Pure Shift NMR

Suppressing multiplet structure in 1H NMR spectra offers a large improvement in spectral resolution (see below), each multiplet collapsing down to a single line at the appropriate chemical shift. The improvement in resolution is equivalent to using a 5 GHz spectrometer rather than a 500 MHz. The pulse sequence for the 1D pure shift experiment using a modified Zangger-Sterk method can be downloaded from here, and the pulse sequence for the 1D pure shift experiment using PSYCHE can be downloaded here. There is a pure shift NMR package available for download as part of our 2017 workshop on pure shift NMR.

(Top) normal and (bottom) pure shift 500 MHz 1H spectra of a calixarene. Taken from Aguilar et al..

Such “pure shift” techniques are readily extended to multidimensional methods. For example, in DOSY the ability to resolve different rates of diffusion depends crucially on resolving signals in the NMR spectrum. Unresolved signals lead to compromise apparent diffusion coefficients, so pure shift DOSY can make DOSY spectra much easier to interpret.

(Left) normal and (right) pure shift 400 MHz 1H DOSY spectra of a mixture of 2-methyl-1-propanol and 2,3-dimethyl-2-butanol. Collapsing multiplet structure avoids signal overlap and leads to all signals appearing with the correct diffusion coefficient. Taken from Nilsson et al..

If pure shift methods are combined with covariance processing it is possible to produce multidimensional spectra in which all signals appear as singlets, greatly simplifying results.

(Left) normal and (right) pure shift 500 MHz 1H TOCSY spectra of clarithromycin in dmso-d6. Taken from Morris et al..

Foroozandeh M, Adams RW, Meharry NJ, Jeannerat D, Nilsson M, Morris GA. 2014. Ultrahigh-Resolution NMR Spectroscopy Angewandte Chemie International Edition, 53:6990-6992.

Aguilar, JA, Faulkner, S, Nilsson, M, Morris GA. 2010. Pure Shift 1H NMR: A Resolution of the Resolution Problem?. Angewandte Chemie International Edition. 49:3901-3903.
Nilsson, M, Morris, GA. 2007. Pure shift proton DOSY: diffusion-ordered 1H spectra without multiplet structure. Chem. Commun. 2007, 933-935.
Morris, GA, Aguilar, JA, Evans, R, Haiber, S, Nilsson, M. 2010. True Chemical Shift Correlation Maps: A TOCSY Experiment with Pure Shifts in Both Dimensions. J. Am. Chem. Soc. 132, 12770-12772.