Dielectric Relaxations in Confined Hydrated Myoglobin

In this work we report the results of a broadband dielectric spectroscopy study on the dynamics of a globularprotein, myoglobin, in confined geometry, i.e. encapsulated in a porous silica matrix, at low hydration levels,where about only one or two water layers surround the proteins. In order to highlight the specific effect ofconfinement in the silica host, we compared this system with hydrated myoglobin powders at the same hydrationlevels. The comparison between the data relative to the two different systems indicates that geometricalconfinement within the silica matrix plays a crucial role in protein-water dielectric relaxations, the effect ofsol-gel encapsulation being essentially a suppression of cooperative relaxations that involve the coherence/cooperativity of solvent motions and solvent-coupled protein dynamics. We also provide direct evidence thatprotein relaxations inside the gel depend on the hydration level and are “slaved” to the solvent -relaxation