Investigation of far-infrared vibrational modes in polynucleotides

Far-infrared measurements (40–500 ${\mathrm{cm}}^{\mathrm{-}1}$) of vacuum-dried, free-standing, unoriented films of the polynucleotides poly(dA)⋅poly(dT), poly(dA-dT)⋅poly(dA-dT), and poly(dG)⋅poly(dC) and the ribonucleotide poly(rA)⋅poly(rU) under various salting conditions are reported. Spectral features that depend on temperature, crystallinity, and salting conditions have been observed. Of most interest are four sharp bands near 63, 83, 100, and 110 ${\mathrm{cm}}^{\mathrm{-}1}$ in polycrystalline poly(dA)⋅poly(dT). These low-frequency (${\mathrm{cm}}^{\mathrm{-}1}$) observations are discussed in terms of a lattice-dynamical model of homopolymer DNA.