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Spin-orbit charge transfer from guanine and 9-methylguanine radical cations to nitric oxide radicals and the induced triplet-to-singlet intersystem crossing.
- Source :
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Journal of Chemical Physics . 8/28/2023, Vol. 159 Issue 8, p1-15. 15p. - Publication Year :
- 2023
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Abstract
- Nitric oxide (●NO) participates in many biological activities, including enhancing DNA radiosensitivity in ionizing radiation-based radiotherapy. To help understand the radiosensitization of ●NO, we report reaction dynamics between ●NO and the radical cations of guanine (a 9HG●+ conformer) and 9-methylguanine (9MG●+). On the basis of the formation of 9HG●+ and 9MG●+ in the gas phase and the collisions of the radical cations with ●NO in a guided-ion beam mass spectrometer, the charge transfer reactions of 9HG●+ and 9MG●+ with ●NO were examined. For both reactions, the kinetic energy-dependent product ion cross sections revealed a threshold energy that is 0.24 (or 0.37) eV above the 0 K product 9HG (or 9MG) + NO+ asymptote. To interrogate this abnormal threshold behavior, the reaction potential energy surface for [9MG + NO]+ was mapped out at closed-shell singlet, open-shell singlet, and triplet states using density functional and coupled cluster theories. The results showed that the charge transfer reaction requires the interaction of a triplet-state surface originating from a reactant-like precursor complex 3[9MG●+(↑)⋅(↑)●NO] with a closed-shell singlet-state surface evolving from a charge-transferred complex 1[9MG⋅NO+]. During the reaction, an electron is transferred from π∗(NO) to perpendicular π∗(9MG), which introduces a change in orbital angular momentum. The latter offsets the change in electron spin angular momentum and facilitates intersystem crossing. The reaction threshold in excess of the 0 K thermochemistry and the low charge-transfer efficiency are rationalized by the vibrational excitation in the product ion NO+ and the kinetic shift arising from a long-lived triplet intermediate. [ABSTRACT FROM AUTHOR]
Details
- Language :
- English
- ISSN :
- 00219606
- Volume :
- 159
- Issue :
- 8
- Database :
- Academic Search Index
- Journal :
- Journal of Chemical Physics
- Publication Type :
- Academic Journal
- Accession number :
- 171316947
- Full Text :
- https://doi.org/10.1063/5.0160921