- K. Saalwächter, R. Graf, H. W. Spiess.
Recoupled Polarization-Transfer Methods for Solid-State
Heteronuclear Correlation in the Limit of Fast MAS.
J. Magn. Reson.
148, 398-418 (2001).
An in-depth account of the effect of homonuclear couplings and multiple
heteronuclear couplings is given for a recently published technique for
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.