The undisputed usefulness in biomedical applications, the high carbon polarization (up to 70%) and the long relaxation time constant after dissolution have made neat [1-13C]pyruvic acid (PA) plus trityl the most studied dissolution DNP sample.
Therefore, sometimes the literature is lacking detailed studies for different trityl-based samples, limiting the potential of other biologically interesting substrates. An example is the so-called “gadolinium effect”: admixture of trace amounts of Gd3+ based compounds to the preparation can double the PA carbon polarization at 3.35 T, but has essentially no effect at higher field.1,2
Herein, we show that the trityl ESR properties, crucial for an efficient DNP process, are sample composition dependent. Working at 6.7 T with a substrate generally applicable mixture such as water:glycerol plus trityl, addition of Gd3+ lead to a dramatic increase of [U-13C,U-2H]glucose polarization from $37\pm4$% to $69\pm3$%. This is the highest value reported to date and comparable to what can be achieved for pyruvic acid.3 Moreover, performing ESR measurements at DNP conditions,using a home-built longitudinal detection (LOD) probe, we provide experimental evidence that gadolinium doping not only shortens the trityl electron spin-lattice relaxation time, but also modifies the radical g-tensor, leading to a considerable narrowing of the ESR spectrum linewidth. In the framework of spin temperature theory both effects, within the right boundaries, can justify an increase of the DNP enhancement.
The present study is of great interest for the hyperpolarization community because of the wide range of applications that highly polarized glucose can enable, and the insight into the DNP mechanism.4
 Yoshihara, H. A. I. et al. Phys Chem Chem Phys 2016, 18.
 Ardenkjaer-Larsen, J. H. et al Appl Magn Reson 2008, 34.
 Mishkovsky, M.et al. Sci Rep-Uk 2017, 7.
 Rodrigues, T. B. et al Nat Med 2014, 20.