Low-power homonuclear dipolar recoupling using supercycled symmetry-based and exponentially-modulated pulse sequences

Aimed at performing dipolar recoupling as part of biological solid-state NMR experiments without using excessively strong rf irradiation, we present a series of low-power supercycled symmetry-based and exponentially modulated pulse sequences facilitating efficient recoupling over specified chemical shift ranges even at high-speed spinning conditions. The experiments are designed through simple phase modulation of known ‘lower-quality’ symmetry-based pulse sequences or highly rf-demanding exponentially modulated recoupling experiments. The methods are described analytically and numerically and demonstrated experimentally by one- and two-dimensional correlation spectra of 2,3-13C2-L-alanine and the fibrillating-core decapeptide SNNFGAILSS of human Islet Amyloid Poly-Peptide (hIAPP, or amylin) uniformly 13C,15N-labeled at the FGAIL residues.