Aqueous NMR Signal Enhancement by Reversible Exchange in a Single Step Using Water-Soluble Catalysts

Area of Science:

• Inorganic Chemistry
• Catalysis
• Nuclear Magnetic Resonance (NMR) Spectroscopy

Background:

• NMR signal amplification by reversible exchange (SABRE) offers enhanced sensitivity but is often limited to organic solvents.
• Developing water-soluble catalysts is crucial for expanding SABRE applications in biological and environmental systems.
• Previous attempts using PEGylated catalysts showed limited activity in aqueous media.

Purpose of the Study:

• To synthesize and evaluate water-soluble iridium-based catalysts for aqueous SABRE.
• To overcome the limitations of existing catalysts in aqueous environments.
• To demonstrate the efficacy of a novel catalyst for in-situ aqueous SABRE.

Main Methods:

• Investigated two synthetic strategies for water-soluble iridium catalysts.
• Developed a novel di-iridium complex precursor with CODDA ligands, replacing cyclooctadiene (COD) rings.
• Tested the synthesized catalyst [IrCl(CODDA)IMes] for aqueous SABRE performance using pyridine in water.

Main Results:

• A PEGylated catalyst showed good water solubility but lost SABRE activity in >50% water.
• The novel CODDA-based iridium catalyst ([IrCl(CODDA)IMes]) demonstrated successful dissolution and activation in water.
• Achieved approximately 32-fold enhancement of 1H signals of pyridine in water using 1 atm of parahydrogen.

Conclusions:

• The CODDA-based iridium catalyst enables a single-step aqueous SABRE process without organic cosolvents or solvent removal.
• This represents a significant advancement for performing SABRE directly in aqueous solutions.
• The developed catalyst holds promise for various applications requiring sensitive NMR detection in water.