Effect of isotope substitution on the Fermi resonance and vibrational lifetime of unnatural amino acids modified with IR probe: A 2D-IR and pump-probe study of 4-azido-L-phenyl alanine

Jun Young Park, Saptarsi Mondal, Hyeok Jun Kwon, Prabhat Kumar Sahu, Hogyu Han, Kyungwon Kwak, Minhaeng Cho

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14 Citations (Scopus)

Abstract

The infrared (IR) probe often suffers from an unexpected complex absorption profile due to the Fermi resonance and short vibrational lifetime, which restricts the application of time-resolved IR spectroscopy to investigate the site-specific structural dynamics of the protein. Researchers have found that isotope substitution to the IR probe not only removes the Fermi resonance but also extends the dynamic observation window with a prolonged vibrational lifetime. This method has been successfully applied to modify the vibrational properties of many IR probes for time-resolved spectroscopy and imaging. In this study, the effect of isotope substitution (15N) on the vibrational properties of the azide stretching band in 4-azido-L-phenylalanine has been investigated using ultrafast pump-probe and 2D-IR spectroscopy. In contrast to the earlier reports, it has been observed that the Fermi resonance remains unchanged even after isotope substitution, and there is very little change in the vibrational relaxation dynamics as well. Anharmonic frequency analysis reveals that the α-N atom of N3 is being shared between the two transitions participating in the Fermi resonance and gets affected similarly due to isotope labeling. Hence, this study unveils the specific circumstance at which the isotope labeling strategy may not be successful in eliminating the Fermi resonance band and explains the molecular origin behind it. This study also suggests definitive approaches on how to overcome the limitations related to the Fermi resonance to extend the development and application of this IR probe for biological research.

Original languageEnglish
Article number164309
JournalJournal of Chemical Physics
Volume153
Issue number16
DOIs
Publication statusPublished - 2020 Oct 28

Bibliographical note

Funding Information:
This work was supported by the Institute for Basic Science (Grant No. IBSR023-D1). H.H. is grateful for the financial support from the National Research Foundation (NRF) of Korea funded by the Ministry of Science and ICT (Grant No. NRF2020R1F1A1049520).

Funding Information:
This work was supported by the Institute for Basic Science (Grant No. IBSR023-D1). H.H. is grateful for the financial support from the National Research Foundation (NRF) of Korea funded by the Ministry of Science and ICT (Grant No. NRF2020R1F1A1049520). The authors declare no conflicts of interest.

Publisher Copyright:
© 2020 Author(s).

ASJC Scopus subject areas

  • General Physics and Astronomy
  • Physical and Theoretical Chemistry

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