The effect of glassing solvent deuteration and Gd3+ doping on 13C DNP at 5 T

Abstract

We report the influence of glassing solvent deuteration and Gd³⁺ doping on ¹³C dynamic nuclear polarization (DNP) nuclear magnetic resonance (NMR) performed on [1-¹³C] sodium acetate at B₀ = 5 T and 1.2 K. Our data reveal that at 5 T, glassing solvent deuteration still results in a 40% improvement of the ¹³C DNP signal when a large electron spin resonance (ESR) linewidth 4-oxo-TEMPO free radical is used, but results in a 60% decrease of the DNP signal in the case of a sample doped with small ESR linewidth trityl OX063. An addition of a trace amount of the Gd³⁺ complex Gd–HP–DO3A led to a negligible slight decrease on the ¹³C polarization TEMPO-doped sample, but is still relatively beneficial for the trityl-doped sample with 30% improvement of the DNP-enhanced ¹³C polarization. These findings indicate that while these DNP optimization steps are still valid at 5 T, the effects are not as pronounced as observed in ¹³C DNP at B₀ = 3.35 T. These DNP results at 5 T are discussed thermodynamically within the framework of the thermal mixing model of DNP.