Microwave-free J-driven DNP (MF-JDNP): A proposal for enhancing the sensitivity of solution-state NMR

TL;DR

This paper proposes a microwave-free method called MF-JDNP that enhances solution-state NMR sensitivity by shuttling samples between magnetic fields to match electron Larmor frequencies, avoiding microwave-related issues.

Contribution

It introduces a novel microwave-free approach to DNP that relies on sample shuttling to achieve electron-nuclear polarization transfer at specific magnetic fields.

Findings

Theoretical framework for MF-JDNP is developed.

Conditions for radicals and shuttling times are proposed.

Potential for microwave-free NMR sensitivity enhancement is demonstrated.

Abstract

J-driven Dynamic Nuclear Polarization (JDNP) was recently proposed for enhancing the sensitivity of solution-state nuclear magnetic resonance (NMR), while bypassing the limitations faced by conventional (Overhauser) DNP at magnetic fields of interest in analytical applications. Like Overhauser DNP, JDNP also requires saturating the electronic polarization using high-frequency microwaves, known to have poor penetration and associated heating effects in most liquids. The present microwave-free JDNP (MF-JDNP) proposal seeks to enhance the sensitivity of the solution state NMR by shuttling the sample between higher and lower magnetic fields, with one of these fields providing an electron Larmor frequency that matches the inter-electron exchange coupling Jex. If spins cross this so-called JDNP condition sufficiently fast, we predict that a sizable nuclear polarization will be created without microwave irradiation. This MF-JDNP proposal requires radicals whose singlet/triplet self-relaxation rates are dominated by dipolar hyperfine relaxation, and shuttling times that can compete with these electron relaxation processes. This communication discusses the theory behind the MF-JDNP, as well as proposals for radicals and conditions that could enable this new approach to NMR sensitivity enhancement.