The dielectric response of DNA polymers dissolved in a water solution plays an important role in the determination of the effect of long-range nonbonded interactions on the vibrational dynamics of DNA. All existing calculations for DNA vibrational modes assume the water dielectric function to be constant, independent of the oscillation frequency. However, in real DNA solutions, modes depend on the dielectric constant and the dielectric constant is strongly dependent on frequency, particularly in the frequency range 0–100 ${\mathrm{cm}}^{\mathrm{-}1}$. We have extended our earlier effective-field approach for dissolved DNA polymers to include the important frequency dependence of the dielectric response function. Using the most recent experimental values for the system parameters, particularly dielectric relaxation time, we have calculated the phonon spectrum of the B-form poly(dA)-poly(dT) DNA polymer. [The notation poly(dA)-poly(dT) means that one strand contains adenine (A) bases, and the other only thiamine (T) bases.] Within a single model and with a single set of parameters our results agree with experimental data on speed of sound and inelastic neutron scattering. Besides this, our calculations also present some lines to be observed in poly(dA)-poly(dT) samples. We have analyzed the eigenvectors of all the modes in the range 0–120 ${\mathrm{cm}}^{\mathrm{-}1}$ and have characterized them in terms of various types of motions such as propeller twist, base-roll, breathing mode, etc. As a result of the frequency-dependent behavior of the long-range forces some new and interesting features are predicted at low frequencies in the millimeter range.

• Received 26 February 1990

DOI:https://doi.org/10.1103/PhysRevA.42.4993