Two-dimensional J-resolved NMR spectroscopy: review of a key methodology in the metabolomics toolbox

One-dimensional (1D) (1)H NMR spectroscopy remains a leading analytical technology in metabolomics. Advantages of this approach include relatively rapid spectral acquisition and NMR resonances that provide a direct measure of metabolite concentration based upon a single internal standard. Severe spectral congestion can, however, significantly hinder both metabolite identification and quantification. Two-dimensional (1)H J-resolved (JRES) NMR spectroscopy retains many of the benefits of 1D NMR, but additionally disperses the overlapping resonances into a second dimension, reducing congestion and increasing metabolite specificity. The usefulness of this approach to metabolomics was first realised six years ago, and since then it has been used in biological, medical and environmental studies of plants and animals. Here we provide a basic introduction to the 2D JRES NMR experiment and then discuss strategies for spectral acquisition and processing in the context of metabolomics applications, concluding with some key recommendations: acquisition using a double spin-echo sequence with excitation sculpting; processing using the SEM window function, tilting and symmetricising, optionally followed by a skyline projection. Strategies for implementing JRES spectroscopy into the metabolomics toolbox are then considered, including its roles in metabolic fingerprinting, metabolite identification and metabolite quantification. Public resources and data standards for JRES metabolomics are reviewed. We conclude by evaluating the advantages (e.g. increased spectral dispersion and confidence in metabolite identification; fully automated processing; reduced batch-to-batch variation) and disadvantages (e.g. longer acquisition times; higher technical variability; phase-twisted lineshapes resulting in quantification errors) of 2D JRES NMR vs the established 1D approach for metabolomics.