Singlet order conversion and parahydrogen-induced hyperpolarization of 13C nuclei in near-equivalent spin systems

We have demonstrated two radiofrequency pulse methods which convert the nuclear singlet order of proton spin pairs into the magnetisation of nearby C-13 nuclei. These irradiation schemes work well in the near-equivalence regime of the three-spin system, which applies when the difference in the two H-1-C-13 couplings is much smaller than the H-1-H-1 coupling. We use pulse sequences to generate thermally polarized singlet states in a reproducible manner, and study the singlet-to-magnetisation transfer step. Preliminary results demonstrate a parahydrogen-enhanced C-13 polarization level of at least 9%, providing a signal enhancement factor of more than 9000, using 50% enriched parahydrogen. (C) 2016 Elsevier Inc. All rights reserved.