Influence of Dy 3+ and Tb 3+ doping on 13 C dynamic nuclear polarization.

Dynamic nuclear polarization (DNP) is a technique that uses a microwave-driven transfer of high spin alignment from electrons to nuclear spins. This is most effective at low temperature and high magnetic field, and with the invention of the dissolution method, the amplified nuclear magnetic resonance (NMR) signals in the frozen state in DNP can be harnessed in the liquid-state at physiologically acceptable temperature for in vitro and in vivo metabolic studies. A current optimization practice in dissolution DNP is to dope the sample with trace amounts of lanthanides such as Gd ³⁺ or Ho ³⁺ , which further improves the polarization. While Gd ³⁺ and Ho ³⁺ have been optimized for use in dissolution DNP, other lanthanides have not been exhaustively studied for use in C13 DNP applications. In this work, two additional lanthanides with relatively high magnetic moments, Dy ³⁺ and Tb ³⁺ , were extensively optimized and tested as doping additives for C13 DNP at 3.35 T and 1.2 K. We have found that both of these lanthanides are also beneficial additives, to a varying degree, for C13 DNP. The optimal concentrations of Dy ³⁺ (1.5 mM) and Tb ³⁺ (0.25 mM) for C13 DNP were found to be less than that of Gd ³⁺ (2 mM). W-band electron paramagnetic resonance shows that these enhancements due to Dy ³⁺ and Tb ³⁺ doping are accompanied by shortening of electron T ₁ of trityl OX063 free radical. Furthermore, when dissolution was employed, Tb ³⁺ -doped samples were found to have similar liquid-state C13 NMR signal enhancements compared to samples doped with Gd ³⁺ , and both Tb ³⁺ and Dy ³⁺ had a negligible liquid-state nuclear T ₁ shortening effect which contrasts with the significant reduction in T ₁ when using Gd ³⁺ . Our results show that Dy ³⁺ doping and Tb ³⁺ doping have a beneficial impact on C13 DNP both in the solid and liquid states, and that Tb ³⁺ in particular could be used as a potential alternative to Gd ³⁺ in C13 dissolution DNP experiments.