High-frequency dielectric study of side-chain dynamics in poly(lysine) aqueous solutions

The high-frequency dielectric properties of poly(lysine) of different chira lity in aqueous solutions have been measured in the frequency range from I MHz to 1.8 GHz. The dielectric spectra show the existence of relatively sma ll dielectric dispersions at around 100 MHz that have been attributed to in ternal motion in the polymer chain, due to side-chain polar groups. Our res ults indicate that the local structure of the chain and its possibility to undergo a conformational transition induced by pH does not modify the main feature of the side-chain dynamics, the dielectric strength being largely p roportional to the concentration of charged groups. A similar behavior has been found in poly(alpha-glutamate) and in poly(gamma-glutamate) aqueous so lutions, where the dielectric parameters appear to be related to the change in the charge density an the main chain, rather than to the accompanying c onformational helix-coil transition. (C) 2000 John Wiley & Sons, Inc.