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?

TY - JOUR

T1 - Electron detachment dynamics of the iodide-guanine cluster: does ionization occur from the iodide or from guanine?

T2 - does ionization occur from the iodide or from guanine?

AU - Cercola, Rosaria

AU - Uleanya, Kelechi O.

AU - Dessent, Caroline E.H.

N1 - © 2019 Informa UK Limited. This is an author-produced version of the published paper. Uploaded in accordance with the publisher’s self-archiving policy. Further copying may not be permitted; contact the publisher for details.

PY - 2019/10/20

Y1 - 2019/10/20

N2 - 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.

AB - 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.

KW - charge transfer

KW - deprotonation

KW - Guanine

KW - photodissociation

KW - radical cation

UR - http://www.scopus.com/inward/record.url?scp=85074409392&partnerID=8YFLogxK

U2 - 10.1080/00268976.2019.1679402

DO - 10.1080/00268976.2019.1679402

M3 - Article

AN - SCOPUS:85074409392

SN - 0026-8976

JO - Molecular Physics

JF - Molecular Physics

ER -