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

Abstract

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 Gd 3+ have recently shown promising results as polarizing agents for 1 H, 13 C, and 15 N nuclear spins. We demonstrate that the widely available and inexpensive chemical agent Gd(NO 3 ) 3 achieves significant signal enhancements for the 13 C and 15 N nuclear sites of [2- 13 C, 15 N]glycine at 9.4 T and ∼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 Gd 3+ polarizing agents.

Polarizing agents for efficient high field DNP solid-state NMR spectroscopy under magic-angle spinning: from design principles to formulation strategies

“…We nally note that moderate SE 13 C and 15 N enhancement factors were reported in water/ glycerol mixtures using the Gd(NO 3 ) 3 , a widely available and inexpensive Gd complex. 129 All these studies provided rational criteria for the search of improved Gd(III) polarizing agents in the future. To date however, Gd(tpatcn) remains the best performing Gd(III) water-soluble complex for MAS DNP at 9.4 T due to its remarkably low ZFS value, in turn due to the symmetry and nature of its ligands.…”