Probing signal amplification by reversible exchange using an NMR flow system

Area of Science:

• Nuclear Magnetic Resonance (NMR) Spectroscopy
• Hyperpolarization Techniques
• Biophysical Chemistry

Background:

• NMR spectroscopy suffers from low sensitivity, limiting its applications.
• Hyperpolarization methods significantly enhance NMR signal intensity.
• Signal amplification by reversible exchange (SARE) is a promising hyperpolarization technique.

Purpose of the Study:

• To optimize the signal amplification by reversible exchange (SARE) technique for hyperpolarizing nicotinamide.
• To investigate the role of the catalyst and experimental parameters in SARE efficiency.
• To analyze the build-up and relaxation of spin order terms in hyperpolarized nicotinamide.

Main Methods:

• Utilized signal amplification by reversible exchange (SARE) for nicotinamide hyperpolarization.
• Employed an automated flow apparatus and parahydrogen spectroscopy.
• Quantified longitudinal spin order terms (1-4 spin orders) using specialized NMR pulse sequences.
• Collected 13C NMR spectra, including quaternary carbons, with and without INEPT enhancement.

Main Results:

• Demonstrated successful hyperpolarization of nicotinamide using SARE.
• Identified the catalyst as crucial for polarization transfer and depletion of polarized states.
• Observed build-up rates of spin order terms following the order: four~three > two > single spin.
• Showcased significant intensity of long-lived quaternary 13C signals, further improved by INEPT.

Conclusions:

• The study dissects the complexity of SARE for nicotinamide, highlighting optimization strategies.
• Catalyst concentration and parahydrogen levels critically influence SARE effectiveness.
• Understanding spin order dynamics is essential for maximizing signal acquisition in hyperpolarized NMR.
• The findings support the future application of SARE for high-sensitivity magnetic resonance imaging (MRI).