Hydration dynamics of collagen in aqueous buffer solution as studied by time domain dielectric spectroscopy

Dielectric relaxation studies of collagen in aqueous buffer solution (pH 3.7) have been carried out at four different temperatures 283, 288, 293 and 298 K as a function of collagen concentration between 0.033 μM and 0.2 μM in the frequency range of 1 GHz to 25 GHz using time domain dielectric spectroscopy technique. Apart from the dominant mode at high frequency around 14 GHz which is assigned to the free water relaxation; we have detected one more pronounced peak close to 1.8 GHz in the δ-dispersion range of the loss spectrum of collagen in aqueous buffer solution. The peak around 1.8 GHz is attributed to hydration water reorientation of the collagen macromolecules and has obtained detailed information on its temperature and concentration dependence. The retardation imposed on the hydration water by collagen is found to be ≈4.7, since collagen can cause long range perturbations beyond the first hydration shell. The activation enthalpy and activation entropy for the dipolar orientation for collagen at different concentrations have been calculated from the Arrhenius plot and is found to be 32 kJ/mol and 4.2 J/mol K respectively. The increase of thermodynamic activation enthalpy and decrease of activation entropy of collagen in buffer in the present study compared to the water have supported the idea that the water associated with collagen is highly ordered.