Parahydrogen and Radiofrequency Amplification by Stimulated Emission of Radiation Induce Through-Space Multinuclear NMR Signal Enhancement

Hyperpolarized (i.e., polarized far beyond the thermal equilibrium) nuclear spins can result in radiofrequency amplification by stimulated emission of radiation (RASER) effect. Here, we show the utility of RASER to amplify NMR signals of solute and solvent molecules in the liquid state. Specifically, parahydrogen-induced RASER was used to spontaneously enhance nuclear spin polarization of protons and heteronuclei (here 19F and 31P) in a wide range of molecules. The magnitude of the effect correlates with the T1 relaxation time of the target nuclear spins. A series of control experiments validates the through-space dipolar mechanism of RASER-assisted polarization transfer between parahydrogen-polarized compound and to-be-hyperpolarized nuclei of the target molecule. Frequency-selective saturation of RASER-active resonances was used to control the RASER and the amplitude of spontaneous polarization transfer. Spin dynamics simulations support our experimental RASER studies.