Systematic evaluation of heteronuclear spin decoupling in solid-state NMR at the rotary-resonance conditions in the regime of fast magic-angle spinning

The performance of heteronuclear spin decoupling sequences in solid-state NMR severely degrades when the proton radiofrequency (RF) nutation frequencies (v(1)) are close to or at multiples of magic-angle spinning (MAS) frequency (v(r)) that are referred to as rotary-resonance recoupling conditions (v(1) = n . v(r)). Recently, two schemes, namely, PISSARRO and rCW(APA), have been shown to be less affected by the problem of MAS and RF interference, specifically at the n = 2 rotary-resonance recoupling condition, especially in the fast MAS regime. Here, we systematically evaluate the loss in intensity of several heteronuclear spin decoupling sequences at the n = 1, 2 conditions compared to high-power decoupling in the fast-MAS regime. We propose that in the fast-MAS regime (above 40 kHz) the entire discussion about RF and MAS interference can be avoided by using appropriate low-power decoupling sequences which give comparable performance to decoupling sequences with high-power H-1 irradiation of ca.195 kHz. (C) 2016 Elsevier Inc. All rights reserved.