Kozinenko, Vitaly P., Alexey S. Kiryutin, Alexandra V. Yurkovskaya, and Konstantin L. Ivanov. “Polarization of Low-γ Nuclei by Transferring Spin Order of Parahydrogen at High Magnetic Fields.” Journal of Magnetic Resonance 309 (December 2019): 106594.
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.