Terminal Diazirines Enable Reverse Polarization Transfer from ¹⁵ N₂ Singlets.

Area of Science:

• Chemical Biology
• Magnetic Resonance Imaging
• Hyperpolarization Techniques

Background:

• Diazirine moieties are chemically stable and compatible with biomolecules.
• 15N2-labeled diazirines offer potential for long-lived hyperpolarized states.
• Polarization transfer from 15N to 1H can enhance detection sensitivity.

Purpose of the Study:

• To investigate the potential of (-CH15N2) diazirine groups as analogues to methyl groups for hyperpolarization.
• To assess the lifetimes of 15N polarization and singlet states in diazirine moieties.
• To explore the formation of hyperpolarized 1H2 singlet states in chiral molecules using terminal diazirines.

Main Methods:

• Synthesis and characterization of 15N2-labeled diazirine compounds.
• Measurement of 15N spin-lattice relaxation times (T1) and singlet lifetimes (Ts).
• Investigation of hyperpolarized 1H2 singlet state formation and lifetimes in chiral molecules.

Main Results:

• Observed 15N T1 times up to 4.6±0.4 min and singlet lifetimes Ts up to 17.5±3.8 min.
• Demonstrated polarization transfer from 15N to 1H, combining long 15N lifetimes with 1H sensitivity.
• Reported terminal diazirines supporting hyperpolarized 1H2 singlet states in CH2 groups of chiral molecules with lifetimes up to 9.2±1.8 min.

Conclusions:

• (-CH15N2) diazirine groups are effective for storing and transferring hyperpolarization to 1H.
• Long-lived singlet states (up to ~17.5 min) were achieved, significantly exceeding typical 1H T1 relaxation.
• Terminal diazirines can generate long-lived hyperpolarized 1H2 singlet states in chiral molecules, offering a new avenue for sensitive NMR studies.