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Media type:
E-Article
Title:
Excited state dynamics of 7-deazaguanosine and guanosine 5′-monophosphate
Contributor:
Krul, Sarah E.;
Hoehn, Sean J.;
Feierabend, Karl J.;
Crespo-Hernández, Carlos E.
Published:
AIP Publishing, 2021
Published in:
The Journal of Chemical Physics, 154 (2021) 7
Language:
English
DOI:
10.1063/5.0038123
ISSN:
0021-9606;
1089-7690
Origination:
Footnote:
Description:
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.