Spinning-rate encoded chemical shift correlations from rotational resonance solid-state NMR experiments
Available online 14 February 2013
Publication year: 2013
Source:Journal of Magnetic Resonance
Structural measurements in magic-angle-spinning (MAS) solid-state NMR rely heavily on 13C-13C distance measurements. Broadbanded recoupling methods are used to generate many cross-peaks, but have complex polarization transfer mechanisms that limit the precision of distance constraints and can suffer from weak intensities for distant peaks due to relaxation, the broad distribution of polarization, as well as dipolar truncation. Frequency-selective methods that feature narrow-banded recoupling can reduce these effects. Indeed, rotational resonance (R2) experiments have found application in many different biological systems, where they have afforded improved precision and accuracy. Unfortunately, a highly selective transfer mechanism also leads to few cross-peaks in the resulting spectra, which complicates the extraction of multiple constraints. R2-width (R2W) measurements that scan a range of MAS rates to probe the R2 matching conditions of one or more sites can improve precision, and also permit multiple simultaneous distance measurements. Unfortunately, multidimensional R2W can be very time-consuming. Here, we present an approach that facilitates the acquisition of 2D-like spectra based on a series of 1D R2W experiments, by taking advantage of the chemical shift information encoded in the MAS rates where matching occurs. This yields a more time-efficient experiment with many of the benefits of more conventional multidimensional R2W measurements. The obtained spectra reveal long-distance 13C-13C cross-peaks resulting from R2-mediated polarization transfer. This experiment also enables the efficient setup and targeted implementation of traditional R2 or R2W experiments. Analogous applications may extend to other variable-MAS and frequency-selective solid-state NMR experiments.
Graphical abstract
Highlights
? Rotational resonance width experiments were performed across a range of MAS rates. ? Matched MAS rates encode the resonance frequencies of recoupled nuclei. ? We describe a protocol that reconstructs 2D data from variable MAS 1D spectra. ? Application of this protocol to peptide and protein samples is demonstrated. ? Substantial time savings versus normal variable-MAS multidimensional experiments.
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