Graduate School in Nonlinear Science

Sponsored by the Danish Research Academy

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


Two lectures

by Giorgio Careri
Dipartimento Fisica
Universita' Roma La Sapienza
Roma, Italy

MIDIT-seminar 421

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.