Dielectric properties of proteins encapsulated in silica gel

The study of the interactions between a silicate gel matrix and proteins encapsulated in such porous materials may help to get further insight on the distribution of water molecules around biological macromolecules experiencing a quasi-physiological environments. In the present paper the Thermally Stimulated Depolarization Currents (TSDC) spectra of tetramethoxysilane based silica gel at different hydration degrees (h=25 to 0. 15 g_water/g_{dry material}) have been monitored in the range 100-300 K, then analyzed and compared with those recorded for myoglobin, lysozyme and lipase embedded in the same matrix. The results obtained allow to identify up to three energetically distinct families of water molecules trapped in the gel network and, in the spectra of encapsulated proteins, to distinguish the contributions coming from the protein aqueous microenvironment and from the water dipoles directly related to the included protein structure.