# 129Xe Dynamic Nuclear Polarization Demystified: The Influence of the Glassing Matrix on the Radical Properties

## TL;DR

This paper explores how to improve the polarization of xenon for MRI using a new sample preparation method and microwave techniques.

## Contribution

A user-friendly sample preparation method and microwave frequency modulation to achieve high 129Xe polarization without deuterated solvents.

## Key findings

- A robust sample preparation method for 129Xe DNP using a Custom Fluid Path system was developed.
- Electron spin relaxation times in xenon DNP matrices are significantly shorter than in water:glycerol matrices.
- Over 20% 129Xe polarization was achieved using microwave frequency modulation without deuterated solvents.

## Abstract

129Xe
dissolution dynamic nuclear polarization
(DNP)
is a controversial topic. The gold standard technique for hyperpolarized
xenon magnetic resonance imaging (MRI) is spin exchange optical pumping,
which received FDA approval in 2022. Nevertheless, the versatility
of DNP for enhancing the signal of any NMR active nucleus might provide
new perspectives for hyperpolarized 129Xe NMR/MRI. Initial
publications about 129Xe DNP underlined the increased complexity
in the sample preparation and lower polarization levels when compared
to more conventional 13C-labeled molecules, at same experimental
conditions, despite very close gyromagnetic ratios. Herein, we introduce,
using a Custom Fluid Path system, a user-friendly and very robust
sample preparation method. Moreover, investigating the radical properties
at real DNP conditions by means of LOngitudinal Detected Electron
Spin Resonance, we discovered a dramatic shortening of the electron
spin longitudinal relaxation time (T1e) of nitroxyl radicals in xenon DNP samples’ matrices, with
respect to more commonly used water:glycerol ones. Mitigating those
challenges through microwave frequency modulation, we achieved over
20% 129Xe polarization without employing any
deuterated solvent.