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 13C, but it is barely used for 1H hyperpolarization, despite the abundance of 1H 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 1H. 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 1H 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 liquid-state T2, and therefore offers superior sensitivity and resolution. The applicability of this method to polarize 1H of selected amino acids is demonstrated.