Fast 2D NMR in Inhomogeneous Magnetic Fields

Benefitting from valuable molecular-level information on chemical shifts and J coupling multiplet patterns, NMR spectroscopy constitutes a powerful analytical tool for studying organic chemistry, protein and nucleic acid structures, dynamic effects, etc. Ultrafast NMR methods based on spatial encoding and decoding techniques enable recording of 2D NMR spectra within a single scan, thus resolving the limitation of lengthy acquisition in conventional 2D NMR experiments. Besides acquisition efficiency, magnetic field inhomogeneity poses another challenge in practical NMR applications, particularly in ultrafast 2D NMR experiments, and this challenge is difficult to resolve by conventional field shimming techniques. Accordingly, in this chapter, we focus on the review of fast 2D NMR methods that can be applied under inhomogeneous magnetic field conditions. Three main types of spatially-encoded fast 2D NMR methods suitable for high-resolution measurements in inhomogeneous magnetic fields, namely, spatially-encoded 2D NMR spectroscopy by tracking chemical shift differences, spatially-encoded 2D NMR spectroscopy combined with intermolecular multiple-quantum coherences, and spatially-encoded 2D NMR spectroscopy based on partial voxel homogeneity, are described.