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Hypershifted spin spectroscopy with dynamic nuclear polarization at 1.4 K
Zhenfeng Pang1, Kirill Sheberstov1, Bogdan A Rodin1
1Laboratoire des Biomolécules, LBM, Département de Chimie, École Normale Supérieure, PSL University, Sorbonne Université, CNRS, 75005 Paris, France.
Science Advances
|December 11, 2024
Summary
This study reveals hidden nuclear spins using spin diffusion enhanced saturation transfer (SPIDEST) in dynamic nuclear polarization (DNP) NMR. The method detects hypershifted spins, offering new insights into radical structures.
Area of Science:
- Magnetic Resonance Spectroscopy
- Physical Chemistry
- Chemical Physics
Background:
- Dynamic nuclear polarization (DNP) significantly enhances nuclear magnetic resonance (NMR) sensitivity by transferring electron polarization to nuclei.
- Detecting 'hidden' nuclear spins, whose resonances are hypershifted due to strong electron-nuclear couplings, remains a challenge in DNP-NMR.
- Understanding these hypershifted spins is crucial for characterizing radical structures and optimizing DNP polarizing agents.
Purpose of the Study:
- To develop and demonstrate a method for detecting and characterizing hypershifted nuclear spins in a DNP-enhanced system.
- To investigate polarization transfer mechanisms from these hidden spins to bulk nuclei.
- To provide insights into the structure of free radicals and improve DNP polarizing agent design.
Main Methods:
- Utilizing spin diffusion enhanced saturation transfer (SPIDEST) to indirectly detect hypershifted spins in a frozen glycerol-water/TEMPOL mixture at ~1.4 K.
- Directly observing 1H NMR signals spanning a 10 MHz range.
- Employing two-dimensional NMR techniques to study polarization transfer across a spin diffusion barrier.
- Validating spectral assignments using simulations and density functional theory (DFT) calculations.
Main Results:
- Successful detection of hypershifted spins in the DNP-enhanced system via SPIDEST.
- Direct observation of broad 1H NMR lines, confirming the presence of the hidden spins.
- Experimental and computational evidence confirming the origin of the signals from intramolecular protons on TEMPOL.
- Demonstration of polarization transfer from hypershifted spins to bulk nuclei, overcoming a spin diffusion barrier.
Conclusions:
- SPIDEST is an effective method for detecting and characterizing hypershifted nuclear spins in DNP-enhanced systems.
- The study provides detailed insights into the structure of TEMPOL radicals and the dynamics of spin polarization.
- This methodology offers a complementary approach to electron paramagnetic resonance (EPR) for studying hyperfine interactions and designing advanced DNP polarizing agents.
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