Spin Relays Enable Efficient Long-Range Heteronuclear Signal Amplification By Reversible Exchange

Area of Science:

• Nuclear Magnetic Resonance (NMR) Spectroscopy
• Hyperpolarization Techniques
• Quantum Information Transfer

Background:

• Signal Amplification By Reversible Exchange (SABRE) enables hyperpolarization of target molecules.
• Direct polarization transfer in SABRE is limited to spins near the complex.
• Long-range polarization transfer to distant spins remains a challenge.

Purpose of the Study:

• To investigate long-range polarization transfer to distant spins in SABRE experiments.
• To examine relayed polarization transfer to protons (¹H) and heteronuclei (¹³C, ¹⁵N).
• To assess the efficiency of different spin networks in facilitating polarization transfer.

Main Methods:

• Systematic experimental study of polarization transfer mechanisms.
• Selective destruction and re-hyperpolarization of ¹H, ¹³C, and ¹⁵N sites.
• Utilized pyridine for ¹H studies and metronidazole-based molecules for ¹³C and ¹⁵N studies.
• Employed Signal Amplification By Reversible Exchange in SHield Enables Alignment Transfer to Heteronuclei (SABRE-SHEATH) for heteronuclear studies.

Main Results:

• Demonstrated efficient hyperpolarization of distant spins via relayed polarization transfer.
• Showed that a network of spin-½ nuclei is crucial for efficient long-range transfer.
• Proton-only relay networks are sufficient for proton SABRE.
• Heteronuclear relay networks (e.g., involving ¹⁵N) significantly enhance SABRE-SHEATH efficiency for ¹³C and ¹⁵N.

Conclusions:

• Long-range spin hyperpolarization is achievable through relayed transfer mechanisms.
• The efficiency of relayed transfer depends on the presence and nature of the spin network.
• Relayed transfer offers a more efficient pathway for hyperpolarizing distant ¹³C and ¹⁵N sites compared to direct transfer.