Off-the-Shelf Gd(NO₃)₃ as an Efficient High-Spin Metal Ion Polarizing Agent for Magic Angle Spinning Dynamic Nuclear...

Area of Science:

• Solid-state Nuclear Magnetic Resonance (NMR) Spectroscopy
• Dynamic Nuclear Polarization (DNP)
• Materials Characterization

Background:

• Magic Angle Spinning (MAS) NMR is crucial for solid media characterization but limited by low sensitivity.
• Dynamic Nuclear Polarization (DNP) enhances NMR sensitivity using paramagnetic agents.
• Gadolinium (Gd³⁺) ions show potential as polarizing agents for various nuclear spins.

Purpose of the Study:

• To investigate the effectiveness of a readily available Gd³⁺ compound, Gadolinium(III) nitrate (Gd(NO₃)₃), as a polarizing agent in DNP-enhanced solid-state NMR.
• To quantify signal enhancements for ¹³C and ¹⁵N nuclear spins in [2-¹³C,¹⁵N]glycine.
• To elucidate the dominant mechanism responsible for signal enhancement.

Main Methods:

• Solid-state NMR experiments were performed on [2-¹³C,¹⁵N]glycine at 9.4 T and approximately 105 K.
• Dynamic Nuclear Polarization was achieved using Gd(NO₃)₃ as the polarizing agent.
• Electron Paramagnetic Resonance (EPR) data and signal enhancement profiles at varying magnetic fields were analyzed.

Main Results:

• Significant signal enhancements were observed for ¹³C and ¹⁵N nuclear sites in glycine.
• Analysis indicated the 'solid effect' as the primary mechanism driving the signal enhancement.
• Gd(NO₃)₃ provided substantial signal amplification without requiring specialized synthesis.

Conclusions:

• Gadolinium(III) nitrate is an effective and accessible polarizing agent for DNP-enhanced solid-state NMR.
• This approach significantly improves sensitivity for ¹³C and ¹⁵N nuclei, facilitating materials characterization.
• The findings enable efficient DNP without the need for complex synthesis of Gd³⁺ polarizing agents.