Dielectric Relaxations in Confined Hydrated Myoglobin

Abstract

In this work we report the results of a broadband dielectricspectroscopy study on the dynamics of a globular protein, myoglobin, inconfined geometry, i.e. encapsulated in a porous silica matrix, at lowhydration levels, where about only one or two water layers surround theproteins. In order to highlight the specific effect of confinement inthe silica host, we compared this system with hydrated myoglobinpowders at the same hydration levels. The comparison between the datarelative to the two different systems indicates that geometricalconfinement within the silica matrix plays a crucial role inprotein-water dielectric relaxations, the effect of sol-gelencapsulation being essentially a suppression of cooperativerelaxations that involve the coherence/ cooperativity of solventmotions and solvent-coupled protein dynamics. We also provide directevidence that protein relaxations inside the gel depend on thehydration level and are "slaved" to the solvent beta-relaxation.