¹H high field electron-nuclear double resonance spectroscopy at 263 GHz/9.4 T

Area of Science:

• Electron Paramagnetic Resonance Spectroscopy
• Magnetic Resonance Imaging
• Biophysical Chemistry

Background:

• Electron-nuclear double resonance (ENDOR) is a powerful technique for studying paramagnetic species.
• Higher frequencies in ENDOR experiments can improve spectral resolution and sensitivity.
• Previous limitations in spectral resolution hindered detailed analysis of complex molecular systems.

Purpose of the Study:

• To evaluate the performance of a 263 GHz electron-nuclear double resonance (ENDOR) spectrometer.
• To assess the impact of enhanced orientation selectivity on spectral resolution.
• To demonstrate the capability of high-frequency ENDOR for uncovering new information in complex systems.

Main Methods:

• Utilized a prototype commercial quasi-optical spectrometer operating at 263 GHz (9.4 T).
• Employed Davies, Mims, and CP-ENDOR pulse sequences with the 1H BDPA radical.
• Verified spectral resolution using a protein sample with a tyrosyl radical at 5 K.
• Performed spectral simulations aided by Density Functional Theory (DFT) calculations.

Main Results:

• Demonstrated increased orientation selectivity at 263 GHz compared to 94 GHz.
• Revealed previously obscured spectral features in Davies ENDOR spectra.
• Identified seven internal proton couplings in a tyrosyl radical due to enhanced resolution.
• Confirmed the fidelity of 263 GHz ENDOR for orientation-selected spectra.

Conclusions:

• 263 GHz ENDOR provides significantly enhanced resolution and sensitivity for studying molecular systems.
• The technique allows for the detection of subtle spectral features and couplings.
• High-frequency ENDOR is a valuable tool for uncovering new insights in biophysical and chemical research.