Low-power ¹⁴N decoupling at fast MAS of 70 kHz

Higher isotropic resolution in solids is essential for accurate assignment of the chemical shifts in multisite chemical and biological systems; consequently, the pursuit of solution-like resolution in solid samples remains an ongoing challenge. MAS provides the effective averaging of the anisotropic interactions to the first-order while the higher order interactions, such as residual dipolar splitting (RDS), and isotropic interactions like J coupling remain. With the emergence of faster MAS, RDS and J couplings become significant constraints in the resolution and sensitivity of isotropic ¹H peaks bonded to ¹⁴N. However, the dominant quadrupolar coupling hampers the decoupling of ¹H-¹⁴N, since the achievable ¹⁴N RF-field strength is much smaller than the size of the quadrupolar coupling. Therefore, ¹⁴N edited spectroscopy is typically performed in the absence of ¹⁴N decoupling, leading to broader ¹H linewidth and reduced sensitivity. In this context, we propose the continuous-wave (CW) ¹⁴N decoupling of ¹⁴N-¹H spin pair under ¹H detection at a fast MAS of 70 kHz. We experimentally show that the on-resonance low-power ¹⁴N CW irradiation at fast MAS yields the narrower linewidth. Utilizing the quadrupolar jolting frame description, a qualitative analysis of the optimum decoupling effect is provided.