High-resolution Overhauser dynamic nuclear polarization enhanced proton NMR spectroscopy at low magnetic fields

Area of Science:

• Nuclear Magnetic Resonance (NMR) Spectroscopy
• Dynamic Nuclear Polarization (DNP)
• Physical Chemistry

Background:

• Dynamic nuclear polarization (DNP) significantly amplifies NMR signal intensity.
• Current DNP applications primarily focus on high-field, solid-state NMR.
• DNP's potential for enhancing solution-state NMR spectroscopy is substantial but less explored.

Purpose of the Study:

• To demonstrate Overhauser dynamic nuclear polarization (ODNP) for high-resolution solution-state NMR.
• To achieve significant signal enhancement and detailed spectral analysis of small molecules.
• To validate ODNP's utility at a lower magnetic field (0.35 T).

Main Methods:

• Application of ODNP spectroscopy at 14.5 MHz (0.35 T).
• Utilized a compact hybrid magnet with integrated shim coils for improved field homogeneity.
• Recorded high-resolution ODNP-enhanced NMR spectra of ethyl crotonate and ethylene glycol.

Main Results:

• Achieved routine proton linewidths below 4 Hz and DNP enhancement factors greater than 30.
• Successfully performed chemical-shift resolved ODNP experiments, observing proton J-coupling in ethyl crotonate.
• In-situ characterization of microwave-induced sample heating in ethylene glycol via spectral peak separation.

Conclusions:

• ODNP is effective for obtaining high-resolution NMR spectra of small molecules in solution at 14.5 MHz.
• The method enables detailed analysis, including J-coupling, and in-situ monitoring of experimental parameters.
• Demonstrates a practical approach for DNP-enhanced solution-state NMR spectroscopy.