Capozzi, Andrea, Saket Patel, W. Thomas Wenckebach, Magnus Karlsson, Mathilde H. Lerche, and Jan Henrik Ardenkjær-Larsen. “Gadolinium Effect at High-Magnetic-Field DNP: 70% 13C Polarization of [U-13C] Glucose Using Trityl.” The Journal of Physical Chemistry Letters 10, no. 12 (June 20, 2019): 3420–25.
We show that the trityl electron spin resonance (ESR) features, crucial for an eﬃcient dynamic nuclear polarization (DNP) process, are sample-composition-dependent. Working at 6.7 T and 1.1 K with a generally applicable DNP sample solvent mixture such as water/glycerol plus trityl, the addition of Gd3+ leads to a dramatic increase in [U-13C] glucose polarization from 37 ± 4% to 69 ± 3%. This is the highest value reported to date and is comparable to what can be achieved on pyruvic acid. Moreover, performing ESR measurements under actual DNP conditions, we provide experimental evidence that gadolinium doping not only shortens the trityl electron spin−lattice relaxation time but also modiﬁes the radical g-tensor. The latter yielded a considerable narrowing of the ESR spectrum line width. Finally, in the frame of the spin temperature theory, we discuss how these two phenomena aﬀect the DNP performance.