Homonuclear Simplified Preservation of Equivalent Pathways Spectroscopy

Recently developed homonuclear transverse mixing optimal
control
pulses (hTROP) revealed an elegant way to enhance the detected signal
in multidimensional magic-angle spinning (MAS) nuclear magnetic resonance
experiments. Inspired by their work, we present two homonuclear simplified
preservation of equivalent pathways spectroscopy (hSPEPS) sequences
for recoupling CA–CO and CA–CB dipolar couplings under
fast and ultrafast MAS rates, theoretically enabling a √2 improvement
in sensitivity for each indirect dimension. The efficiencies of hSPEPS
are evaluated for non-deuterated samples of influenza A M2 and bacterial
rhomboid protease GlpG under two different external magnetic fields
(600 and 1200 MHz) and MAS rates (55 and 100 kHz). Three-dimensional
(H)CA(CO)NH, (H)CO(CA)NH, and (H)CB(CA)NH spectra demonstrate the
high robustness of hSPEPS elements to excite carbon–carbon
correlations, especially in the (H)CB(CA)NH spectrum, where hSPEPS
outperforms the J-based sequence by a factor of,
on average, 2.85.