Constant-time evolution enhances the resolution of triple-quantum NMR spectroscopy at fast MAS

Abstract

¹ H multiple-quantum/single-quantum (MQ/SQ) NMR experiments at fast MAS have 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 sequences has boosted proton TQ excitation efficiency beyond 30%, leading to dramatic sensitivity enhancement in 2D TQ/SQ correlation spectra and shortened experimental time. Nevertheless, the resolution along the TQ dimension is still quite limited due to the widespread dipolar couplings among protons and their narrow chemical shift dispersion. Herein, it is demonstrated that the constant time evolution along the TQ dimension can significantly enhance the resolution of the TQ dimension at the expense of signal sensitivity. A compromise between resolution and sensitivity can be achieved and optimized via appropriate settings for constant TQ evolution time in order to obtain a high resolution TQ/SQ spectrum that can reveal proton networks.