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

Magic angle spinning nuclear magnetic resonance spectroscopy experiments are widely employed in the characterization of solid media. The approach is incredibly versatile but deleteriously suffers from low sensitivity, which may be alleviated by adopting dynamic nuclear polarization methods, resulting in large signal enhancements. Paramagnetic metal ions such as Gd3+ have recently shown promising results as polarizing agents for H-1, C-13, and N-15 nuclear spins. We demonstrate that the widely available and inexpensive chemical agent Gd(NO3)(3) achieves significant signal enhancements for the C-13 and N-15 nuclear sites of [2-C-13,N-15]glycine at 9.4 T and similar to 105 K. Analysis of the signal enhancement profiles at two magnetic fields, in conjunction with electron paramagnetic resonance data, reveals the solid effect to be the dominant signal enhancement mechanism. The signal amplification obtained paves the way for efficient dynamic nuclear polarization without the need for challenging synthesis of Gd3+ polarizing agents.