High DNP efficiency of TEMPONE radicals in liquid toluene at low concentrations

Abstract

We show that at low concentrations (≤5 mM) TEMPONE radicals in liquid toluene exhibit higher DNP efficiency than in water. In spite of reduced coupling factors, the improved DNP performance in toluene results from favourable saturation and leakage factors, as determined by pulse electron–electron double resonance (ELDOR) and NMR relaxation, respectively. The extracted coupling factors at 0.35 Tesla support theoretical predictions of the Overhauser mechanism.