• Medientyp: E-Artikel
  • Titel: Excited state dynamics of 7-deazaguanosine and guanosine 5′-monophosphate
  • Beteiligte: Krul, Sarah E.; Hoehn, Sean J.; Feierabend, Karl J.; Crespo-Hernández, Carlos E.
  • Erschienen: AIP Publishing, 2021
  • Erschienen in: The Journal of Chemical Physics, 154 (2021) 7
  • Sprache: Englisch
  • DOI: 10.1063/5.0038123
  • ISSN: 0021-9606; 1089-7690
  • Schlagwörter: Physical and Theoretical Chemistry ; General Physics and Astronomy
  • Entstehung:
  • Anmerkungen:
  • Beschreibung: <jats:p>Minor structural modifications to the DNA and RNA nucleobases have a significant effect on their excited state dynamics and electronic relaxation pathways. In this study, the excited state dynamics of 7-deazaguanosine and guanosine 5′-monophosphate are investigated in aqueous solution and in a mixture of methanol and water using femtosecond broadband transient absorption spectroscopy following excitation at 267 nm. The transient spectra are collected using photon densities that ensure no parasitic multiphoton-induced signal from solvated electrons. The data can be fit satisfactorily using a two- or three-component kinetic model. By analyzing the results from steady-state, time-resolved, computational calculations, and the methanol–water mixture, the following general relaxation mechanism is proposed for both molecules, Lb → La → 1πσ*(ICT) → S0, where the 1πσ*(ICT) stands for an intramolecular charge transfer excited singlet state with significant πσ* character. In general, longer lifetimes for internal conversion are obtained for 7-deazaguanosine compared to guanosine 5′-monophosphate. Internal conversion of the 1πσ*(ICT) state to the ground state occurs on a similar time scale of a few picoseconds in both molecules. Collectively, the results demonstrate that substitution of a single nitrogen atom for a methine (C–H) group at position seven of the guanine moiety stabilizes the 1ππ* Lb and La states and alters the topology of their potential energy surfaces in such a way that the relaxation dynamics in 7-deazaguanosine are slowed down compared to those in guanosine 5′-monophosphate but not for the internal conversion of 1πσ*(ICT) state to the ground state.</jats:p>