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Conformational Switching Controls Biradical Spin Dynamics in Flavin-Tryptophan Dyads
Guzel Musabirova1, Olga B Morozova2, Alexey S Kiryutin2
1Department of Analytical Chemistry, Leipzig University, Linnéstr. 3, 04103 Leipzig, Germany.
Journal of the American Chemical Society
|March 23, 2026
Summary
Proline isomerization in flavin-tryptophan dyads acts as a switch, controlling radical recombination pathways. Field-cycling NMR reveals how proline conformation impacts spin dynamics and biradical formation.
Area of Science:
- Photochemistry and photophysics
- Biophysical chemistry
- NMR spectroscopy
Background:
- Flavin-tryptophan dyads are crucial for studying photoinduced electron transfer.
- Proline isomerization (cis-trans) significantly impacts molecular conformation and dynamics.
- Photo-chemically induced dynamic nuclear polarization (photo-CIDNP) is sensitive to radical pair spin dynamics.
Purpose of the Study:
- To investigate how proline cis-trans isomerization influences spin dynamics in flavin-tryptophan dyads.
- To elucidate the role of proline conformation in controlling intramolecular versus intermolecular radical recombination.
- To assess the utility of field-cycling NMR and time-resolved photo-CIDNP in studying these systems.
Main Methods:
- Synthesis of flavin-tryptophan dyads with varying oligoproline linkers.
- Field-cycling NMR spectroscopy under photo-CIDNP conditions.
- Time-resolved photo-CIDNP measurements.
Main Results:
- Minor cis-proline conformers favor compact structures enabling intramolecular biradical recombination, observed via J-resonance photo-CIDNP.
- Dominant trans-proline conformers and longer linkers lead to intermolecular radical encounters, indicated by Δg-dominated patterns.
- Time-resolved studies confirmed the prevalence of intermolecular processes, with some dyads showing intramolecular contributions.
Conclusions:
- Proline isomerization acts as a structural switch, modulating donor-acceptor distances and the balance of intra- vs. intermolecular spin-selective pathways.
- Field-cycling photo-CIDNP is effective for identifying transient biradical states in biomolecular models.
- Understanding these dynamics is key for designing systems with controlled radical pair behavior.
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