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Abstract

1H multiple-quantum/single-quantum (MQ/SQ) NMR experiment at fast MAS has been widely used for probing the proximity of protons in various molecular systems. In particular, the recent development of γ-free triple-quantum (TQ) recoupling pulse sequence has boosted up the proton TQ excitation efficiency beyond 30%, leading to dramatic sensitivity enhancement in 2D TQ/SQ correlation spectra and thus time savings. Nevertheless, the resolution along the TQ dimension is still quite limited due to the widespread dipolar couplings among protons as well as their narrow chemical shift dispersion. Herein, it is demonstrated that the constant time evolution along the TQ dimension is able to significantly enhance the resolution of TQ dimension at the expense of signal sensitivity. A compromise between resolution and sensitivity can be achieved and optimized via correct setting of constant TQ evolution time in order to obtain a high resolution TQ/SQ spectrum for revealing proton networks.