Prof. Fabio Bruni
Physics Dept. E. Amaldi, Università di Roma Tre
Conference room Querzoli - LENS - via Nello Carrara 1 - Sesto Fiorentino (Florence)
Published on-line at 02:54:24 PM on Wednesday, June 6th, 2012
Dielectric studies on water confined in porous glasses and on a protein surface
Broadband dielectric spectroscopy on water confined at the surface of a globular protein or inside the small pores of two silica substrates.
Broadband dielectric spectroscopy data on water confined in three different environments, namely at the surface of a globular protein or inside the small pores of two silica substrates, in the temperature range 140 K < T < 300 K, are presented and discussed in comparison with previous results from different techniques.
It is found that all samples show a fast relaxation process, independently of the hydration level and confinement size. This relaxation is well known in the literature and its cross-over from Arrhenius to non Arrhenius temperature behavior is the object of vivid debate, given its claimed relation to the existence of a second critical point of water. We find such cross-over at a temperature of about 180 K, and assign the relaxation process to the layer of molecules adjacent and strongly interacting with the substrate surface. This is the water layer known to have the highest density and slowest translational dynamics compared to the average: its apparent cross-over may be due to the freezing of some degree of freedom and survival of very localized motions alone, to the onset of finite size effects, or to the presence of a calorimetric glass transition of the hydration shell at about 170 K.
Another relaxation process is visible in water confined in the silica matrices: this is slower than the previous one and has distinct temperature behaviors, depending on the size of the confining volume and consequent ice nucleation.
For further informations, please contact Dr. Renato Torre.
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