Low frequency dielectric study on hydrated ovalbumin

Abstract

This paper reports the use of low frequency dielectric measurements (0.1 Hz–1 MHz) in the investigation of low hydrated ovalbumin (<0.3 g H 2O/g ovalbumin), for the purpose of examining the nature of water–protein interactions. Dielectric spectra for each hydration of ovalbumin showed two distinct processes at low and high frequency. The low frequency response showed anomalous dielectric behaviour, in which the real and imaginary permittivities are parallel and increased dramatically toward low frequency. This anomalous dielectric response followed a universal fractional power law of permittivity versus frequency and was ascribed to the quasi-dc percolation of protons through the protein matrix. The high frequency response showed a dielectric loss peak which was modeled by the Davidson–Cole expression, and was ascribed to proton hopping at the scale of the protein macromolecule. A temperature study (253–363 K) on the hydrated ovalbumin revealed that a percolation process was associated with the dielectric response of the hydrated proteins. By calculating fractal dimension from the percolation threshold, it was possible to define a hydration level of 0.08 g/g at which the surface of the protein was saturated by water.