Abstract
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 (S1), 3-(imidazole-1-yl)propyl (S4), and 2-(2-pyridyl) (S5) 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 (S5) 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.
Highlights
Hyperpolarisation techniques are regularly employed to overcome the inherent sensitivity issue that is associated with NMR, and by extension, MRI
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When the 1H T1 values of pyridine are considered alongside the shortest sampling time utilized for the inductively coupled plasma-optical emission spectroscopy (ICP-optical emission spectroscopy (OES)) measurements (2 min), it should be stated that 98% of the hyperpolarised signal would have been lost
Summary
Hyperpolarisation techniques are regularly employed to overcome the inherent sensitivity issue that is associated with NMR, and by extension, MRI. Dynamic nuclear polarization (DNP) [1,2,3], quantum-rotor induced polarisation [4], spin-exchange optical pumping (SEOP) [3,5], and parahydrogen induced polarization (PHIP) [2,3], are hyperpolarisation methods that lead to improved population differences. These methods are extensively used for the analysis and detection of metabolites or pharmaceuticals [6,7], catalytic intermediates [8,9,10], and for medical imaging purposes [11,12,13,14,15]. An iridium-centered SABRE catalyst is typically employed to propagate polarisation, via
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