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Paramagnetic Relaxation Enhancement for Detecting and Characterizing Self-Associations of Intrinsically Disordered Proteins
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Sensitivity Enhancement in Pulsed Hyperfine EPR Spectroscopy with Hadamard-Encoded Acquisition
Alexey Bogdanov1, Boris Epel2, Veronica Frydman3
1Department of Chemical and Biological Physics, The Weizmann Institute of Science, P.O. Box 26, Rehovot 7610001, Israel.
The Journal of Physical Chemistry Letters
|December 1, 2025
Summary
Hadamard multiplexing enhances electron-nuclear double resonance (ENDOR) sensitivity for paramagnetic systems. This method improves signal-to-noise ratio (SNR) in frequency-domain ENDOR spectroscopy, aiding structural determination.
Area of Science:
- Spectroscopy
- Quantum Chemistry
- Biophysics
Background:
- Electron-nuclear double resonance (ENDOR) is crucial for characterizing paramagnetic systems.
- Limited signal-to-noise ratio (SNR) hinders ENDOR analysis of small hyperfine couplings and long-range interactions.
- Current methods face challenges with radiofrequency power and relaxation effects.
Purpose of the Study:
- To enhance sensitivity in frequency-domain ENDOR spectroscopy.
- To overcome SNR limitations for analyzing complex paramagnetic systems.
- To broaden the applicability of ENDOR and related EPR techniques.
Main Methods:
- Implementation of a Hadamard frequency multiplexing strategy.
- Simultaneous or sequential excitation of multiple nuclear frequencies.
- Spectral reconstruction using Hadamard transform for improved data analysis.
Main Results:
- Demonstrated up to a 2-fold improvement in SNR for fluorine ENDOR.
- Successfully applied to fluorinated small molecules and spin-labeled proteins.
- Presented approaches to mitigate radiofrequency power and relaxation limitations.
Conclusions:
- Hadamard multiplexing significantly boosts ENDOR sensitivity.
- The strategy is effective for organic radicals and paramagnetic metal complexes.
- Hadamard encoding shows broad applicability across EPR methods, including electron double resonance detected NMR.
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