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Published on: June 27, 2014
Probing the Triplet State by Cryogenic Ion Trap IR Spectroscopy─Application to Protonated Lumiflavin
Sotaro Ohara1, Keisuke Hirata1, Gilles Grégoire2,3
1Department of Chemistry, School of Science, Institute of Science Tokyo, 2-12-1 4259 Ookayama, Meguro-ku, Tokyo 152-8550, Japan.
None:
Flavins are essential biological cofactors and their protonation isomers (protomers) generated upon photoexcitation play a crucial role in their photochemical reactions. Here, we identify the triplet-state (T1) protomer of protonated lumiflavin (LFH+) in a cryogenic ion trap by visible-pump infrared-probe photodissociation spectroscopy using H2-tagging (H2-tagging Vis-IRPD). This approach yields high-resolution IR spectra of cold triplet ions which, along with quantum chemical calculations, enables structural assignments and population analysis of the identified O2-cis@T1 protomer of LFH+. Furthermore, the implementation of a tickle radio frequency technique (Vis-tRF-IRPD) effectively removes nonexcited species from the ion trap, allowing vibrational signatures of the T1 state to be isolated. This work establishes a fundamental platform for monitoring protonation-site switching in photoexcited flavins (Sn or Tn) and demonstrates the broader utility of H2-tagging Vis-IRPD spectroscopy for electronic-state- and conformation-resolved studies of cold molecular ions.
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