Recoupled Polarization-Transfer Methods for Solid-State H–C Heteronuclear Correlation in the Limit of Fast MAS |
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Authors: | Kay Saalwchter Robert Graf Hans W Spiess |
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Institution: | Max-Planck-Institute for Polymer Research, Postfach 3148, D-55021, Mainz, Germany |
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Abstract: | An in-depth account of the effects of homonuclear couplings and multiple heteronuclear couplings is given for a recently published technique for 1H–13C dipolar correlation in solids under very fast MAS, where the heteronuclear dipolar coupling is recoupled by means of REDOR π-pulse trains. The method bears similarities to well-known solution-state NMR techniques, which form the framework of a heteronuclear multiple-quantum experiment. The so-called recoupled polarization-transfer (REPT) technique is versatile in that rotor-synchronized 1H–13C shift correlation spectra can be recorded. In addition, weak heteronuclear dipolar coupling constants can be extracted by means of spinning sideband analysis in the indirect dimension of the experiment. These sidebands are generated by rotor encoding of the reconversion Hamiltonian. We present generalized variants of the initially described heteronuclear multiple-quantum correlation (HMQC) experiment, which are better suited for certain applications. Using these techniques, measurements on model compounds with 13C in natural abundance, as well as simulations, confirm the very weak effect of 1H–1H homonuclear couplings on the spectra recorded with spinning frequencies of 25–30 kHz. The effect of remote heteronuclear couplings on the spinning-sideband patterns of CHn groups is discussed, and 13C spectral editing of rigid organic solids is shown to be practicable with these techniques. |
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Keywords: | REDOR TEDOR distance measurements dipolar couplings recoupling methods spinning sideband patterns |
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