Electron detachment dynamics of the iodide-guanine cluster: does ionization occur from the iodide or from guanine? does ionization occur from the iodide or from guanine?

Rosaria Cercola, Kelechi O. Uleanya, Caroline E.H. Dessent*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


Laser photodissociation spectroscopy of the I·guanine complex has been conducted for the first time across the regions above the electron detachment threshold to explore the excited states and whether vertical ionisation occurs from the iodide or the nucleobase. The photofragment spectra reveal a prominent dipole-bound excited state (I) close to the calculated vertical electron detachment energy (∼4.0 eV) and a second excited (II) centred around 4.8 eV, which we assign to π-π* nucleobase-localised transitions. The ionic photofragments are identified as I and I·[G-H], with the later fragment being produced significantly more strongly than the former. Both photofragments are observed across the two excited states, with production of the iodide being attributed to internal conversion to the ground state followed by evaporation. We trace the formation of the I·[G-H] photofragment to initial vertical ionisation of guanine, followed by ejection of a proton. This two-step process is important as it follows known steps in radiation-induced damage to DNA, namely initial formation of a guanine radical cation which then forms a free radical [G-H] moiety through deprotonation. Production of the I·[G-H] photofragment is pronounced through II indicating that its formation is enhanced by coupling of the π-π* transitions to the electron detachment continuum.

Original languageEnglish
JournalMolecular Physics
Early online date20 Oct 2019
Publication statusE-pub ahead of print - 20 Oct 2019

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  • charge transfer
  • deprotonation
  • Guanine
  • photodissociation
  • radical cation

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