Combined maximum‐quantum and DOSY 3D experiments provide enhanced resolution for small molecules in mixtures

Abstract

We illustrate here as the combination of high-order maximum-quantum (MaxQ) and Diffusion-Ordered SpectroscopY (DOSY) NMR experiments in a 3D layout allows superior resolution for crowded NMR spectra. Non-uniform sampling (NUS) allows compressing the experimental time effectively to reasonable durations. Because diffusion effects were encoded within multiple-quantum coherences, increased sensitivity to magnetic field gradients is observed, requiring compensation for convection effects. The experiment was demonstrated on the spectra of a mix of small polyaromatic molecules. Specifically, in the case analyzed, the experiment provided an extreme simplification through the MaxQDOSY-MaxQ projection plane that presents one peak per molecule. Copyright © 2016 John Wiley & Sons, Ltd.

Matrix-assisted DOSY

“…Here species are separated based on the highest order quantum coherence which can be established within a spin system in a given molecule, with the MaxQ signal being a singlet in the multiple quantum dimension [47]. MaxQ and DOSY have been combined to give improved separation in a three dimensional experiment with a given projection able to reduce the spectrum to a single peak per species [48]. Filtering spectra based on other spin-dependent parameters is also possible, for example, complex mixtures may be analysed based on their sensitivity to paramagnetic relaxation [49].…”

NMR methods for the analysis of mixtures

“…61 Maximum quantum NMR was also combined with DOSY NMR to benefit from the separation power of the two methods simultaneously. 62,63…”

Resolving DOSY spectra of isomers by methanol‐d4 solvent effects

“…Diffusion‐ordered spectroscopy has been used for the analysis of drug formulations, biological extracts, protein aggregation, intramolecular interactions in supramolecular chemistry, structures of organometallic complexes and evaluation of polymer MWs . Spectral overlap issues in complex samples have been addressed by combining the diffusion experiment with a 2D NMR experiment (creating pseudo‐3D experiments, such as DOSY‐COSY, DOSY‐TOCSY and DOSY‐HSQC), with the pure shift experiment, maximum quantum experiments or detection via nuclei other than proton (i.e. fluorine, carbon and silicon).…”