SABRE Hyperpolarization with up to 200 bar Parahydrogen in Standard and Quickly Removable Solvents

Parahydrogen (p-H$_2$)-based techniques are known to drastically enhance NMR signals but are usually limited by p-H$_2$ supply. This work reports p-H$_2$-based SABRE hyperpolarization at p-H$_2$ 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-H$_2$ 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 H$_2$ solubility increased linearly with pressure from 1 to 200 bar, indicating that p-H$_2$ 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 CO$_2$ as removable solvents for hyperpolarization was demonstrated. ... mehrThe 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.