Determination of hydrogen exchange and relaxation parameters in PHIP complexes at micromolar concentrations.

Lisanne Sellies,Marco Tessari,Ruud L E G Aspers

doi:10.5194/mr-2-331-2021

Abstract

Non-hydrogenative para-hydrogen-induced polarization (PHIP) is a fast, efficient and relatively inexpensive approach to enhance nuclear magnetic resonance (NMR) signals of small molecules in solution. The efficiency of this technique depends on the interplay of NMR relaxation and kinetic processes, which, at high concentrations, can be characterized by selective inversion experiments. However, in the case of dilute solutions this approach is clearly not viable. Here, we present alternative PHIP-based NMR experiments to determine hydrogen and hydride relaxation parameters as well as the rate constants for para-hydrogen association with and dissociation from asymmetric PHIP complexes at micromolar concentrations. Access to these parameters is necessary to understand and improve the PHIP enhancements of (dilute) substrates present in, for instance, biofluids and natural extracts.

Highlights

The intrinsically low sensitivity of magnetic resonance techniques is a strong limitation to their application in fields such as chemical analysis, metabolic imaging and biomarker identification
We have previously demonstrated that such an asymmetric complex is an ideal nuclear magnetic resonance (NMR) chemosensor (Hermkens et al, 2016; Sellies et al, 2019): molecules capable of associating with the para-hydrogen-induced polarization (PHIP) catalyst can be probed by a pair of hydride signals enhanced by ca. 3 orders of magnitude with respect to thermal NMR measured at 500 MHz
We have presented an efficient approach for the experimental determination of the relaxation rates and kinetic parameters for p-H2 association/dissociation in asymmetric PHIP complexes

Summary

Introduction

The intrinsically low sensitivity of magnetic resonance techniques is a strong limitation to their application in fields such as chemical analysis, metabolic imaging and biomarker identification. PHIP has grown into a versatile technique since the recent discovery of non-hydrogenative routes to achieve nuclear spin hyperpolarization (Adams et al, 2009). Subsequent complex dissociation releases hyperpolarized substrate molecules in solution, which can be detected with nuclear magnetic resonance (NMR) with sensitivity enhanced by several orders of magnitude (Theis et al, 2015; Rayner et al, 2017; Rayner and Duckett, 2018; Iali et al, 2019; Gemeinhardt et al, 2020)

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Results

Conclusion