DIELECTRIC-RELAXATION OF A DNA FRAGMENT

The real part of the dielectric permittivity in the frequency range 4-50 MHz of a monodisperse DNA fragment in aqueous solution at 23-degrees-C as a function of concentration is determined by time domain reflectometry. The fragment is short enough to be considered a rigid rod. The data are interpreted in light of a microscopic model based on a forced diffusion equation. The observed dielectric dispersion derives from counterion motion perpendicular to the rod axis. Using parameters derived from analysis of transient electric birefringence using the same model, the model predicts a slower response in the zero concentration limit than the extrapolated experimental data exhibit. The discrepancy presumably lies with the extrapolation that is hindered by lack of data at very low concentrations and the sensitivity of polyelectrolyte solution properties to even small salt concentrations.