Protonic and ionic conduction in lysozyme. Hydration and field-dependent effects

Abstract

Solid-state conduction and dielectric measurements are reported for lysozyme as a function of hydration and applied electric field. Mass spectrometry and electron-probe microanalysis have been used to detect protonic and ionic conduction processes. For electric fields < ca. 8 × 10⁵ V m^–1 the electrical conductivity in lysozyme is predominantly protonic for all hydrations above 5 wt %. For higher electric fields Poole–Frenkel-dominated ionic transport processes become progressively more dominant as the hydration content is increased. The observation of a pronounced isotope (deuteration) effect and the result of prolonged field cleaning of the test samples support these conclusions. The low-frequency dielectric dispersion (known as the Ω-dispersion) commonly observed for protein samples has been found to be associated with interactions between ions and the metal electrodes.