J-Driven dynamic nuclear polarization for sensitizing high field solution state NMR.

Area of Science:

• Nuclear Magnetic Resonance Spectroscopy
• Quantum Chemistry
• Physical Chemistry

Background:

• Dynamic nuclear polarization (DNP) significantly enhances Nuclear Magnetic Resonance (NMR) sensitivity, primarily in solid-state applications.
• Its effectiveness in liquid-state NMR diminishes rapidly with increasing magnetic field strength (B₀).
• This limitation has restricted the broad application of DNP in solution-state structural and dynamical studies.

Purpose of the Study:

• To overcome the magnetic field dependency of DNP in liquid-state NMR.
• To enable efficient DNP signal enhancement across a wide range of magnetic fields relevant to contemporary NMR.
• To expand the utility of DNP for analyzing small- and medium-sized molecules in solution.

Main Methods:

• Investigated biradicals with specific exchange couplings (Jex) comparable to electron Larmor frequency (ωE).
• Employed numerical and analytical calculations to model DNP phenomena.
• Analyzed the influence of microwave irradiation on nuclear spin polarization.

Main Results:

• Demonstrated a DNP mechanism effective at all relevant NMR magnetic fields.
• Observed efficient transient nuclear polarization build-up.
• Showed applicability across diverse rotational diffusion correlation times for small- and medium-sized molecules.

Conclusions:

• Introduced a novel DNP approach using biradicals with Jex ≈ ±ωE for enhanced liquid-state NMR sensitivity.
• This method overcomes the magnetic field decay limitations of conventional DNP.
• The findings pave the way for broader DNP applications in solution NMR spectroscopy.