MIDIT OFD CATS Modelling, Nonlinear Dynamics Optics and Fluid Dynamics Chaos and Turbulence Studies and Irreversible Thermodynamics Risø National Laboratory Niels Bohr Institute and Technical University of Denmark Building 128 Department of Chemistry Building 321 P.O. Box 49 University of Copenhagen DK-2800 Lyngby DK-4000 Roskilde DK-2100 Copenhagen Ø Denmark Denmark Denmark
by Giorgio Careri
Universita' Roma La Sapienza
Monday November 16, 1998, 14.00 h and 15.30 h.
at MIDIT, IMM Building 305, room 053
Abstract: We consider two real systems, both exhibiting biological
function at room temperature: (1) our hydrated protein powders, where the onset
of function occurs at the percolation threshold of bound water, and (2) Kilibanov's
nearly anhydrous enzymes in alcohols, where function requires a very small water
contents and appropriate pH of the mother solution. We look for a common low
frequency dynamics by models available in statistical physics.
To this end we have extended our early treatment of percolation in a 2D lattice to the "blobs, nodes and links" model, to describe the hydrated surface as patches of H-bonded -OH groups centered on ionizable side-chains, and singly connected in the percolating cluster which includes all side-chains. Since charged and polar side-chains are coupled to the protein 3D backbone by strong side-chain to main-chain H-bonds, a dynamical pathway between surface and protein core is identified. The functional relevance of these few but strong H-bonds will be discussed.
Recent work in collaboration with F. Bruni and G. Consolini shows that protons migrating between ionized side-chains display the dielectric behaviour typical of frustrated systems, namely progressive kinetic slowing down above the freezing temperature and lack ergodicity below. We have modelled proton frustration in the polarizable protein surface by the "2D Ising net", and in collaboration with D. Stauffer we have found by Q2R cellular automata with Kawasaky dynamics that this system fails to reach internal equilibrium. The functional relevance of a glassy dynamics near room temperature will be pointed out.