Understanding substrate substituent effects to improve catalytic efficiency in the SABRE hyperpolarisation process
Emma V Stanbury1, Peter M Richardson1, Simon B Duckett1
1Centre for Hyperpolarisation in Magnetic Resonance , Department of Chemistry , University of York , York , YO10 5NY UK .
Catalysis Science & Technology
|December 10, 2019
Summary
Para-hydrogen hyperpolarization via SABRE catalysis is enhanced by understanding substrate-iridium interactions. Stronger binding reduces dissociation but can decrease hyperpolarization efficiency by shortening NMR relaxation times.
Area of Science:
- Nuclear Magnetic Resonance (NMR) Spectroscopy
- Hyperpolarization Techniques
- Catalysis
Background:
- Para-hydrogen (PH) based hyperpolarization is increasingly utilized in NMR.
- SABRE (Signal Amplification By Reversible Exchange) catalysis transfers polarization from PH to substrates via a metal complex.
- Understanding substrate-metal interactions is crucial for optimizing SABRE efficiency.
Purpose of the Study:
- To quantitatively study substrate-iridium ligation effects in SABRE catalysis.
- To evaluate the role of substrate properties in SABRE performance.
- To establish a route for achieving optimal SABRE performance.
Main Methods:
- Utilized SABRE catalysis with para-hydrogen.
- Investigated substrate-iridium ligation using 4-chloropyridine, 4-pyridinecarboxaldehyde methyl hemiacetal, 4-methylpyridine, and 4-methoxypyridine.
- Performed variable temperature studies to analyze exchange rates and NMR relaxation times (T1).
Main Results:
- Stronger substrate-iridium association led to slower substrate dissociation rates (kd).
- Catalyst residence times influenced substrate NMR relaxation times (T1).
- Extended catalyst binding to iridium promoted relaxation, reducing SABRE efficiency and overall hyperpolarization levels.
Conclusions:
- Substrate-metal binding dynamics critically impact SABRE performance.
- Optimizing catalyst residence time is key to balancing substrate binding and relaxation.
- The study defines a pathway towards enhanced SABRE hyperpolarization efficiency.
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