Critical exponents of protonic percolation in hydrated lysozyme powders

Abstract

The dc protonic conductivity of powders of lysozyme was calculated from capacitance data measured for the frequency range 10 KHz to 10 MHz and for varied levels of hydration. Analysis of the hydration dependence of the conductivity close to the percolation threshold gave the value for the critical exponent t=1.29\ifmmode\pm\else\textpm\fi{}0.05. This value is in close agreement with expectation from theory for a two-dimensional percolative process. These results support the idea that the threshold for hydration-induced protonic conduction (and, quite possibly, for enzymatic activity) corresponds to the formation of a percolation network of absorbed water molecules on the surface of this protein macromolecule.