Dielectric relaxation in slightly hydrated bovine tendon collagen

Abstract

With an aim to reveal the mechanism of water–protein interaction from the dielectric response of a model fibrous protein, the dielectric constant ε′ and loss factor ε″ have been measured in air dried and vacuum dried samples of bovine tendon collagen in the frequency range 30 Hz–3 MHz and temperature range 30–200 °C. An anomalous low frequency dispersion (LFD) and an intermediate frequency strong α-dispersion peak were the two main dielectric responses observed in the air dried sample. The LFD followed the fractional power law of frequency while the α-dispersion conformed to the Cole–Cole modified Debye equation. These dispersions, respectively, have been attributed to percolation of protons between and within the clusters of hydrogen bonded water molecules bound to polar or ionizable protein components. In the vacuum dried sample, however, a very weak high frequency α2-dispersion peak was observed, which was hidden below the strong α-dispersion in the air dried sample. This peak may be attributed to reorientation of polar components of the collagen molecule.Temperature dependence of the dielectric data shows release of bound water as a four-step process with discrete peaks at 50, 90, 125 and 160 °C. These peaks have been attributed to the onset of the release of adsorbed surface water, water bound to exposed polar sites, water bound to internal polar sites and very strongly bound structural water, respectively.