Theoretical Description of Hyperpolarization Formation in the SABRE-relay Method

TL;DR

This paper presents a theoretical model for understanding and optimizing the SABRE-relay hyperpolarization method, which enhances NMR signals by transferring spin order through chemical and spin dynamics.

Contribution

A novel theoretical approach that models both spin dynamics and chemical kinetics in SABRE-relay, enabling detailed analysis and optimization of polarization transfer efficiency.

Findings

The model accurately describes polarization formation in SABRE-relay.

Dependence of polarization on kinetic and spin parameters is quantitatively analyzed.

Potential for optimizing hyperpolarization levels in NMR applications.

Abstract

SABRE (Signal Amplification By Reversible Exchange) has become a widely used method for hyper-polarizing nuclear spins, thereby enhancing their Nuclear Magnetic Resonance (NMR) signals by orders of magnitude. In SABRE experiments, non-equilibrium spin order is transferred from parahydrogen to a substrate in a transient organometallic complex. Applicability of SABRE is expanded by the methodology of SABRE-relay, in which polarization can be relayed to a second substrate either by direct chemical exchange of hyperpolarized nuclei or by polarization transfer between two substrates in a second organometallic complex. To understand the mechanism of the polarization transfer and study the transfer efficiency, we propose a theoretical approach to SABRE-relay, which can treat both spin dynamics and chemical kinetics as well as the interplay between them. The approach is based on a set of equations for the spin density matrices of the spin systems involved (i.e., SABRE substrates and complexes), which can be solved numerically. Using this method, we perform a detailed study of polarization formation and analyse in detail the dependence of attainable polarization level on various chemical kinetic and spin dynamic parameters. We foresee applications of the present approach for optimizing SABRE-relay experiments with the ultimate goal of achieving maximal NMR signal enhancements for substrates of interest.