contrast to other liquids in similar confinements. Furthermore, it implies that deeply supercooled water in biological systems, such as membranes and proteins, generally shows only a local $\beta$ relaxation, a finding of importance for low temperature properties of biological materials.

It is well known that fast ionic conductivity can be obtained by doping modified oxide glasses with a metal-halide salt. The role of the dopant salt, apart from providing additional charge carriers, for the ionic conductivity has been a much debated issue. Using conductivity and density data for different host glasses mixed with various metal-halide salts, we find a remarkable common cubic scaling relation between the conductivity enhancement and the expansion of the network forming units induced by salt doping. This suggests that the glass network expansion, which is related to the available free volume, is a key parameter determining the increase of the high ionic conductivity in this type of fast ion conducting glasses.