Homonuclear J-Coupling Spectroscopy at Low Magnetic Fields using Spin-Lock Induced Crossing

TL;DR

This paper introduces a novel low-field NMR technique called SLIC that enables J-coupling spectra acquisition without high magnetic fields or heteronuclei, broadening low-field NMR applications.

Contribution

The paper presents a new pulse sequence, SLIC, that allows low-field J-coupling spectroscopy for most organic molecules without requiring heteronuclei.

Findings

SLIC spectra can be obtained at 276 kHz and 20.8 MHz.

SLIC spectra are accurately simulated and match experimental results.

The method works on various small molecules in their native state.

Abstract

Nuclear magnetic resonance (NMR) spectroscopy usually requires high magnetic fields to create spectral resolution among different proton species. At low fields, chemical shift dispersion is insufficient to separate the species, and the spectrum exhibits just a single line. In this work, we demonstrate that spectra can nevertheless be acquired at low field using a novel pulse sequence called spin-lock induced crossing (SLIC). This probes energy level crossings induced by a weak spin-locking pulse and produces a unique J-coupling spectrum for most organic molecules. Unlike other forms of low-field J-coupling spectroscopy, our technique does not require the presence of heteronuclei and can be used for most compounds in their native state. We performed SLIC spectroscopy on a number of small molecules at 276 kHz and 20.8 MHZ, and we show that SLIC spectra can be simulated in good agreement with measurements.