Tackling a Curious Case: Generation of Charge-Tagged Guanosine Radicals by Gas-Phase Electron Transfer and Their Characterization by UV-Vis Photodissociation Action Spectroscopy and Theory
| Autor: | Congcong Ma, František Tureček, Yue Liu, Aleš Marek, Calvin Jon Antolin Leonen, Gabriela Nováková, Champak Chatterjee |
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| Jazyk: | angličtina |
| Rok vydání: | 2021 |
| Předmět: |
Chemistry
Radical 010401 analytical chemistry Photodissociation Guanosine Hydrogen atom 010402 general chemistry Photochemistry 7. Clean energy 01 natural sciences Article 0104 chemical sciences Dication chemistry.chemical_compound Electron transfer Deuterium Structural Biology Kinetic isotope effect Spectroscopy |
| Zdroj: | J Am Soc Mass Spectrom |
| Popis: | We report the generation of gas-phase riboguanosine radicals that were tagged at ribose with a fixed-charge 6-(trimethylammonium)hexane-1-aminocarbonyl group. The radical generation relied on electron transfer from fluoranthene anion to non-covalent dibenzocrown-ether dication complexes which formed nucleoside cation radicals upon one-electron reduction and crown-ether ligand loss. The cation radicals were characterized by collision-induced dissociation (CID), photodissociation (UVPD), and UV-Vis action spectroscopy. Identification of charge-tagged guanosine radicals was challenging because of spontaneous dissociations by loss of a hydrogen atom and guanine that occurred upon storing the ions in the ion trap without further excitation. The loss of H proceeded from an exchangeable position on N-7 in guanine that was established by deuterium labeling and was the lowest-energy dissociation of the guanosine radicals according to transition-state energy calculations. Rate constant measurements revealed an inverse isotope effect on the loss of either hydrogen or deuterium with rate constants k(H) = 0.25–0.26 s(−1) and k(D) = 0.39–0.54 s(−1). We used time-dependent density functional theory calculations, including thermal vibronic effects, to predict the absorption spectra of several protomeric radical isomers. The calculated spectra of low-energy N-7-H guanine-radical tautomers closely matched the action spectra. Transition-state-theory calculations of the rate constants for the loss of H-7 and guanine agreed with the experimental rate constants for a narrow range of ion effective temperatures. Our calculations suggest that the observed inverse isotope effect does not arise from the isotope-dependent differences in the transition-state energies. Instead, it may be caused by the dynamics of post-transition-state complexes preceding the product separation. |
| Databáze: | OpenAIRE |
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