Hyperpolarization of Frozen Hydrocarbon Gases by Dynamic Nuclear Polarization at 1.2 K
We report a simple and general method for the hyperpolarization of condensed gases by dynamic nuclear polarization (DNP). The gases are adsorbed in the pores of structured mesoporous silica matrices known as HYPSOs (HYper Polarizing SOlids) that have paramagnetic polarizing agents covalently bound to the surface of the mesopores. DNP is performed at low temperatures and moderate magnetic fields (T = 1.2 K and B-0 = 6.7 T). Frequency-modulated microwave irradiation is applied close to the electron spin resonance frequency (f = 188.3 GHz), and the electron spin polarization of the polarizing agents of HYPSO is transferred to the nuclear spins of the frozen gas. A proton polarization as high as P(H-1) = 70% can be obtained, which can be subsequently transferred to C-13 in natural abundance by cross-polarization, yielding up to P(C-13) = 27% for ethylene.