Efficient symmetry-based γ-encoded DQ recoupling sequences for suppression of t1-noise in solid-state NMR spectroscopy at fast MAS
Highlights
- Efficient DQ recoupling sequences at fast MAS is proposed.
- γ-encoded RNnν sequences have high DQ recoupling efficiency.
- The effect of MAS fluctuations on t1-noise is discussed in detail.
- t1-noise in DQ/SQ experiment is reduced by γ-encoded RNnν sequences.
Abstract
Solid-state NMR spectroscopy has played a significant role in elucidating the structure and dynamics of materials and biological solids at a molecular level for decades. In particular, the 1H double-quantum/single-quantum (DQ/SQ) chemical shift correlation experiment is widely used for probing the proximity of protons, rendering it a powerful tool for elucidating the hydrogen-bonding interactions and molecular packing of various complex molecular systems. Two factors, namely, the DQ filtering efficiency and t1-noise, dictate the quality of the 2D 1H DQ/SQ spectra. Experimentally different recoupling sequences show varied DQ filtering efficiencies and t1-noise. Herein, after a systematic search of symmetry-based DQ recoupling sequences, we report that the symmetry-based γ-encoded RNnν sequences show superior performance to other DQ recoupling sequences, which not only have a higher DQ recoupling efficiency but can also significantly reduce t1-noise. The origin of t1-noise is further discussed in detail via extensive numerical simulations. We envisage that such γ-encoded RNnν sequences are superior candidates for DQ recoupling in proton-based solid-state NMR spectroscopy due to its capability of efficiently exciting DQ coherences and suppressing t1-noise.