Proton signal enhancement of three orders of magnitude in high-field liquid-state NMR

Dissolution-dynamic nuclear polarization (d-DNP) is a hyperpolarization technique that is used to enhance the sensitivity of liquid-state nuclear magnetic resonance (NMR) in biophysical and chemical applications. D-DNP is used widely for the sensitivity enhancement of hetero-nuclei such as 13 C, but it is barely used for 1 H hyperpolarization, despite the abundance of 1 H in organic matter. Here we show that OX063, a radical that has so far been used only for the hyperpolarization of low-γ nuclei such as 13C, may be used also to hyperpolarize 1 H. This hyperpolarization route is enabled by the use of a klystron amplifier that provides three orders of magnitude more power than conventionally used solid-state microwave sources. Following hyperpolarization, the sample is ejected from the polarizer and liquefied, yielding 1 H signal enhancements of ~ 1000 in high-field NMR. The use of OX063 limits not only T1 relaxation during sample transfer, but we also show that it preserves the liquidstate T2, and therefore offers superior sensitivity and resolution. The applicability of this method to polarize 1 H of selected amino acids is demonstrated.