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

TL;DR

This study develops a theoretical approach to calculate DNA conformational vibration intensities in Raman spectra, revealing how different counterions influence low-frequency vibrational modes and their intensities.

Contribution

A new valence-optic theory-based model for predicting DNA Raman band intensities considering counterion effects is introduced.

Findings

DNA backbone vibrations near 15 cm-1 have highest intensity.

Na-DNA shows dominant H-bond stretching modes above 40 cm-1.

Cs-DNA exhibits prominent ion-phosphate vibration modes with higher intensity than Na-DNA.

Abstract

The approach for calculation of the mode intensities of DNA conformational vibrations in the Raman spectra is developed. It is based on the valence-optic theory and the model for description of conformational vibrations of DNA with counterions. The calculations for Na- and Cs-DNA low-frequency Raman spectra show that the vibrations of DNA backbone chains near 15 cm-1 have the greatest intensity. In the spectrum of Na-DNA at frequency range upper than 40 cm-1 the modes of H-bond stretching in base pairs have the greatest intensities, while the modes of ion-phosphate vibrations have the lowest intensity. In Cs-DNA spectra at this frequency range the mode of ion-phosphate vibrations is prominent. Its intensity is much higher than the intensities of Na-DNA modes of this spectra range. Other modes of Cs-DNA have much lower intensities than in the case of Na-DNA. The comparison of our calculations with the experimental data shows that developed approach gives the understanding of the sensitivity of DNA low-frequency Raman bands to the neutralization of the double helix by light and heavy counterions.