NMR Spin-Lock Induced Crossing (SLIC) dispersion and long-lived spin states of gaseous propane at low magnetic field (0.05 T)

When parahydrogen reacts with propylene in low magnetic fields (e.g., 0.05 T), the reaction product propane develops an overpopulation of pseudo-singlet nuclear spin states. We studied how the Spin-Lock Induced Crossing (SLIC) technique can be used to convert these pseudo-singlet spin states of hyperpolarized gaseous propane into observable magnetization and to detect H-1 NMR signal directly at 0.05 T. The theoretical simulation and experimental study of the NMR signal dependence on B-1 power (SLIC amplitude) exhibits a well-resolved dispersion, which is induced by the spin-spin couplings in the eight-proton spin system of propane. We also measured the exponential decay time constants (T-uss or T-s) of these pseudo-singlet long-lived spin states (LISS) by varying the time between hyperpolarized propane production and SLIC detection. We have found that, on average, Ts is approximately 3 times longer than the corresponding T-1 value under the same conditions in the range of pressures studied (up to 7.6 atm). Moreover, T-s may exceed 13 s at pressures above 7 atm in the gas phase. These results are in agreement with the previous reports, and they corroborate a great potential of long-lived hyperpolarized propane as an inhalable gaseous contrast agent for lung imaging and as a molecular tracer to study porous media using low-field NMR and MRI. (C) 2017 Elsevier Inc. All rights reserved.