Polarization of low-γ nuclei by transferring spin order of parahydrogen at high magnetic fields

In this work, we optimize the performance of a previously proposed method for transferring parahydrogen induced polarization to "insensitive" spin-1/2 NMR (Nuclear Magnetic Resonance) nuclei, which have low gyromagnetic ratio and low natural abundance. By optimizing the reaction conditions and pressure of the parahydrogen gas and using adiabatically switched radiofrequency fields we achieve high polarization transfer efficiency and report carbon spin polarization of dimethyl acetylene dicarboxylate reaching 35%, which corresponds to ¹³C NMR signal enhancements of about 43,000 at 9.4 Tesla. Such polarization levels allow one to work with mM concentrations at natural carbon abundance and to detect ¹³C NMR signal in single scan. In combination with a pseudo phase cycle, the polarization transfer method used here also enables efficient suppression of unwanted background signals.