Intensities of the raman bands in the low-frequency spectra of DNA with light and heavy counterions

Abstract

For calculating the mode intensities of DNA conformational vibrations in the Raman spectra, a spatial
approach is developed. It is based on the valence-optic scheme and four-mass model with counterions. In
frames of this approach, it is grounded that the vibrations of nucleosides as physical pendulums with
respect to the phosphate groups of the double helix backbone and the internucleoside vibrations make the
greatest polarizability changes in the DNA monomer link. The calculations for Na-and Cs-DNA low-frequency Raman spectra show that in both cases the modes near 15 cm^-1, characterizing the vibrations of nucleosides as pendulums, have the greatest intensity.In the Na-DNA spectra at a frequency range of upper than 40 cm^-1, the modes of H-bond stretching in base pairs 60 and 115 cm^-1 have the greatest intensities. The mode of internucleoside vibrations 79 cm-¹ has lower intensity. Taking into consideration the heterogeneity of macromolecule structure elements, the resulting form of Na-DNA low-frequency spectra in the middle frequency range looks like a continuous band with the center near 80 cm^-1 that corresponds to the experimental data.In Cs-DNA spectra at this frequency range,the mode of iron phosphate vibrations 115cm^-1 is prominent. Its intensity is much higher than the intensities of Na-DNA modes of this spectra range. The intensities of other Cs-DNA modes are much lower than in the case of Na-DNA. The comparison of our calculations with the experimental data shows that the developed approach describes well the changes in Raman spectra, observing under the substitution of Na⁺ counterions for Cs⁺The determined the sensitivity of the intensities of DNA low-frequency spectra to the counterion type proves the existence of the ion-phosphate modes.