Dynamics of layered adenine molecules

Coherent inelastic neutron-scattering measurements have been carried out on a hydrogenous single crystal of 9-methyladenine (9-MA), a methylated form of the DNA base, adenine. Several low-lying acoustic modes have been measured. In particular, detailed measurements have been made of the dispersion of the longitudinal-acoustic mode propagating perpendicular to planes parallel, on average, to those of the planar adenine molecules. The sound velocity corresponding to this acoustic mode is similar to that obtained for sound propagation along the DNA helix axis in dry films, but significantly greater than for corresponding velocities obtained from measurements on stacked pyrimidines. The biological relevance of the measurements is discussed in relation to physical properties that may be associated with long stretches of adenine (poly-A) known to exist in certain regions of RNA.