ABSTRACT
Parahydrogen (p-H2)-based techniques are known to drastically enhance NMR signals but are usually limited by p-H2 supply. This work reports p-H2-based SABRE hyperpolarization at p-H2 pressures of hundreds of bar, far beyond the typical ten bar currently reported in the literature. A recently designed high-pressure setup was utilized to compress p-H2 gas up to 200 bar. The measurements were conducted using a sapphire high-pressure NMR tube and a 43 MHz benchtop NMR spectrometer. In standard methanol solutions, it could be shown that the signal intensities increased with pressure until they eventually reached a plateau. A polarization of about 2%, equal to a molar polarization of 1.2 mmol L-1, could be achieved for the sample with the highest substrate concentration. While the signal plateaued, the H2 solubility increased linearly with pressure from 1 to 200 bar, indicating that p-H2 availability is not the limiting factor in signal enhancement beyond a certain pressure, depending on sample composition. Furthermore, the possibility of using liquefied ethane and compressed CO2 as removable solvents for hyperpolarization was demonstrated. The use of high pressures together with quickly removable organic/non-organic solvents represents an important breakthrough in the field of hyperpolarization, advancing SABRE as a promising tool for materials science, biophysics, and molecular imaging.
