Homonuclear rotary resonance

Dipolar recoupling may also be accomplished using continuous rf irradiation as demonstrated in the heteronuclear and homonuclear case by the CP at MAS conditions (or for low-y heteronuclear spins called double-cross-polarization, DCP [103]) and HORROR (homonuclear rotary resonance) [26] experiments, respectively. These experiments may easily be described by transforming the description into the interaction frame of the rf irradiation using (14a) exploiting... 

N. C. Nielsen, H. Bildspe, H. J. Jakobsen and M. H. Levitt, Double-quantum homonuclear rotary resonance efficient dipolar recovery in in magic-angle spinning nuclear magnetic resonance. J. Cherrt Phys., 1994. 101, 1805-1812. 

While the Ur — 2uj DQ-HORROR condition selectively recouples dipolar interactions, the homonuclear rotary resonance condition = leads to single-quantum and double-quantum recoupling, including recoupling of CSA. Accordingly, the homonuclear n = I condition with Wr = has also been called MSD-HORROR (mixed single- and double quantum HORROR) " and has been employed to determine the orientation of the two C chemical shielding tensors in 2,3- C2-labelled L-alanine. However, the homonuclear resonance condition simultaneously represents a heteronuclear n = 1... 

Applying a spin-lock pulse with an rf amplitude equal to one or two times the rotor frequency leads to a recoupling of heteronuclear dipolar interactions (rotary resonance recoupling) [85] a spin-lock pulse with an amplitude half of the rotor frequency recouples homonuclear dipolar couplings (homonuclear rotary resonance... 

Recently a new type of proton assisted recoupling experiments has been developed for coherence transfer where rf irradiation is taking place on all involved rf channels. This embraces the homonuclear proton assisted recoupling (PAR) [45, 140, 141] and the later resonant second-order transfer (RESORT) [142] experiments, as well as the heteronuclear proton assisted insensitive nuclei (PAIN) cross polarization [44] experiments. In PAR and PAIN, spin-lock CW irradiation is applied on both passive ( H) and active spins (13C, 15N) without matching rotary resonance conditions. In RESORT a phase alternation irradiation scheme for the passive spins is used. 

It is known that, at the HORROR condition, homonuclear dipolar couplings between xHs are reintroduced, leading to partial removal of the heteronuclear coupling.28 29 It is worth noting that at 60 and 120 kHz the proton decoupling is insufficient due to the rotary resonance effect. It has been shown theoretically by Emsley and co-workers,19 that the first and second rotary resonances are partially quenched by the presence of homonuclear couplings. 

Z.H. Gan, J.-P. Amoureux, J. Trebosc, Proton-detected N MAS NMR using homonuclear decoupled rotary resonance, Chem. Phys. Lett. 435 (2007) 163—169. 

R -HMQC spectra ofHA and tHA, presented in Fig. 4.16. The N=2 rotary-resonance condition (cOrp = 2(0 was chosen rather than the N= I condition to avoid recoupling of homonuclear recouphng. 

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