DOSY-shift reagents

A well-known procedure to separate resonances that would otherwise overlap in crowded NMR spectra is by adding to the sample some paramagnetic substance, the so-called shift-reagent. The most commonly used shift reagents are complexes of paramagnetic lanthanide ions such as europium(III) for down field shifts and praseodymium(III) for upfield shifts.

A similar approach has been recently reported to resolve mixture components via DOSY-NMR. It’s not very uncommon that in some mixture analyses, 2 or more compounds have diffusion coefficients so similar that they cannot be resolved by any mathematical procedure. For example, the figure below shows a synthetic DOSY spectrum (based on Figure 2 of the original article) of a mixture of two peptides, Trp-Gly and Leu-Met having D values nearly identical

M. E. Zielinski and K. F. Morris proposed in their article to add perdeuterated surfactant micelles to the mixture. Analogous to the chemical offsets induced by shift reagents, the molecules in the mixture under analysis interact differentially with the micelles and thus have different Diffusion values.

Using perdeuterated surfactant micelles to resolve mixture components in diffusion-ordered NMR spectroscopy
Matthew E. Zielinski, Kevin F. Morris, Magnetic Resonance in Chemistry
Volume 47 Issue 1, Pages 53 - 56