Low-power broadband homonuclear dipolar recoupling without decoupling: Double-quantum 13C NMR correlations at very fast magic-angle spinning

We report novel symmetry-based radio-frequency (rf) pulse sequences for efficient excitation of doublequantum (2Q) coherences under very fast (>60 kHz) magic-angle spinning (MAS) conditions. The recursively generated pulse-scheme series, R2(2p)(1)R2(2P)(-1) (p = 1; 2, 3,...), offers broadband C-13-C-13 recoupling in organic solids at a very low rf power. No proton decoupling is required. A high-order average Hamiltonian theory analysis reveals a progressively enhanced resonance-offset compensation for increasing p, as verified both by numerical simulations and 2Q filtration NMR experiments on C-13(2)-glycine, [2,3-C-13(2)] alanine, and [U-C-13] tyrosine at 14.1 T and 66 kHz MAS, where the pulse schemes with p >= 3 compare favorably to current state-of-the-art recoupling options. (C) 2012 Elsevier B.V. All rights reserved.