The Absorption Spectrum of Guanine Based Radicals: a Comparative Computational Analysis. Issue 9 (22nd July 2019) - Martínez Fernández, Lara
Abstract: The excited states of three radical derivatives of guanine, i. e. guanine cation (G + ) and its two main deprotonated derivatives (G−H1 and G−H2), have been characterized in the Franck‐Condon region by TD‐DFT, using different functionals, CASPT2, and EOM‐EE‐CCSD calculations. In the gas phase, all the methods provide a similar description of the main spectral features, the pictures provided by TD‐DFT, with long range corrected functionals, and EOM‐EE‐CCSD being very close. Solvent effects are then taken into account by a mixed discrete‐continuum approach, including five water molecules of the first solvation shell and the Polarizable Continuum Model (PCM). The vibronic absorption line‐width has finally been simulated at the TD‐M052X level by a time dependent method within the harmonic approximation. The resulting absorption spectra are in good agreement with their experimental counterparts, providing useful indications on the use of PCM/TD‐DFT based approaches to interpret the spectra of guanine based radicals within DNA. Abstract : The guanine radical cation and its deprotonated radical derivatives have very similar absorption spectra, making their identification within DNA very challenging for both experimental and computational methods. We are compute their absorption spectra by using TD‐DFT, EOM‐CCSD and MS‐CASPT2, both in the gas phase and in solution, also including vibronic effects. The computed spectra are in good agreement with experiemnts, providing interesting methodological indications.