Isotropic mixing in liquid-state Overhauser dynamic nuclear polarization

Area of Science:

• Chemistry
• Spectroscopy
• Organic Chemistry

Background:

• Carbon-carbon bond detection via NMR at natural isotopic abundance is limited by low signal sensitivity.
• Conventional methods struggle with molecules lacking 1H or 19F nuclei, hindering structural elucidation.
• Overhauser-effect dynamic nuclear polarization (OE-DNP) offers significant signal enhancement for specific carbon types.

Purpose of the Study:

• To demonstrate hyperpolarization transfer between 13C nuclei in challenging systems using OE-DNP.
• To enable detection of 13C-13C satellite signals for scalar coupling constant (1JCC) determination.
• To integrate isotropic mixing (IM) into OE-DNP enhanced NMR experiments.

Main Methods:

• Development of an NMR-optimized OE-DNP setup for enhanced sensitivity.
• Application of 1D and pseudo-2D isotropic mixing (IM) experiments for hyperpolarization transfer.
• Utilizing OE-DNP-enhanced IM in multiple pulse NMR sequences, including 2D OE-DNP-IM-HETCOR.
• Theoretical analysis using product operator formalism and numerical simulations.

Main Results:

• Achieved signal enhancements of up to two orders of magnitude for chlorinated/iodinated carbons lacking 1H/19F.
• Successfully detected 13C-13C satellite signals at natural abundance, allowing 1JCC measurement.
• OE-DNP-enhanced IM experiments outperformed conventional 1D INADEQUATE in sensitivity for these systems.
• Demonstrated IM as a versatile preparatory block in advanced OE-DNP NMR sequences.

Conclusions:

• Hyperpolarization transfer via isotropic mixing is feasible in OE-DNP enhanced systems.
• This approach significantly improves the ability to study carbon-carbon connectivities in challenging molecules.
• The developed methods offer a powerful tool for structural characterization in organic chemistry.