Protein-Solvent Interactions in Solids

The biological function of solid assemblies as fibrils, membrane proteins, or cytoskeletal proteins critically depends on their interactions with the solvent, similar to soluble proteins; as a consequence, the characterization of the dynamic properties of the water–protein interface in solid matter is of great interest. Water–protein interactions can be measured by NMR via polarization transfer between the two entities. Solid proteins, as studied by NMR, are generally heterogeneous systems with respect to dynamics: the biomolecule is immobilized, whereas the solvent behaves like a liquid. Polarization transfer mechanisms in the solid state include, as in solution, chemical exchange and dipolar cross-relaxation processes. Adding to the complexity of transfers are coherent dipolar interactions, which are strong in solids. Intra- and possibly intermolecular spin diffusion take an important place in the interplay of polarization transfers. © 2010 by John Wiley and Sons, Ltd.