Comment on mr-2022-19

Abstract

Proton-detected local field (PDLF) NMR spectroscopy, using magic-angle spinning and dipolar recoupling, is presently the most powerful experimental technique to obtain atomistic structural information from small molecules undergoing anisotropic motion such as peptides, drugs, or lipids in model membranes. The accuracy of the measurements on complex systems is however compromised by the number of transients required and by the difficulty of fitting experimental data due to the omnipresent RF spatial inhomogeneity in NMR probes. Here, we present a new methodology to analyse R-type PDLF NMR experiments that brings a significant improvement of accuracy and that enables to address more complex systems. The new methodology consists of fitting the time-domain data with NMR simulations accounting for RF spatial inhomogeneity, making it possible (1) to use shorter experiments which enables to measure samples with lower material content and prevents RF-heating, (2) to measure smaller C–H bond order parameter magnitudes, |SCH|, and smaller variations of |SCH| upon perturbations of the system and (3) to determine |SCH| values with small differences from distinct sites having the same chemical shift. The increase in accuracy is demonstrated by comparison with 2H NMR quadrupolar echo experiments on mixtures of deuterated and non-deuterated dimyristoylphosphatidylcholine (DMPC). The methodology presented enables an unprecedented level of structural detail and will be highly useful for investigating complex membrane systems as illustrated with membranes composed of a brain lipid extract with many distinct lipid types.