Rapid SABRE Catalyst Scavenging Using Functionalized Silicas

In recent years the NMR hyperpolarisation method signal amplification by reversible exchange (SABRE) has been applied to multiple substrates of potential interest for in vivo investigation. Unfortunately, SABRE commonly requires an iridium-containing catalyst that is unsuitable for biomedical applications. This report utilizes inductively coupled plasma-optical emission spectroscopy (ICP-OES) to investigate the potential use of metal scavengers to remove the iridium catalytic species from the solution. The most sensitive iridium emission line at 224.268 nm was used in the analysis. We report the effects of varying functionality, chain length, and scavenger support identity on iridium scavenging efficiency. The impact of varying the quantity of scavenger utilized is reported for the three scavengers with the highest iridium removed from initial investigations: 3-aminopropyl (S-1), 3-(imidazole-1-yl)propyl (S-4), and 2-(2-pyridyl) (S-5) functionalized silica gels. Exposure of an activated SABRE sample (1.6 mg mL(-1) of iridium catalyst) to 10 mg of the most promising scavenger (S-5) resulted in <1 ppm of iridium being detectable by ICP-OES after 2 min of exposure. We propose that combining the approach described herein with other recently reported approaches, such as catalyst separated-SABRE (CASH-SABRE), would enable the rapid preparation of a biocompatible SABRE hyperpolarized bolus.

Automated summary

In recent years, the NMR hyperpolarisation method signal amplification by reversible exchange (SABRE) has been applied to multiple substrates of potential interest for in vivo investigation. Unfortunately, SABRE commonly requires an iridium-containing catalyst that is unsuitable for biomedical applications. This report investigates the potential use of metal scavengers to remove the iridium catalytic species from the solution using inductively coupled plasma-optical emission spectroscopy (ICP-OES). The effects of varying functionality, chain length, and scavenger support identity on iridium scavenging efficiency are analyzed. The study finds that exposure to the most promising scavenger (S-5) results in less than 1 ppm of detectable iridium by ICP-OES after 2 minutes. It is proposed that combining this approach with other recently reported methods, such as catalyst separated-SABRE (CASH-SABRE), could enable the rapid preparation of a biocompatible SABRE hyperpolarized bolus.