A Straightforward Method for the Generation of Hyperpolarized Orthohydrogen with a Partially Negative Line

Area of Science:

• Catalysis
• Nuclear Magnetic Resonance Spectroscopy
• Quantum Chemistry

Background:

• The hydrogen molecule exists as two spin isomers: ortho- and parahydrogen.
• Parahydrogen is crucial for Nuclear Magnetic Resonance (NMR) signal enhancement via hyperpolarization.
• Signal Amplification by Reversible Exchange (SABRE) is a key technique for hyperpolarization.

Purpose of the Study:

• To present an approach for obtaining orthohydrogen with a Partially Negative Line (PNL) signal.
• To investigate the influence of catalysts (Ir-IMes, Ir-IMesBn) and solvents on PNL signal generation.
• To propose a working hypothesis explaining the observed PNL phenomenon.

Main Methods:

• Utilized Signal Amplification by Reversible Exchange (SABRE) with iridium-based catalysts (Ir-IMes, Ir-IMesBn).
• Conducted SABRE experiments in various solvents: benzene, acetone, and methanol.
• Monitored the PNL signal during the initial stages of pre-catalyst activation.

Main Results:

• PNL signals were readily generated in benzene with both catalysts, showing higher intensity for Ir-IMesBn.
• PNL was observed in acetone exclusively with the Ir-IMesBn catalyst.
• No PNL was detected in methanol; the effect was transient, disappearing as catalyst activation progressed.

Conclusions:

• Solvent choice and catalyst type are critical factors for observing the PNL effect in orthohydrogen.
• The PNL signal is predominantly observed during the early phase of pre-catalyst activation.
• The findings provide a basis for further research into PNL applications in material science and catalysis.