Low Frequency Coherent Vibrations of DNA: The Role of the Hydration Shell and Phosphate-Phosphate Interactions

Abstract

The vibrational modes of DNA span a range from high frequency localized vibrations, through low frequency collective modes to over-damped Brownian fluctuations. Presumably the most important motions from a biological standpoint are the lowest frequency vibrations (involving the largest units) that are not overdamped by the viscous action of the hydration shell. I describe observations of low frequency collective vibrational modes of DNA which couple to the hydration shell. The dynamics of the hydration shell becomes important in a frequency “window” between the viscoelastic transition of the primary hydration shell (roughly 4 GHz.) and the viscoelastic transition of the secondary shell (roughly 80 GHz.). The role of coupled solvent — DNA dynamics in the A to B and B to Z transition is discussed in terms of the phosphate-phosphate interactions which probably dominate conformational stability. Excitations of coupled modes of the DNA-hydration shell system may also account for the resonant microwave absorption observed in restriction fragments and plasmids.