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Resolving spectral overlap in ENDOR by chirp echo Fourier transform detection
Julian Stropp1, Fabia Canonica2, Nino Wili3
1Department of Chemistry and Applied Bioscience, Institute for Molecular Physical Sciences, ETH Zürich, Vladimir-Prelog-Weg 2, 8093 Zürich, Switzerland. daniel.klose@phys.chem.ethz.ch.
Physical Chemistry Chemical Physics : PCCP
|November 21, 2025
Summary
This study introduces 2D Chirp Echo Epr SpectroscopY (CHEESY) ENDOR, a new method to resolve crowded spectra in paramagnetic systems. CHEESY ENDOR enhances spectral analysis for transition metal complexes and metalloproteins.
Area of Science:
- Spectroscopy
- Chemical Physics
- Biophysics
Background:
- Electron nuclear double resonance (ENDOR) spectroscopy probes paramagnetic centers by measuring electron-nuclear spin interactions.
- Crowded ENDOR spectra in systems with multiple magnetic nuclei, common in transition metal complexes and metalloproteins, hinder analysis due to anisotropic hyperfine (HF) and nuclear quadrupole (NQ) interactions.
- Existing ENDOR techniques struggle with spectral overlap in disordered systems.
Purpose of the Study:
- To develop a novel ENDOR technique for resolving spectral overlap in complex paramagnetic systems.
- To improve the analysis of hyperfine and nuclear quadrupole interactions in disordered systems.
- To enhance the sensitivity and applicability of ENDOR spectroscopy.
Main Methods:
- Substitution of the Hahn echo in Davies ENDOR with a chirp echo from the Kunz-Böhlen-Bodenhausen scheme.
- Application of Fourier transformation to the chirp echo, generating an additional EPR dimension.
- Demonstration on 1H, 14/15N, and 63Cu in the copper protein ScoI.
Main Results:
- 2D Chirp Echo Epr SpectroscopY (CHEESY) ENDOR successfully resolves spectral overlap by revealing correlations between nuclear and electron transitions.
- The method effectively disentangles small copper NQ-coupling from large, anisotropic HF-coupling.
- Frequency-domain simulations accurately reproduce experimental 2D CHEESY ENDOR spectra, enabling spin Hamiltonian parameter extraction.
Conclusions:
- CHEESY ENDOR offers a competitive signal-to-noise ratio compared to established techniques like 2D Mims ENDOR and HYEND, due to FT advantages and RF-chirp compatibility.
- The technique expands the scope and feasibility of ENDOR investigations for a wider range of applications.
- CHEESY ENDOR provides a powerful tool for detailed structural and functional analysis of paramagnetic centers.
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