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 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.

Automated summary

This work demonstrates p-H-2-based SABRE hyperpolarization at pressures up to 200 bar, which is much higher than previously reported. The study shows that increasing pressure enhances signal intensities until reaching a plateau. It is also found that H-2 solubility increases linearly with pressure, indicating that p-H-2 availability is not the limiting factor beyond a certain pressure. Additionally, the use of liquefied ethane and compressed CO2 as removable solvents for hyperpolarization is demonstrated.