Low frequency dielectric relaxation and light scattering under AC electric field of DNA solutions

Low frequency dielectric relaxation of aqueous DNA was measured in a frequency range from 0.1 Hz to 30 kHz. Agreement was found between dielectric relaxation time and rotational one estimated from reduced viscosity for dilute solutions of DNA. The low frequency relaxation is thus ascribed to rotation of the major axis of DNA chains elongated by electrostatic repulsion between charges on the chain. A quasi-permanent dipole moment of DNA estimated from the dielectric increment is well explained by the fluctuation of dissociation of DNA. The above conclusion was confirmed for DNA samples of various molecular weights and for solutions in water ethanol mixtures. Effects of binding of salts and dyes are also interpreted in terms of the same mechanism. Light scattering of aqueous DNA under a.c. electric field supports the above conclusion.