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Combination of DQ and ZQ Coherences for Sensitive Through‐Bond NMR Correlation Experiments in Biosolids under Ultra‐Fast MAS
Author(s) -
Webber Amy L.,
Pell Andrew J.,
BarbetMassin Emeline,
Knight Michael J.,
Bertini Ivano,
Felli Isabella C.,
Pierattelli Roberta,
Emsley Lyndon,
Lesage Anne,
Pintacuda Guido
Publication year - 2012
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.201200099
Subject(s) - chemistry , magnetization , magic angle spinning , spectral line , dephasing , analytical chemistry (journal) , molecular physics , nuclear magnetic resonance , nuclear magnetic resonance spectroscopy , physics , condensed matter physics , quantum mechanics , magnetic field , stereochemistry , chromatography
A double‐zero quantum (DZQ)‐refocused INADEQUATE experiment is introduced for J ‐based NMR correlations under ultra‐fast (60 kHz) magic angle spinning (MAS). The experiment records two spectra in the same dataset, a double quantum–single quantum (DQ‐SQ) and zero quantum–single quantum (ZQ‐SQ) spectrum, whereby the corresponding signals appear at different chemical shifts in ω 1 . Furthermore, the spin‐state selective excitation (S 3 E) J ‐decoupling block is incorporated in place of the second refocusing echo of the INADEQUATE scheme, providing an additional gain in sensitivity and resolution. The two sub‐spectra acquired in this way can be treated separately by a shearing transformation, producing two diagonal‐free single quantum (SQ‐SQ)‐type spectra, which are subsequently recombined to give an additional sensitivity enhancement, thus offering an improvement greater than a factor of two as compared to the original refocused INADEQUATE experiment. The combined DZQ scheme retains transverse magnetization on the initially polarized ( I ) spin, which typically exhibits a longer transverse dephasing time ( T 2 ′) than its through‐bond neighbour ( S ). By doing so, less magnetization is lost during the refocusing periods in the sequence to give even further gains in sensitivity for the J correlations. The experiment is demonstrated for the correlation between the carbonyl (CO) and alpha (CA) carbons in a microcrystalline sample of fully protonated, [ 15 N, 13 C]‐labelled Cu II , Zn II superoxide dismutase, and its efficiency is discussed with respect to other J ‐based schemes.