Unveiling coherently\xa0driven hyperpolarization dynamics in signal amplification by reversible exchange

Jacob R Lindale,Shannon L Eriksson,Guannan Zhang,Warren S Warren,Zijian Zhou,Thomas Theis,Junu Bae,Christian P N Tanner,Eduard Y Chekmenev,Johannes F P Colell

doi:10.1038/s41467-019-08298-8

Abstract

Signal amplification by reversible exchange (SABRE) is an efficient method to hyperpolarize spin-1/2 nuclei and affords signals that are orders of magnitude larger than those obtained by thermal spin polarization. Direct polarization transfer to heteronuclei such as 13C or 15N has been optimized at static microTesla fields or using coherence transfer at high field, and relies on steady state exchange with the polarization transfer catalyst dictated by chemical kinetics. Here we demonstrate that pulsing the excitation field induces complex coherent polarization transfer dynamics, but in fact pulsing with a roughly 1% duty cycle on resonance produces more magnetization than constantly being on resonance. We develop a Monte Carlo simulation approach to unravel the coherent polarization dynamics, show that existing SABRE approaches are quite inefficient in use of para-hydrogen order, and present improved sequences for efficient hyperpolarization.

Highlights

Signal amplification by reversible exchange (SABRE) is an efficient method to hyperpolarize spin-1/2 nuclei and affords signals that are orders of magnitude larger than those obtained by thermal spin polarization
We have shown that the DARTH-SABRE and coherent SHEATH experiments boast the ability to monitor the coherent hyperpolarization dynamics under the influence of chemical exchange
Accessing the coherent SABRE dynamics has shown the ability to bypass the damping of the hyperpolarized signal by the SABRE exchange dynamics in certain regimes, which is critical for ligands with exchange rates disparate from the period of their coherent evolution

Summary

Introduction

Signal amplification by reversible exchange (SABRE) is an efficient method to hyperpolarize spin-1/2 nuclei and affords signals that are orders of magnitude larger than those obtained by thermal spin polarization. Large magnetic fields increase the Zeeman interaction energy, inducing higher polarizations, but realistic field strengths still imply very small fractional magnetization near room temperature Such issues may be circumvented by hyperpolarization methods, which afford significantly higher nuclear polarization and provide signals that are orders of magnitude larger than those achieved with thermal polarization. These couplings convert hydrogen singlet order to flow into magnetization on the target ligands, including the very interesting case of direct transfer to heteronuclei such as 15N This flow of order is achieved by level anti-crossings at low (micro-Tesla) field (SABRE-SHEATH and later variants) or at high field in rotating frames created by very weak rf irradiation (LIGHT-SABRE and later variants)[19,21,24,25,30,39,40,41,42]. The MC simulations require fewer assumptions about the system and outperform current models[19,20] in the prediction of experimental data

Methods

Results

Conclusion