Propane-d₆ Heterogeneously Hyperpolarized by Parahydrogen

Long-lived spin states of hyperpolarized propane-d₆ gas were demonstrated following pairwise addition of parahydrogen gas to propene-d₆ using heterogeneous parahydrogen-induced polarization (HET-PHIP). Hyperpolarized molecules were synthesized using Rh/TiO₂ solid catalyst with 1.6 nm Rh nanoparticles. Hyperpolarized (P_H ∼ 1%) propane-d₆ was detected at high magnetic field (9.4 T) spectroscopically and by high-resolution 3D gradient-echo MRI (4.7 T) as the gas flowed through the radiofrequency coil with a spatial and temporal resolution of 0.5 × 0.5 × 0.5 mm³ and 17.7 s, respectively. Stopped-flow hyperpolarized propane-d₆ gas was also detected at 0.0475 T with an observed nuclear spin polarization of P_H ∼ 0.1% and a relatively long lifetime with T_1,eff = 6.0 ± 0.3 s. Importantly, it was shown that the hyperpolarized protons of the deuterated product obtained via pairwise parahydrogen addition could be detected directly at low magnetic field. Importantly, the relatively long low-field T_1,eff of HP propane-d₆ gas is not susceptible to paramagnetic impurities as tested by exposure to ∼0.2 atm oxygen. This long lifetime and nontoxic nature of propane gas could be useful for bioimaging applications including potentially pulmonary low-field MRI. The feasibility of high-resolution low-field 2D gradient-echo MRI was demonstrated with 0.88 × 0.88 mm² spatial and ∼0.7 s temporal resolution, respectively, at 0.0475 T.