Fluorescence Quenching for Determination of Catalyst Concentration in the Parahydrogen-Induced Polarization Method SABRE

Abstract

In recent years, parahydrogen-induced hyperpolarization has become a focus for future medical applications. Similar to the established dynamic nuclear polarization method, a biocompatible bolus from a hyperpolarized sample can be produced for in vivo studies. However, this requires removing toxic hydrogenation catalysts, which inevitably must be used. Additionally, the ratio between the substrate to be hyperpolarized (e. g. pyruvate) and a mandatory catalyst must also be maintained. Even the smallest differences can lead to a reduction in generated signal amplification. In particular, weighing small amounts of catalysts leads to inaccuracies in sample preparations. Fluorescence spectroscopy provides a rapid and sensitive enough approach to determine catalyst concentration. The Ir-IMes metal complexes used in SABRE lead to a quenching of the fluorescence of the solvent, dependent on its concentration. This can be used to quickly estimate the actual concentration in a solution with very small quantities of catalysts. Hence, fluorescence spectroscopy offers a rapid and reliable quality control method for the preparation of samples to be hyperpolarized. In addition, it can also be used as a quality control method to assess filtration efficacy before administration of hyperpolarized samples.